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Ollies930's Avatar
 
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Crankshaft cross drilling

Does anybody know if cross drilling the crankshaft improves oiling at higher rpm
(8000+)? My car will be subjected to very high boost pressure and high rpm and I am trying to make the bottom end as bullet proof as I possibly can. This is a 74.4mm crank (+ 98mm pistons).

Oliver

Old 08-20-2009, 11:49 PM
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yes, yes, a thousand times yes. the better question
is how are you planning to get 8K+ rpm from a 74.4mm crank? there are ways, none cheap and none stock 3.2...
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Old 08-21-2009, 12:21 AM
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Definitely not stock. 54 mm Titanium intake valves, 44 mm Inconel exhaust valves, Haltech efi, twin plug, 1 3/4" headers, twin GT35R turbos, etc.
Just want to make sure the bottom end holds up, as I have destroyed two crankshafts previously(with a different set up).

Oliver
Old 08-22-2009, 02:41 PM
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Oliver make sure you contact Mike at JB Racing. He re-machines and modifies the center main bearing to help from oil starvation at the crank. This is a crucial area and the bearings must be modified to eliminate the cranks starving for oil. 8K isn't a problem for the 74.4mm crank it is the oiling that will if it isn't addressed.
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Old 08-22-2009, 04:03 PM
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you should consider a supertec supercrank
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Old 08-22-2009, 05:07 PM
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Quote:
you should consider a supertec supercrank
Not sure how much a Supertec Supercrank costs.... though I imagine needing a really big pile of Benjamins to buy one...

Having a crank cross drilled and race prepped would take a much smaller pile of Benjamins..

We send the cranks out for drilling



We modify the bearing in house



This is a 3.8 shifts at 8k in this video, has been run up to 9k a bunch of times in the red mist

http://www.rudtnersracing.com/Videos/LRP.wmv
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Old 08-23-2009, 04:31 PM
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I think these are 8.5K shifts....

http://www.rudtnersracing.com/Videos/WatkinsGlen05.wmv
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who are those guys? <<< ( Butch Cassidy and the Sundance Kid)
Rent a GT3RS from us!! Call or e-mail.
Transportation and Track support
Rudtners Racing

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BBS wheels
Fikse wheels
Redline motors oils
Swepco
1500 hp chassis dyno
Old 08-23-2009, 04:38 PM
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Khenikh, even though Henry's cranks are beautiful pieces, they just are not in the budget. And as long as the stock(reworked) crank holds up, I do not need one.

TimT, that car sounds fantastic, thanks for the video and the pictures of the crank and bearings.

Oliver
Old 08-23-2009, 11:58 PM
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At $2500, they aren't cheap, but they are a great alternative to a GT3 crank at that price. FWIW, Marine crank will build you a crank of any spec at that price, too.
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Old 08-24-2009, 03:42 AM
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Did the factory cross drill the 935 crankshafts? At what RPM is this modification considered beneficial? Interesting this was not done at the factory as cost would be minimal during manufacturing.
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Old 08-24-2009, 11:08 AM
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2 GT35s! whoa, is this the same Ollies from Rennlist with the seriously modded 930, 6 speed etc?

That video is incredible Tim, any more info on that car anywhere?
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Old 08-24-2009, 11:24 AM
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Quote:
Originally Posted by lite75 View Post
Did the factory cross drill the 935 crankshafts? At what RPM is this modification considered beneficial? Interesting this was not done at the factory as cost would be minimal during manufacturing.
Not from the factory, but...there is a funny story about this, told to me by Steve Weiner. I'll try not to butcher it in the retelling:

Back in the days that Porsche was actively campaigning 935s, the 935s kept breaking during test laps at Portland Raceway...they were toasting the middle main bearing during the test runs.

Dick Evelrude who is and was an expert race mechanic (for a non-factory car, I believe) pulled the head factory tech aside and asked him if they had cross-drilled the crank. With a snotty reply, the head mechanic said "No, it is not necessary - we will find the problem."

The next day, the 935s were running without failure. Dick asked one of the other mechanics (NOT the head mechanic) what they did to solve the failures to which the reply was:

"We cross-drilled the crank."
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Old 08-24-2009, 11:29 AM
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No one ever talks about the oil pressure relief valve that determines max oil pressure.

Should we be doing anything here to help high rpm operation.

I put a cross drilled and modified crank in a 2.4S once and still lost a rod bearing because the max oil pressure was to low.
Old 08-24-2009, 03:36 PM
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Quote:
Originally Posted by kenikh View Post
At $2500, they aren't cheap, but they are a great alternative to a GT3 crank at that price. FWIW, Marine crank will build you a crank of any spec at that price, too.
That price is a bit more than $1K short of the quote I received on the supercrank. There were also concerns around minimum orders to justify runs. I'm not saying that they don't approximate engineporn but that's a pile of coin to most.
Old 08-24-2009, 06:21 PM
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I must have remembered the price wrong. DAMN! $3500 is dough, no matter how you cut it.
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Old 08-24-2009, 06:25 PM
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Spence88mph, no that is not me.

GJF, I am sure that JB racing does great work, but I like to be able to deal with shops face to face and Florida is way too far away to hand deliver parts.

I did however talk to Ollies Machine today and had an interesting talk about worthwhile crankshaft prep. They recommended machining the rod bearing journals an additional .001" to help oil escape and cool the bearing surfaces (.0020 to .0025 clearance). According to Ollies, considering I am using Carrillos, it is more important than it is with factory rods (more flex in factory rods gives more clearance at rpm).

Next problem is trying to find a set of oversized cylinder studs that will work.

Oliver
Old 08-24-2009, 07:20 PM
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Quote:
Originally Posted by Ollies930 View Post
According to Ollies, considering I am using Carrillos, it is more important than it is with factory rods (more flex in factory rods gives more clearance at rpm).

Next problem is trying to find a set of oversized cylinder studs that will work.

Oliver
I've never heard of the stock rods flexing giving more clearance. Hmmm....

Next time (if ever) I have the motor apart, I'll have JB machine my crank journals to 2" so I can use any number of GM main bearings at a fraction of the P cost.

What is an oversized cylinder stud?
Old 08-25-2009, 06:11 PM
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Quote:
Originally Posted by TimT View Post
Not sure how much a Supertec Supercrank costs.... though I imagine needing a really big pile of Benjamins to buy one...

Having a crank cross drilled and race prepped would take a much smaller pile of Benjamins..

We send the cranks out for drilling. We modify the bearing in house
Tim, what kinda Benjamins are we talking for this mod including the bearing?


DonE, does the JB Racing mod include wotrk to the bearing as well? Cost?

Thanks
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Old 08-26-2009, 06:25 AM
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FWIW, Marine Crankshaft in San Diego modded my 66mm crank for GT3 rods. For $650 I got:

Cross drilled and grooved main bearing
57mm crank journals ground to 52mm (SC/GT3) @ 66m stroke
Plugs removed and crank flushed
Micropolish
New crank plugs
Nitride rehardening

Damned nice work - btw, these are the guys that make Henry's cranks and can build a custom crank for any car using the latest alloys and technology.
They rock.
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Old 08-26-2009, 06:34 AM
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DonE, what I meant with an "oversized cylinder stud" is a bigger diameter than stock. Even the Supertec or SRP studs are essentially only a stronger version of the stock studs(similar dimensions). I am looking for a stud that has a much larger base thread(thereby eliminating the need for case inserts), and a bigger diameter throughout to better cope with the much higher cylinder pressures I am planning to subject my engine to. From what I am told, all commercially available studs will fail at the 25-30lbs boost range.

Oliver

Old 08-26-2009, 11:32 AM
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