-87 vs 88 NA Head Differences?

[kdjones2000]

I just noticed in PET that the '88 NA head is a different part number than the earlier ones.

Can anyone tell me the differences? I have an '88 head with good valves and an '85.5 one with 8 bent valves. I am wondering what is not interchangeable between the two?

Thanks, Keith

[Techno Duck]

Only difference there might be is the pressure relief valve. The earlier style heads were like 2-3 pieces, the later was a 1-piece valve that was removable by removing like a M4 allen head bolt. Cant remember if that was a '88 or '89 thing though.

[VirginiaF1]

My '88 has the 1-piece OPRV..
Clark's shows the details of the 1987 MY OPRV changeover:
Oil Pressure Relief Valve General Information


The '88 n/a had the M44/09 engine code with a slight bump to 158BHP in USA through ROW pistons yielding 10.2:1 compression.. Evidently, the '87 had the M44/07 with same bhp..?

I did not know that.

[9FF]

My '88 has the 1-piece OPRV..

Clark's shows the details of the 1987 MY OPRV changeover:

Oil Pressure Relief Valve General Information





The '88 n/a had the M44/09 engine code with a slight bump to 158BHP in USA through ROW pistons yielding 10.2:1 compression.. Evidently, the '87 had the M44/07 with same bhp..?



I did not know that.

What they did in 88 was not use the previous ROW pistons that were 10.6cr. Instead they had a new 10.2cr piston just for the 88 model in all markets, so the ROW cars lost hp and the US gained. It was an interim measure to make everything the same in all world markets. Then it 89 they bumped everybody to 10.9cr.

[Techno Duck]

Originally Posted by VirginiaF1

My '88 has the 1-piece OPRV..
Clark's shows the details of the 1987 MY OPRV changeover:
Oil Pressure Relief Valve General Information

I am referring to a different relief valve, this is one inside the cylinder head.

This is the one piece valve i am talking about;

[kdjones2000]

Thanks, Jon. I am thinking that that might be the difference.

I am asking about the head itself, not the pistons or OPVR.

So the castings would be the same, sounds like. I will take a look at that relief valve and see if there's a difference.

Cheers, Keith

[Chunkerz]

Originally Posted by VirginiaF1

My '88 has the 1-piece OPRV..
Clark's shows the details of the 1987 MY OPRV changeover:
Oil Pressure Relief Valve General Information


The '88 n/a had the M44/09 engine code with a slight bump to 158BHP in USA through ROW pistons yielding 10.2:1 compression.. Evidently, the '87 had the M44/07 with same bhp..?

I did not know that.

I thought the ROW pistons were 10.5:1? Also, I thought the 88+ N/A's had more like 160 or 163hp? Or is that just the Euro version?

[kdjones2000]

If you look at the Porsche shop manual for Engine, pages 0.2 and 0.6a you will find your answers.

M44/01-08 are 10.6:1 for ROW and 9.5:1 for USA cars (That covers all NA's up through 1987).

The 1988 models use the M44/09-10 engines, which are 10.2:1 for both ROW and USA cars.

SAE Power output changed from 143hp to 158hp with the compression increase.

Cheers, Keith

[Chunkerz]

Seems odd that they would decrease the compression ratio in the Euro cars.

[VirginiaF1]

Originally Posted by Techno Duck

I am referring to a different relief valve, this is one inside the cylinder head.

[/IMG]

Cool valve!
Never knew/saw that one.. Thanks for the Edu!