VP

I just purchased a single engine 29 ft Fountain with a 575 SCi in it.

In the interest of going just a few mph faster (to try and beat my good friend's 35 footer with twin 525's) does anyone know if I can simply reduce the blower pulley size a size or two, without changing fuel pressure, or the fuel pump, or the mapping, or adding an intercooler, or any other of the more involved modifications??

I realize this seems like too simple of a change, but knowing Mercruiser a little, I thought they might have designed this motor way on the conservative side, to allow a simple pulley change without too much risk of reliability loss.

Also, if someone has really done some work in this area, would you know what the stock setup exhaust temperature should be (at about 1/2" from the head) and what a pulley change would produce. Also, was there any oil temperature increase observed??

I only need a couple mph

LapseofReason

SupeChiller make's two kit's, one is like 2k the other3k. They are more than just pully but the engine will live longer. Even if you didn't up the boost a intercooler will up the hp and help engine life. If you only need a few MPH you might want to look at better props and a nose cone.

Whipple Charged

I would highly recommend against the superchiller kit, they do nothing for the ECU and they increase fuel pressure. This is somewhat close at WOT peak rpm, but everywhere else, is incredibly rich. I cannot explain to you how rich the motor is at this point, I've fixed a few, Az. Speed and Marine has as well.

If you want more power, you can increase the boost to 5-6lbs. from the stock 4. Should pick up about 25-35hp. Installing an intercooler with 4lbs. of boost will not do much if anything. It will lower boost to 3lbs. and will have very little cooling because there is very little temp increase at that psi level. Probably maximum gain without changing boost/pulley is 10hp. The power increase comes from increasing cylinder pressure, which means more boost and in order to fight detonation, an intercooler is needed for anything over 6 lbs. of boost. The motor has 7.5:1 compression.

So if you want a minor power increase, just up the boost a tad bit and know that your voiding your Mercury warranty. If you want more power, install intercooler, run 8lbs. of boost and have somebody reprogram the ECU for proper management.

Thanks,
Dustin

VP

Thanks for the info Dustin. I appreciate the expert advise. I will think about this somemore.

Also, I asked if anyone knew exhaust temps of the stock 575 verses one with a little higher boost (but without an intercooler). I figured that info might be near impossible to find.

The reason I asked is that I still have the thermocouples and pyro that I used to monitor my exhaust temps on a 540 blower motor that I built personally. I relied on those temps (along with my knock sensor) to keep an eye on things and to help me set my timing. I never had a failure thanks to those, even with a far from ideal setup using a very small 177 blower on a big cube motor -- my oil temp would never stop climbing -- i would have to ease off after a 5 mile WOT run to cool the oil. High piston temps I am assuming, due to small blower -- I was making 4 psi at 5400 rpm.

thanks again,
gary

Whipple Charged

EGT's at the head before water cooled exhaust is around 1350-1400. The added boost raises the temp approx. 30-50 degrees and is in no way enough to burn a piston. It would be ideal to drill your stock thermostat so it will run about 20-30 deg. cooler which will also lower your EGT's accordingly (20-30).

Your motor has a knock system that will retard timing if it sinces some detonation, it also runs 36 total timing so EGT's will stay pretty low. There is no real tuning to do it.

Thanks,
Dustin

VP

Thanks again Dustin,

one last question though ---- do you know what pulley size i might go down to, to get the boost up to 6 psi - it runs about 4.5 psi now, or is it simply a linear relationship between diameter change (ie: blower rpm change) and boost change.

You have been very helpful -- Its not easy to get reliable information like this. I appreciate you sharing it with me, because I am sure it came from many hours on the dyno.

This help you offered me will hopefully come back your way. A very good friend of mine in Charlotte is looking closely at a Whipplecharger package for his HP500 carb'd motor. He ownes a 1999 27 ft Formula and I am pretty sure I will be putting a blower on it sooner than later. We were discussing if it might fit under his current hatch, without punching a hole in it (wants to keep the sunpad as is if at all possible). We would have to relocate the lift mechanism, as that already touches the top of the air cleaner with hatch fully closed, but do not know what the total height of a charger package would be, measured from exactly where.

gary