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Old 02-07-2012, 08:38 AM   #1
No Limit Motorsport
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Default To billet crank or to not billet crank, that is the question

Time has come to start building the spare race engine for the car a friend and I are doing. (The one I made the 400lph Walbro post about) The engine in the car currently has a BC 83mm stroker kit in it unsleeved. We assume at 650whp its only a matter of time before she explodes which is OK. He wants to push it, and we have at least doubles if not triples of every part.

The spare motor is getting sent out to get sleeved as soon as the pistons get here

I ordered the JE Billet FSR pistons with coated skirts and domes (balllllin) and a set of Carrillo Pro H rods to compliment. Nicest lightweight rotating assembly, that can handle the abuse that this car will see. Really broke the bank on that one though, lets see if it pays off. This combo is 508 grams, or 1.12lbs lighter than the standard Manley/CP piston + Turbo Tuff rod combo. That is a lot less weight to be swinging around in an engine.

The only thing we are on the fence about now is crank selection. I am torn between using a nitride coated 2011, which I know is a good unit, but unsure of its HP limits, or a K1 or Manley 79mm crank. The money for a $3500 Cosworth isn't in the budget.

If this motor was going to make 500, 550, or 600 I wouldn't think twice and go for the OEM. I want this thing to be able to do a real 750 on a good day. I have no problem admitting that HP level is virgin territory for me with a Subaru.

Planning to rev it on the drag strip to 7500-8000 with a shimmed 11mm pump or the high flow Cosworth (which is probably overkill).

So I am looking for some real world racing advice here.

Japan made? OEM crank vs China made billet crank?
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Last edited by No Limit Motorsport; 02-07-2012 at 09:43 AM.
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Old 02-07-2012, 11:01 AM   #2
MartinSTi05
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I spun a 83mm cross drilled BC 2.7 stroker to 8500 routinely with their heavy rods, and non lightened CP pistons. I used a shimmed/ ported 10mm pump. When the motor was torn down the bearings looked great.
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Old 02-07-2012, 11:32 AM   #3
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Wait, didn't that crank break though, martin????

Carmi
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Old 02-07-2012, 11:35 AM   #4
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I'd think that the forged crank would be stronger. I'd move to the billet cranks for the improved oiling and weight.
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Old 02-07-2012, 01:06 PM   #5
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Are the newer 08+ STI "black nitrided cranks" forged or cast?

I'm glad to have the old 07 STI crank.
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Old 02-07-2012, 06:36 PM   #6
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Quote:
Originally Posted by soon2bblackongold View Post
Wait, didn't that crank break though, martin????

Carmi
Yes it did. However it failed due to heat treat and tiny fillet radii. Those problems have been adressed by that manufacturer and are not present in others' cranks such as Manley. I am just saying that with proper prep of the oiling system I was able to hit 8500 at the dragstrip and the bearings looked good upon teardown.
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Old 02-07-2012, 07:18 PM   #7
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this is JC's time attack car on a BC 83mm crank, BC I-beams, and JE FSR pistons:



Broke an H-beam going to 8500, kept this under 8200.

Worked great until a sleeve cracked (stock with a deck plate) and hydrolocked the motor.
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Old 02-07-2012, 08:08 PM   #8
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You need to consider the upgraded oil passages on the billet cranks, not just strength
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Old 02-07-2012, 08:38 PM   #9
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Quote:
Originally Posted by mick_the_ginge View Post
You need to consider the upgraded oil passages on the billet cranks, not just strength
I realize that as a positive, in addition to the strength. This is why I wanted to do it. My deliberation comes from the parts possibly having manufacturing issues.

My fears are of the journals being improperly shaped, sized different, the crank not being "true", and having to do work to get the bearing clearances right

Either way I guess we will find out. I bit the bullet this afternoon and ordered a Manley 79mm.

I guess we will find out soon enough. Ill post up with the results.
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Old 02-07-2012, 09:09 PM   #10
MartinSTi05
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Quote:
Originally Posted by mick_the_ginge View Post
You need to consider the upgraded oil passages on the billet cranks, not just strength
Mick speaks the truth. Straight shot oiling passages alone can be worth the price of admission when it comes to stick stroke billet cranks.
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Old 02-07-2012, 09:26 PM   #11
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Quote:
Originally Posted by No Limit Motorsport

I realize that as a positive, in addition to the strength. This is why I wanted to do it. My deliberation comes from the parts possibly having manufacturing issues.

My fears are of the journals being improperly shaped, sized different, the crank not being "true", and having to do work to get the bearing clearances right

Either way I guess we will find out. I bit the bullet this afternoon and ordered a Manley 79mm.

I guess we will find out soon enough. Ill post up with the results.
Although I've never been happy with how the Manley cranks balance....
image-1251916319.jpg

The last couple I've mic'ed were toleranced fairly well at max variation of .0001" and the journals were round.

The Manley option saves us from having to deal with the ******** at Pankl.

Centrifugal force isn't your oiling system's friend at bigger RPM, so straight shot oiling is going to help.
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