2.1 Long Stroke
 

My 69T car is relatively original but has been modified to S spec aesthetically and mechanically in every way by a PO, its a 69S except for chassis number. It has a 1969S MFI engine built on its original 1969T case and crank (i.e. pistons/heads/cams/MFI etc). I also have a 2.7 7R case lying around. My intention longterm was to shelve my original case and build a 2.5SS engine by selling on the 69S heads and pistons etc and buying the necessary heads and 90mm pistons with the 7R case. However part of me wonders if I am better with sticking with what I have as they are period correct 1yr only parts that would be hard to get back even if technically they arent original to the car.

Another option I have read about is to fit a long stroke crank into my 2.0 to build a 2.1LS engine. Giving me some extra capacity (hp) but also more torque. The CR would be upped to 10.4:1 so this would need twin plugging. It would still be able to rev up to 7500 like it does now however I can find very little information about this engine format. Are there pros/cons? Would I really notice much of a performance gain over my std single plug 2.0S? Does anyone have any experience of this vs a 2.5SS? The pros for me are that it would be an easier build as I wouldnt have to buy P&Cs, buy 2.4S heads and get them rebuilt etc etc and obviously it would be cheaper. It would also give any future owner the ability to revert back to the 69S format if they wanted, (even though it wasnt a 69S originally).

what kind of hp/tq can this set up make?
what cams would you run this on the street? my current S cams or would it be best to change them?
would you need piston squirters? (im guessing yes)
im assuming I would be able to adjust the MFI pump to fuel a 2.1 without having it recalibrated completely?

Just my opinion keep your S as standard…..I have a 71 T 2.2 which is 130hp compared to the S at 195hp .
I am using my original case for a 2.5LS with 40mm webers and all the machine work which will at least match S performance . Its very expensive

The value of an S is as original as possible .
At most shelve the orignal and build whatever you want .

Good point about the value of a 69S engine. Especially if it's a real S engine. The 69S is the holy grail of 2.0L S engines, and one year only. The heads in particular. You mention keeping the parts to revert if needed, that's a good idea.

Others may have to comment on making a long stroke 2.1. Not sure that's a popular combination. The 70.4 stroke is known to be hard on crankcases. A 2.0L mag case is the weakest of all 911 cases and may not like the stress. One random thing - I think I've heard you have to trim the bottom of the pistons from a 2.2L when switching to a longer stroke crank to avoid the pistons hitting the case at the bottom of the stroke. Perhaps the same for 2.0 pistons?

2.5L is an interesting option. Couple considerations:
The factory pistons are low compression to begin with (8.5:1 I think) and would be even lower with a shorter stroke. You could get some JE or CP pistons to get compression where you want it.
Re: squirters, do whatever the factory did for whatever engine size you choose. If you use 2.7L P&Cs for a 2.5, I believe clearances usually assume cooling from squirters so you'd want them.
Early S cams are pretty aggressive for street use and would be fine for 2.5L. No recommendations to give, but if you're looking to optimize, there are more modern options out there from grinders like Web, Dougherty, and Elgin.