2.4 PMO build suggestions

[ddubois]

I own a 71T and plan to remove the original matching 2.2 and store it so it stays with the car. I recently purchased a complete 73.5T 2.4 CIS engine and will rebuild with 40mm PMOs then install it in my 71T. I'm looking for suggestions on pistons/cams that would work well with the PMOs. I'm not looking for a hot rod engine, just a reliable around town 2.4 driver to drop in my stock 71T.

The options I'm looking for suggestions are:
1.) Rebuild using the stock 2.4 CIS pistons/cams/heads. I know I will need to plug the injector ports in the heads.
2.) Rebuild using a piston/cam combo that will better match the 40mm PMOs. I'm not adverse to purchasing new 84mm P&C sets but would like to use the stock 2.4 CIS heads.
3.) Any other suggestions?

I have an older 2010 edition of Wayne's rebuild book but the closest I could find were ideas for bumping a 2.2 to 2.4 with higher performance goals.
I tried searching the forum but couldn't find applicable ideas.

[Henry Schmidt]

Originally Posted by ddubois

I own a 71T and plan to remove the original matching 2.2 and store it so it stays with the car. I recently purchased a complete 73.5T 2.4 CIS engine and will rebuild with 40mm PMOs then install it in my 71T. I'm looking for suggestions on pistons/cams that would work well with the PMOs. I'm not looking for a hot rod engine, just a reliable around town 2.4 driver to drop in my stock 71T.

The options I'm looking for suggestions are:
1.) Rebuild using the stock 2.4 CIS pistons/cams/heads. I know I will need to plug the injector ports in the heads.
2.) Rebuild using a piston/cam combo that will better match the 40mm PMOs. I'm not adverse to purchasing new 84mm P&C sets but would like to use the stock 2.4 CIS heads.
3.) Any other suggestions?

I have an older 2010 edition of Wayne's rebuild book but the closest I could find were ideas for bumping a 2.2 to 2.4 with higher performance goals.
I tried searching the forum but couldn't find applicable ideas.

New pistons and cylinders for valve pockets and 9.0:1 or 9.5:1 compression and Mod Solex cams or Mod :S: for a little more performance. If you choose the Mod "S" cams I would open the intake port to 36mm.
I have some pretty good results building a 2450 (70.4 X 86mm) engines with Mod "S" cams, 9.5:1 comp and 36mm ports. 180 RWHP @ 6400 and very fun /easy to drive.

[ddubois]

I often hear about 'Mod' cams and pistons. I'm not familiar with 'Mod'. What, or who, is that?

[Henry Schmidt]

Originally Posted by ddubois

I often hear about 'Mod' cams and pistons. I'm not familiar with 'Mod'. What, or who, is that?

Back in the day before billet cams were available, cam grinders were looking for ways to modify 911 cams to add performance without the need to hard weld the lobes.
Harry Weber played with the CIS cams in the early 70s and came up with the 2021 cam that offered a profile that enhanced performance and still cleared the squish chamber pistons. Still one of the best options for stock CIS or Motronic engines
Dima Elgin came up with the same type of solution for MFI and carburetor cams. The Mod "S" cam is a reground "S" cam that adds lift and reduces duration without the need to weld the lobes.
The Mod Solex is similar . With the Mod Solex you can use the Solex cam or an "E" cam. Many companies can do these grinds but I have had the best luck with Dougherty Racing Cams https://www.drcamshafts.com/911profiles.htm
or Web Cam
https://www.webcamshafts.com/

The clearance issue was a challenge so valve pockets in CIS pistons was an ingenious attempt to create the needed clearance, all be it relatively half-assed.

[ddubois]

Thank you Henry for all the information!