Would I benefit with 3.73 gears?

[jdpolzin]

Well I have a spare 3.73 posi 8.5 rear end in the garage. I'm needing to run a slightly shorter tire on my car because it's lowered. I'm wondering if the 3.73 gears would benefit me at all running a 26 or 27" tire?

My combo:
249 Stage 2
GN1 heads
3200 PTS 9/11 billet convertor
full roller full billet 200r4
70HPQBB turbo

 

[Adrian87]

I've always heard that 3.42's are optimal, anything deeper and it won't take advantage of the torque curve these TR's have..especially your combo!!

 

[Russ Merritt]

Well I have a spare 3.73 posi 8.5 rear end in the garage. I'm needing to run a slightly shorter tire on my car because it's lowered. I'm wondering if the 3.73 gears would benefit me at all running a 26 or 27" tire?

My combo:
249 Stage 2
GN1 heads
3200 PTS 9/11 billet convertor
full roller full billet 200r4
70HPQBB turbo

You'd want to go the other way, 3.23 gear

 

[boostingbuick]

I agree. ^^^

 

[toofastforyou]

You'd want to go the other way, 3.23 gear

X3!...I understand that you want to compensate for using shorter tires, but you'd have to go the other way around!...Using 3.73's will WORSEN the problem...If you really want to try some other gears, then you should go with some 3.23's...

Claude. :smile:

 

[jdpolzin]

Yep I just realized that. I may just use this rear end for my turbo V8 car. I was thinking bass ackwards!

 

[bison]

If you had a solid cammed engine with more turbo you MIGHT benefit. Probably not though. Most likely better off going the other way as Russ suggest. You gear the car to use its power range and be able to go through the quarter without running out of gear. I would not want to try and run a car with a really short tire myself. 60' times will be all over the place. Post some data logs of quarter passes so we can look at your rpm and see how efficient your converter is. I cant make any useful rec without data.

 

[mygn276]

I went with the 3.23 gear and a 30 inch tire and lm happy

 

[SPOOLFOOL2]

Years ago, on my 99.9% street driven GN, I went to a 28" tire. Only to realize that I did'nt like the way it made the car bog in stop and go traffic. I then went to a 373 gear to bring the gearing back to close to stock. I think that it ended up being 10% lower. I've had this combo in my car for about five or six years now and love it. When my car ran a 11.17 @ 122 mph, I hit the traps right at 6000 RPMs. Now that I should be running in the tens, I may need to shift to OD at about 1000 ft.

For a 99% street driven car, with a big 28" tire, I highly recomend a 373 gear for streetability. With a little lower gear, one might even be able to get away with a little tighter stall on the converter.

I'm guessing that my car might be a tenth quicker in the quarter mile with the stock gear. However, I'm not willing to give up the fact that I've got a ten second car that drives like a stocker in stop and go traffic, to change it back.

Happy spooling

Mike Barnard

 

[SGRIM]

You'd want to go the other way, 3.23 gear

DING DIND DING!!! Good call Russ!

 

[Warp6]

Don't do it. It slowed my car down. I went back to 3:42s. Russ is correct, with a shorter tire go with a higher gear

 

[Fuelie600]

I remember years and years ago (Red's old), Red Armstrong telling me he went to 3.31's in his black car to take advantage of the torque these motors make. I feel these cars wind out a little too quick, and a taller gear would really benifit.

 

[bison]

Years ago, on my 99.9% street driven GN, I went to a 28" tire. Only to realize that I did'nt like the way it made the car bog in stop and go traffic. I then went to a 373 gear to bring the gearing back to close to stock. I think that it ended up being 10% lower. I've had this combo in my car for about five or six years now and love it. When my car ran a 11.17 @ 122 mph, I hit the traps right at 6000 RPMs. Now that I should be running in the tens, I may need to shift to OD at about 1000 ft.

For a 99% street driven car, with a big 28" tire, I highly recomend a 373 gear for streetability. With a little lower gear, one might even be able to get away with a little tighter stall on the converter.

I'm guessing that my car might be a tenth quicker in the quarter mile with the stock gear. However, I'm not willing to give up the fact that I've got a ten second car that drives like a stocker in stop and go traffic, to change it back.

Happy spooling

Mike Barnard

If your going into OD then you are probably losing more than a tenth. Especially if your at over 6000rpm (even with 3.73's) on a 122mph trap speed. Your converter is eating up a lot of mph. Chances are even if you switched back to 3.42 you would still be at too high of an rpm for the best et's. AC converters are fine up to about 120mph trap speeds in these cars. After that they seem to slip a lot when you throw a lot of power in them. I had a similar situation where i was at about 6k trapping 126mph with 3.42's and a slick that was over 28". Now i have a drag radial that doesnt get over 27.5" and a PTC converter combo that trapped 133.4mph crossing at 5700-5750. Huge difference. Converter slip was 3-3.5%. The PTC slips less on light cruise also.

 

[SPOOLFOOL2]

If your going into OD then you are probably losing more than a tenth. Especially if your at over 6000rpm (even with 3.73's) on a 122mph trap speed. Your converter is eating up a lot of mph. Chances are even if you switched back to 3.42 you would still be at too high of an rpm for the best et's. AC converters are fine up to about 120mph trap speeds in these cars. After that they seem to slip a lot when you throw a lot of power in them. I had a similar situation where i was at about 6k trapping 126mph with 3.42's and a slick that was over 28". Now i have a drag radial that doesnt get over 27.5" and a PTC converter combo that trapped 133.4mph crossing at 5700-5750. Huge difference. Converter slip was 3-3.5%. The PTC slips less on light cruise also.

Good info.

Thanks.

Mike B.

 

[dr_frankenstein]

hmm........... this might lead me to pull out my 4.56's for a set of 3.73's or lower!

A.j.