Modding a 2.2 to a 2.5 ST Variant

[Uwon]

Long story short-a friend of mine who runs am indi shop got stuck with this ’71 911T project car when the owner bailed. I ended up acquiring it.
Still had its original 2.2 motor with Weber carbs, probably not original but who knows. Motor was recently rebuilt by a third party engine builder just before the owner bailed and according to my indi shop friend it only had about 45 minutes run time, half of it on the highway. Due to privacy issues, I cannot get the full rebuild story but I do have this hard to read partial list of parts replaced….



Rings were apparently also replaced but no significant machine work was done .
I am reasonably familiar with the later 3.2 motor but am butt ignorant about the early smaller displacement engines. And I have read Wayne’s opinions on the 2.2T.









I am not taking anything for granted so I intend to fully tear down the motor and am prepared to stay with the 2.2 engine case (matching number to chassis) and make the necessary changes to a 2.5 ST variant or something of the sort that generates about 190 DIN HP. Motor will go into an ST tribute used primarily for touring not track, so it must be reasonably well mannered and not finicky at the stoplight.
I am prepared to replace the P&C’s to LN or equivalent, change cams, port, and even twin plug if need be. I don’t know anything about these Weber carbs-seems you either love them or hate them-I’m prepared to stick with them for now but could easily be convinced to go with Electromotive that I’m already quite familiar with in my RST.
I would welcome lots of advise and information from the brain-trust. A couple of things that I would like to know from the outset (as I have not yet found suitable answers) are:
1) Can the 911T “unbalanced” crank be balanced to resemble the 2.2S “balanced” crank?
2) What was the base engine of the ’72 2.5 ST that ran and won so many races (e.g. the Targa Florio) and what modifications were generally made?
And, most important how do I get to 190 DIN hp using the 911T case and sticking to about 2.5?
TIA
Johan

[SBell]

My understanding is that there are 2 ways to get to 2.5L. One is the 66mm crank and 90mm P&C and the other is 70.4mm crank and bored out 84mm cylinders. My dad has both variations but used mahle 86.7mm P&C instead of boring stock ones with the 70.4mm crank.

[al lkosmal]

https://forums.pelicanparts.com/porsche-911-technical-forum/1053128-x-faktory-2-2e-2-5ss.html

[stownsen914]

The non-S cranks aren't unbalanced - they just don't have counterweights. You'll get different opinions on the necessity of the counterweights for a high performance engine.

[Henry Schmidt]

There are all kinds of small bore options. Just keep in mind that boring the 2.2 case to accommodate 90mm cylinders compromises cylinder stability.
The last 2 engines I built for my own 2.0/2.2 cars were 2450.
That is 70.4 x 86.
With 40mm Webers, 9.5:1 compression, Mod"S" cams and mild porting the engine produced 180 RWHP. I twin plugged them for the wow appeal but it was really needed for achieve the HP.
Easy to drive, great acceleration and relatively inexpensive.

As for the non-counter weighted crank, they were designed for 5000 rpm. If you want to spin it, the flyweights help to reduce vibration.
MOD"S" are still making power at 6,400 so if that is your cam choice, think about a different crank.

[Uwon]

Thank you all for your responses.

Originally Posted by Henry Schmidt

There are all kinds of small bore options. Just keep in mind that boring the 2.2 case to accommodate 90mm cylinders compromises cylinder stability.
The last 2 engines I built for my own 2.0/2.2 cars were 2450.
That is 70.4 x 86.
With 40mm Webers, 9.5:1 compression, Mod"S" cams and mild porting the engine produced 180 RWHP. I twin plugged them for the wow appeal but it was really needed for achieve the HP.
Easy to drive, great acceleration and relatively inexpensive.

As for the non-counter weighted crank, they were designed for 5000 rpm. If you want to spin it, the flyweights help to reduce vibration.
MOD"S" are still making power at 6,400 so if that is your cam choice, think about a different crank.

Thank you Henry. Your 2450 motor with the 70.4 crank would then be described as a “long stroke” right?
I was not aware that the 90mm cylinders requires mild case boring. Good to know.
I do like the wow factor of twin plug.
Now as for the Webers, do they get bent out of shape in cooler weather or rain?
TIA
Johan

[Henry Schmidt]

Originally Posted by Uwon

Thank you all for your responses.



Thank you Henry. Your 2450 motor with the 70.4 crank would then be described as a “long stroke” right?
I was not aware that the 90mm cylinders requires mild case boring. Good to know.
I do like the wow factor of twin plug.
Now as for the Webers, do they get bent out of shape in cooler weather or rain?
TIA
Johan

I live in California where it rarely gets cold but I've never heard of Webers having an issue with the cold, sans warn-up issues of course.

[Uwon]

Originally Posted by Henry Schmidt

I live in California where it rarely gets cold but I've never heard of Webers having an issue with the cold, sans warn-up issues of course.

Thank you, That is re-assuring. I would assume that a cold start at, say, 50F could be handled with the manual throttle lever.

So, it is apparent that I will have to either get a 2.2 66mm counterweighted crank for a short stroke or a 2.7 70.4mm for a long stroke. The search is on.

Another question for the brain trust- How reliable is a bored out 2.2+new pistons setup to, say 86mm, vs. going directly to LN's Mahle/Nickies offering?

Johan

[Henry Schmidt]

Originally Posted by Uwon

Thank you, That is re-assuring. I would assume that a cold start at, say, 50F could be handled with the manual throttle lever.

So, it is apparent that I will have to either get a 2.2 66mm counterweighted crank for a short stroke or a 2.7 70.4mm for a long stroke. The search is on.

Another question for the brain trust- How reliable is a bored out 2.2+new pistons setup to, say 86mm, vs. going directly to LN's Mahle/Nickies offering?

Johan

The stock Mahle 84 mm cylinder can't be bored to 86mm. You can bore them to 85 which is a very common modification. We generally bore them and have them Nikasil coated.
The Nickies are a great product if your budget allows.

[Uwon]

Resurrecting this stale dated thread.
I went searching for a 2.7 crank and ended up with a complete 2.4S instead. I’m told it ran fine when it last removed from a 911 some 15-20 years ago. It’s complete with MFI.



I am going to completely dismantle it so I know exactly what I have to work with. So, on the assumption that the motor is basically good, I would like to do a complete well executed rebuild and go for a 2.5 or 2.7, ported and twin plug. Budget not that important-increased power with reliability very important. Strictly for street and twisties, no track.
I know next to nothing about MFI but have gathered from comments on Pelican that it’s a very responsive system so I would like to retain it. No idea if the MFI would require mods.
I would appreciate any and all suggestions, comments, even “you are off your rocker” opinions.
TIA
Cheers,
Johan

[targa72e]

I will throw out my thoughts.
If the engine is an actual stamped 2.4S motor with all the appropriate parts I would sell it. It is worth good money to someone with a S with the wrong motor. If you are planning on building a hot rod you would be better of starting with a 2.4 T engine or 2.7. The T or 2.7 engine will have almost the same parts as your S engine.
The exception is the T has smaller stack diameter, different space cam in the MFI pump, different port sizes in the heads and different pistons.

The heads and intake stacks are the two most unique parts on the S engine.

The MFI pump will need to have the space cam changed unless you build a factory replica engine, so might as well start with a T pump as it’s the same as S except for the space cam you will be changing.

Heads: 2.4-2.7 are the same casting. You could have 2.4T heads ported or start with large port 2.7 (same port size as S).

Throttle bodies: T and S have the same casting only difference is bore. Since they probably need to be rebuilt might as well have T bored out and have larger plates installed.

Stacks: S stacks are unique to S and 2.7 RS engines which make them rare and expensive. You can have T or E stacks bored out to the same dimensions.

Dyno below is same car same gear about a year apart. 2.4 MFI with S pistons and E cams vs 2.7 with 8.5 to 1 RS pistons, big port heads, Mod S cams and Webers.



Since you want power for the street 2.7 (or larger) is the way to go. I would go with 2.7 ported heads, Mod S cams, 9.5-1 compression.
ITB EFI for old look and modern tuning. MFI can be fiddly to get tuned correctly with non factory engine specs.
Use the early heat exchangers on S motor with sport muffler. This should be a great street engine with 210+HP at the wheels.

john

[Trackrash]

As a data point, I had a 2,2 increased to a 2,5 using 2,7 RS P&Cs, E cams, Webers, 35mm ports, and a sport muffler. Dinoed at around 190. That was with a stock T crank and only 8.4-1 CR.

An S motor just sold on BAT for around $50k.

Decisions, decisions. Either way splitting a mag case can cost $$$ to make it right.

[Uwon]

John & Gordon, many thanks for your thoughtful comments and input. Lots for me to take in and digest which led me back to Bruce Anderson’s and Wayne Dempsey’s books for more info. I note that both of them mention (and one of them ever graphs) the surprising increase in power with a “sport muffler”. So, what sport muffler are they referring to given that these books were written some years ago?
Johan

[Trackrash]

Originally Posted by Uwon

John & Gordon, many thanks for your thoughtful comments and input. Lots for me to take in and digest which led me back to Bruce Anderson’s and Wayne Dempsey’s books for more info. I note that both of them mention (and one of them ever graphs) the surprising increase in power with a “sport muffler”. So, what sport muffler are they referring to given that these books were written some years ago?
Johan

Lots of options on mufflers. Dansk makes some good sport mufflers. Some guys will use a dynaflow or similar. Back in the day stock mufflers were modified. There are a number of threads on mufflers if you spend some time searching.

[targa72e]

Both of the Dyno graphs I posted were from a 914 with headers and "sport muffler". In my case the sport muffler is a stock two in single out muffler modified with two outlets and original outlet capped off. I dynoed this muffler configuration many years ago and it was within a couple HP of megaphones
Sport muffler




john

[Trackrash]

Originally Posted by Trackrash

Lots of options on mufflers. Dansk makes some good sport mufflers. Some guys will use a dynaflow or similar. Back in the day stock mufflers were modified. There are a number of threads on mufflers if you spend some time searching.

BTW. The muffler you have pictured in your 2-20 post is a pos and from my experience will not produce good power.

[Uwon]

Originally Posted by Trackrash

BTW. The muffler you have pictured in your 2-20 post is a pos and from my experience will not produce good power.

Just awful looking. Hate looking at it. LOL
Johan

[Uwon]

Originally Posted by targa72e

Both of the Dyno graphs I posted were from a 914 with headers and "sport muffler". In my case the sport muffler is a stock two in single out muffler modified with two outlets and original outlet capped off. I dynoed this muffler configuration many years ago and it was within a couple HP of megaphones
Sport muffler


john

John, did you open it up as well to gut the innards or just grafted the tail pipes? Would there be any advantage/disadvantage to grafting the tail pipes further apart or closer together?

Johan

[targa72e]

Johan, I modified this muffler around 20 years ago when it was on my wife's 911 and do not remember for sure but I think I just capped the original outlet and added the new pipes.
I did dyno several muffler configurations on my SC and compared them to megaphones. On my SC (Stock internals with CIS and headers) this style as well as the style with the outlets at either end were the same and very close to megaphones. With two outlets and relatively low HP I don't think the muffler is that restrictive. Based on my testing I do not think the position of the outlets is critical if HP is relatively low.
You can see the inside of these early mufflers and how others have modified them in the threads below.

Carrera Muffler adapted for 993 engine?

SC, Carrera Bischoff Muffler Modification, Mod, Gut, Gutting, Dual, Two Out

john

[Trackrash]

There is an old thread on modifying the stock muffler to the dual out old school sport style. Those can be loud, but work well.
Maybe someone can find the link.