Rod journal size??? Chevy-Porsche-Capri?

Thursday, 26-Oct-00 22:23:11

209.179.229.248 writes:

Hi guys ,I`m back and I was reading one of the posts on rod journal sizes and I had to comment.

Boy ,I guess theres a few people who`ve had problems with Porsche jounal or knew someone who knew someone who had problems. Well just to

cheer for the Porsche camp a little I have to say I seen some really big PRA pro turbo motors use Porsche rod journals and have no problems what

so ever! In fact Mark Emerald has an 88x92 turbo motor with Porsche journals and he almost never replaces his bearings,even on between race

teardowns.

Dean lowery built Three Liter VW motors with nothing but Porsche journals for decades!

When Chevy journal cranks first came out , the same thing was said about them. " a two inch journal! those things will eat bearing for sure!"

Well they didn`t and neither do Porsche journal cranks. If you motor smokes a bearing its usually because it ran low on oil pressure or there is not

high enough oil pressure to begin with. Don`t be afraid to run your oil pressure high. Just make sure its not too high when cold or you`ll be chasing

your oil filter down the street! :-)

On race motors you can really run it up and its a good idea to. Personally I think the old stand by 70 lb VDO guage is wrong for a VW. Other

makes of cars including watercooled VWs all run the 150 lb guage.

As far as journal size effecting crank strength , its the long stroke (88+)Chevy journal cranks that the PRA guys are snapping right and left!

The (wider) the journal the thinner the crank cheeks and the cheeks are whats cracking. Also the smaller the journal diameter the weaker the crank is.

Chevy journal is both wider and smaller than Porsche! The porsche journal is the better choice for strength. BUT....... That being said, a Chevy

journal size is NOT bad. In fact its all thats available from many crank makers now so thats what you have to use. The fact is that the chevy cranks

that have broken are in 16to1 compr. 9000rpm full race motors that make nearly 300HP! and they still last a few YEARS before they break. If you

are building a 10 to 1, 7000 rpm motor you`ll most likely never break it.

Well thats my two cents on crank theory this month. My next street motor will have a giant stroke with Porsche or capri jounals ( I think they`re

almost the same) No more silly 84s for me. :-) Of coarse I have to find one first.

Mark h

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Replies:

YAAAAAHHH Marks back! =) (n/t) (Dave Conklin) (26-Oct-00 22:43:48)

Mark, I am just relaying what I was told by Pauter. They were one of the first guys to run the capri journal size and they got out of it real quick because of the high failure rate. I t is due

in part to the inferior bearing that are on the market. The backings are to hard and they cause pieces of the bearing to chip off and cause a nuclear meltdown. If you could get a good

bearing it would probably help out alot. You also have to realize that the rod bearings don't take as much abuse in a turbo situation. Most of the capri bearing failures occured in

normally aspirated setups. (n/t) (Chuck) (26-Oct-00 22:55:24)

Re: Chuck, I think Pauter is way out of our league. His motors run 351 ford size stuff so I can see how our little parts wouldn`t work. I don`t think turbos put LESS stress on

bearing though ??>> ( Mark H) (26-Oct-00 23:49:19)

Turbos have a lot of exhaust back pressure, and this cushions the piston, and the bearing, into a gradual change in direction at the top of the exhaust stroke. Aspirated

engines have low exhaust back pressure, and the rod is YANKED at the same point. Turbo engines are easier on rod bearings than aspirated ones (also because they

turn lower RPMs) (n/t) (John Connolly) (26-Oct-00 23:54:51)

What low RPMS Ishift mine at 8600...without bearing problems. (n/t) (Dominick Luppino) (27-Oct-00 00:41:46)

Pauter are the guys that came up with the buick rod bearing size. They saw the problem of other rod journal sizes and their limitations and fixed it. (n/t) (Chuck)

(27-Oct-00 11:05:36)

Good to hear at least some good feedback about the Porsche journals. Need more... (n/t) (27-Oct-00 01:03:52)

Re: First, Mark that was well written. I think you are correct and will stand with you on this, I do like the chevy choice of bearings... Art Thraen (n/t) ([email protected])

(27-Oct-00 02:09:53)

AHH, Art I see you're the CLF this early morn.!!!HA HA (n/t) (Chris L.) (27-Oct-00 03:03:18)

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Re: Chuck, I think Pauter is way out of our league. His motors run 351 ford size stuff so I can see how our little parts wouldn`t work. I don`t

think turbos put LESS stress on bearing though ??>>

Thursday, 26-Oct-00 23:49:19

209.179.229.248 writes:

I know super High compression ratios can really mess bearings up on crank up but most race motors have large over lap cams that bleed off some

of that pressure.

Reguardless the bearing material is important like you said. I know a guy who has researched materials for capri and 302 ford? and hes found some

Nascar bearing that should work... I hope.

I guess I`ll be the guinny pig!! Ha ha ha

Mark H