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Tractor Pulling Discussion Forum

H bore

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05-31-2005 21:27:09

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Building an H 5.5 stroke how big can I bore a stock H block or does anybody know the cyl wall thickness with out the selve don't want to buy a 350 block Thanks

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06-01-2005 06:41:32

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 Re: H bore in reply to IRISH RED, 05-31-2005 21:27:09  
Red, Block limits and still have meat left over to run, is 3-13/16. please note, that most H blocks rust from, the outside in, and surely, one cyl will have a pit dimple somewhere in the block bore, simply have the machinist install a repair sleeve, hard block it up to the bottom of the water plate. My H block checked out for the thinnest spot was .180, thickest was .225 at 3-13/16. Use 806 gas pistons, remachine them to fit with a shoehorn in the head, and youll have a good engine with high compression. Or, if you dont want to use 13/16 piston, use a 3-3/4 from the 706 291 gasser same compression height as the 806, just a smaller bore. It cost me right at 200$ to build my new H block for Something wilder,,, with one repair sleeve. ChadS

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06-01-2005 09:01:29

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 Re: H bore in reply to ChadS, 06-01-2005 06:41:32  
Hey Chad - What's the measurement for compression height on the 291 piston?

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06-02-2005 06:39:24

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 Re: H bore in reply to Augie, 06-01-2005 09:01:29  
All IH gassers, with the exception of the 460 C-221,,, The C-263,291 and 301 has a compression height of 2.02. H's have a stock height of 2.5. When you use the firecrater pistons, you put them in with the arrow pointing forwards to the front of the block. That puts the dome on the spark plug side of the engine. This makes a nice dome to fit inside the compression chamber with a bit of machining to the piston head for clearence. The crater, will go under the flat part of the head. .625 will be the offset of the crank, for a total of 1.25 stroker. (5.5 inch) Now since the 6 cyl piston has a compression height of 2.02, If my math is correct, the piston should now stick out of the top of the block .290 with the wrist pin dead center. Note,,, if that seems like alot sticking up, you can offset the wrist pin bushing, .180,, so it will stick out of the block .110. Machine off the excess, either mill them off flat, or be creative and build a dome from whats left over. I ended up using stock firecraters from a gasser 806, in My 270 H engine, I thought to myself,, thats an awful deep crater in that piston,, I made a mock piston yester day to fit properly in my 5-3/4 stroker, and I was amazed!! I built the dome in the head, enough to compensate for the crater in the piston. I think, that it will still create the same amount of compression, if not just a tad more than what I origianly run in the first 270 engine I had built years before. Please double check my math,, cause I may be missing something in the measurements, I did it off the top of my memory, and I havent had my coffee yet this morning!! LOL!! at 3-3/4, X5.5, if you get 250 psi, you could be looking at 80 hp if tuned correctly. You will be grinding down the rods, inbetween the lobes of the cam, the oil gallery, and in the block sides. Hope this helps you guys out! ChadS

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06-02-2005 09:14:45

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 Re: H bore in reply to ChadS, 06-02-2005 06:39:24  
Thanks for the info.

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