I've been in the marine racing engine business for almost 20 years now and I haven't seen two the same yet. I've seen some crazy numbers on the forums from time to time I personally take two or three engines a year to a couple of different places to compare with my own numbers to make sure my calibrations and correction factors are were they need to be . Sincerely Laz

The engines I am speaking of are the new 540's 680 hp @ 5,600 and 675 ft lbs of torque @ 4,900. I am now having the Dart Pro One aluminum heads CNC'd. The shop doing my porting on my 310's thinks he can get another 40 hp. But we both wondered about the initial dyno figures.

Do you have bsfc numbers from the dyno? RM builder was explaining to me how the numbers correlate to correction factors and realistic hp numbers,if you post them I'm sure he will pipe in. Were your motors dynoed with dry dyno headers or marine exhaust and were the accesories installed or left off? Those are good numbers,even if they are high from using dry headers etc,your still should be making 640 or so in "marine trim". What kind of tq were you making around 3800-4200,sorta surprised to see only 700 rpm's between tq peak and hp peak and tq peak farely high up the rpm band,you must have a pretty big cam. In your other post you were asking about having your heads ported /cnc'd,personally I'd be worried about shifting the tq and hp peaks up higher yet to the point where your boat will be hard to prop and cruise with but I'm no expert,all my fast marine stuff has been supercharged,there are others that may pipe in with more hands on experience with N/A marine motors, Smitty

Smitty, I believe it is fine of what you said. It's good to focus on the topic, but it's also good to be aware some of those "variables" of what can happen to a consumer who doesn't always know any better and give them a bit of a "heads up".

Rebel Heart,

Your engines sound very close to the 540's I once had. A few years ago I was running a pair of 540's that made something like 682hp @5700rpm on Tom Earhart's dyno with some fully ported 310cc Dart Pro-1 heads by JimV. I was using a Crower hydraulic roller cam 236*/244*@ .050" (300*/307* advertised duration) on 114* lobes, 950cfm Holley carb, Dart intake, 8.7 comp ratio, 32* of timing.

Peak torque came out at 4800rpm. It sounds like you have very close to the same cam in yours as I did. However, my heads were already fully ported by JimV. We didn't dyno the engines above 5700rpm though...so, if there were any better HP numbers I obviously cannot report any after that and I wasn't really interested as 5700rpm was as high of RPM that I wanted to turn the engines with my 32" labbed props.

By the way, the type of exhaust that we were using at the time on the dyno were dry tubular dyno type headers that I believe had 1-7/8" primaries. I use Stellings full length dry tubular headers in the boat.

Thanks for your replies. I had spoken to Jim V. at the Shootout last year and was impressed with his knowledge. I just spoke with him again last weekend about what he would be able to do with my application. Again, I thought he had some great ideas. Is there anyone else that I should be talking to about porting the heads or is he the best?

Another thing to consider is what are your correction standars sae or stp. At my work we can gain 30 hp or more just by using stp versus sae

HVH is one if not the best in the cylinder head porting business. There number is 865 573 9151. Ask for Joe Petelle and tell him Chris Straub had you call.

Other good guys are
Larry Meaux in LA
Ron's Porting in St. Louis
Carl Foltz in MI
Wilson's in FL

just to name a few other good guys.

When comparing dyno's there are multiple factors to consider. First most shops correct to Standard, not SAE. SAE corrections will show lower HP figures. The way the testing is done will also change the numbers. A dyno is a great tool for comparisons if used properly. The majority of dynos in the country are used as very expensive test stands. The engine didn't leak water, and it had oil pressure send it on its way. There are some very good shops out there with Great equipment, and procedures but you will pay for that. Testing procedures can vary the repeatability of the numbers you're looking at.

You can spend 20 Grand, get a used dyno and with your buddy the plumber and an electrician your a dyno operator. OR, you can spend hundreds of thousands of dollars to build the "proper" cell for repeatable testing. I try to always keep an engine within the same environment that it will run in. If in the boat it's going to run at 120 degrees water temp that's what you run it at. All pulls should be started within a degree of each other on water, and oil temp. This is not something most shops can do due to time constraints, nor is it something most people would be willing to pay for.

When it comes to dyno testing there are a few bottom lines. First, a good dyno test should save you time, and money setting the engine up in your application (boat, car, etc.). Second, they are a good tool to compare on that specific dyno. Not all dynos are set up the same so not all comparisons are fair. LASTLY, we don't race dynos. You've if you had 500HP, and your boat runs 80, what good is a dyno sheet that says you have 600HP if you run 75! Unless you're working on R&D how the engine performs in it's intended application is the only thing that matters.

Lots of good advice here. If you really want to compare numbers between dynos, you have to be sure that the engines were accessorized the same. Most dynos use a load cell to measure the torque and you want to see proof of recent calibration. After that you get observed HP from the test, the actual HP under the temp, pressure and %RH in the cell.

For your corrrected HP numbers to be valid the values used for these weather conditions must be accurate. Check the dyno sensor for air temp against a thermometer that you know to be accurate. Use barometric pressure and %RH from an instrument you know to be accurate. Now you have corrected HP figures that you can trust.

The easiest way to increase the corrected HP is to stick the dyno air sensor in a location where it is measuring higher air temp than is actually going into the engine. That would be called cheating.

We actually have to make sure that we don't accidentally do the opposite; measure a room air temp that is actually lower than what is entering the blower. Centrifugal blowers are mounted down near the valve cover and it is quite possible to suck hot air into the blower from the vicinity of the headers.

Tom