Ordering New Transmission, but What Gears ?

[Sean Marconette]

The statement on what is considered a good SLR being 9,10, or 11 for the Walace Racing calculator might be fine for automatics but is completely wrong for a stick car. We do not have a torque multiplier. So our SLR will be higher. Sorry I did not elaborate on SLR earlier.

So what clutch did you get? The dual 7" is very user friendly and extremely predictable.

Sean

[Aubrey N Bruneau]

No, not quite that exotic, Sean. Still just single disk. Rob set it up so it has a "soft hit".

[BRIAN SEATE]

You also have to look at the strongest column with regard to gear selection. We have a 3.08 Jerico in our Vette, but the car is light at 3000 pounds . The old Doug Nash was a 3.25. I would try to talk to Richard Feldman if possible. I don't know him but hes been at it for a long time with the big car and stick. Good luck my friend.

[Adger Smith]

Aubrey a little math:
3.19 1st gear to a 1.91 second is a 40% drop 7,000 - 40% =drop to 4,200
3.08 1st gear to a 1.91 second is a 38% drop 7,000-38% = drop to 4,340
after you get past the first gear:
1.91 second to a 1.32 3rd is a 30% drop 7,000 - 30% =drop to 4,900
1.32 3rd to a1 to 1 is a 24% drop 7,000-24% = drop to 5,320
you always want the % drop less as the gears go up. The 1.91 may have just a little too much drop with either the 3.19 or the 3.08 with your high torque engine it migh not. Either way I would try to work it from peak Tq to peak HP since it is not an RPM combination. This ain't your Dad's Small Block Chevy! That low gear will have to be determined by testing just how much "Hook" you really have.
When I ran a stick I kept 2 low gear ratios and 2 different weight flywheels to tune to track conditions and available "Hook"
Keep in mind that if you are crossing too high at the finish line you can always take a little rear gear out and add the starting line ratio back with low gear in the tranny.
More Math: pick your poison!
2.83 X 5.13 = 14.52 That you had trouble hooking @ 6,200 leave
3.19 X 5.13 = 16.37 Proably too low leaving at a high RPM
3.08 X 5.13 = 15.80 leave at just above peak Tq 4,300
3.19 X 4.88= 15.57
3.08 X 4.88 = 15.03
That is the beauty of using a stick. You can vary the leave RPM, clutch and gearing combos and do like Todd said, Drive it off the line!!
just my .02 for free!
Good luck.

[terry1]

I don't want to steal the thread but; I have always done(and read) finish line RPM,shift RPM and launch RPM calculations off of engine max HP not max torque.
May be I've been looking at this wrong!?

[Adger Smith]

Terry,
You are right, but he has no real RPM HP he has a torque engine. A 409 will not RPM like a SBC. You have to "work" the engine differently. If you have ever seen a 409 piston and pin you don't want to RPM one of those. Just the sheer weight will take things apart. Right Aubrey? I feel 7,000 is really pushing it. BTY you aren't stealing the thread, you are adding to the discussion.. :~)
If I was gearing a good RPM engine I would go for 8-10% RPM over peak Hp as a shift point and then figure the % gear pull back based on that to keep the engine right around peak HP. I would also work the ratios to get it in high gear somewhere around the 330' on the track.
Sean added a good point about stick cars not having the TQ multiplier of a TQ converter. The old rule of thumb that we used was add at least 20% to the low gear ratio of a stick over an automatic.
My 330 ft mark may be a little early for a stick, but a good automatic will respond to that. It would be interesting to watch a stick Comp car with about the same power to weight ratio as he has and see where it goes to high. On second thought that may not be the real deal because most all Comp cars are 5 speeds. Hummm, might be interesting just to watch!! :~)

[Aubrey N Bruneau]

Thanks Adger. No, Terry, you're not stealing the thread.
Just looked at my old dyno chart. Same cam, using stock stamped rockers.
Here's what I have: ( stupid printout wasn't legible in places... or maybe I'm over 50 ? )

4000 450 350
4100 465 361
4200 467 373
4300 473 384
4400 475 398
4500 481 410
4600 479 420
4700 482 429
4800 479 438
4900 479 444
5000 478 456
5100 477 461
5200 477 472
5300 477 478
5400 476 481
5500 465 485
5600 461 491
5700 459 495
5800 446 493
5900 443 496
6000 437 500
6100 439 508
6200 429 507
6300 423 505
6400 419 511
6500 ??? 512.6
6600 407 510
6700 ??? 509
6800 384 501
6900 ??? 497
7000 372 497
7100 ??? 490
7200 357 486

You're right, need to be careful about RPM, but Adger, the failures have never been pistons !... it's the damn "super duper" race car parts on the uncontrollable intake lobe... shattering retainers !
Have a toned down intake lobe now.

I've used the "average horsepower" system.

[Run to Rund]

Scott at Jerico talked me into 3.08 first (1.93, 1.34, 1.00) and said it could be changed to about 3.19 later if needed. His argument was that I would have no time in first with 3.19. I have found with the right clutch slippage, I am OK, but still wonder if 3.19 would be better. If I do decide to change, I will discuss gear strengths with Scott.
I also have a torque type engine that I don't want to over-rev and gear the diff for the top end, then take what I can get in terms of first gear.

[Adger Smith]

Aubrey,
I think the 3.19 is too steep a gear for you combination. It will have too much 1-2 drop and with the 5.13 rear gear you have you will never hook it. IF I tried it I would use 4.88's in the rear. I think you have the shift point just about right. You might want to pull it 200 early in low to second with all that new gear ratio. then string it out in 2-3 & 3-4.
One thing about it is all the thinking and planning needs to be verified by testing.
Do Not shove what you want at the car.
Let the car tell you what it wants.

[Troy Henderson]

Lots of good information, give us an update when you do some testing.