Relieving Pistons for Hotter Camshaft

[cds72911]

Hi all,

I did an archive search, but didn't find the info I'm looking for.

I've started to tear my engine apart and saw that it has been apart in the past, but it doesn't look like it was done by a professional. Some sort of orange sealant squished out of the cylinder to case mating surfaces, was used on an oil return tube, mismatched fasteners on the heat exchangers, etc. I do not know the mileage on the engine, so I want to make sure it is ship shape before I run it and chance destroying it.

Last night I talked with my wife and we decided that I should rebuild the engine over the winter (my wife is the best!). I am not trying to build a hot race motor or anything, just a street motor that will be fun for the occasional DE or so. Before you suggest 3.2 liter upgrade, let me say that do not want to change the displacement. 3.0 is fine for me.

About the engine - it is a '79 SC ROW 3.0 liter (930/03), originally CIS but I have Weber 40 IDA 3Cs that I am going to run with a set of SSI heat exchangers with a stock '72 bannana muffler. I'll probably run an MSD 6AL, although that probably isn't important for this discussion.

In the past folks have suggested a cam change to match the Webers and take advantage of the SSI exhaust. I decided not to do that prevously, due to the fact that I've been told that CIS pistons may interfere with valves if I use a hotter cam. However, now that I am going to have it all apart, I think I can remedy this.

Can a good machine shop relieve my pistons (cut eyebrows in the tops) to make room for valve clearance? Who does this in the Porsche world? Would this be something that a non-porsche machine shop could tackle? How much does this sort of work cost?

I do not really want to replace the pistons unless I need to based on damage I discover as I tear it apart. Although I do wonder if I should buy a set of aftermarket pistons instead. Would I be better off buying a set of JE pistons that are already made with the clearance? Who sells these (Wayne do you?)? What do these run?

Thanks for the help.

Charlie

[john walker's workshop]

engine builder's supply has J+E pistons. that's the best way to go. they also up the compression a bit, which translates into more power. the CIS pistons are too thin in the areas that would have to be eyebrowed, and the shape is not the best.

[jabb]

New JE Pistons and Cylinder from EBS $1745 ... Mahle
Cylinders... Wristpins and rings.... Without cylinders $900

any Compression ration you want....

[cds72911]

John - Thanks. I've e-mailed EBS for more info.

Jabb - Are the Mahle pistons from EBS also or another vendor? Have you heard whether they are available with the piston relief cuts? Aren't Mahle pistons cast rather than forged?

It seems like it is about $900 either way and the JE pistons have a better shape for combustion. In fact, I found an old post from Warren which said that the JE pistons may be less than that with racer net pricing. I'm still a licensed SCCA ProRally driver, so perhaps I can get that discount and the JE pistons would even end up being less expensive in the end...

Thanks,
Charlie

[jabb]

Those were the recent prices I got from EBS....