Building a 3.6 from a 3.7 CMW mess.

[ONQRACIng]

We are doing our CMW 3.7 Stroker engine over, since the crank snapped two seasons ago.
We have a 2010 997 GT3 street crank, part number 996.102.021.94
inbound, and need the specs on the stock 997 GT3 Street Rods, Part number 996.103.012.89.

We need Big end bearing bore, and Big end width for custom 131.1mm R+R Rods, LN Engineering order, which is pending these numbers.

Our engine will run the 76.4 crank, 131.1 rods and 100mm pistons, just over 3.6 I believe, minus the torque of the stroker, but more race reliable..

The original build was 77.5 stroke (offset grind on a stock 3.0 shaft) 130mm Cunningham Rods and 100mm Custom JE 12.5/1 pistons. Engine was orginally built by PAul Schwarz at Cyntex in West Chester PA, and ran very strong and hard until we had out mishap..

Any specs that can be provided, or a place to search myself, would be great. We have found very little on the GT3 specs via the WW Web..

TIA

Andrew

[BURN-BROS]

Hi Andrew,

GT3 journals are the same as SC

Journal dia in 53mm

Journal width is 22mm

[ONQRACIng]

Ah,, SC rods WILL run on a GT3 shaft.. Thanks

[BURN-BROS]

Your welcome Andrew.

[ONQRACIng]

GT3 Crank is in house. Amazing that a new 997 GT3 Cranks is less expensive than a used 993 crank.. Even with the added expense of a new pulley, this is a no-brainer... Now, Carrillos are next, estimate 498 grams, so we will spin into the 9's again.. $2.2K not too shabby.. Need to see what R+R weights are before we order anything..

Thanks for all the info and help..

I will document ths build, and post details..

[BURN-BROS]

Originally Posted by ONQRACIng

GT3 Crank is in house. Amazing that a new 997 GT3 Cranks is less expensive than a used 993 crank.. Even with the added expense of a new pulley, this is a no-brainer... Now, Carrillos are next, estimate 498 grams, so we will spin into the 9's again.. $2.2K not too shabby.. Need to see what R+R weights are before we order anything..

Thanks for all the info and help..

I will document ths build, and post details..

You will have to shorten the snout by approx 4mm and redrill the pin for the pully.

IMHO, the recommended RPM for a 2 valve 3.6 is still 7500 regardless of crank choice. The piston weight and rods are too heavy to safely spin above this without running in to harmful harmonics. Beyond this rpm and you are on significantly diminished time regardless of your rod choice. There is not enough room to make a stronger crank to deal with the high piston weights.

Weights I have recorded for a 130mm Carrillo are around 540-560 grams. A Ti 130mm GT3 rod is about 480 grams

GT3's have very light pistons(less than a 2 liter piston), along with a light rod and pin give it a higher rpm limit. The decreased weight keeps Harmonics and rod bearing loads within reasonable limits.

[ONQRACIng]

Aaron,
Understood.. We tear down after 45 hours on each of our race engines, the 2.9 revs to 7400 on the Motec. We had the 3.7 limited to 7600 during race days, but dyno time we pulled to 9K with no issues. Granted, I agree that this eats away at engine time between repair numbers.

We are leaning toward either Carrillo or Cunningham Ti rods @ 490 grams..

the plan is to have the Motec set to a 7800 limit, keeping the inners happy..

Thanks for all the feedback, it helps keep one honest..

Andrew

[BURN-BROS]

Sorry for the misunderstanding When 9K and 3.6 are in the same sentence the following sentence usually involves writing big checks.

Nevertheless! Check the snout of your crank for the dimensional differences if you did not know already.

Hope your weekend is going well!

[ONQRACIng]

Working with Clewett on their GT3 friendly Pulley.. I am finishing up the Rod specifics before Carrillo gets the spec sheet for an accurate quote.

I should have been more detailed with the 9k Revs statement.. I like the grunt,but not the rebuilds, so 7600-7700 it shall remain. Unless I land a big paying Sponsor, than 3.8 will get transplanted...

Ahh.. nice to dream..

[CMMTracknut]

sounds like a great motor, can I ask where you got your GT3 crank?

I am building a 964 case, 3.8 motor and looking to use a GT3 crank but was just told they are currently hard to find?

thanks
C

[ONQRACIng]

Dealer item.. If you are looking for a Motorsports crank, that is gonna be hard.. Mine is a GT3 Street car crank. There are differences, motorsports does a piece inspection on every crank, all are weighed to be the same,and each gets mag'd and xrayed, from what I was told by a Grand Am Crew chief..
Street cranks are lot inspected like every 500 or so... Still a great deal, 1600ish from the dealer, compair that to a 964 crank, used.,.

[CMMTracknut]

our local dealer said he could not find one in the country? I read that PP may have them so I will try there. Thanks

C

[ONQRACIng]

there were 3 incountry, US, as of last week..

[ONQRACIng]

Here is the 2010 997 GT3 Crank we are using..

[CMMTracknut]

Please help, I tried to buy one again yesterday and I was told by 3 different dealerships that there are zero in country and I need to get from Germany.
TIA

[racing97]

I noticed that the crank does not have the current trend in oiling such as cross-drill and groved mains.

regards

[ONQRACIng]

Well, it is the current Street GT3 shaft.. Sure you didn't see a Porshce Motorsports shaft?

[oemexp]

I have torn down several GT3 RSR and Brumos DP motors that PMNA supplied. I have never seen a cross drilled crank or boat tail work on any of these engines. They never do it and these motors run 9600 rpm and sometimes higher.

[racing97]

That has been my experience as well. It seems like the oiling issues are self imposed

regards

[BURN-BROS]

GT3s have almost 50% reduction in rod a piston weights over it's aircooled bretheren. Spin a 3.0 liter to 8500 rpm and take a look at what the rod bearing will look like at 25 hrs and report back...
Apples and oranges fellas.