Anyone running Euro Mahles 9:8:1 CR in 3.0SC

[1987 Porsche]

I am doing a top end rebuild on my 1978 911 with the 3.0.
Currently have Alusil P/C and was looking to purchase new Mahles. The best price for the euro 9:8:1 I found was around $3100. I did see 9:3:1 mahles for $3500. Wanted to get some opinions on using Euro Mahles with 9:8:1 CR in a 3.0SC. I will be getting the cams regrind by John. Any issues with detonation or should I pay the extra and get the 9:3:1.

Thanks,

Lou

I did post on the engine rebuilding forum but thought I may get more looks here. Thanks

[Iciclehead]

I had a Kremer 3.2 that was custom built for me, it was 9.8 compression using CIS and stock cam. I did fit a J&S safeguard, but never had a problem with premium fuel.

Dennis

[Bphawk1]

My car in a 83 SC with 3.0 and I used the Malhe 9.8 PC's with stock cams and really like it. Can still use pump 93 or 94 octane gas. I paid around $3,500 for the Malhe. Well worth it in my opinion My rebuild was completed last fall.

[1987 Porsche]

So no detonation issues as long as you are running the 93 octane? How was the performance increase because stock compression on your car was 9:3:1? Thanks again.
Just trying to gather some info prior to making the purchase of the P/C. Dont want to make the wrong decision.

Lou

[Ryce Stallings]

I have run the 9.8 PC with CIS and stock SC cams in a 3.0 for years with no problems. I do use Premium. No idea about performance gains but would be interested if anyone knows.

[emcon5]

If you are buying new pistons and cylinders, look hard at going to 98mm bores, and sticking with ~9.5:1 compression. The cost difference between stock 95mm and 98mm is not huge, and it is cheap horsepower, which pretty much never happens in a 911.

On one plug you want the Max Moritz wedge style pistons.

[darrin]

tying this to the other thread on the engine rebuilding forum -- 9:8:1 mahle cylinders

Interested in what changes need to be made to the WUR and fuel distributor to adapt to the change in CR.

[emcon5]

Originally Posted by darrin

Interested in what changes need to be made to the WUR and fuel distributor to adapt to the change in CR.

If past experiences are any indication, absolutely nothing. If someone tells you that they do need to be changed, it is because he is trying to sell you something.

[targa72e]

The dyno below is from my car. 78 big port, CIS and SSI heat exchangers. Missed a shift and put engine back together with 9:3 to 1 instead of 8:5 everything else the same. Second is dyno with 9:8 to 1. The improvement from 8:5 to 9:3 was pretty good, 9:3 to 9:8 was much smaller.









john

[jamesjedi]

There are conflicting opinions on this. There is a great deal of information about it. Search Steve Wiener on the subject. He recommends being conservative.

It also depends on the induction system such as carbs.

E Class Race Cars W/9.8 Compression

compression how high?

[1987 Porsche]

Guys I really appreciate the replies to this thread.

Lou

[Bill Douglas]

9.8:1 was stock compression ratio for 1981 to '83 ROW engines. It shouldn't be a problem.

[Bphawk1]

I can't say specifically the real hp gains as I am in the breaking in process. The 9.8 CR was used in the Euro cars so my engine builder recommend it as he use this set up on his 78 SC. I do have a stock CIS with a rebuilt WUR and fuel distributor along with SSI's and a dansek two in and one out exhaust. The cars seems to run well. I will know more in the spring once this Cleveland, Ohio snow is gone.

[emcon5]

Originally Posted by emcon5

If past experiences are any indication, absolutely nothing. If someone tells you that they do need to be changed, it is because he is trying to sell you something.

Just to follow up on this, my 9.8:1 3.2 Short stroke CIS Lamda runs great on the stock CIS, as did rdane's 3.4 CIS basic engine. He got 217 HP to the ground with a stock early SC CIS system, with 9.8:1, 98mm bore and a 3.2 (74.4mm stroke) crank.

There are a lot of others, but these are two easy examples of higher compression, with more displacement and hotter cams (mine 964, Dane's 20/21) running fine on stock CIS.