[Jim]

I have a new N47 head and a used '83 block and crank. I would like to prepare the block and crank to accept my new N47 head. Are there any changes other than putting dished pistons onto this block that I should know about? Is the crank in the '83 block the same as the'77 that the head is from? I know that the compression would be too high if I bolted the N47 to the flat-top piston block. So now that I have installed dished pistons into this block (hypathetically speaking)what can I do to just slightly raise the compression? Any other tips to help me would be much appreciated. Are there any other problems I may run into?

 

[Ian]

First of all, why would you want to use the dished pistons? With the flattops and the N47, the cr will be less than 9.5 to 1. This is what Nissan should have done!!! Well, they had to contend w/somg laws. ****!!!

The '83 block you have is identical to the '77 block, except for the flattops and some sturctural changes in the block's casting. There will be no modification needed to put the N47 head on this block. If I were you, I would bolt the two together and reap the benefits of the slightly higher cr. If you use the dished pistons, the cr will be a lowly 8.3:1. Thats great if you were going to turbo it. If not, use the flattops. Plus, you won't have to go through that hassle of tearing down a perfectly good shortblock.

Here is another reason to use the flattop pistons. The flattops will provide a better squish in the combustion chamber. This promotes better, cleaner, more complete combustion. You will also notice more power. The dish pistons will not be able to compete in this area. Also, the cr will not be so high that you won't be able to use pump gas in it. You may even be able to use 89 octane. I think you should reconsider and use the flattops. Have I made this clear???? Good Luck!!!!

Ian

 

[Jim]

> First of all, why would you want to use the
> dished pistons? With the flattops and the
> N47, the cr will be less than 9.5 to 1. This
> is what Nissan should have done!!! Well,
> they had to contend w/somg laws. ****!!!

> The '83 block you have is identical to the
> '77 block, except for the flattops and some
> sturctural changes in the block's casting.
> There will be no modification needed to put
> the N47 head on this block. If I were you, I
> would bolt the two together and reap the
> benefits of the slightly higher cr. If you
> use the dished pistons, the cr will be a
> lowly 8.3:1. Thats great if you were going
> to turbo it. If not, use the flattops. Plus,
> you won't have to go through that hassle of
> tearing down a perfectly good shortblock.

> Here is another reason to use the flattop
> pistons. The flattops will provide a better
> squish in the combustion
> chamber. This promotes better, cleaner, more
> complete combustion. You will also notice
> more power. The dish pistons will not be
> able to compete in this area. Also, the cr
> will not be so high that you won't be able
> to use pump gas in it. You may even be able
> to use 89 octane. I think you should
> reconsider and use the flattops. Have I made
> this clear???? Good Luck!!!!

> Ian
Thanks for the words of advice Ian.
From th beginning i wanted to use the flat tops,
And a page that i read it said compression would
be about 10.4 which im sure would cause pinging.
Im not even concerned with smog laws there are ways around that here in Chicago.But i am concerned with valve clearances when using
flat tops with the small chambered N47.After all i am very reeeev happy i would hate to have a problem with that.After reading your re i`m happy to tell you that you have influenced my decision
greatly.But i`m still going to tear down the
shortblock to rering,freeze plugs,bearings,and
to further my piece of mind i`m also having
everything professionaly balanced.Of course the flat tops too. Thanks again for your help
i will keep postin my progress.PLease feel free
to give any other tips i may need.
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