hacker-pschorr

Previous thread related to this project: https://rennlist.com/forums/928-forum/157893-how-many-different-16v-heads-and-or-cams-are-there.html

Looking at the 928 International website, these are the different valve sizes:

78 - 84 intake & exhaust = Euro 78-79, All US
80 - 85 intake & exhaust = all Euro


Eventhough the casting numbers on the 78-79(all) 80-82(US) 83-84(US) are different, they are bascially the same head - the different casting numbers were used with different cams.

Per Mark A:
Heads
78-79 casting #345 single valve spring
80-82 casting #346 double valve spring
83-84 casting #356 "
80-86 casting #348 " larger valves and ports

Combustion area:

Has anyone measured the combustion areas of the different heads? The Euro heads are known to offer a high compression ratio vs the US heads.
Is the combustion area on the 78-79 heads the same as the 80-82 & 83-84 US heads?
Is the combustion area on the 80-82 & 83-84 US the same?


Port Size:

What are the different Port sizes betweent the different casting numbers?

BC

I have the cc's of the 81ish heads, which I believe are the same as 78s and 79s.

I have no notes here, but I think its 55.4ccs. That, with the CC's of the piston (kind of negative, as they are protruding crown 10:1 euro pistons) makes it a 10.14 CR engine cold.

hacker-pschorr

Since the bore and stroke on the 4.5 motors is 95 x 78.9 that is 7,495.5mm total volume per piston, right?

What is the formula for figuring out CR, is there any more data needed other than bore, stroke, and head volume? This is assuming the piston is perfectly flat (I know that is not realisitc on all motors, I'm just trying to undertand the math here.)

BC

Well, as a matter of fact, I believe I also needed the hieght of the head gasket when "squished" if you will, as well as the info on how far the piston comes out of the bore. In my case, the outside edge was 2 thousands. (.002) or a little more.

Then when CCing you'll want to figure in the spark plug, as in my mind it does fill in the chamber a bit.

hacker-pschorr

I understand the head gasket, piston height, spark plug come into play. I'm just trying to figure out the basic formula.

Lets Assume:
1. There is no head gasket (the indy motor was welded)
2. Piston is 100% flat with the top of the block when at TDC
3. There is no spark plug (could be diesel)
4. Nothing else taking up space in the combustion chamber.

SharkSkin

Using this quick calculator with the bore radius & stroke in cm I get 559.26 cc swept volume per cylinder. So, static compression ratio would be:

559.26/H : 1

Where H is the head volume in ccs. So if the head volume in ccs is 55.9, the static CR would be 10:1.

sublimate

Dave, was that ':' a typo?
I think the formula should be (559.26/H) + 1

SharkSkin

It wasn't a typo, but my formula was wrong. What I was trying to say is that for the number on the left side of the ratio, e.g. X:1 you would find X as follows:

H=Combustion chamber volume in ccs
S=Swept volume(derived from bore & stroke)

X=(H+S)/H

Using the 55.4 combustion chamber volume and Hacker's 95 & 78.9 Bore & Stroke above, we get:

X=(559.26+55.4)/55.4
X=614.66/55.4
X=11.09

So that would be X:1 or 11.09:1 static compression ratio.

Seems a bit high, but I think the combustion chamber volume must be a bit more than 55cc.

hacker-pschorr

Ok, the formula is secondary to the first original questions.

Does anybody know the combustion chamber volume's of the different 16V heads & the valve size?

sublimate

Yeah, that looks better. You can divide H into (H+S) and simplify to:

X = 1 + S/H

which is what I wrote.

jpitman2

To get unswept volume, use U= swept/(CR-1). eg for a 4.7L (4664 or 583 each hole), 10:1CR,
Unswept = 583/9= 64.78cc. Note that this is Unswept volume, not necessarily same as chamber volume. With non flat piston crowns, you would need to cc the chamber, and add/subtract hollow crown/protruding crown volume. I dont know about 928s, but many makers change piston crown to change CR - easier than changing head castings.
HTH
jp 83 Euro S AT 48k

SharkSkin

I see... You're right of course, I just didn't think it through. Also, I seem to be a bit math challenged ATM. I goofed the numbers above, and have now corrected them.

hacker-pschorr

So back to the combustion chamber sizes on the different heads - anyone?

C'mon, a few of the 5.0 hybrid owners must have looked into this before.

mark kibort

the 82 US heads were 53ccs and so were my old 84 US heads.

the 82 euro heads cc'ed out to 48, and it was pretty hard not to get this number.

port size on the euro vs US was 1.5 vs 1.6" across. valves were 2mm smaller. piston cuts were reflective of the proper valve size. 43 vs 45mm intake valves.

Mk

918-S

I just tore down my 1980 "S" motor. I'll read through this and see if I can help fill in some of the gaps. This is a new motor to me. I'm much more accustom to BMW's and Big Block Chevy's. So I have a little learning curve I'm working on.