Inside my transmission

Jack Olsen · 12:44 AM

I finally got the gear ratios for my transaxle, which is a mag cased box from a 77 with billet bearing reinforcements, internal spray bar and external cooler, internal Wevo gateshift, external Robotek spring-loader, custom GT gears, and GT limited slip at 80%.

It's got a taller-than stock second, and close-ratio jumps up to a very low fifth.

1st 11:35 (3.182) Stock
2nd 20:32 (1.600) 3 steps taller -- stock is 1.833
3rd 23:29 (1.261) Stock
4th 25:27 (1.080) 2 steps shorter -- stock is 1.00
5th 26:25 (0.962) 4 steps shorter -- stock is 0.821

With my current rear tires, my gearing should work out like this:

47 to 135 mph is all above 4000 rpm, with very short throws. It's ideal for the track, since none of the gearing is wasted.

With the tires I'm planning on running during the OTC, the top speed goes up to 141.

Superman · 04-23-2002, 12:35 AM

Ah Hah! So the tall gearing really is fairly wasted in these cars. I don't dwell on it, but my car would be fine if it were geared a little lower. Heck, I can go almost 100 mph in third gear. Freeway onramps work like this: First is over in a snap. At the end of second gear, I'm going highway speeds, albeit only about 65mph. Then I shift to third and in a short few seconds I'm going over 90. So, what am I going to do with the last two gears? I guess the track is the only real place for these cars.

It sounds like you're really pleased with your race tranny. It looks like, with your 3.6L power and early car weight, you must be a bit of a local bully. Friendly bully, I mean.

Bill Verburg · Bill Verburg's Garage

Very nice Jack!, thats going to be one tall first when you get the new boots on(I'm assuming 275/40x17?), but since you are not into drag racing that's ok. The rest will be very useful on the track.

Jack Olsen · 04-23-2002, 02:37 PM

Yeah, it's the opposite of a 0-60 car. The jump from 1st to 2nd is very big. But with this tranny, it's all about 2nd/3rd/4th/5th.

Really, it's more like 2.4/3/3.6/4.2 .

Right now, Tyson is hard at work modifying the front upper strut mounts for a much more radical caster/camber serup. We've also moved the fuel pump to the front of the car, cut out a bunch of dead weight in the back, and re-established better mounting points for the rear swaybars. We're also adding a front splitter and 13-pound race seats and pulling all of the heavy stereo nonsense for the Open Track Challenge.

Piece by piece, we're going to build a very capable little 911.

Bill Verburg · Bill Verburg's Garage

I kept the stock 1^st, lower 2-4, and a tall 5^th. 3^rd & 4^th are the track gears and a taller 5^th for the freeways

Glasgow 911SC · Glasgow 911SC's Garage

Jack,
With all these mods are you still going to use the car on the street, or has it become a track only car?

Superman · 04-23-2002, 02:45 PM

"Piece by piece, we're going to build a very capable little 911."

A tad bit understated, methinks.

Jack Olsen · 04-23-2002, 03:59 PM

It's still a street/track compromise car, and probably always will be. Even the new race buckets are leather, and the AC is here to stay.

The street tires will wear a little faster on the inside, now. And the B&B muffler, solid rear motor mounts, and short gearing will make it what my wife would consider a less than ideal trip car. She might even take the Jaguar to Cambria, for instance. That way she can go and antique (or whatever it is they do) during the long stretches where I just want to take pictures of wheel treatments and engine bays.

katigbr · 04-23-2002, 07:07 PM

Jack (and Tyson),
That is an even more incredible weapon that she was before. That is one phenomenal car. I'd love to see it tearing up the track and the competition. I'm new to the track also but from everything I've read the key components are weight, power, gearing and skill. Admittedly, you guys may not feel as equally skilled as the others but it sounds like you may the advantage in some or all of the three areas. It should be fun. I wish I lived on the west coast. I can't wait to see the videos.

Incidentally, I went through the same re-gearing opportunity and ended up with nearly the same ratios. I went with the following:
Revised Ratio Max Speed (6750 RPM)
1st 16:35 (2.188) 57
2nd 20:32 (1.600) 77
3rd 23:29 (1.261) 98
4th 25:26 (1.040) 119
5th 27:24 (0.889) 139

The only real difference is my first gear is equivalent to my old 2nd gear. It was a little scary commiting to go with "no" 1st gear. "Gretchen" isn't a daily driver and should not see any hills or stop and go traffic situations (except for staging). It has become a "real" 5-speed. Previously, you were almost pulling for second after you get rolling. Now once I get rolling, I've got a lot more rev range to go and am able to keep her on full boil through the rest of the gears. I've lost any ability to do any serious 0-60 duels but anyone wanting to run against me with a rolling start should be toast (once I get the fuel problem sorted).

Enjoy the Open Track Challenge and keep us posted.

Rick

Jack Olsen · 04-23-2002, 07:39 PM

Rick, do you have the 7:31 or 8:31 ring and pinion? Is it still the 72 transaxle?

katigbr · 04-24-2002, 07:08 PM

Jack,
I was advised by several people, including Steve at Rennsport, to go with the 8:31 vs. the 7:31 for reliability purposes. I knew that I was eventually going to hotrod the 3.6 so I thought that I should upgrade to the 8:31. I kept the original case and some of the shafts. I purchased a new mainshaft with replaceable gearing to give me some flexibility later should I find the 1st too low. I added a 80% ZF-type LSD with billet diff cover and bearing retainers. I also forgot to mention that I lost my speedo drive during the process by going to the 8:31. I was going to convert to the electronic speedo but ran out of money at that point. I think that another option is to weld a speedo drive to the pinion on the 8:31. This was described in a recent series in a euro sports car mag. The name escapes but they did a series on upgrading an early 911. It was one of my early inspirations to go with the early 911s. I also regret not putting in a trans cooler, as I'll have to crack open the case to do it later. I don't really miss the speedo as the tach tells me what I need to know. It doesn't take long to adjust. I probably should have done what Bill V. did by looking for a Euro 915 with oil cooler and lsd. I would have re-geared the tranny anyway however.

Regards,
Rick

Jack Olsen · 04-24-2002, 08:08 PM

Yes, the 8:31 is much stronger. If it weren't, there'd be no good reason to use it. I added an electronic speedo sender to mine (it didn't have one when I got it, since it was a track box), and swapped in a later speedo.

I don't think you need a cooler unless you're tracking the car. I've never seen high tranny temps in the most spirited street driving. You've got to really be pushing it, for a long time, at very high rpms.

It sounds like a great setup, though. You've got to bring that thing to California, some time.

katigbr · 04-26-2002, 06:22 AM

Jack,
I've been tempted to drive to Cambria since I saw the pics. It is exactly the kind of group that I've been looking for. We don't have that kind of thing in the Northeast.

I will be tracking my car and that is what is concerning me. I know that there may be some passive cooling options but haven't really gotten serious about it. I'll put the active cooler in next winter when the car goes in for a bare metal repaint. I am worried about the tranny because I'll be doing about 6-8 events this year at Mosport and Mont-Tremblant. What kind of warning signs did you get prior to failure. Are you aware of any temp gauges I can put into an exisiting tranny without drilling/tapping?I'm also planning to go to Watkins Glen if my family vacation plans work out. It is tough balancing family, work and car obligations. So far so good.

Enjoy the OTC and send those videos out when you get the chance.

Rick

Jack Olsen · 07:46 AM

Rick, here's an easy way to see if you've got a problem. Clean off a section of the transaxle, and stick one of these on it:

It's a stick-on nonreversible horizontal 4-temp indicating label with a range of 175 F to 250 F degrees. Packs of ten of them sell for US$14 here.

Look for part number 5951K44, and then click on 'catalog page' to see all your options.

With one of these on, you'll at least be able to know if things are getting worse than 225 F, which is where I'd start to be concerned, or 250 F, where I'd start to worry about damage being done.

Tinker · 04-26-2002, 08:43 AM

Jack/Rick,

I think we had a gearing discussion in an earlier post. My experience/thoughts are different. Ideally you would need specific gearing for a specific track, anything else is a compromise.

My experience comes from running most of the west coast tracks. I had been running a 8.3:1 and later a 7.3:1 with a 3.6 in an early car with a mag housing. There is little or no difference between the latest style 7.3:1 and 8.3:1. In my early days with the motor/trans combo I destroyed two 7.3:1 input shafts due to the torque of the big motor. The design of the early 7.3:1 shafts does not provided adequate support for the first gear cluster. I enjoyed using the 8.3:1 as it permitted taller gearing which I think is better suited for the torque range of the 3.6 motor. I have a friend how is also running a 3.6 in a dedicated earlier race car. The motor was stock with a Motec system. He is in the process of changing the 7.3:1 to a 8.3:1. That car has special ratios. On the tracks were are rusing, he is running out of gear. The trans was originally set up for a high revving 3.2 and later 3.5 motor. I was about perfect for that combination. With the current 3.6 and its torque band, the ratios are all wrong and he is about 2-3 seconds slower. He claims he is running out of gears.

Your experiences may vary. I know Jack disagrees with some of my views and I am anxious to see how his new gearing effects (improves) his times. I am hoping I can meet up with Jack and others and chase you guys around some tracks before I go to a smaller motor.

Tinker

scca_ita · 04-26-2002, 02:00 PM

OK I will ask, Jack - What does a trans like yours cost? Or better yet how much did you pay (so I can feel envious)?

Jack Olsen · 04-27-2002, 10:16 AM

Uh, more than I paid for my engine.

It's the first part of the car where I let go of the "I can do this whole thing for less than the price of a Camry" idea, and drifted into "It's a race car; you spend what it takes" category.

katigbr · 04-27-2002, 01:15 PM

I'll second Jack's comments on the cost. It very expensive to re-gear the tranny and add the other support components. Gears are running about $300-500 PER gear. Add a limited slip for $1200, billet diff cover and bearing retainers $300-600, Oil cooler $500, new rebuild components $200. You're looking at about $4000 grand without labor and original tranny costs.

Having said that, a good set of gear ratios will make the car feel like it has an extra 50 horses. I never run out power once I get rolling. The car is always in the heart of the powerband.

Tinker,
You are absolutely right about matching the gear ratios to the engine and primary track characteristics. Do you want to drag race or road race, tight curves or sweeping curves, long straights or short. You can be close but unless you have several trannies you'll never be perfect for every track.

I'm only a week away from trying out my new gears at Mosport. I can't wait.

Regards,
Rick

katigbr · 05-17-2002, 08:54 AM

Tinker,
Just wanted to follow up on the gearing vs. track thread. My car's gearing was setup for a shorter track (Mont-Tremblant) and when I ran at Mosport , I definitely ran out of gear about 1/2 way down the back straight. I might go with taller tires to help me there. Based on my calculations I might be able to pick up an extra 10 mph at redline the top end.

Jack,
Thanks for the tip on the temp stickers. I bought a pack and installed a set. The ambient air temp was around 68 degrees. I didn't even register. I might place the sticker higher up on the case next time. Do you think it makes a difference? I figured that if the tranny gets to 225 the case is going to get hot EVERYWHERE.

Regards,
Rick

Tinker · 05-18-2002, 06:29 AM

Rick,

I think Jack is out racing this week.

It should not matter where the temp stick is placed, although I would recommend low on the case so you can look under the car and see it without having to jack it up.

It would be nice to have a cooler on those trans with the 3.6 motors, although it is not critical. I have raced mine out here in the So. Cal deserts in 100 degree heat for several years with only one problem. Blew the main shaft seal out at Buttonwillow. Puked alot of oil, but it made it home (2.5 hour drive). They (trans) start to get a very vague and balky in the shift pattern and gear change at those extreme temps. But again no problems. Use of a good gear lube (Swepco) will limit problems. Up there in Canada do you ever experience temps in the 90`s??

Your car sounds identical to my 72 T.

Tinker