Mudball

Oh, I forgot to mention....

Cdscarab mentioned a big question!! GAS MILEAGE!!

I used to be able to hot rod around this lake all weekend on 50 gallons. NOW, If I am into the throttles at all, I can almost WATCH the gas gauge go down!!

I was running hard (NOT at WOT) a couple of weeks ago, and burned up 50 gallons in about 2 hours!!!!!!!

There is a HUGE difference in gas consumption with horsepower!!!!

Take care,
Kent (Who needs a bigger gas tank now!)

SeaRay Jim

Yes, that was mine in pieces. I've only seen pictures of the inside though it's not a pretty sight!

Quick low-down on the engine. It was bone stock but had to come out for a coupler failure. While it was out........I wanted to add Corsa. While it was out, it got Corsa, plus significant head work including bigger valves, cam, injectors from an HP500EFI I believe (take outs from Tyler Crockett as he was programming the ECU) becasue the stock injectors weren't near enough, ECU programming and other little minor goodies. 2-3 tries at the ECU via long distance trial and error and it appeared to be about as right as it could be. It ran very good for about 60 hours and one very cool morning running just shy of WOT it dropped a valve and went boom! Valve appears to have stuck in the guide and of course the piston hit it and the rest is history....and I have the pictures. Rod with nothing left of the piston, a hole in the cylinder wall and a bent headless valve stem pearing out of the head.

Moral of the story is that Bob really, really wanted to rip the restrictive MPI off and go carb and manifold for both performance and reliability reasons since it would be sooo much easier to get the A/F right. I was stubborn and wanted to keep the MPI, not realizing just how resrictive it was and how much of a PITA it would be to get the ECU re-programmed right. Mid-range was awesome but top end pretty much died off over 4000 - 4200 RPM just like stock. I got 3-4 MPH more overall but that includes labbed and cupped prop at the same time. Lesson learned.

I would agree that if you want more power, repower and sell your 7.4 to someone needing to repower a small pocket cruiser that can use the reliable, flat torque motor. Otherwise, plan on spending a lot of money on head work, cam and CARB/MANIFOLD and get 400-425 HP. Not sure it's worth the $$$$ for that gain. The guy that bought my heads and cam will be doing the same thing to his (Volvo 7.4 GXi) but he's saving a ton of money buying my heads and cam so his will be more worth it.

We decided not to rebuild the 7.4 so Bob's building a 540 for mine right now. This one will be just a little more significant motor than the 7.4.

BTW, I still have pieces, I mean parts left from the 7.4 to sell!!

David Haag

Mudball, I see you are up in austin TX. I am right down here on lake McQueeney. We just had some big flooding down here alot of people lost boats. Did you do that swap yourself. If I buy s 502 could you help me put it in the boat? Oh yeah, my 454 is a carbed motor. No EFI.

David Haag

Sorry I see you had full throttle marine do the work. I was to tired to read all the post. Is that shop up in austin?

cdscarab

Mudball, your right, a small gas tank can take some of the fun out of bigger power. My 21 scarab only carries 60gals. of gas which used to take me anywhere and back on this end of Lake Ontario. But after moving up to a Hawk 525sc, fuel load now plays a much larger part in planning a trip. Not that the 525 doesn't get good milage, it does, if I can resist playing with the power. Which I normally can't, way too much fun. But then that is why I went to the trouble of changing motors.

Dave Haag, one other thing you should do before driving that Hammer with +500 ponies. While the drive is off, have it checked by a reputable drive specialist. Repair and strenghten it where it needs it. Otherwise your new found fun could be short lived. I had mine checked by Chris Martin, Sterndrive Specialist, here in NY. It had about 400hrs. on it and would not have lasted the 1st weekend out with the 525 had I not had it rebuilt. I'm sure some of the guys on the board can direct you to some one in your area.

Jigsaw89

I have the same need for reliable speed as David Haag mentioned above. My boat is a 1989 SeaRay 260 Cuddy (similar to the Pachanga) equipped with a 7.4L Carbed Merc 454 mated to a Bravo 1. The motor and drive are original with approx 790 hours. The entire boat has been well maintained and performs flawlessly, but I figure a repower is in order by this time next year. According to what I’ve read in this thread, it sounds like the best way to increase reliable power is to order a new 8.2L 502 rated at 435hp for approx $5k @ 1800runsnew.com and bolt on my intake, carb and accessories. Does anyone recommend an alternative or a different/new carb to install on this setup? Should I go MPI and where should I look to purchase the intake, injectors, wiring harness and computer? Following are pics of my boat and engine compartment. Thanks for all the help!
Dan

Payton

Instead of your stock 7.4 intake. Find a Wieand Team G and a 800 Holley or a Mighty Deamon Marine 750. You will be much happier. Even a stock 454Mag intake is an alum high rise, that would be better than the 7.4 cast iron intake.
The Team G is what Merc used on their hi perf 454s like the 420.


I may have a 454 Mag intake for sale. PM me if intrested.

Madmax

I have a 2001 HP500 that I will be letting go. I think I have it sold, but if not, keep me in mind. I sold the boat it was going to go in, so I have no use for it. e-mail me offline at [email protected] if interested in more details. Don't worry, it's cheap...

David Haag

Madmax, I sent you email.

Dave M

I'm replacing my 454 Mag with a 496 HO. I thought about custom power but I don't want the headaches. I was also thinking about the gas thing too. I have a 60 gal. tank. With my 454 Mag I was averaging about 10 GPH. So, I could run about a 5 hrs on a tank. I figure the 496 will burn about the same fuel.