My 85 Trans am has 4.11 gears now(says the mexican I bought it from). Going 70 in od the tach says 3100 rpm. I want to know which gears would give me the fastest times? I ran the car last week and the best it would do was 16.263@85.6mph in the 1/4 ,10.442@67.29mph in the 1/8,60' time of2.343. The problem is that I need to rebuild the motor. It smokes like crazy. When the car shifted at the track 1st and 2nd would shift at about 6100rpm. Is a 85 305tpi suppose to shift that high?

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85 305tpi Trans am
flowmaster exaust
K&N air filter, 4:11 rear gears

 

with 3100rpm @ 70, I would guess you have a hella lot of gear; 4.11's aren't out of the question, but maybe 4.56's if you have stock height tires and your tach is accurate.

I like the 3.73's w/ a T5, but I do highway driving so I would never go higher. You probably should figure out what motor plans you have.. are you going to build a screamer or a stump puller, and then decide on gears.



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jmd
L69 / T5

 

I plan on getting a 81 305 block. Bore it .30 over, install world 305 torquer heads, comp cam and headers. I think that should put me at a mid 14 pass.

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85 305tpi Trans am
flowmaster exaust
K&N air filter, 4:11 rear gears

 

I have 3.73's in mine an I run around 2400-2500 RPM at 70mph. With my original 2.73's i think I was at about 1800RPM if I remember right...

Just as a side note, I really felt a difference when I went from 2.73-3.73 on my old LG4 4bbl. night & day, it was more fun to drive. I thought about the 411, but decided tat a 3.73 would be a better gear since I could get the right speedo gears for the Trans from SLP.

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87 Formula 5.1 converted to TPI Yellow/Black
SLP Dur 206/212, Lift 480/487, Cent Line 112 cam, SLP headers, SLP cat-back exhaust
Modified Stock cold air intake
Ported & polished Stock TPI intake
AC Rapidfire Spark Plugs.
Gil Younger (no yo-yo) Shift Kit
Aluminum Driveshaft
3.73 Posi gear
Baer 12" brakes 4 wheels
KYB AGX Adjustable Shocks & struts
Hotchkis strut tower brace
South side machine frame connecters
Custom reinforced control arms and pan hard bar.
Custom Leather interior
CUSTOM Yellow Gauge Faces

87 Formula TPI (5 Speed) Yellow/Gray STOCK

1967 Buick Riviera 430hp Turns high 14's (Not bad for 4300 lbs)

83 Camaro (Parts)
83 T/A (parts)

http://www.3rdgenformula.com

 

He has an 85, and if it's the stock transmission then it's the 700R4. There were no T5 TPI setups until at least 87 I believe. Also, IIRC, the 85 TPI standard rear end was a 3.23 or 3.27. I have the 3.27 9 bolt.



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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, Rapidfire #2 @ .055", MSD 6AL, 1.6:1 Roller tipped rockers, Homemade AFPR, K&N cone, no airbox, Aluminum Driveshaft, Wonderbar, TB Coolant Bypass, Ported Plenum, Descreened MAF, Syclone Fuel Pump, JET Airfoil, Mobil 1 synth in all but transmission.

http://www.geocities.com/transam85tpi/

 

I have a 85 IROC which is similar to you. I have TPI with auto an it has stock 3.42 rear. For the auto I feel this gear is the best. First gear in the auto is pretty steep (3.08) and with a gear over 3.42 it is too much. My car with similar mods as you turns in the low 14's. She shifts at about 5000 in 1st and 2nd. Shifting at 6100 is much too high. You're way out of your power range.
Rick

 

I had the tranny rebuilt last year. Will changing the rear gear back fix my shift problem? How can I tell what size of axle I have? It has 9 bolts on the differential cover. Will the 81 305 block work with my 85?

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85 305tpi Trans am
flowmaster exaust
K&N air filter, 4:11 rear gears

 

It has been said that 3.42's are the best for a tpi engine because of its good torque. 3.73's are the only other gear i'd use. Derrick

 

It has been said that 3.42's are the best for a tpi engine because of its good torque. 3.73's are the only other gear i'd use. Derrick

 

Rick85iroc- what have you done to your car to get into the low 14's, ive done about all I can and cant get past 15.2. My next step is a 350.

Thanks, Curtis

 

Shouldn't your car be running about 15.2 stock? Mine is right about 15.4 a 2.3 60ft with 88,000 miles and stock everything. You should be mid 14's eighty5trans if you've done everything maybe even low 14's.

 

Sorry for the confusion... my car is not an f-body, it was an L69 4bbl A4 3.73's. It is now L69 longblock, 86 Iroc TPI, M5 3.73's. Since he was talking about choosing gears, I figured 3.73's would be in the realm for his future...


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jmd
L69 / T5

 

The fastest 350 TPI times in Vettes and TPI cars have been shown to me to be 3.07 or 3.08 gears.
I run 3.73 and its fun around town but may hurt my 1/4 mile times..I dont drag race right now so it doesnt mean much to me...0-60 stomp times is great!

TPI engines peak out aroun 4500 rpms or so, so stay under 3.45 gears...any more on a 305 engine is a waste of money,especially if youre concerend greatly about 1/4 mile times.
Even going from a measly 2.73 gears to a 3.08 is night and day for the car...dont overkill it.

One reason I got 3.73 is I had planned to add a mini ram style manifold down the road...since I have the stock TPI right now, if I hammer the gas on take off, the car takes off like a bat out of hell sideways and I sometimes lose control of the car as the back end flies back and forth screaming..its insane with 3.73 gears but fun.
A 1/4 mile racer...it will suffer then for best times.

 

rigthnow i have 3.08 - and I've been wanting to change to 3.42... but it the quarter times are better (i'm guessing because traction is less of a problem) should I keep them and not do the swap??? I like mpg I get with the 3.08s especially with gas being $3.30 for 92 octane where i live... I just want my car to be anywhere in the 13's. It was around mid 14's when I had my old engine, but I've yet to run it with the new one which is actually much slower due ti the fact that the long block I got had a peanut cam(see post about non peanut cam car getting one) - well im doing a cam swap soon maybe next week to get rid of that POS...

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91 z28 lb9 5 speed - hooker 1 5/8 headers - high flow cat- full 3 inch exhaust - home made ram air - tpis airfoil - dual chamber flowmaster - Stage 2 Jet Chip and 160 stat - 8 mm Msd plug wires - 55,000 v hypertech coil/rotor/distrib. cap - Mac. White face gauges - lots of sound system crap...

 

I plan on getting 3.73 gears for my 86 TPI Trans Am 5 speed car.
Should help to get my times a little lower.

Also, I need to edit my sig banner, since I no longer have an Edelbrock Performer RPM carb/intake setup.


High Speed Run: 157mph
Best 1/4 mile run: 14.94@91.67mph
WS6 Trans Am.

[This message has been edited by Zepher (edited June 22, 2001).]