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Transmission choice

04/15/2021 10:52
FIRSTLAST
421 HO block, going into a automatic rope drive car now so there will be some tunnel cutting on the 63 Tempest any way you choose. Question is where do I go when my rear starts at 4.90 ratio. I would guess that will be re-geared at some point when I learn I can't drive faster than 55 with out extreme RPMs. The options here are a Gear vendor overdrive for road use, behind a M21 trans, or go to the Tremec TKO 600. Car needs to be street-able so there this is not a pure race build. Please don't puke up this thread.
04/15/2021 11:19
ASHLEY P
Great topic. Now, what is the end goal....what do you want the car to accomplish?
04/15/2021 15:14
FIRSTLAST
Tribute 421 SD car but I see it running track sometimes, never into the roll bar category. At least not in this go round. I would expect max HP to be about 450 on the limitations of the build, since using authentic components, not aftermarket heads, etc... Pro street in some handling characteristics. Do be determined how I lay out the rear suspension. Track bar has a few limitations, and I am still exploring outside shops who may have a better solution like Art Morrison. I am just on the transmission on this post. The 4.9 12 bolt is already in the project, the engine is pretty well set if I can ever get any shop cooperation on the ridiculous long wait.
04/15/2021 15:23
FIRSTLAST
I need clarification on the starter mounting. Pre 65 had start on the bell housing as I understand. Post moved it to the block. Did I just reverse that? That would possibly require a change in transmission choice. Borg Warner T10 ended about 63 and Muncie M20 started. I don't know what that means for my options since this is a 63 421 block. I will study some conversions people did when I get a little sit down time.
04/15/2021 17:14
ASHLEY P
I have no knowledge on starter mounting for 63. And I've never heard of a 4.90 rear gear. Do you mean 4.88? Or perhaps 3.90? Either way, I'd suggest "working backward" on your design. Work from your "knowns": Peak HP and car race weight will give you trap speed. Trap speed, rear tire circumference, and max engine RPM combine to tell you what rear gear to run. Then think about trans gearing.
04/16/2021 12:21
ASHLEY P
Another way of looking at this subject: how fast (1/4 mile trap MPH) do you think your car will be when finished?
04/16/2021 12:21
FIRSTLAST
I need clarification on the starter mounting. Pre 65 had start on the bell housing as I understand. Post moved it to the block. Did I just reverse that? That would possibly require a change in transmission choice. Borg Warner T10 ended about 63 and Muncie M20 started. I don't know what that means for my options since this is a 63 421 block. I will study some conversions people did when I get a little sit down time.
04/16/2021 12:25
ASHLEY P
What?
04/16/2021 18:43
ASHLEY P
Use the calculators at Wallace racing.
04/19/2021 12:27
ASHLEY P
What distance will you race the car, 1/4, 1/8, 1000'? If you're going beyond 1/8, you need to change the 4.90 gear (IF it's indeed 4.90).
04/19/2021 22:43
FIRSTLAST
1/4 mile. Its only partial track, I would say mostly road. But if it was a good build and strong, drag week would be a blast. The rear is about a 68 Olds 442, makes it a 3 year oddball rear. Diffs are hard to find. So maybe I threw money away. aIf Art Morrison could devise me a rear, I would end up with a Moser or Strange center section most likely, and Ford diff. There is no bolt up kit. Everyone of these is highly custom, and why most let channel steel midway into floor, build a track race multi link. Simple,,effective, strong, but not road course appropriate.
04/20/2021 13:00
ASHLEY P
How can anyone provide accurate advice without knowing your race weight, tire size, or actual rear gearing? And you bought an Olds 12 bolt? Not the best choice for drag racing....why did you buy it?
04/20/2021 20:13
ASHLEY P
I cannot find a 4.90 gear for the Olds "12 bolt". So, what do you actually have?
04/20/2021 21:57
ASHLEY P
Build a 4 cylinder, manual transaxle 63 Tempest. Use the stock rear transaxle, mod the 4 cylinder by de-stroking it, aluminum rods, ported head, roller cam. Cam it to turn high rpm (7500). Those engine mods will make much more HP than stock without making a lot more axle breaking torque. I've got the transaxle, two factory cranks, and factory 4 barrel intake for sale. Your car would be quick and unique.
04/23/2021 17:09
ASHLEY P
You should also consider adapting a late model IRS system into the Tempest. I know of 2010 ish model Caddy CTS-V cars that are running 6.50s/110 mph in the 1/8 mile drags while still running the stock rear diff and axles, in cars that weigh 4400 lbs! What's the tread width of the Tempest? See of offset wheels might make the Caddy setup fit the Tempest....might save you lots of fab time/money.
04/28/2021 15:44
ASHLEY P
What's the status? Got any input on your weight, rear gears, tire size...ect?
05/03/2021 23:52
FIRSTLAST
I have tge vover number on the 68 Olds 12 bolt. Need to pull cover, or spin and count to affirm the 4.9 ratio. One oddity , the Olds had 12 bolts on cover but 10 on the diff. So it would not be as robust as the Chevy 12 bolt. In the positive, the Olds did not have the inside C clips.
05/14/2021 16:48
ASHLEY P
Do you have any interest in mounting the complete rear "subframe" from a late model independent rear suspension car into your Tempest? That would likely be easier than fabricating a 12 bolt suspension from scratch. Just center the wheels from front to back, from side to side, angle the subframe to get the correct pinion angle, then connect the subframe to your roll cage.
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