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Old 06-18-2002, 10:34 AM   #1
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Join Date: May 2002
Location: Nazareth, PA
Posts: 55
Car: 89 Trans-AM
Engine: 305 TPI
Transmission: 5 Sp.

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308 or 373 gears???

Can anyone help me with this

I have an 89 TA 5-speed. I have the 308 in it now and want to upgrade to 373. Will this benfit me at all?? What will be the downfalls if any
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Old 06-18-2002, 10:39 AM   #2
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It will benefit you, but you will have to calibrate your speedo.
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Old 06-18-2002, 10:42 AM   #3
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Car: 89 Trans-AM
Engine: 305 TPI
Transmission: 5 Sp.

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So do i need a new cable or something that goes from the speedo to the transmission???
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Old 06-18-2002, 10:59 AM   #4
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No, it's more involved than a cable, you will have to replace the speedo gears in the tranny. Now don't read into that wrong, if you put the 3.73 gears in it won't mess up your tranny, you could actually talk to a local mechanic and find out who does it. I wish I could give you an average price, but I can't remember.
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Old 06-18-2002, 12:12 PM   #5
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I went from the 3.08 to a 3.42 posi rear, now you will need to buy a carrier 3 rear end if you want 3.73's. You can't just stick the 3.73's into the stock rear.

I bought my posi from slp which will fit your axle's since you have a 89, and thats a carrier 3. 1988 and up switched to 28 spline axles. If you buy a new rear, heres the info you need:

GM 7-1/2'' & 7-5/8'' 10-Bolt, 26-Spline (yrs.76-88)
gear ratio of 3.23-Up = carrier 3
gear ratio of 3.08-Down = carrier 2
GM 7-1/2'' & 7-5/8'' 10-Bolt, 28-Spline (yrs.88-Up )
gear ratio of 3.23-Up = carrier 3
gear ratio of 3.08-Down = carrier 2

I got my ring and pinion from GearsareUs.com. Just look for GM 10 bolt 7 1/2'' & 7 5/8".

The speedo has to be calibrated with the gears in the tranny. Since its a manual you have to drop the tranny to get to them, and I ordered the gears from a dealer.

BTW, I heard thats 5 speeds prefer 3.42's over 3.73's and vice-versa for auto. But, I don't think it matters. I bought 3.42's cause I wanted gas milage.

Hope that helps a bit
~Tim
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Old 06-18-2002, 12:49 PM   #6
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What is your setup tranny89. that is really imporntant to know. What are you using the car for? What cam, intake, exhaust.
Is your suspenion built? With a stock motor and suspension, I don't think 3.73s will help all that much. You will smoke the tires, and run out of gear in the quarter.
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Old 06-18-2002, 06:12 PM   #7
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Car: 1987 IROC
Engine: 350 or 305 not sure yet
Transmission: 700R4
Axle/Gears: 3:23

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With TPI you won't benefit as much with 3:73s in the 1/4 as you would with 3:42s. It's important to match your gears to your powerband.
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Old 06-18-2002, 10:08 PM   #8
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Car: 1990 Trans Am
Engine: Lb9
Transmission: factory T5
Axle/Gears: 3.08 limited slip

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my 84 t/a came stock with 3.73 with the l69 motor and 700 and it flies, but i also think that the 3.73's match the l69 which is a 6000rpm motor and due to having some cam makes power up high, im not too sure how well they match lb9's though, they get there power in the low 4k rpm range and run out past 5k, id say go with 3.42 and concentrate on other mods, oh and 3.73's mean worse gas milage and higher cruising rpm
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Old 06-19-2002, 08:21 AM   #9
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Car: 1987 IROC
Engine: 350 or 305 not sure yet
Transmission: 700R4
Axle/Gears: 3:23

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I'm no expert, but I doubt the L69 is a 6k rpm motor. I doubt the cam has a high enough lift, and I"m sure the intake doesn't make power that high.
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Old 06-19-2002, 08:47 AM   #10
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Car: 89 Trans-AM
Engine: 305 TPI
Transmission: 5 Sp.

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Thanks guys for the info. The only reason I figured on 373's is b/c i was going to get them cheap. 100.00$ shipped to my door. But after hearing from all u guys I figure I might just go with 342's. My T/A is stock. I just bought it about a month ago. No work done what so ever. It had 64, 000 miles. Just trying to get a little more take off power.
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Old 06-19-2002, 12:39 PM   #11
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Join Date: Oct 2001
Location: Englewood, CO
Posts: 926
Car: 1990 Trans Am
Engine: Lb9
Transmission: factory T5
Axle/Gears: 3.08 limited slip

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mark, i have an l69 in my t/a and the hp peaks at 4800 and doesnt seem to start to struggle till the late 5k range in the tach warning which is from 5.5k to 6k, a good shift for racing is around 5700 rpm. The cam has around .415 lift and good duration too and duration is a major factor in rpm, not just lift, these motors rpm better than any other 305 and 350 in thirdgens and that is why they were more commonly stuck with 3.73's, just as v6's usually got lower gears as did 4cyl'ers because they rpm better and can suffer the slight loss in mpg
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Old 06-19-2002, 12:39 PM
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