Help with a newly rebuilt HP 500
 

I just had my HP 500 rebuilt from a reputable engine builder in my area.The entire engine was gone through will all new parts,cam,pistons, rings,etc.The engine was tuned and run on the dyno.The peak torque was 592 ft.lbs.from 3800 rpm's to 4600 rpm's.The peak horsepower was 566 @ 5600 rpm's.The #'s looked good on the dyno.I have a 95 27 foot Fountain.The boat ran 68 gps @4600!!WTF!!The boat ran 68 last year with what turned out to be a broken spring running on 7 cylinders.When the motor was at its prime prior to it being rebuilt,it would run 74-75 all day everyday.My engine builder is scratching his not knowing what could possibly be the problem. ANY HELP OR SUGGESTIONS WOULD BE GREATLY APPRECIATED!!!

It's only running on 7 cylinders.

Interested to hear input on this

It was before i had the motor rebuilt.

I am running a brand new hydromotive 25 pitch prop.I was spinning a 27 pitch mach prop before the rebuild.

What rpm are you spinning the new prop?
Have you verified the ignition is good on all 8 cylinders?
Have you done a compression test on all 8 cylinder? (Rebuilt or not)

Verify good fuel pressure when wide open?
Timing?

Agree^^^^^

Basics first.

Compression and fuel psi....fuel psi at WOT too and especially.

Carb could be out of whack....sitting does strange things to them.

Timing ?

And then....what cam was used in it ? The HP500 (Crane '721) ? Or ????

I am spinning the new prop @ 4600 rpm's.The prop is not the issue.I had them replace my msd ignition box with a new one and the distributor as well.I have not done a compression check again since the rebuilt.Fuel pressure was checked at idle and not at open throttle yet.The timing is at 34 all in.

The carb was rebuilt.I can't remember the brand for the cam but it's definitely more aggressive.

I was told the cam is made by cam motion

Did you run the new prop with the old motor?

What prop ran 74-75? Put that prop on and try again. The hyrdo's can be stiff props out of the box.

No i didn't.The fastest running prop was a 27 pitch mach prop.Since that,its been twisted and repaired a couple of times.That is why i bought a new hydromotive.

We need info if the engine is healthy.

And then, if it is, we need exact info on what the engine was rebuilt with.

I can't tell you how many times I've tried to tune an engine that was supposedly 'off' that wasn't.

Just $$ and time wasted.

That's why we need the basics covered first.

If all checks out, and should be making more power, we can further help from there.

Sounds to me like the engine is down on power. Why? Need to do some checking...

Is 4600 all you can get? Also why go up in power and down in pitch?

I am bringing it back to the engine builder tomorrow.Some of the new parts used are ss intake valves,inconel exhaust valves,srp forged pistons,hastings piston rings,cam motion cam,m77 connecting rod bearings,m77 main bearings,melling high volume oil pump.I went down in pitch because that was a starting point from the tech at hydromotive.I should be able to spin that prop at much higher rpm's then what i currently am doing.Hopefully i will have more answers tomorrow.Thanks for the input so far!

Did you verify the throttle is opening all the way?

No i didn't.I will have them look into that tomorrow.

How about the heads, what heads do you have now and what heads did you have?

Stock heads with new valves,springs,etc.

well 4600 with a 25 prop, something is wrong, you are 1000 RPM down, thats your speed loss...make sure no plug wires crossed, yes plugs wires, verify timing again at full advance, with a different light, if everything ck out there cut the oil filter open to make sure this thing is not eating its self up. If it made that power on the dyno and now in the boat won't turn 5500-5600 something took a crap...

I completely agree. But the only thing differant is the prop. You have your baseline with your old prop. So try the new motor with your old prop. That old prop may have been labbed or pitched. Even though you should be turning a 26-28 prop see what it does with the old one. After all it's just one nut right,,,,with a 25 you should be bouncing off the chip but I still say go back to the baseline. Also how do you know the Dyno sheets are for your motor?

Any way to post dyno sheet? How dramatic did the toque drop from 4500-5500?

To start with, put the original prop back on and get a base line. Hydromotive is more true to pitch and bigger diameter than the turd prop you were running before.

Have a rev limiter w/ that box ? If so, what chip is in it ?

Remember, MSD and others start randomly dropping cylinders here and there before the rpm limit you set to help keep you going over the limit.

Glenamy,The torque went from 592 @ 4600 to 536 @ 5550.Drew555 I don't know 100% if this is my dyno sheet other than my name and motor info on it.I was not there when the engine was dynoed.Is it possible to dyno the engine installed in the boat?If so,how comprable is it to being dynoed out of the boat?

Sb They didn't change the chip from 5200.The new box has a 4000,6000 or 8000 chip.I wasn't close to 5200 so i didn't even think twice about that.I will put a old hydro 24 pitch on tomorrow and put the 6000 chip in and run it and see what i get.

If I remember correctly, the chips are just resistors so you could remove it and eliminate that element

Totally correct.

If all pretty much is the same / stock (cid/heads/etc) on this motor but a larger cam, the powerband has simply shifted higher.

Many instances like this, the original 'best prop' will work just as well but now faster because it's being spun faster.

So many people thing they need a larger prop, but many times they don't.

Simple math syays if you can spin the same prop faster, the boat will be faster.

Only time to go larger on prop is if the 'new mods' spins the prop past the engine's usable rpm.

If you spin the original prop slower, well, you have a tuning, rigging and/or engine problem. Atleast the prop is removed from the equation.

SB The motor was bored 030" over.

NPerfect statement if you pushing more torque and horsepower or if your bouncing off the chip only then would I increase pitch of the SAME style and brand of my best prop. Labbed or not. For instance I increased my hp by 100hp per motor. So I went from stock 28 bravos to 30 labbed bravos. Turns out at this point in testing I made the right choice since I still plain out at 2000rps and I'm running 45 mph at 2900 no trim.... Man I can't wait till I break these motors in this weekend for final oil change and see what see will do. But it is probably all in the prop for you.

Rev limiters should be NOT used as a top speed limiter. This is what a prop is for.

They should be used to protect the engine from too high a free rev if issues happen.

BTW, I have a sweet labbed 26 hydromotive right hand for sale $350 shipped :eekdrop:

Perhaps the newer motor doesn't like the old gas in the tank? If it ran fine on the dyno the odds are good that it's a simple linkage out of adjustment or pissed off fuel pump that didn't like sitting for a few months. Best of luck!

I think others have touched on the need to make sure you are getting adequate fuel to the engine. Have a buddy ride along to peek at the fuel pressure gauge while you give it gas to make sure that you are not dropping pressure under load. It's possible that your pump is getting tired and not keeping up with the increased demands of the new engine. I encountered similar issues - built a 489 that produced 585 HP / 605 ft/lbs on the dyno, and then could not get the RPM's I should be getting in the boat. Determined that my fuel supply system was not up to the task. I'm in the process of addressing that right now.

^^^ agreed. Check fuel pressure

Great input here for sure... I don't know about the 5 blade props but how are your mid range numbers? Better or worse than with the old prop? I understand you gain efficiency in the mid rpm range but top end may suffer a bit? I built a 502 for my 26ZX and I tried to copy the HP 500 engine. I ran a best of 70 at 4950rpm on a 93*day. Cruise was excellent at 3,500 rpm giving me 50mph in ideal conditions...... I am using a 26P 4blade Bravo1.... It does not cavitate or blow out and gets on plane easily....... We have similar size boats and my drive seems to sit very deep in the water........ Definitely make sure you are not running lean as it would be a tragedy to hurt your new motor. I am using a wide band AFR gauge to tune my carb and it has been a huge help and piece of mind knowing exactly where my carb is at.......

I would also put your old prop back on and see where you stand....... You have a known baseline top speed so you can compare apples to apples........

Reputable marine shop or reputable make the 72 nova haul butt shop?