MILD THUNDER

I can tell you, I have had these engines on two separate dynos, and both times they made 800hp. One was a DTS dyno, one was a superflow 902, in full marine trim. Neither dyno shop built the engines.

800HP is not alot of power for a forced induction big block. The 900sc, was nothing exotic. A 540 cubic inch, with vintage brodix heads, a low lift solid roller cam, 8:1 static, 1071 blower and lee intercooler. I believe they made 900HP on merc's dyno, with 10lbs of boost. On someone elses dyno, probably a little more. Even if we call them 1.7HP per ci builds....why would that be so insane to think, that a 468, can't make 1.7HP per ci with a blower ?

Crude Intentions

Well these are dyno numbers with full accessories and a 96 mph straight bottom fountain. All seems about right. It's hard to imagine anyone could put a better combo together than merc.

donzi matt

6000

MILD THUNDER

What does my mph have to do with anything? My non stepped, 10,500 lb Fountain went 96.6. When the boat was brand new, with 420HP 454's, and TRS drives, it went 68-69mph. Its not a race hull, has full cabin with a/c unit, old speedmaster drives, turning 17x28 props to 6200-6300RPM. I can tell you, with an old straight bottom 38 Fever, your aren't getting 96-97mph, with a pair of 650's.

Theres a local guy I know who raced a straight bottom 38 Fever named "juwanna" . Stripped hull for racing. Had 750hp engines, #4 drives. They spent a bunch of time dialing the boat in at lake X. The boat ran 90mph once dialed in, many years ago.


I also have some data from a brand new 1994 Straight Bottom 42 staggered setup, with 6's. Full pleasure boat. Merc 800sc engines, which made i believe 750hp ish at the flywheel. Boat ran 84mph on radar when new. There used to be a race layup 41 Apache around here with merc 800sc engines, that ran pretty strong.

How fast is your race apache with the 950's? What props at what rpm do you turn?

MILD THUNDER

The 800sc merc, was a 572ci. Had a 240/240, flat tappet camshaft, 559 lift. Had GM Iron rectangle port heads, 7.5:1 static. B&M 420 Megablower, making about 7-8psi at 18% overdriven. I believe Mercury rated it at 750HP at the flywheel at 5000-5200rpm. Non intercooled.

Im not surprised, that your 572, with a much better flowing Dart heads, similar duration but hyd roller cam with 642 lift instead of 560 lift, with a better blower, pair of dominators instead of 700cfm carbs, intercoolers, and an extra 1-2 lbs of boost, plus another half full point of compression, another 800rpm, makes 150hp more than the 800sc station wagon merc engine, using a STD correction factor in dyno trim.

mike tkach

what size are the new carbs joe?

14 apache

My boat started out at 640hp with no accessories on dyno fresh water cooled crash boxes and wet sump #6 went 84mph. Changed camshaft added fuel injection went 92mph. Changed heads and camshaft again ended at 110mph. around 6500 spinning a 17x31 five blade.

MILD THUNDER

850's Mike. I got rid of the 850 holleys I had, as the 2 corner idle circuits weren't cuttin it, and I wanted the nice features of screw in everything on the new quick fuels. I went with the Marine 850s, with the black coating.

MILD THUNDER

Thats moving. If memory serves, the 41 Apache race hull over here, that had the 800sc merc's, ran 90ish . I dont remember if they were dry or wet sump 6's.

Theres a few full pleasure 41's around here, one has blown 540's, I think it runs 80ish.

You run big chief heads on your N/A engines don't you? What kind of hours do you get out of the valvetrain before freshening?

mike tkach

do you think there would be a power gain or loss with the 1050s?