Porsche 911 ST 89mm. P/C Mahle

[Olsen911]

Finally found me set of P/C Mahle 89mm. 10.3:1 Compression on a 66 mm. Crankshaft Short Stroke. For my new race engine. Porsche 911 ST 1971 racecar.

I would be keeping my 2.2 heads (allot of time and money are put into these) But the heads (2.2) should be chamfer, to accept the 89mm.

Here is Grady:
The 2.2 (2195 cc) and 2.4 (2341 cc with longer stroke) heads, designed for 84 mm bore cylinders have a sharp step at the mating surface between the cylinder and head. The 2.7 heads have a champer in this area

This silly little area in the combustion chamber has a LOT to do with the engine’s performance. I have posted previously about this. This has to do with “squish” and piston to head clearance. You want this as tight as you can get it without EVER running the risk of contact between the piston and head.

Too large clearance (too cautious build) makes for poor performance and possible detonation. Other than bearing clearances and valve seating, this is possibly the most important dimension in the engine.

I think this is the most often overlooked when building a hotrod.

Thanks Grady.

But i can't see there is enough "meat" to make the chamber on the heads.? It looks like it Will Cut into the valve seats, if we try to Chamber.?

So I thought that maybe it was my heads that had been fly-cut and therefore, but found some almost new heads in the garage, and those looks the same.

Please chime in.

Thanks - Cheers - Olsen911
Tommy Olsen

[Steve@Rennsport]

Hi Tommy,

Unfortunately (and sadly), Grady passed away last year so don't expect a reply from him to your questions.

I can tell you that a qualified & experienced 911 machinist can chamfer your 2.2 heads to work with the 89mm bore to provide the proper squish band; we've done a lot of these and it doesn't come close to the seats.

Remember, excess material removal results in a loss of compression so one should remove as little material as necessary to do the job. I'd strongly advise measuring CR after this is done.

[Olsen911]

Helle Steve.

Thank you joining in.

Very sorry to hear about Grady. - God speed.

Please teach me how to chamfer the heads - so i can instruct my machinist.

Any pictures or measurements will be grateful.

Thanks - Cheers - Olsen911
Tommy Olsen

[Olsen911]

Anybody.?

Thanks - Cheers.

[crg53]

Why not send your heads to Steve and let him do them, then you know they will be done right, and when you get them back, you will have all the pictures needed.

[Olsen911]

Will like to sent the heads to Steve and have these done.

But the heads are halfway around the World from Steve so shipping will exceed the cost of having the heads done.

And then there is customs here in Europe - every time you send something out of the country - It´s pain in the a.. to get it back, without paying huge amounts in tax.

Thanks - Cheers - Olsen911
Tommy Olsen

[Trackrash]

This is what the champher looks like. However, any experienced Porsche machinist, in my opinion, should be familiar with this operation. I had this done on my 2,2 when I installed 90mm cylinders back in '82. Was commonly done back in the day.

[BURN-BROS]

Originally Posted by Olsen911

Will like to sent the heads to Steve and have these done.


And then there is customs here in Europe - every time you send something out of the country - It´s pain in the a.. to get it back, without paying huge amounts in tax.

Thanks - Cheers - Olsen911
Tommy Olsen

Hi Tommy,

You may not know that customs will recognize that your property can be sent to other countries for repair. All that you would pay duty for is the new parts that you bought in regards to the repair. You may need to post a bond if the cost is above a certain amount.

https://help.cbp.gov/app/answers/detail/a_id/590/~/temporary-imports-for-repair%2C-alteration%2C-or-processing-without-duty

[Henry Schmidt]

Originally Posted by Trackrash

This is what the champher looks like. However, any experienced Porsche machinist, in my opinion, should be familiar with this operation. I had this done on my 2,2 when I installed 90mm cylinders back in '82. Was commonly done back in the day.

If you're going to post one of my pictures you should post the "after" pictures as well.

[Olsen911]

Gents.

Thanks all - found a used 2.7 head, which has the chamfer - so it was delivered to my machinist as a model - mark-up.

Thanks for the help.

Thanks - Cheers - Olsen911
Tommy Olsen