Building a 3.6 from a 3.7 CMW mess.

[Tippy]

I've no contributions to this thread but >9000 RPM is insane! Would love to hear that.

[txhokie4life]

I contacted Sunset and Suncoast -- there are no GT3 cranks to be had anywhere -- including Germany.

I was told I could order -- but there was no expected date when they would be available.

M

[oemexp]

Tippy,
Go to an ALMS (IMSA) race and listen to the flying Lizards motor. You will see the light and hear the sound.

As to piston / rod weight

GT3 RSR piston 428g
JE 11.5:1 piston 464
GT3 RSR 137mm rod and bolts 369g
stock 3.0L rod 4xx?

It's not as different as you might think. The water boxes and other castings reinforce the motor and case a lot on the GT3 and basically, everything stays much more geometrically and thermally stable. That's and the superior valve train design are the big difference.

[BURN-BROS]

Originally Posted by oemexp

Tippy,
Go to an ALMS (IMSA) race and listen to the flying Lizards motor. You will see the light and hear the sound.

As to piston / rod weight

GT3 RSR piston 428g
JE 11.5:1 piston 464
GT3 RSR 137mm rod and bolts 369g
stock 3.0L rod 4xx?

It's not as different as you might think. The water boxes and other castings reinforce the motor and case a lot on the GT3 and basically, everything stays much more geometrically and thermally stable. That's and the superior valve train design are the big difference.

Nice try,
You are not counting pins/ rings on the JE piston. The GEN1 piston with pin and rings is 490 grams and that is not the lighter later pistons
A 3.6 piston with pin is dancing around 625-630 grams.
A 3 liter rod is 680 grams without bearings. a 3.6 rod is similar in weight.

The GT3 crank will produce significant harmonics in an aircooled engine above 7000 rpms whereas the GT3 reciprocating mass does not exhibit that particuar problem. Another reason why the 3.8RSR engines did not go higher than 7500 without significant problems.

2x's the weight is a bit of an overstatement but 1.5 times is very close to true.

[PFM]

I did not re-run the calculations for the longer stroke of the 3.6 but just for reference on a 70.4 stroke crank a 90 gram reduction in weight of a piston / pin / rod assembly assembly at 8000 is a 631 pound reduction in load at the crank pin. The longer stroke would make this number larger, only 90 grams....

Stay tuned,

PFM

[ONQRACIng]

OK, From what I can gather, it seems my new R+R Racing Rods, 131mm will be using a standard SC bearing, now, I am hearing two different schools of thought on this. Our Crank is a 2010 GT3 Street crank, and has the SAME journals as the SC, and our rods are custom and also are EXACT to the SC on the BE dia. So, one would think that the SC bearings are a go. I know my friend and builder (Paul Schwarz from Cyntex and Bodymotion Fame) wants GT3 rod clearaces, so, first, what are those specs, and second am I correct on the SC bearing thought?

TIA

Andrew

[ONQRACIng]

Aaron,
We are running Custom JE pistons (From CMW Stroke) 100mm, with a new set of R+R rods (131mm) on the gt3 crank, in a Euro SC case (all mods have been done). We have a new Clewett GT3 custom pulley as well. Now, our old CMW based engine ran into the high 8's all day long, and we want to get this new setup into low 8's on occasion, but will live around 7600 as a redline. We are sending the entire spinning assembly to our Machinist to be balanced. From what you have said earlier in this thread, we are asking for trouble with this GT3 crank?

Thanks for the explanation..

Andrew

[BURN-BROS]

Hi Andrew,

My statements above are to clarify that the GT-3 crank is no better than a 964 crank in regards to strength. The engine will not immediately blow above 7500 rpm or even 8000 rpm, they just do not like running up there for extended periods of time.

If you plan to use a 7600 rpm redline you will be fine. Anything above that you should monitor very carefully.

The 100 JE pistons use 100mm forging dies so the weight is as reasonable as they can be. I would definitely have them remove material from under the crown or better yet run the Forged Side Relief piston (FSR) to get the weight down and a set of Ti wristpins wouldnt hurt if you have the budget. You may be able to shave 50 grams from the standard JE package. Short spurts up to 8 may be tollerable but I could not recommend it.

[ONQRACIng]

Aaron,

My mentor, and friend, Paul Schwarz, agrees, and I have the 7600 pill ready once the engine is assembled. We are running an old CMW 2.9 now for the season, and will post the build of the 3.6 once we start.

[BURN-BROS]

I look forward to seeing it.

Enjoy the rest of your season!

[ninesixfour]

Originally Posted by BURN-BROS

Hi Andrew,

My statements above are to clarify that the GT-3 crank is no better than a 964 crank in regards to strength. The engine will not immediately blow above 7500 rpm or even 8000 rpm, they just do not like running up there for extended periods of time.

An SC case will accept a GT3 crank? I know the early GT3s used the 930 case but I thought the newer ones were different.

Originally Posted by ONQRACIng

OK, From what I can gather, it seems my new R+R Racing Rods, 131mm will be using a standard SC bearing, now, I am hearing two different schools of thought on this. Our Crank is a 2010 GT3 Street crank, and has the SAME journals as the SC, and our rods are custom and also are EXACT to the SC on the BE dia. So, one would think that the SC bearings are a go. I know my friend and builder (Paul Schwarz from Cyntex and Bodymotion Fame) wants GT3 rod clearaces, so, first, what are those specs, and second am I correct on the SC bearing thought?

TIA

Andrew

Interesting. I just installed GT3 rod bearings onto my SC crank for my SC motor. Why do you want the SC bearings?

[BURN-BROS]

Originally Posted by ninesixfour

An SC case will accept a GT3 crank? I know the early GT3s used the 930 case but I thought the newer ones were different.

Yes, the crank should drop in. The new GT3 case reinforced the weakspot on the #7 main web and removed the provisons for oil return tubes and other air cooled related castings. The cranks have a few changes to them but retain most of the original aircooled dimensions that are important to us.