QUOTE (Aaron Cox @ Dec 17 2005, 09:30 PM)

915's dont have names im aware of...just ratio's (which is all that matters no???) AA -> 901 fan

im a doof...

cut from carquip website....

901s had letter names to the gear set,

915s they just published numerical ratios

Find what an HB is numerically and find a matching 915 gearset

Also the R&P ratio on 915s and 901s are the same 7:31, unless a special ratio was ordered.

Also the gear sets in 901 and 915 changed almost yearly, as new more powerful engines were brought online, the transmissions were geared to take advantage of the additional power

and bottom line 915 transmissions are stronger than 901s

I do have a 901 bolted to my modded 3.2, but I have a transmission on standby, and a few parts transmissions at hand also

Aaron,

I wasn't really trying to compare them to start any controversy...just my seat experience of driving my 911's versus driving my 914. It's about the tall gearing for highway speeds for me. I have a 3.2l engine to put in my 914 that already has a rebuilt 915 attached to it...I'm just planning on keeping them mated since they were made for each other versus cutting on my 901 to fit the sensors and putting in a taller 5th gear. Just adding an opinion. I do hear too many talk about the gearing for cruising at highway speeds as an issue with the 901's (which I do alot of highway driving). With the taller 5th and the different sized ring gear...seems like my 915 will be better suited for me.

Jim

QUOTE (TimT @ Dec 17 2005, 09:45 PM)

901s had letter names to the  gear set, 915s they just published numerical ratios Find what an HB is numerically and find a matching 915 gearset Also the R&P ratio on 915s and 901s are the same 7:31, unless a special ratio was ordered. Also the gear sets in 901 and 915 changed almost yearly, as  new more powerful  engines were brought online, the transmissions were geared to  take advantage of the additional power and bottom line 915 transmissions are stronger than 901s I do have a 901 bolted to my modded 3.2, but I have a transmission on standby, and a  few parts transmissions at hand also

werd...915 is stronger.... but a pita and the wallet to utilize...

rick ollah.... a flipped HB is a ... 31:19

QUOTE

Flipped HB 5 31 : 19 (0.613)

Use a gear calculator to put together your gearsets. I thought there was an Excel spreadsheet in the download area.. if not I have a couple of gear calculators I cen email

You enter tire diameter, final drive ratio, redline, shift points.. then plug in gears and see how they work..

QUOTE (TimT @ Dec 17 2005, 09:57 PM)

Use a gear calculator to put together your gearsets. I thought there was an Excel spreadsheet in the download area.. if not I have a couple of gear calculators I cen email You enter tire diameter, final drive ratio, redline, shift points.. then plug in gears and see how they work..

tim... i think i have most of the data charts you have...

mind sending me what you got?
acox914@comcast.net

They are excel spreadsheet been around for awhile. Ill email them, but Ill have to fire up some of my laptops and see which one they are one

but yea Ill shoot them over to you tomorrow maybe

QUOTE (TimT @ Dec 17 2005, 10:04 PM)

They are excel spreadsheet been around for awhile. Ill email them, but Ill have to fire up some of my laptops and see which one they are one but yea Ill shoot them over to you tomorrow maybe

coolio.

i think i have all the same ones... but its good to check
thanks tim

AA

I have every calculation sheet for every 901 and 915 version...let me boot up my laptop...hold on.

-Britain

QUOTE (Britain Smith @ Dec 17 2005, 09:18 PM)

I have every calculation sheet for every 901 and 915 version...let me boot up my laptop...hold on. -Britain

Ah, Britian lives.
What's going on with the 912?

Thanks for all the great info guy's!

My head is swimming

If I'm reading this correctly the 901 ZD gear is the same ratio as the 5th gear in the 915. Looks like they both have the same R&P so I'm not saving anything by buying a 915. I will have to have the R&P flipped, machine work done, install my HB gear, shorten the bellhousing for my conversion, build a tranny mount, build linkage, have a custom speedo cable made, adapt axles, etc,

I guess my 901 goes out for a build.

But I like that cool linkage!

QUOTE (rick 918-S @ Dec 17 2005, 10:24 PM)

Thanks for all the great info guy's! My head is swimming If I'm reading this correctly the 901 ZD gear is the same ratio as the 5th gear in the 915. Looks like they both have the same R&P so I'm not saving anything by buying a 915. I will have to have the R&P flipped, machine work done, install my HB gear, shorten the bellhousing for my conversion, build a tranny mount, build linkage, have a custom speedo cable made, adapt axles, etc, I guess my 901 goes out for a build. But I like that cool linkage!

a 901 gear wont fit on a 915........

ZD 5 is too short for small tires and high freeway speeds on a 901.....
thus flipped H, HA, HB applications....

use the 901 be done

Ok, here is an article of every Porsche tranny ratios:

Page1:

Page 2:

Just in case you wanted to know the Cayenne ratios...its on there.

Now for the calculation sheets...they are in excel format and I am not sure if they will load here...lets try the first one.

-Britain


Nope...won't do it. Let me load them to my site.

thanks for sharing brittain

AA

Wow! Cool!

QUOTE (J P Stein @ Dec 17 2005, 10:23 PM)

QUOTE (Britain Smith @ Dec 17 2005, 09:18 PM) I have every calculation sheet for every 901 and 915 version...let me boot up my laptop...hold on. -Britain Ah, Britian lives. What's going on with the 912?

Hey JP!

Not much going on here...freezing my ASS off!

I need to get a heater in the garage...it is just too damn cold to work out there.

My new years resolution is to get the car running...wanna help?

You getting your car back together? Let me know when you are putting the tranny back in, I will come up and help out.

-Britain

Alright, this is what I got.

All the files are located here:

Tranny Calculation Files
FYI: You have to right click the files and save to your computer...

Now, I made these some time ago. Let me know if you have any issues. Remember to enter the correct tire sizes (i.e. 205/50/15) to make the speed calculations work. Also, these sheets are based off engine RPM and torque values.

-Britain

Just is case...here are some instructions:

Also, remember to check the tabs at the bottom...there are additional charts.

Another...

Last...

I have both the 916 transmission and a Velios conversion. Both have been worked on extensively.

The Velios is in the race car and is the smoothest shifting transmission you could imagine. It has the stock 915 shifter, relocated back about 2 inches. It also includes a spray bar, which helps keep the temp down to around 230 degrees on hot track days.

The 916 is an interesting tranny in that the magnesium conversion parts were made by Porsche (later copied by Velios, with improvements). They had some inherent problems (two gears at once- leaks) but were made with stock SC gear ratios. That combo is great with my 2.7l. I use a Wevo shifter, but made the rods from "73" pieces. They were a pita to set up, but it now shifts fine.

For the 915 in general, you get a better shifting pattern! 3d and 4th are on the same shifting plane, very handy at the track. But my main point is that you can still buy the 916 tranny: they only made, what, 11 of the cars, but a slew of the transmissions. And I know of a fellow in PA who claims to have 2 of them for sale. He mentioned $2500, and all the tough work is done.

Once you blow up an engine with an antiquated 901 tranny with a mystery shifter, you tend to look for a better way. Now, if I could only find a good sequential box...

Rick,

FYI so you make the right decisions. The ring gear is NOT the same ratio's at the 901 on the 78 and newer 915's. In 1978 the factory switched to an 8:31 from the previous 7:31's. This will help you out with your higher speeds and the later 915's taller 5th gear.

Jim

.

Here is the explosion of an 84 915 gear set:

FYI... for those of you who were toying with the idea of tying a 915 to a 4 cylinder..... the factory did that. The results were called a 912E.


The 912e uses a special input shaft and clutch release arm to work with the 215mm 914 clutch setup. Both parts are very rare and expensive.

QUOTE (jim912928 @ Dec 18 2005, 07:01 AM)

Rick, FYI so you make the right decisions. The ring gear is NOT the same ratio's at the 901 on the 78 and newer 915's. In 1978 the factory switched to an 8:31 from the previous 7:31's. This will help you out with your higher speeds and the later 915's taller 5th gear. Jim .

Oh... So Who can calulate this? I wouldn't know how to do it if the instructions were on the back.

box (1) is 901 with an "HB" 5th gear.

box (2) is a 915 with the higher 8:31 final drive

Car has 28" tall tires

Q.) What is the RPM's at say 75 mph?

Does this seem like school to anyone?

QUOTE (ClayPerrine @ Dec 18 2005, 07:41 AM)

FYI... for those of you who were toying with the idea of tying a 915 to a 4 cylinder..... the factory did that. The results were called a 912E. The 912e uses a special input shaft and clutch release arm to work with the 215mm 914 clutch setup. Both parts are very rare and expensive.

Oh... see that's the kind of info we need. So if I got this right, there is definitely going to be the need to run a different pressure plate and "T" bearing.

Is that right?

Nope. If you are using the 4 cylinder pressure plate and throwout bearing, you can use that with the 912E transmission.


But you have to find a 912E transmission first......

QUOTE (ClayPerrine @ Dec 18 2005, 08:06 AM)

Nope. If you are using the 4 cylinder pressure plate and throwout bearing, you can use that with the 912E transmission. But you have to find a 912E transmission first......

wise guy!

QUOTE (rick 918-S @ Dec 18 2005, 09:16 AM)

QUOTE (ClayPerrine @ Dec 18 2005, 08:06 AM) Nope. If you are using the 4 cylinder pressure plate and throwout bearing, you can use that with the 912E transmission.   But you have to find a 912E transmission first...... wise guy!

the type 923

all of what 3000 912E's made or something?

You mean one of these...



This is my 923 Transmission. I got it as a core in nasty shape for $750 (from HPH). I replaced the 1/2 syncros and upgraded the 3/4 slider to the late model style. It was rebuild by WEVO with WEVO goodies. If you look closely, all of those screenshots of sheets I posted above where from the 923 transmission.

You are right, it has a 901 mainshaft and using a early 911 or 914 215mm clutch set-up. This particular one had the crossover point on the bottom where the cable goes knock off. I had to have it magnesiem welded. Here is a picture before I cleaned it up completely.





This tranny also has a taller 5th gear that allows it to travel at highway speeds and the engine to not be screaming.



It will go nicely with this:

QUOTE (Aaron Cox @ Dec 18 2005, 10:31 AM)

QUOTE (rick 918-S @ Dec 18 2005, 09:16 AM) QUOTE (ClayPerrine @ Dec 18 2005, 08:06 AM) Nope. If you are using the 4 cylinder pressure plate and throwout bearing, you can use that with the 912E transmission.   But you have to find a 912E transmission first...... wise guy! the type 923 all of what 3000 912E's made or something?

Actually, IIRC there there 2199 made.

I know where two of these transmission are possibly.

-Britain

Hey all,

Have any of you ever had any experience with Rod Simpson's 915 shift kit?

Thanks.

Dino

errrrrrrrr