Pat McPherson

The last time I did a cam swap and computer changes to one of these engines the outcome was not all that great. I had use AZSpeed to reprogram and reprogram and reprogram, but in their defense, I did not use a cam they had done before.
The next go around, I will definitely have an O2 sensor to check the air fuel ratio while running the engine under load in the boat. The ignition timing would be something I hope has been worked out for the HP500 cam.

AIR TIME

he never had it dynoed so it could be 525 to 575, I sold him my old heads intake and the cam was the 731 crane I believe. like I said his is deep plus fat trs plus tranny = 76 all day long he has owned it for 16 or 17 years and its had a stock 330 to a gale banks twin turbo 454 in it, now a 502 with dart, nick 850 ,cmi exh heads rec with work 731 crane= teage stage two cam. your boat has a hire drive height no tranny, step? that adds up. he can mash the throttles at a standing start which we can't do other wise it a new coupler or drive. and he needs ex steering the chinewalk gets bad real quick if he hits a wake or wave. I told him to convert it but he won't.

jayhawk261

We tried the Hydromotive today. It is a new Quad IV-X 26 P. We first ran on the 25P Mirage + with the BBlades lab work. With 2 200+ lb guys and between 1/4 to 1/2 tank of fuel we hit just over 74 at about 5300 - 5400 rpm. With the Hydromotive, we got about 75 at about 5100 rpm. The Hydro was a little faster than the M+. The best thing about it was that the boat finally felt like it came up out of the water and got on the step. The hydro prop mad the boat feel more like I think it should. I'm REAL eager to try a 26 B1 or a labbed version of the Hydromotive.

Also, I may be switching over to a carb to get the rest of my power. I really think this stock intake (my engine guy does as well) is kiling the power. He wants to try an 830 with a brodix type intake and see what we can do with that.

jayhawk261

Here's a little video from yesterday's run. Lots of wind noise and bouncing. It's our first one, so hopefully we'll get better.

http://www.youtube.com/watch?v=G9D5bkgwr-8

scarrab30

Randy, sounds like you like the bow lift. Put a carb on dat thing and go fast. Brian

jayhawk261

Yeah, it definitely felt more "right" with the Hydromotive. The bow lift was there. Now we may have gotten more speed than we did with some better water. We made our first runs with the 25 Mirage + with just a light chop. By the time we changed the prop to the Hydromotive, the water had gotten a bit rougher and we couldn't maintain the speed over the bigger waves. I'd bet if we ran it first, we would have seen another mph or so. I'm guessing with just me and low fuel, I'd see 78 with the Hydromotive. How soon do you need it back Brian? I'd like to test it a couple more times in different conditions and see how it goes. A labbed version of that may be dead on.

Thanks for the loaner!

Pat McPherson

Hi Randy,
Did your engine dyno 501HP with dry headers or with wet exhaust like in a boat?
Did you dyno with long tube headers or short like your CMIs?
If the exhaust used when you dyno'd is not the same or vary similar to what you're running in the boat, your engine is not making the same power in the boat.
It is sounding to me like you have more like 450HP in the boat. If you had 500HP in the boat you could spin a 28p B1 to 5100-5200rpm and run over 80mph.
As for the Merc MPI Intake; it is adequate for a 500HP 460cube engine. There are many guys that are using them on 525HP 502cube engine with success. There are also proven mods that shorten the runners for better flow if you like.
I would agree that switching to a carb and high rise intake is a lot easier to tune and get that last bit of power out of the engine though.
If you do pull the EFI stuff off, shoot me a price for the goodies. I plan to build a 450+HP 454 this winter.
Have fun and be Safe...

jayhawk261

Hey Pat, the engine was dynoed with long tube dyno headers. Other than that, all accessories including raw water pump were in place. I think we can assume we're losing some power due to the difference in headers as I'm sure it likes the long tubes much better for scavenging.

That being said, I may pull it again this winter to do something more powerful. We will most likely keep it for another couple of years at least, so I'm going to try to have some fun with it.

The reason we're leery of the intake is that the power curve goes flat at 5200 rpm. You could hear it on the dyno. My engine guy built a 502 with a similar cam/intake/head setup, and it went flat in the same manner at 4800 rpm which makes sense being that it is more cubes. After running in the boat, they switched over to a single plane and an 830 and were able to nail the rpm and get a fair amount more power. He hasn't dynoed it since the change, but he feels it made a drastic improvement.

Pat McPherson

Yup, the engine with dry long tube headers is definately going to make more power than the short wet exhaust in the boat. Don't know if it's 50HP, but your top speed numbers are the same as I had in my old boat and vary similar to what Dave gets with a 425HP 496 in his 98 24'.

The water mixing in will the exhaust hold it back as much as anything. I've done some testing with a bud with an engine running with a cross over and no thermostate. The more water we dumped outside the exhaust the faster the boat went, that was also with Stainless Marine manifolds not headers.
It sure does sound like the MPI intake could be a bottle neck.
I've read that the Merc intake is good to 5200 on a 502 stock and even a 540 with porting/shortened runners.
I bet if you went for a bigger cam in your engine along with a carb and high rise instead of the MPI you could easily gain 50HP.

scarrab30

Randy, Go ahead do more testing. Just remember, your taxing your drive and probably getting the drive pretty warm. Just keep an eye on it. I ussually spin those at59 to 6300rpm. Say hi to your wife for us. Brian