Dammit
Dammit New Reader
1/24/18 4:10 p.m.

Evening chaps, I need the benefit of your experience - I'm re-building my Porsche M96 engine toward the end of this year.

As part of that re-build the existing liners will be machined out and new, larger liners fitted. As part of this process the deck is closed.

The crank will be changed for one from a later engine, this combination of increased bore and increased stroke takes the 3.4 litre engine to 3.9 litres.

Now- the 3.4 cams are shared with the 2.5 litre Boxster. At just under 4 litres the engine will be poorly served by the stockers.

In an ideal world we'd grind cam-blanks to our own specification, but it's proving impossible to find a source of blanks.

Therefore we have two options, re-grind the lumpiest, highest duration cams we can find, or use billet cams.

It's the second choice I'd like input on - billet cams are fine in a race engine, but a race engine spends minimal time at idle, where the majority of the wear occurs. Being a road car, my engine will spend a lot of time at idle - potential bringing significant reliability issues.

Can anyone weigh in on this who has done it/has experience of this situation?

Thanks all.

AngryCorvair
AngryCorvair UltimaDork
1/25/18 6:59 a.m.

I don't know the answer, but it's a great question so I'm replying to bump it to the top of the list.

Dammit
Dammit New Reader
1/28/18 9:05 a.m.

I think I may go the re-grind route, with all that that entails as I can’t find any data on the billet/road car situation. 

bentwrench
bentwrench Dork
1/28/18 10:15 a.m.

You cant run flat tappets on a cam made from a billet, billets are used with roller lifters. One of the cool things about a billet cam is you can weld it up to fix it or re-profile it.

You might be able to use a billet with flat tappets if you chose the right material and heat treat it and do some kind of thick surface hardening before the final finish is ground in. I dont think you can treat it after the finish grind without spoiling the finish grind.

 

Many modern roller cams are made from segments furnace brazed onto a hollow shaft.

 

What about finding a pro team who has raced one of these motors and see what they have laying around for sale?

wearymicrobe
wearymicrobe UberDork
1/28/18 10:43 a.m.

I am willing to bet that if you call sharkworks they will be able to get you cam blanks or at least point you in the right directions.

 

They made a number of them for the 3.6 to 4.0 conversions they did back in the day.

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