should i advance my cam

[dave186]

ok, so i got this thing running pretty good, and all the work i did to the motor gained me 200rpm. i assumed it just needed some tuning, but i havent been able to gain a thing, went from a 750 vac secondary, to a 650 double pumper and no change at all, other than it ran better with the mechanicals. now im back to the 750 with some way bigger jets, bigger squirters and a metering block instead of a plate. no change there either. i know there is more HP in this engine and i think it lies in the cam. i gained a total of 200rpm over a stock 460, i have more compression, bigger cam, ported heads and changed from logs to headers. compression is 10.5:1+, cam is a Lunati 280/292 .514/.543, i can post more details tommorow that is just off the top of my head. im thinking advancing the cam could help get the power band down a bit so i can use it.

[Squirtin Thunder]

Put a 850DP on it and see if there is any change.
How many Rs are you turning and what impeller ???
From stock I gained 700rpm, 4600-5300.

[NorCal Gameshow]

what do the plugs look like? that should help you with the carb, more isn't always better ;)
what is your top end rpm?
THIS A AMERICAN TURBINE IMPELLAR CHART:
H.P. 9.5 9.25 AA A B C
150 2900 3050 3200 3600 3800 4050
200 3200 3350 3500 4000 4200 4450
250 3450 3600 3700 4300 4500 4800
300 3800 3950 4050 4550 4800 5100
350 4050 4200 4300 4750 5100 5350
400 4250 4400 4500 5050 5300 5600
450 4450 4600 4700 5250 5500 5850
500 4650 4800 4950 5400 5700 6050
550 4800 4950 5100 5550 5850 N/A
*THESE RPM VALUES MAY VARY ACCORDING TO HOW YOUR BOAT ALLOWS THE PUMP TO LOAD
HORSE POWER REQUIREMENTS ARE AT THE PUMP SHAFT

[Wicked Performance Boats]

MOST jetboats like the camshaft installed 4 degrees advanced. If you didn't degree it when you put it in, now is the time to check it. For top performance it must be degreed. Budlight :idea:

[FASTRAT]

MOST jetboats like the camshaft installed 4 degrees advanced. If you didn't degree it when you put it in, now is the time to check it. For top performance it must be degreed. Budlight :idea:
does this apply to blown mtrs as well as normally aspirated mtrs?
fastrat

[Floored]

not unless cam has too much duration and is bleeding off boost then advancing will help trap some of the charge by closing the intake early. blower motors have more torque than 2 gravitationally challenged dudes on a 12 ft cheater pipe :wink: so usually not needed.

[Wicked Performance Boats]

My motor has the cam 2 degrees advanced per George S. @ Clay Smiths Cams. The same as his personal jetboat, according to him. Budlight

[FILUCKY]

Theres a good chance that your bigger cam and head work has moved your power curve a little beyond your impeller cut and is hurting your overall performance. You might look into cutting a little off your impeller to get your new engine combo were it wants to run.

[dave186]

i was spining 4600 rpm, now im spinning 4800. i think i remember reading on the cam card that its got something like 5 degrees advance ground into it, but i would have to double check. i have a 9 keyway timing set, so i may just try it at +2 and see what happens. for the carb, im going to get one of those proform main bodies for the 650DP and kick the vac. secondaries to the curb.
i was thinking about cutting the impeller down, but its not even been in there a year, so i will mess with the motor first.

[Squirtin Thunder]

i was spining 4600 rpm, now im spinning 4800. i think i remember reading on the cam card that its got something like 5 degrees advance ground into it, but i would have to double check. i have a 9 keyway timing set, so i may just try it at +2 and see what happens. for the carb, im going to get one of those proform main bodies for the 650DP and kick the vac. secondaries to the curb.
i was thinking about cutting the impeller down, but its not even been in there a year, so i will mess with the motor first.
Put a 850DP on it and see if there is any change.
How many Rs are you turning and what impeller ???
From stock I gained 700rpm, 4600-5300.
Dave,
When I put my 750vac on I lost almost a full 300RPM !!!
Fords love carberation. Believe it or not on most BBF bigger is better. Dave on my Off-Road truck I run the 750 with no loss in rpm, it will turn 5800-6000K depending on elavation. In the boat it is lean with the 750 at 5000-5100. Don't waste your money on that 650.
Give me a call before you do anything Please !!!
1-928-704-1158

[Wicked Performance Boats]

When degreeing the cam, I'm not talking about what the timing set keyways say is advanced or retarded. I'm talking about finding top dead center and putting a degree wheel on it and checking the true position of the camshaft. Then you will know where to move it. I wouldn't run any performance motor without degreeing the cam first. Ever wonder why some motors run like a striped ass ape and some are dogs? Degree it, don't wonder or guess. Budlight :hammerhea

[EXTREMEBOATS]

Some thing to add to what Wicked said. Putting the cam where it was ground to work is one thing, but by advancing your cam you move the power band up a few hundred rpm,retarding lowers the power band.So it may or maynot help your problem. Just some thing to consider befor you try it. Mike :idea:

[dave186]

i thought it was the other way around, advance the cam to lower the power band in the RPM range. I would degree the cam, but i dont have the tools or know anyone that does.

[Wicked Performance Boats]

It's worth the money to buy the tools, try Jeg's or Summit. They'll last you a lifetime and you can do your buddies engines and make money and make them think your hotshit! Budlight :D

[Wicked Performance Boats]

Denis, I always knew that you where retarded, just not 3%, just joking!!! Did you get the Eliminator on the water yet? Budlight

[Squirtin Thunder]

i thought it was the other way around, advance the cam to lower the power band in the RPM range. I would degree the cam, but i dont have the tools or know anyone that does.
Your right Dave !!!

[Wicked Performance Boats]

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[FILUCKY]

Most likely your not running enough cam to be a problem, but keep in mind that when you change your degree on the cam you also change the valve to piston clearance. At the RPM your running 4 degrees advance would work great.

[Wicked Performance Boats]

Most likely your not running enough cam to be a problem, but keep in mind that when you change your degree on the cam you also change the valve to piston clearance. At the RPM your running 4 degrees advance would work great.
I 2nd that! Budlight

[Moneypitt]

Since you didn't mention valve lash, it must be hyd. Without adjustable rockers?.....Lifters are possibly bleeding off?.......???????????MP

[RiverRacer]

My motor has the cam 2 degrees advanced per George S. @ Clay Smiths Cams. The same as his personal jetboat, according to him. Budlight
Hate to say this, but in my experience 2 degrees is not enough to show anything either way as far as torque or power. ALSO, Advancing the cam lowers the rpm at which peak torque and power occurs, while Retarding raises these numbers. At the specs you gave(adv duration and lift) your cam sounds quite mild. I doubt whether advancing will help you. You might try retarding it 4 degrees and see what happens WITHOUT touching/changing anything else. That's what I would do first.

[steelcomp]

No.
Arbitrarily moving your cam without knowing where it is to start with is a mistake. If you're going to go to all the trouble of pulling the front cover off and messing around with that, take the time to degree your cam. You can't just "guess" at what you're doing...well, you can, but you're pretty much wasting your time. If you find that you're within a couple of degrees of where the mfgr says to put it, then you aren't going to get much by moving it, at your power and performance level. I agree with what's been said about your impeller cut, and the fact that you've probably raised the power level to an unusable rpm with your current combination. The power's probably there, you're just not seeing it. A 750 is certainly big enough for what you're doing. Fords, because of their rod/stroke ratio respond better to a smaller carb that something like a BB Chev. You could try the 850, but if you can't pull that impeller past 4800, I think you'll waste your time there, too. You need to get your motor up in the 5300-5500 range to take advantage of what you've done to your motor. You can keep the vac carb, just put the lightest spring they make in the vac diaphragm, or get a DP.

[dave186]

so, my best performance gain is going to come from the impeller. also, it is a hydraulic cam but i have adjustable rockers.

[Wicked Performance Boats]

Denis, Cool, good to hear from you. keep me posted. Budlight 104 degrees today :D