964 ,Gt3 crank and bearing choice

[puddy1]

After a spun rod bearing , I have decided to replace crank with a Gt3 crank rather than repair old crank on advice from my machine shop who advised against .50 regrind .

can some one tell me which Gt3 one I need please or point me to a link with info. Do I need 964 shells or Gt3 shells or do they both fit I am planning on using my existing rods and pistons if possible . Looking for around 3-340 max bhp .
The engine will be a transplanted into my 79 SC when I get my rebuild finished .
Many thanks Henry

[Flat6pac]

The GT3 crank has color code markings on the crank for buying the correct bearings from Porsche Motorsport.
Bruce

[Henry Schmidt]

It seems there is some information you're missing.
First, GT3 rod journals are not the same as a 964 or 993, 930 or Carrera for that matter.
The GT3 uses a connecting rod that is similar to the 911SC rod but it has a longer center to center measurement. 130mm vs 127.8 mm ?
If you're replacing a 3.0 SC crank then the piston height is wrong.
If you're replacing a 964 crank, the rod journal, rod length and the wrist pin is the wrong size.
Using a GT3 crank also requires the use of a custom made crank pulley in addition the a different pulley bolt.
There are a plethora of things to consider but number one is that it is only a direct replacement for a GT3 crank. If you're hell bent on using a GT3 crank (don't get me wrong I love them) you will have to consider the entire package as complete build not a replacement.
That said, main bearings are pretty much the same from 3.0 SC all the way to GT3.
Cheers

[JV911SYDNEY]

There are a number of gt3 cranks you can use: 996, 997 even 4.0, but you are opening a can of worms:

Rod journals are different sizes so you will need to change them. Pauter and Carillo make rods specific for this application. GT3 bearings should be used too. This combo will allow you to access higher RPM.

You'll also need to change front pulley (Rothsport make a nice kit) and may need to clearance the oil pump (?)

[puddy1]

Hmmm , thanks guys glad I posted this! So a Gt3 crank may be out for me as hadn't budgeted for custom rods , quite pricey ,to have in an otherwise stockish motor .

Annother option that I have been considering is using a 993 crankshaft and its rods and pistons . I have been offered a set from a 60,000 mile car that was upgraded to Gt3 and further mods. Its a complete assembly and I was told the rods and pistons are lighter than 64 ones which makes for a nice motor .
Second hand worries me though which is what led me to a nice new Gt3 one with thoughts of upgrading at a later date maybe .

[puddy1]

Has anyone had experience with the 993 crank ,rods and pistons being used in a 964 engine ? is a good idea and is it a straight forward swap?

[Henry Schmidt]

Originally Posted by puddy1

Has anyone had experience with the 993 crank ,rods and pistons being used in a 964 engine ? is a good idea and is it a straight forward swap?

993 rods are slightly narrower and the crank pulley is different. Beyond that, I like the 993 crank design better than the 964.

As for the serviceability of a used crank, I would say that when inspected by a competent machinist a used crank within spec can be used with confidence. In my experience, crank problems occur when cranks are repaired. Welding, nitriding and grinding offer challenges in that you are at the mercy of the crank shop.

[puddy1]

Originally Posted by Henry Schmidt

993 rods are slightly narrower and the crank pulley is different. Beyond that, I like the 993 crank design better than the 964.

As for the serviceability of a used crank, I would say that when inspected by a competent machinist a used crank within spec can be used with confidence. In my experience, crank problems occur when cranks are repaired. Welding, nitriding and grinding offer challenges in that you are at the mercy of the crank shop.

Appreciate your input Henry many thanks ,

just so I fully understand the stroke and displacement will be exactly the same using the 993 crank rods and pistons in my 964 engine , is the piston design different if so does it matter as long as its compatible , would power output be exactly as before keeping the same compression ratio? I plan to run the engine with 993 headers and custom exhaust with a live remap once run in . Presumably I need new 993 rings as they differ from 64 ones .

Would you see this setup as a slight and preferable upgrade with improved engine characteristics ? Cheers H

[Rufian]

I have hear that on the crank issue, you will need Special Pistons (JE is a good source), Pauter Rods with the correct length,on the crank you can use an early 996 GT3 crank (no need to change the pulley), still pricey!!!

[YermanCars]

I have a the right gt3 crank for you. NIB. williamknight@mac.com can assist you in the right bearings and possible engine combo for you.