ok, here is the deal. i have 2.73s in my car now, and i am going to get my rear end rebuilt this spring.

my engine is the GM Performanec parts 350 HO. here are some specs...

torque peak of 380 @ 3800 rpm
horsepower peak of 330 @ 5000 rpm

cam: .435/.460 212*/222* I/E

redlines at 5500.

these ratings are of course for a carb, and i am running TBI, but i am assuming that the numbers will be relatively close with the TBI.

i have been tearing my hair apart about this gear swap. ideally, i would like to run stock tires at the track and on the street. (245/50 @ 25.7" diameter).

BUT i am looking for the best acceleration as well. my tranny is rebuilt 700R4 with all of the performance goodies including a 2500 stall converter.

i am on the street a lot, but i may go to the track occasionally.

basically my question is this: with 3.73s, do you guys thing that i will just plain run out of speed on the 1/4 mile? I plan on a 13.xx at 100-110 mph. i really dont want to overrev the engine. ideally i would cross the line at 5300ish rpm.

will 3.73s require a 28" tall tire? will there be a huge difference as far as 1/4 mile times between 3.42s and 3.73s?

i can figure out the mathematical stuff, but there is a parasitic loss in there as well as aerodynamic drag, etc. that makes them inaccurate.

i would like all the advice you guys have to offer, preferably with experience. i was planning on 3.42s, but for some reason i am doubting myself. i do not care at all about mpg, basically just rpms. i would hate to get 3.73s, go to the track, and hit top speed with a couple hundred feet of track left. then i would be forced to go out and spend like 500 bucks on a set of 15" rims and 28" drag radials .

i need help!!!!!

thanks guys.

-brian

------------------
1991 Camaro RS
GMPP 350 HO crate engine w/TBI
Homepage z28boy@twcny.rr.com AIM - "Z28 Boy"


[This message has been edited by Z28 Boy (edited December 14, 2001).]

 

well if it's crbed and your power peak is aat 5000, you should do all right, although with the 700r4 you could probly run slightly higher gear ratios, more street friendly, 3.42's would be more streetable. the tires will be fine, but if you ever hope of knockin 13's youll need some serious suspension work, aand slicks or drag rdials. you wont jhook with that much power nd torque in that car. oh and you might want to run a high stall converter, 3000 or so, so you can launch in the powerband. and just for your info, if you toss that engine/tranny combo in but dont mess with the suspension or tires, youll be starin mid to low 14's, maybe high 13's depending on your launch. you gotta hook it to make the times.

 

Z28, IMO, you need the tallest tire (bigger contact patch) that you are comfortable to run and set your gears to max out at 5500rpm at the traps. with 28" tire and 3.73 you'll be at 120mph at 5375rpm without slippage, so at least at 5500rpm at 120mph. This would be close enough for me. And you'd still only turn 2195 in lock-up on the highweay in OD. I would NOT run 25.7 inch tires! You might like the look, but bigger is usually better if you want to max you times. Plus the heavier/taller tire will actually help you launch and not spin so much.

Now, if you want to use all 4 gears in the quarter mile, you'll need some SERIOUS chassis work, bigger tires and about 5.13 gears. With 5.13's and 28" tires, you'll be at 5174rpm at 120mph without converter slippage. You will have a TERRIBLE time hooking up in 1st off the line without major chassis work and need soft tires aired down to wrinkle. Posi/locker required and a worked-over TH700 to have nice shifts into ALL the gears, and actually, a more mellow 1-2 shift as not to break loose. You'd be at 3000rpm locked on the highway at 70mph, though...

 

Brian, I think 3.73's are too much gear for your setup. You won't run out of steam at the end of the 1/4mi, but technically that "be at your peak rpm in the traps" rule was generally for the gearing in a th-350. You are going to spin the $h!t out of your 60ft times with 3.73's, due to the super-low first gear of the th700. Your motor has plenty of torque to pull into the 13's. I would reccomend you get 3.42's. But on the other hand, if you get 3.23's, you won't have to change your drive gear for the speedo, just the driven gear. One more thing to consider is your OD when cruising on the highway. Unless you have the stuff done to the trans that allows 2/3 throttle in OD, you may not be able to hit OD at 80mph. I saw that happen to my buddy before I chose 3.23's for my car. -Randy

 

A 3.73 ratio with a 24 to 26" tall tire
will be just about right for quarter mile performance for your car. Consider a set of BFG Drag Radials to help you hook all the new power at the track.