Chevy Rod Bearings for Porsche

[daloff]

In speaking with a number of very competent racers and engine rebuilders, many of them have gone to turning the crank down to use Chevy rods bearings. (and of course the associated proper rods) The reason for this is the current dearth of Porsche rod bearing failures (even the 962 engine guys have them) lately the rod bearings seem even more fragile and less tolerant of any fuel deviations or other sort of abuses. Just wondered what the general rebuilding community opinion on this is. This mostly concerns engines that are used for more than just casual street driving.

Cheers,
David

[Lukesportsman]

I honestly don't see why not, if the crank is out anyways. Surely there will be those purist, but then again Chevy guys are running Honda bearings to offset grind the crank.

Does anyone offset grind Porsche cranks for more displacement? We always see P&C's but rarely do I see a mention of stroke. Sure the oversquare character is one of our cars, but you don't see too many 2.0 out pulling the 3.6 down a straight. I'm not suggesting a 80mm stroke on a 87mm bore, but there might be something to gain from a offset grind when turning down to Chevy rods.

Any additional thoughts on this?

[Henry Schmidt]

Any quality bearing should work on the mains and rods.
The key will be the quality of the crank work.

As for longer stroke Porsche engines.
The 911 engines with longer stroke already have design problems. There is a principle of rod length to stroke ratio that gets ignored as the stroke get longer.
In order to keep this very important ratio you would have to make the engine extremely wide.
This would make chains too short, fan shrouds fit strange, exhaust would have to be modified and on and on.
If you want 3.6 performance get a 3.6.

Have people offset ground cranks for more displacement ?
Yes, that is how CMW built the 4.0 911 engine.

[daloff]

Henry -
Your statement that any quality bearing should work is true, however that is the crux of the matter. The Porsche bearings have become, well less quality than they used to. The Chevy bearings are stronger and won't disintegrate as easily when say detonation may occur. At least that is the premise.

Cheers,
David

[Lukesportsman]

Ok to stay more on target this time: I agree that it doesn't matter what the dimensions or original intent as long as the bearing and sufaces are ideal.

The fact that there are many application specific bearings readily available of varying quality for domestic race cars would make you ponder the issue. I don't run regular bearings on my 9 liter race engine from off the shelf. If you did what David suggested you'd open yourself up to MANY affordable bearing choices.

Air cooled Porsches have a much narrower selection of.....just about anything. Sure that hopefully eliminates the need for newspaper in the bearings (refer to other thread) but it may limit the upper end too. Time marches on and is there a better "mouse trap"?

[James Renfroe]

I'm curious, if you intended to machine a 911 crank for Chevy rod bearings, would the rods have to be custom made to match. This seems like a pretty serious and costly undertaking considering there dissimilar engine designs.

It would be cool to factor in your Chevy "economy of scale” during your next 911 rebuild!

[daloff]

Both Carillo and Pauter make the appropriate rods that are no more expensive than their standard Porsche rods. In the long run this actually a cheaper way to go than having to replace cranks and rods every time a rod bearing failure occurs where the Porsche rod bearings can't hold up.

[Lukesportsman]

If your using "billet" rods or Ti for that matter, they are usually custom anyway. I would think the ultimate solution here would be a custom ground crank, Chevy steel rod, custom small pin JE piston to fit the Chevy rod.

This would allow that economy of scale thing to help your Porsche build. Obviously this wouldn't be a cheap alternative to "stock", but might allow options when going full tilt.

There are some really hi tech pins out for domestic race cars, are these available for Porsche's?

BTW, my Ford engine costs more than my Porsche.....so quality costs no matter the nameplate

[ErVikingo]

Originally posted by daloff
Both Carillo and Pauter make the appropriate rods that are no more expensive than their standard Porsche rods. In the long run this actually a cheaper way to go than having to replace cranks and rods every time a rod bearing failure occurs where the Porsche rod bearings can't hold up.

Correct and I just had major bearing failures that destroyed my case + + +

Going with a stock crank machined to use bearings from IRL engines with Pauter rods (the best in my experience).

[jluetjen]

Originally posted by Lukesportsman

Does anyone offset grind Porsche cranks for more displacement?

Any additional thoughts on this?

Sure. Porsche offset ground their 66 mm 2.0/2.2 crank to make the 2.4/2.7 crank. They ran into a number of issues with that solution on their 8000 RPM race cars and as a result developed an interim 66 mm stroke "2.5 ST" in addition to the earlier 70.4 mm stroke "2.5 ST" engine. Once they got the problems figured out, they were on their way to the reliable 2.7 RSR engine.

As far as the bigger engines with the 74 mm stroke, I'm not sure.

[James Renfroe]

Luke,

I compared the crankshaft big rod diameters of common SBC engines to the 2.7 911 big end rod diameters. I found that the later 350s rod diameters were too large to be able to utilize them on the 2.7 911. It seems that 66 millimeter 911 cranks with their larger rod diameters could be machined down to the 350s rod bearing diameters.

It seems to me that there is still a significant stroke difference between the SBCs and the 911 engines, early and late. Do the SBC and the 911 rods have similar rod center-to-center measurements? Can a stock measurement SBC (350) rods be used in the early 911 engines w/o major re-engineering of the piston pin location? Does JE produce such a piston for this application?

Thanks!

[daloff]

Ervingo -
What are the specs for machining the crank for IRL bearings and where do you get t he bearings. Do you think this is better than using the Chevy bearings ? (which of course are relatively inexpensive and easily had)

Cheers,
David

[anh911]

I've also recently started looking into this. One of the things I've found so far is that you don't have to compare stock Pporsche to stock Chevy as there are so many available combinations and variations of lengths etc for the SBC that stock dimensions are almost not relevant. (Sorry I don't have numbers on this computer)

[Henry Schmidt]

Originally posted by daloff
.......... The Porsche bearings have become, well less quality than they used to...........
David

We have been building Porsche engines in quantities greater than most and to this day have not noticed the lack of quality you speak of.
It is true that more Porsches engines have rod bearing failure than that of earlier designs but I would attribute that to poor engine design not poor quality bearings.
We only use Glyco bearing (OEM) and Glyco is now owned by Federal Mogul a well know manufacturer of top quality bearings.
Even in the world of Chevy builders

[daloff]

Well Henry -
Quite a number of engine builders that we know including the guys that run 962s have noticed the lesser quality bearings coming through. In any case, the frequency of rod bearing failures is on the increase and while you could argue that this could be a combination of other factors, here is one undeniable fact, when you have any sort of detonation, the Porsche rod bearings basically disintegrate. This is not the case with Chevy bearings. They at least can take some abuse without destroying the crank etc. Thus the reason for the switch.

Cheers,
David

[TimT]

Are the rod bearing failures caused by lesser quality bearings or are they caused by oiling issues?..

which rod bearings are failing? 2 or 5

just curious

we have modded our shop racecar with chebby bearings..shifting at over 8600 along with the cross drilled crank and modified main bearing..

BTW its not just an off the shelf chevy rod bearing you want, its a special Nascar bearing..

[daloff]

TimT -
Plenty of oil, cross drilling has improved oil flow but bearing failure associated to detonation is the issue.
What kind of special NASCAR bearing ? (Set of mains and rods are what, and where do you buy them ?)

Thanks
David

[TimT]

The mains are fine, you only modify one bearing for rod bearing longevity

Ill have to look up the p/n for the rod bearings.. its not an off the shelf clevite bearings

CCR can tell you this

[gtu935]

Armondo at CCR in Cali will help you out here. The "NASCAR" type rod bearings can be had directly through Pauter Machine. All is for NIL if you don't modify the crank and use a specially grooved center main bearing. I would imagine that a Ti rod made for 2" rod journals running the NASCAR rod bearings would be the ultimate. A bit beyound my personal budget