964: my new (to me) race tranny

[kurquhart]

One side effect of all my recent posts regarding non-stock gearing, etc. was contact with a fellow Pelican that was selling a race box. I ended up purchasing it for about half of the cost of the G50/32 package I was considering. UPS delivered it to Black Forest this past week:



The transaxle started life as a stock G50/20. Stock first and second were retained. Stock 5th was moved to 6th and three custom ratios inserted:
3.81
2.04
1.56
1.22
1.02
0.92

Six steel syncros.
Setrab external oil cooler, pump, and plumbing, including temp sensor.
ZF 80% LSD. Not the ideal Guard unit I wanted, but it should work just fine for me.

The only thing I need to change is the R/P. It currently has a 8:32 Motorsports R/P, but this is too short for the tire diameter I am running (24.9"). Top speed would be limited to less than 140mph, but I currently enter turn 1 at Cal Speedway at 145mph. So the plan is to send the tranny to a race box specialist for freshening and installation of a 9:31 R/P.

The end result will be 3-5th pretty darn close to a G50/32 with the short 6th that I wanted.

[Bill Verburg]

Provide the tooth counts and I can show you what it looks like

[kurquhart]

Thanks, that would be nice.

42:11
43:21
39:25
28:23
51:50
35:38

1, 2, and 6 are accurate, but 3-5 are just guesses at this point; we will know better when it gets opened up.

[Don Plumley]

Nice. I like the shipping container - great idea!

[Bill Verburg]

[kurquhart]

Thanks, Bill, I appreciate the chart.

[jeff91C2T]

Hi Bill...the chart you came up with is excellent. I'm was hoping you might be able to run two scenario's for me as I just regeared my G50/52 trans with 2-5 gears from and 03 box. Details are;

R&P:
3.444 (stock)

Ratio's:
1st 3.5 (41/13) stock for /52
2nd 2.059 (35/17)
3rd 1.407 (38/27)
4th 1.086 (38/35)
5th 0.868 (33/38)

The two scenario's are for my street tires (285/40 17's....26" dia according to tirerack) and track tires (285/30 18's....24.8" according to tirerack).

Thanks in advance!!!

[Bill Verburg]

[jeff91C2T]

That information is very useful...thanks again!

I like the RPM drop and top speeds for the gears. This should make of a good improvement over the long ratio's of the /52. For top RPM's...if I look at my HP/torque plot I'm about done at 6,100 rpm. I usually like to go not much past 6k to go easy on the motor. Also the rpm drop should keep me in the meat of the torque curve as well...

[kurquhart]

Originally Posted by kurquhart

Thanks, that would be nice.

42:11
43:21
39:25
28:23
51:50
35:38

1, 2, and 6 are accurate, but 3-5 are just guesses at this point; we will know better when it gets opened up.

Exact ratios were pretty close to the guesses:
42:11
43:21
39:25
40:33
42:41
35:38

[kurquhart]

Well, the planned freshening turned into more of a rebuild:

R/P shot (knew that in advance)


5th gear broken


3-5 steel synchros shot
1-2 steel synchro cones shot


various bearings, etc.


I am off to Willow Springs next Friday for a test/tune day. Hopefully, this tranny will be worth all the time/money/effort expended so far.

[kurquhart]

Originally Posted by kurquhart

I am off to Willow Springs next Friday for a test/tune day. Hopefully, this tranny will be worth all the time/money/effort expended so far.

Mixed results from Willow Springs: while the shorter gears helped on several slower corners, they actually hurt on one of the faster corners where I had to short shift to avoid redline before track out. The end result were lap times the same as before. Willow Springs is a relatively fast track that relies more on handling than acceleration; hopefully the shorter gears will be more noticeable on some of the tighter tracks (e.g. Buttonwillow).

Interestingly, I could not discern the presence of the LSD: I never had a braking stability problem before and track out performance was the same as my old TBD. Then again, I have not yet altered my braking style for more trail braking.

[Flieger]

Did you try the Streets?

[kurquhart]

Originally Posted by Flieger

Did you try the Streets?

I was at the big track. Streets is very tight, but I don't go there very often.

[Flieger]

I realized you ran the big track, I was just wondering if your ratios would be good for the twistier Streets.

[kurquhart]

Originally Posted by Flieger

I realized you ran the big track, I was just wondering if your ratios would be good for the twistier Streets.

Sorry, I misunderstood your question. I would guess that the shorter ratios would be quite helpful at Streets, particularly coming out of the bowl.

[Bill Verburg]

Originally Posted by kurquhart

Mixed results from Willow Springs: while the shorter gears helped on several slower corners, they actually hurt on one of the faster corners where I had to short shift to avoid redline before track out. The end result were lap times the same as before. Willow Springs is a relatively fast track that relies more on handling than acceleration; hopefully the shorter gears will be more noticeable on some of the tighter tracks (e.g. Buttonwillow).

Interestingly, I could not discern the presence of the LSD: I never had a braking stability problem before and track out performance was the same as my old TBD. Then again, I have not yet altered my braking style for more trail braking.

That's the down side of shorter gearing, the range of each gear from low to high(doesn't matter whether you want to think in terms of speed or rpm) is reduced. That raises the chance of running out of gear at the wrong time. The choices are to over rev or shift.

The pros can use different gear stacks for each track to avoid these issues.

It also helps a lot if the rev range of the engine can be extended. The latest RSRs are going to 9K. But theya also rebuild frequently and use little tricks like altering the oil pressure springs differently for sprints vs enduros

[Tom W]

It's a problem I face a lot with my /32 transmission. I run out of gear at a place where it makes no sense to shift. I make do by using the extra rev range of my engine. While the dyno says I should shift at about 6500, I have an engine built to rev to 8000 so I just keep going up to about 7400 before or during a few corners. The stronger engine has also saved my butt/wallet twice when I missed a shift and hit 3rd instead of 5th and rev'd it up to 8100 rpm for 0.5 seconds.

[lucittm]

Jeff,
Where did you get that most excellent graph?

Mark

[herman maire]

To bad about the condition of the stuff inside the gear box. Just wondering... any chance you bought this transmission from canada?

Good luck