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porting/polishing


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Guest mescalinedreamz

i only had one reply,,the guy though gave me pictures of rebello street port on a n42 head here are the pics http://mywebpages.comcast.net/datsundoug/ it has helped me a little,but your best bet is to make a flow bench,,unshroud the valves,,smooth the transition from the valve seats to the inner side of the port,dont jump into this,,dont enlarge the ports,,anything you do can decrease horsepower easily,,i said decrease,,when you think you might be doing something good,,the only way to find out is a flowbench,,

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Try to find some books on other cylinder heads, and check out some older issues of grassroots motorsports. They might not be datsun specific, but the principles are the same.

 

I can't remember offhand if "How to modify your datsun/nissan OHC engine" had any info... anyone recall? If not, the book is good and well worth the money, so you might check it out anyway.

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Guest mescalinedreamz

and it dont tell sh@t it sucks,,i couldnt wait to get that book in the mail and now that i have it i want to sell it,,it doesnt help at all

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Guest mescalinedreamz

of good places,,we have only one out here,,i started porting my head before i read about the damage i could do,,so i bought a manometer off ebay to do some flow testing of my own,,hopefully i can figure it all out since i have no money to send the head out

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I cc'd my head and polished the combustion chambers and did a little port work myself. It is not that hard. And the How to Modify book helped me A LOT. First thing I did was lay the head gasket down on the head and trace out the pattern. Then I unshrouded the valves to the fire ring line. When I had all of these done, I took a piece of Lexan and cut it so that it fit over one combustion chamber. I drilled a hole in the Lexan, then filled the chamber with water from a graduated cylinder. I did have to drill some vent holes with a pin drill to get the air out of the chambers. I kept grinding away on the chambers one by one until I got all of the chambers within .5 cc.

 

I even went further and notched the block to match the head so that there was as much open space around the side of the valve for air/fuel to get by as possible.

 

As far as ports are concerned, I did a lot of smoothing on the short side radius with my finger and a piece of sandpaper, but the bowls and the runners were already pretty good, since they had been worked on previously, so I cant give you too much there.

 

So you're not flow testing. At least you know that the chambers are the right size and shape, and that you've removed all of the sharp edges in there. Datsun ports are pretty good anyhow. I would match the gasket to the head and the manifolds, clean up the big errors in the casting of the runners, then work on the chambers.

 

Jon Mortensen

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its all about saving money

 

Oh, okay. As long as it isn't about making horsepower, then it would be the classic "cheap horsepower" paradox.

 

What Jon said will probably help and can't hurt, unlike a full blown kitchen table port & polish. Do what he said and you'll be fine.

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