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Over bore vs high altitude

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Bob

04-03-2002 13:46:39




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I am pondering whether to use overbore pistons (3 1/8 " instead of 3") or high altitude ones in my B rebuild. Any thoughts on which will net more horsepower would be appreciated.




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gene b

04-03-2002 17:36:42




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 Re: over bore vs high altitude in reply to Bob, 04-03-2002 13:46:39  
go with the 1/8 over and hi-dome you will have 123ci.in. and 23 h.p. when you are done makes quite a difference if you want to machine the sleeves you can go to 3 1/4 bore



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Steven@nd

04-03-2002 15:15:53




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 Re: over bore vs high altitude in reply to Bob, 04-03-2002 13:46:39  
Most rebuild kits come with the option for step-head pistons, along with the overbore. For my 42 H, the step head was $10 more than flat top pistons. I couldn't find any sources for rebuild kits using standard bore pistons, unless going NOS.

Do both, these tractors were designed for 70 octane fuel, we now have 87 octane minimum.

Steven



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john d

04-03-2002 14:01:47




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 Re: over bore vs high altitude in reply to Bob, 04-03-2002 13:46:39  
Probably not a lot of difference. If your tractor was a "distillate" model that started on gasoline and then switched to distillate, you have a low-compression head. If that's the case, the high altitude pistons will simply put you at about normal compression for a gas engine.

You won't gain gobs of horsepower with either one by itself, but together you could get a very noticeable increase! There's no substitute for cubic inches when the tractor starts to lug under a heavy load. I'd say that if you're only going to do one of them, do the overbore kit. If I was into that many $$ on it, I'd do both.

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Salvage Man

04-03-2002 22:00:55




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 Re: Re: over bore vs high altitude in reply to john d, 04-03-2002 14:01:47  
On the B farmall the pistons were different between the gas and fuel tractors. There used the same head.



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john d

04-04-2002 05:52:54




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 Re: Re: Re: over bore vs high altitude in reply to Salvage Man, 04-03-2002 22:00:55  
Thanks for the info! I didn't know that. Just another example of how valuable these boards are for sharing details!



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