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Old 06-30-2009, 09:06 AM   #1
puyi
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Default Flat crankshaft

Hi all,

Is there someone who provided at any time flat crankshaft for the 928 and related camshaft?

Thank's for all

Puyi
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Old 06-30-2009, 09:13 AM   #2
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Not that I am aware, there would be a lot of potential development issues especially with vibration. No real advantage either.

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Old 06-30-2009, 09:16 AM   #3
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It would be cheaper to drop in a Ferrari V8 from the get go.

355 motors appear to be going for about $10,000.
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Old 06-30-2009, 09:29 AM   #4
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OK, totally had to look this one up. I'd never even heard of it, but this website has a very cool write-up on the difference between flat plane cranks and cross plane cranks (for those of you following at home like me).



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Old 06-30-2009, 09:35 AM   #5
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Get (i.e., make) cross-over headers instead! Way cheaper and with almost all the benefits.
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Old 06-30-2009, 09:46 AM   #6
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There was a long thread discussing the pros and cons of this idea a year or two ago. I tried searching but I cannot find it.
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Old 06-30-2009, 10:00 AM   #7
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Quote:
Originally Posted by ptuomov View Post
Get (i.e., make) cross-over headers instead! Way cheaper and with almost all the benefits.
Except that the primary lengths would be way too long.
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Old 06-30-2009, 10:15 AM   #8
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Quote:
Originally Posted by 123quattro View Post
Except that the primary lengths would be way too long.
Not really, since 928's gearbox is far in the back. The long runners can have a narrow resonance tuning rpm range, so the exact length of long runners is important. Scavenging should be excellent with the pulses matched.
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Old 06-30-2009, 11:25 AM   #9
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Didn't Tom Cloutier "The Power Broker" make a set of headers for this specific purpose several years back? I believe he was crossing the primarys across to achieve the exhaust scavenging and tone associated with the flat crank. Now that I think of it, I think he called it The Scavenger or something like that.

BTW, here is the old thread on flat-plane cranks:

http://forums.rennlist.com/rennforum...28-engine.html
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Old 06-30-2009, 11:40 AM   #10
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Well, this got me thinking, and I dont have any pics saved of the Scavanger, and Tom's website www.thepowerbroker.net is gone, but I was able find this text written by Tom about his Scavanger system and how it applies the concept of a flat-plane crank to the standard cross-plane of the 928:

http://members.rennlist.com/pirtle/zexh_science.txt

If anyone has a pic saved of the system, it would be nice if they would post it in the thread, as it was a true work of art.
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Old 06-30-2009, 12:02 PM   #11
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Tom Cloutier's exhaust headers.
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Old 06-30-2009, 12:25 PM   #12
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Mike Frye

Thanks for the link; I never really understood the difference between cross and flat-plane cranks.

Now I do!
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Old 06-30-2009, 01:25 PM   #13
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I will read the other "flat plane crank" thread. But for a race car, the pros for that is :
Cost
Reliability
weight

A+

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Old 06-30-2009, 02:38 PM   #14
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Great write up by Tom Coultier. He references many reasons why crossover pipes scavenge better but he does say this is best applied to engines with a lot of valve overlap. Then he goes on to say the S4 engine, for example, has little overlap.

There are no before/after dyno comparisions on a 928 engine so it is hard to know just what sort of performance gain can be realized by one of these systems.

Has anyone here built/put on one of these corssover systems and also have dyno charts as comparision? I am interested in this.


Quote:
Originally Posted by hans14914 View Post
Well, this got me thinking, and I dont have any pics saved of the Scavanger, and Tom's website www.thepowerbroker.net is gone, but I was able find this text written by Tom about his Scavanger system and how it applies the concept of a flat-plane crank to the standard cross-plane of the 928:

http://members.rennlist.com/pirtle/zexh_science.txt

If anyone has a pic saved of the system, it would be nice if they would post it in the thread, as it was a true work of art.
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Old 06-30-2009, 03:32 PM   #15
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If the crankshaft could be made cheaply enough (hah hah), you could have a killer cheap upgrade for the 2 valve cars. 100mm 944 2valve pistons ALMOST work in the 928s but are 2mm too short. Increase the stroke by the correct amount on the Flat Plane crank to compensate. Use 944 camshafts on the existing 928 heads with the larger 944 valves.

On the same note, custom ~2mm longer rods would accomplish the same job with stock crank.
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Old 06-30-2009, 03:32 PM
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