Transformer

I just took my 88 GTA to the track sporting my new 3.70 gears. My stock ones were 3.27 and I was really hoping to see better results than a 1/10 improvement. Does anyone have an idea why? even my MPH dropped from 97 to 95. Im running the Nitto drag radials and they were hooking up so needless to say Im baffeled.

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88 GTA Hypertach TM pulleys C.T.switch MSD 3.70 gears SLP runners 1 3/4 headers 58MMTB 210-220-480 cam nitto NT555Rdrag radials

MrJ

3.27 are pretty decent gears to begin with in an auto TPI car. It sounds like your new gears are making your motor rev right out of its powerband too soon.

QUICK305

You need to take into consideration outside temperature and other variables such as how much gas you have in the tank, etc.
The higher outside temp will slow your car down. I dont see how those gears could have made you slower if you are hooking.

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1989 IROC
305 TPI/A4

-just trying to keep it running

Transformer

Its been 100 degrees for the past month. I havent made any other changes since the last time i was there last week. Im still shifting at 4800.

MrJ

Isn't 4800 a little low to be shifting? I shift 1-2 at around 5300 to help cope with the 700R4's bad 1-2 gear drop.

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91 Trans Am WS6
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

supposed 'peanut cammed' car (yeah, right)

MoreMoodThatMod

Ray87Z

Other than outside temp, were all the other weather variables equal? Humidity, etc?

And what about engine temp, all runs in the same ranges or did you allow for some cool down on the previous runs perhaps?

You say you were hooking up but what were the actual 60 foot numbers from both before and after the gear swap?

Check for the obvious, slightly burnt plug wires, fouled plugs, etc. Wouldn't be the first time something unrelated threw off someones comparison tests.

Just tossing some ideas out.

Oh yeah and 4800 struck me as kinda low as well, especially w/ you having runners, a cam, TB, etc. I assume you have experimented w/ the best shift points though.

This is probably no help I know. Hope you get it sorted out though.

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

Dan87IROC-Z

If I were you, I wounldn't go off of only one trip to the track, going from 3.27 to 3.70 should take a good .2 to .4 off your 1/4 ET. Like was mentioned above that there are lots of outside variables that can effect your car's ETs. Also, with the mods you have, I would take the car to the redline when racing, thats where I got my best numbers, but I do have a 2.77:1 rear end.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission

Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip, 160* Thermostat, Accel 8.8mm Ignition Wires, K&N high flow air filters, gutted air box, gutted MAF sensor, Throttle Body Coolant By-Pass, Homemade Ram-Air, Falken ZIEX Z-Rated Tires.

1/4 mile times without chip:
Best ET: 15.7 @ 89MPH
Best Corrected ET: 14.5 @ 96MPH

GTA Jim

As mentioned, there are a lot of variables.. Heck, I can vary 2/10 on the same day with the same gears.. Engine temp alone plays a big role.

Do you keep your old slips ? If so, average up the last 10 runs, then average 10 runs with the new gears.. That should give you a better idea of how you're doing..

And... As Ray87Z mentioned.. How's your 60 ft time.. Are the lower gears giving you more wheel spin off the line ?? You might have to modify your launch to compensate.

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1990 GTA L98/4L60

zippy

well, adding that much more gear to an engine that doesn't care to rev is really your condition. you will find that you can run and other degree or so of advance though. but likely only going to see another tenth or so from your change. another consideration is adding gears also tends to cause more traction problems than you had before. adding deeper gears is really only needed when you have something that really likes to rev. this is why the 2.77 gear cars aren't that much slower than the 3.27 gear cars (not counting the dual cat option on the 89 and newer).