Bobtail,
I think its difficult to compare both engines. Holzapfels engine used a WBX or as I believe oxyboxer as it is called here, as a basis. His engine was used to race on a circuit; yours I believe is to drag race. His heads were a one-of OHC heads, specially designed for that engine, not 911 parts.
Its a very impressive job you have done though, especially for the relatively low costs involved.
Shad,
I am very pleased to hear your expert opinion on the parts, despite the 'bad' news. I was kind of hoping/afraid you would respond to my experiment.
I totally agree with Richard that this is of course by no means a replacement in any way of the fine piece of engineering you have pulled of with your specially designed Nickies set, period. If the experiment threatens to costs more than a normal set of p+c, its stops there.
The good news is that the measurements really don't differ that much:
Stud spacing from opposite studs (accuracy little difficult):
type 4: 124,5 mm
911 100 mm Nikasil cylinder stud hole spacing: 127,5 mm, so the cylinders have to be drilled 1,5 mm closer towards the bore center, but that should be easy/still safe.
Type 4 case opening with case cleared for 103 mm p+c: 107 mm inner diameter.
911 cylinder bottom outer diameter: 107 mm !!
The case will therefore have to be opened up a tiny bit more (108 mm or so)
Type 4 head opening, machined for 103 mm p+c: don't have one of these yet, but that will probably be appr. 115 - 116 mm.
911 cylinder outer diameter at top (head location): 113 mm (6,5 mm wall thickness), so this can be made to fit as well.
The part of the top of the cylinder that goes into the head is too small on the porsche cylinder, but it could be machined down, so the cylinder would go all the way into the head.
Type 4 cylinder length (original 94 mm 914 GB engine): 92 mm . This is measured from the mating surfaces of the head to case - distance.
911 cylinder : 83 mm
So the cylinder is indeed very short looking only at the mating surfaces, but total cylinder length is 120 mm, all Nikasil plated and the wall thichness at the very bottom of the alu cylinder is still 4 mm. A cylinder spacer may just solve that problem and could also be used to counter the different piston heigth of the 911 piston.
Type 4 piston pin diameter is 24 mm
911 pin diameter is 23 mm.
Well, if 22 mm bushings can be installed in a stock 2 ltr rod, so can a 23 mm bushing imo.
Just leaves the piston top issue, which is rather domed indeed. This would require a trial install on an engine to determine at what heigth the valve will just clear the dome, so what heigth spacer to use and what compression ratio would still be left. Or I could maybe buy a new set of JE 100 mm forged pistons, since the Nikasil cylinders have not a mark on them and the bores can be cleaned as was showed to us in one of the former threads of Pillow. Locating a set of 911 turbo pistons which have flat, and probably forged, pistons (thanks Richard for pointing that out) will be very hard, I think, but still also a possibility (I only need 4 good ones, not 6).
Cooling fins on these cylinders is very limited and will leave therefore indeed an opening between them when installed on a type 4 case, but if a small insert of some form, would be fitted between the cylinders and attached to the case, I would doubt if cooling would be a problem with the Nickies.
I did't realize the original Porsche pistons were cast though. Pity. Turbocharging them is therefore not a good idea, I agree. But hey, with 100 mm bore and 71 mm stroke, I would still have a N/A 2230 cc T4 engine with nickies!
All in all, I can even more understand Shads love for nikasil cylinders, as this nikasil set is excellent technology and thrills me! As for now, I will proceed with it (slowly) and keep you posted on the forum if even only one of you is still interested in this route.
Walter
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