All Big Six ProMAXX CNC ported big valve heads are now available.

Relates to all big sixes

Pontus

Well-known member
Supporter 2021
Im hoping to have it running here soon, i got new bearings in, my pistons are at the shop getting changed out, i have the head, i have the ausie intake manifold with a 2100 carb… only things im missing are the scorpion rockers and then the push rods that will go with it
The CNC version comes with valves that are 4.92" long but still have pedestal mounted rockers, right? Are you changing those to stud mounted? If not, is it ok to shim them up that much? Since the Scorpions are designed for the EFI head with 4.75" valves (unless you go with the stud mounted version), that'll mean 0.17" of shim, nearly 3/16" which is more than the depth of the pedestal bar. I suppose you could put the shims UNDER the bar... and longer bolts? Seems like a lot of leverage too far away from the casting for something under tension and moving a lot. What was the plan for that @pmuller9 ?
 

pmuller9

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Supporter 2018
Supporter 2021
The CNC version comes with valves that are 4.92" long but still have pedestal mounted rockers, right? Are you changing those to stud mounted? If not, is it ok to shim them up that much? Since the Scorpions are designed for the EFI head with 4.75" valves (unless you go with the stud mounted version), that'll mean 0.17" of shim, nearly 3/16" which is more than the depth of the pedestal bar. I suppose you could put the shims UNDER the bar... and longer bolts? Seems like a lot of leverage too far away from the casting for something under tension and moving a lot. What was the plan for that @pmuller9 ?
The Scorpion roller rockers have a different Geometry that the stock stamped rocker.
The installed rocker height will be different.
Shims should go under the rail.
 

Frank

Well-known member
Supporter 2021
Horsepower potential from cfm the formula I use is cfm ×.2575× number of cylinders. I know someone asked recently.
Green ford f150- good afternoon. I'm a bit confused by your formula. If you are using cfm, then how does the # of cylinders affect it? I assume you mean total induction cubic feet per minute? I like engine math, so if you could expound on this I would appreciate it. Thanks.
 

80f150custom

Well-known member
Green ford f150- good afternoon. I'm a bit confused by your formula. If you are using cfm, then how does the # of cylinders affect it? I assume you mean total induction cubic feet per minute? I like engine math, so if you could expound on this I would appreciate it. Thanks.
I'm probably wrong but I would assume the formula of cfm x .2575 is the amount of HP that 1 cylinder would make and since there are 6 cylinders. I'm just guessing here but that is how I interprete it
 

InlineDave87

Well-known member
Pistons are back! And then to give myself a little motovation i decided mock up the promaxx head to the block… then it hit me, lets see what the piston will see! Hope yall enjoy this one
 

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Green ford f150

Well-known member
Supporter 2021
I'm probably wrong but I would assume the formula of cfm x .2575 is the amount of HP that 1 cylinder would make and since there are 6 cylinders. I'm just guessing here but that is how I interprete it

Green ford f150- good afternoon. I'm a bit confused by your formula. If you are using cfm, then how does the # of cylinders affect it? I assume you mean total induction cubic feet per minute? I like engine math, so if you could expound on this I would appreciate it. Thanks.
You are figuring the potential for horsepower from one cylinder we have 6. Other formulas are simplified for ease kind of like displacement for a v8 say we have a 302 it would look like this . bore x bore x stroke x6.2832. 4x4x3 = 48x6.2832=301.5936
 

Green ford f150

Well-known member
Supporter 2021
Green ford f150- good afternoon. I'm a bit confused by your formula. If you are using cfm, then how does the # of cylinders affect it? I assume you mean total induction cubic feet per minute? I like engine math, so if you could expound on this I would appreciate it. Thanks.
could also just use cfm x 1.545 but I wanted folks to see how it worked for more than just a 6 cylinder. Sorry for the confusion. By the way that formula I use is from superflow aka the dyno people.
 

Frank

Well-known member
Supporter 2021
could also just use cfm x 1.545 but I wanted folks to see how it worked for more than just a 6 cylinder. Sorry for the confusion. By the way that formula I use is from superflow aka the dyno people.
Ok, just in from long work day/week, so maybe my brain isn't functioning right- I gave you a thumbs up then pulled out my calculator, and I'm still not getting it. I took "cfm" to be cubic feet per minute, which is a dynamic variable based on total engine displacement, independent of cylinder count. . So if cfm= cubic feet of air ingested per minute this formula doesn't work: A 300 pulling 300 cubic feet of air/min =300 x .2575= 77.25 x 6 cylinders = 463 HP. A 300 can make 436 HP but not @ 4000 rpm and 300 cfm. ?? The 302 example you gave used the displacement as a foundation, not cfm. .
None of this is criticism or challenging- I am wanting to understand, would love a new formula to add to my collection. I know more about engines from the math than from hands-on overhauls. :rolleyes:
 

80f150custom

Well-known member
Ok, just in from long work day/week, so maybe my brain isn't functioning right- I gave you a thumbs up then pulled out my calculator, and I'm still not getting it. I took "cfm" to be cubic feet per minute, which is a dynamic variable based on total engine displacement, independent of cylinder count. . So if cfm= cubic feet of air ingested per minute this formula doesn't work: A 300 pulling 300 cubic feet of air/min =300 x .2575= 77.25 x 6 cylinders = 463 HP. A 300 can make 436 HP but not @ 4000 rpm and 300 cfm. ?? The 302 example you gave used the displacement as a foundation, not cfm. .
None of this is criticism or challenging- I am wanting to understand, would love a new formula to add to my collection. I know more about engines from the math than from hands-on overhauls. :rolleyes:
I understand cfm in this case to mean how much the head flows and the formula an estimation of how much HP that flow can support.
 
Howdy Ya'll; I know I'm late to the party, and my question has probably been answered, but what's the latest on a cross-flow head for the mighty 300?
 

InlineDave87

Well-known member
Howdy Ya'll; I know I'm late to the party, and my question has probably been answered, but what's the latest on a cross-flow head for the mighty 300?
🤔 prior air force, navy or marine? For the cross flow head the thing has been putting 2 LS heads together for max air flow. There are some youtube videos on it. This promaxx head is an upgraded stock efi head that has good power potential. Welcome to the club, this is actually one of the best forums out there.
 

THE FRENCHTOWN FLYER

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Supporter 2021
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Supporter 2018
Howdy Ya'll; I know I'm late to the party, and my question has probably been answered, but what's the latest on a cross-flow head for the mighty 300?
 

brnwaxa52

New member
Supporter 2018
Supporter 2021
A good job on this head especially for the money. Unfortunately for me for now, 10 years ago I spent mega hours and money on a used head that can not be better than this one if that good. It's a value
 

Pontus

Well-known member
Supporter 2021
Has anyone checked their valve guide clearance/size? Unless the CNC version comes with replacement guides, (or mine was a reman) I don't think they would use a different size guide ream. Mine were cut at about .345" which is .003" clearance (max wear limit).
 
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