promaxx 317 heads
 

i am interested in hearing from guys that are using these heads,information about engine build and dyno results.

Mike I'm surprised you didn't get any response on this thread so I thought I would at least bring it to the top and hopefully get some activity. I will however just add that after Valako worked on mine he was impressed with the quality of the head and flow numbers he ended up with. I'm excited to see the real results on dyno but just not ready yet because of some unfortunate delays non engine related. Intake runners ended up close to 340 cc's and flowed 407 and exh was just under 300 @ .650 lift im pretty certain. The casting look really nice and have a generous thick deck.

From what I've heard from others with some non extensive port work they are a great improvement over any GM stock head at an affordable price. Wish I had true results but I know there's others on the form here who have them and just was hoping they'd chime in for you.

Im still a little ways away from results... but my short block is turning into a long block monday. I do plan on dynoing and I do plan on flogging the motor without mercy once its in the boat....

keep us informed.
Tks
jr

I will know before to long. My 548 builds with heads and 871 blowers will give us a clue. Jim has no doubt we'll see 1,000 hp with 8 pds boost but time will tell. I'm only after 900 to save drives but he did same builds not long ago that dynod ove 1,000 hp on 540's. I'm using different cams though that he's not thrilled about. Same as merc 900sc. The heads are a basic test for first engine. Cams will be swapped out on dyno to what Jim v wants. Shorter duration and higher lift. Either way valvetrain will take a beating but I really don't care as boat will be limited use given short season etc.

definately solid roller regardless. Otherwise billit hyd roller with solids.

What are the specs on the 900sc cam?

i built a pair of 548,s with 8.71,s they had dart 320 heads,they made 950,they had crane 651 hyd roller cams.i set it up for 8 to 9 lbs boost,the 320 heads had no port work done to them.imo they needed a bigger blower like a 10.71.i used to run the crap out of that thing every weekend and fixed the xr drives monthly.

There like 252/257-672/672 SR. Can't remember lsa. There a little hard on valvetrain but I don't log many hours anyway. I thought about going back to hyd roller but have bad luck with hyd lifters and already have new SR lifters.

Mike that cam is the ticket and I know you and several others have had great success with similar builds both NA and SC. I've been looking at another Lunati SR cam. Both carb guy and Valako would like to see me with a little less duration. I already have the cams and could likely make more power with cam swap but like I mentioned I'm concerned about the drives but suppose I could always just run less boost and install more preferred cams.

Lunati

• Advertised Duration (Int/Exh): 273/279
• Duration @ .050 (Int/Exh): 243/249
• Gross Valve Lift (Int/Exh): .655/.663
• LSA/ICL: 110/106. Timing events look good but if I went this route I'd have Lunati do a custom grind on a 114. How do blowers react with a tighter lsa?

those 651's would be the smartest thing to do but... Any other solid rollers that come to mind please post. I'm not sure what ones Valako was running but I'm almost certain they are hyd rollers with solids.

what did you end up for cam?

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...

so Mikey... step right up, ya won't be sorry :thankyouthankyou:

Damn Everyone is making 1000 hp with 548ci and 8-71 651 cams 8 lbs of boost .. I didn`t even hit 900hp with a dart 345s and 10-71`s. :(:(

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.

90mph in a mid 80s 38 Flatdeck, they are making some steam. I'd be willing to bet, you throw a pair of those supposed 1000hp engines in your boat, you wouldnt see a speed increase.

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

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.

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. :)

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.

I definitely think retarding my cam 4* didn`t hurt anything , quite the opposite. Good advice as usual :thankyouthankyou:

It would be nice to know how much exhaust system plays into this, I believe I have 651 cams, CMI big tubes and shotgun inserts in the tails. Is the duration accounting for wet header/tail/muffler? inefficiencies beyond the exhaust port?

I did believe that additional exhaust duration aided when there is a fairly restrictive exhaust system. I don't know if that is in fact true. Only way to know this, would be to test it back to back.

What I do know about exhaust duration, is a certain amount is needed to sustain a specific rpm . As well as, the proper exhaust opening and closing points. That can have a substantial impact on low speed torque , and overall power production. Too much isn't good, not enough isn't good.

From some experts, what they have found during testing , was that when exhaust duration was increased, the engine did not nose over as hard at peak, but was down a bit on average power. Example would be, and engine that maybe makes peak HP of 700 at 6100rpm, but maybe only falls to 690hp at 6400. Vs shorter exhaust duration, where the engine may have peaked at 690 at 6100, but by 6400, was making 660hp.

When you play with programs like pipemax, and plug in say, the 651 cam specs and what not, you might find the intake side is good for 5900rpm, and the exhaust side is good for 6400rpm. Just throwing those numbers out there as I'm not in front of my computer, but just making an example . So that may be what you get with the 244/256 cam with 109 icl. Now, let's say you switched to a 244/250 , the intake side would still be good for 5900rpm, while the exhaust drops to maybe 6100rpm .

Works the same way with things like valve diameter. While the intake side with that cam may be good for 5900rpm with a 2.3 valve, if you stick a 2.19 valve in it, it may be good for only 5700rpm.

These modern programs are pretty interesting. Certainly a better way of picking a cam for the diy guy, than the old days of basically throwing darts based on something we heard at the bar over a few Budweisers:)

The talk over a few beers ar the bar usually involves the guys sitting next to you drinking Budweiser and smoking Marlboro reds saying how kick azz their 3/4 race cam is. Hah.. I've read how the 3/4 race cam came about but never actually confronted any individual that said they had one. Probably because I wouldn't understand them cause most their jibs (teeth) are missing.

-JRider your post makes good sense and would imagine comes into play more than most think.

-MT good post also...

Ok, so playing around right now. Lets look at the 651 cam. 244/256 @ .050 , .632/.632 lift. 114 LSA , 109 ICL . With a 2.30 intake valve, and 1.88 exhaust valve.

Intake = 5913 RPM
Exhaust=6343 RPM

Now, I'll change to a 2.19 Intake valve
intake=5824 RPM.

Now Ill increase lift from .632, to .700 on the intake side, with the 2.3 valve
Intake=6131 RPM

As you can see, increasing lift, also increased RPM potential. Increasing valve diameter, also increased RPM potential.

I had a 3/4 cam once but it ran a lot better with the whole cam. that or it was a v6 cam, either way it didnt make the power they claim.

i have to admit I'd expect to see more gains. Does your software show flow difference when inputting changes in valve size?

This particular program, does not. I do have a more advanced program, that can sort of simulate changes in velocities based on valve diameter, throat diameter, CSA, and so on. Thats really for head porters. Some things I have learned in regards to that.

Sticking a big valve in a head, doesnt necessarily equate to gains in airflow.

Enlarging a port, doesnt always mean more flow.

Reducing a ports volume, doesnt always mean more velocity.

Adding valve lift, can amplify low speed reversion. Adding valve diameter, can amplify low speed reversion. Think about it. We know intake reversion, is from the intake valve not being fully closed , and some charge is pushed back into the intake. How much of that gets pushed back, can vary not only when the valve actually closes, but how much of that charge can be put back into the intake due to the valves position during that period, and , the size of the valve. A .700 lift setup, is going to have the valve open further at this timeframe, than a .550 lift setup. This is why GM RV engines dont like big valves. They are a low rpm engine, and need to be efficient at low rpm. A good head porter, will focus on developing not only good flow from the port at higher lifts, but also design it to flow bad at very low lifts due to this. You dont want a setup that flows big air at .100 valve lift. That usually means big reversion as well.

Lots of guys go to a bigger head, and many times this bigger head, also includes a larger valve. They blame the head's port volume, when the engine is lacking low speed power. But, it may not really be the ports volume thats causing it directly, it likely is the larger valve that is hurting at low speeds. You go sticking a 2.4 intake valve, on a 502 with .720 lift, and some duration, you're not gonna wanna go pulling tubers around. That thing is gonna run like a bag of chit until very high rpm.

Pretty basic info. We all learn from and have our favorite head guy. There was a time I learned from mine many years ago and I will say it was several trips back to the flow bench to make sure I was going in the right direction and not all trips were gains but learned a lot. I now only do very basic bowl and chamber work. When I want to see real gains on bench and dyno as well as on the water or at the strip they get dropped off to my head guy. I leave all the "doesn't means" up to him.

Alot of this stuff, you can get super deep. Some of it applies to guys building pro stock stuff, or max effort competition engines where 5hp means the world.

In the marine world, I've seen guys spend buko bucks on trick headwork, freak over a few degrees of cam duration, or .030 worth of valve lift, intake manifold mods, and then go throw on an exhaust setup that is totally not what the engine needs/requires.

Played around with the dyno simulator earlier tonight. Did a 540ci, are 315 flow numbers, 9.6:1 compression, 1050 dominator with large tube headers. 244/256 .632 lift "651" crane cam.

Initial simulation showed a peak HP of 687 at 6000rpm. I started shortening exhaust duration 2 degrees at a time. 254 deg of exhaust was the only time peak power increased. It went up 1 single hp to 688. I kept decreasing. Each time I decreased it, there was a small drop in peak HP, and a small gain in low speed torque. Really wasn't much power to be lost or found from simply changing the exhaust duration .

What was drastic, was how fast power dropped off after peak HP, when shortening the split. For example, at 6500 , the 651 cam was still making 670hp. Only down 18hp from its peak. Running it as a 244/244, did make more low speed torque, and only gave up about 8hp at peak, but by 6500, it was down 49hp!! The engine basically nosed over after peak HP. This is exactly what I had expected based on what I stated earlier.

Decided to see what happens, if I took that 651 cam, and ground it with a 110lsa, and 106icl. Engine now made 712hp at 6000, and torque was up slightly as well from 3000-6000. By 6500, it dropped 25hp, to 687hp.

did he post the details on those engines?

Joe you did exactly what I was thinking if cam was ground on 110 lsa. That's awesome your able to play around with simulator. It can honestly get a build starting out in the right direction rather than complete guess work. Seriously that's pretty cool stufff. Your contributing to the forum is helpful to many I'm certain. I as well as all others appreciate it. I am curious what those custom cams I had from comp would show in comparison but I don't have cam card to give u timing events. They were 244/248-648/648 on a 111. I'm going to try and find cam card but considering for my 548 sc's. They made 621 hp 6k for kreed in the na 496's.

Thanks John, its all good shop talk.

As for that cam, I'd need the .006/.004 numbers, and the ICL. The ICL and LSA, will dictate what the exhaust timing events are. In otherwords, a 111LSA cam, with a 107 ICL, will have diffent exhaust timing events than a 111LSA with a 110ICL or 109ICL , etc.