Here’s the details, 1.8 case 66mm crank, 96mm pistons, stock 1.8 heads 55cc’s, deck height .059”. Webcam 86. It calculates out to 8.3 to 1 CR. I was hoping for 8.5 to 1. I can get there if I take .010 off. How big a deal is the difference? I will be going to a set of DRLA 36’s for carbs with Triad exhaust. And a new 123 distributor.

Air cool.net recommend:edit

This is a nice upgrade on mild engines, it's an outstanding bus cam! HD Springs are required! This cam works best with Compression from 7.75-8.25:1. Power band is from 2000-5000.

this was direct from web cam:
Good overall performance for carbureted mechanical mild track engines. RPM range 2500-5500. The perfect street cam! Requires New lifters required.

Thanks, I did see that but thought it was for bus engines.

I would think that would be more applicable if you're running stock fuel injection. I thought the web cam 86 was a mild upgrade over stock but still compatible with FI. Since you're planning on carbs you should be fine (I would think). On the other hand, there are other, more aggressive, cams out there you could choose.

Most recommend a minimum deck height of .040", so you have plenty left on the table in order to get to your target CR.

I have the short block assembled I think I’ll finish it up and give it a try. Good point if I don’t like I can go back in. It’s my first air cooled engine build so I figured it will be a good learning curve for the next one.

James Id push that (static) CR. That deck is huge.

What’s the best option take .010 off the heads or the cylinders?

Running the numbers I would need to decrease the cc’s from 55 to 53 to get to 8.5 or take .010 off the cylinders. How easy is it to take .010 off of the cylinders?

Find a local machine shop. For a competent machinist it's very simple. Doing the cylinders is easier than trying to change combustion chamber at this point.

Just to be sure, you are not running head gaskets, right?

If you are - don't. That will tighten up your deck height - to the point where you may need to add base shims.

Zach

No, not running head gaskets.