Mooncut cylinder ?

eintz911's · 01-13-2005, 05:41 PM

I'm wanting to boattail my case and mooncut my cylinders while my motor is apart.what are the measurements for moon cutting the cylinders.My Uncle owns a machine shop,so I do have access to the right equipment to do this?
Any info appreciated!
Thanks! Charles

Jeff Alton · 01-13-2005, 07:09 PM

Good question! I have wondered this myself.

Jeff

asphaltgambler · 01-14-2005, 06:23 AM

I've heard here that the general concensus is that it will only benefit at higher (6K+)RPM's. That most street cars would not really 'see' gains.

I'm considering it as I would do most myself so just my labor involved. My school of thought is every little bit helps. Any one want to chime in?? Maybe Henry??

ChrisBennet · ChrisBennet's Garage

I boat tailed the case on my 3.2 but I didn't touch the cylinders because they only stuck "out" a couple of millimeters. I probably wouldn't even bother with the boat tailing if I was doing it again.
-Chris

BK911 · BK911's Garage

Stick the cylinder in the case. You can trace where you need to grind off.

addictionMS · addictionMS's Garage

feed back I got from local experts was the boat tailing and mooning only came into effect after 7K+ rpm, maybe even 8K+ so fun to do, but the return is small beyond the bragging rights.

I boat tailed anyway.

Jim

Henry Schmidt · Henry Schmidt's Garage

All good advise.
For my money, both are a tremendous waste of time and will offer no benefit in all but the most extreme racing engines. We have not been able to measure a benefit on the dyno.
That said, 14 mm deep by 70 mm wide.
The pictures are of a cylinder from one of Dick Barbour's 935.

asphaltgambler · 01-14-2005, 01:02 PM

Henry, as always, not only are you informative, you are an honest guy which is a rare commodity in the car business.

Jeff Alton · 01-14-2005, 01:25 PM

Thanks, that saves me some work!!

Jeff

350HP930 · 01-14-2005, 05:03 PM

As far as arguments against it goes, the piston will stick that much farther out of the jug which will create extra piston stress and wear.

So essentially, all con, little to no pro.

Wayne 962 · Wayne 962's Garage

I agree with Henry. Unless you're trying to extract one more 1/2 HP from a high-RPM race motor, it's really not worth it. I basically said this in the Engine Book too. Also included in this is boat-tailing - not a real good return on your time/effort/money.

-Wayne

Eagledriver · 01-14-2005, 09:47 PM

Actually I don't think the piston will stick out at all there. The Mahle pistons have almost no skirt on the sides where the "moon" is.

-Andy