LT Texan

handy picture:

mark kibort

so where is this notch and how much CC did it cause to be increased?
Is this a euro S head for LH?

mk

LT Texan

Mark,

This is an 86 euroS head from a M28/22. I bought a pair while living in London a few years back. I measured the intake valve for confirmation, but it being a UK spec car, I did notice that the intake valve was on the wrong side. I don't think this will matter.

(Oh, it cc'd at 48cc)

Ian928

So, there really is a difference in S and S2, heads! Below are my 1980 982S head (confirmed to be S by measuring valve sizes). They measured 52.5cc. This confirms my suspicion that the S2 really had 10,4:1m whereas the S in reality had 9,3-9,5.

mark kibort

I had the 80 euro S heads and they measured 48ccs. if you measured 52 ccs, it may be a US set of heads. you said you measured the valves. remember, the valves are still pretty close 43 compared to 45mm for the intake valve.
I also measured Scots 82 euro heads and they were also 48ccs.

anyone else measured the euro (early) heads?

mk

mark kibort

the heads do look different though. how can the intake valve be on the wrong side??
mk

toofast928

I measured 54 cc on the 1982 USA head chamber.
In the pic above I herd the "notch" #4 was to help swirl. #3 the bump -don't know what for.

I measured exactly 9.0:1 C/R with 1 mm head gasket. My heads were replaced before (not machined)so the replacement head gasket measured 1.4mm. That lowered the C/R to 8.7:1.

drnick

what are the casting numbers on these S2 heads?

GlenL

Good thread.

I've been thinking about my re-built engine. It's a Euro S engine (M28.11) with the heads decked 0.4mm and the block decked 0.009". It's got ultra-rare 98mm Euro S pistons of 1984 vintage so the smaller valve reliefs.

Working all the numbers with some estimates, I'm getting a static compression ratio of 11.1:1.

Anyone care to verify that or take a shot at the dynamic compression ratio?

I've been running a mix of premium gas (91-93) with 110 race gas to get 95 or 96 octane. Any opinion on if that's enough?

IcemanG17

many newer cars run at least that much CR..... even turbos are 10.5CR....the Corvette Z06 is 11.0 and V8 M3's are 12.0.... I think you would be fine with normal 93 octane.....since your dynamic compression will be lower....

Vilhuer

Some early '84 ROW S still use older S head design same way as they use old style pistons. Basically they have late style stuff above heads while everything below is '83 MY style. So there can be slight hp & tq difference between early and late '84 MY ROW engines. Its very probable piston and head design didn't change at same time so there are also mixed combinations.

GlenL

Porsche didn't throw anything away. They threw it into the next model year!

Let me be clear the block and heads are 1980 S (M28.11) with over-sized pistons from a later vintage.

With the CIS there are no knock sensors which modern engines use to manage knock. I've dialed back the spark advance to stock numbers to keep cylinder temps a bit lower. Previously I was running an extra 3 or 4 degrees.
.

918-S

Mine is a 5.0 M28/11. I have shaved heads. I can't remember what my numbers are now but with Cometic head gaskets I think I'm still under the maximum cut on the heads. I run 10 deg with premium. BTW: I have one of those stupid timing lights with the builtin advance. You have to zero it out every time you use it. When I was at Tisdel's Garage we discovered way more timing than stock. Must have failed to zero out my timing light. Funny how that eliminated my spark knock. I am buying an oldschool timing light.

I would check your spark plugs after a couple runs to see if they look like they are running hot.

123quattro

I would expect you to be ok running 93 at 11:1 with stock timing. I am at about 10.5:1 with 5 degrees of advance with no issues on 93 octane. This is assuming that your fuel injection is working as intended.

LT Texan

I calc'd out about 10.5:1 on my 4.5 with stock vale reliefs and euro S heads and cam.

I run premium and stock advance with no detonation problems.

I think Porsche had a very good combustion chamber design for octane tolerance.