Upgrade 2.4 to 2.5?

[Fdalgas911T]

OK, I am considering upgrading my original 1972 911T 2.4 engine a bit (69K miles). After studying the charts on all the 911 engines I discovered this one is really very low compression and low horsepower… 7.5:1 and 140hp. Was considering replacing the cylinders and pistons moving displacement to 2.5 changing bore from 84 mm to 86 mm. I would like to do the work myself but don’t want to screw anything up or end up with an engine that is finicky. I am trying to assess whether this is something that I can do or not. My experience with rebuilding is lawnmowers, motorcycles, and small block Chevys, but never a Porsche!

Having never done nor witnessed a Porsche rebuild (except reading Wayne’s and others books) I have some questions:

Does the case need to be machined to accept the larger bore cylinders? 84 to 86 mm

Are there any particular piston / cylinder brands or compression ratios that are preferred and not unreasonably priced? 9.5:1?

Would I need to change the camshafts?

I have read about several of the magnesium cases pulling head bolts. How risky would it be to try to torque the head bolts down and only resort to thread inserts if one of the bolts will not reach proper torque.

I have of course MFI and would need to get the pump recalibrated. Is this expensive to send off and have done?

Would also upgrade to the carerra hydraulic timing chain tensioner upgrade.

If I need to open the case for something, I would have the holes drilled to squirt the piston skirts and change to the appropriate oil valve.

Am I leaving out any other important stuff?

Looking for opinions…, sound like a reasonable quest? Can a novice such as myself do this?

[Fdalgas911T]

No responses... hugh. Just looking for opinions on converting a stock 2.4T 7.5:1 to a 2.5 9.5:1. Is this a good idea? Have heard the 2.5 motor can be awesome.

[Scott Clarke]

F-
I think hat you are generally on the right track. From what I understand, the early T, E, and S cylinders can be re-bored for reasonable money. However, 86mm is pushing your luck. 85mm is no problem. For a reasonably priced rebuild, re-bored 85mm cylinders with JE pistons would be good combination. This would get you a little displacement, and resolve your compression ratio issues. Porsche produced long-stroke 2.5 race motors, but these had special 86.7mm cylinders. They are unobtanium. Your case would not need modification for any of these cylinders. A nice upgrade would be to find a set of Biral cylinders from a 2.2 or 2.4 E or S. These cylinders had iron liners within aluminum cooling fins. They are lighter than your iron T cylinders, and will dissipate heat better. You could likely find a worn out set cheap, and have them bored to 85mm. You might find a set of new Mahle pistons and cylinders. They would be expensive, and the cylinders would be Nikasil. This would be more likely to require case savers (see next papagraph). No one disputes that Mahle is the best, but JEs work, and work well. Do a search for much debate about the two.

Your motor should already have piston squirters. As for case savers, they are always a good idea, but not critical for a motor with iron or Biral cylinders. Head stud problems are primarilly a function of Nikasil/Alusil cylinders, which expand with temperature at a different rate than the steel head studs. The oil bypass modifcation is a good idea, along with a SC or late 2.7 oil pump.

As long as you use the T cam, you should be able to adjust the pump as it is. If you change cams, you would need to have the space cam changed in the MFI pump. That seems to cost about $800.

If you have some mechanical experience, read Wayne's book, and ask a lot of questions here you can do this.

-Scott

[kenikh]

Originally posted by Scott Clarke
F-
Porsche produced long-stroke 2.5 race motors, but these had special 86.7mm cylinders. They are unobtanium.

I believe that you could get Nickies and JEs made to this spec with no problems.

http://www.lnengineering.com/911.html

[mpwrcpe]

Set of new 2.5 10:3 Mahle pistons on e-rip, errrr e-bay--

Pistons

I'm in the same position, but I think biral to 85MM w/JE ~9.5:1 pistons, MFI and E cams is where it's at for me That gives me 2.5L w/good midrange power for the twisties.

Hmmm, I guess I'd better get to work on that!

-Dave.

[camgrinder]

If you end up with more than 9-1 compression, the T cams should be upgrade to E specs at least. This way you can still run pump gas.

[kenikh]

Jeez, if I were to build a long stroke 2.5, those (ebay) pistons in nickies would be one HELL of a setup.

[Fdalgas911T]

On June 28 Scott Clarke wrote:
A nice upgrade would be to find a set of Biral cylinders from a 2.2 or 2.4 E or S.
======================================
Scott, Thanks for your post, it has been helpful. I have assumed the 2.2 birals would not work for boring to a 2.5, wouldn't they be too short? or perhaps a special piston is required? I like the idea of boring the biral cylinders to avoid the expansion and magnesium case stud pulling problems with other cylinders. Heat dissipation is important for me too and it is hot in texas 6 months of the year! So far, I have been unable to locate any used 2.4E or S biral cylinders. Have located used 2.2 birals a couple of times but hare ruled them out (perhaps in error). How do you like your short stroke 2.5?

[304065]

F,

Any 2.2 (84mm) Biral cylinders you found ARE from the E or S.

A 2.2T cylinder would be cast-iron. Therefore, if it's an 84mm Biral, it's an E or an S.

Depending on your budget, also consider Nickies which are sold by our host, and their creator, cnavarro, is a frequent participant on this forum.
They have a host of metallurgical and physical advantages over the stock cylinders, but are more expensive.

[Fdalgas911T]

Thanks for the input John. I have looked at the nickies and like them a lot but am trying to avoid installing the timecerts if I don't need to... maybe even save some money with the used birals. I am under the impression that the nickies also expand at a higher rate than the headbolts and would pull the original magnesium case threads. Open to your opinions... I am no expert. Fred.

[Scott Clarke]

F-
The thinking behind the biral cylinders is that they are cheap! I thought I just saw some for sale with S pistons (Cornpanzer on this board had them). If you keep your nose to the ground, you will find some. Yes, they will disapate less heat than alusil, but more than cast iron. Unless you go crazy with the ports and cam, you should be able to keep this motor cool with those cylinders. With an E cam, I'd hazard a guess that you wouldn't need an external oil cooler. With an S cam, you likely would.

It's always a good idea to install case savers, but you are right in that the risk is low with the biral cylinders. Again, the amount of power you intend to extract may play a role.

All cylinders are the same nominal length, so things are interchangeable. The diameter does change.
-Scott

[304065]

Fred,

Many knowledgable engine builders, Competition Engineering for one, recommend the installation of Case-savers (not time-certs) in any magnesium case when you are doing a rebuild. It adds a little to the cost, but it buys you a lot of peace of mind, and is the kind of thing that looks good if you ever sell the car or the engine.

Porsche used Biral cylinders all the way until the 2.4S, which made 190 hp, so if you are keeping it below that power level the Biral material should be adequate. That assumes, of course, that you have a good external oil cooler setup, which is a must.

[cnavarro]

Fred, you are correct on the mag case. I really do recommend installing case savers in any mag case when going to an aluminum cylinder, regardless of whose it is. I've even seen many shuffle pin the case halves when exceeding 200 HP, but some question the necessity of the operation. Swapping out the head studs for a set of Supertec, ARPs, or Performance Developments is also recommended. As long as you keep under 250 HP, you should be fine.

I wouldn't recommend using a set of overbored used birals. If you use new birals, that's a different story OR if the birals you overbored were well within tolerances before boring them out- less chance of the cylinder being tired or overheated from the separation of the aluminum from the liner. You'd be better with a set of bored out cast iron cylinders that have been cryogenically treated, and don't go over 85mm. 9.5:1 or even a 9.8S spec JE will work great (the higher of the two depending on what gas is available to you, as I would prefer the lower compression with more advance than the higher compression and less advance). You can coat the pistons and even step-cut the heads.

It's a shame those factory mahle 86.7 pistons were ended early, they would have made a hell of a match with a set of Nickies, however a set of carefully thought out JEs will work just as well for Nickies. We've done 87.5s a few times and even done a set of slip in 89s (yes, the skirts are thin and the cylinders were also cyro'ed).

[Henry Schmidt]

An email I received this am:
Hi Henry...
It was interesting to read your comment about the piston sizes for the STs.
I was under the impression that they started out in 1970 at 84 mm, then enlarged to 85 and finally ending up at 87.5?
You mentioned an 86.7?
History?
Thanks,
Todd R********
Tustin, CA
Hi Todd
Not much to say. Porsche was a small company willing to try new things. The ST was a rally car and needed to fit in a special category so they tried different means to achieve the same end. Hence the 86.7 It was used with a 70.4 crank to make a 2.5 ( 249?) liter MFI race engine.
I'll post this response and some pictures on Pelican. Take a look.
Here are a few of the odd ball cylinders.
Note they all have full fins. They are all Nikasil or Chromal.
The last picture is of a 962 2.8 piston & cylinder. It is 92.8 mm and ran on a 70.4 crank.
Look at the thickness of the 962 cylinder. Do you think they were turning up the boost on this one?

Who is this guy and were do all these cool parts come from?

Cheer
85, 86.7, 87.5

[Henry Schmidt]

opps, got mouse happy

[Henry Schmidt]

Just a few more images



2.0 906 The real deal




2.8 962 92.8 mm

[cnavarro]

That's one hell of a collection of rare cylinders Henry!

[Fdalgas911T]

Thanks everyone for all the advice. I sincerely appreciate it and it is helpful.

Cnavarro wrote:
You'd be better with a set of bored out cast iron cylinders that have been cryogenically treated, and don't go over 85mm. 9.5:1 or even a 9.8S spec JE will work great (the higher of the two depending on what gas is available to you, as I would prefer the lower compression with more advance than the higher compression and less advance).
===========================================
Does LNengineering perform the cryogenically treated service for cast iron cylinders? I haven't actually openned my cast irons up but only expect normal wear. If these are as expected, in decent shape, and cryogenically treatment is performed, what would be the limit on horsepower per cylinder? Currently I am under the impression that cast iron is limited to about 25HP per cylinder. I am wanting 30 to 35 and service to 100k+ mi.
Is this a pipe dream?

[cnavarro]

I have had two companies in the past do my cryogenic treatment- 300 Below and Performance Cryogenics. Years ago, we actually did a test where we compared non cryogenically treated heads and cast iron cylinders to having both cryo'ed and we were able to register a repeatable 25F drop in head temps @ the spark plug. This basically tranposed to about 37.5 hp per cylinder out of the cryogenically treated cylinder with a serviceable life of about 60,000 at which time the cylinders were replaced and the heads needed to be rebuilt. Also one must take into consideration that many different coating were used to reduce temperature and friction, as well as upgrades made to increase oil cooling, the amount of air delivered to the cylinders, and reduce exhaust restriction and backpressure.

All considered, most customers still perfer to go with the aluminum cylinders regardless for all the same reasons Porsche went to them.

I have had some customers cyrogenically treat the cylinders then have me bore them out, nikasil plate, and then match hone to their new JEs, with the appropriate rings, in an attempt to reduce wear and lower the friction of the rings against the bore to increase the useable life, but in every case the overbore was ever so slight of no more than 1mm from the original size, as you want to keep the cylinders as close to the original thickness to take advantage of the thermal stability of the cast iron.

In either case, if you exceed the original horsepower recommended by Porsche with the cast iron or biral cylinders, a CHT gauge is a must.

[Fdalgas911T]

Now that i think about it... with input from you pelicans, the Nickies and JE 9:1 really seem like a solid choice. With that said, 2.5L does not seem to be so desireable but the choice of 2.4 standard is quite good. What horsepower would such a motor produce? That is a 2.4L MFI E cam JE 9:1 with Nickies cylinders. The closest match I find is the 911/52 with E profile, 8:1 with 165HP. Guessing, changing from 8:1 to 9:1 would produce 10 extra HP... sound about right?