Half-Mooning lower cyl sleeves

[asphaltgambler]

Saw in Waynes book about 'half-mooning" the lower cylinder skirts to aid in piston down/out air flow. Can anyone tell me if this is really beneficial on a performance street engine? If so, what are the dimensions of the cut away and locating points??

[ChrisBennet]

The effectiveness of airflow mods like this are open to debate. Like someone pointed out, you don't see these mods on any Porsche race motors. I think it was Henry Schmidt who wrote about this. (Do a search.)
On a 3.2L motor the cylinder only protrudes past the inside of the case 1/10".
-Chris

[Eagledriver]

Probably about the same as a .010 decrease in the "squish" area.

-Andy

[350HP930]

Short skirt pistons need all the cylinder they can get. I would not think there would be enough benefit to justify compromising the cylinder.

[Carrera3.5L]

Here's what Ollie's Porsche Machining did to mine on my 3.2 to 3.5 Motronic conversion. They said it was a good idea to do if the case is being boattailed as well. Call up George or Ike at Ollie's, they both have been doing this a long, long time.



It cost me $80 for this service.

Ralph

[Wayne 962]

Not worth it for a street motor...

-Wayne

[Nitrometano]

look cool!!

[Henry Schmidt]

Originally posted by Wayne at Pelican Parts
Not worth it for a street motor...

-Wayne

I agree with Wayne, only I would take it one step further. The cylinders on a 3.2/ 3.5 conversion 100mm are so thin that I think removing material is a mistake. 100 cylinders split more often than they should. Keep the material for strength if nothing else.
BTW: ask George for a dyno sheet that shows any benefit from this modification. My guess, they won't have one.

[Carrera3.5L]

I guess my home-brewed motor is doomed!

Ralph