AX transmission Options

[r_towle]

So,
I want to stop shifting so much at the Autocross.

What gears would you all recommend???

Rich

[ChrisReale]

Not a professional answer (ill leave that to the "others"), but a friend of mine has a taller 3rd gear. While I spend about 95% at high rpm's in second, he used 3rd almost the whole way through. I think it also depends on the course layout. Just bring like 3 tranny's and bolt them on as neeeded (IMG:style_emoticons/default/tongue.gif) Somebody else will have a better idea, but thats a start

[Zeke]

In that case, Chris, I think you're friend has a shorter 3rd gear (closer to 2nd than yours), otherwise he'd be traveling a lot faster thatn you on the course. I hear a shorter 3rd gear is the hot ticket. Maybe 4th as well leaving 5th for the freeway. On my race car, I've shortened 3rd, 4th and 5th. We'll see how it works.

[J P Stein]

I would like an A or B first. We are pretty much SOL with 2nd. My only solution is to either shift to 3rd or put in the 7300 rpm chip.....that's good for about 30 feet more.(IMG:style_emoticons/default/blink.gif) I don't have any problem with my 3rd (stock 4 banger gearbox). It doesn't drop the motor off the cam, so... what the hell.

You may be able to tell that I seldom get into 3rd at out local AXs. I agree, tho, it does complicate things......but not enuff for a 904 mainshaft.

Maybe larger diameter rear tires?

[ChrisReale]

Zeke, he IS going faster than me, by about ten f'in seconds! He runs GTU. I could have it backwards though!

[J P Stein]

Zeke, he IS going faster than me, by about ten f'in seconds!  He runs GTU.  I could have it backwards though!

Well.......comparing your stockish set up against (as I understand your class structure) a GTU car is a bit absurd......then there is the driver (no offense (IMG:style_emoticons/default/rolleyes.gif) ). What's the seat time comparo?

[ChrisReale]

we dont run together, we just shoot the shit before, during and after. I have a total of five runs under my belt, he has a few years under his.... :cursor:

[Dave Cawdrey]

So, 5 or 10 minutes, huh chris (IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/tongue.gif)

[ChrisFoley]

Try building an engine that has a higher redline and a wider torque band instead. (IMG:style_emoticons/default/smile.gif)
If the rules allow alternate gears, they must allow engine mods too, no?

OTOH, a taller first gear, as J.P. mentioned will get you at least through the first turn before shifting.

[ChrisReale]

He has a 1.7L with big bore, 22mm torsion bars, different tranny, 22mm sway bar, 225 rear springs, and hoosiers.

I have a stock 2.0L with stock bars, 22mm swaybar 180# rear springs and F'in all season yokohamas!
Im going to steo up to 21 or 22mm torsions, stick with my tire size. That way I can stay in P1.

It may take me a few years and a feew rebuilt butts (sitting on seat without cushion so my fat head and helmet can fit) but I am young and determined and greedy, so one of these days.... (IMG:style_emoticons/default/ar15.gif)

Im curoius what Brad has to say about racing trannys.

[J P Stein]

we dont run together, we just shoot the shit before, during and after.  I have a total of five runs under my belt, he has a few years under his.... :cursor:

He,he.....thas what I figured.
3-4 seconds from the car.....the rest is operator error (IMG:style_emoticons/default/tongue.gif)

NOBODY is competive the first time out (write, if you're an exception)....or the first year or 2. Track guys come out with a big Johnson and....oops....the excuses flow like beer....."I got lost" is a good one "My car ain't set up for this" is another. I've used them both (tho I'm not a track guy). Everybody nods and says "Sure"... which really means "This guy won't be back".
My latest one is "I'm workin' on it".....which really means "I'm learning to do this". I'll hang with that for a while.

The only way to measure your progress is to pick a consistently fast guy and start working at improving your times vs his. Get the car set up and leave it alone for several events(or the whole season). Then it's just driver.

Chris:
You're right.
1st is good for about 60-80 feet....tain't enuff, sometimes. When that is the case, I've been short shifting as soon as the rear tires hook up.....just to get it done with. I haven't come up with a good launch sequence other than to abuse the trans. One of these days there's gonna big this big BANG :toilet: and I'll be needing a new 901.

[ChrisReale]

. Get the car set up and leave it alone for several events(or the whole season).

err...umm...cant comprehend this statement... system overload....malfunction...... :toilet:

[Dave Cawdrey]

. Get the car set up and leave it alone for several events(or the whole season).

err...umm...cant comprehend this statement... system overload....malfunction...... :toilet:

Its like tellin' a crack head to not smoke all summer (IMG:style_emoticons/default/finger.gif) (IMG:style_emoticons/default/tongue.gif)

[Dave_Darling]

NOBODY is competive the first time out (write, if you're an exception)....or the first year or 2.

Locally, Scott Winders showed up to the Zone 7 AutoX school (same one I attended) and by the beginning of the next season, was an instructor and a consistent top-10 finisher.

One or two of the people B has built cars for have wound up very competitive in their first year.

The common denominator, I think, is motorcycle racing. They didn't road race or autoX, but the fine art of balancing a motorcycle on the ragged edge of control teaches you some very good reflexes and skills. And a good mindset.


...Hmm, so in a way those weren't 1st-year drivers, were they??


As for the original question--
The easiest way to change your gearing is to change your tire sizes. Taller tires will make your gearing taller, shorter tires will make your gearing shorter. Taller gears will lose you some torque but you won't have to shift as often; shorter gears will gain you some torque but you will have to shift more frequently.

If I were you, I'd just drive the car.

--DD

[Brad Roberts]

I'll answer in more detail later:

Take off in second and bog the motor. Keep both hands on the wheel for the first turn.


B

[r_towle]

Ok,
I'll be more descriptive.

I short shift to second ASAP. first in the 914 is only good till 13 mph, so basically useless.

the problem I have is that the courses are set up to keep the 911 drivers coming back, so they are fast courses.

This means that I must redline second, or shift to third. I would like a second gear that goes a little faster, or a second/ third gear combo, where I can short shift to third and keep it there through a 180, and back down a long straightaway.

I have listened to another 914 in our club, and he can stay in third an alot slower than I can...

I was just wondering if there is a standard swap to accomplish this.

So to recap,
Option A is a second gear that is for higher speed (not sure if that is taller or shorter)
Option B a second/ third set that are closer to each other to enable staying in third at slower speed.

BTW, I am really asking if this can be done, and what do I need to buy??? (IMG:style_emoticons/default/driving.gif)
Thanx
Rich

[TimT]

Option A is a toughy,

second gear is part of the input shaft. so to change second you have to get a 904 input shaft, and a taller second gear. Porsche did make a few different ratio input shafts so getting another is an option, but they are expensive too.

Option B is the way to go. find out what gears you have in the gearbox. then "build" your ideal gear box. Often you can shift gears around use 4th as 5th,3rd as 4th, and buy a shorter 3rd.
The 4th and 5ths in hat come with the cars are comprimises, and usuallu much to tall.

If you have a Z 5th gear, that is good for about 145 at 700rpm, but you will never see that in a ax, and you wont use it on most racetracks either.

Another option is to keep the stock fifth ( so you can still drive on the freeway and keep the rpms cool), throw away the existing fourth, move 3rd to 4th, and get a shorter 3rd..

you have lots of options just depends if you want to make a dedicated ax car, or a car that will still see some street use..

(IMG:style_emoticons/default/beer3.gif) <<<

[mskala]

Rich,
Some people were saying it in a roundabout way in their
messages; You can't change second gear in a 901 trans.
It is part of the mainshaft. To change it, you have to buy
the '904 mainshaft', which allows changing 2nd gear ratios.

And I assume you mean 31mph in first, I can do about that.

I can only get to 52mph in second with 205/50 tires and a
6300 redline.

Mark S.
'70 914-6

[J P Stein]

I watched a 914 w/alloy Buick at the last AX.
He did 2nd gear launches. I figure he has about (maybe more ) the same torque than ulf...he claims about the same hp. I was not impressed.

In a heads up drag race, I would put a bus length on him using 1st with my car. When the trans is nice and warm, I can bang off 2nd pretty quick. I short shift (when necessary) to get both hands on the wheel before the first turn.

Mark:
52 mph @6300?
Humm, what's the link to CDs gear chart? I wanna do some figuring on my car.

[ChrisFoley]

Mark's numbers closely match what my speed graph tells me for 23 inch tall tires.