Autocross with a 901 ?

[Tspringer]

Im going to be autocrossing my '69 911S soon, its almost finished and sorted.

The car has full track setup suspension, track wheels and tires and a 2.6 MFI engine good for perhaps 220hp.

It has the 901 trans which I understand is weak on first gear and has mainshaft weaknesses. I am adept at heel and toe and I double clutch all my downshifts. I can downshift smoothly into first gear but have not been doing it in "anger" just for the heck of it.

So.... pushing hard in an autocross that is sure to use first and second gears the most and require downshifts to first followed by hard power.... how long should I expect my 901 to last?

[ubiquity0]

I wouldn't attempt a downshift into 1st @ an autocross. Then I have an SC though, with more low end torque. Even w/ an early S it would have to be a VERY tight corner to justify a downshift.

[304065]

Hmm, you have a 2.6 MFI and a full track setup, why not do the box?

Get a nice short second gear?

I've AXd my 901 a couple times, I end up running the whole course in second, I don't care if I have to do a slow launch in first, it's not worth tearing first off the mainshaft.

[Superman]

At our AX events, the decision for 911 drivers is whether to touch third. Usually the correct answer is no. The entire course is a second-gear operation.

[GIBSON]

I autocrossed a '67 911 with an AFMSX 901 box, it worked well but I never really used 1st. The car was a blast to drive but don't be surprised to have Bug-eye Sprites and Miatas turning faster times, depending on the course layout. You'll be ok on larger, faster courses but the slow twisties will put you at a disadvantage.
At least that's how it worked out for me and my somewhat limited
driving skills. Still, it's lots of fun.

[milehi914]

In my 914 I don't go back to first after I am out of it. It seems that it takes more time to get it back into first than it is worth, plus all the grinding distracts me. On the upside, if you get first gear out of your mind you will find yourself trying to carry more speed and rpm's through corners (safe to do on the autocross course) to compensate. My .02 for what it's worth...I still get waxed by Miatas everytime out. Sure is fun though.

Chris in Denver

[Grady Clay]

Terry,

Your ’69 901 should have the “reinforced” input shaft. It has a larger thread to hold 1st gear on. Don’t let the term “reinforced” fool you; it is just as weak as the other “non-reinforced’ input shaft.

I auto-Xed my ’68 911 with 901 AFMSX, AEKQV, CAJPU, and more. You can take a 4-speed A shaft or 901/911/914 F or GA shaft and weld onto it any 904 second or 901 second-third. You can use others but it adds stress to the pinion and input shaft bearings.


Here are two good choices:

Find a spare 901 4-speed. It has a A first gear in the normal 2nd position. Install really short other gears (2-3-4).

Install a 915 with a taller 1st and shorter other gears. A 915 is much stronger and better for auto-X.


I assume you have a 225 mm clutch. You want to have it as slightly expendable so you can abuse slip it under power. You want everything strong enough so you can dump it in a lower gear and cause drastic over-steer into a sharp corner.

With your driving and heal-toe skills, you can just use your stock 901 if you are careful.

Please give me some feedback. What is the type number of your 901? What gears does it have? Is it aluminum case or magnesium? Does it have an open differential or LSD?

Best,
Grady

[skinnerd]

I'm agreeing with most everyone saying once out of 1st, you never go back.... even for fairly slow corners. Most 911's (even smaller displacement motors) will have enough torque to pull the corners in 2nd.

[Superman]

Miatas do not wax the 914's at Bremerton. 914 guys quit thinking about first gear about the time their rear wheels cross the start line. Their race is in 2nd and 3rd, and their tough decision is whether to use 4th. You must have carbon-fiber/ceramic Miatas in Colorado.

[milehi914]

Super - I keep telling myself that we do. In reality, in CS the 914 is a long shot versus brand new miatas running hoosiers and kuhmos. You must have some exceptional 914 drivers in the NW to complete in the miata class...er...CS.

Chris in Denver moving to CSP soon...

[sundaypunch]

I have a pretty good shifting 901 but I would have a hard time downshifting first on the fly during an autocross.

[A Quiet Boom]

MY 901 has held up to all the abuse this former drag racer and my 3.0 can through at it. However I did use a relatively weak clutch on purpose thinking a stronger one would certainly be the death of it. I find that with the 3.0 as opposed to the 2.0 the car came with I never need to downshift to first, in fact I routinely start out in second when I'm out leisurely driving around. All in all I like the 901.

[Tspringer]

Great replies guys! Thanks!

I dont know what gears are in the 901 in the car currently. Its a mag case trans. It shifts great now, but does make some pinion shaft bearing type noise on power application.

Good points about possibly not needing first gear. Depending on the coarse that could easily be true! I may also just opt to not use first even though it may cost me a tad of time.

I dont want to rebuild that trans with short gears just for autocross because i also willl be tracking the car. Given choices between setup for AutoX or track.... ill go with track. I like autocross though and will run some PCA and SCCA events.

Im figuring in SCCA the car will be ASP so its probably not going to be competitive anyhow, but should be fun. I really want to flail it around the autocross coarse a few times before tracking it. Test everything out, get familiar with its handling at the limit.... all that good stuff.

[jjwood]

I'm staying w/my 901 box for autoX (as opposed to a 915- which is heavier and doesn't shift as smooth). Like all the folks above, I never need 1st after I've left the start. Sure wish I had a shorter 2nd and 3rd though.

Anyone using WEVO products on their 901 box?

Jeremy

[69911e]

The only place you will need first is a tight pivot. Downshifting into first to do some of the deceleration will weight transfer to the front, allowing better turn in and faster acceleration out.

[JWest]

Check out the RennShift for your 901 - now available from Pelican.

[sithot]

The 901 box was designed along the lines of a "race type" box where 1st would be rarely used other than launching the car.
All you need is in the "H". I always liked the 901 box for this reason.

Tom

[mskala]

On the 901's in any of the 914's I've owned, you really
cannot shift back down into first. Try not to slow down
so much that you bog the motor in second (may be
tough with S cams).

I autocross my -6 all the time, and I usually don't beat
the car on the start line. Unless you're vying for a
national championship or something, launch safely,
go to second, don't worry about a few 10ths.

You could change second gear to whatever you want
if you get a 904 mainshaft.

Mark S.
'70 914-6

[kenikh]

Originally posted by James Adams
Check out the RennShift for your 901 - now available from Pelican.

Anybody have one of these installed on a 901? Opinions?

[Joe Bob]

Originally posted by Tspringer
Great replies guys! Thanks!

I dont know what gears are in the 901 in the car currently. Its a mag case trans. It shifts great now, but does make some pinion shaft bearing type noise on power application.

Good points about possibly not needing first gear. Depending on the coarse that could easily be true! I may also just opt to not use first even though it may cost me a tad of time.

I dont want to rebuild that trans with short gears just for autocross because i also willl be tracking the car. Given choices between setup for AutoX or track.... ill go with track. I like autocross though and will run some PCA and SCCA events.

Im figuring in SCCA the car will be ASP so its probably not going to be competitive anyhow, but should be fun. I really want to flail it around the autocross coarse a few times before tracking it. Test everything out, get familiar with its handling at the limit.... all that good stuff.

Look on the bottom rib of the trans...there will be a trans type stamped on it. Then either look it up in Bruce Anderson's book or post it and we can tell you the stock gears that came from the factory with that case.