whats pre-detonation feel like?

[thor'svr4]

is there any difference in the 'feel' of the car? for example when i got spark blow out before dyno tuning the car actually seamed to violently sputter/ slow down. it was as if someone stabbed the brake peddle for a milli-second. So what’s knock feel like? does the car buck, sputter, go lean, ect?

also is .032" to large of a spark plug gap?

and yes i do have a data logger. but im also still in school and swamped with homework so i doubt ill have a chance to play with the data logger, boost, timing, plug gap, afr, ect for at least a week or two so any info on how a car reacts to knock would really help me out right now. the cars acting wierd at 12+psi. ive got a walbro, hot wire, 550s, 10:1 afr and the car still seams to be breaking up at 12+psi. im hoping it spark blow out and not knock.

[Austin@STM]

First of all, dont go WOT anymore until you have time to fix the problem.

What is the feeling you have with your car now?

10:1 is REALLY rich and could be the reason for your misfires, because chances your not knocking to bad with that much gas in there, but you still could be, as it doesnt sound like your car is very tuned.
Do you know what fuel cut feels like? It basically feels like the car shuts off for a second, is that what you feel?

[thor'svr4]

well i was running the car tuned, then spun a bearing. so i rebuilt the short block. the only thing i really changed was the piston compression. my new pistons are ross 8.5:1 vs the stock 8:1. but when i started driving the car around after the rebuild i thought i noticed the car was running a little lean. under boost i thought i used to be ~11.5-11.7:1 afr. but now i would start out at 10:1 and by ~5000rpm i was at mid 13's afr at just 6-8.5psi! As much as i hated to mess around with my old dyno tune i felt the car was running way to lean so i just added some fuel to the tune to keep things safe for a little while, till i figure this situation out. however adding fuel didnt effect the issue. at ~12psi my car would still start sputtering.

the car does feel a little like its getting fuel cut, but it cant be a fuel cut if im still at 10:1 afr right?

as the car sits ive just got the boost set to 8.5psi (spiking to 9.2) and it seams perfect other than running really rich. its just that the instant i hit 12psi the car stops reving up. it almost feels like ive got a 5000rpm rev limiter.

edit:
im still running stock timing (6-7* iirc) and have not played with the cam sensor at all since ray last adjusted it. i did remove the head and cams when i rebuilt the motor, but i left the sensor bolted to the head and never messed with it so i should still be at stock timing.

[KeithMac]

There`s no mistaking fuel cut, it`s like hitting a brick wall!.

[GTwizard]

Dude. your tuning is way way off. 10 to1 AFRs is nuts. You are pig rich and fowling the crap out of your plugs. 14.7 to one is still nornel driving range and as you add boost you do wish to get richer and you are getting leaner. Idle should be 14.7, as boost goes up a little richer and even at full boost you most likely will never need 10 to one. That's just strait up crazy. As far as what does pre ignition feel like? It's a full lack of power and sounds like pinging or valve clatter. If you keep running as rich as you are you will fill the chamber with carbon deposits and get some good preignition going do to all the hot spots from all that carbon glowing red hot and igniting the fuel before you get to TDC.

[stealthee]

Adding fuel wont solve predetonation. Predetonation is a spark timing issue, not a fuel issue.

[thor'svr4]

Dude. your tuning is way way off. 10 to1 AFRs is nuts. You are pig rich and fowling the crap out of your plugs. 14.7 to one is still nornel driving range and as you add boost you do wish to get richer and you are getting leaner. Idle should be 14.7, as boost goes up a little richer and even at full boost you most likely will never need 10 to one. That's just strait up crazy. As far as what does pre ignition feel like? It's a full lack of power and sounds like pinging or valve clatter. If you keep running as rich as you are you will fill the chamber with carbon deposits and get some good preignition going do to all the hot spots from all that carbon glowing red hot and igniting the fuel before you get to TDC.

sorry maybe i didnt word that correctly. i wasn’t running 10:1 at idle. i was 14.7-15:1 at idle and light cruising (-8 to -5 vac). during wot the car would richen to 10:1 but start to lean out a little past 5000ish rpm. I know 10:1 is pig rich, I just richened up the tune to eliminate the possibility of pre detonation caused by the motor running lean. Ill lean the motor back out to 11.7ish during boost as soon as I can.

i went out and bought a timing light so i could check my timing. when i was getting dyno tuned my base timing was at 3-4* advanced, but I was told that was really retarded and I should have been around 6* advanced. After adjusting the base timing the car picked up ~70 whp iirc. later when i had to rebuild my motor i now knew how much timing affected the tune so i never moved the CAS. i had to remove my cams to replace my VSS but I figured since i never moved the CAS sensor my timing would still be at 6*. however when i threw my timing light on the car i was at ~22-25* advanced at idle. so i backed timing down to 6* and was able to log many clean pulls at 7, 8.5, 10, 11.5 and 12 psi. however at 13.5 psi i got 24 counts of knock right as i let off the gas at 6400rom. im not sure what caused the knock, but i couldn’t get it to happen again. to be safe i backed down the timing to 5* at idle because i figured retarding the timing 1* more would help out with the slightly higher comp pistons. now i dont get any knock when i log, but the car still felt like it would 'stumble' at above 5000rpm. my HKS EVC was having a difficult time holding my boost steady so i started playing with the gain settings and that seamed to help steady boost and the car feels strong but im still getting a little bit of stutter as i get up past 5000rpm. my data logger shows the stutter in the rpm graph but doesn’t show any knock or any timing getting pulled due to knock.

So i think my knock issue was due to having such an advanced base ignition timing, but I think I also discovered a possible ignition issue. my plug wires had a little problem with arcing, (shocked the hell outta my hand) so i did a ghetto fix and wrapped them with electrical tape until i can find some new wires. however i think the wires are either still arcing (only above 13+psi of boost???), or the plugs are getting blown out. but whatever the issue is its not knock according to my data logger.

The only thing that’s making me feel uneasy is my oil pressure at idle. Since retarding the timing my idle dropped from ~1000-1100 to ~700-8500rpm and my two oil pressure gauges no longer agree with each other. My factory gauge used to be exactly at the lower ‘big’ line and my sunpro autozone gauge always read 20-22psi at idle. Now my sunpro will read ~18psi at 800 rpm but my oem gauge reads about halfway between the bottom the gauge and the lower ‘big’ line. While im cruising they both seam to give a good read out. The sunpro says ~40-60 depending on the rpm while the stock gauge is almost always a little over halfway between the lower ’big’ line and the upper ’big’ line. Ive got a brand new bottom end so hopefully the small drop in oil pressure at idle is just because of the drop in my idle and not because of the small amounts of knock I was getting. Ill change the oil this weekend and see how it looks.

If the oil looks good then ill buy some new wires and plugs. Try to up the boost and data log. If everything looks good with no knock ill start leaning out the afr, buy a safc II or neo and then bring the car back to ray to see what the car can really do.

:crosses fingers for 450+ awhp on 13T’s with a stock dp / exhaust:

Oh and on a side note I could not hear any knock coming from the car, even during a pull where 2-8 counts were recorded. On the one pull with the 24 count spike I felt a stutter, but while looking at the data log I realized the stutter happened at ~5000rpm and the knock happened right as I lifted at 6400rpm so I want able to hear or feel the knock. Maybe I’m just deaf? I’ve got a stock exhaust so its not like my cars loud…

[thor'svr4]

There`s no mistaking fuel cut, it`s like hitting a brick wall!.
is it possible to get fuel cut but not run lean? i know that sounds stupid but i figured i would ask.

[stealthee]

For 12 psi .032 is more than small enough. Going too small is detremental. You only want to run the smallest gap needed to avoid blowout. He's not going to get blowout at .032 ast 12 psi.

[stealthee]

Say what? Thats more fuel. Fuel might foul the plugs, but its not going to cause blowout.

[thor'svr4]

i bought a book on forced induction engine management a little while ago and ive been reading it quite often lately. its not the most specific book but it seams to cover all the basics and get as detailed as i could ever need. Page 48 "The spark initiates the combustion process in normal operation. for this to happen, the spark energy must be great enough to create an arc across the plug gap. as the air/fuel ratio charge mixture density increases, more energy is required to create the electrical arc in the gap. charge density is directly proportional to the engine load, so it is directly affected by throttle position, port velocity, compression, and manifold "boost.""

to me this seams to mean that if you run a lot of boost with a wide plug gap (a/f ratio is irrelevant) that your spark plug may not spark because it didn’t have the energy needed to jump the gap. that also seams reinforced by the fact that i got sparkplug blowout on the dyno due to my plugs being at .045". im sure if 'blow out' was caused solely by a rich afr than i wouldn’t have been told i needed to replace the plugs and re-gap them before the dyno tuning could continue...

ill try to lean it out a bit for wot but im 99% sure im not feeling the car misfire because of it being rich.

[Chris@Rvengeperformance]

yes, once you get near 10.0:1 the ignition system may have a hard time. With mixtures that rich it is harder to light off and you may misfire.

[thor'svr4]

alrighty ill back the afr down to mid 11's. that should be lean enough to avoid misfires right?

[Chris@Rvengeperformance]

even 10.5 is