Vilhuer

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EB338

Thanks! Sterling, if your reading this, what made you choose to modify your heads rather than retrofit the 968 heads to your engine in their entirety?

EB338

Ok, now I have done some reading through the archives, and I will be doing more, thanks guys. But this reading has lead me to a couple extra questions.


Greg Gray: just to clarify, when you talk about different valve spacing on 944 heads do you mean the valves are physically located differently within the head or are you referring to the different sequence and lobe spacing on their camshafts for 4 cyl use? If it is a physical casting difference in the heads themselves Is this valve spacing issue on all 944 heads 2 and 4 valve or just the 2v units? This would mean the 2v cam banks would be different as well to make for proper lifter positioning, correct? Do the 968 heads have the same issues with valve spacing?

What about port and combustion chamber sizes in 968 heads? Are there different 968 heads to choose from? What is the biggest bore diameter that 968 heads can accept? I know we have discussed cylinder head design being a limiting factor in bore diameter but no one has really stated what that limit is, is this issue any different on 968 heads?

Has anyone here done the 968 head on 928 block mod? What exactly is the timing belt tentioner issue Sterling pointed out? Are you into fabrication of a custom tentioner or do you just have to use the 968 unit?

Also I am not sure I understand the exhaust cam tower not being long enough for the covers to fit if your going to have to use 968 covers for the vari setup anyway.

Are the intake ports in different locations or simply larger thus preventing the use of the factory intake manifold? Is this issue carried over to the exhaust side making "off the shelf" 928 headers useless?

How much porting will the 968 heads take?

I do realize the cams need to be different both because of the gear teeth for the vario as well as the 8cyl lobe orientation. On a project of this complexity I think custom camshafts are really a necessity anyway.

Does anyone have a detailed "map" of the vario cams action on the 968? what advance at what rpm, etc. What are its limits, how much advance/retard? Does it advance and retard or only advance? And the system only works the intake cam, correct? The exhaust cam is the driven cam so the only variance there would have to be an adjustment to the belt drive sprocket or am I wrong here?

EB338

Sterling:

Why exactly wont the 32v intake bolt up? Are the ports in different locations or are they simply larger? I would agree a ITB setup would be the way to go but I am just trying to learn the real differences in the heads themselves.

The cam tentioner mounting point issue and the 968 tentioners not working with S4 cams would all be solved with custom camshafts? You are referring to the tentioners for the chain that ties the cams together (the vario part itself in the 968) and not the timing belt tentioner, right?

You mean that the head which would be sitting reversed from its position on the 968 engine has the exhaust cam end farther from the front of the block from the other? And when the cam is installed to be driven from that end it will stick 2"+ beyond the head? Other than that the timing belt system does work? I thought I had read in another thread you posted in that the tentioner would have to be different? Or did I misread that as this unsupported camshaft end issue? Also I believe I read in that post something about the covers not fitting properly because of this, were you referring to the timing belt covers? Surely some sort of support could be fabricated to solve this unsupported cam end issue.

What is the functional range of the vario cam system? Does it advance and retard or strictly advance? How far can it advange/retrd the cam timing?

EB338

Is the Vario cam timing an on/off function (full advance or full retard) or is it variable within its operation range?

slate blue

O.K what I found in relation to this issue with valve spacing was the valves have widewr spacing between them, that means that the cam boxes also have different spacing so as to match the location of the valves. Bob Devore for who I have great respect, did this development work and he said that this setup had better flow characteristics than the 928 head which has the valves closer together.

Now one of the reason it may have flowed better in his situation was that he had a bigger bore to work with than me, he had 4.115" I have a 4.060" so if his valves were wider spaced there is potentially less reversion. I don't know what cams he had but it he had 0.600" and his portwork was equal to mine he would have heads capable of flowing in excess of 600hp. This for people who aren't right up on flow figures means these 928 2 valve heads are a match for most of the best aftermarket cnc'd chevy heads. His claim for his 6.2 liter was slightly more than 580hp which is very believable.

I don't think it is worthwhile to use 944 heads for two main reasons, you need a really big bore size, this leads to trouble with the blocks as far as thicknesses are concerned. Bob did his a different way which is now no longer used. Second you need custom cams. If I was going to use custom cams I would put that custom grind to better use like changing the lift and LSA. My cams have a 0.550" lift on the intake and 0.505" on the exhaust. The more lift you can get with these heads the flow figures go crazy. Massive power is possible. Remember higher lift means less spring life as a general rule. I believe I have a happy medium. I am using beehive springs which are lighter and along with lighter valves, at around 75 grams each means my spring pressures are pretty low and thus less stressful on the whole valvetrain and timing belt.

With the lift I have, my heads are capable of 580 hp. If I come out over 500 hp that will be a big success, remember the 2V engine is a simpler engine and it is lighter by 25 kgs. It will also means that many off the shelf componants can be used in this engine as apposed to the 4 valver for which there is very few. Once this engine is built I would like to see others built to bring down the cost , but I suspect that the supercharger crowd has more support.

Cheers Greg.

Nasty 928

Early 924's(not 924s) have alot of interchangeability with old audi vw trucks vans..., but the 924 parts are crappy, expsensive, and well the 924 is slow not to mention worthless.

EB338

So am I correct in assuming the 944 head has a larger combustion chamber to accommodate this wider valve spacing? Your flow numbers are based on highly ported EuroS big valve heads not us heads, right? and the 944 head is closer to the Euro than the us 928 head.

slate blue

You are correct as the 944 had a 100 mm bore vs the 95 mm that the 928 started out with. The one thing that clouds the issue is the shrouding of the valves by the walls. This is where a bigger bore would come in handy. Albeit 4.060'' is a big bore already and in F1 100 mm or a bit under 1 inch is about the limit due to efficiencies (read peak effiencies)in the combustion chamber.

If we had some more info on Bob's engines and what happened to them I think we could draw more accurate conclusions. I know a fellow out here (Oz) who made his own blocks, he is a pattern maker by trade. You would use a different aluminium, the same as used by Chevy so that you could successfully sleeve the block with a steel sleeve to get by that problem of the Alusil expansion rate. Remember Bob used wet sleeves and had a lot of trouble in doing it BTW. (read lots of money)

As to making the stroke longer I don't think this is possible past what the strokers are now. I.e 95.25mm or 3.75'' this is due to deck heights, please post the deck height of a LS7 if you have it, the 928 is 232 mm or 9.134'' If you did the rod to stroke ratio would get even worse and tolerances would have to be supertight to stop popping pistons out of the block believe.

I think you can just make the engine more efficient to gain the power. Also you don't want too much torque otherwise you will just destroy the driveline, I would be looking at weight reduction rather than more power once you get to these lofty levels. I think that will give you most bang for buck, as your dollars will start giving much smaller returns after you go past what I intend doing. If my goals are reached I will have exceeded the LS7 anyway with an engine that is less likely to break things as it has less torque down low and more revs which spread loads better.

Pleasure sharing this info with you.

Greg

FBIII

Aren't the valves in the Euro S fairly widely spaced? It seems as if there is quite a lot of meat left between the valves. Even in the stock configuration they appear awfully close to the outside of the combustion chamber. On your heads with the oversized intakes, how close are the intakes and exhausts valves from touching? It seems you have an interesting trade off here. Separate them more and you increase the shrowding problem. The largest intake valves I can remember in a small block engine were in the Boss 302's. I'm really testing my memory here but I think they were in the neighborhood of 2.19 inches. In fact the first Boss 302's ran a larger intake valve than was in later high performance Cleveland engines. The only other small block engine that I can think of that runs an intake on the order of what you are doing is the is the two valve Aston Martin V8. They run huge valves for an engine of only 326 cu in.

slate blue

You are correct on all counts, the size of the valves I have managed to fit are 2.080" intake and 1.65" exhaust. Yes they come close but are perfect for the chamber. I just still have to check they clear the bore. On the clevelands they sometime notch the bore for clearance when using high lift cams. So if you were to use the same size pistons as mine it would be a total waste of effort and counter productive to use 944 heads.

As for 2.19" valves in the Boss 302 yes that is big, most Nascar engines are using 2.18" The Cleveland especially the 4V engines have a problem with their ports being so large that they don't have much velocity. It is the total opposite with our 2 valvers, they have very high velocity ports. This should make for good drivability despite the 284 degree cams.

Cheers Greg

Vilhuer

968 heads seem to have few more differences compared to other 4V heads than I thought. Still it should be possible to install them on 928 block. Probably better start with late 928 heads though.

slate blue

If you decide to go for a 4 valve head, I have Gt heads upgraded to GTS spec and a fully ported GT manifold that is a work of art, well almost, I could have the heads ported here at a cheaper price than what you pay in the states. I also have some nice cams to go with those heads.

Cheers Greg.

EB338

So are the Euro S heads different valve spacing than the us heads? When looking for heads do i neeed the cam banks too or can I use my us ones?

slate blue

Your U.S ones should be fine. the part/casting no. I have on mine is 928 105 251 1R both sets have the same nos. I can get you a set of euro heads or you could just buy my euro valves. I just had a set of euro heads lightly worked over,(minor port work) brand new guides head skimmed to give 11 to 1 Cost me $850 AUD. They will now flow 485 hp versus standard at 435 hp. These figures were taken at 0.500" lift. Cheers Greg.