To maximize my 914's performance on the track, I've put together several different gear sets for my 901. This has helped me to maximize my top speed on the straights, as well as acceleration out of the corners. This has proved to be a great advantage over stock geared 914s.

I want share the info I’ve collected, as well as what I’ve learned from these projects.

I’ve put together a Click to view attachment Gear Ratio Tech Article that includes: why you might consider re-gearing; ways to approach this project; the 914 901 Gear Ratio Workbook (MS Excel required); and references to 914World members that provide related products & services.

Lastly, and perhaps most importantly, I’ll be maintaining the Member Gear Set Library that includes the various gear ratio setups that Members are using for different applications & situations. This centralized repository will greatly facilitate finding information applicable to your re-gearing project. Important Note! The ‘right’ gear set for you is particular to many factors. To list a few, the car’s weight, suspension, engine, and DRIVER! Don’t take the gear-sets listed for a particular application as your ideal setup. Contact the owner, compare corner speeds, suspension setups, engine characteristics, driving skills, etc. All of these factors play into what will work for you.

If you'd like to contribute to the "Member Gear Set library", post your info on this thread and include:

* Applicable Category (Autocross, Street, Track (including track name)
* Engine (cc & cylinders),
* HP,
* Redline RPM,
* Tire Diameter,
* Weight w/driver,
* 1st-5th gear codes, and
* Any short comment that you’d like to pass on, or better yet, a link to the applicable 914World discussion thread on your setup

This is for road racing at Road Atlanta and Roebling Road.
2.0 liter six cylinder
175 hp
max 7500 rpm
tire diameter 23.6
Gears A, I, N, S, X

I have not run the box as yet but these ratios are suppose to work well on track. These are very fast tracks so first igear s considered to be a pit gear only.

* Applicable Category Track: Laguna Seca
* Engine 2480cc Six
* HP: 200
* Redline RPM: 7400 RPM
* Tire Diameter: 25.2 and 23
* 1st-5th gear codes and A F M S X
Video of the car on 25.2" tires: http://www.youtube.com/watch?v=aSaL5XpVTt8

On 23" tires the car accelerates even faster and can be shifted into 5th gear on long straights as opposed to 4th.

* Applicable Category Track: Daytona rennsport III
* Engine 2.0 type 4
* HP: not enough
* Tire Diameter: 21.5
* 1st-5th gear codes and A F M S Z

Worked ok not quite right for Daytona....

914 #59

Tony

* Applicable Category Track: Watkins Glen, Lime Rock
* Engine 2.7L 6
* Max RPM 7500
* HP: 260
* Tire Diameter: 25.5"
* 1st-5th gear codes and A KA P S U

A little tall for Lime Rock, good for Watkins. I have also used a GA first gear at Pocono Raceway, which has a hairpin turns in some configurations. 5 usable track gears!

Scott

Scott how did you get a GA first? Also are you using a 904 mainshaft? If I understand correctly you can use any 2nd through 5th gear in any position on a 904 shaft. Correct?
Len

Len,

The way I did it was to:
1. Take the fixed gear from a stock first gearset, and turn it down on a lathe to knock off the teeth.
2. Sacrifice a GA mainshaft by cutting the shaft off. Then bore a hole in the gear just large enough so it can be pressed onto the turned-down first gear from #1 above.
3. TIG weld the assembly.
4. The standard non-fixed gear from the GA gearset just plops right into place without mods.

Note that you don't get reverse when you do this mod, since there is no matching reverse idler gear.

Ideally I could have annealed the gears before welding and then re-heat treated, but I did not have that done. The gearset held up OK, though I recently had a bearing plate warp and a mainshaft bearing go bad in my trans. Could be due to use of first gear on the track, since that is a weak spot in the 901? The GA first does make for a killer close ratio gearbox though ...

I have heard that another way to accomplish all this is to use a GA second gearset from a 904 mainshaft. You can have an adapter made to match the larger 904 second gear internal splines to the first gear splines.

Scott

where is the transaxle code located?

mike

Mike,

It should be stamped on the bottom of the case.

Does anyone have a pic that they can post showing the location? If so, I'll add it on the '901 Transaxle Codes' tab of the Workbook.

Greg

Scott thanks for the info. That's a pretty cool arrangement. Unfortunately SCCA requires we have a functioning reverse gear.
Len

Race 914 ,

I tried several times to download your article but got a warning .

" Microsoft Word 97 Conversion " - Unable to load graphics conversion filter . Continue with document conversion .

1) what is a graphics conversion filter ?
2) what does this warning mean ?

I tried several times clicking on the yes and nadda . But on the 6th click a window opened up titled " Regearing - 080120 [1] - Word Pad " . This small article referred to a " 914 901 gear ratio work book " .

Was that article the workbook or is there another download available ? My PC has 2.66ghz and is about 3 years old so it isn't quite obsolete quite yet .

Thanks for any feed back on this one .

GTP

The article is MS Word 97 and includes the workbook which is an MS Excel 2007 file.

I can't be certain, but from your info above, it sounds like your system may be trying to open the article in Word Pad?

You might try clicking the article link again, and then instead of clicking 'open', 'save' the document file on your system, then launch MS Word and open the article from there.


EDIT 1/22: If you don't have Microsoft Word or Excel here is a 'free' option:

Microsoft provides downloads for a Word Viewer & Excel Viewer

I'll also add that Open Office is an excellent solution for both opening and editing MS Word and Excel docs. For free!

So I tore open three boxes and found two with the same gear stacks and one that was way different. I still have the one in my 6 that I am not too sire what is in there and another that has AFMSX. I am going to be building one box that has AFKaSZd, but I'm not too sure what I am going to do with the other gears. I am going to build one backup box as soon as I know what all gears I have. I will keep you posted.

Can anyone explain what the 'gear codes' mean? For example, the 'A', 'I', 'N' or 'X'. Are these codes universal, are just for the 901?

My Dad and I are rebuilding a '72 4 cyl. We've increased the displacement to 2L and switched to carbs. I'm not sure what hp or torque it produces.

thanks for posting the excel file

Tim
Las Vegas

Hi Tim,

The codes you mention are specific to the 901 and are used to designate the ratio of each gear set. The Tech Article listed in the first post of this thread talks about the gear codes, and also contains an excel spreadsheet (click on the '914 901 Gear Ratio Workbook' link, then go to the third tab or worksheet: '901 Gear Ratios _ RPM_MPH Table') that includes all 901 codes and their ratios.

The Tech Article can be accessed by the main header: '914 Info' ; 'Tech Articles' ; 'Re-gear your 914'. or click here

Greg

Thanks for the information, Greg, I'll work though that excel file.

I'm hoping that a 'custom' set-up will add just a bit more zip!

Regards,
Tim

With Santa's help, I just finished gathering the parts for my Laguna Seca gear setup: 904 mainshaft with A-H-Ka-Q-V. Here's the chart from the Gear Ratio Workbook link in this thread.

Click to view attachment


The issue I'm working is turn 11 which leads onto the main straight. The stock F 2nd was too low, and my Ka 3rd was a little too high. The turn before the longest straight is the most important turn related to lap times, and I was probably losing a couple car lengths there when I'd lose my momentum in traffic, so this was my highest priority off season improvement.

The H second will let me take that turn around 4K rpm. The video of the the original setup A-F-Ka-Q-V is here. Will post the results once I get the upgrades done and get back to Laguna.

Thank you Santa!

Here's my plan for autocross:
F, K.

How can I get my top speed up. I dont race but would like to get my freeay rpm's down and a faster top speed

Here's a recent thread on ways to achieve a taller 5th

Went to the "914 901 Gear Ratio Workbook" but couldn't find the tabs in that .xls spreadsheet.

Help, where are they hidden?

Nice work pulling all that information together!

Hi Randal,

When you open the 914 901 Gear Ration Workbook, open the excel sheet in full screen. Sometimes you won't see the excel tabs (worksheets) on the bottom of the page if not in full screen.

Here's what you should see at the bottom of the excel sheet

Click to view attachment

Let me know if that works.

Greg

I basically did what's in the link above 'to achieve a taller 5th'.

Stock was A F N V ZD
Flipped 5th to 3rd, and 3rd to 5th, and swapped V 4th to R, I now have:

A F KA R Z

It's a real cheap way to bring all the ratio's down for MUCH better acceleration, only have to buy 4th.

When someone asks, I say it feels like I have a 2 1/2, 3 1/2 and 4 1/2 gear, not 3, 4 and 5.

So:
* Applicable Category - Track
* Engine - 2.2 liter 6 cyl
* HP - approx 200
* Redline RPM - 7400
* Tire Diameter - don't know?
* Weight w/driver - 2000
* 1st-5th gear codes, - A F KA R Z

Works great at CMP, VIR, Barber, Watkins Glen. Not so great for Road Atlanta - could use a taller 5th.

Specs of the shitbox.....er...Britbox:
Wt approx 1700 wet.
204 hp @ 6300 at the wheels.....bout the same torque 3500 to 5100.
rev limit 7100.
Gearing F, ZD (flipped 3rd).
Tire dia 22.5 in back.

Need more "umph" to run with the real big dogs.

Doesn't get much taller then a ZD, does it? I've got one if you need it.

Tom B.

* Applicable Category Track: Portland (w/festival corners), Oregon Raceway Park
* Engine 2.7L 6
* Max RPM 7100
* HP: 228
* Tire Diameter: 25.4" (245/40-17)
* 1st-5th gear codes are: A GA M Q V

I have two tranny's, one stock with the ZD, and the other listed above. I change over to the stock one for Road Atlanta...

I have now run these gears and they are not correct. The "I" second is too low to use on track. I believe an "M" in second would make a better choice. I still need to optimize the rest of the gears.

IMHO I think its just the opposite.'I" is too tall and "M" will be way too tall for 2nd.
You might think about the F,G,H/HA for second depending on revs and torque curve.

"A" should just be a paddock gear and I can't imagine you coming to a 'green flag" with an "m" or anything close to it.The N,S,X package is nice.

(MHO based on racing a production based 914 for the last 15 years at the national level , from Daytona to Mosport)

Tom B.

I am blown away with how versatile my ratio's are
my 5th is too high for the little tracks around here but will be great for big tracks
I never find a hairpin that I can't use either my 1st or 2nd gear in.

F - 1st
J - 2nd
O - 3rd
S - 4th
V - 5th

seriously its a lot of work to put into a box
but then you have a box that will do nearly any track
it sure makes tow's to other states and first time visits to new tracks a lot more reassuring!

brant

Do you have reverse with the F 1st? I just bought a JNSX for my 914.

no reverse... The F gear is too physically wide. The F gear doesn't actually fit inside of the case either because of it's size. The case has to be machined larger on the inside and then layers of magnesium weld are built up on the exterior to re-seal the case where the F gear now resides.

mechanic jokingly told me; "its part of the commitment"
I've run this way for about 4 years and its ok to give up reverse. There are a lot of 915's out there without reverse and its more common in the PCA club race ranks than I realized.

but on the upside, its 5 useable gears (theoretically kinda like having a 6speed box). And with F and J, there is always the right gear for a rolling start or hairpin corner.

Must have reverse in SCCA.

I have been using the third ("N") at turns 5, 7, and 10A at Road Atlanta with good results, that is when I can find it, shifter issues. Road Atlanta is a very fast track.

I know one ex-914/6 racer who ran a J 1st gear at Road Atlanta, if you can believe that. He was also fond of M for second. Personally I have a "KA" second (ZD flipped backwards and welded in place of second gear on the mainshaft), and for most tracks it's great. For some tracks with slow corners, KA is too tall and I have a GA first gear. No reverse when using that ratio, but that has been inconvenient only a few times. The bigger pain is getting the car rolling in 1st when an unsprung clutch disk!

Scott

Any proven setups for Road America?

Just had Doc rebuild my transmission for the following:

Use: Street
Engine 3.2 (1987) Sixer
Hold max RPM to 6000
Wheel size: 17 inch Cup II rims, diameter - approx 25.3 inches
Weight: Estimated 2,200 to 2,300 lbs.
Gearing: 1st - A; 2nd - F; 3rd - O; 4th - X; 5th - Flipped H

Goal: To have good gear ratios in each gear for peppy response and shift points; fifth gear to run somewhere below 2800rpm for extended highway cruising - have large front cooler to compensate for any increase in the oil temperature from running at lower rpm levels. Oil capacity is approximately 20 plus quarts and has been running 180 degrees at 7000ft without thermostat bypass opening; at temperature and lower altitude targeted to run in the range of 200 to 215 (temperature in target plan is at 100degrees and more; desert type environment).

Use: Rally
Engine 2.2S
Max RPM: 7300
Wheel size: 17/65-15, diameter - 25.6
Weight: 2600lbs.
Gearing: A, F, HB, M, Q

Limited top speed but excellent acceleration out of slower corners. Needed an E 2nd but never got around to it. Transits were strictly speed limited so Q 5th was OK.

Click to view attachmentHere's a chart I've used for years.
The lower 2 gears of the 914 box are not so good for a six but they'll do for around the block. You decide what speed in gears *you* want and have the hp/torque to pull.

Right as usual JP, i.e., pick your poison and live with the decision.

I personally love a high reving 6, but a 4 with torque that runs at (relative) low RPM can be a great AX car.

But there are always trade offs with either decision.

If your driving a 4 the table below tells the tale. Of course I'm talking about a Porsche 4.

Click to view attachment

So a fast light 4 will require a bunch of shifting. Shorter tires (21's) will require even more. Bigger tires (16's) remove performance and handling.

Hey JP, you coming down to Medford to co-drive with me the end or March at the Spring Enduro. Hopefully I'll have the Avon's on, but if not will be staying with the Goodyears which work great there. Figure with a few practice laps we could set some respective times.

I could be talked into it. Of course I realise that you want me there so you *know* there is someone there to beat up on.....I'm good with that.

At the WCR I wasn't feeling well.....new drugs can be some bad shit and mine was.
I may be no quicker but prolly more fun to be around.

Lemmeno the dates and where your staying.....if in a hotel.

BTW, bring the Goodies for the enduro. No sense me burning up your good Avons.
I think they have a practice day before the enduro.

The new company has me hammered, so doubt I will have the rims done for the Avons by the time Medford rolls around. But I will have some fresh Goodyears and we know they hook up at Medford. I'll try to bring a set for practice and a set for the event.

I've asked Kim about saving you a spot. Will report back shortly.

The event is on Saturday March 31 and Sunday April 1st.

I have some "special needs" and would rather rent a hotel room......but thanks for the thoughtful gesture.

I've sent you an email JP. Let me know if you can make it.

We'll have some real fun against those fast hill climb boys and girls.