Transmissions and Drivetrain Need help with your trans? Problems with your axle?

383 tpi vortec heads 3.73 back to 2.77

Old 01-12-2019, 01:37 PM
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Car: 89 Firebird Formula
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383 tpi vortec heads 3.73 back to 2.77

ok maybe this is crazy or just plain stupid but here is my question. I have a 383 vortec head tpi producing over 450 ftlbs torque with 3.73 gears and 700r4 rebuilt.
the car is an 89 formula ws6 no suspension modifications. Since I am producing so much torque and spinning like crazy does it make sense to drop back down to stock 2.77 gears.
i assuming since I have more than enough torque from the engine I can sacrifice some low end torque to wheels for high end speed.
does this make sense? Responses with some real world experience or explanations are appreciated
thanks
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Old 01-12-2019, 02:30 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

What tires are on your car
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Old 01-12-2019, 02:36 PM
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Engine: 383 tpi vortec heads Xr 269 cam
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Re: 383 tpi vortec heads 3.73 back to 2.77

Tires are 255/50 r16 at back
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Old 01-12-2019, 02:37 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

What kind

Originally Posted by toronto formula View Post
Tires are 255/50 r16 at back
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Old 01-12-2019, 02:38 PM
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Engine: 383 tpi vortec heads Xr 269 cam
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Re: 383 tpi vortec heads 3.73 back to 2.77

Bfg sport comp 2
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Old 01-12-2019, 02:51 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

Torque converter stall?

i never hated 2.73-2.77 but 3.73 is alot of first gear in a tpi car

you can go drag radial and tweak suspension some or drop gear down. Lower gear should pick up mileage too
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Old 01-12-2019, 03:01 PM
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Engine: 383 tpi vortec heads Xr 269 cam
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Re: 383 tpi vortec heads 3.73 back to 2.77

I have my stock 2.77 in the garage- will switching back hurt or help my 1/4 mile?
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Old 01-12-2019, 03:21 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

That's a hefty change. Would you prefer it? Depends on if you enjoy the rpm it turns at the speeds you use it at.

If you're crossing the 1/4 finish around redline with the 3.73, the change will not improve the overall usability of the car at the track. Traction will. Usually a 3.42 is an ideal gear for the TPI powerband. If you're considering doing a smaller change, try taller tires.

If you're blowing the tires off at the launch, you might have a MPH at the finish you are happy with, but it will be lower if/when you get traction. Don't let pride mess with you.

A 2.77 rear sitting around for sale doesn't get much interest, and that's for a reason. It's not going to improve the drivability or performance of the car. It's going to add mileage.

Figure out what you really want the car to accomplish and whether a change will do it, and whether you want to spend the time to do it. Traction can be added with suspension or tires, or by possibly pulling some timing but letting it advance back in.
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Old 01-12-2019, 03:45 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

It depends on the actual powerband and converter some.... i had an ls1 car not pickup more than 0.06 et goin from 2.73 to 3.73

my bolt on tpi stuff did pick up a good bit going from 2.77 to 3.27 then to 3.42.
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Old 01-12-2019, 05:28 PM
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Engine: 383 tpi vortec heads Xr 269 cam
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Re: 383 tpi vortec heads 3.73 back to 2.77

So is it fair say without any other changes a change to 2.77 gears would improve 1/4 time with better traction and therefore reduce overall mph at end of 1/4?
i really love my stock formula rims and the tire profile so I prefer not change tire or rim- for me the formula is the rims
thanks for replies
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Old 01-12-2019, 06:40 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

Hard to say if the gearing will change traction. It could but might not. Have you done any suspension work? Lca and brackets?
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Old 01-12-2019, 07:07 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

No suspension changes just welded sub frame connectors . Are there any fool proof suspension changes to gain traction or are they all install and adjust until optimum is reached.
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Old 01-12-2019, 07:12 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

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Old 01-12-2019, 07:12 PM
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Engine: 383 tpi vortec heads Xr 269 cam
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Re: 383 tpi vortec heads 3.73 back to 2.77

Is this what your are suggesting as a first mod to suspension?
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Old 01-12-2019, 07:24 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

Those def helped on my cars. Especially if lower than stockride height.
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Old 01-12-2019, 08:06 PM
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Engine: 383 tpi vortec heads Xr 269 cam
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Re: 383 tpi vortec heads 3.73 back to 2.77

Suspension is bone stock- no changes
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Old 01-12-2019, 09:15 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

What about a different intake than the stock TPI to kill some torque? Likely gain some HP too. Then add traction till you get the right balance. I would stay with the 3.73 personally and build around it.

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Old 01-13-2019, 08:37 AM
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Car: 89 Firebird Formula
Engine: 383 tpi vortec heads Xr 269 cam
Transmission: 700R4
Axle/Gears: 3.73
Re: 383 tpi vortec heads 3.73 back to 2.77

I have done some mild porting on intake, axel runners and plenum and my preference is to stay tpi looking.

so the question is does a high torque 383 match better with 2.77 or 3.73 gears for 1/4 mile time?
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Old 01-13-2019, 10:06 AM
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Re: 383 tpi vortec heads 3.73 back to 2.77

I installed LCA relocation brackets, new LCA's and an adjustable torque arm and it helped traction a TON. Night and day. From my reading, it was likely the new angle with the LCA relocation brackets. This was done with a 3.27 and a 2500 stall on a bolt on L98. I can't see changing gears or an intake (both good ideas) before properly setting up the suspension.
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Old 01-13-2019, 10:55 AM
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Re: 383 tpi vortec heads 3.73 back to 2.77

If your worried about the best 1/4 mile time then the gears are only a small portion of the equation, you have to look at your entire combo and where your making power etc. I'd work on your suspension first IMO

Originally Posted by toronto formula View Post
I have done some mild porting on intake, axel runners and plenum and my preference is to stay tpi looking.

so the question is does a high torque 383 match better with 2.77 or 3.73 gears for 1/4 mile time?
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Old 01-20-2019, 01:46 AM
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Re: 383 tpi vortec heads 3.73 back to 2.77

I have a good 9 bolt with 2.77 gears I have to check the cones but I don't think they bottomed out I don't even have 99,000 yet on my car
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Old 01-24-2019, 07:59 PM
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Re: 383 tpi vortec heads 3.73 back to 2.77

Originally Posted by toronto formula View Post
I have done some mild porting on intake, axel runners and plenum and my preference is to stay tpi looking.

so the question is does a high torque 383 match better with 2.77 or 3.73 gears for 1/4 mile time?
I setup a 1987 Firebird 350 TPI with Dart iron eagle 180s and a GM Hotcam with a TH400 with a 2,800 stall converter and 2.73 gear. Car still roasts the P275s off the back.

I also had 3.07 gears in my old G20 van with a TPI 383. Stock 1,600 rpm converter in a beefed up 4L60E. It ran a 13.9 @ 101 mph.

Last edited by Fast355; 01-24-2019 at 08:03 PM.
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