Pfc. Parts

Hello List -

I've nearly finished restoring my street car and I'm beginning to plan my next project. I have to admit I've toyed with crossing over to the Dark Side and building a 3.0L 951. This isn't entirely out of character, the 928 is my fourth Porsche (though I've been it's original owner since 1986). I've also built a 916 from a 1971 914-4 (1.7L), a 931 and the now infamous 928 twins. My dilemma surrounds either parting out my donor 928 and starting on a new platform or keeping it and trying to build the Death Star, a car capable of devouring 944 S2 Turbos and then snacking on 911s.

I was pretty well down the road to building the 3.0L 951 Turbo Cup (I know, it never existed in real life but in my opinion it should have) when I stumbled on a thread concerning adapting the 8V 2.7L 944 head to the 928. Until I read that I had been of the opinion the N/A 16V 5.0L 928 was a very rare high performance configuration only available in Europe. I had been advised that I would be much better off finding and installing 8V heads on my 5.0L than supercharging it. Of course the punch line was that finding 8V heads for the 928 was akin to finding hen's teeth. Practical experience has proven that correct.

Then I found these 2.7L 8V heads (well, head really, I've only found one) and I found a thread (here) suggesting they might be adapted fairly easily to the 5.0L motor. I became intrigued. My wife would say I became schizophrenic, but she's not a licensed psychotherapist so I don't grant her much credence.

So here's the concept; two 2.7L heads stolen from recently deceased (and short lived) 944s. 16 49mm sodium filled valves. Intake and exhaust manifolds from 2.5L 951s. Two turbo chargers.

Any hope of success? Anyone ever tried it (besides the now legendary John Kuhn, who only works on S4s)? Looking for other crazy bastards. Have chassis, will pimp.

No LART jokes.

ptuomov

It must be early in the morning. I am reading this to say that you're planning to take of the 4-valve heads and replace them with 2-valve heads with great adaptation effort and expense. I probably misunderstood that, but just in case I didn't, what's the motivation?

Fabio421

John is planning on building some stuff for the early cars later this year. He's doing it mainly for his brothers car but you might be able to get him to build you some stuff while he's at it.

JEC_31

Putting the late 16v 928 - that is 8v per bank - Euro top end setup of heads, intake, ignition, etc on a US-spec 85-86 5.0 liter bottom end is common enough, though twin turboing such a hybrid build is not. What advantage do these rare 2.7 8v heads have?

FBIII

I think Bob DeVore ran 944 heads on his early strokers. Probably easier to find at the time than Euro S heads and I think the 944 heads all had the bigger valves. I'm pulling at straws but I recall something about the port spacing being different.

Fabio421

The ports are slightly different. From my understanding the 928 cam lobes will not be perfectly centered over each lifer but it can work. I have not done it myself. I have used 951 exhaust valves in a 928 head but that was the extent of it.

ptuomov

I recall that the stock S4 cams are offset by 3mm relative to the lifters. This I believe is to rotate the lifter to reduce wear, both by moving the new oil covered surface under the lobe and to prevent the lobe from always wiping the lifter at the same spot.

I can't imagine it ever being more cost effective to start swapping 944 heads onto 928 than just finding the best 928 parts and using those.

For example, the bone stock '87 S4 engine has 9.4:1 compression ratio and can take 10 psi of boost at the mid range and 20 psi of boost at the redline.

For higher boost levels, one can dish the stock '87 piston more, or, at extra cost and expense, put S4 heads on top of block with S3 pistons.

Mix and match from here: https://rennlist.com/forums/928-foru...c-numbers.html

hacker-pschorr

Correct, the 944 valves are spaced further apart than the 928 16V heads. The cam lobes will be off-center unless custom cams are made. Not ideal but it should be OK. Not something I would experiment with.......

Another difference is the wider valve spacing puts the edge of the valve closer to the cylinder wall. When I showed both heads to a couple of engine builders, they said the 928 EuroS head was definitely they way to go as it "should" flow better with more open area around the valves.

944 / EuroS intake valve - 45mm
944 2.7 intake valve - 48mm

Frankly, if you were trying to wring out every last drop of power from a N/A engine, this would make sense. Otherwise with a boosted motor this is going to be a lot of work for probably very little gain.
Granted EuroS heads are not the easiest to find, neither are 2.7's.

A lot of good information comparing the heads in this thread:
https://rennlist.com/forums/944-turb...project-6.html

As for the intake and exhaust manifolds from the 944..... what is so "wrong" with the 928 16V intake and 32v exhaust manifolds (85/86) that they will not work?

Pfc. Parts

There are several, the first may be based on urban legend, the second is based on the idea re-using factory parts wherever possible will decrease the cost of building the engine. The 4.7L engine built with the 8 valve heads (Austrailia) had a published production of 275 HP as compared to the 16V 5.0L @ 288. Several people have said the 16V head performs better than the 32V, though I haven't seen actual dyno numbers to support that. It seems very possible however given the comparison between the 4.7 and 5.0 mentioned above.

More important is the belief the 2.7L 8V head is more easily adapted to a turbo. The intake and exhaust manifolds for the 951 are reputed to bolt directly to that head. Sodium filled valves from a 951 can be used directly. So far I haven't come across a factory built 16V head originally sold on a turbocharged engine of that vintage, though I've heard rumors Porsche built a 16V turbo 944 for Le Mans in the first year of the 944 Turbo Cup. I haven't confirmed that, but the 8V turbos are well known.

This is why I raised the question. There are several threads on this forum discussing the possibility of using that head with the 928 block, though none I've found specifically mention using the 2.7L head on a 5.0 block. It seems quite a few people have talked about trying it, I haven't heard from anyone who's done it.

Pfc. Parts

One is pragmatic; I already own one. The other is more practical, they accept stock 951 valves & manifolds.

ptuomov

You are going to find that the heads are the least of your problems and that packaging the turbos into the engine bay is the real problem. It's like fitting the turbo on the exhaust side of the 951, except both sides are exhaust sides and you have to do it on both sides! You are going to buying turbo exhaust manifolds from the same source I did or fabricating your own, $1.89 and 951 exhaust manifold is not going to get you a cup of coffee at Starbux... See also here: https://rennlist.com/forums/928-foru...e-streets.html

The 951 exhaust ports have a ceramic lining, which is nice. However, the 928 4-valve heads have small enough exhaust ports that they'll work very well with turbos. Also, you can always get the exhaust ports and valve backs ceramic thermal barrier coated at Swain, if you think it's important. It isn't that important, because recall your turbo is now close and not on the other side of the engine.

The pent roof head with a central spark plug is going to require less octane, allow for timing closer to best torque, allow for more compression, and/or allow for more boost than the two-valve head. The four-valve head is just going to walk away from the two-valve head, boosted or not. See the 2013 EMC results, for example, the one and only year when they allowed 4-valve heads in that competition: No two-valve heads in the top three.

This is not to say that the two-valve head can't make power, it can. Look at the hot rodded 951s, plenty of power there. It's just that if you already have a four-valve head, why go thru all the effort to go to a two-valve head?

Pfc. Parts

I did exchange some eMail with him, at the time he was focused on the S4 engine and who can blame him?

I'm really trying to figure out where my starting position could be and the decision is complicated by the fact I already have a running '85 5.0L in perfect shape to become a track car. It's much easier to find information on building a 944 S2 Turbo, but I just can't escape the idea I'd do better with the 928 in the long run. It's a larger displacement engine, it's literally two 944 blocks, and it only weighs 300 lbs more than the 944. There has to be a pony or two in that room.

ptuomov

If you want to get faster quickly, bolt on a supercharger kit to your car while you think about your next move.

Turboing the 928 is going to require non-factory exhaust manifolds if you don't want to modify the frame. Frame modification is not a small project either, some would argue even bigger than two exhaust manifolds...

Pfc. Parts

I do understand this. The few turbo builds I've seen so far put them far away from the heads, most just in front of where the cats would be. There is some room down there.

Pfc. Parts

Good advice. I've seen several turbo 928s that didn't require frame mods but did require a custom exhaust and intake. Thanks, this was a very useful reality check.