1971 911T 2.2L -> 2.4L Rebuild: 2024 Specs

[spastrone]

Hello All,
Old topic, new question...maybe...

I am embarking on a 2.2L to 2.4L rebuild (old topic) and am planning to basically follow Wayne Dempsey's advise on page 112 of "How To Rebuild And Modify Porsche 911 Engines" where he specs the following:
- Case: 2.2
- Crank: 2.4/2.7 (70.4mm)
- Pistons: E
- Cylinders: 2.2 (84mm)
- Cam: E
- Fuel: Carbs or MFI (Still deciding between using my Zeniths or going with "Webers"
- Heads: 2.2

I don't want to go beyond this because I don't want to push the magnesium cases, or double plug due to > 10:1 compression, or loose the low end torque, compared to something like an "S" build. The goal is an excellent build that will have good to great performance and longevity for a daily driver / canyon cruiser.

Now, to the "new question"...
In 2024, 20+ years since the publishing of Wayne's book, what additional knowledge, in this forum and beyond, has coalesced about the quintessential (ultimate) 2.2->2.4 rebuild (without going insane on $$$), given both, tried and true practices, as well as new materials / technology that has come about since then?

I know there will be some debate about certain fringe aspects of this topic, which I fully appreciate and can sort through, but I am really looking for the consensus views, here. Ideally, a list of the obvious as well as the more minor, yet important, mods will come of this. Perhaps it already exists!

Thanks very much in advance. I know this is a very worn out topic, but I hope this will still peak some interest from the vast knowledge base here.

Scott

[Bob Ashlock]

My personal experience: 2.2T engine modified with stock 66mm crank, 86mm AA barrels and JE pistons at 9.7 compression. Piston squirters added, E cams, Zenith carbs. Delightful! Pulls like crazy from 3500 to 6000. Seat of the pants 160 - 170HP . Idle jets at 52, mains at 130. Gives 24 mpg on road trips. Still running 27mm venturis, makes it very driveable at lower rpms, gives up a little at the top end. Will experiment with 30's at some point.

[SWS911]

Be sure to get all the critical studs inserted and use the stock steel head studs. I am doing a similar conversion on my 2.2T. You already have squirters in your 71 case so money saved there. 2.2T heads have the smaller ports combined with the T cams are great for low end torque which is why I'm keeping them. Of course the 2.4/2.7 crank and rods, but I'm using 2.4S pistons to keep the comp ratio the same as the 2.2T at 8.5/1. Another mod I'm doing is the oil by-pass mod along with an SC 4 rib oil pump and of course an external oil cooler. I've ditched the Marelli distributor for a Bosch 008 with Pertronix and have a set of Webers. Oh, what's nice about the 2.2T heads is that they don't have the injection port drilled in 'em that would have to be filled if running carbs. Good luck with your build!

[spastrone]

Thanks Bob. So, if I have this right, your build differs from Wayne's in that the crank is stock and the pistons are larger (86mm vs 84mm), correct?

Also, is your case pre '71, which is the first year that the piston squirters were stock, I believe?

I love that you are using the Zeniths, as I really want to try to make mine work, too.
Do you know anything about a recommendation for a plastic spacer below the carbs? I have seen that mentioned a few times.

[spastrone]

Thanks SWS911.

Regarding the '71 squirter thing, I wonder if they started that mid-year or something, because my case doesn't have them. It's the numbers matching case, too, so strange.

Is what you say about the compatibility of the 2.2T heads and cams, not true with the 2.2T heads and E cams?

Also, why did you want to keep the compression lower... perhaps to reduce heat and stress, etc.?

I've noted your other recommendations...thanks!

[SWS911]

Are you gonna use 2.4E pistons or 2.2E pistons? 2.4E pistons on a 2.4/2.7 crank will only be an 8.0/1 compression ratio where as 2.2E pistons on a 2.4/2.7 crank will have an appx 9.5/1. E cams will work, but the T cams will give you a broader torque curve. I wanna run pump gas and keepin' the compression ratio at 8.5 is a good solution for me. My 71 case has the squirters, I thought all 71MY cases had 'em. My bad. Also I think the Zeniths will work better with the smaller ports of the T heads. If you decide to open up the intake ports and E cams, I would go with the Webers since there are a lot more jets and venturis to choose from to accommodate the need for a richer mixture at higher RPM with the bigger ports.

[doswald]

Scott, I stayed with the stock crank, as Bob did, bored the stock cylinders to 85 mm, 9.5:1 JE pistons, Solex cam, modified Zeniths. There is a thread in the engine building forum where I posted the dyno results. I am very pleased. The piston squiters were mid-year in ‘71. My October ‘70 did not have them.

dho

[spastrone]

SWS911,
My understanding from Wayne's recipe in my original post is that since the pistons are E, and the cylinders are 2.2 (84mm), to answer your question, I think that would be 2.2E pistons. Sound correct?

I plan to keep the 2.2T heads unmodified.

[spastrone]

Doswald, Okay, interesting twist. I don't suppose you know the displacement you ended up with, do you? I will check out your other post and thanks for the squirter clarification.

[doswald]

Scott, I bored the original cylinders 1 mm, to 85, which was the maximum recommended. With the stock 66 mm crank, this yields a displacement of 2247, round up to 2.3 ��.

doswald

[SWS911]

2.2 and 2.4 had the same cylinder bore, 84mm. The longer stroke crank and rods made the 2.4

[spastrone]

So, the 2.2 T and E pistons are identical, then... or are the E pistons more domed, further adding to the increased compression along with the longer stroke of the E crank?

[SWS911]

2.2E pistons are different from 2.4E pistons. Also the wrist pin heights are different.
2.2 cranks are different from 2.4 cranks. 2.2 rods are different from 2.4 rods.
Rods and cranks are not interchangeable, but pistons are.

[targa72e]

I built and dyno compared several of these early engines, results in thread below.

https://forums.pelicanparts.com/porsche-911-technical-forum/1151593-dyno-summary-testing-early-2-4l-2-5l.html

Take away, bigger ports and better cams help a lot.

john

[spastrone]

Thanks All.
I'm starting to really like the idea of going with a set of new 86mm P&C's (https://aapistons.com/collections/piston-liner-kits-sets/products/porsche-911-86mm-je-piston-cylinder-kit-2-2-2-4) with 70.4mm crank/rods.

targa72e,
Regarding the below excerpt from your other thread, how do you think using the stock 2.2T heads would effect things AND can you please also comment on using the T cams OR using E cams?

The last engine I built is still in the car. It is a long stroke 2.5L 70.4MM stroke with 86MM bore for 2.452L. This engine uses 86MM nikasil cylinders and JE pistons. After CCing the compression ratio is 9.8 to 1. Heads were like previous 2.4L, they started as 73 CIS heads and were bored and ported to match 2.7S heads with 36MM intakes and 35mm exhaust ports. Cams are Elgin MOD S and induction is Zenith carbs on PMO manifolds.

Sorry if my questions seem pedestrian and naive, but that's what I am when it comes to this stuff. I'm learning, though...and very stoked about it!

[Rosco_NZ]

70.4 x 86.7 = Long stroke 2.5. Makes a great road engine but your T heads will restrict HP.

[spastrone]

Thanks Rosco_NZ.
I think I have heard, here or on other threads, that porting the heads will make it harder to use my Zeniths. Any thoughts on that?

[Rosco_NZ]

I’m not familiar with Zenith tuning but I’d be careful about building an engine for which appropriate carburettor tuning parts are available. Bigger displacement will want more air. Variety of chokes, emulsion tubes and jets is really the reason why Webers are so good.

[targa72e]

Regarding the below excerpt from your other thread, how do you think using the stock 2.2T heads would effect things AND can you please also comment on using the T cams OR using E cams?

The first two engines I built with E cams were pretty similar except for the induction and port size. The first had small ports and MFI and the second had big ports and Zeniths. Second engine made more power and torque everywhere with larger ports.

My take away from the various builds is, go with bigger ports, use modern cams.
I would not use factory T or E cams when much better cams are available.

I am using Zeniths on my current 2.5 with PMO manifolds. The stock manifolds do not have enough material to bore much larger to match the intake ports if enlarged. I would enlarge the ports on your existing heads and get appropriate PMO manifolds to match.
You can get different chokes and jets to have your Zeniths match your engines needs from multiple suppliers (see Alpha1750 on Ebay). Air correction jets at high RPM seem to be the biggest limitation with Zeniths.

With the cost to build these engines I would not skimp in two areas that for me made such a big difference in power.

john

[spastrone]

Thanks, John. Just to be clear, those two areas are: porting the heads (with new manifolds), and using "modern" cams, correct?

I'm trying to find a local head porter with a flow bench for proper tuning, which I'm told is important when porting, since you supposedly want all the heads flowing the same amount and also if you do it wrong you can end up flowing less in any particular head. In case I can't find a local shop, please let me know if you or anyone else knows of a porting shop to which I can send my heads.

Also, do you have a recommendation for where to get the modern cams and which one to get for a 2.5L build?