What are your thoughts on that?

Depends if the boat will react to another 10-15hp. Oh, forgot too mention, he pulled off flame arrestor to make sure that wasn't causing it. It wasn't.

Haha, probably not, but I need all I can get. Good info. I think I'll have to drill and tap a port into the intake manifold as I don't think there is a bung for a vacuum gauge there.

SB is correct, I pull 2" at WOT with a light load. More if I have it loaded with fuel or a couple of people. However, my hull is about topped out, and another 15-20 hp won't do much. IMO, 850 cfm is too small even for a mild marine motor. I'd like a 950 or even 1000.

Theres guys who think 750 CFM, is plenty for a 6500RPM 572, and theres guys who think a 5000RPM 454 mag, needs an 1150 dominator.

If I had your combo, I'd be looking at a set of the quick fuel Black Diamond coated Marine 850's. They sell for 650 bucks each at summit, and are a dam nice carb for that money.

I wouldn't expect much in terms of power, going from that carb you have now, but you would get a much nicer running, more tuneable carb with the quick fuel M-850. The black coating on them is really nice, and stays looking good, which we all like.

You want to carb it for max power? Any wide-open vacuum more than 1.3" is hurting your max output.
If I'm looking for all out max for a combination, I don't want to see more than 1.0" of vacuum.

But, if you carb it for less than 1" of vacuum, it will not behave as well when nursing the sticks in rough water since the signal thru the venturies is weaker at real low vacuum. You can make up for it with the accel pump cam, but then you end up squirting the heck out of fuel in there. If you commonly run wide open in rough water where you have to be constantly on the sticks, then stay above 1.5" of vacuum wide open.

Tapping for a vacuum gauge? if your intake doesn't have a tap, most carbs either have a port on the baseplate OR many are spotdrilled in the correct location for you to install one there.

Having a vacuum gauge hooked up also helps you get your idle mix and static timing figured out. Sometimes hotrod boat motors end up with way too little initial timing, and too much centrifugal advance with soft springs that end up with "hunting" off idle around the docks. It's not just a supercharged thing.

Intake manifold restrictions will not show up on a vacuum gauge. The gauge is on the wrong side of the manifold to mean anything if you suspect your intake of being a problem.

M

Good conversation here....... I have a 555 CID AFR 335 cnc heads, Edelbrock Victor, 4500 flange, 9.7 CR.... 255/262 .722/.702 solid roller with a 1050 Holley modified by BG way back when 6300 rpm target.
It's sitting here on the dyno, it should be at 750 hp... ran shy of 721 hp with mufflers on exhaust, torque was 683 @5100. Ran without mufflers torque jumped to 693, HP dropped 703 @6100. AF went from 12.8 to 12. I took fuel away no change... I data logged with a Daytona CD-1 made my pull from top down on de acceleration from 6200
MAP dropped from 100 to 75 ? my dyno data showed 1 ". I have a 1200 cfm coming tomorrow to try, then go from there..
It's a strange issue, I can build a 540 hydraulic roller, use a 2000 cfm TB and make 740 hp @ 5900 and the MAP will hold 98-99 Kpa until i get out of the throttle.

How was the exhaust set up in your shop. Meaning, where the mufflers connected directly to the header collectors or how long of pipe before mufflers ? Was pipe same diameter as collectors ?

Without heavy thought, sounds like an exhaust wave tuning issue where the mufflers had you at a better length.

You sure your throttle was opened all the way?

I hear ya. If I were to do it what do you think of the carb you suggested vs a 950 holley? With a future ci increase in nind?