Seeing that I'm likely to take the gearbox apart at the pending Dr. Evil workshop in Orange County, I would be the time to get the ratios right. I intend to use the car for longer distance touring events, meaning lots of relatively high speed miles but with lots of twisty bits.

Can you all take me to school here please?

Thanks (and Happy Friday)

Great topic; I need this guidance also.

Bump because, really now, who doesn't like popcorn?

I need the same advice.
I am running a 3.2 with a stock side shift.
1st is geared a little too low.
Could also use a taller 5th for freeway travel.

A lot of peeps push a flipped H for 5th but I think it's too tall for an aircooled street car. I have a flipped HA and with 205/60-15 tires and I'm barely at 3000rpm at 80mph. IIRC I'm closer to 85mph.

Running A, F, O, X, HA on a hot street twin plug 3.0

I have a flipped H for 5th but I think i can get away with it with the 3.2. I feel ike it should have enough torque to handle cruising at lower revs. But if Im wrong, I'll change it.
I deleted first gear but I wish I kept it.

Gearbox newbie here, but deleted first because it was just to low? Do you literally just flip the gear pattern on fifth?

Aircooled /4 or /6 you shouldn't run under 3000rpm for cooling.
Head temps spike when you lug an aircooled engine, watercooled cars can get away with it due to superior cooling.

A lot of guys don't use first since it's an unsupported gear and vulnerable to damage from high torque. I live on a hill so it would have made life easier when I have to get moving on an incline, drive it into a trailer, ect. Saved some money at the rebuild time but I'm not thrilled. I'll use it until my other car with the 915 trans is done and then go back in.

You can drive using 2nd through 5th with a 3.2,
but 1st gear is good to have when starting out on a steep incline.

I do use 1st, often it's just to get rolling, but really useful crawling uphill behind traffic at a stop sign, etc.

I’m running CA, H, KA, Q, and ZD. The engine is a 3.0. Makes all the lower gears usable. Steep hills are a little work, but I don’t drive the car very often and I’m out of practice slipping the clutch.

So it would seem that keeping first, but not driving like a gorilla with it, and a taller 5th are the way to go?

Any issues sourcing the taller 5th?

Just put a WTB on world and pelican. Mine was $300 but that was 5 years ago.

I have a 3.2 with a 1986 915 gearbox. I thought lighter car, etc. I could go with a taller 5th. The tallest 5th put me at 3k rpms at 80mph in my 915 gear box. If I stayed above 80 on flat ground it was fine. Any incline below 80mph and I lugged the engine. I switched back to the stock 915 fifth gear which is 3200 RPM's at 80mph. Lot's of variables, the 914 has a 7:31 ring & pinion versus late model 915 is 8:31. The higher ring & pinion makes all the gears taller.
IMHO your driving style and street versus track will change what gearing your happy with. For me a stock 914 trans was perfect for any motor up to a 3.0 with injection. Yes there is the 1st gear issue, but just don't do burnouts. My car used to be a 2.7 with webers and headers. I was happy with the stock 914 gear box. As soon as I replaced it with my stock euro injected 3.2, all the shifting stop light to stop light drove me up the wall, however it was a blast on the track. Now with the 915 all the gears are taller, I don't shift as often, but smaller displacement 914's are quicker than my car, due to the lower gears / ring & pinion.

Try 911S Registry for gears and gear sets.

I've seen a lot of that stuff over there. Maybe even ask here?

Interesting tid bit. The 915 7:31 ring and pinion trans has shorter gears than the 914 gear box. Reason being that the six engine has a higher red line than the 914-4. So besides the 1st gear issue with the 914, the 914 trans already has taller gears for a six, which is nice since our cars are lighter. Personally I would not go below 3k rpms at 80 mph in 5th unless your running a 3.6 or greater engine.

I see you guys specify if you are running carbs or injection. Does it make a difference when considering the gearing?
The conversion that I am about to finish has a 3.0L with webers, 901 with LSD, and I have no idea which gears are in it. All I know is that they are short. On the highway, 8omph comes at close to 5K. Trying to decide "learn" what to do about it.
Bill.

Hmm, I have a 7:31 915 I am going to put in some day. I was going to swap it to a 8:31 R&P for longer gears. But maybe instead I will just get a taller 1st and 5th for it.

What size tires are you running? IMHO when I ran 17" rims with closer to 25" tires I thought factory gearing was great with my webber 3.0. Now I have 23" tires (225/45/15) and its a little faster but on the freeway I'm at 3800 rpms.

When I was running 205/60/16's the stock gearing felt pretty well matched with the 3.2. Now that I have switched to 205/60/15's, it's up a couple hundred RPMs at freeway speeds.

A stock 3.0 with Weber’s is going to be close in HP to a stock fuel injected 3.2.
More power = quicker through the gears

OK.

Guys - I need me some gears. Fancy ones.

Waiting......


Waiting......


Waiting......

= More fun !!!

I’m building an early 915 trans with a 7:31. It might not be a freeway flier but it will be really fun around town.
I think Eric drove his GT across country at 3600 rpm.

Justin,
I am running 245-50 16 tires.

I would look at a gear chart to figure out what you want and then check ebay and do a WTB on the Pelican 911 forum. Tons of activity there.

Porsche also went with a 8:31 ring and pinion as well as aluminum cases versus magnesium starting with the 3.0 motors due to the additional torque of the motors. There was a one year 915 that was magnesium and 8:31. Very sought after since the magnesium case is 10 pounds lighter than the aluminum cases.

Didn't they also make the change due to the gas crunch in the early 70's. Better MPG.

Yep!!
Here is a link to a wiki with tons of info on the 915 and how to rebuild it.
http://porsche.wikidot.com/porsche-915-tra...repair-tutorial

Behind the 2.4l MFI motor, I run A, GA, flipped ZD, S, ZD. I tried an HB for fifth, and I couldn't drive 60 mph. Fourth was too high revs at 60, and it overheated. Fifth was too low at 60 and it overheated.

The current set is spaced well for the enigne's torque range.

Yes, will do Steve,maws just having some fun with that.

OK - now I am good and confused,

I am going to run a narrow body, so don’t think I can get much beyond 205/60 under there.

I do want a first gear.

Does that suggest I should just leave everything as is in the 901?

Slippery slope. I would start with the stock gear box. What sucks about the 914 gear box is that 2nd gear is part of the mainshaft. To change 1st and 2nd you would have to buy a 904 mainshaft. Once you start adding up all the costs a 915 or other trans starts to look attractive. Too bad nobody offers a Boxster s trans kit. That would be a killer solution.

Oh and narrow body, means really bad throttle induced oversteer with all that power. I would look into a limited slip. I’m a big fan of the TBD.
Otherwise you can go with a big front sway bar, to get more understeer to fight the oversteer or drive nice, but that’s no fun.

Good morning Steve, thanks for the responses.

915s go around 3500 bucks, plus or minus, right?

That’s correct and unless you are sure of the condition, it’s easy to put that much and more into a rebuild. You will also need a Wevo side shift conversion kit or a Martin Bott 916 kit. Both are around $3,500 and pro installation is suggested. Then you need a 911 shifter and custom shift linkage. I would suggest sticking with the 914 trans for now. Unless you pound in it, it should hold up fine and you can always go 915 in the future if you feel you need it.

1k-3500 depending on condition and then you need to flip the differential and buy a shift kit. Wevo is the most popular. I’m running a 916 kit from Martin Bott. Regarding tires, I would figure out how to get 225’s in the rear. You can pull the fender a bit and get the right offset rear to make it work. I know it can be done, but I don’t know the combo.

I have an H I would sell cheap

Also have a 904 Main with a C in second place, again I would go let it go pretty cheap.
N
M
and a few other gear sets I would go cheap on.

Heck as of today I would make a package deal on this stuff. Tax man cometh.

I was getting ready to post a FS Add with the gear sets I have I will not be using for my -6 build. Have not done it yet as I need to snap pictures of everything.

PM sent

I generally agree with Mark Henry where a flipped H 5th may be low of gearing. I am always watching the oil temp and the CHt (both banks) and have been having high oil temperatures during the hot summer months of New Mexico. I think the CHt per each bank is a critical key.

I have a 3.2 Carrera engine 1987 with 901 transmission gearing of: 1st A,
2nd F, 3rd O, 4th X, 5th flipped H. At 70 miles per hour in 5th I run about 2700-2800 rpm which appears to be a little too low for the goal of 3000 rpm. I have had increasing oil tempers in the 240 plus range and CHT unknown.

Running Cup II 17 inch rims on all four corners; front G-Force 205/50ZR17 with width of 7 inches; rear G-Force 245/50ZR17 9 inches width.

I did not have any problems with the external oil cooler system (front, finned tube type) installed in Oregon, but when moved to New Mexico started having increase in oil temperature of 240 plus.

I may have a problem with the CHT and the flipped H 5th so I am in the process of installing the dual bank CHT temperature measurement on each bank. My intent here is to monitor the CHT of each bank from the central spark plug and using this as a partial guide to driving in fifth gear or lower gears. Combined with the CHT temperature system, I am installing fuel ratio on each bank and EGT temperature system on each bank.

The external oil cooler system is being revamped to provide additional cooling for the hotter New Mexico summers. The revamped system will consist of a 9in x 4in x 4in cooler enclosed by ducting from entrance to exit . The fan system will be one fan temp controlled to turn on at 180 degrees automatically; second fan will turn on at 190 degrees automatically. Each of these fans 4 inch 250 cfm which will provide me with a total of 500 cfm setup to automatically control and react to the oil temperatures; two secondary fan systems (each 250 com; total 500 com) are available for increased fan cooling under manual operation. I therefore have a total of 1000 cfm total available for the cooling of the oil. In addition, the external cooler system has a by-pass valve which opens about 195-200 degrees.

How does all these systems etc affect the possible CHT temperature increases with the flipped H e5th gear?

The flipped H 5th gear appears to be somewhat board line and may increase the CHT as has been said in the threads. In my opinion and experience, I may have temperature increases (oil and CHT) that relate to this problem. My 3.2 turns at 2700-2800 rpm at 70 miles per hour and definitely in New Mexico having a tendency to increase temperatures. As it has been stated the magical rpm for the 3.0 and 3.2 is 3000 rpm. I am just short of that goal by 200-300 rpm. Very borderline in my setup.

Can the rpm difference be made up in changes in tires/rims?

Really love problems like this.

Stock gearing is completely fine.

The 901 box will always have the 1st gear power limitation, meaning, no burnouts in 1st or you will blow the rear cover off the transaxle.

Respect that limit and all will be good.

Yes Tire diameter changes have a direct effect on final gearing.

I am working on it.

Go Big or Go Home - My build thread

My 3.2 currently has a 901 that belongs to McMark. It’s an unknown box that was “set up for a V8.”

It will get a 915. I owned the 915. It was in my 911 and it broke a synchro and mangled some gears. I had McMark replace all the synchro’s and the lunched gears, install a Quaiffe TBD, and flip the R&P. If we figure the replacement 915 that went in to my 911 was $1000.00, I have about $4500.00 in it. But once it’s in, I’ll have stock gearing, which I wanted. I really love the TBD. All or most of the benefit of the LSD, none of the bad parking lot manners.

Is there any Option of a different pulley size for the fan belt..??
Maybe an A/C pulley Or someone modify a factory crank pulley.??
Would be a lot easier than gear changes and with a big 6
I doubt the extra power needed to turn the fan would be
Noticed..

The fan can only do so much.

Yeah, TRUE..... but if it is turning a % faster it should be able
to compensate for a few hundred RPMS.... I would think..
Just like tire diameter would..

the 915 uses the following gears 915/08 AZ HX NT RP TM
the 914-4 used the following gears 914/11 A F N V ZD
the 914-6 used the following gears. 914-6 A G N V Z

1st 915 AZ < 901 A so it is lower still, but heavier car.
2nd 915 HX = a 901 G the F in a 914-4 slightly lower the GA on a 914-6 slightly higher.
3rd 915 NT = a 901 N perfect match
4th 915 RP = a 901 V perfect match
5th 915 TM = a 901 ZA slightly higher than a 914-6s Z slightly lower than the 914-4 ZD

ZA is an M flipped Can that be done?
Z is the N flipped again can this be done.

Now two other things to mess with you.
Tire diameters where not included in this
Ring and Pinion not included
Fan Pulleys don't find undersized pulleys are larger sized pulleys listed. You would need a larger sized pulley to speed up the fan, not undersized.

The 245/50-17 if your running the 915

Click to view attachment

Drop them to a 245/45-R17 if your running the 915

Click to view attachment

The 914-4 901

Click to view attachment

Custom geared 901 A C K V H

Click to view attachment

Great set for a water-cooled car. A first would have to be gingered, but on flat stuff you could pound on that C and watch CV balls fly.

You can mess around with this here. And here is the listing of most of the ratios

For all of you thinking the Boxster trans is the be all end all solution. Here is the chart. Remember that car is water cooled.

Click to view attachment

If it was me I would run the stock 914-4 trans, and drop your tire size down to 245/45-R17. You have a much better selection of tires, some true performance tires. And you slightly increase the revs on the engine.

Note the above charts where done with 17" wheels and Tires. I have included the stock gearing charts from Retro-Sport.com for your pleasure, use at your own risk.

Also note these all get thrown out the window when we start talking about gearing for a race track or other such scenario.

Enjoy

Is there anywhere I said Undersized pulley .
You guys got to Learn to read..