How Much of a Power gain swapping to P51 Heads...

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How Much of a Power gain swapping to P51 Heads...

Post  514F-1 on April 4th 2016, 8:41 pm

Just wondering what my motor would make if I used P51 heads instead of A429 CJ's. Not going to get rid of my CJ's, but considering another build in the future with the P51's and mafia intake basically a clone of the current motor with P51's I want to keep the low compression for pump gas and longevity as well.
Basic specs:
514
9.8:1 comp
.726/.692 312/319 adv Dur cam

I'm thinking its making somewhere in the neighborhood of 650 now, never had it on a dyno. Its been 6.23 at 2900 pounds but that was mineshaft air. Its a 6.30-.35 average in the 1/8th.


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Re: How Much of a Power gain swapping to P51 Heads...

Post  supervel45 on April 4th 2016, 9:30 pm

I would guess you would pickup 50-60HP if the P-51's or flowing pretty good at least.

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Re: How Much of a Power gain swapping to P51 Heads...

Post  514F-1 on April 5th 2016, 5:44 pm

supervel45 wrote:I would guess you would pickup 50-60HP if the P-51's or flowing pretty good at least.

That's about what I was thinking....or slightly more
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Re: How Much of a Power gain swapping to P51 Heads...

Post  supervel45 on April 5th 2016, 6:49 pm

I was being pretty conservative. Like I said it will depend on how they are flowing and kind of assuming you were going to have them ported to make bigger numbers.

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Re: How Much of a Power gain swapping to P51 Heads...

Post  Dave De on April 5th 2016, 7:22 pm

A cam like that could support 11.?? on pump gas. It must be around 270/275 duration at .050? Are you using regular gas in that?
I went from SCJ's to P51's and only dropped about .15 in the 1/4 mile. You would probably do the same depending upon the work done on the old A429's.
Most of these heads are street heads that will yield similar results. If you want to step up the TFS A heads would be the ticket but not for the street.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  514F-1 on April 5th 2016, 7:59 pm

Dave De wrote:A cam like that could support 11.?? on pump gas. It must be around 270/275 duration at .050? Are you using regular gas in that?
I went from SCJ's to P51's and only dropped about .15 in the 1/4 mile. You would probably do the same depending upon the work done on the old A429's.
Most of these heads are street heads that will yield similar results. If you want to step up the TFS A heads would be the ticket but not for the street.

Not a street ride. I mix 110 and pump gas 50/50. Thinking if I ever put another car together, I would like to keep the motors close to the same, so each motor could work in either car, parts could be interchanged in a pinch. Etc.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  Dave De on April 5th 2016, 8:56 pm

514F-1 wrote:
Dave De wrote:A cam like that could support 11.?? on pump gas. It must be around 270/275 duration at .050? Are you using regular gas in that?
I went from SCJ's to P51's and only dropped about .15 in the 1/4 mile. You would probably do the same depending upon the work done on the old A429's.
Most of these heads are street heads that will yield similar results. If you want to step up the TFS A heads would be the ticket but not for the street.

Not a street ride.  I mix 110 and pump gas 50/50.  Thinking if I ever put another car together, I would like to keep the motors close to the same, so each motor could work in either car, parts could be interchanged in a pinch. Etc.

I'm confused ....
Less than 10 to 1 and it needs 100 octane. It should make more power with 87-90 octane? You do know that the valve reliefs are different for A429's and P51's so interchangeability goes away unless the pistons are made for both.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  514F-1 on April 5th 2016, 9:35 pm

Dave De wrote:
514F-1 wrote:
Dave De wrote:A cam like that could support 11.?? on pump gas. It must be around 270/275 duration at .050? Are you using regular gas in that?
I went from SCJ's to P51's and only dropped about .15 in the 1/4 mile. You would probably do the same depending upon the work done on the old A429's.
Most of these heads are street heads that will yield similar results. If you want to step up the TFS A heads would be the ticket but not for the street.

Not a street ride.  I mix 110 and pump gas 50/50.  Thinking if I ever put another car together, I would like to keep the motors close to the same, so each motor could work in either car, parts could be interchanged in a pinch. Etc.

I'm confused ....
Less than 10 to 1 and it needs 100 octane. It should make more power with 87-90 octane? You do know that the valve reliefs are different for A429's and P51's so interchangeability goes away unless the pistons are made for both.

It doesn't need it, but its muchh more consistent with some 110, mixed in. Reliefs are diffent I know, but most other things can be kept the same.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  supervel45 on April 5th 2016, 9:46 pm

I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.

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Re: How Much of a Power gain swapping to P51 Heads...

Post  Dave De on April 5th 2016, 10:04 pm

Just a thought..
If the heads flow give it some wind and put the compression to it, 13.5 to 1? You'll probably get it into 6.0's in the 1/8th.

I remember running 6.0's for the longest time saying I just want to go 5.9's, now its 5.7's and heading for 5.6's. It really feels the same but that's progress.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  FalconEh on April 5th 2016, 10:28 pm

Dave De wrote:Just a thought..
If the heads flow give it some wind and put the compression to it, 13.5 to 1? You'll probably get it into 6.0's in the 1/8th.

I remember running 6.0's for the longest time saying I just want to go 5.9's, now its 5.7's and heading for 5.6's. It really feels the same but that's progress.

Not meant to hijack the post, but Dave I remember when you made the switch to P-51's and you slowed down...and you are truly a street strip real meal deal, what compression are you running now? I believe you have the long arm of mr frosty. Very Happy
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Re: How Much of a Power gain swapping to P51 Heads...

Post  Dave De on April 5th 2016, 10:41 pm

FalconEh wrote:
Dave De wrote:Just a thought..
If the heads flow give it some wind and put the compression to it, 13.5 to 1? You'll probably get it into 6.0's in the 1/8th.

I remember running 6.0's for the longest time saying I just want to go 5.9's, now its 5.7's and heading for 5.6's. It really feels the same but that's progress.

Not meant to hijack the post, but Dave I remember when you made the switch to P-51's and you slowed down...and you are truly a street strip real meal deal, what compression are you running now? I believe you have the long arm of mr frosty. Very Happy

No I didnt slow down but ran about 5/100ths faster while having trans problems with low line pressure. Once I got the drive line issues repaired the P51's were about .15 faster in the quarter.
This is on motor w/o any power adders and E85. If I tried Mr. Frosty I'd probably destroy the C6 for sure.
580, 13.5 comp., P51 ported, smaller roller than 514F-1, TFS intake, 1350 Dommy, big tube headers, 4" full exhaust with Flowmaster 44's.
This year taking the exhaust off, adding an air pan, and doing some aero changes but no power changes.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  FalconEh on April 5th 2016, 10:51 pm

Dave De wrote:
FalconEh wrote:
Dave De wrote:Just a thought..
If the heads flow give it some wind and put the compression to it, 13.5 to 1? You'll probably get it into 6.0's in the 1/8th.

I remember running 6.0's for the longest time saying I just want to go 5.9's, now its 5.7's and heading for 5.6's. It really feels the same but that's progress.

Not meant to hijack the post, but Dave I remember when you made the switch to P-51's and you slowed down...and you are truly a street strip real meal deal, what compression are you running now? I believe you have the long arm of mr frosty. Very Happy

No I didnt slow down but ran about 5/100ths faster while having trans problems with low line pressure. Once I got the drive line issues repaired the P51's were about .15 faster in the quarter.
This is on motor w/o any power adders and E85. If I tried Mr. Frosty I'd probably destroy the C6 for sure.
580, 13.5 comp., P51 ported, smaller roller than 514F-1, TFS intake, 1350 Dommy, big tube headers, 4" full exhaust with Flowmaster 44's.
This year taking the exhaust off, adding an air pan, and doing some aero changes but no power changes.

Sorry Dave,
I thought you were on the juice, damn I have to stop getting old Laughing The car Rocks though even more impressive w/o the juice!
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Re: How Much of a Power gain swapping to P51 Heads...

Post  IDT-572 on April 6th 2016, 1:20 pm

Just to put into perspective, for the ones who spout off the only difference between A 429's and P-51's in E.T.

I run 5.40- 5.45 Normally, I sprayed my car with a 200 shot and when I got it tuned to as fast as it would go, I picked up .17 in the eighth.

It takes a ton of beans to drop E.T. when your running mid to low 5's. and even more the faster you go.

I made 861 hp with my 557 and it went 5.67-5.70, I'm at 1000 hp now with P-51s and running 5.40's .27

You can see the pattern here.

I could see a street deal / pump gas picking up a bunch with the swap.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  BigRigTech on April 7th 2016, 11:20 am

supervel45 wrote:I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.
I have a set of those dual fly-cut Probes in my 472. My "Freelander" A429's are milled to 62cc so our compression math came out to 11.4:1. I run 100 octane AV gas in mine.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  gmsmkr on April 7th 2016, 1:15 pm

BigRigTech wrote:
supervel45 wrote:I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.
I have a set of those dual fly-cut Probes in my 472. My "Freelander" A429's are milled to 62cc so our compression math came out to 11.4:1. I run 100 octane AV gas in mine.

Same pistons here my comp worked out to 10.8 with my scj heads. Im in the process of swapping it over to meth and changing some nitrous jetting on the fogger going for some low 9sec pass with a pump gas 472 Very Happy
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Re: How Much of a Power gain swapping to P51 Heads...

Post  514F-1 on April 7th 2016, 1:57 pm

Thanks for the response's guys. What are these pistons you all speak of?
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Re: How Much of a Power gain swapping to P51 Heads...

Post  gmsmkr on April 7th 2016, 2:14 pm

At one time Carl had some pistons with dual valve pockets for standard lay out and scj/P51 heads for stock stroke combo. They were a 15cc dish forged piston
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Re: How Much of a Power gain swapping to P51 Heads...

Post  68formalGT on April 7th 2016, 2:57 pm

supervel45 wrote:I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.

514F-1 wrote:Thanks for the response's guys.  What are these pistons you all speak of?

gmsmkr wrote:At one time Carl had some pistons with dual valve pockets for standard lay out and scj/P51 heads for stock stroke combo. They were a 15cc dish forged piston

I'm pretty sure he still can get them, I used those 14:1 standard valve pistons and when I need a couple replacements he just called Diamond and had them drop shipped.

514F-1 We're talking about Carl Hanson(carsbycarl) from Colorado Springs I think he's a vender here.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  68formalGT on April 7th 2016, 3:07 pm

BigRigTech wrote:
supervel45 wrote:I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.
I have a set of those dual fly-cut Probes in my 472. My "Freelander" A429's are milled to 62cc so our compression math came out to 11.4:1. I run 100 octane AV gas in mine.

I think he's(if we're talking about Carl) getting those pistons from Diamond now.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  Carl on April 7th 2016, 4:12 pm

68formalGT wrote:
BigRigTech wrote:
supervel45 wrote:I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.
I have a set of those dual fly-cut Probes in my 472. My "Freelander" A429's are milled to 62cc so our compression math came out to 11.4:1. I run 100 octane AV gas in mine.

I think he's(if we're talking about Carl) getting those pistons from Diamond now.

Yes, Diamond is my source for those pistons now. We can do any dual relief combination needed on any piston, 429/460/521/557, with OEM/SCJ, SCJ/AFR, OEM/AFR, OEM/A460, etc.

We did a large run of several sets of 460 pistons with those dual reliefs from Probe, but they just weren't all that popular, even at the insanely low price we sold them for, so we didn't do any more big runs like that with Probe, and now Probe is gone, so we have them made one set at a time by Diamond at about twice the price. I might be able to have them made by Racetec, but nowhere near the low price that we were doing with Probe. If you guys haven't looked around lately, forged pistons have really gone up in price, even the old two-ton specials from Speed Pro.

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Re: How Much of a Power gain swapping to P51 Heads...

Post  rmcomprandy on April 7th 2016, 6:02 pm

Carl wrote:
68formalGT wrote:
BigRigTech wrote:
supervel45 wrote:I see what you are doing and it makes perfect sense to me. Flycuts are no big deal and pretty cheap. Those Carls pistons where a hell of a deal, I should have picked up a set while he had them but they where for a 472 I believe.
I have a set of those dual fly-cut Probes in my 472. My "Freelander" A429's are milled to 62cc so our compression math came out to 11.4:1. I run 100 octane AV gas in mine.

I think he's(if we're talking about Carl) getting those pistons from Diamond now.

Yes, Diamond is my source for those pistons now.  We can do any dual relief combination needed on any piston, 429/460/521/557, with OEM/SCJ, SCJ/AFR, OEM/AFR, OEM/A460, etc.

We did a large run of several sets of 460 pistons with those dual reliefs from Probe, but they just weren't all that popular, even at the insanely low price we sold them for, so we didn't do any more big runs like that with Probe, and now Probe is gone, so we have them made one set at a time by Diamond at about twice the price.  I might be able to have them made by Racetec, but nowhere near the low price that we were doing with Probe.  If you guys haven't looked around lately, forged pistons have really gone up in price, even the old two-ton specials from Speed Pro.

PROBE is NOT gone ... just moving across the country so they are shut down for a while.

I paid $814.00 for a set of forged "brick" pistons from Jahns in 1969. It is probably the only engine part which hasn't increased in price 3 fold since then.

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Re: How Much of a Power gain swapping to P51 Heads...

Post  Lem Evans on April 7th 2016, 6:09 pm

Probe is closed. CHP was sold and moved to Al.

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Re: How Much of a Power gain swapping to P51 Heads...

Post  Dave De on April 7th 2016, 6:22 pm

Lem Evans wrote:Probe is closed. CHP was sold and moved to Al.
Sad to see Probe go away.
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Re: How Much of a Power gain swapping to P51 Heads...

Post  Lem Evans on April 7th 2016, 6:40 pm

Sad indeed.

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