Need Engine Help Quick!!
 

Ok everyone, I need some help here. As many of you know, I have been redoing my engines over the winter. What I did was take my stock 525SC’s and replaced the blowers, carbs, pulleys, belts, etc. Prior to this I was running 88-90 with standard Bravo’s on my single step 35’ Fountain. After the new 420 mega-blowers, new carbs, belts, pulleys and nose cones on the drives were added, I’ve lost 3-5 mph. Obviously we thought it was the drives or props so we tried a 26, 28 (original), 30, and 32 pitch prop with little to no difference in any of them. We then tried 2” shorter drives because we could not get the props to blow-out getting on plane like they had been, still no change and still lower speeds. We got anywhere from 5400-6000rpm’s with then props, but nothing helped. Finally, we thought maybe the engines had a compression issue or leak, but we tested them both and they were perfect. The only thing we can think of is that we aren’t getting the horsepower we should. If so, how’s that possible? What could possibly be mismatched that would be causing this problem? Should I spend the money to have them dynoed, then find out it isn't producing the horsepower, but not know where the problem is or find out they are producing more with lower speeds? Everyone working on this is completely frustrated!! Help!!!!!!!

Is your boost pressure higher now than before?

still running 5lbs of boost

When you replaced blowers, carbs etc, you gave yourself the potential to run more boost while creating less heat. Now if you want more horsepower, you'll have to turn up the boost. Continuing to tune will probably get back the lost mph, but to go faster you will have to change pulleys.

Did you have the carbs bench flowed and tuned to you setup? When I had mine done at Pro Systems they found 62 more ponys, best 400.00 I ever spent worth every penny!

Shouldn't the bigger blowers alone produce more horsepower at the same boost?

Yes, the carbs were completely rebuilt and flow smooth.......

Perhaps, if the charge is cooler and denser. But the larger blower also takes more hp to turn. You have lost a sizable amount of horsepower so I would look at what has been changed. I'm assuming that all normal tune up stuff has been done like making sure it's firing on all cyl. and sparkplug wires and cap and rotor are good. The first thing I would look at is carb jetting. Is the engine getting enough fuel? The second thing is ignition timing. Did you retard the timing any? I don't think the nosecone slowed you down any.

The boat also had scoops installed, so the engines are running really cool. All the top end engine stuff has been gone over a few times and checks out. Brand new spark plugs, wires, etc. We had problems with the carb lines, but they reworked them to flow smooth. The timing was set and doesn't seem to be a problem. We are just totally lost...............

What carbs are you using?

HOLLEY 850CFM

TTT

what are the guys at Advance saying about it?
are they still helping?

Matt still has the boat and he's been more than helpful. That group over there is amazing. We are looking at the MSD box now because it has some technology in it that allows it to retard the timing depnding on the boost. We thought we had bypassed it by locking the timing at 34, but we may not have been totally successful. Does anyone have experience with this type of MSD boxes?

TTT

MSD 6 BTM ? Boost timing master? It will retard timing regardless of what the distributer is doing. I have no first hand experience but the literature says it is adjustable from 0 to 3 degrees of retard for every pound of boost. Sounds like a great idea, set timing at 36 and have the box take out 1 degree for every pound of boost.

Motors are not very smart. 5 pounds of boost is 5 pounds of boost. On a 420 vs a 170 cfm there may be a slightly cooler intake air temp which would help HP.

Your jetting should be in the high 80's with 2 X 850 carbs, which is too much carb for your setup. But it will work, the venturi signal will be less than desirable since one 850 can support over 500 hp. Two are good over 1000hp. Stock 850's usually come with 80 jets, and this is most likely where your horsepower is lost. If its this lean you will kill the motor, especially at 34 degrees timing!

If the timing is locked at 34, this is too much, but Mercury seems to recommend 34. Maybe they can get away with it with a 7.5 CR. I would try 28-30.

John B

What are some baseline stats???

What props, what rpm, and what speed did you normally get with the stock 525's???

Then using the same props, what happened????

You need to figure out some prop slip numbers to determine whether you lost HP with the engines or increased prop slip with the nosecones.

If the slip is the same, then the engines are down on power. If the slip is up then its the nosecones.