Q on crank journals Tuesday, 18-Jul-2000 12:49:00 Message: 18.104.22.168 writes: Hi Guys, I've seen the different cranks out there and have wondered what the different rod journal options are. from what I've seen there's the stock VW, Porsche, and Chevy. Now the VW rods have a 2mm offset right, and the Porsche and aftermarket rods are straight (no offset) right? Also the Porsche rods are 2mm thinner, allowing for thicker cheeks on the crank, correct? Both the VW and Porsche are the same journal diameter. Now, for the chevy journals. Are they a smaller journal diameter? Are they thinner like the porsche? If they're a smaller diameter wouldn't that make the crank weaker, more prone to flexing? Also, are the cranks out there made to compensate for a 0 offset when using Porsche, or chevy rods? Sorry for all the questions, just some things I've been thinking about, hope it makes some sense to ya all... matt matt souza
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some help (John Connolly) (19-Jul-2000 17:20:05)
Re: Actually John ,Iv`e seen lots of Chevy 88mm Scat cranks brocken in 2 lately... ( Mark H) (20-Jul-2000 05:05:54)
Wednesday, 19-Jul-2000 17:20:05
VW journals are big (which makes for tight clearances on stroker engines). Good bearings are VERY expensive, but they last a long time since the bearings are large.
Porsche journals are narrower. Bearings are expensive (again), and since they are so narrow, bearings are used up faster. However, a narrow rod and bearing means a stronger crank (but weaker bearing area).
Chevy came on the scene (actually BUICK). Smaller bearing, but wide. This means less clearancing on the case. Also, you can get real good bearings cheap, and they last a long time since they are wide. Yes the crank is "weaker", but IMO this isn't an issue (V-8s run TWO rods on the same journal with a LOT of power with no problem, and NASCAR has moved to HONDA journals (small) and it's working. I think crank strength is not an issue unless you are like Tracy in Fla.... :-D
Anyhow, I run VW for up to 82 stroke, and then switch to Chevy for everything else. Porsche is obsolete IMO.
Re: Actually John ,Iv`e seen lots of Chevy 88mm Scat cranks brocken in 2 lately... Thursday, 20-Jul-2000 05:05:54 22.214.171.124 writes: Of coarse these were well used 16 to 1 compr. 9000 rpm motors but there is definately a limit in my opinion. I think if they were porsche journal and the cranks were not cross drilled they would not have broken. They seem to crack from the crossdrill out to the journal side or maybe the opposite. But its the weakest point on the crank ,no doubt. If the cheeks were thicker and the journal was larger it would not have cracked as easy. I like porsche journal and its too bad that the industry has abandoned it. I think that the carnks were cross drilled differently then you could get away with the smaller journal size of a chevy but I really don`t like the width at all. I think Berg used to make special bearing that were chevy diameter and porsche width? As scary as that sounded when I first heard it ,I think its better than straight Chevy. I really do think its the width of the journal or lack of cheek width that kills cranks. Of coarse all this dosn`t mean much because the average person dosn`t come close to stressing their crank enough to brake it. But it will be interesting to see how long some of these giant strokes last on the street. Mark H