SB

iTrader: (1)

Say your engine makes 400hp at 4800 rpm, but at 5400rpm it is making 450hp....where would you want to be propped for ? 400hp or 450hp ?

What if your old motor made the same 400hp at the same 4800rpm ?

Exactly......That's why same prop is doing same rpm at WOT. Note: saying this to my example, possibly not yours, I need to run some brain functions to try to compare the two engines to see what else may be causing you power issues. I'll be back with MY comparisons on your two builds later.

jeffswav

I see were you guys are going with that. I assume if I were propped correctly with the first scenario I may be seeing a different result. A friend loaned me his 24 pitch hydromodive 4 blade. But I have not tried it because I heard 3 blades work better on deep props. I appreciate every ones input. If this were an exact science none of us would have anthing to talk about. Any more input would be appreciated.
Thanks,
Jeff

coryj

Are you using Ethanol gas blend. I have heard from others that you can get more power out of straight Gasoline. Just a thought

jeffswav

You cannot get anything but E10 in Illinois or Missouri. It sucks for boats. I store it NO longer than 3 weeks.

Turbojack

I still want to say it is the cam. Just would hate to have you change it out to prove that I am right or wrong. I agree with your reasoning about going to a smaller prop will not gain you anything.

I do think you need to try a smaller pitch prop to at least see if the motor will turn more rpm's. You might have some problem that is causing the motor to turn more rpms and not be the cam.

When I was doing motor upgrades I could not get the motor to rap up. I could break the prop loose at 2500 rpm, rap to 4200 almost as soon as I went wot, but when the motor hit some point (do not remember the rpm) it would not rap past that point. I ended out changing the plugs, wires, coil, and sill no inprovement in the RPM. Once I changed out the MSD box I had the rpm's I was looking for.

Can you run a computer log on a run. That may give us an idea as to what may be wrong.

jeffswav

I have a dataloger on the program but I have not used it. I usually make the adjustments on the fly. I may try it next time I go out. I am not going to change the cam anytime soon but I am just aggrivated when I don't see results. Every upgrade I have made I have seen a 1 to 3 MPH gain. I have done all of my changes one step at a time and has given me encouragement. But when you loose MPH that sucks!!!

You make a good point with the MSD box. I am using ACCEL HEI electronic modual, Cap, Rotor and Coil, with 8.8 300+ wires. I used to run Bosch Platnum plugs but I now am using NGK BR6. Do you see any proplems here? However the only change from before are the plugs.

Thanks,
Jeff

John B

Check the valve spring tension. You can check the seat pressure without taking them off the head. This happened to some of my motors. Very basically, the cam lift caused the springs to bounce and killed them. After two sets went dead, I went to a milder cam and the problem was gone.

This is just a thought! Since after adding 100 hp per motor, my boat went slower. It took two years to get it right.

JB

jeffswav

I just had the heads rebuilt with new springs & retainers. They were set up at the machine shop to cam specs. I don't think that is the problem. When you did your upgrades had you done any head work or was that part still stock?

SB

iTrader: (1)

I finally got the chance to do the cam comparisons. The lunati only shows valve events at .050" so I could only compare those.

Then.......A bell rang in my head which was 'That cyl head casting # is one I don't know of." So, I checked it out at mortec.com and found this:

3993820....71......oval...OPEN...402, 113cc chamber, 255/114 ports

Unfortunately, I have no experience with this head so I don't have anything to report to you. No experience stock and no experience with what it takes to mod them to make more power.

I just have experience with the typical 118cc / 122cc open chamber 049 and 781 large oval ports.

I apologize. i really like to help people in these dilemma's. I don't always have an answer but sometimes my brainstorming help's the person find it.

Sorry dude. I'm bummed I can't help brainstorm with you further.

SB

iTrader: (1)

BTW: since everyone's mentioning valvesprings and you mentioned your other cam wore out, are we sure this new cam is not going flat ?

This is a huge possibility with any flat tappet cam if not broken in corect (as we all know) but even more importantly now is if normal oil is used. Normal oil no longer has the % of ZDDP that keeps flat tappets alive. there are only a few oils now that do have it - some diesel, motorcycle, and racing oils. I wrote a huge thread (okay a few threads) about this over the past year os so elsewhere. if you want me to dig the threads up and provide you links to follow and read feal free to let me know.

As a side note to this: many companies don't use proper cam cores and lifters to help keep this away also.

Ton of odds against the unknowing and unfortunately, the knowing too. It suggs and really has kicked the industry on it's azz. Thus why all the Hyd rollers you see now.

Sorry for rambling.