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Blown3000
11-13-2012, 09:29 PM
What are the benefits of boost on a low compression engine VS high compression engine? Is there really a need to lower your compression ratio if you are going to use sometype of forced induction? If so why?

RealMcCoy
11-13-2012, 10:55 PM
Yes, you will severely limit the amount of boost you can run by using too high compression ratio... The cylinder pressure gets pretty extreme.

Blown3000
11-14-2012, 07:44 AM
Yes, you will severely limit the amount of boost you can run by using too high compression ratio... The cylinder pressure gets pretty extreme.

Can you be more specific.

IPD
11-14-2012, 07:45 AM
wait....aren't you the dude with the supercharged 3/s?

Zaroth
11-14-2012, 08:06 AM
Can you be more specific.

Too much pressure, engine go boom.

whitedragon
11-14-2012, 08:42 AM
How to add a turbo to a non turbo car. (http://www.torquecars.com/tuning/adding-turbo.php)

Some light reading that should break it down simple enough.

IPD
11-14-2012, 09:30 AM
i swear this is the same guy who loudly protested when he was told that superchargers aren't that great of an option for these cars. i don't know if he'd take the advice of people who run turbochargers.

Blown3000
11-14-2012, 11:44 AM
wait....aren't you the dude with the supercharged 3/s?

Yes and still running fine.

Blown3000
11-14-2012, 11:48 AM
How to add a turbo to a non turbo car. (http://www.torquecars.com/tuning/adding-turbo.php)

Some light reading that should break it down simple enough.

Have done so now I want to hear from the forum.

futurevr4man
11-14-2012, 11:49 AM
blown3000, you need to look at the effects of gasoline at a high pressure. as you increase the pressure, the gasoline will ignite sooner. when you increase the pressure high enough, gasoline will ignite with no spark, thats called pre-detonation (or knock). so when you have a high compression engine, then throw boost on top of that, you can cause the gasoline to ignite before the piston is at the top of the stroke. as you can imagine, that is extremely hard on your engine internals, and more specifically, your bearings. this is how you flatten out your main bearings (rod bearings are affected more by oil starvation).

and just so you are aware, what i just explained is how a diesel works. they dont have spark plugs. they also run like 16:1 compression ratio so they can get a whole lot of cylinder pressure built up. also, diesel burns at a lower temp than gasoline FWIW which is why gasoline wont run in a diesel... ignition wouldnt occur as it should. diesel: ~210C, gasoline: ~230C

Blown3000
11-14-2012, 11:55 AM
i swear this is the same guy who loudly protested when he was told that superchargers aren't that great of an option for these cars. i don't know if he'd take the advice of people who run turbochargers.

I think the only person that was loud was you. I will listen to anyone, especially if they are knowledgable and have first hand experience.

Blown3000
11-14-2012, 12:03 PM
blown3000, you need to look at the effects of gasoline at a high pressure. as you increase the pressure, the gasoline will ignite sooner. when you increase the pressure high enough, gasoline will ignite with no spark, thats called pre-detonation (or knock). so when you have a high compression engine, then throw boost on top of that, you can cause the gasoline to ignite before the piston is at the top of the stroke. as you can imagine, that is extremely hard on your engine internals, and more specifically, your bearings. this is how you flatten out your main bearings (rod bearings are affected more by oil starvation).

and just so you are aware, what i just explained is how a diesel works. they dont have spark plugs. they also run like 16:1 compression ratio so they can get a whole lot of cylinder pressure built up. also, diesel burns at a lower temp than gasoline FWIW which is why gasoline wont run in a diesel... ignition wouldnt occur as it should. diesel: ~210C, gasoline: ~230C

I understand the principles of pre-detonation and have addressed that issue. Wondering whether there are limits among other issues. Also like to hear the upside to boosting higher compression engines.

IPD
11-14-2012, 02:05 PM
I understand the principles of pre-detonation and have addressed that issue. Wondering whether there are limits among other issues. Also like to hear the upside to boosting higher compression engines.

the only upside to boosting a higher-compression engine is that you "peak out" at a lower PSI...which means that you don't have to have your boost system held together with massive amounts of force to prevent boost leak.

you will make less power on the same octane.

futurevr4man
11-14-2012, 02:18 PM
the limits are your cylinder compression. you can lift heads on these cars readily without taking the proper precautionary measures. fuel is your biggest limit in general though, as it is what is creating the power. obviously if you knock early enough and frequently enough, your limits would be whatever your pistons/rods/crank/bearings can take.

upsides are that you can make the same power at a lower boost level. to be honest, the honda platform doesnt even tune for knock detection, they tune for most power made. i have a lot of honda buddies that are actually knowledgeable and not just honda fanbois, and they have made some impressive numbers out of their little engines. they last as well, but that has a lot more to do with honda materials engineering than anything. they are durable little engines.

there is also a benefit of more torque with higher compression, whereas you can have a higher horsepower with lower compression. higher compression changes quite a few things, and depending on your ecu, it may not like it as well.

im being nice and playing this question game here, but what is your goal? high compression boosted engines are nothing new, not even for this platform. there is no secret to it, its physics and intuition that will tell you what you can and cannot, should and should not do. if you are sticking to super charging, you very well may want higher compression because you probably wont push that much boost. you will need to make sure your intake temps dont get too high because that will set off detonation earlier as well.

are you the older (40's maybe) guy that came to NG with the red supercharged 3k?

RealMcCoy
11-14-2012, 02:58 PM
Can you be more specific.

I'm not sure what you're looking for...? A lesson in simple physics? how a motor works? Maybe I'm not grasping the question, but it seems pretty simple to me... Do you understand why you can't run 20:1 compression in a gasoline motor? If you increase the volume of air in the cylinder by one atmosphere, you've already compressed it 2:1. Do the math, and you'll find that the difference in compression between our N/A motors and turbo motors is no accident...

ibsorgn
11-14-2012, 07:33 PM
What are the benefits of boost on a low compression engine VS high compression engine? Is there really a need to lower your compression ratio if you are going to use sometype of forced induction? If so why?

You raise a good question, maybe I can help shed some light without talking about specifics.

The higher the compression ratio (CR) the more power an engine will deliver. With that said The rule of thumb is that a higher compression engine (HCE) will perform much better 'off boost' than a lower compression engine because it has its own natural compression to generate power. Generally speaking a HCE will not have as big a jump in power as will a lower compression engine (LCE) will have as boost is applied. Normally the boost threshold will be much lower in a HCE than in that of a LCE.
Normally speaking the higher the compression ratio, the more basic or natural torque the engine will produce. By adding boost, regardless of the means, increases the effective compression of an engine. This increase in cylinder pressure will translate into more power and torque due to greater expanding exhaust pressures.
By dropping the compression ratio allows a higher amount of boost to be used, which translates into a greater volume of fuel and air to be introduced into the cylinder. Naturally this generates more hp and torque - so long as the greater volumes of air and fuel are being delivered. Off boost the LCE will perform more poorly than that of the HCE.

As said by others, forced induction devices which increase effective compression ratios can and will cause denotation but that problem and well as other issues, due to increasing cylinder pressures, will have to be dealt with as boost pressures increase.

IMHO, a higher compression engine with moderate levels of boost make a good combination for a street machine.

Jeremy C
11-14-2012, 08:01 PM
the only upside to boosting a higher-compression engine is that you "peak out" at a lower PSI...which means that you don't have to have your boost system held together with massive amounts of force to prevent boost leak.

you will make less power on the same octane.

There's also the benefit of better off-boost performance. Turbo lag is not as noticeable.

As for why you can't run higher compression and higher boost? There's no reason why you can't really. You'll be spending more money to use less boost, and I don't believe the higher comp is going to offset the hp loss from less boost. This chart isn't for our cars specifically (don't think anyone has done one specific to our vehicles) but it's not going to change much:

http://img28.imageshack.us/img28/7950/crchart.jpg

Not taking credit for this chart at all, but I can't find the one I had made for the Starion/Conquest group a decade ago so I have to make do.

Using this chart and knowing how much work 3S guys put into their cars to run specific psi on their cars can give you an idea of how much you will have to do as well. Want to run 15psi on 10:1? Prepare to build the car as if you were going 22psi on an 8:1 motor and you should be safe.

There are other variables that will change this depending on your setup (direct injection motors run higher compression and higher boost due to how the fuel charge is injected), but general rule when not talking about new, high tech motors is that higher boost + higher compression = lot more build money and more things to break.

Blown3000
11-14-2012, 09:27 PM
are you the older (40's maybe) guy that came to NG with the red supercharged 3k?

Nope - not me

Blown3000
11-14-2012, 09:32 PM
I'm not sure what you're looking for...? A lesson in simple physics? how a motor works? Maybe I'm not grasping the question, but it seems pretty simple to me... Do you understand why you can't run 20:1 compression in a gasoline motor? If you increase the volume of air in the cylinder by one atmosphere, you've already compressed it 2:1. Do the math, and you'll find that the difference in compression between our N/A motors and turbo motors is no accident...

Sorry, You may think your answer is pretty simple but I'm not understanding what you are trying to say. Why don't you put it in simplier terms and help me with the math!

Blown3000
11-14-2012, 09:49 PM
You raise a good question, maybe I can help shed some light without talking about specifics.

The higher the compression ratio (CR) the more power an engine will deliver. With that said The rule of thumb is that a higher compression engine (HCE) will perform much better 'off boost' than a lower compression engine because it has its own natural compression to generate power. Generally speaking a HCE will not have as big a jump in power as will a lower compression engine (LCE) will have as boost is applied. Normally the boost threshold will be much lower in a HCE than in that of a LCE.
Normally speaking the higher the compression ratio, the more basic or natural torque the engine will produce. By adding boost, regardless of the means, increases the effective compression of an engine. This increase in cylinder pressure will translate into more power and torque due to greater expanding exhaust pressures.
By dropping the compression ratio allows a higher amount of boost to be used, which translates into a greater volume of fuel and air to be introduced into the cylinder. Naturally this generates more hp and torque - so long as the greater volumes of air and fuel are being delivered. Off boost the LCE will perform more poorly than that of the HCE.

As said by others, forced induction devices which increase effective compression ratios can and will cause denotation but that problem and well as other issues, due to increasing cylinder pressures, will have to be dealt with as boost pressures increase.

IMHO, a higher compression engine with moderate levels of boost make a good combination for a street machine.

Let me see if I understand, by lowering compression you are able to run more boost effectively by adding more air to the cylinder thereby generating more power. In higher compression engines power is derived not so much by adding air but more along the lines of compressing the air tighter.

Is this why big supercharged dragsters run compression ratios as low as 5 to1?

RealMcCoy
11-15-2012, 12:13 AM
Let me see if I understand, by lowering compression you are able to run more boost effectively by adding more air to the cylinder thereby generating more power. In higher compression engines power is derived not so much by adding air but more along the lines of compressing the air tighter.

Is this why big supercharged dragsters run compression ratios as low as 5 to1?

You're starting to catch on....

There are two completely different factors at play. A motor can be envisioned as simply an air pump... The more air you can pump, the more power you can make. The secondary factor is how much energy(power) you can extract from the mixture you have. The more you compress it, the more energy will be released during combustion. This is not only mechanical compression ratio in play, but also camshaft profile and cylinder head design. There is always a limit to the amount of cylinder pressure any given motor can withstand on the fuel used.... The higher you go with the octane rating of the fuel, (burns slower with higher flash point) the more pressure you can get away with...

Boyle's law states that gas volume and pressure are inverse at the same temperature. As one doubles the ether halves for a fixed amount of gas... That can also be interpreted by if you double the amount of gas in a fixed volume, you double the pressure. Let's imagine you have a perfect intercooler, and you get no temperature or pressure drop as you compress the air: If you increase the the amount of air by one atmosphere(14.7 lbs/sq.in) you have doubled the air charge in the cylinder, and doubled the pressure.

At 10:1 ratio, you decrease the volume by 90%, so your pressure rise on a 100% efficient N/A, with no thermal expansion calculated, would net 147 psi.

At 8:1 compression you decrease the volume by 78%, so your two atmospheres of boost would net you a pressure rise to 134 psi.

At the same boost level (two atmospheres) a 10:1 motor would net 291 psi... Seeing a problem with this picture?

Of course those are all theoretical numbers that would be complete bullshit in the real world when you factor in thermal expansion, pressure drop, and fuel mass... But I think it makes the point.

ibsorgn
11-15-2012, 08:53 AM
Let me see if I understand, by lowering compression you are able to run more boost effectively by adding more air to the cylinder thereby generating more power. In higher compression engines power is derived not so much by adding air but more along the lines of compressing the air tighter.

Is this why big supercharged dragsters run compression ratios as low as 5 to1?

Yes. Of course you can boost higher compression engines for performance improvements but to build for significant boost the CR should come down to be effective.

ibsorgn
11-15-2012, 09:09 AM
you will make less power on the same octane.

I would like to hear more details concerning your statement. Please be specific. Thanking you in advance.

IPD
11-15-2012, 10:59 AM
I would like to hear more details concerning your statement. Please be specific. Thanking you in advance.

based "unscientifically" on me never having seen any 10:1 3/s run above 350awhp on pure pump. 8:1's can break 500 without breaking much of a sweat on pure pump.

RealMcCoy
11-15-2012, 11:01 AM
I would like to hear more details concerning your statement. Please be specific. Thanking you in advance.

Pretty simple statement... You will reach the knock limit of your fuel with less boost. Therefore you will move less air, and make less power.

ibsorgn
11-15-2012, 02:39 PM
based "unscientifically" on me never having seen any 10:1 3/s run above 350awhp on pure pump. 8:1's can break 500 without breaking much of a sweat on pure pump.

Was looking for a technical explanation. Might want to quantify your statements so that folks know when you're writing from a point of knowledge or just making an off-handed remark.

ibsorgn
11-15-2012, 02:51 PM
Pretty simple statement... You will reach the knock limit of your fuel with less boost. Therefore you will move less air, and make less power.

Yes that's a pretty simple statement, however I thought IDP was equating octane to energy not resistance to ignition. Actually I still don't know, maybe he was. Many times these off-handed remarks are very nebulous while others are very direct and informative such as your answer in post #21.

IPD
11-15-2012, 04:25 PM
Yes that's a pretty simple statement, however I thought IDP was equating octane to energy not resistance to ignition. Actually I still don't know, maybe he was. Many times these off-handed remarks are very nebulous while others are very direct and informative such as your answer in post #21.

i put in my $.02 from what i've observed. i'm not the resident expert in fluid-dynamics, physics or engineering. i'll let everyone else fill in the blanks as to why something is the way it is--which mccoy did nicely.

DrGonzo
11-15-2012, 04:45 PM
Here are my opinions from driving both a stock TT and now having a boosted 10:1.

At 6-8 psi the 10:1 TT felt stronger in the bottom end and had more punch to it that a stock TT. This is due to the higher compression giving it a better bottom end and helping the turbos spool faster. About 6-8psi on a 10:1 TT would probably be about what a stock TT runs HP wise.

I was able to get to 12 psi before having to add a FMIC to keep the intake charge temps down as the stock SMIC were not up to the task.

At 14psi I had to add 50/50 meth to keep knock under control. I was able to get it to 16psi and stable before started having knock issues again. I relate this to running out of injector where even bumping the base fuel pressure to over run the stock 360's would not help.

I now have a set of 450's I'll be adding come spring and re-tuning. Hoping to get to 18psi but I'm pretty doubtful. At the 16psi limit I hit I'm guesstimating 360-380 hp. Never was able to get it on the dyno as I don't have one close by me.

I'm basically testing the limits of boosted 10:1 to see what my limit will be. This is on a complete stock cast crank bottom end and stock heads.

ibsorgn
11-15-2012, 07:01 PM
Here are my opinions from driving both a stock TT and now having a boosted 10:1.

At 6-8 psi the 10:1 TT felt stronger in the bottom end and had more punch to it that a stock TT. This is due to the higher compression giving it a better bottom end and helping the turbos spool faster. About 6-8psi on a 10:1 TT would probably be about what a stock TT runs HP wise.

I was able to get to 12 psi before having to add a FMIC to keep the intake charge temps down as the stock SMIC were not up to the task.

At 14psi I had to add 50/50 meth to keep knock under control. I was able to get it to 16psi and stable before started having knock issues again. I relate this to running out of injector where even bumping the base fuel pressure to over run the stock 360's would not help.

I now have a set of 450's I'll be adding come spring and re-tuning. Hoping to get to 18psi but I'm pretty doubtful. At the 16psi limit I hit I'm guesstimating 360-380 hp. Never was able to get it on the dyno as I don't have one close by me.

I'm basically testing the limits of boosted 10:1 to see what my limit will be. This is on a complete stock cast crank bottom end and stock heads.

Don't want to hijack Blown's post but out of curiosity did you try any high octane fuels (racing fuel)? What type of Air fuel ratios (if you monitored) did you hit at 16psi? Very nice to have a fellow that has actual experience in this matter.

DrGonzo
11-15-2012, 07:57 PM
I have only ever run 93. No race gas around me and the few times I went to the track they only had leaded which I don't want to run.

I'm really trying to see what she is capable of on pump gas. So staying away from the 100+ & E85.

AFR's tuned to about 11.0 with the meth on full.

Once I get the 450's installed I'll have to do a full re-tune and mess with the timing more to squeeze the last power out of it.

IPD
11-16-2012, 03:12 AM
Don't want to hijack Blown's post but out of curiosity did you try any high octane fuels (racing fuel)? What type of Air fuel ratios (if you monitored) did you hit at 16psi? Very nice to have a fellow that has actual experience in this matter.

lots of people have 10:1 tt experience. Gonzo's just gone a bit further with meth, etc--whereas most everyone else throws in the towel and goes 8:1 when they hit the wall way below 400whp.

i don't think ethanol/race gas is relevant. compare pump+meth numbers are available on several dr750 cars. the gap between thier whp and gonzo's on a 10:1 is almost 300whp. no need to compare multiple fuels when 93+meth already shows the contrast nicely.

http://www.3sgto.org/f2/dyno-results-my-dr750s-2102.html

now i'm assuming that gonzo is running 9b's. even so, if he upgraded to, say, 13t's...the limit would be the compression ratio of the engine, not the capability of the turbos (and we know that 9b's start to fall down after 14-15psi). my hypothesis is that on a good day (50 degree temps) and pump + meth-on 13t's--gonzo might be able to scratch 400whp...but that's it; larger turbos wouldn't add any additional benefit. and 400whp can be done without breaking a sweat on basic turbo upgrades for an 8:1.

Keyan
11-16-2012, 08:04 AM
You're starting to catch on....

There are two completely different factors at play. A motor can be envisioned as simply an air pump... The more air you can pump, the more power you can make. The secondary factor is how much energy(power) you can extract from the mixture you have. The more you compress it, the more energy will be released during combustion. This is not only mechanical compression ratio in play, but also camshaft profile and cylinder head design. There is always a limit to the amount of cylinder pressure any given motor can withstand on the fuel used.... The higher you go with the octane rating of the fuel, (burns slower with higher flash point) the more pressure you can get away with...

Boyle's law states that gas volume and pressure are inverse at the same temperature. As one doubles the ether halves for a fixed amount of gas... That can also be interpreted by if you double the amount of gas in a fixed volume, you double the pressure. Let's imagine you have a perfect intercooler, and you get no temperature or pressure drop as you compress the air: If you increase the the amount of air by one atmosphere(14.7 lbs/sq.in) you have doubled the air charge in the cylinder, and doubled the pressure.

At 10:1 ratio, you decrease the volume by 90%, so your pressure rise on a 100% efficient N/A, with no thermal expansion calculated, would net 147 psi.

At 8:1 compression you decrease the volume by 78%, so your two atmospheres of boost would net you a pressure rise to 134 psi.

At the same boost level (two atmospheres) a 10:1 motor would net 291 psi... Seeing a problem with this picture?

Of course those are all theoretical numbers that would be complete bullshit in the real world when you factor in thermal expansion, pressure drop, and fuel mass... But I think it makes the point.

You make a very good point, but leave out what the pressure actually does in the cylinder. It is (mostly) not the pressure that makes the gas preignite, but the temperature. By severly increasing the cylinder pressure, you exponentially increase the temperature of the air charge. Which is basically what an intercooler tries to prevent. By chilling the air, you make it denser. Which increases the in-cylinder pressures....but at the same time, significanly reduces the temperature that can be generated FROM that pressure (if the air had 0 energy, compressing it wouldnt create any....but there was energy, compression causes all the molecules to bounce around in a smaller space, which causes friction and an increase in temperature. there is a simple equation for how pressure and temperature relates but i can't seem to remember it right now.) Basically, the lower the temperature going in, the less hot it can get, which reduces pre-ignition potential.
All race gas does is resist pre-ignition at a higher temperature than an equivelent fuel at a lower octane. So it can be safely injected into a higher temp environment with no worries (or less worries) of preignition.

It is finding the balance of compression ratio / intake air temp / octane used that is the key to turbocharged, supercharged, and even naturally aspirated very high compression engines.

DrGonzo
11-16-2012, 08:08 AM
Yeah I'm running stock 9b's. There is no need to upgrade turbo's as the limit of the 9b's is matched to the limit of the 10:1 from what I have done. I have a good feeling that I have hit my max with the 16psi not only with the 9b's but with what the 10:1 can handle. I still want to see if I can get to the 18psi mark even though I know he turbo's will not hold it to redline....

I'm currently building a stock TT block and once I have it completed I'll be swapping out the 10:1 block. Then I start tuning it with the 9b's, get it stable and maxed, then probably look at dr650's. It will probably be 2 years before I get to the dr650's as Iam in no rush to build the engine up.

DrGonzo
11-16-2012, 08:17 AM
You make a very good point, but leave out what the pressure actually does in the cylinder. It is (mostly) not the pressure that makes the gas preignite, but the temperature. By severly increasing the cylinder pressure, you exponentially increase the temperature of the air charge. Which is basically what an intercooler tries to prevent. By chilling the air, you make it denser. Which increases the in-cylinder pressures....but at the same time, significanly reduces the temperature that can be generated FROM that pressure (if the air had 0 energy, compressing it wouldnt create any....but there was energy, compression causes all the molecules to bounce around in a smaller space, which causes friction and an increase in temperature. there is a simple equation for how pressure and temperature relates but i can't seem to remember it right now.) Basically, the lower the temperature going in, the less hot it can get, which reduces pre-ignition potential.
All race gas does is resist pre-ignition at a higher temperature than an equivelent fuel at a lower octane. So it can be safely injected into a higher temp environment with no worries (or less worries) of preignition.

It is finding the balance of compression ratio / intake air temp / octane used that is the key to turbocharged, supercharged, and even naturally aspirated very high compression engines.

That statement is completely true and it was one of the walls I hit multiple times. Hence the reason for having to add the large FMIC and the water/meth injection. At a certain point, it was all about keeping the air intake charge cool with the high compression. The stock SMIC are just not efficient enough to keep the charge cool. Even just regular driving if I got on it I would get knock. Just not enough area in the SMIC to keep the charge cool enough.

Keep in mind that I have enough bolt on's to properly support a 600hp TT "Minus turbos" and I am not to the 400hp mark. But I also know that all of those bolt on's will be moved over and help support the next 8:1 engine I am building so the money spent was not in vain. After I finish the block my only cost will be the DR650's since I have all of the supporting mods already.

Blown3000
11-21-2012, 07:19 PM
I really appreciated the numerous points you have all made. From your inputs forced induction on a NA, in my case supercharging, has its benefits although somewhat limited by comparison to motors using lower compression ratios. From what I've read and your posts, combining a higher compression engine with forced induction gives you better low end throttle, which as a street engine and a daily driver is where I live. From what I gather, my combination was a good choice and I'm happy to have learned that.

ibsorgn
11-24-2012, 10:38 AM
I really appreciated the numerous points you have all made. From your inputs forced induction on a NA, in my case supercharging, has its benefits although somewhat limited by comparison to motors using lower compression ratios. From what I've read and your posts, combining a higher compression engine with forced induction gives you better low end throttle, which as a street engine and a daily driver is where I live. From what I gather, my combination was a good choice and I'm happy to have learned that.

Glad to see you probed this issue. You will have no regrets supercharging your NA. I've been running my Magnuson MP90 for 4 years without a hitch. These little motors respond well with the low rpm boost provided by the supercharger, and your right about the power being provided in our normal low throttle DD rpm range. I'm can be at full boost at 2500.

Blown3000
01-01-2013, 07:21 PM
Glad to see you probed this issue. You will have no regrets supercharging your NA. I've been running my Magnuson MP90 for 4 years without a hitch. These little motors respond well with the low rpm boost provided by the supercharger, and your right about the power being provided in our normal low throttle DD rpm range. I'm can be at full boost at 2500.

Long time getting back to this forum. 4 years problem free! That statement really knocks a hole in those that nay say supercharging. I've been into my mods for about a year and haven't experienced any problems to speak of. I just don't see any drawbacks on supercharging these little motors other than it's not the normal power adder route.

retrorocked
01-30-2013, 12:37 AM
I am a bit late to this thread, but perhaps this will help the OP. There are a couple of things to keep in mind when comparing two engines with differing static compression ratios and boost.

Temperature and pressure are both factors and they are interrelated but it is not necessarily as straight forward as it may seem. Doubling the air/ fuel charge in the chamber (through boost) results in an increase in peak cylinder pressure by approximately 20%, but average cylinder pressure throughout the cycle is much higher, resulting in significant power increases. The static compression ratio will raise peak pressure as well, but will result in a much smaller increase in power due to much lower average cylinder pressure throughout the stroke.

Compressing the air prior to entering the cylinder through forced induction creates heat, the amount of additional heat is determined through various factors, one of which is the efficiency of the device used to compress it. Intercoolers are used to reduce the temperature of the incoming charge, thereby increasing the air density and allowing higher boost levels. Reducing the charge temperature through proper intercooling significantly reduces the chance of detonation, which is what allows you to run slightly higher boost.

Because the higher static compression ratio increases peak cylinder pressure without the corresponding significant increase in average cylinder pressure (which is where the real power is made), you give up some power because you have to give some boost-- assuming of course that all else remains the same.

donniekak
02-01-2013, 12:59 AM
Part of the problem in this thread is that most people in the 3s community have not ever written a timing map. A 9:1, and 8:1 engine can run the same boost, but the 9:1 engine will need less ignition timing, and the room for error between mbt, and detonation will be much smaller. The new BMW turbo's run 10.2:1 compression, and can make plenty of power.

IPD
02-02-2013, 04:15 AM
Part of the problem in this thread is that most people in the 3s community have not ever written a timing map. A 9:1, and 8:1 engine can run the same boost, but the 9:1 engine will need less ignition timing, and the room for error between mbt, and detonation will be much smaller. The new BMW turbo's run 10.2:1 compression, and can make plenty of power.

"plenty" as in limited to 12psi max?

familyMAN
02-02-2013, 10:22 AM
^have you not seen any "chipped" Beemer results? They do well.

I wouldn't run high compression turbo for pump gas only, but I wouldn't run any turbo car, pump gas only:) E85 is allowing 1000+whp 10:1 supra's and 600++, 10:1+ evo's.

donniekak
02-02-2013, 10:31 AM
"plenty" as in limited to 12psi max?

Last I checked, they were making 700hp on the stock engine.
There are also some evo, and Dsm guys making huge power on the new wiseco high compression pistons, 10.5:1.

IPD
02-02-2013, 11:04 AM
^have you not seen any "chipped" Beemer results? They do well.

I wouldn't run high compression turbo for pump gas only, but I wouldn't run any turbo car, pump has only:) E85 is allowing 1000whp 10:1 supra's and 600+, 10:1+ evo's.

until e85 is the standard (99% of gas stations carry it) i wouldn't count it. what good is having a car where you are on a leash or risk blowing up the engine?

donniekak
02-02-2013, 11:44 AM
until e85 is the standard (99% of gas stations carry it) i wouldn't count it. what good is having a car where you are on a leash or risk blowing up the engine?

Ive seen the beemers hit almost 600whp on pump gas.
I know it's hard to believe in 3s land, where hardly anyone actually knows how to tune a car, but writing a good timing map goes a long way with high compression turbo cars.

IPD
02-02-2013, 01:43 PM
Ive seen the beemers hit almost 600whp on pump gas.
I know it's hard to believe in 3s land, where hardly anyone actually knows how to tune a car, but writing a good timing map goes a long way with high compression turbo cars.

well then be my guest and volunteer to be the guinea pig who hits 600whp on 10:1 with pump gas on a 6g72.

DrGonzo
02-02-2013, 06:20 PM
"plenty" as in limited to 12psi max?

Uhh... Whats limited to 12psi? Surely not a stock block 6g72 - 10:1. I run 14psi on the street and 16psi on the track. That was only with an SAFC2.


well then be my guest and volunteer to be the guinea pig who hits 600whp on 10:1 with pump gas on a 6g72.

I just got a Emanage blue so I can play more with the timing and see what I can push out of it. I also just got finished rebuilding my 450's which will be dropped into the car here soon also. Couple weeks and I should have a decent tune back on it. Surely it won't be anywhere close to 600. Probably around 400+ on my stock 9b's. Then again I don't really know of anyone on a TT motor running 600whp on pump gas.

IPD
02-03-2013, 03:25 AM
i was referring to 12psi on a 10.5:1--pure pump. i can't see how you could push it further without hitting knock every time (no meth, no power adders).

and you're right, i don't know of anyone at 600whp on pure 93 octane with a 3.0L 6g72. easy with meth, but that's not pure. i am going to try it with 3.5L though.

donniekak
02-03-2013, 11:25 AM
i was referring to 12psi on a 10.5:1--pure pump. i can't see how you could push it further without hitting knock every time (no meth, no power .

Less timing advance, and a very good combustion chamber design. Have you never seen the Honda guys running 20+ psi with the higher compression engines they use? It does however come to a point where the amount of timing you have to pull cancels any increase in power you get from more boost. You also drive the egts up running such low timing.
Even though it's not on a high compression engine, there are Dsm guys making 600-700 horsepower on pump gas. http://www.dsmtuners.com/forums/dynosheets.php?&do=Pump%20Gas

If I recall, Chris hill was trapping 140 in the 1/4 with a fwd 10:1 setup to.
What it comes down to is tuning ability. The area between running great, and blowing up gets smaller the higher the compression is.

NickS VR4
02-03-2013, 11:34 AM
Just as the chart showed earlier. If you change the compression, and the boost levels stay the same, the internal cylinder pressure will go up. Pressure and Heat create knock. Unless you are able to change the heat, the increased pressure will, IMO, generate knock.

DrGonzo
02-03-2013, 01:36 PM
If I recall, Chris hill was trapping 140 in the 1/4 with a fwd 10:1 setup to.
What it comes down to is tuning ability. The area between running great, and blowing up gets smaller the higher the compression is.

Yeah, But I don't think he was on pump gas when he did those runs. He also didn't care if he broke anything as he would just slap in some new/used parts and do it again. I spoke with him a bunch about it when I first started my project.


Just as the chart showed earlier. If you change the compression, and the boost levels stay the same, the internal cylinder pressure will go up. Pressure and Heat create knock. Unless you are able to change the heat, the increased pressure will, IMO, generate knock.

Yeah was the problem I run into. EGT's too high. That was the reason to move to the FMIC and then Meth injection. I had to keep the intake charge cool to keep the EGT's down. I'm also running a little richer to help cool things down. The knock always seems to be around the 4k mark when it hits. So with the emanage in their now and more fine tuning and timing control, I hope to really be able to push things on this engine.

donniekak
02-03-2013, 03:25 PM
Pencil racers........

J. Fast
02-04-2013, 12:43 AM
Greg, Ivan and I have shared a ton of information comparing a number of high compression and low compression setups here locally. If the turbo, heads, cam overlap, and timing is identical the major difference between the two is the effective cylinder pressure.

At 6000ft a 10.5 static compression engine generating 15psig generates an effective cylinder pressure of 20.01psi

At the same elevation an 8.5 static compression engine requires 22psig to generate an equivalent effective cylinder pressure. The resultant is 20.02 psi.

What this data illustrates is one setup produces more heat from the combustion process (high compression) and the other produces more by introducing more boost (low compression). You can cool the combustion chamber with fuels such as ethanol. The negative effects of the turbos external heat are greater than the internal effects from heat caused by equivalent effective cylinder pressure on a high compression setup.

If you can introduce an adder into the combustion chamber (meth, ethanol) to keep it cooler you will benefit more by going high compression becase you do not have the exponential thermal stress caused by turbo at higher boost pressures.

This is the benefit of high compression over low compression.

The fix is E85. And here's where this will all start to make sense. At 25psi the 10.5 engine has an effective cylinder pressure of 27psi. The low compression 8.5 engine requires a boost pressure of 35psi to generate the same effective cyliner pressure. Which one of these turbos is going to be generating more heat? There's your answer guys.

...and donniekak, quit talkin shit if you have no knowledge, experience, or results of your own to share.

donniekak
02-04-2013, 09:00 AM
...and donniekak, quit talkin shit if you have no knowledge, experience, or results of your own to share.
I'm not the proven troll, kicked off another board.

In case you don't know, higher compression increases the thermal efficiency of an engine, requiring less timing to reach mbt. This is a good thing. The lower the timing advance you have to run to reach mbt, the less degrees of crankshaft rotation you are trying to puch a piston up against an already semi ignited charge, and the more efficient the engine is.
I'm also willing to bet I've written more complete timing maps than you from scratch. I've personally seen some timing maps written by some premier 3s tuners, and they scared the shit out of me.
I have a personal car right now at 9:1 compression that I run at about 26 psi, on straight 93 octane. I also know people that run almost 40 psi on straight pump, you should school them on how to tune.

J. Fast
02-04-2013, 09:58 AM
...and this is on oem cams, oem overlap and lift, oem cam timing, oem heads, oem dsm intake, oem turbo? What style of piston crown? I think you need to give a little more information in order to validate your findings. Please elaborate on you setup.

donniekak
02-04-2013, 10:48 AM
Wiseco 9:1 dish pistons, no quench, cams are 212* @.050", and 111* lsa, stock head, stock intake, td05h20g turbo. More of an enemy than static compression ratio to pump gas, is exhaust gas reversion from a small turbine. I've seen people with gt40 turbines run way over 30 psi on straight pump gas. I have never seen anyone ever measure exhaust manifold pressure on a 6g7x setup. Lots of serious Dsm guys have a pressure sensor off the exhaust manifold, that is logged.
This platform is in the dark ages. If it wasn't for merkel bringing his gm v6 experience via pampena, and aem making a plug in unit, it would still be running afcs spinning bearings constantly, at 3 liters.

Don't get me wrong I love these cars, but most of the people in the online communitys for them have never built and tuned anything else, and have no idea about general building, and tuning concepts.

J. Fast
02-04-2013, 11:06 AM
Wiseco 9:1 dish pistons, no quench, cams are 212* @.050", and 111* lsa, stock head, stock intake, td05h20g turbo. More of an enemy than static compression ratio to pump gas, is exhaust gas reversion from a small turbine. I've seen people with gt40 turbines run way over 30 psi on straight pump gas. I have never seen anyone ever measure exhaust manifold pressure on a 6g7x setup. Lots of serious Dsm guys have a pressure sensor off the exhaust manifold, that is logged.
This platform is in the dark ages. If it wasn't for merkel bringing his gm v6 experience via pampena, and aem making a plug in unit, it would still be running afcs spinning bearings constantly...

What generation of dsm is this setup on? what's your stock lobe separation angle and lift, and your current lift?

I agree with most of what you stated... Especially regarding the reversion window. Yes, the back pressure has never been measured to my knowledge, and there have been no published results.

familyMAN
02-04-2013, 11:14 AM
Only logged ex pressure I have ever seen for a 3S...

http://shop.midwestturboconnection.com/media/MTC%207659%20Stage%204%20vs%20MTC%206954%20Stage%2 02.png
http://www.3sgto.org/f43/group-buy-midwest-turbo-connection-billet-td05-turbos-td05-manifolds-7580.html

donniekak
02-04-2013, 11:45 AM
Only logged ex pressure I have ever seen for a 3S...

http://shop.midwestturboconnection.com/media/MTC%207659%20Stage%204%20vs%20MTC%206954%20Stage%2 02.png
http://www.3sgto.org/f43/group-buy-midwest-turbo-connection-billet-td05-turbos-td05-manifolds-7580.html
Nice find.

2:1 exhaust/intake pressure ratio is definetly not pump gas friendly. Most big time pump gas cars are right around 1:1.

familyMAN
02-04-2013, 11:49 AM
Interesting that the MTC stage 4 (with bigger comp wheel, turbine wheel and "heavy duty" MHI housing) doesn't have a backpressure benefit over the stage 2 turbo. Not sure if the HD MHI housing flows better (or different AR) or if it just has more material to be able to machine for bigger wheel. Because of jrinks results, I wanted to do a stage 3 (bigger comp wheel but same turbine) on my 3.5, but MTC won't make any bigger than stage 2 anymore. I figured it could make the same (or really close) power, without sacrificing spool, since I interpret the data as housing restriction (or exhaust) and not turbine wheel restriction.

Ultimately, better housing is necessary. Would love to see what a FP or PTE turbine housing would do on Jrinks car.