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3Bar or Anyone re: Boost Pull Back At Track

 
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Old 14 Jan 2004, 09:29 pm
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Default 3Bar or Anyone re: Boost Pull Back At Track

Running at the track Sunday Night with automatic and mods listed below (Mainly Stage 1 & Nitrous 50 hp shot) and a set of Kosei K-1 Wheels with BFG Drag Radials 205 15 50 tires. Due to 10% speedometer error car shifted into OD just before end of quarter.

After each run I had to check 1st gear boost then reset PCM because boost was being cut back below 10 psi without the reset. Once reset ran with normal boost. No Codes were set.

What was happening that casued this pullback? Was it speed/OD related (101mph), or could it have been all the wet system nitrous fuel added (very conservative jetting) combined with the very rich engine that seems to be the case throughout the higher rpm range. Our guess was that the pcm saw the flood of fuel and cut boost back until reset. Pyrometer readings never exceeded 1320 and plugs so no meaninful signs of detonation.

If it was none of the above, any ideas??

Thanks
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Old 14 Jan 2004, 10:08 pm
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Lots of things can pull boost, but most likely you are setting Long Term Knock pullback. The knock sensor is calibrated pretty finely based on combustion noise - and NO2 changes that noise even without heavy knock (if you're too rich, misfire won't trip it). NO2 burns REALLY fast, and causes in-cylinder pressure to spike WAY up. That's my bet. Also, light knock is enough to trip the sensor - long before plugs show signs of damage. Usually if you can hear it in the car, then something is REALLY wrong - sensor isn't functioning, etc. Still, audible knock (knock that you can hear) has to be pretty loud before you hurt something. I would try re-jetting the NO2 first, but ultimately you'll either need higher octane or some way to pull back spark advance when you're on the bottle.

The controller has no way of detecting fuelling other than strictly rich or lean of stoich because the O2 sensor is a switching type rather than a wide-range.

If you bump the speed governor, you'll know it - it is like hitting a wall (a soft wall).
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Old 14 Jan 2004, 10:18 pm
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Thanks, 3BAR, that helps a lot!

There is no discernible knock or plug problems. What's odd is I do not notice boost pull during the run and pyrometer readins seem reasonable. However, when starting back up return road with Nitrous off I check boost at WOT in 1st Gear and that's when I discover boost being limited. Also, as I understand your response the overly rich state should not be thte culprit.

I assume when you suggest re-jetting the NOS you mean richen the mixture slightly?

Thanks

Frank
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Old 14 Jan 2004, 11:11 pm
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Yep, rich is always the first direction you should go if you suspect knock
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Old 22 Jan 2004, 04:52 am
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i have a similar problem, maybe you can help me out.
apexi b-controller set at 15 max on the wastegate, bypassed the stock solenoid, greddy bov, stock one disconnected and plugged line. i get 10-12 lbs and in mid rpm range i get a flutter, dont know if either bov is leaking, if i let off the throttle i get a pop in the front engine compartment with a loss in boost. now i get 10 lbs but dont know how the reduction can work if i bypassed everything. so i think. stock everything else 'cept for k&n cone filter and i do hear a ping. so my main question is how can you tell if the bov is leaking other than taking it out.
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Old 22 Jan 2004, 09:31 pm
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The stock bov can needs to see boost to seal. I garauntee it is leaking, and I am surprised you can even get to 10 psi. You will need to remove it totally and plate it off in order to not leak, or you could just plug the boost reference line back in.
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Old 23 Jan 2004, 03:26 am
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that makes alot of sense. duh!! why didnt i think of that. the greddy bov works the same way it uses boost to "help it" keep closed. i guess if i use a direct manifold boost source i can keep the puter from pulling boost away right? or does it really do that. one more question now that i have you on the line.
im looking at the apexi safc fuel controller it says it is for HOT WIRE,FLAP,PRESSURE SENSOR AND KARMAN. will it work for me.
im actually one of few that want mopar s2 and these products will be going on my vw when the s2 gets here. and i want to experiment with it first on the gt.
thanks for any and all your help
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Old 24 Jan 2004, 12:30 am
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The surge solenoid line (which controls the bov) doesn't ever open to reduce boost, but you could connect a line directly to the port in the compressor housing and bypass the solenoid completely if you were worried about that.

Don't know anything about fuel controllers. But the names you describe are for Mass Air Flow-based engine controllers, which the PT turbo definitely is not.
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