Help Porsche 911T 2.4 MFI 1972 Pistons and Barrels Needed

[BasherBell]

Hi from the UK.
I've had a continuing problem with gas in the oil. Beyond my capabilities. So working through various issues as encountered investigated and hopefully solved. .
Put it into a garage and the emissions were way erratic. Had the MFI and injectors refurbished by an expert over here, which they needed , cams all out.

Lack of compressions so now on a top end rebuild and have measured the pistons and barrels . Barrels are oval and way out of spec as are pistons and rings. Beyond repair So I need new pistons and barrels.

Looking at the Pet I'm confused as to what each Part difference is beyond Schmidt - Mahle etc. Schmidt not available any more . Can't seem to get an answer out of any suppliers on which ones are correct.?
FYI Looking inside a Pistons the codes are: B5 on top
084 075 +1+ 1275 12 and $

Can anyone enlighten me. Tried to search the web to see if any better explanations can be found and had no success
What does Group 5 and Group 6 mean for example on the PET ?
These are the applicable parts on PET for the T-E which is my car/engine group.

Part PCG503 1890 Cylinder with piston complete FA Mahle only by sets 911 T-E T-V
(These are the cheapest I have found - Don't know why ?
Part 91110394201 Cylinder with piston complete Group 5 Mahle 911 T-E T-V
Part 91110394202 Cylinder with piston complete Group 6 Mahle 911 T-E T-V
Part 91110394205 Cylinder with piston complete group 5 Schmidt 911 T-E T-V
Part 91110394206 Cylinder with piston complete group 6 Schmidt 911 T-E T-V

My garage have asked Porsche and they haven come back yet after two weeks .......
So at an impasse until I can clarify the right barrels and pistons to fit and will mate with the crankcase correctly which is our main worry.
Background info:
Vin 9112102847
Engine Number / Type 6124381/911-51
Crank Case Numbers 901 101 101 5R and 901 101 102 4R
Production Completion 01/07/72
Transmission 720428/915-12

Cheers from UK
Dave

[tharbert]

It appears you have KS 84mm T p/c's. There's a little more info here.

It's my understanding that pistons come in different groups of deck height, weight and size and those specifications are stamped inside the piston. If you replace one piston, you need to make sure it "matches" the others of your set. If you replace the whole set, presumably, the vendor will make sure all your bits match.


There are a lot of options to replace your p/c's as a set. The 72 T's came with cast iron cylinders, not the best for heat dissipation. I'm not sure you really want to replace with similar quality. You can upgrade to 84mm Mahle p/c's, T,E, or S spec. There are also vendors who sell JE Piston/AA cylinders reworked with a Brial coating, a less expensive option to Mahle. A popular mod would be to get a set of 86mm P/C's bumping up the displacement a smidgen without having to modify heads or case spigots. And, 2.2E style of cylinders will bump the anemic 8:1 to roughly 9.5:1 compression ratio. I'm not sure how those two minor changes will affect the MFI... Consider getting these two book and look them over. I'd bet they answer a lot of your questions: How to Rebuild and Modify Porsche 911 Engines, by Wayne R. Dempsey and Bruce Anderson's Porsche 911 Performance Handbook, 1963-1998: 3rd Edition both available in this site.

[BasherBell]

thanks for the fast response, much appreciated.
Its a full set I will be going for and have managed to find 6 off of 9110394201 Group 5 Mahle I have no idea if these are cast iron or not but they are a very good price , so looks like that will be the choice.
The MFI was set up for the existing displacement and I have been advised it would need to be changed again for a diff compression ratio power requirement . We got the MFI done first hoping that may solve the problem, then found the oval pistons and barrels . So If I was doing it all again I would have gone for the E or S spec pistons but think I'm going stock. Its lively enough for me on those weaving windy British roads.

It will just be nice to get it back again and run it when its not popping and farting on warmup and dumping huge amounts of fuel into the oil . I guess thats what happens when the barrels are way off spec and oval. I could have lost my car keys down the gap........

Cheers

Dave

[tom1394racing]

Dave

You could have your existing cast iron cylinders bored to 86 mm and use replacement JE 86 mm pistons. The cost would be around $1300.

[BasherBell]

would that have any major effect on compression and the previously set up MFI do you think ?

Dave

[tom1394racing]

86 mm would produce about a 5% increase in displacement. The MFI injection pump should be able to handle that. You can get replacement pistons with T type of compression ratio.

[BasherBell]

Absolutely Excellent.

Thank you all for your detailed and valuable posts it is very much appreciated.
Dave

[rads]

I have a used set of B+C's from my 2.4T MFI car. I'm also here in the UK.
PM me if you are interested.

[BasherBell]

Thanks Rads, Ive just ordered a set from Rose Passion , but appreciate the offer
Cheers
Dave