901 trans on a 7R case possible?

BartdeBruijn · 07-12-2016, 06:03 AM

Hi,

I know it sounds strange as people normaly want to go the other route.

I plan to build different engine (more peaky -> +4000 rpm) but will stay below 200hp
It will be based on based on a 2.4T (7R-case).
I have a fully rebuild and healty 901 5 speed transmission. I like the dogleg shift pattern

So question is if I can mate my 901-transmission to a 7R-case?

Thanks,
Bart

JmuRiz · JmuRiz's Garage

I would hope so, that's my plan...but with a 2.7

My engine/trans guy said a 200hp engine is totally fine with a well built-stock 901. Once you go over that you need to beef it up a bit to make it totally reliable.

Fudge factor would say up to 225hp should be OK on a small-ish <2.7 engine's torque if you're not too rough on it.

Steve@Rennsport · 07-12-2016, 07:50 AM

You can use the 901 with a 2.4 (bellhousing bolt patterns are all identical), however I would strongly recommend installing a billet intermediate plate with a 2.7.

Its not a power issue as much as a torque problem.

Mark Henry · 10:32 AM

914 guys do it all the time, even bigger engines. 3.0 and bigger need conversion flywheel/clutch set-ups.
The 914 trans is a 901 with a few shifter differences and a flipped diff. Consensus is it's good to about 250hp.

The weak link is first gear, use it as a granny gear, no hard starts (burn outs, dumping the clutch) on it and you will be fine.
If you plan to track the car you will need to do major oil/cooler mods, but for street you would be OK.

My 3.0/6 twin plug will be right at the peek HP, but it's a street car and I have a fresh backup trans on the shelf.
My VW bug has a 180hp 2.6 T4 and a 911-901, I'm easy on 1st but other than that drive it hard, 3 years no problems.

I suggest you rebuild the trans they are not that hard to do. The billet intermediate plate would need a R&P reset, again IMO only needed if you are racing or planning to be real hard on the trans.

BartdeBruijn · 07-13-2016, 12:19 AM

Hi,

Thanks for the valuable info!

I do realize that it is more (only) a torque issue then an HP issue.

Plan was to build a engine based on 7R-case that comes 'on-cam' after 4000rpm's.
so probably a high(er) CR 2.4 then a 2.7 RS-spec like car.....not sure yet.

I have been reading already a lot of info on this GREAT forum, however I would really like to know where twin plugging is needed with respect to CR.
Octane numbers in the Netherlands are 95 or 98 ;-)))

I also do realize that it also has to do with piston and cylinder head shapes....
So is there a rule of thumb to stay on the save side with respect to European octane numbers !?

Cheers,
Bart

Steve@Rennsport · 07-13-2016, 07:39 AM

Hi Bart,

Based on 2.2-2.7 heads:

With 98 RON fuel, anything 9.8:1 or more should get twin-ignition.

Using 95 RON fuel, anything over 9.5:1 needs twin-ignition in order to use decent ignition timing.

BartdeBruijn · 07-14-2016, 01:57 AM

Hi Steve,

Thanks again!

So guess we are lucky in The Netherlands RON-wise ;-)

Will start reading Bruce Anderson's book and try to figure out what I would really like to build...
Any other read suggestion? SOme extensive build stories on this board or another book?
(for me that's the pre-fun of it!

A relative high revving peaky engine or try to find some consensus in a bit more bottom torque.
In the end it is all a matter of taste(like many things in live!)

Cheers,
Bart

Matt Monson · 07-14-2016, 05:27 AM

Wayne's engine rebuild book is a good read even if you are paying someone else to build it. Covers all the updates and improvements you can do during the build.

Steve@Rennsport · 07-14-2016, 09:33 AM

Quote:

Originally Posted by BartdeBruijn

Hi Steve,

Thanks again!

So guess we are lucky in The Netherlands RON-wise ;-)

Will start reading Bruce Anderson's book and try to figure out what I would really like to build...
Any other read suggestion? SOme extensive build stories on this board or another book?
(for me that's the pre-fun of it!

A relative high revving peaky engine or try to find some consensus in a bit more bottom torque.
In the end it is all a matter of taste(like many things in live!)

Cheers,
Bart

My pleasure Sir! Lucky indeed,...

If you choose a relatively peaky camshaft, I would strongly recommend close-ratio gears in order to enjoy all the benefits of the additional performance. It keeps the engine in its most productive RPM range for maximum acceleration.

Walt Fricke · 07-14-2016, 08:42 PM

Bart - you have noticed, have you not, that the 901 is set up for a push clutch, while any 2.4 or 2.7 donor motor will have the flywheel for a push clutch? But a 2.0 flywheel will work with the pressure plate you need for a push clutch. Or maybe someone makes a push pressure plate which will bolt up to the flat later flywheel with its separate ring gear.

Mark Henry · 07-15-2016, 05:13 AM

The early 911-901 and 914 uses a pull arm (I believe technically this is a push clutch) and the 70- 911 uses a push arm.
Besides the pressure plate (PP) and release bearing the the main difference on the trans is the the pivot point is moved slightly over and there is a boss on the trans to mount the cable.

The only thing wrong with the '70- 901 is PP and the throw out bearing is expensive.

On my '67 bug with a 911-901 trans I converted it to pull by cutting bending and welding an early arm to line up proper and installed an early pivot ball. It works better than expected with 4 years and zero issues.
It's a 180hp 2600cc type 4.

Except for the crank bolt pattern the -'69 911, 914/6 and 914/4 flywheels are the same and use the same 215mm PP. The -6 as I did 911 flywheel would bolt to the 2.7 and you could make it work as pull as I did in my bug.
This setup is good to about 180hp

You can also use the 2.7 flywheel with an adaptor assembly and a HD 228mm VW bus PP, again you would have to mod the throw out bearing arm to pull as I did in my bug.
Below is the adaptor ring and 228mm pressure plate I made for my 914 3.0 six conversion, but you can buy this ready made from KEP.

stownsen914 · 07-15-2016, 05:13 AM

Walt makes a good point about the flywheel and clutch difference. The '70-71 901/911 trans has a different clutch fork to use the later style flywheel. Or you can convert an earlier 901 to use the '70-71 clutch fork - the case needs to be machined for an insert for the fork mount. May be easier to put a pre-1970 flywheel on the motor if you have a pre-1970 trans.

Scott

Mark Henry · 05:34 AM

Quote:

Originally Posted by stownsen914

Walt makes a good point about the flywheel and clutch difference. The '70-71 901/911 trans has a different clutch fork to use the later style flywheel. Or you can convert an earlier 901 to use the '70-71 clutch fork - the case needs to be machined for an insert for the fork mount. May be easier to put a pre-1970 flywheel on the motor if you have a pre-1970 trans.

Scott

Slightly beat you to it but you can just modify a 914 arm as I did in my '67 bug.

Retro · 07-15-2016, 10:17 AM

I have a 914/6 conversion. Rothsport just dyno my 3.0 twin plug, at 288.8 HP, 238 torque. I have been running a 901 with short gears and limited slip rear end for many years. Hard street driving with occasional DE day. No problems, I love my 901/914!

Retrotech: Classic and vintage Porsche cars, accessories and Porsche parts

pemz0r · pemz0r's Garage

my 901 bolted to a 2.7

https://www.youtube.com/watch?v=TqfzCsiOE4M

BartdeBruijn · 07-16-2016, 05:44 AM

hi Walt and others,

thanks for the info!
yes I did know the difference in pull/push, however the question remains that if I exchange the bearing can I still use the 901 setup on a 2.4 (7R) cases?

changing fork beacuase of pivot point differnce between 901 and 915?

is there somewhere a thread that explains this?
as i read confusing stories now

thanks,
Bart

stownsen914 · 07-16-2016, 06:46 AM

The different clutch fork is for the '70-71 901 trans (called a 911 trans technically I believe) compared to the earlier 901s. This is only relevant if you wanting to use the later style clutch and flywheel with a 901. 915 trans use a totally different type fork.

The 901 will bolt up to a 7R case. And even to a 3.0 and possibly later ones too.

There are other threads on this, as I recall chiming in on this topic before, but I don't recall offhand.

Scott

Quote:

Originally Posted by BartdeBruijn

hi Walt and others,

thanks for the info!
yes I did know the difference in pull/push, however the question remains that if I exchange the bearing can I still use the 901 setup on a 2.4 (7R) cases?

changing fork beacuase of pivot point differnce between 901 and 915?

is there somewhere a thread that explains this?
as i read confusing stories now

thanks,
Bart

Mark Henry · 07-16-2016, 11:40 AM

Quote:

Originally Posted by stownsen914

The different clutch fork is for the '70-71 901 trans (called a 911 trans technically I believe) compared to the earlier 901s. This is only relevant if you wanting to use the later style clutch and flywheel with a 901. 915 trans use a totally different type fork.

The 901 will bolt up to a 7R case. And even to a 3.0 and possibly later ones too.

There are other threads on this, as I recall chiming in on this topic before, but I don't recall offhand.

Scott

Sir Andy from 914world has a 3.6 on a 914-901, so it can be done. He has DE and AX'ed his car with no issues, so as long as you respect the limitations of 1st you should be fine.

I know saying 914-901 or 911-901 isn't technically correct terminology, but they are all based on the 901 trans with a large amount of interchangeable parts. I just do it so the other person knows which 901 I'm talking about.

Mark Henry · 05:21 PM

Quote:

Originally Posted by BartdeBruijn

hi Walt and others,

thanks for the info!
yes I did know the difference in pull/push, however the question remains that if I exchange the bearing can I still use the 901 setup on a 2.4 (7R) cases?

changing fork beacuase of pivot point differnce between 901 and 915?

is there somewhere a thread that explains this?
as i read confusing stories now

thanks,
Bart

For the 911 trans the only bolt on solution is the 911 clutch assembly (all), the 2.7 (2.2/2.4) flywheel using the 911 (911-901) transmission in the push configuration.

There is two ways to modify the 911 tranny to use a pull style clutch assembly in the 911 trans.
1/ disassembly of the trans and redrill/tap the location of the pivot ball, then use the 901 or 914 pivot ball, release bearing arm TO bearing and early 901 or 914 215mm flywheel, disc and PP.

2/ Cut bend weld the 914 arm, then use the 901 or 914 pivot ball in the stock 911 location and the stock 901/914 TO bearing and early 901 or 914 215mm flywheel, disc and PP

Or instead of the stock 901/914 215mm clutch assembly you can use the 2.7 flywheel with the adaptor set up in the pictures I posted, this assembly can handle more HP.

If you don't think you can modify the release bearing arm this guy will make you one:
http://www.bugat5speed.de/en/beetle-co/transmissions/conversion-parts-porsche-transmission-901-914

Walt Fricke · 07-17-2016, 09:03 PM

I believe that the air cooled VW, the 356, and all the air cooled Porsche 911s use the same engine to transmission bolt pattern. So they bolt up easily enough. The tricky parts are the different clutch and pressure plate styles and sizes, and I think being sure you have the clutch disk which matches the mainshaft splines (not actually tricky, if you know what you need).