HiPerf2000

iTrader: (2)

You should change the water seperator at least once a year. Usually when you "de-winterize". It will catch any water that may have accumulated in the tank over the winter. I change mine twice. I usually run the antifreeze out of the boat in the spring and then change it. Then i change it again after another tank of fuel runs through.

Your fuel pressure seems like a problem. It could be caused by a bad (dirty) water separator....so start there. Otherwise i would put a mechanical pressure gauge in where your electric sending unit is to verify the pressure reading. You should be reading 7 - 8 lbs.

The fuel press may not be your idle problem, but it could lead to a MAJOR problem down the road if not corrected.

Airpacker

its all in the balancing act of timing versus idle mixture. that engine should be able to idle at 600 rpm no problem.

Griff

There is NO WAY you are making 550-600 hp through the stock exhaust with 5lbs of boost on a 174.

You NEED to find out where the timing is at and what kind of advance module you have.

The fuel pressure needs to be at least 7lbs.

Until these are fixed, there is no way to make suggestions to fix your problem.

HiPerf2000

iTrader: (2)

I'm sure they used a different exhaust system on the dyno, and probably a bigger flame arrester. I have the same setup, and those numbers are in the ballpark.

But i agree that now "installed" in the boat with the other (stock) components the HP numbers have fallen.

Vmax

I have now idea what exhaust and spark arrester that were used for the test. What HP is there is enough to make the pitot kick up at 75 mph and she kept pulling all the way to 5300 and wanted to go faster with a 7/8 fuel load. Did not stay into it to see if she would pull to the 5600RPM dyno reading that made max HP. The boat reacts squirrley with lots of chine walk unless trim is way up when exceeding 4600 RPM. Runs on rails with lots of trim but also gives a lot of rooster tail. Any recommendations for a pitot that will stay down? Tried some short term fixes shy of epoxy none have done the job.

Anyone know if fuel line size going to carb would decrease fuel pressure? There are some large dia lines. I was also going to look for the check ball at tank for anti siphon thinking that could be affecting fuel pressure. Any oen experienced in procedure to remove check ball.

Also any one know a good reasonable electric fuel pump and the best way to install plumbing wise to use with the Mechanical pump. Also what is the best way to wire the fuel pump. Do I need to add a relay to ignition. Does any Pump come with relays?
I noticed the Gaffrig gage is set up with all degradations past 5 PSI. Is 7 PSI continuous something I need to shoot for? So far this boat has been lots of project so I'm knocking off each issue slowly. By spring I'm hoping fro a turn key season next year.

RLW

To many questions for one thread Vmax. You have to slow down and address one problem at a time. Do yourself and us a favor and try a search for the numerous questions you have. You will be surprised as to the many answers that already exist in the archives of OSO.

mcollinstn

The old pressure-assisted Medallion performance pitots are still around. They won't kick up at speed, but at 45 mph they WILL kick up if you hit something (if you hit something above 65, it will just shear off the pitot blade - I used to have a bag of replacement blades for them).

Too small of a line can choke off the fuel supply at high speed and cause pressure drop at the carb. Too large never hurt anyone.

Dirty strainer/separator can cause lack of fuel pressure.

Too small of a spring ball in the tank can reduce pressure. Don't remove the ball unless you are sure you will NEVER get a leak in your fuel system (the spring ball keeps from siphoning all your fuel into your bilge).

If you have a mechanical pump, stay with a mechanical pump - they are the best and most reliable. You may need to upgrade to a larger marine one, though. They make marine mechanical pumps that will support 800 hp.

aTX427

My recomendation is to loose the carb set up and go EFI. I have a hp500EFI with a Whipple and it is the most mild mannered engine I have ever seen. Idles at 750, goes into forward and reverse without stalling and most importantly, I don't have to throttle up when I shift. As far as big props, I am turning a lab 30 with 1.34 gears. This is a close to turn key hi-perf as you get.

Griff

Somehow, I don't think he's wanting to spend 10k on a Whippled EFI set up.

I can tell you that cam is a flat tappet hydraulic very similar to the 525SC cam except on a 112 lobe sep.
It has 226/236 duration @.050 and .534/.553 lift.

There is no reason your engine with that cam should not idle at 900rpms or less. I had the same one in a N/A 454 and it idled at 900rpms in neutral and 750 in gear with 12* initial timing.

I would check your timing first and verify the amount of advance, Get the fuel pressure up to at least 7#'s and then send the carb to Nickerson to be set up for your engine.

Boostdaddy

Vmax - The fuel pump should be 120GPH for a Supercharged Engine. The fuel pressure should be 7-8lbs. at low speed and not drop below 5lbs at wide open throttle.

My guess is the Carb came off a HP 500 and is not set up to flow enough Air & Fuel for the Supercharger. Proper adjustments should take care of the situation as long as everything else is good to go.

Good Luck!