p51 cumbustion chamber size

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p51 cumbustion chamber size

Post  wayney on October 15th 2016, 11:16 pm

how small can you get a p51 chamber down to? how much can you mill the heads without compromising the deck surface ?

thanks, wayne

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Re: p51 cumbustion chamber size

Post  Lem Evans on October 15th 2016, 11:17 pm

They are small as it is....where are you going with this?

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Re: p51 cumbustion chamber size

Post  wayney on October 15th 2016, 11:36 pm

boost in cr without getting into the short block.

wayne

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Re: p51 cumbustion chamber size

Post  cool40 on October 16th 2016, 1:15 am

Know your valve clearance before you get started cutting.
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Re: p51 cumbustion chamber size

Post  Lem Evans on October 16th 2016, 10:27 am

cool40 wrote:Know your valve clearance before you get started cutting.
Good point and a guy would need to correct the intake side of the head so the manifold would still fit correctly.

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Re: p51 cumbustion chamber size

Post  Lem Evans on October 16th 2016, 10:30 am

wayney wrote:boost in cr without getting into the short block.

wayne

I suspect .100" could be done. How many CC you need to get from the milling? .005"-.006" cut will reduce the chamber by 1 cc.

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Re: p51 cumbustion chamber size

Post  wayney on October 16th 2016, 10:30 pm

like to get the chambers down to 60cc. i am just thinking about winter changes, i don't feel that the motor makes the power i think it should and i know the compression is not where i would like it to be. I have been told that there is not much power to be gained in the heads to justify the cost of port work.

wayne

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Re: p51 cumbustion chamber size

Post  IDT-572 on October 17th 2016, 9:10 am

35 cfm @ 2.25 hp per cfm is right at 80 hp. that's what a good port job with a 2.300 valve is worth. But it's several $ too.

One pint of compression wont get you near that. Maybe 30 HP from 72 to 60 cc chamber.
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Re: p51 cumbustion chamber size

Post  rmcomprandy on October 17th 2016, 10:20 am

wayney wrote: I have been told that there is not much power to be gained in the heads to justify the cost of port work.

wayne

I guess that would entirely depend upon how much more power you are seeking versus how cheap you are.

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Re: p51 cumbustion chamber size

Post  IDT-572 on October 17th 2016, 10:26 am

rmcomprandy wrote:
wayney wrote: I have been told that there is not much power to be gained in the heads to justify the cost of port work.

wayne

I guess that would entirely depend upon how much more power you are seeking versus how cheap you are.


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Re: p51 cumbustion chamber size

Post  dfree383 on October 17th 2016, 11:43 am

I'd put a G in a set of Pistons before I jacked up a set of heads. Just saying.

Why ruin a good set of heads?
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Re: p51 cumbustion chamber size

Post  10.0 on October 17th 2016, 2:00 pm

If you mill a bunch on the heads, they will be less saleable and may have deck problems as well.
Might be opening a can of worms.

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Re: p51 cumbustion chamber size

Post  Lem Evans on October 17th 2016, 7:11 pm

10.0 wrote:If you mill a bunch on the heads, they will be less saleable and may have deck problems as well.
Might be opening a can of worms.

This statement is spot on.

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Re: p51 cumbustion chamber size

Post  wayney on October 17th 2016, 8:25 pm

Lem Evans wrote:
10.0 wrote:If you mill a bunch on the heads, they will be less saleable and may have deck problems as well.
Might be opening a can of worms.

This statement is spot on.


this is what i was wondering about. compromising the deck. wondering if anyone had done it .060-.080 in a higher pressure motor. high compression or middle of the road boost/ nitrous.
i am just thinking out loud. if i was going to go through the expense and time of piston replacement i would probably just build a new short block or motor.

wayne

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Re: p51 cumbustion chamber size

Post  Lem Evans on October 17th 2016, 8:29 pm

wayney wrote:
Lem Evans wrote:
10.0 wrote:If you mill a bunch on the heads, they will be less saleable and may have deck problems as well.
Might be opening a can of worms.

This statement is spot on.


this is what i was wondering about. compromising the deck. wondering if anyone had done it .060-.080 in a higher pressure motor. high compression or middle of the road boost/ nitrous.
i am just thinking out loud. if i was going to go through the expense and time of piston replacement i would probably just build a new short block or motor.

wayne

I looked back at some of your post......you have a big dish piston now as I see it?

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Re: p51 cumbustion chamber size

Post  wayney on October 17th 2016, 8:50 pm

IDT-572 wrote:35 cfm @ 2.25 hp per cfm is right at 80 hp. that's what a good port job with a 2.300 valve is worth. But it's several $ too.

One pint of compression wont get you near that. Maybe 30 HP from 72 to 60 cc chamber.  

don't take this the wrong way your car/ motor runs great and i know you know what you are doing.

if i could get them ported and pick up 50 to 80 hp i would definitely be interested . I know more cfm does not always add a given amount of HP. i have personally changed ported dove heads to ported aluminum cj heads on the same motor in the same car milling the alum heads to gain a point of CR and only picked up .5 mph after tuning. the cj heads flowed 50cfm more than the dove heads (on the same bench) at the dove head peak (.600 lift) and outflowed them across the board. the heads were the only thing changed. Has anyone on here done a A-B ported VS unported P51 head dyno test? The shop that i spoke to about porting the p51 heads is a very competent and respected engine shop . it was a simple question of " on a 521 is there much gain to be had from porting my p51 heads" answer was " a full competition port job would see 15hp and it is usually not money well spent" . I am not sure what it cost anymore to get the port work done as it has been 12 or so years since i have had a set of heads ported ( cnc c-460 heads ).

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Re: p51 cumbustion chamber size

Post  wayney on October 17th 2016, 8:52 pm

Lem Evans wrote:
wayney wrote:
Lem Evans wrote:
10.0 wrote:If you mill a bunch on the heads, they will be less saleable and may have deck problems as well.
Might be opening a can of worms.

This statement is spot on.


this is what i was wondering about. compromising the deck. wondering if anyone had done it .060-.080 in a higher pressure motor. high compression or middle of the road boost/ nitrous.
i am just thinking out loud. if i was going to go through the expense and time of piston replacement i would probably just build a new short block or motor.

wayne

I looked back at some of your post......you have a big dish piston now as I see it?

yes, when i started building the motor it was going to be a very mild flat tappet street motor but i am bored to death at car shows and don't drive it much on the street.

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Re: p51 cumbustion chamber size

Post  IDT-572 on October 18th 2016, 9:24 am

wayney wrote:
IDT-572 wrote:35 cfm @ 2.25 hp per cfm is right at 80 hp. that's what a good port job with a 2.300 valve is worth. But it's several $ too.

One pint of compression wont get you near that. Maybe 30 HP from 72 to 60 cc chamber.  

don't take this the wrong way your car/ motor runs great and i know you know what you are doing.

if i could get them ported and pick up 50 to 80 hp i would definitely be interested . I know more cfm does not always add a given amount of HP. i have personally changed ported dove heads to ported aluminum cj heads on the same motor in the same car milling the alum heads to gain a point of CR and only picked up .5 mph after tuning. the cj heads flowed 50cfm more than the dove heads (on the same bench) at the dove head peak (.600 lift) and outflowed them across the board. the heads were the only thing changed. Has anyone on here done a A-B ported VS unported P51 head dyno test? The shop that i spoke to about porting the p51  heads is a very competent and respected engine shop . it was a simple question of " on a 521 is there much gain to be had from porting my p51 heads" answer was  " a full competition port job would see 15hp and it is usually not money well spent" . I am not sure what it cost anymore to get the port work done as it has been 12 or so years since i have had a set of heads ported ( cnc c-460 heads ).

Cfm is hp, if air speed is not lost in getting it. I did not take what you said the wrong way, But I have yet in my years of porting heads seen a good full out port job, (not a hogging out job) not make more tq and hp.

(If), the air pump under them is up to moving the air the heads can handle.

As I said is it worth the money to you? With that being said, I'm not sure with a low compression 521 you have enough air moving ability to get a good bang for the buck on a port job, if your porter increases your cross section very much, it may negate any gains because of the low air speed and TQ loss.

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