Promaxx Heads
04-02-2025 | 01:19 PM
#44
Registered
Joined: Jan 2009
Posts: 682
Likes: 177
From: Finland
06" intake valve. But hey thats just me 🤣. Every one who builds their own engines, should bolt the cylinder head to their bare block and look that nasty ridge that is in way of air flow. Real eye opener.
04-02-2025 | 01:33 PM
#45
Registered
Joined: Jan 2009
Posts: 682
Likes: 177
From: Finland
Those ProMaxx heads sound pretty interesting.
I have a pair of 482cid BBC NA engines in a heavy 40' Hustler Fiore. I wasn't initially intending to put that those small of a CID in my big heavy boat, They only made 510hp @5000rpm on the dyno with GM Rectangle port cast iron heads with some clean up and blending of all the ports.
I also had the cylinder bores "bore notched" on both intake and exhaust sides of the cylinders to unshroud the valves for better breathing/flow for the 4.25" bore size, but the bore notching creates a drop in my compression ratio.
I cannot remember if the pistons are a true Flat Top or maybe have a slight dome. I would have to wait until I would remove the GM heads and look and see what I have as far as my pistons go and see how far they sit in the hole at TDC.
I think the hydraulic roller Cams may be the old Merc 502cid/HP500 cams, but I am Not exactly sure, but the engines only make peak power up to 5000rpm according to the dyno @32° with only a stock Merc Thunderbolt distributor and stock Merc/Holley 800cfm carbs.
I am kinda thinking that my Comp Ratio may be as low as 8.0 to 8.6 ratio which is a bit low.
So, I thought that maybe the ProMaxx heads would be a good solution to my issue especially with their 110cc combustion chamber size.
I am only looking for a little more KICK in power to maybe about 580-600hp while retaining the same Cams and I thought I could accomplish this without swapping out the Cams.
Also, I want to try and avoid putting to much strain on my XR Bravo drives and I thought that perhaps the ProMaxx 290cc head would be the ticket. I've been watching Eric Weingartner's videos and doing a lot of research on them.
I am wondering what you guys think or would appreciate any input/feedback.
Thanks 👍 🇺🇲
I have a pair of 482cid BBC NA engines in a heavy 40' Hustler Fiore. I wasn't initially intending to put that those small of a CID in my big heavy boat, They only made 510hp @5000rpm on the dyno with GM Rectangle port cast iron heads with some clean up and blending of all the ports.
I also had the cylinder bores "bore notched" on both intake and exhaust sides of the cylinders to unshroud the valves for better breathing/flow for the 4.25" bore size, but the bore notching creates a drop in my compression ratio.
I cannot remember if the pistons are a true Flat Top or maybe have a slight dome. I would have to wait until I would remove the GM heads and look and see what I have as far as my pistons go and see how far they sit in the hole at TDC.
I think the hydraulic roller Cams may be the old Merc 502cid/HP500 cams, but I am Not exactly sure, but the engines only make peak power up to 5000rpm according to the dyno @32° with only a stock Merc Thunderbolt distributor and stock Merc/Holley 800cfm carbs.
I am kinda thinking that my Comp Ratio may be as low as 8.0 to 8.6 ratio which is a bit low.
So, I thought that maybe the ProMaxx heads would be a good solution to my issue especially with their 110cc combustion chamber size.
I am only looking for a little more KICK in power to maybe about 580-600hp while retaining the same Cams and I thought I could accomplish this without swapping out the Cams.
Also, I want to try and avoid putting to much strain on my XR Bravo drives and I thought that perhaps the ProMaxx 290cc head would be the ticket. I've been watching Eric Weingartner's videos and doing a lot of research on them.
I am wondering what you guys think or would appreciate any input/feedback.
Thanks 👍 🇺🇲
04-02-2025 | 02:07 PM
#46
Registered
Joined: Jan 2009
Posts: 682
Likes: 177
From: Finland
One more thing about bore notching. Sorry! I made 4.25" bore fixture with notches, for superflow flow bench. It was worth of 15cfm peak flow vs no notch fixture. And this was with 2.06" valve in poor peanut port head, so think about that. Wonder about the results with 2.25 or 2.3" valve.
04-02-2025 | 03:49 PM
#47
Registered
Joined: Jan 2006
Posts: 3,863
Likes: 793
From: St. Pete Beach, FL
One more thing about bore notching. Sorry! I made 4.25" bore fixture with notches, for superflow flow bench. It was worth of 15cfm peak flow vs no notch fixture. And this was with 2.06" valve in poor peanut port head, so think about that. Wonder about the results with 2.25 or 2.3" valve.
04-02-2025 | 06:04 PM
#48
Registered
Joined: Aug 2019
Posts: 1,223
Likes: 414
From: BC
I would take the bore notches any day, over the 1/10 point compression. I even notched my 4.5" bore 502 block for my first bbc build with 2.
06" intake valve. But hey thats just me 🤣. Every one who builds their own engines, should bolt the cylinder head to their bare block and look that nasty ridge that is in way of air flow. Real eye opener.
06" intake valve. But hey thats just me 🤣. Every one who builds their own engines, should bolt the cylinder head to their bare block and look that nasty ridge that is in way of air flow. Real eye opener.
I'm big on using the biggest CR you can safely use. It's more about the part throttle cruise in cyl dynamics.
KAAMA: I think the Promaxx 290s are a great choice for you. Eric's vids are a great asset. The one issue is the oddball Roval port. You may have to get a new intake as well. You're likely not into your full throttles very often either. The intake valve kept at 2.25" may be more beneficial in the shrouding dept. and have less pumping losses at part throttle, due to a smaller cross section of the valve port flowing more. Part throttle is mostly about efficiancy...BSFC...or you just add more throttle for more power. Dynos generally don't do part throttle testing with cam influence etc. Mostly that's a marine thing.
04-02-2025 | 08:50 PM
#49
Registered
Joined: Oct 2000
Posts: 4,541
Likes: 107
From: Western Michigan
Thanks for all the feedback response guys. It's all good news and info that everyone here can use.
Yeah Tart, if I pull the trigger on those PROMAXX 290 heads then I will probably get some Edelbrock RPM Air-Gap Oval Port dual plane intake manifolds and have either Eric Weingartner go over the heads or even Brian Salter of Salter Racing Engines (he's a very successful NASCAR Cup builder, etc, etc) down in NC.
And also have them port/message the intake manifolds as well. Like I have said, I don't want to swap out the cams even though it looks like they only Peak at 5000rpm.
I'm already running Stellings full length tubular open dry headers...so that greatly helps the equation.
I have to check things out after I get the old rectangle GM cast iron heads off and see what's what in there so as to get an idea on my Comp Ratio, piston crown and Cam Lift, etc.
And keep in mind that I just have these little baby 482cid engines with only a 4.25" cylinder bore.
The ProMaxx 290cc heads might create too much Compression with their 110cc combustion chamber... So I may need to use a different brand of head but I will have to wait and see once I get the old GM heads off.
Yeah Tart, if I pull the trigger on those PROMAXX 290 heads then I will probably get some Edelbrock RPM Air-Gap Oval Port dual plane intake manifolds and have either Eric Weingartner go over the heads or even Brian Salter of Salter Racing Engines (he's a very successful NASCAR Cup builder, etc, etc) down in NC.
And also have them port/message the intake manifolds as well. Like I have said, I don't want to swap out the cams even though it looks like they only Peak at 5000rpm.
I'm already running Stellings full length tubular open dry headers...so that greatly helps the equation.
I have to check things out after I get the old rectangle GM cast iron heads off and see what's what in there so as to get an idea on my Comp Ratio, piston crown and Cam Lift, etc.
And keep in mind that I just have these little baby 482cid engines with only a 4.25" cylinder bore.
The ProMaxx 290cc heads might create too much Compression with their 110cc combustion chamber... So I may need to use a different brand of head but I will have to wait and see once I get the old GM heads off.
Last edited by KAAMA; 04-02-2025 at 09:09 PM.
04-02-2025 | 09:06 PM
#50
Registered
Joined: Oct 2000
Posts: 4,541
Likes: 107
From: Western Michigan
I also appreciate you other guys about the "bore notching" subject and input....
It's all super interesting to me and I believe bore notching the cylinder walls is a very beneficial and cheap way of unshrouding the valves for better/more flow for a 20-30hp gain...so 1 or 2 10th's of a Compression Point is almost nothing. After all these are only little baby engines with only a 4.25" bore.
I really enjoy the detailed discussion. 👍🇺🇲🏁
It's all super interesting to me and I believe bore notching the cylinder walls is a very beneficial and cheap way of unshrouding the valves for better/more flow for a 20-30hp gain...so 1 or 2 10th's of a Compression Point is almost nothing. After all these are only little baby engines with only a 4.25" bore.
I really enjoy the detailed discussion. 👍🇺🇲🏁
Last edited by KAAMA; 04-02-2025 at 09:12 PM.
