Hi,

 

GTA,

That's no a huge surprise. Unless you do some PROM reprogramming, the ECM is going to trim fuel and spark just as if nothing had changed. That is one of the weaknesses of the speed-density control scheme. You're probably getting all kinds of good air flow with the new can and no extra fuel to compensate, so you are running lean, hot, and powerless.

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

I kinda have to disagree. If a larger cam is installed, it will open the valves further and hold them open longer, allowing more airflow into the cylinder. This would cause a lean condition, but the fuel trim capabilites of teh computer would adjust and add more fuel.

I think where he is hurting is that the cam is capable of allowing more air to flow, but either the intake, exhuast, or a combination of both is negating any benefits that the cam may have made.

What other mods does your friend have? Definatly want to open that exhaust up some.

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Guy's

 

Well, could be a few things, maybe too much cam for the reargears to handle down low in the RPM band, along with the need for some tuning.

An AFPR should help with a fuel issue.

 

I thought all GTA's were 350 / A4, or 305 / M5 not 305 / A4. Plus, with GTA's being very much "loaded" why wouldn't a 1991 have G92 and thus dual cats?

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jmd
L69 / T5

 

I just put a 350 in a 1990 TA with a nice cam and heads and the 2.73 gears are killing the whole thing. Yea 5,000 bucks for nothing. I would look to the gears first.

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1990 TA 350 TPI
SPORTSMAN II HEADS
COMP CAMS 224-230@.50
52MM THROTTLE BODY
24LB INJECTORS

 

What are the specs on the cam? The gears have gotta go. You need at least 3.23s or 3.42s with most mild aftermarket cams not to mention the need for a higher stall speed from the torque converter. The stock Corvette converter may be just right for your combo with better gears- but even if you opt not to get the gears get the higher stall speed converter.

On a Speed Density car you really need to get a prom burned for your exact application and tune with the fuel pressure from there. FYI -The Mass Air cars can handle about a 15% increase in airflow unlike the SD setup.

Again -about the cam... remember this -The more duration a cam has the higher the RPM at which it will make power and torque -hence the need for the gears and higher stall speed <-- this is all needed just to get the engine into it's "new" power band.

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89 IROC-Z 5.7L
130,000 MILES
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K&Ns FILTERS
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I'm agreeing with Vader on this one.

A SD computer will not make real-time adjustments to compensate for the over-lean condition the cam has created. SD has no adaptive learning like MA does.

Get a PROM burned, a gear in the rear, and a tuner who knows WTF he's doing.

That was a bad idea in the first place replacing the cam. I would have spent the time/money on more effective bolt-ons first.

Good luck....


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Mike L.

"If it feels good - stay in it "

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

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