Re: Engine gurus!!!!!!!!!!
 

Why not lab the 25 Mirage? You are at 80 with a 25 Mirage at 5,000 RPM. You might pick up about 300 RPM with labbing. Wouldn't that be about right or should this combo pull more RPM than 5,300?

Re: Engine gurus!!!!!!!!!!
 

My little bit of input,,advancing to much will help the power peak lower and this could be what's happnin'. Still could make more at higher if propped right but will pull like a mother down low,,like at 4300. Try smaller props and then this winter put the cam in straight up,you probably have plenty of power for take off as it is. Just my .02. But listen to Mcollinstn, he knows his ----

Re: Engine gurus!!!!!!!!!!
 

You think 2 degrees of cam timing caused this? His cam is only advanced 2 degrees from where it is ground.

Re: Engine gurus!!!!!!!!!!
 

Not caused, just helped go 80 at 4300rpm,,, and it's 7 deg adv not 2. If he were running 80 at 4900 everyone would say so what.

Re: Engine gurus!!!!!!!!!!
 

The cam is installed 2 degrees advanced from where it was ground.

The Crane 741 cam is ground with 5 degrees of advance. Just as most Comp Cams are ground 4 degrees advanced.

In this case Straight up would be 5 degrees of advance. Which really should be nill.

Re: Engine gurus!!!!!!!!!!
 

I understand that. I also understand that most cams are ground for cars needing good pull from 1000 RPM and most boats go to 2500-3000 win you "hit it". Also, you need peak torque close to top speed and if he's only turning 4300 advancing some would help explain his very good descent speed at very low R's.

Re: Engine gurus!!!!!!!!!!
 

i have instaled 741 cams as much a 4degrees and still seen them pull to 5800 and make power and torque i do not think the cam has a thing to do with it i would want to try a 1.5 that boat needs a big prop to free up the bottom when you pull a small prop on a boat like that it can not free up the boat like a bigger pitch will i say 1.5 with 28 hydro and the boat will go also the older fountains do not like bravos as the x is to low

Re: Engine gurus!!!!!!!!!!
 

There is a guy on the board that has a 1991 fountain with 600hp 502s. With 27 hydros, he goes 87-88

Re: Engine gurus!!!!!!!!!!
 

I would bet he has 1.5 drives

Re: Engine gurus!!!!!!!!!!
 

Your right about that. Is the ratio determined by the lower, or do you have to do both uppers and lowers?