# porsche 914 coupler diemensions



## broomhandle (Jul 22, 2009)

i have a GE motor from about 1999, and i have a porsche 914 with a 901 transaxle. i need to make a coupler, but need dimensions. does anybody know how far the flywheel sticks out from the ICE motor? or the diameter of the bolt holes to mount?

have accsess to Auto CAD and a CNC, but need a place to start.

any help will help.....


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## O'Zeeke (Mar 9, 2008)

broomhandle said:


> i have a GE motor from about 1999, and i have a porsche 914 with a 901 transaxle. i need to make a coupler, but need dimensions. does anybody know how far the flywheel sticks out from the ICE motor? or the diameter of the bolt holes to mount?
> 
> have accsess to Auto CAD and a CNC, but need a place to start.
> 
> any help will help.....


Broom, Check out Otmars 914, and follow the links. I think he also uses the 901.
http://www.evalbum.com/293


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## DavidDymaxion (Dec 1, 2008)

I have a 1977 Porsche 911, I'm not sure if my year is the 901 tranny, how do I check that? Anyway, here are the drawings I made and used. Of course, measure against your tranny! So far so good, my adaptor works great, the clutch is smooth, and it doesn't vibrate. I jacked up the car under the adapter to test it for strength.

http://explodingdinosaurs.com/9electric/adapter/

http://ExplodingDinosaurs.com

Note the depth of your adapter (thickness of the spacer) will vary depending on your coupler design and it's placement on the motor shaft.


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## broomhandle (Jul 22, 2009)

great, this really helps. but you dont have much for measurements for the coupler, more for the adapter plate. the 914 uses the 901 transaxles, and the early 911's use it as well. like up to 72 i think. so yours is different.

i am looking for how far the original fly stuck out from the ICE motor?

or measurements of the bolt holes for the VW/Porsche fly?

i think your 911 is much different, the VW was setup to mount up to a VW bus motor.

i have an adapter plate from a S10 that i will use so not too worried about the plate.


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## DavidDymaxion (Dec 1, 2008)

I just bought my coupler from http://www.electroauto.com/ , and then built the adapter around those dimensions. The electroauto piece is a work of art and worked well for me.

If I were going to do it again, I would do the coupler like http://www.grassrootsev.com/ videos show. They bolt on a taperlock adapter, and spin the electric motor to machine it to size. This is an especially good idea, as this will guarantee the coupler is machined relative to the axis of rotation. The trick on the Porsche is the bolts are so close to the center, you need a really deep coupler. I would look into a Chevy V8 clutch system, or maybe even machining my own flywheel, that could move the bolts out, and make the coupler much less deep.

The coupler needs to be super accurate, just a few thousandths off can mean 100's of pounds of imbalance force that leads to vibration.

I did a bunch of measurements and averaged, and got 0.534 inches for my magic number (motor/tranny interface surface to flywheel face distance). You need to preserve this distance for proper clutch operation, but the clutch does have some adjustment range. Since we might have different trannies, you should be sure to measure yours.



broomhandle said:


> great, this really helps. but you dont have much for measurements for the coupler, more for the adapter plate. the 914 uses the 901 transaxles, and the early 911's use it as well. like up to 72 i think. so yours is different.
> 
> i am looking for how far the original fly stuck out from the ICE motor?
> 
> ...


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## broomhandle (Jul 22, 2009)

yeah, i thought that as well. your transaxle is the 915, which were used in the 911's from mid 70's to the 80's. its a better transaxle. and can handle more. but i am stuck with the 914 transaxle. and, i would like to buy one, but i am building a budget EV. ill see what i can come up with, the chevy conversion is a good thought.


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## electromet (Oct 20, 2009)

Broomhandle,

The first thing I would do is go to one of the 914 forum groups and find out exactly what the difference is between the 901 and 915. It may be nothing more than internal components, leaving the mounting engineering the same. One thing you do have to take into consideration if you're inclined to swap to the 915 tranny is whether you have a side shift linkage or rear shift linkage. Porsche changed the shifting linkage in '72 or so. I believe the later trannies were side shifters. Don't hold me to it though.


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## broomhandle (Jul 22, 2009)

electromet said:


> Broomhandle,
> 
> The first thing I would do is go to one of the 914 forum groups and find out exactly what the difference is between the 901 and 915. It may be nothing more than internal components, leaving the mounting engineering the same. One thing you do have to take into consideration if you're inclined to swap to the 915 tranny is whether you have a side shift linkage or rear shift linkage. Porsche changed the shifting linkage in '72 or so. I believe the later trannies were side shifters. Don't hold me to it though.


i would go with the 915 if i could, it can take more HP and torque. 73 was the 1st year for the side shift in the 914, but it still used the VW setup. 

has anybody done a VW bus? they have the same setup.


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## lhogberg (Oct 30, 2009)

DavidDymaxion said:


> I have a 1977 Porsche 911, I'm not sure if my year is the 901 tranny, how do I check that? Anyway, here are the drawings I made and used...


Great job!
I'm interesting in manufacturing a motor adapter too, and I'm wondering; how did you perform the measurements?


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## DavidDymaxion (Dec 1, 2008)

Many thanks for the kudos!

I just bought the coupler, so no measurements for that. I put it on, put on the flywheel, and carefully measured the distance from the flywheel face to the motor face. This distance minus the "magic number" (gas motor flywheel to tranny/motor interface distance) told me how deep to make my adapter.

I measured the magic number using a stack of washers. I measured the height of the stack that was on the motor/tranny interface surface, then measured down to the flywheel face (this avoided a flywheel lip).

I was lucky on the Porsche. I checked and the crankshaft center was equidistant from several spots on the tranny centering ring -- so I could machine on a rotary table and things would line up. I used a large caliper to measure the diameter of the centering ring, and frequently checked the diameter of my adapter's centering ring while machining.

Once I had the diameters right and the adapter finished, I put it on the tranny with c clamps. I then got punches that fill the hole and have a sharp spike. I picked a size that just fit the tranny mounting holes, and hammered a divot into my adapter. This told me where to drill those holes. Those holes did not need to be super accurate, since on the Porsche the centering ring provides your accuracy in positioning. (Side note, if you need to position accurately, don't use a bolt. It needs some slop to slide into its hole. Instead use a pin that you have to press fit on one part, and barely fits on the mating part.

I just started making a web page showing some of this, I'll post when that's done. You can see my drawings at http://explodingdinosaurs.com/9electric/adapter/ .

Some further comments: If something needs to be a slip fit (like the Porsche adapter into the tranny), you need to allow a couple of thousandths of slop. There are tables of how much extra, the number grows a bit with the part size. Also, I think metal calipers are more accurate, the plastic ones are fine for small parts but flex a bit for bigger things. You need to measure things 0.001 inch accurate. Measure everything several times and average. If something almost fits but not quite, a little hand sanding will often do the trick. I prefer to sand the part I made, and not the expensive Porsche tranny!

Finally, Steve Clunn did a great job making an adapter. Instead of accurate measurements, he taps things with a hammer to adjust position until there is mininum noise. http://www.grassrootev.com has his videos. (Disclaimer I do not stand to profit from the success or failure of grassrootsev.)


lhogberg said:


> Great job!
> I'm interesting in manufacturing a motor adapter too, and I'm wondering; how did you perform the measurements?


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## lhogberg (Oct 30, 2009)

DavidDymaxion said:


> Many thanks for the kudos!
> ...(this avoided a flywheel lip)...



Oh, that was really helpful!! I'm starting to feel confident on making my own now. I think I got it all, except one thing, what's a flywheel lip? 

I ought to buy those Steve Clunn videos...

Thanks a lot!


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## DavidDymaxion (Dec 1, 2008)

Happy to help. You can see the flywheel lip in the first couple of pics on this page: http://explodingdinosaurs.com/9electric/adapter

Short story: You can forget what I said about the flywheel lip, just be careful you measure from the flywheel face. Longer story: This was important for me, since I was changing flywheels, and distance to the flywheel face is more important, and the lip size might have been different between the two brands of flywheels. My flywheel had a lip that centered the pressure plate. That prevented me from measuring the magic number directly, as that would have measured from the lip rather than the flywheel face.

Also lhogberg check your PM.


lhogberg said:


> Oh, that was really helpful!! I'm starting to feel confident on making my own now. I think I got it all, except one thing, what's a flywheel lip?  ...


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## broomhandle (Jul 22, 2009)

are you using the 915 as well? or the 901? they are very diffeerent. one is porsche, the other is vw.

my 914 came without the motor, did you get any measurements?








lhogberg said:


> Oh, that was really helpful!! I'm starting to feel confident on making my own now. I think I got it all, except one thing, what's a flywheel lip?
> 
> I ought to buy those Steve Clunn videos...
> 
> Thanks a lot!


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## Tangerine Racing (Jan 3, 2010)

broomhandle said:


> are you using the 915 as well? or the 901? they are very diffeerent. one is porsche, the other is vw.
> 
> my 914 came without the motor, did you get any measurements?


Actually, both transaxles are Porsche, however Porsche and VW transaxles all bolt up interchangeably with Porsche and VW engines, assuming you can come up with an appropriate flywheel/pilot bearing/clutch assembly and starter.
914s all came with a version of the 901 trans called the 914. A popular upgrade for high torque engine conversions is to install a 915 trans converted for mid engine use. 
911s used the 901 trans through about 1972, then started using the 915. One of the biggest functional differences is the position of first gear in the gear stack. The 901/914 trans has first gear hung outside the bearings, making it the weak point for high torque applications. The other functional difference related to this is the shift pattern. 901/914 has a unique shift pattern while 915 has a conventional pattern compared to most modern vehicles.


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## DavidDymaxion (Dec 1, 2008)

Thanks, good to know I have a 915, thanks for the "spotters guide."


Tangerine Racing said:


> Actually, both transaxles are Porsche, however Porsche and VW transaxles all bolt up interchangeably with Porsche and VW engines, assuming you can come up with an appropriate flywheel/pilot bearing/clutch assembly and starter.
> 914s all came with a version of the 901 trans called the 914. A popular upgrade for high torque engine conversions is to install a 915 trans converted for mid engine use.
> 911s used the 901 trans through about 1972, then started using the 915. One of the biggest functional differences is the position of first gear in the gear stack. The 901/914 trans has first gear hung outside the bearings, making it the weak point for high torque applications. The other functional difference related to this is the shift pattern. 901/914 has a unique shift pattern while 915 has a conventional pattern compared to most modern vehicles.


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## broomhandle (Jul 22, 2009)

Tangerine Racing said:


> Actually, both transaxles are Porsche, however Porsche and VW transaxles all bolt up interchangeably with Porsche and VW engines, assuming you can come up with an appropriate flywheel/pilot bearing/clutch assembly and starter.
> 914s all came with a version of the 901 trans called the 914. A popular upgrade for high torque engine conversions is to install a 915 trans converted for mid engine use.
> 911s used the 901 trans through about 1972, then started using the 915. One of the biggest functional differences is the position of first gear in the gear stack. The 901/914 trans has first gear hung outside the bearings, making it the weak point for high torque applications. The other functional difference related to this is the shift pattern. 901/914 has a unique shift pattern while 915 has a conventional pattern compared to most modern vehicles.


awesome. i knew the bolt up was the same, but i thought the depth was different. so measurements would be the same? such a pain to get an adapter. i would like it cnc'd to make it balanced. 

and the 915 is the way to go, just pricey! ill use the 901 until its eaten.


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