P51 head 557 build questions

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P51 head 557 build questions

Post  FORDMUD on January 6th 2017, 9:47 pm

I've been collecting parts for years. Traded a dude from here a kx250 about 8 years ago for the heads. Bought the rotating assy from him, sold it several years ago and have now bought it back. I've got a mafia intake, qf1250, a dove a block and some 4bolt caps. Planning to make 900 and ocasionally spray up to 400 through a plate. May end up with a fogger at some point.

Few questions..
will a 2000 bolt be Ok In a scat hbeam?
what would be the minimum wrist pin? I have the standard .16x that come in diamond shelf pistons.
Rings are 1/16 whats a good ring for this application?
3/8 thick wall or 7/16 pushrods?

I run thin mud and dirt drag 200'
Plan to spin it to 7k-ish
Im sure I'm forgetting a few other questions.
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Re: P51 head 557 build questions

Post  csdrag on January 7th 2017, 5:15 pm

I learned a long time ago working in conjunction with jesel that you put the biggest pushrod you can fit in. Diameter resists deflecting better than added wall thickness. Have proven this many times. Now I don't know what kind of cam your running but if your making 900 it has at least respectable lift. Power is going to give theexhaust even more cylinder pressure to open against. I don't see any downside to a larger push rid if it will fit. For whatever that's worth to you.
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Re: P51 head 557 build questions

Post  Lem Evans on January 7th 2017, 5:34 pm

FORDMUD wrote:I've been collecting parts for years. Traded a dude from here a kx250 about 8 years ago for the heads. Bought the rotating assy from him, sold it several years ago and have now bought it back. I've got a mafia intake, qf1250, a dove a block and some 4bolt caps. Planning to make 900 and ocasionally spray up to 400 through a plate. May end up with a fogger at some point.

Few questions..
will a 2000 bolt be Ok In a scat hbeam?
what would be the minimum wrist pin? I have the standard .16x that come in diamond shelf pistons.
Rings are 1/16 whats a good ring for this application?
3/8 thick wall or 7/16 pushrods?

I run thin mud and dirt drag 200'
Plan to spin it to 7k-ish
Im sure I'm forgetting a few other questions.

At 7000ish the Scat 2000 deals should be fine.
If you are going to spray that much you'd be better off having the H13 tool steel pins.
The ring selection for that size bore is limited and I suspect the pistons are a 1/6"-3/16" spec so that's about what you've got. I'd run a better top ring with the spray too.
Like has been said, the bigger pushrods are better but, that will vary some what depending on how much valve spring you have.

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Re: P51 head 557 build questions

Post  FORDMUD on January 7th 2017, 6:31 pm

Cam is 272/283 .770/.730 on a 111. It's in my iron headed 528 right now. Springs were around 275/800. Im going to use parts from the 528 to save some money. But I'm thinking about going to 1.8 rocker in the p51 heads. I'll buy new springs.
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Re: P51 head 557 build questions

Post  Lem Evans on January 8th 2017, 12:34 am

FORDMUD wrote:Cam is 272/283 .770/.730 on a 111. It's in my iron headed 528 right now.  Springs were around 275/800. Im going to use parts from the 528 to save some money.  But I'm thinking about going to 1.8 rocker in the p51 heads. I'll buy new springs.

3/8" x .135" wall will be good.

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