2.4 MFI heads on 2.7 w/ Webers

[911s]

I want to take a set of 2.4E heads, open up the ports to 36mm, and use them on a 2.7 engine with Webers, RS pistons, E-cams and headers. What am I going to need to do to the heads (aside from porting) to make this work? Do I need to cut the heads for the larger cylinders? How about the combustion chambers? Will I need to enlarge them to clear the larger piston (I'm, guessing not, as the RS pistons are basically flat, and the deck clearance should prevent contact between piston and head). Also, can I expect an increase in compression from doing this? Is there a difference in combustion chamber cc's between the 2.4 head and the 2.7?

Thanks in advance!

[Steve@Rennsport]

Hi:

Everything you propose here is very doable and worthwhile.

Open up the intake ports to 36mm and make sure they match the bottoms of your intake manifolds. You do not need to cut the combustion chambers, only the case spigots for the 90mm cylinders.

You should certainly check deck height and set to .040.

The final compression ratio really depends upon your heads. Whether they were resurfaced or not and what year heads are, as they vary a bit in volume; early 2.4 ones being a tad smaller.

[911s]

Ok, thanks Steve. Just to be sure, in order to set my deck heights, I'll need to use shims under the barrels to get the heights to where they need to be, right? This is the way I used to do them with VW engines, and the only practical way I can see it being done. If this is so, can you steer me in the right direction to obtain these shims for 90mm barrels (obviously, I'll have to check the heights so I can determine what thickness I'll need, if any).
Thanks,

P.S.: Can the process of opening up the cylinder spigots in the heads be done by most machine shops, or should I be taking it to one that specializes in doing Porsche engine parts?

[Steve@Rennsport]

Yessir,.....one sets deck height in the same fashion. 90mm shims in 2 to 3 thicknesses are available from various sources.

We machine cases (and other mods) here and I would not entrust these operations to a shop that does not do these. There is a lot at stake,....

Use a specialist.

[Wayne 962]

Originally posted by Steve@Rennsport
We machine cases (and other mods) here and I would not entrust these operations to a shop that does not do. There is a lot at stake,....

Use a specialist.

Sage advice.

-Wayne

[911s]

Good info, thanks!

Just to reiterate, I am wanting to put 2.4 MFI heads on a 2.7 case, therefore I will not be needing to machine the case for the 90mm barrels. My question here regards needing to machine the barrel spigots in the HEADS in order to fit 90 mm barrels. I am assuming that this is necessary, right? If so, same recommendations on using specialist for head work?

[turbo dave]

Open up the intake ports to 36mm and make sure they match the bottoms of your intake manifolds. You do not need to cut the combustion chambers, only the case spigots for the 90mm cylinders.

Sorry to hijack the thread, but how about going the other way- can you use 2.7 heads on 2.4 cylinders? In my case, I'm trying to understand what options there are for my good 2.7 top-end- can I use some of it on a 2.4T bottom end? If I understand things right, the OD of the cast iron cylinders and the Alusil 2.7 cylinders is the same, the Alusil just has thinner walls. Yes or no?

Thanks,
David

[Henry Schmidt]

The 2.4 heads should be chamfered to accept the larger pistons. It is a very slight chamfer but it is there. This allows for a little more dome clearance. I have built this engine many times and would highly recommend Solex cams over the "E" cams. The only cam built by Porsche with a clean sheet of paper ( less compromise). Very driveable and better over all performance.