promaxx 317 heads
09-30-2017, 11:16 AM
#11
Platinum Member
of the several sets that I've done with AK Racing mods ... Eddie did the dyno on 2 509 EFI (Merc 500 intakes) in full marine wet trim they made 622hp - 625Hp and as he stated there was a cluster of injector issues and with more time and money and a different camshaft he could have gotten more. my thoughts are that 640ish wouldn't be impossible... now with that said if we were talkin carbed I'm sure these numbers would have significantly been higher.
I have several other sets out there in use with more than happy customers, however people these days are understandably strict with $$$ and not wishing to add the expense of dyno fees to their build... IMO the heads speak for themselves my mods are not life altering and they lean more to making them marine friendly and helping the exhaust side out, boxed heads don't usually address the specific needs of the marine world as we all know...
I have several other sets out there in use with more than happy customers, however people these days are understandably strict with $$$ and not wishing to add the expense of dyno fees to their build... IMO the heads speak for themselves my mods are not life altering and they lean more to making them marine friendly and helping the exhaust side out, boxed heads don't usually address the specific needs of the marine world as we all know...
The following users liked this post:
chancer540 (12-10-2020), cig92 (10-05-2017)
10-01-2017, 11:28 AM
#14
Registered
iTrader: (3)
I'd worry more about timing events, than just the .050 duration numbers. There is no good reason to run a cam that beats the valvetrain up with a S/C combo like that. The added lift , say going from .650 to .700, likely wont change the speedo reading one bit. Screw up the timing events, and that certainly can make a difference. Billy boats made 1150hp with a 540ci and pump gas, with a mild endurance solid roller 636 lift cam. (whipple build).
Simply changing the ICL and ECL can have a much larger effect than a few degrees of duration at .050.
Simply changing the ICL and ECL can have a much larger effect than a few degrees of duration at .050.
10-01-2017, 11:32 AM
#15
Registered
iTrader: (3)
Heck, my old dyno sheets from 2012 showed i made 804hp. New dyno sheets from 2016, showed 818hp. Boat gained 8mph though. Whats that tell ya. lol
10-01-2017, 02:07 PM
#16
Registered
iTrader: (7)
Your right MT timing events are cruicial and will certainly dictate the outcome of a builds potential power. That's why my first choice was to go with same cam merc used in their 900 sc which by coincidence has very similar timing events as the 651 with the biggest dif is the intake opening apprx + - 5 deg later. Then again HR/SR not a good comparison. Seems like most good ol bobs cams had very similar timing events regardless of builds. Hah. I'm going to compare with Valako's card just for chits and grins. He's running same cam as he did with his SC engine. Not really certain what I will end up with but will likely end up doing a cam swap on dyno and will post results for anyone interested. Sending my carbs out to norm next week to work his magic. He'd like to have cams narrowed down before starting though.
The cam swap on dyno wil be more for knowledge gained than anything else. All I can do is wait and see. I get the whole dyno happy bs trust me.
The cam swap on dyno wil be more for knowledge gained than anything else. All I can do is wait and see. I get the whole dyno happy bs trust me.
10-01-2017, 03:33 PM
#17
Registered
iTrader: (3)
Exhaust timing events are really crucial with a forced induction build. Just playing around with my simulator,
548ci with dart 345s and 1071s, with 8lbs boost.
Crane 651 cam. 880HP at 6000 RPM. exhaust timing events open 67, close 9.
Change to 112 LSA. Intake events do not change. But exhaust is now 115ECL, vs 651's 119 ECL. Ex valve opens at 63, closes at 13. 905HP at 6000RPM.
Shorten exhaust duration from the 651's 244/256, to 244/250. Again, the intake valve events stay same, but exhaust now open at 60, close at 10. 915HP at 6000RPM.
What also changes when making changes to the exhaust valve timing , is the intake manifold pressure (boost). On the dyno, we always adjust pulleys to get the boost we want to run. So, to keep the data correct, I also changed pulley ratio in the simulator, so that I maintained 8psi on the above numbers. So, just by manipulating exhaust valve timing events, not even touching intake valve events, there was a change of 35HP at 6000RPM, with same amount of boost. No changes in valve lift either. still .632 lift. Along with the HP increase at 6000, the torque also went up in the midrange.
You can have an exhaust port that baby jesus ported, and flowing 350 cfm on the bench. If the valve is opening at the wrong time needed for an efficient blowdown period, it wont do squat for ya.
The 651 cam is a nice cam, but imo, its a better fit to a build using a chitty exhaust port (like a 088 head), and 12-15lbs of boost. A low boost deal with a strong exhaust port like a dart head, you just dont need a 12* split in pattern. I have no solid proof of this theory, but one of these days would like to try it back to back on the dyno.
548ci with dart 345s and 1071s, with 8lbs boost.
Crane 651 cam. 880HP at 6000 RPM. exhaust timing events open 67, close 9.
Change to 112 LSA. Intake events do not change. But exhaust is now 115ECL, vs 651's 119 ECL. Ex valve opens at 63, closes at 13. 905HP at 6000RPM.
Shorten exhaust duration from the 651's 244/256, to 244/250. Again, the intake valve events stay same, but exhaust now open at 60, close at 10. 915HP at 6000RPM.
What also changes when making changes to the exhaust valve timing , is the intake manifold pressure (boost). On the dyno, we always adjust pulleys to get the boost we want to run. So, to keep the data correct, I also changed pulley ratio in the simulator, so that I maintained 8psi on the above numbers. So, just by manipulating exhaust valve timing events, not even touching intake valve events, there was a change of 35HP at 6000RPM, with same amount of boost. No changes in valve lift either. still .632 lift. Along with the HP increase at 6000, the torque also went up in the midrange.
You can have an exhaust port that baby jesus ported, and flowing 350 cfm on the bench. If the valve is opening at the wrong time needed for an efficient blowdown period, it wont do squat for ya.
The 651 cam is a nice cam, but imo, its a better fit to a build using a chitty exhaust port (like a 088 head), and 12-15lbs of boost. A low boost deal with a strong exhaust port like a dart head, you just dont need a 12* split in pattern. I have no solid proof of this theory, but one of these days would like to try it back to back on the dyno.
10-01-2017, 03:59 PM
#18
Registered
iTrader: (7)
No doubt regarding the 651 cam liking a poorer flowing exh port. Like you said designed more for GM heads. Hard to get through to many people but that's the beauty of a good flowing set of heads. You can end up with a smaller cam in a sense and drastically reduce premature valvetrain wear.
