2.4 conversation to 2.7

[Allen,N]

Some great information on here!
Very helpful!

Will keeping the T cams and just opening the ports to 36 and opening up the spigots for 2.7 offer an increase?
I am not sure I can afford to do everything at once. But could probably add E cams in a few years.

Can I run E or S cams with CIS? I think I remember reading somewhere this would have some problems.

[edmayo]

E or for sure S cams will have valve interference with CIS pistons. I have never tried 2.7 with 2.4 CIS but I think the stock injection could handle the bore increase. Any one done that?

[blucille]

Some great information on here!
Very helpful!

Will keeping the T cams and just opening the ports to 36 and opening up the spigots for 2.7 offer an increase?
I am not sure I can afford to do everything at once. But could probably add E cams in a few years.

Can I run E or S cams with CIS? I think I remember reading somewhere this would have some problems.

I’ve got a set of E cams that are ready to go.. https://www.early911sregistry.org/fo...highlight=cams

[geneulm]

Don’t use the cis pistons. Use the 2.7rs. They have a better shape dome and will allow you to switch cams/intake if you end up doing so at a later date. My first engine build had these + cis system, cis cams. 36mm ports. Good motor but you always want more. :-)

While the overlap of E and S cams won’t work with the cis system, there are more performance oriented cams that will work with cis system. Webcam, Elgin and Dougherty racing all make them. Even 964 cams are better than what you have — yours should be able to be reground. Talk to John Dougherty, Dougherty racing cams.

[HarryD]

Personally, if you are going to these heroics, I would consider preserving the 2.4 CIS motor and put it on a pallet for some later time when you (or the new owner) wants to go back to stock. Find a nice 3.0 or 3.2 Liter motor and drop it in.

[Tom F.]

Personally, if you are going to these heroics, I would consider preserving the 2.4 CIS motor and put it on a pallet for some later time when you (or the new owner) wants to go back to stock. Find a nice 3.0 or 3.2 Liter motor and drop it in.

Yes, I agree. It's such an easy swap for the 3.0 liter, you can even plug in the CIS without much trouble. But you should add a front oil cooler, IMHO.

[HarryD]

Yes, I agree. It's such an easy swap for the 3.0 liter, you can even plug in the CIS without much trouble. But you should add a front oil cooler, IMHO.

Front cooler most definitely should be added, just like the factory did.

My stock 2.4 CIS motor would get too hot (230+) when I did a 20 minute HPDE in the summer. Added factory brass lines and trombone. Seems to be adequate. If not, next will be a Carrera cooler.

[Allen,N]

Thank you for all the knowledge!

I am leaning at staying at 2.4 and the original CIS.

I am now considering 2.4 high compression pistons and E or 964 cam. Will this work with the current CIS?
I have heard it gives ~20HP. Anyone have expert with this?

One mechanic said the CIS will not work with E cams. He couldn’t explain why. Thoughts?

[HarryD]

CIS will not work with with Cams that have a lot of overlap such as those used in E or S cams. Also, the dome shape in a CIS piston is unique when compared to other pistons to get the proper swirl of the fuel air mixture.

If you machinist does not know/understand the why behind these issues, IMHO, I would find one that does.

This Website may help you understand more about CIS. https://jimsbasementworkshop.com/

[cscrogham]

A stock piston from a 2.2L 911S with give you a nice compression bump and cleaner combustion chamber, just need to check the skirt to rod clearance that can get tight. You can't use the stock CIS pistons for any update.
Update the heads (and intake valves) to 36mm S
Let Glenn Yee update your stock oil pump
S or Elgin Mod S cams a good choice, others have had great success with E just not my formula
Throw the CIS into the dumpster and light it on fire, get a good set of PMO's or Webers or even better MFI