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Discussion Forum

Any suggestions on polishing and porting G head?

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Kurt

04-14-2002 15:06:28




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Was wondering how other people did their head on a John Deere "G". And should the manifold be done also.




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lynn

04-14-2002 17:33:32




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 Re: Any suggestions on polishing and porting G head? in reply to Kurt, 04-14-2002 15:06:28  
Kurt..jerrys in wichita does a fine job of putting in larger valves and porting and sells new manifold with large passages very large..if you have a flat head would recommend one of his new heads as the flat heads have problems holding high compression..lynn



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Gman

04-14-2002 16:51:04




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 Re: Any suggestions on polishing and porting G head? in reply to Kurt, 04-14-2002 15:06:28  
Kurt there is a lot of different opinions on this subject of polishing the head and intake ports on a low rpm engine. One thing I know for sure were the intake runner and head mate up they should mate up with no offset,and be smooth,mine isn't polished but its smooth. Use the biggest valve the head will accommadate mine are 2 7/8ths,and 3" or better exhaust,good luck and keep on "G"ing Gman



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JDGnut

04-15-2002 09:22:37




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 Re: Re: Any suggestions on polishing and porting G head? in reply to Gman, 04-14-2002 16:51:04  
I'm not sure which head you are working on Styled head?? or a flat head. Lynn is right Jerry's does a good job, I sure like my flat head, but it is a little big for the tractor I have been running it on, but it sure runs good. One other thing to look at on the Styled G head, is the material around the valve, inside the chamber. If you look at a flathead the valve is open 360degrees around the valve. On the styled headed half of the valve is shrouded, by the eyebrow. When the valve is open, the clearance between the valve and the casting on 50% of the valve is only about 1/16th.. maybe less. You can remove some material off the casting to allow the valve to breath easier.. Remember you are cutting off inside the camber so you will want both side to be equal.. Also put an old valve in to save the valve seat, from the cutter.. and watch out for the water jacket.. haha.. Good luck
JDGnut

Added.. try a Brake hone in the intake port on the head.. it won't cut much, but will make is smooth..

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lynn

04-15-2002 18:08:30




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 Re: Re: Re: Any suggestions on polishing and porting G head? in reply to JDGnut, 04-15-2002 09:22:37  
JDGnut..worked on serveral styled and unstyled a and g ..i agree with you that the eyebrow head restricts air flow around the valves..good idea about removing it to get better airflow..lynn



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G Taylor

04-16-2002 15:27:52




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 Re: Re: Re: Re: Any suggestions on polishing and porting G head? in reply to lynn, 04-15-2002 18:08:30  
The swirl induced by the eyebrow will contribute to power especially when lugging due to improved air/fuel mixing and flame travel that resists detonation. Testing on a flow bench is the only way to know how much the eyebrow impedes flow. Most restriction is at the valve/seat area.



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