K100 8V Piston cut outs required for boosted engine?
Turbo Mini Forums

Hi, I have tried to find this info everywhere with no success.

I am building a K100 8V turbo and I am trying to avoid making cut outs on the pistons but I haven't seen anywhere evidence that this can be done and what gasket and CR would be required for that. Assuming 2mm lift on valves at TDC overlap and what seems to be a 1.5mm gap from intake valve tip to cylinder head surface, that should give me some 0.6mm gap if using a 1mm gasket (with the 20 deg angle of valves).

I am trying to have the highest CR possible as I am wanting to run a low boost turbo, around 7psi, so I am trying to find the smallest gasket thickness I can get away with.

It would be great if there are people out there who have successfully done this.

Cheers,

Will

The cut outs give marginal gains to total CC's, you want a little clearance for safety.
any reason why you are trying to avoid the cut outs?

Shane

It's not just clearance at TDC that you need to look at. There's very little piston movement at TDC but quite a lot of cam movement, so clearance could be fine at TDC but you may have issues at say 20 Deg BTDC. The only way to know for sure is a dry build without a head gasket and some plasticine on the top of the pistons. Cut outs are generally a good thing as you end up with a non-interference engine, so no catastrophic events if the cam belt fails.

Yes, my intent was to modify the block myself and avoid removing the piston/conrods in the process. I don't see the point of skimming the block after adding the plugs if these are below gasket level. I agree that it makes things neat but I am trying to make this as DIY as possible, and skip as many "good to have" steps as safe to. Trying to find out where I am crossing the line...

Very good point! Thank you for that. I will try this method out to find out how close I'm getting to interference. I'll try plot these relative positions on an excel too and see how bad it looks, using the cam profile shared by Paul S in this forum.

For the time it takes to remove an engine, strip it to modify and clean it post works it really isn't worth risking IMHO.
It will take far longer to clear up the aftermath of disaster (plus the expense) for the sake of just to doing it right ONCE!
This is from experience after dealing with a failure caused by poor workmanship from a reputable local engine builder.

Shane

Edited by shane on 19th Sep, 2023.