Gearing

[M. Hendrix]

I had a question about my gearing a couple months back.

When I got my new car, all other variables aside, it didn't feel like my other cars... couldn't put my finger on it.. I had a top speed run in the 135 range.. that seemed odd..

Welp, I looked up all the info I could find on it, d'led the 901 gearing .xls, plugged my rolling diameter in and went for a drive.

A
H* <--- culprit! I knew it!
N
V
ZD

Damn, I need a B to go with that H, and an X to give 3rd some legs, or I need an F to give 3rd back a little room...

25.33 rolling diameter, all tests done @ 3500 & 4500..

Claims ZD is 142 @ redline. What am I missing?

What do you guys like for 1st, and 5th?


M

[red-beard]

What is the SN on your tranny case? And what engine are running in the car? I'd tune the transmission to go with the engine.

James

[M. Hendrix]

Yeah, tuning the tranny was my thought too..

I haven't gotten up under there yet, but it's a 2.0/4, it was all just rebuilt, I dunno how much I like H.

I knew something was up.. you seem to be pretty tuned in with the transaxles, this is my only jaunt with a non-stock gear.

I need to drop 5th, and raise 1st, suggestions?

Thanks.

M

OH! By the way, anyone who drives their car near redline *ever* should take a look at the gears.xls, and test a little, I found my tach reading a deadly 200+/-20 low.

Ouch, I don't goose her so hard anymore anyhow.

[neilca]

The stock 914 gears are
1st AA 12/34; 2.833 ratio
2nd F 18/34; 1.889 ratio
3rd N 23/29; 1.261 ratio
4th V 27/25; .9259 ratio
5th ZD 31/22; .709 ratio

The second gear is fixed on the shaft. To change it you must change the input shaft. If you want I will trade you a F set up for your H set up (input shaft and layshaft gear). I also have a stock AA first (all three gears) for $60. By the way the A gear is 11/34; 3.182 ratio. Send me an email if you are interested.

neil

[M. Hendrix]

I appreciate the offer.. I am doing a 2.7RS, does the H do me any good there?

It's always somthin'..


M

What are you planning on doing with the car? If you aren't going to track it than you should stick with stock gearing. If you are putting a 2.7 in it you might want to go with the stock 6 gearing which was A,GA,O,V,ZA. Are you sure you have an H for second? Sounds like something that would be done with an 8 conversion.

[red-beard]

The stock 4 redlined I think at 5500 and the 6 at 6500. The gearing on the 4 was a bit longer to allow higher speed with the lower rpms.

With a 2.7, especially if you will have an external oil cooler, I wouldn't bother with regearing the tranny.

To fix your 4 cyl, the cheapest and easiest solution would be change the tranny, not the gears.

If you were going to an 8 cylinder, I hear there is a way to reverse the H gear to give a much higher overdrive final ratio. I am not sure how this works, since the gears are made that one side is splined and one side runs on a caged set of needle bearings. Unless the "H" gear normally runs this way in the position it normally occupies. Hmmmm. Thinking about this, I think that is what is going on. You are shifting a 3rd gear position to 5th gear and that will invert the gear ratio since you are flipping which shaft it normally resides on.

James

[M. Hendrix]

James, go on..

I have heard of reversed 2nd, back when I had a V8, I actuall just brough that up in someone else's thread.

It doesn't bother me that much, but it was noticeable the first time I shifted past 3rd.

I think I am having a transaxle built for the 2.7, I just need to gain access to a couple friendly guys who know their gear set... for very low speed testing..

:-)

I promise.

Thanks guys..


M

[confused]

Hmmm, I don't know what I have, I have 5 914 transmissions that i have collected, at least one is a 914-6 tranny with a bad pinion. The one I just put in my 914-6 3.0 had a hole for the throttle linkage piece... but it was from a 4cyl. I don't know what the gears are set at but they feel good. What is a good gear set to run on the street with some autocrossing?

I haven't realized the need for a limited slip yet, but I hear I will really want one.

Now I need better tires so I don't slide off the road.

[M. Hendrix]

Confused.. from my research so far, you might do well with a 7.27 r&p, stock it 7.31, add some legs to the whole stack, and seems to be an available set.

(20/4 redlines @ 5800 btw James)

My 4 does 60 in second @ redline, I need a little shorter tire, I guess.


M

[fetus]

I have a 3.2 with a stock 75 901 gearbox.
What gearing do you recommend?
It feels like its reving to high in 5th.
I would like 5th to be around 2500 rpms at 70 MPH.
I read an article on Rich Johnsons car and he was running:
1st stock
2nd stock
3rd Flipped ZD
4th Flipped N
5th Flipped H (70mph at 2300 rpms)
Does the above sound good for a street car??

thanks,

Steve

[Dave at Pelican Parts]

Well, you don't want the revs to be too low on the freeway. Evidently some Six conversion cars have overheated from using the stock Four 5th gear, which is taller than the stock Six 5th gear. The fan didn't turn fast enough for the power required from the engine at that speed, and it overheated.

I'd seriously consider a 915, though, with a 3.2 motor.

--DD

[M. Hendrix]

Ok, and what was the formula on flipping gears?

(intrest piqued again.. math hurts)



M

[fetus]

I'm running a GT front oil cooler and fan assembly.
I was stuck in bumper to bumper traffic today in LA for over 3 hours and the temp never went above 190.
The thermostat opens at 180.
Air conditioning would of been nice. Maybe that should be my next project instead of fooling around with the gear box....

thanks,

Steve

[Dave at Pelican Parts]

Hendrix, the formula on flipping gears is just (1/ratio), where ratio is the old gear ratio. Or, if you go by Porsche's practice and list the ratio as the number of teeth (e.g., 27:28 instead of 0.964) you just swap the numbers to get 28:27.

--DD

[fetus]

Dave,

After comparing the stock gear charts for my stock 914 901 vs. the stock 915 3.2 motor gear charts there's not much of a diference and I agree that I should leave it alone. The factory way is usually the right way.
I wish I could afford the 915/916 conversion but it won't be in the budget for quite some time. I should of bought the matching trans with my motor at the same time. My next investment will probably be steel gt flairs and a paint job. People at work are harassing me about my riveted on rear GT fiberglass flairs.

thanks,

Steve

[red-beard]

Originally posted by fetus
People at work are harassing me about my riveted on rear GT fiberglass flairs.

As they should....

[fetus]

Thanks James!!
It looks better than it did with cut off fenders and tires sticking out...

Steve

[bumble]

FWIW, I have almost completed a 914/6 project with 2.7L as a car dedicated to Tarmac rally events (ref: Howard Robillard's post a while back re: Targa Tasmania). A big decision was what transmission and ratios to use. I decided to convert my tail-shift 901 to side-shift and rework the internals (basically new everything plus a Quaife torsen diff). We also spent a lot of time positioning the engine/transmission and gear-shift mechanicals to get a straight linkage!

For this type of event, you need as many useable ratios as possible and stock first is ridiculously low (there are no events on Mt Everest to my knowledge!) and stock fifth way too high (the roads are generally too narrow and bumpy to do 150mph!) so three gears ain't gonna cut the nut!

Soo... I bought a new first (C - 15:36) and a new third (I - 20:31)
to make:

1st = C - 15:36 (2.40:1) - New ratio
2nd = F - 18:34 (1.889:1) - Original 2nd
3rd = I - 20:31 (1.550:1) - New ratio
4th = N - 23:29 (1.261:1) - Original 3rd
5th = V - 27:25 (0.926:1) - Original 4th

The effect is a set of well-spaced close but useable ratios. Ist may be a bit high for 4cyl cars and fifth probably a bit low for relaxed highway cruising - but hey, if you want relaxed highway cruising, go buy a Caddy!!!!

BTW, I will post more details and photo's of this project soon - it really is something special....

Mark
Sydney,
Australia