My Notes:

The car was sold to me 15 years ago with the representation that it had M S X for gears 3, 4 and 5

Actually, yesterday, we discovered what was in there was MSV. Thus 5 gear was way too short — only 8 mph difference from 4th. Stampings on the 5th gear are confusing so that the mistake may not have been deliberate. But it is definitely a V as it had 26 teeth.

We are going to change to M, V, ZD. ZD has 34 teeth.

The set up of V to ZD for 4th and 5th is the stock set up so it should be a good spread and about 1,000 RPM slower at 70 MPH from the prior set up.

Second gear is F 18:34 which is correct

Rebuild needs: first gear synchro. Third gear, synchro. Fourth gear synchro. In summary, we’ll buy five synchros. 1st/reverse operating sleeve. Pinion shaft bearing in the intermediate plate

My wife likes to do the work. I think ahead and hand her the tools. Then, to Jay Kjoller's shop to take it apart and determine what is needed. I wanted a long 5th gear and finally got around to doing it.

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I am exceedingly lucky to have a wife who likes to get her hands dirty and an expert like Jay Kjoller. He is a wealth of knowledge and experience. Anything air cooled.

And cleans up well:

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spreadsheet showing new M V ZD setup:

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That's a nice gear selection for your application. I should move to something similar for mine but the car just doesn't get driven enough to justify the effort. What tire are you running? My trans has a "Y" top gear and Toyo 245/45/16 with diameter of 24.7" is 71 mph at 3500 rpm in 5th.

I have a "while I'm in there question" on gear ratio's. Since I up sized to the 2056 first gear feels short. Is there a recommendation out there for a different first gear set? Maybe not possible given the 1/R design. Or should I shorten 2nd and not use first? Or leave it alone so as not to screw it up? Thanks.

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I have my 2nd in first
It’s not something you can do yourself
You lose reverse. And have to weld the case window in mag alloy
Very expensive as you need a 904 shaft and as I said you lose the reverse
Race only

Thanks for the info. Obviously not an option for this street driver.

The stock 2nd gear is fixed onto the shaft
So your options are to use it
Or buy a GA main shaft or a 904 shaft

You need a dyno sheet and the longest straight away to design/pick a set of gears

That spreadsheet looks helpful, do you mind sharing the excel file?

Go to "WWW.COGSGEARS.COM" Joe has some charts there.

http://www.914world.com/specs/regearing_901.php

https://blueskymotorsports.com/901%20Series...ransmission.pdf

I have all the parts you need, and a few 904 shafts for those feeling really adventurous.

The stock 914 all had A, F, N, V, ZD so changing your 5th to ZD is back to stock. No need to really do much else. M 3rd will be taller than N so 2-3 will have a wider spread than stock.

On the freeway, the MSX boxes are not pleasant. They are better for AX.

Gotta chime in here....consider getting a "S" for 4th and do the 3-5 swap to get A /F/ KA/ S /Z....it's a very pleasing spirited setup and keeps the revs up nicely in 5th...

Whoops, slight correction, googled joe cogs and this came up:

www.cogscogs.com

Thanks!

I did the ZD and S swap as well. I am running A,F, Flipped ZD (KA), S and ZD for 5th. My car is a -6 conversion (2.5L) and I really like the close spaced 2,3,4 for driving around on the street and ZD for highway. I am running 195/65-15 tires.

john

In the orange car, we had a flipped H for 5th. With 205/50-15 tires, it helps with the freeway RPM and makes it nicer to drive.

With the 2.4L and the 901 trans, I had A-F-flipped ZD-S-ZD in it. It kept the RPMs up on the engine so it wouldn't overheat. I had a flipped HB in there, but I couldn't drive 60 mph without overheating. The fan wasn't spinning fast enough to keep it cool.

Clay

Supposedly the reason that the stock Six had a lower 5th gear was to keep the cooling fan running faster on the freeway. So you're not the only one to run into that.

--DD

Flipped H in 5th is the tallest gear you can have in a 901. There is no more base circle left after this to shrink, and no gear options left. I tend to talk people out of a flipped H on anything not water cooled for exactly the reason of RPM = Cooling and lowering it too much risks overheating. So many seem to want an air cooled engine that runs at V8 RPM on the freeway, different beasts, different diets.

"Sorry, officer, but I had to go this fast otherwise my engine would overheat!!!"
.
.
.
(A-HB-N-U-ZA with 4.83FD on the race car, stockers on the 2056 street car for that ^^^^ reason).

The only reason we are running an flipped H in the 4 cylinder car has to do with the low profile tires. With the stock ZD 5th gear, the engine spun at almost 4 grand on the highway. With the HB, it is right at 3 grand.

But if you are running stock height tires, don't try to use a flipped H or HB for fifth. It will overheat because the fan is not turning fast enough.

front wheels 7x16, 21mm 944 spacer

rear wheels 8x16

tires: TOYO Proxes R888 225/45ZR16 front, 245/45ZR16 rear

I used a D of 24" for the spreadsheet.

I thought/worried about the heat, but now I have a front oil coiler. It never gets too hot.

The fan also cools the heads
Which are not benefited by an oil cooler

I’ll purchase your old S 4th gear if you want to sell.

Charlie

If you google "tire speed calculator" or "wheel speed calculator" you come up with bunches of really cool sites with calculators to see what wheel speed will be and you can back calculate to engine RPM, or find a calc that does that for you. I used to have a link to one that did it all, that is either no more, or I cant find it easily. The link was lost several computers ago. Here is a fun one:

http://www.agcoauto.com/content/plugins/Ti...speed/calc.html

Another interesting phenomenon evidenced here is preference. I get asked weekly about gears and gear ratios and I usually reply with, "That would be like me trying on a pair of pants for you and then telling you that you should buy them because they fit me so well." I can make most people happy with some generic recs based on a few parameters figured out during a discussion. But, for real custom fit gearing one needs to start with a ball park set up and put their but in the seat with their wheels and tires, and engine, and see what they like/hate and go from there. Takes far longer, more expensive, but when that is what you want then nothing else will suffice.

I'd suggest one basic question first: why do you want to change it? What is your mission? What is it about the current ratios that don't meet that mission?

It's not that the stock ratios are written-in-stone perfect; of course they're not. But it's what Porsche (or VW?) decided the mission was for the stock 4-banger cars.

Of course, changes in engine mods and/or expected vehicle use will change that equation.

My race car, for example, significantly changed that mission from stock: I needed a basic 1st gear to get me off the grid once per session (hopefully), then a close ratio 2-3-4-5 H-pattern for racing on the track. I had an expected highest and lowest speeds (roughly 40 to 115), a higher expected shift point (roughly 6300), and an adjusted (and dyno'd) torque band to keep RPMs within. I did not care about revs at cruise because I was never going to be at cruise. I did not care about fuel economy. I did not care (as much) about engine longevity.

Until you define your mission, you really can't start talking about even *if* to change ratios or not; you're certainly not ready to begin discussing any specific ratios.

GA

This thinking will destroy engines.
You oil cooler is doing nothing to keep your heads cool. Air going over the heads is entirely governed by the fan. If the fan is running too slow, your heads will bake even while your oil is showing normal. Baked heads drop valves. Dropped valves bend rods.
It is imperative that both oil temps and head temps stay in check.

Get a CHT gauge, and mount the sender on your hottest cylinder (#3 on a Type4). Happy head temps are ~275-375. At 400 the heads are overheated. It will happen FAST if you are driving on the freeway and the fan is not spinning fast enough to keep the heads cool. Like within minutes. You will find yourself driving at lower gears in order to keep the heads from cooking. This is the same reason why many people recommend not using 5th gear till you are going ~70mph on a stock gearset - to keep RPMs over 3000.

Zach