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Ok I am going to rebuild a early 72 head and put it on my late 240 73 Motor, and I beleive it was Jeff who said that the late 73 240 engine had slightly domed Pistons, can anyone confirm this?? Jeff also stated that the early e-88 on a late 73 motor would raise the compression to about 9.5:1 is that correct? If that is correct what kind of HP gain will that give me from my 8.8 or 8.9 compression ratio. Is their anything I can do to raise the compression in my car with out spending spending too much or using the parts I have already??

Dustin Morris
 

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Compression Ratio Answers??

> Ok I am going to rebuild a early 72 head and
> put it on my late 240 73 Motor, and I
> beleive it was Jeff who said that the late
> 73 240 engine had slightly domed Pistons,
> can anyone confirm this??
NEVER HEARD OF STOCK DOMED 240Z (83mm) PISTONS. THEY WERE ALL FLAT TOPS FROM WHAT I UNDERSTAND.

Jeff also stated
> that the early e-88 on a late 73 motor would
> raise the compression to about 9.5:1 is that
> correct?
GET SOME FACTS FIRST. ASK WHAT COMBUSTION CHAMBER CC HE IS USING TO CALCULATE HIS CR. A STOCK E88 HEAD IS 44.7cc. THE 'EARLY' HEADS ARE SUPPOSED TO BE SLIGHTLY DIFFERENT COMBUSTION CHAMBER SHAPE, ALTHOUGH I DOUBT THE CC'S ARE THAT DIFFERENT. MAYBE UP TO 1-2cc DIFFERENCE.
JUST FOR GRINS, CR IS CALCULATED WITH THE FOLLOWING FORMULA:

CYL. VOLUME = PI/4 X BORE2 (CM) X STROKE (CM)
FOR A 2.8L = .7853982 X 8.6 SQUARED X 7.9 = 458.9cc

CHAMBER VOLUME = HEAD CC + GASKET CC + DISH CC(- DOME CC)

COMPRESSION RATIO = CYL. VOLUME + CHAMB VOL./CYL. VOLUME

If that is correct what kind of HP
> gain will that give me from my 8.8 or 8.9
> compression ratio.
I WOULD GUESS MAYBE 5-10HP AT MOST. THIS DEPENDS ON YOUR PARTICULAR SETUP, AS THERE IS NO DIRECT WAY TO MEASURE C.R. TO HP.

Is their anything I can
> do to raise the compression in my car with
> out spending spending too much or using the
> parts I have already??
YOU CAN SHAVE THE HEAD, OR INSTALL A HEAD WITH SMALLER COMBUSTION CHAMBER TO BEGIN WITH. ALSO THE 1mm HKS HEAD GASKET IS SLIGHTLY THINNER THAN THE STOCK (1.25mm) GASKET.

> Dustin Morris
 

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> Ok I am going to rebuild a early 72 head and
> put it on my late 240 73 Motor, and I
> beleive it was Jeff who said that the late
> 73 240 engine had slightly domed Pistons,
> can anyone confirm this?? Jeff also stated
> that the early e-88 on a late 73 motor would
> raise the compression to about 9.5:1 is that
> correct? If that is correct what kind of HP
> gain will that give me from my 8.8 or 8.9
> compression ratio. Is their anything I can
> do to raise the compression in my car with
> out spending spending too much or using the
> parts I have already??

> Dustin Morris
Motorsports Auto sells high performance cast pistons for the 240Z and 260Z. These pistons are the exact same ones that came with the '73 240Z motor. I think I miss lead you with the dome part, they have a raised compression height (which displaces about 3cc's over the early 240's and all 260's style pistons) kind of like a slight dome effect. As for the heads, the difference in combustion chamber cc's from a '72 E88 to a '73 E88 is about 3cc's (I think its a little more but I don't have my chart with me).
With just the stock 83mm bore (I would get the motor bored when installing new pistons) the high perf or '73 pistons will give you about 9:1 compression ratio with a stock unshaven, untouched '72 E88. If you bore the motor out to 84mm with all the same parts (but use 84mm '73 pistons of course) you'll get (as I mentioned) 9.5:1 compression ratio. A word of wisdom, if you get the motor bored try and take it to a place that uses a torque plate (this will make the motor live longer and the rings sit better).
 
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