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Discussion Starter · #1 ·
Hey all,
I have a late 73 240Z. If I don't put 91 octane(even in the oil capitol we don't have 93 octane) in my car it Runs like ****!! It diesels and sputters and in general runs like ****. I have a slightly odd head block combo and I was once told on this board that I have 9.5:1 compression. Could you people help me compute the CR??

Late 73 Block with the Domed Pistons(it makes up for the late 73 head that has the slightly larger chambers)
Early 72 head (has smaller Chambers)
Nissan gasket 1mm I think.
What else do Need??

What kind of Compression would I get If I put an e-31 or N-42-7 on my late 73 block??

Please help me!!

Dustin
 

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> Hey all,
> I have a late 73 240Z. If I don't put 91
> octane(even in the oil capitol we don't have
> 93 octane) in my car it Runs like ****!! It
> diesels and sputters and in general runs
> like ****. I have a slightly odd head block
> combo and I was once told on this board that
> I have 9.5:1 compression. Could you people
> help me compute the CR??

> Late 73 Block with the Domed Pistons(it
> makes up for the late 73 head that has the
> slightly larger chambers)
> Early 72 head (has smaller Chambers)
> Nissan gasket 1mm I think.
> What else do Need??

> What kind of Compression would I get If I
> put an e-31 or N-42-7 on my late 73 block??

> Please help me!!

> Dustin
What is a domed piston ?All 240s have flattops If u have special pistons u need to find specs for them.Stock 240block w/EARLY E31gives 9.5:1 not all E31 are the same.Compression ratios use a formula Try the book Auto Math by HP Books
 

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Discussion Starter · #3 ·
Hey,
Wait I do have domed pistons (they have a small hump on the center) because it makes up for the slightly larger camber size of a late 73 head. Not much of adome just about 4 cubic cc but it does raise the compression of that early E-88. check out the Texas Z site and they have all that head info you will see what I mean.

Dustin
 

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Stay with what you have.

> Hey,
> Wait I do have domed pistons (they have a
> small hump on the center) because it makes
> up for the slightly larger camber size of a
> late 73 head. Not much of adome just about 4
> cubic cc but it does raise the compression
> of that early E-88. check out the Texas Z
> site and they have all that head info you
> will see what I mean.

> Dustin
Dustin,

Your stock block/head should be giving you 8.6:1. I have read that domed pistons raise compression about half a point. (Of course, this depends on the spec. of the particular piston) Thus, you shouldn't be too far north of 9:1. Even at 9.5:1 you should be running o.k. on 91 octane. With 93 (available everywhere in my area) you should be fine. According to the Texas Z Club, N42 and N47 heads have a volume of 44.6 (compared with 44.7 in the E88). Thus, these heads are no answer to your problem. I know that this may sound rather simple, and I'm sure you have already tried it, but why not back off the advance of the timing a bit? You really should not have a serious problem with the set up you have.
 
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