Have a 91 5.7 Z-28, currently has the basic bolt on mods....Edelbrock and Flowmaster exhaust, F.P reg, ign stuff etc. Runs 14.40 at 94 mph (1.95 60' on an old pair of DOT slicks) Now has 3.23 gears am goin to do some porting on the heads this winter and was wondering what anyone thought as far as 3.73 or 3.42 gears? Just doin minor stuff to the heads....bowl blend and port match, was also gonna clean up any problem areas in the intake. Seems like 3.73's may be a bit much for the stock cam and mild heads?? Any suggestions or experience here are welcomed.

 

If you are staying with the stock cam then I would not spend money on 373, maybe 3.42. You will see a little difference in 1/4 mile maybe .2 off.

However anytime you change your ratio your gas mileage will go down on highway bacause your RPM will be much higher.

Myself I am staying with my 3.08 and will be adding a ZZ3 cam soon with ported stock heads.

Anyways that is just my opinion but again what the hell do I know!!!

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89Iroc, 305 TPI, WC T5, 3.08 Posi, Headers, Hooker Y-Pipe, 3 inch over the axle, Flowmaster 80, No Cat, Aluminium Driveshaft, Ported Plenum, Air Foil, K&N, AFPR, All free mods,

 

I am a new GTA owner but the way I see it, it certainly couldn't hurt as long as you expect a dramatic loss in mpg. Any mods you pick up down the road will only be multiplied by the new rear.

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Tony Rolof
'89 GTA 5.7L, T-Tops

 

29mpg here with 3.42 gears and a T-56 manual trans. Same setup with the TH700R4 auto ran 13.19sec @ 103mph in the 1/4mile.

Keep it tuned, pick your parts carefully...stick with what is proven to work.

The head work you mentioned is a good start. I'd punt the stock cam, add headers and better exhaust, and clean up the stock TPI plenum and runners. That EGR bump in the plenum is good to remove. You can also clean up the runners where the tubes meet the plates, noticeable obstructions there.

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1982 Z-28

See http://www.mycar.net/mafb/registry/detail.cfm?id=276 for details

 

I think I would go with the 3:45 3:73 is alittle low you may also want to lok in to a better torque converter.

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87gta 355 fastburn heads,slp headers,flowmaster exhaust, LT4 hot cam and a lot more

 

The higher the gearing the smaller the pinion, on a rear end as fragile as the 3rd gens have stick with the 3.23s. Especially if you have an auto, unless you just want to spin the tires and not really go anywhere. 3.08 first geat and 3.73s is a bit much for the street. Now a 200R4 with 3.42 is another matter, or stick. I put almost 200K on my FBod with the 700R4 and 3.23s and overall was a nice package. I have a bunch of miles on a 200R4 and 3.42s that is also a nice match.

 

Hey, kevinc do you know what kind of gas mileage you got on the highway with the 700R4?

Ben