Opinions on 3.42 or 3.73 on 383 Tpi
02-04-2018, 12:44 PM
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Car: 89 Firebird Formula
Engine: 383 tpi vortec heads Xr 269 cam
Transmission: 700R4
Axle/Gears: 3.73
Opinions on 3.42 or 3.73 on 383 Tpi
Looking for some opinions
car currently has 3.73 rear and thinking of changing to 3.42 on stock rear 10 bolt. Obviously swap will help when I on highway. Car is driven around city and highway and once a year to track
1. Which gear is better for my combo in 1/4 mile
2. Will switching to 3.42 decrease the chance of rear end blowing up.( I have not used slicks at any time)
I will be adding alu diff cover to beef it up a little and better quality ring and pinion if I change
car details
1989 firebird
383 Tpi with accel runners sdpc Intake vortec heads with mild porting throughout
stall is 2600 or 2800 rpm can’t remember
engine made about 400 hp at flywheel
Subframe connector and no other suspension mods
ws6 car
opinions are appreciated
car currently has 3.73 rear and thinking of changing to 3.42 on stock rear 10 bolt. Obviously swap will help when I on highway. Car is driven around city and highway and once a year to track
1. Which gear is better for my combo in 1/4 mile
2. Will switching to 3.42 decrease the chance of rear end blowing up.( I have not used slicks at any time)
I will be adding alu diff cover to beef it up a little and better quality ring and pinion if I change
car details
1989 firebird
383 Tpi with accel runners sdpc Intake vortec heads with mild porting throughout
stall is 2600 or 2800 rpm can’t remember
engine made about 400 hp at flywheel
Subframe connector and no other suspension mods
ws6 car
opinions are appreciated
02-04-2018, 12:55 PM
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Car: 89 GTA ASC Conv., Prev: 89 GTA 6.3L
Engine: 5.7L L98 TPI
Transmission: 700r4 Automatic
Axle/Gears: 3.27:1 w/ JG1 Options:B2L, N10, U1A
Re: Opinions on 3.42 or 3.73 on 383 Tpi
I ran 3.27 factory gears w mine. But had a shorter tire. 245/45/16. The effective ratio was much closer to the 3.42 you are suggesting. It's about perfect IMO.
Not 3.73 or greater.
Car ran 12.2@115 on those street tires. For what it's worth. That was fast in the mid-90s.
Not 3.73 or greater.
Car ran 12.2@115 on those street tires. For what it's worth. That was fast in the mid-90s.
02-04-2018, 01:34 PM
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Re: Opinions on 3.42 or 3.73 on 383 Tpi
The 3.42 will be slightly stronger, but I don't know how much difference it will make is strength. Any time you increase the size of the pinion head the strength will increase. I'm assuming that the aluminum cover will have the preload bolts for the bearing caps. This will also help.
02-04-2018, 01:50 PM
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Car: 89 Firebird Formula
Engine: 383 tpi vortec heads Xr 269 cam
Transmission: 700R4
Axle/Gears: 3.73
Re: Opinions on 3.42 or 3.73 on 383 Tpi
The 3.42 will be slightly stronger, but I don't know how much difference it will make is strength. Any time you increase the size of the pinion head the strength will increase. I'm assuming that the aluminum cover will have the preload bolts for the bearing caps. This will also help.
my wheels are 245/50/16
what are preload bolts and what purpose do they serve?
02-04-2018, 03:55 PM
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Re: Opinions on 3.42 or 3.73 on 383 Tpi
Covers like the T/A Performance cover have preload bolts that apply slight pressure to the center of the bearing caps to support them when the gears are trying to push everything out the back of the housing.
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02-05-2018, 08:27 PM
#8
Re: Opinions on 3.42 or 3.73 on 383 Tpi
Well assuming 26" tire, 3.42 gives you more room if you go to the track and run 1/4 mile. 3.73 will cause you to run over your peak rpm. Over rev slows you down.
I have done 2.77 to 3.27 then 3.42 and 3.42 gave best performance but it was only marginally better than 3.27. So you start getting into diminishing returns
If you dont run at the track then a 3.73 can be fun on the street. I have tuned a car with a 4l60e and 3.73. Lt1 thirdgen swap car but it was fun! But lt1 can run 800-1000 rpm more than tpi intakes
I have done 2.77 to 3.27 then 3.42 and 3.42 gave best performance but it was only marginally better than 3.27. So you start getting into diminishing returns
If you dont run at the track then a 3.73 can be fun on the street. I have tuned a car with a 4l60e and 3.73. Lt1 thirdgen swap car but it was fun! But lt1 can run 800-1000 rpm more than tpi intakes
02-06-2018, 06:05 AM
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Car: 89 Firebird Formula
Engine: 383 tpi vortec heads Xr 269 cam
Transmission: 700R4
Axle/Gears: 3.73
Re: Opinions on 3.42 or 3.73 on 383 Tpi
Well assuming 26" tire, 3.42 gives you more room if you go to the track and run 1/4 mile. 3.73 will cause you to run over your peak rpm. Over rev slows you down.
I have done 2.77 to 3.27 then 3.42 and 3.42 gave best performance but it was only marginally better than 3.27. So you start getting into diminishing returns
If you dont run at the track then a 3.73 can be fun on the street. I have tuned a car with a 4l60e and 3.73. Lt1 thirdgen swap car but it was fun! But lt1 can run 800-1000 rpm more than tpi intakes
I have done 2.77 to 3.27 then 3.42 and 3.42 gave best performance but it was only marginally better than 3.27. So you start getting into diminishing returns
If you dont run at the track then a 3.73 can be fun on the street. I have tuned a car with a 4l60e and 3.73. Lt1 thirdgen swap car but it was fun! But lt1 can run 800-1000 rpm more than tpi intakes
3.73 is fun right now on street but highway driving is not.
i think it is time to swap back to 3.42 ......
02-06-2018, 06:24 AM
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Car: '86 Bird, 96 ImpalaSS, 98 C1500XCab
Engine: LG4, LT1, L31
Transmission: 700R4, 4L60E, 4L60E
Axle/Gears: 3.73 Tors, 4.88 spool, 3.73 Eaton
Re: Opinions on 3.42 or 3.73 on 383 Tpi
Even for a modest 350 CID in a 3rd Gen, I prefer 3.42 for the street. For a torquey 383, even more so.
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