I have read in a couple of different books on improving 3rd gen performance that the 91/92 TPI engines do not have a mass airflow sensor (MAS). They suggest that this fact will cause problems when things are done to the engine to improve the airflow into the engine because the actual airflow is not measured. I am thinking about adding headers and a cat-back exhaust to my Z-28 (305 ci)to improve performance, but don't know if I need to do anything elsewhere to compensate for the extra airflow. Any help would be appreciated.

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90-92 TPI engines use a MAP sensor, which measures the vacuum in the plenum instead of the airflow coming into the plenum with a MAS system. There is a lot of rumors and myths about these engines, and most of it is outdated. You can do any bolt-ons you want to a MAP engine, and it will hardly affect the computer. It is smart enough to compensate. Where you might get into trouble is if you have a 350 or larger engine with a wild cam and large heads, but something like that would affect a MAS engine too. So add headers or a cat-back or anything else you want with no problems.

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

a fuel pressure ragulater will help.this is a valuable tool with a MAP system.

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1991 banditt2 #130 of 600
Project 350 TPI Banditt II
http://www.street-dawg-racing.cityslide.com
http://photos.yahoo.com/tonysams72
http:/discussion-board.com/GreaterCincinnatiFBodyAssociation

 

I don't know if I can agree with that 91Z. U know that when u mod a Speed Density system the ECM doesn't make changes to compensate and needs PROM work. The MAF though, makes all the changes and compensations without anything having to be done to it at all.

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Looking For:

87 IROC-Z28 350 TPI
The car I want.

84 TRANS AM 305 H.O.
Another car that would be OK to own while I still look for the IROC-Z!!

 

Another fine example of the myths and rumors I was talking about.
My previous engine was a 350 TPI, with ported ZZ4 heads, a ZZ4 cam with 1.65 roller rockers, ported stock TPI intake, and SLP 1 5/8" headers. You can see the rest in my sig. I used a stock 305 5-speed chip in the computer. It idled rock solid, even with the air conditioning on. The only changes I had to make was more timing and a little bit of fuel at WOT.
Now, my current engine, I added an LT4 HOT cam with 1.52 roller rockers, TPIS intake/runners, and SLP 1 3/4" headers. For that engine, I did have to play with the idle and part throttle settings in the chip, because the larger cam threw the MAP sensor off. Once I did that, it now idles like a kitten. You can hardly tell there's a large cam in it.

 

So what your saying is that headers and exhaust won't require any adjustments to the PROM with SD, right?? Wouldn't it run better if u did anyway though?? I already know that the bigger mods need PROM work,(such as heads and cam)with SD no matter what, but I have always heard that it needs it with the mods that aren't as big also, and I have read lots of stuff on this.

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Looking For:

87 IROC-Z28 350 TPI
The car I want.

84 TRANS AM 305 H.O.
Another car that would be OK to own while I still look for the IROC-Z!!

[This message has been edited by IROCZTWENTYGR8 (edited March 26, 2001).]

 

Any fuel injected car will benefit from a custom chip tailored to that car, no matter what the mods to it are. MAF, MAP, TBI, V6, etc. The factory programming is on the rich side so the general public doesnt get detonation from a lean engine. But that hurts performance.

 

I know that, but.... n/m I don't want to get into another big conversation about this!! I like MAF and I know u like SD, this will only make another MAF/SD topic again.

------------------
Looking For:

87 IROC-Z28 350 TPI
The car I want.

84 TRANS AM 305 H.O.
Another car that would be OK to own while I still look for the IROC-Z!!

[This message has been edited by IROCZTWENTYGR8 (edited March 26, 2001).]

 

Thanks for the good discussion. There are obviously differences of opinion on the topic. I would like some extra performance without trashing gas mileage which this car does quite well at. If there was a need to modify the PROM after putting on headers or a cat-back how would it show up? Would there be no performance gain, would it run terrible, would the gas mileage be terrible or a combination of the three?

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You don't need a custom prom w/ your planned exhaust mods, period. So don't worry about it. The modding that may or may not need chip tweaking is far more extensive than some exhaust or intake bolt ons.

Bottom line is that headers and a cat-back will be an excellent pair of mods to do to your car. To complement that I would add an adjustable fuel pressure regulator (<$75) and port the plenum. That should really wake up that engine...

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray


[This message has been edited by Ray87Z (edited March 27, 2001).]