Pump Gas Limitations

[NOMIEZVR4]

also gotta keep in mind...as far as pump gas limits for our rivals that came out in the same era, were all relatively in the same ballpark. BPU supra's normally can't run more than 17-18lbs on pumpgas, RX-7's I barely see running more than 13lbs and 300ZX's are also limited to the mid-teens. The EVO and STi are almost 2 generations newer so its kinda apples to oranges comparison.

[Julianvr4]

2slow2tedius on 3si...I don't post much here but here is my take on it:

Our rear manifold is a 1n3/4 collected cast manifold, our front is a 1n3/4" half-ass log manifold, feeding a turbine housing as wide as my thumb, using a wheel that was devised in the 80's.
This is why the stock exhaust is ok'ish...we have several restrictions in place, and no matter what you upgrade downstream, it doesn't fix the bunk ass hotside we have (and share with many bolt-on turbos) then if you look at the microscopic internal waste gates we have...another fail. We are supposed to be sending exhaust gas outta that straw hole. Someone needs to cast a bigger hotside.

Adam vr4 running 14b's and adapter plates was able to squeeze out more boost after he got an actual manifold setup.

DSM's and EVO's get a set of hks 272's almost immediately because the are so inexpensive to get their stock cams reground ($200) for us, it's about $400 from Delta camshaft who will copy the lift/duration of the HKS 272's. They also have a much newer front mount, and a BIGGER TURBO. EVOs run 20-21 psi stock on the 16g. They don't have 3 cat converters or limited to a 3" down pipe for 3L of displacement. Packaging constraints are less of an issue for them.



Half-ass proof
My last setup on 9b's and stock cams, I would hit fuel cut before I got any knock at 18-19psi. The car was FAST after I put a fuel pump and a clutch in it. The car weighed 3500lbs with a 1/4 tank of gas. This was on a JDM ecu and I had gone through the combustion chambers with 220g and 320g sand paper to knock down the high spots and smooth out the texture. Nothing to it. Note that I was also running open downpipe the entire time. On 9b's. Stock side mounts. Very healthy engine, perfect compression, NEW OEM IGNITION (coil pack/ptu/plug wires).


This next build that I'm very close to finishing (twin HX35's on a BONE STOCK 6G74) will probably poop out at 15-16psi without meth injection just because of the high compression (making 550whp on 93oct) I've done everything I can to make sure that my biggest restriction is the cylinder heads lol.

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[J. Fast]

Lets compare real airflow and timing numbers and see where the discrepency lies. I think the low knock thresholds are functions of end user, tuning strategy, and true EFI fundamentals. I looked at my AEM timing maps for a number of pumpgas setups. Not one has timing over 18 degrees with as much as 22 psi on pumpgas on TD04's.

I think tuning is still very much a black art and premonitions made based on information provided by highly regarded and influential people has been reared and repeated like gospel. When I went to EFIU I discovered much of the information being passed around this community is ultra conservative and no where near optimal.

It will show itself with real data. Lets see some timing maps and the results with them.

[keo92stealth]

Completely agree. Everyone is so bent on sticking with the stock cams...

It's really more of a bang for the buck mentality with this group though. 4 cams are expensive to swap out and no one can "prove" results from just a cam swap alone.

I also agree. Every other platforms cams are 300 to 400 bucks where ours are 700 to 800.

By the way this is a great topic.

[Julianvr4]

Deltacam will copy an hks272, 264, or 280 cam for $93 per cam. They send you the shims, no re-degreeing necessary as if they were new billet cores.

Buying new valve springs to capitalize on the cams is another adventure though. I would also be hung up on paying $500 for a set of springs

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[keo92stealth]

But I was always told, cams don't mean shit if they're in stock heads . I would atleast put bigger valves before I went cams.

[futurevr4man]

But I was always told, cams don't mean shit if they're in stock heads . I would atleast put bigger valves before I went cams . I would just skip the pump gas altogether and just go e85. Chris hills car is the prime example . Shit made 8xx awhp on ethonal type fuel . Probably would have tapped out way before that on pump gas . Cars a beast .

im not just aiming this at you, but in general it really freakin frustrates me when people say things like this. not everyone has e85 available and its ignorant to think they do. i have 1... ONE station within like 60 miles of me. it is NOT pump gas, and more than that, the beginning of this thread said to take e85 and race gas off the table.

this thread has absolutely nothing to do with what fuel you are using. its a discussion of efficiency and power and why we have less of each compared to other platforms. please do not fill this with 'just use e85 cause joe schmo and his brother made more power using it'. of course they did. its the most oxygen rich fuel on the market.

[NickS VR4]

Just a thought... Is it possible we are limited due to the Cast Iron block not able to disperse heat as well as aluminum? Maybe our cylinders are getting too hot.

[masterjr33]

im still going with crappy manifolds causing to much exhaust gas restriction.if you cant clear the stock chambers of recently burnt fuel and gas that is 1400* plus. how are you going to effectivly control the next mitxture coming in from pre igniting.

[keo92stealth]

im not just aiming this at you, but in general it really freakin frustrates me when people say things like this. not everyone has e85 available and its ignorant to think they do. i have 1... ONE station within like 60 miles of me. it is NOT pump gas, and more than that, the beginning of this thread said to take e85 and race gas off the table.

this thread has absolutely nothing to do with what fuel you are using. its a discussion of efficiency and power and why we have less of each compared to other platforms. please do not fill this with 'just use e85 cause joe schmo and his brother made more power using it'. of course they did. its the most oxygen rich fuel on the market.

correct smart ass . I misread the first post . E85 is not in the topic .carry on .