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Tractor Pulling Discussion Forum

G model JD is 421.5 cubes stock

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johndeere_john

01-12-2004 09:22:17




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Boring to .125 over gains 17 cubic in, or to 429.5, how much horse power increase can you expect?

Jon




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a puller

01-12-2004 16:07:53




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 Re: G model JD is 421.5 cubes stock in reply to johndeere_john, 01-12-2004 09:22:17  
A G John Deere is 413 cubes stock, and with .125 alum. it is 430 cubes.....We have one with a flathead and .090 pistons with 68hp.



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toot

01-12-2004 14:02:54




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 Re: G model JD is 421.5 cubes stock in reply to johndeere_john, 01-12-2004 09:22:17  
if you're going from cast iron flat tops to the higher compression aluminum pistons, shave the head .250 and properly tune it, horsepower will be 50-55 range. Been there done that with a dyno.



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buickanddeere

01-12-2004 11:32:33




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 Re: G model JD is 421.5 cubes stock in reply to johndeere_john, 01-12-2004 09:22:17  
A whole 1.5 HP or 4% more at most figuring the stock and the over bore seal the same. The intake system will not quit keep up with the extra airflow so 1.5HP is optimistic.



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yeah, but

01-12-2004 13:48:04




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 Re: Re: G model JD is 421.5 cubes stock in reply to buickanddeere, 01-12-2004 11:32:33  
if that's going from regular to gas pistons you're gaining compression there too. Most people say about a 5 hp gain.



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buickanddeere

01-12-2004 17:16:19




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 Re: Re: Re: G model JD is 421.5 cubes stock in reply to yeah, but, 01-12-2004 13:48:04  
He didn't say anything about mods other than increasing the bore. If doing other mods just machine the bore the minimun to get round holes, rather than going 125 over standard. A power block is required to gain serious HP from an overbore and stroking. The stock 4 to 1 compression of a G puts most of the gasoline fuel energy up the stack. If the fuel will pour and burn, a stock G will run on it. After all that's what Mother Deere intended back in the 30's. Valves, valve bowls and cam need work to improve breathing.

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johndeere_john

01-12-2004 13:07:38




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 Re: Re: G model JD is 421.5 cubes stock in reply to buickanddeere, 01-12-2004 11:32:33  
I also plan on converting the oil bath air cleaner to a dry filter insert, this will proably get me more than the over bore.

Jon



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Tyler Neff

01-12-2004 20:33:56




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 Re: Re: Re: G model JD is 421.5 cubes stock in reply to johndeere_john, 01-12-2004 13:07:38  
I built a G years ago that was .125 over . I also planed the head .125 and the front and back of the block .125 . I dont really remember what kind of compression it had. Other than that I did nothing and had around 62hp.It just depend on what you wanna do with it plow or pull?



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