That is true. The unrevised head casting for the 32v heads has smaller valves and larger combustion chambers. The safest thing is to get S3 (i.e, unrevised, original casting) heads.

Now, for an adventurous project, S4 .R1 heads could be used. This would bring up the static compression. Then, one would have to modify the S3 cams to run in the S4 heads, and possibly regrind them for a later intake valve closing to reduce the effective compression. Retarding might work as well. One would also probably have to widen the valve reliefs in the pistons. Finally, there are always unforeseen issues. This would be an adventure and not a repair. Don't try this at home.

That would be the hot ticket but you'd also need the exhaust manifolds for the different bolt pattern. Maybe the valve covers too?

I've got an extra set of S4 exhaust manifolds, because of the turbo project. I don't think those are expensive or hard to come by.

I was under the impression that the valve covers are the same, but I was probably wrong. S3 part number is 928.104.461.06 and the S4 part number is928.104.461.08.

More to the story
 

Ok, Here is the rest of the story since there are so many listeners.
My brother in law had the 928 on the west coast, he offered it to me at no cost, being all I need to do is get it to New Jersey. That is $1000.
So, I got the car for nothing, except shipping it across the country.
When it arrives, in about two weeks, I will start evaluations on the engine. Working on imports is nothing new to me, If you can fix Jaguar XJS V12, I think I can fix this. I have all winter.

So, should I put a belt on it and do a compression test first? Or just pull the motor?

Ps: thanks for all the welcome suggestions in advance. Are there any other 928 owners near Atlantic City NJ?

Also, the engine was running, the hot light came on so he pulled over and shut it off, then tried to start, would not start as timing belt had melted due to a frozen water pump. Engine was not fried, it was shut off as soon as light came on.

$1K is good. Yes, I am sure you can work on it. Just takes patience.

Here's the thing, if you bent valves, there could be piston and all the way down to the rod damage.

I'm not a 32v expert, but I would no longer trust the engine enough to just pop on some new heads.

Also, FYI, there is a post out there where somebody has a complete S4 engine out there. does anyone know if this would work in his 86.5?

Mike,

Are you selling 85 - 86 heads? Are they in good shape? Do they come with cams? Please PM me with the price. I may be interested if the deal w/ Tuomo doesn't go through. I'm in the same boat. early 32v engine with timing belt failure. I've got a whole lot of broken and bent valves. :(

Don't do a compression test as that will require you to crank the engine. Try turning it over by hand once to make sure you don't have any broken valves in a cylinder. Then do a leak down test. This will tell you if you have problems. Most likely you will be pulling the heads. The 85 - 86 engines will require the engine to be out to get the heads past the head studs. Then it becomes a "while your at it" project. While the engine is out you should look at doing the motor mounts, master cyl blue hose, oil pan gasket, front main seal, cam shaft seals etc. It's not that bad, just $$$. Once you're done you will have a dry engine, and that's priceless.

Swapping 85/86 and S4 is an electrical pita, different brain types 25 wire vs 35 wire.

I've got two sets of heads off 85/86 motors with cams etc (I've been working at building Euro hybrid motors, so I only keep the short blocks). PM me if you want to talk details.

Broken timing belt and valve damage is almost certain. One of mine had 32 bent valves, not one good valve, but so far I haven't seen a bad piston.

Good Porsche trained mechanics screw up 928's on a regular basis. If you assume nothing and follow the workshop manual and ask plenty of questions though, you should be fine.

You should figure out what heads best work for you and then buy those. There's plenty of original casting ('86 32v) and .R1 (S4) heads for sale. If you are retaining the stock pistons, then original casting heads on S4 bottom end may give you the nice low compression for a boosted motor and the ability to run S3 cams without mods. If you are installing low-compression pistons (or would like to get a high compression ratio for a NA engine), then S4 heads with big valves may be better.

From http://forums.rennlist.com/rennforums/928-forum/344250-head-and-piston-top-cc-numbers.html

Piston dish sizes:
S ROW '80-early '84 8.7cc
S3 US '85-86 6.5cc
S3 ROW '86 11cc
S4 '87-January '88 25cc
S4/GT February '88-91 20cc
GTS '92-95 25cc

Head combustion chamber sizes:
S ROW '80-86 16V 48-52.5cc
S US '83-84 56cc
S3 '85-86 56.5cc
S4/GT/GTS '87-95 40-42cc

I have a complete 87 engine and a complete 85 parts car.

The 85 is a healthy running car but since the interior is ratty it's worth more as parts, it has a bonafide M28/11/12 5 speed LSD transaxle that shifts perfectly. I'm willing to tug parts off the car and send them away.

BTW, what's this about turbo projects you're working on? I'd love to know more but haven't noticed any threads here or on RL. Talk to me!:)