91 vette tpis headers
Thread Starter
Burning Brakes
Joined: Jun 2003
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From: smithtown ny
91 vette tpis headers
i noticed bottom end loss with my headers i do have a 6spd and 3:45 gears how can i get that back?? should i go up to 4:09's i don't do much highway driving mostly around town and car shows. will it be a decent increase???
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
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Re: 91 vette tpis headers (6spd)
What other mods do you have; do you have an AFPR?
You might check your TPS & base timing settings; give it a little more base timing and maybe fuel pressure.
You should already have plenty of grear for an L98; I think you just need a little tuning.
You might check your TPS & base timing settings; give it a little more base timing and maybe fuel pressure.
You should already have plenty of grear for an L98; I think you just need a little tuning.
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 949
Likes: 0
From: smithtown ny
Re: 91 vette tpis headers (65Z01)
the timing is set at 6 degrees btdc 52mm throttle body,vortex ram air,adjust reg set at 42psi with line off,new injectors,ported plenum,accel large tube runners ported,160 stat, frisbee removed, my tps is set at .60 i also have muffler eliminators. as far as a tune up everything is new i put in on the ez link scanner it showed everything is good.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
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Re: 91 vette tpis headers (6spd)
Oops, I foregot your TPS isn't adjustable.
Anyway, try increasing base timing till you just see a little knock retard on the scanner; then back off a deg or so. Recently a fellow Forum member noticed a real improvement in low end performance from base timing tweaking.
Also, I think your fuel pressure is very low, if you're running stock size 22lb/hr injectors. In any case, set fuel pressure for about 920mV on the O2 sensor and see if performance improves. With stock injectors I'm running 48psi and dyno pulls show 12.6:1 at WOT.
Anyway, try increasing base timing till you just see a little knock retard on the scanner; then back off a deg or so. Recently a fellow Forum member noticed a real improvement in low end performance from base timing tweaking.
Also, I think your fuel pressure is very low, if you're running stock size 22lb/hr injectors. In any case, set fuel pressure for about 920mV on the O2 sensor and see if performance improves. With stock injectors I'm running 48psi and dyno pulls show 12.6:1 at WOT.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: 91 vette tpis headers (6spd)
Woooa, 780mV at WOT...you should realy feel a difference from increasing fuel pressure as that is way lean, especially with 21lb/hr injectors. I would think that around 50psi would be a good start on fuel pressure.
Set/check fuel pressure at idle with the vacuum line disconnected and plugged to the plenum.
Also, use the scanner to verify that at steady speed the ECM is in closed loop mode with the O2 sensor swinging between say .350mV and the peak value. This will assure that the O2 readings at WOT are valid.
Set/check fuel pressure at idle with the vacuum line disconnected and plugged to the plenum.
Also, use the scanner to verify that at steady speed the ECM is in closed loop mode with the O2 sensor swinging between say .350mV and the peak value. This will assure that the O2 readings at WOT are valid.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: 91 vette tpis headers (6spd)
If your ECM is in closed loop mode at idle (it should be) the O2 sensor readings should swing between say 350mV and 900mV.
If you increase RPM the readings should temporarily go high and settle back into oscillations when the RPM is held constant.
If you increase RPM the readings should temporarily go high and settle back into oscillations when the RPM is held constant.
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Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: 91 vette tpis headers (6spd)
Try raising the idle to say 2,000rpm and see how it oscillates; I think it should swing to it's max value.
When I raise fuel pressure I monitor the O2 sensor readings at high RPM, i.e. just before the shift points. Under those conditions you can be sure that it will go to the max value and stay there long enough for your scanner to capture a few readings.
When I raise fuel pressure I monitor the O2 sensor readings at high RPM, i.e. just before the shift points. Under those conditions you can be sure that it will go to the max value and stay there long enough for your scanner to capture a few readings.
