How much HP can I make with...
 

What's an honest number of hp I could make with a naturally aspirated 540? I would probably run the Dart Pro 1 310cc runner aluminum heads and a Barry Grant Dominator with Stainles Marine exhaust. I would want a healthy cam but be able to idle without major concern and have a fully rollerized valve train. I would want the compression to be either 9:1 or 9.5:1. What would be the difference in hp between the two ratios?

600-625 should be very do able with a respectable idle.

Katdrvr, what would be the difference with a compression ratio of 9:1 and one with 9.5:1? If not much i would go with the 9:1 in case I wanted to supercharge later on. Could I run 5lbs. of boost with an intercooler for both or would I be pushing it with either one?

I do not know what HP difference between the 2 compression ratios would be but if you are planing to put a blower on it I would not go over 8.5 at max. Tearing up motors is not a fun thing to do. Procharger had a 502 putting out 565HP with marine exhaust natural before they put blower on it. With 10lbs they made i think 980HP with 10lbs. The lower the compression the more boost you can add safetly.

My 540 dynoed out at 683 @ 5680
 

They didn't take the dyno any higher because of the hyd. roller cam.
So I probably got 600 to 625 at the prop @ 5300 to 5400.
My SR-24 is running around 84 to 88 with two people and 60 gals of fuel.
Barry from PA came down one weekend. We have the same 1.36 gear, same cu in, and dyno sheets were very close and we ran side by side on a somewhat cool summer day at around 88.

SR-24,
My 540 is putting out around 675 with 9:1CR.
It's doable (?) but your going to have to spend some money on the heads, intake and cam development, especially if you want to use a hydralic roller.
Here's some info from an earlier post of mine:



I found my dyno sheets from my old 502.
This motor had iron oval port (Merlins) , with a Brodix intake , 1050 dominator and 8:5.1 CR.
The cam is a solid roller.
.715/.715 258/[email protected] on a 112 , I think we had in installed 4 deg advanced.

These dyno pulls were using 89 octane gas. And 34 degrees of timing.

At 4000rpms the torque was at 522 and it peaked 571ft/lbs at 5100rpms, it stayed at around 560 ft/lbs all the way to 6000rpms.

At 5800rpms it had 620hp , 625hp at 6000rpms.
I ended up grenading this motor. I purchased one of those Carter mechanical fuel pumps from CPperformance that I was told would work in place of the Merc fuel pump (Gen6) well that was a joke, when I put a gauge on it I think it had 2lbs of fuel pressure, not even enough to keep the float bowls full. The combination of that and a major reversion problem caused the motor to detonate to death.
I have all those problems fixed and now am even happier with the 540 !

Using Dart Pro 1 heads, Valako Race Head porting, they have dynoed 700+ HP with a 540. :D :D :D

Edlebrock makes a good mechanical fuel pump but you have to use a fuel pressure regulator with it.

Too Old, I wanted to build a 572 but I'm pretty sure you have to have a tall deck and I just have a standard height 502. Thanks for all the info from everyone. I don't know what to do, it seems so easy to just bore my 502 to 509 and put a blower on and make more horsepower, but I don't know if I want the headaches of trying to dial one in. What would you guys do if you had a standard 502? The only other thing is my crank is already 20/20 so I would probably have to buy a new crank anyway.

SR-24;

In my opinion you need more head for that Motor. A 310 would really choke it down unless you only want to turn 5000 rpm. I would go with the Dart 345 Pro 1, (the 325 as a BARE minimum)10.00:1 CR, Dart or Merlin Intake and a 975 BG Race Demon. With Hyd roller you should make close to 700hp, solid maybe 750hp @6200, 775 if you really buzz it (like 6700). BG does a good job setting up their carbs..near perfect out of the box if you give the tech guys all your info. Dominators can be a real headache to get dialed in...I have been there and done that.

My 632 has Dart 360 fully ported and polished heads, 10.5:1 CR, dart tunnell ram, 2X775 race demons, 280/288 .785/.760 lift on 115 centerline. Made 901HP@6700. I run 93 Octane with never a sign of detonation, but your cam choice is critical to bleed down cylinder pressures.

jdnca1, Thanks, I might try contacting you for help with cam selection when the time comes because that's one area I don't quite understand everything that needs to be happening and why.

SR-24;

Anytime, I'm not an expert by any means but have direct numbers to several that will give you some great insight on the correct cam. The first thing they will want to know is CR, heads, flow, intake, carb, expected rpm's, etc. But you really need more head, thats where most of your power is made.:cool:

SR-24,
Go with the Brodix intake over the Dart;)

Jdnca1,
Why go with the bigger heads ? I thought that was the problem with making power on a marine engine (low rpm) there isn't a good enough head unless you want to spin it past 6000.
That's why you go with a smaller runner and port it to make it more effienct at lower rpms. I've got Oval port Merlins and they have been welded up and ported and I still have to spin it relatively high 5800 to make any power.
I'm not an expert but have friends that are and I have learned a little thru osmosis :)

26 scarab;

A 540 inch motor needs flow to make power. ;) If he only wants to turn 5000 r's then I agree with you on using small heads. However, when you are talking higher compressions, large roller cams and Dominator carbs you need a head that can support a 540 inch motor (a 454 is a different story) or the rest is a waste, because airflow will be severely restricted especially @6,000 rpm.
It really depends on what a person wants. But if someone is going to spend the money, it really doesn't cost anymore to set up the motor to make some power and you need to turn it to do so.
I know someone running a 540, 10.25:1, with Dart 345 Pro 1's solid roller (270ish duration) and 1150 dominator that makes 775hp on pump gas. :cool: Should be pretty easy to duplicate. :p

my idea
 

in my opinion keep the comp low.that matters maximum 20-30 hp but it is safe.you alredy have lots of hp ,do not risk your engine and loose the idle just for 20-30hp.I made the same mistake 4-5 years ago . was using a 502 with 11:1 cr very rough idle, believe me it is headache!!! when you enter marinas or try to pick some one ,engines always turn off-you always have knock problems-you should make 1500-1700rpm idle which is serious trouble for drives....etc.....etc...
just fly low and enjoy your boat...

The great marine head debate!!!!
 

Here is the question. At what point (rpm, cubic inch, compression and cam) do oval port heads just run out of breath? I built a 454 with 9:1 compression, hydraulic cam, worked over 049 big valve oval port heads, matching intake, 228/235 dur at .050 with .540" lift hyd flat cam and headers. The boat was a blast and gained 10 MPH over the stock 330 motor and put me in the mid 70's with a 210 Baja Sport. This combo worked great down low and pulled good to 5400 rpm or so. Now compare it to my current 496" motor that is about 22 MPH faster than that 454. It has fully ported 325 pro 1's, solid roller 272/280 at .050 and .714" lift, 13.16:1 compression, 1175 CFM Nickerson Dominator, among a bunch other HP goodies. How would oval port heads do on this motor? I think they would give mondo low end and would start to suffer at around 3500 RPM compared to the rect ports. I think a milder 540 could run very well with ovals as 26Scarab and KAAMA have shown, but you are at the outer limit of those heads. It is my opinion that a 325 CC runner is ideal for a mild 540 at 5500 to 6000 RPM on a boat motor. A 345 will be ideal on a 572 to about 600". Above 600" you are probably looking at 360 to 400 CC to keep them breathing. Just my opinion and you know what they say about those. Just like a-holes, we've all got them. :D I would like to hear jimv's opinion as well as some of the other OSO gear heads.:) I hope we are helping this guy!

I agree with you guys on the smaller heads. I don't plan on turning the motor past 6,000 because the cam is only good to 6,000 and I bet it will be more like 5,800 and that's why I said I planned on using the 310cc runners. I will continue to ask around and yes I wish Valako or somebody with alot of experience would read this and tell us all. I am currently running the Merlin 269cc runners on my 502 with a Merlin dual plane and a short duration cam because of silent choice (don't worry, I'm losing the silent choice) and it is very strong. I imagine the torque is astronomical compared to the horsepower though. I read in the Big Block Marine book by Dennis Moore that you needed to be able to turn the stock 320cc runner chevy heads 6,000 to 6,500 before you would benefit but who knows. Thanks to everybody for the input and keep it coming.

SR-24;

I would talk to DART. I'll bet they tell you the 325. I also have the Dennis Moore book and there is a ton of useful info in there. However, it seems he focuses more on the "smaller" cube Big Blocks. Food for thought...Let us know what you find out. :p

I will. I've got some emails out to some engine builders now, just waiting for replies.

Sr-24 if you don't mind me asking what are your cam specs.The specs on chevy high performance 502/500 that used oval port heads and is what I went but I have merlin 269. chevy part number 12366542. 224 intake 234 exhaust .527in .544 ex lift and 110 LSA install on a 110 center line.:cool:

FWIW, here's the built sheet on my 572 - no replacement for displacement. At 8.75:1 (assuming I'm not jetted too lean or have to much ignition advance) I should be able to run on dirt gas.

Yes, stepping up to a 572 requires a tall deck block...... But once you have that, you could go 600CID+ with notching the block on a 4.75" stroke.

I have not seen the dyno sheets, but was told 675hp @ 5400 rpms - not spun higher, as it has a hydraulic roller.

Attached is a link to the build sheet. The only thing different is that it's running a single Dominator - was trying to avoid hatch clearance issues by going with a low rise dual quad, but could not get to run well.


I would think you could get over 600hp with a similarly prepped 540. $.02

kook's build sheet