2.8 mahle pistons with 2.0 case

Dan Morton · Dan Morton's Garage

I picked up a '68 911 a few months back and am in the process of rebuilding the engine. Somewhere along the line it was rebuilt with 2.8 mahle Pistons and 2.7 cylinders bored to match.

I've sent the case (2.0 original mag case), crank, P's&C's to Ollies for machine work and the cams to Elgin for a regrind (E spec).

I'm sticking with the 2.0 heads as well.

My question is where can I find head gaskets to fit? I found that Stoddard has piston rings (not on Pelican).

Also, anyone else with this engine config?

Thanks

Flat6pac · 05-09-2009, 05:23 PM

get rid of the 2.0 heads and get a set of 2.7 S then you ll have something that will breathe.
2.7 CE gaskets for the top of the cylinder should probably work, 2.7 to 2.8 should be close to the same as theyre made on 2.7 cylinders..It shouldnt be that complicated.
Youre on a short stroke crank, look to get a 2.4/2.7 crank and rods so you can make the power you have the ability to make
Bruce

Dan Morton · Dan Morton's Garage

Thanks Bruce!

356RS · 356RS's Garage

Wow, I don't know how much power that 2.0 Mag case can take. Why not just keep the 2.0 crank & rods and stay with the short stroke fun?

Steve@Rennsport · 05-10-2009, 12:42 PM

Dan,

A few thoughts about this project,...

1) Bruce's suggestion about using 2.7 heads is right on target. 2.0 heads (all) are THE worst design, especially with larger bores and high compression.

2) I'd strongly recommend that you have Ollie's shuffle-pin that 1R/2R case.

3) If you have Mahle 92mm RSR pistons, you will have a compression ratio thats challenging for pump gas, even with your 66mm crank. I would be careful about camshaft selection if you are using single-ignition with pump gas unless you get the CR down a bit.

Dan Morton · Dan Morton's Garage

So I've heard various opinions with this engine setup. My usage is for street, not track. I would prefer lower end power. When talking with George at Ollie's, he suggested not going with bigger heads unless it was going to spend more time on the track.

I will definitely check that the case be shuffle pinned too. The cams were re-ground by Elgin (Solex grind) specific to this build.

The crank is stock as well. The heads were rebuilt by Ollies too. I am a bit concerned with the compression ratio as well. Any thoughts as to keeping the CR down?

The engine ran strong when I bought the car but all the heads were loose and the webers were not dialed in very well. There will need to be a lot of tweaking to get right I'm sure.

Thanks

Steve@Rennsport · 05-10-2009, 05:33 PM

As a talking point, 92mm RSR pistons with the 66mm crank yields something around 10.5:1 using 2.2-2.4-2.7 heads. With 2.0 heads, its a bit higher.

IMHO, you will need twin-ignition to safely operate such a setup on 93 octane fuel, especially in Texas summers. I'd kindly suggest that you carefully measure your CR as you build the engine so you do not have a problem with expensive consequences.

MBEngineering · 05-10-2009, 11:44 PM

HI Dan
when you get your engine parts back check the clearance on the case through bolt washers and the bottom of the cylinders, as this conversion catches the through bolt washers right on the edge of the bottom of the cylinder, either change the washers for the later ones or mod the bottom of the cylinders, I have a engine in the shop at the moment from the USA and has the same ?? (heads loose) prob as yours!

clearance cuts in the bottom of the cylinder,

this engine is in a 914-6 and has been fitted with 2.7 cylinders and pistons on the STD 2.0Lt bottom end with heads to match.

please check before fitting together that the cylinders clear the washers.

regards mike