HELP. New boat, prop issues need education!
 

Hey guys, new on here. I reside in Central Kentucky and spend most of my summer on Lake Cumberland. Having a few boats in my time i have finally gotten to a boat I've wanted for some time now.

1990 Baja 265DVX. 502CI built with 650+ HP. Bravo I outdrive. Keel was taken out or modified of the hull.

Here is my issue, The boat came with a hydromotive quad IV prop 24P. It ran about 5100 RPM @ 64MPH NOT WHAT I EXPECTED.

So, i had been talking with Mark @ marks high performance props. He recommended a Bravo I 4 blade 26P. Bought the prop, dropped to 4200RPM at the exact same speed 63MPH. Since then i have had the prop repitched to 25 had the blades thinned out and cup taken out, got my RPM back up to around 4600 but still running 63MPH (GPS everytime). Needless to say i am very dissapointed with these type of numbers i was for sure this would be a 75MPH boat. Especially since the keel was taken out of the hull of the boat. Oh and the other thing, this boat comes out of the water like a monster! I mean the hole shot is better than any boat i have ever owned even with a prop that lets me tach at 4600. So, just looking for some help, advice, am i missing something here? Anything is appreciated guys. Thanks.

You sure you have 650 HP?? With that much actual HP, I would also expect speeds in 70's. Get specs on motor and post on here.. lots of motor heads on here that can help you out!! Slips looks OK, so it may be lack of HP.. sorry, but Congrats on the new boat nonetheless

Thanks. Yes I know the previous owner and the guy that built the engine. Dart heads, crane cam, solid lifters, 950cfm Holley, it has the power. Funny thing the low end and mid range power is unbelievable comes on plane in seconds effortlessly even when it would top out at 4200. I did just find the msd distributors advance is locked out...little confused there. Going to hook up a timing light and see what its set at. I'm thinking it may have just the wrong cam in it. Can't get dyno sheets but the boat is built for sure. Any advice or knowledge is welcome. I'm a gearhead myself but just enough knowledge on the water to be dangerous. I have an extra mkhammer distributor in the garage from a 454 I may swap them out see what that does.

By the way. Are you using some sort of prop tool? Which one do you use? All the prop tools i use say i should be at least in the 75-80 range.

What do you mean about the "keel taken out or modified" ???????????

There is no way to tell what HP the engine is making without some actual specs. Cam specs, head specs, what exhaust???
Its highly unlikely that an N/A marine 502 will make 650hp unless you spin it to about 5800rpms.

If you know the prior owner, what speed does he say it ran at what rpm???
Where is the engine build sheet????

I normally use blades slip calculator. To be honest I didn't check your slip but as i was running a 25 p m+, I was able to make an educated guess based in my slip, rpms speeds and a friend who is running 26p b1 and our #s were identical. As for top speed, having a 25 ol with only 385hp, 650 HP would that boat near 80, but I was conservative that you would run in 70s..prob high 70s if HP is there.

Problem is, the previous owner was 80 yrs old. He never had it up to speed and never knew how fast it truly went. I am finding more and more out. The "hook" in the rear of the hull was taken out, he referred to it as a keel. I did find the ignition advance locked out on the distributor. And the cam spec is a crane p/n 13SR00027 Grind # SR-246/362-2S-8 IG

Here is your cam specs. http://www.cranecams.com/product/car...detail&p=24626
Not what I would want in a marine engine since its a solid roller, but it should not be hurting top end HP. Its really too much cam for a 502.
It won't make its peak power until close to 6000rpms.

What is the timing set at????

Couldnt tell you what timing is at just yet. i am going to check it when i get back down there this weekend. So why wouldn't you want this cam, why do you think its too much for a 502? It doesn't idle rough at all. By the way, I've decided to put my 24P intimidator prop back on once i have it re-pitched to a 23, add parabolic rake and sharpen the leading edges. I am convinced the engine isn't turning fast enough.

If you weigh the boat with fuel and people and gear we can do a HP/weight calculation that will be quite accurate as to the speed potential.

Brett

I am going to estimate 4600lbs with gear, fuel and people in it. It isn't packed full of stuff, it has a 60 gallon fuel tank and is usually 2 people in it. 4 at most. Keep in mind that the keel was taken out of the back of the hull, not sure if this is good or bad yet.

Because its a solid roller and will need valve lash checks every 25-50hrs. IMO, it also has too much duration. Solid rollers make there power at high rpms(6000rpms+).
For a marine engine, you want a cam that will make more torque at lower rpms.
You won't get 650hp out of a NA 502ci unless the engine is spinning 6000rpms.
You need to make sure the engine is tuned correctly before you try to prop it correctly. It could be that the timing is way off.

Your boat is listed at 4650lbs dry weight. With fuel, light normal gear, and 2 people, you will be around 5200-5300lbs min.

Thats going to be the first thing i do is check the timing. I'm also going to ask the builder why the timing is locked out. There is no advance on the timing at all. With no advance who knows how much power I'm losing.

26 inches of pitch at 5400 should give you 78mph with a 13% slip.

This is what the boat should do with 650HP. Give or take of course. 80mph would not be out of the question.
It usually goes back to HP.

Brett

Got an update. The prop i was running is a 23P that was re-worked and apparently one of the blades were a little bent so there was some slip there. I added parabolic rake and sharpened leading edges. I was running 5000RPM with this prop already so well see where this goes.

How did you add parabolic rake?

Brett

Talked to hydromotive and they recommended marks performance props in shelbyville indiana. He is doing the work today and shipping the prop back to me tomorrow. Should have it Thursday for a test run on Friday.

Most likely, it has locked timing to help it stay running at idle with the solid roller cam. Running locked is fine as long as it is set to 32-36* but it can be hard on the starter.

It does have some sort of high torque starter on it, reminds me of my old drag strip days ( the sound of the starter ) . Would it be possible i will see more top end power with having a mechanical advance? Right now, it runs perfectly fine at idle and i would be OK with it running a little rough i think it sounds better any way.

Can't change parabolic rake. That is built into the blades. Small rake angle adjustments can be made other ways though. Maybe that is what he was talking about.

Brett

I assume he meant to increase the angle when he said add rake. I just know that Hydromotive and Mark were talking together about this boat specifically. Brett what is your professional opinion on what type of prop I should be using? I looked your website over and I see you guys sell the hydromotive products.

You need to find out what the timing is set at. Is it supposed to be locked or has the advance froze up???
If it is set 10* plus off from where it should be, you could be losing huge power. Its also not good for the engine and causes high EGT's if you run too little timing.

i assume it is locked since there are no springs or any thing in the distributor. I tried to free it up and it is locked without a doubt. What do you think the timing should be set at? I think it could be locked out and really advanced to make it idle better with that cam??? Is that possible?

Timing should be set at 32-36*

Ill check it out this weekend. I actually have a timing light i can set the degrees advance and then just line up the 0 mark on the harmonic balancer.

I have my timing locked out and I have no problems getting on plane. With the cam you have you will need to keep it locked to get it to idle. It really sounds to me like to cam timing is off. If your timing were retarded enough to affect top speed, with your cam it would affect idle also.

I have no problem getting on plane at all, it is unbelievable hole shot, faster than my 23ft crownline 454 w/bravo III

I installed the hydromotive prop with the re-work on it. I am running 66-67 MPH @ 5100 RPM. Speed does not change with 6 people or 2 people in the boat. Thinking i still need to run a little higher.

Until you find out if the engine timing is set up correctly, you're wasting time with swapping props. You might pick up 500-1000+ rpms if the timing is way off.

A guy I know couldn't get past 3200 rpms last Summer on a fresh rebuild. His timing was off about 15*+. Timing fixed and he was at 5000+ rpms.

Dart heads with 950 Holley and that big cam would give you peak power up around 6,000 rpm or probably higher ? Does it have a single plane intake as well? I Would say you are leaving plenty of power on the table by spinning only 4800-5000rpm. Smaller cam and dual plane intake should give you a ton more torque exactly where you need it........ TBF