Can't decide! 2 or 3 speed for my combo?

Old 12-28-2009, 10:07 PM
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Join Date: Aug 2007
Posts: 9
Default Can't decide! 2 or 3 speed for my combo?

I have a 68 firebird that weighs about 3300 lbs with driver. It is driven on the street short distances to and from the local car cruises, shows, etc. It may see up to 200 miles in a year.

- 474ci Pontiac

- 742 HP @ 6300 rpm and 672 TQ @ 5100 rpm at the crank

- TH350 with 4500 stall on foot brake

- Ladder bars & coil overs

- 9" rear with 3.70 gear ratio & 28" tall tire

1/4mi ET on motor= 9.90s @ 135 mph @ 6400 rpm (1.42 @ 60')

I plan to start using up to 200hp NOS and want to upgrade to a stronger transmission with a transbrake. That being said, I want to be able to stay with a 28" tall tire and a tall enough gear to drive on the street and keep the engine under 7000 rpms on Nitrous.

Will this combo work better with a glide or Th400?

I would like to go with a glide for several reasons:

- Around 30 lbs less weight

- About 15 HP less to run

- Easier, less costly conversion from a Th350 (uses same length driveshaft, same cross member, turbo spline shaft can fit the Th350 converter).

What changes, if any, would you make to my combo using either transmission for optimum performance?
Robsinno is offline  
Old 12-29-2009, 07:48 AM
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Join Date: Sep 2007
Posts: 4,140

I would go to a 4.56 gear and run the glide. If keeping the 3.90 gear then might lean toward the 400. Just my opinion
Tod74 is offline  
Old 12-29-2009, 08:49 AM
Join Date: Oct 2004
Location: Hudson FL
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sommersracing is offline  
Old 01-13-2010, 12:57 AM
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Location: Napier, New Zealand
Posts: 230

That application would be better with a built TH400. Any gearing more than that 3:70 will be revving too much on the street and you'll hardly get it out of 1st gear.

My 69 Camaro was originally running 28 tires with 4:11 gears and TH400. I changed to 3:70 gears to get the finishing revs down. It still had plenty of torque off the start line with 200hp nitrous and the finishing revs dropped 500rpm. It was a hellova lot more street friendly too.

I think you have it pretty right. Just chuck in the TH400. Much better on the street.
chevyfireball is offline  

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