"New" Engine Very Low on power

[JeffCh48]

Hey everyone I've got a 24' Enforcer. With the original 330hp engine I was able GPS the boat at 63mph with a 24p 4blade.

I wanted to leave this engine completely whole and build a new engine and pick up speed, in the end this worked to my benefit...

I picked up a 427 on the (very) cheap. I know... no replacement for displacement, but this is what and I had didn't feel it would be hard to build 450hp with this setup. I re-used this original Mercruiser 325hp short block as it looked clean.

So, I picked up a set of oval port ProComp.. head castings from my very reputable machine show who did the machine work and had them put quality stainless valves in them. These heads are 115cc chamber and my factory 427 pistons are popup, what I believe to be 11cc. I'm running Edelbrock Air Gap oval port intake. And my cam is from Schneider cams "JB-3H" .540 lift and at .050 duration intake 224 and exhaust 230. We set the timing all the way up to 39 deg, trying several different settings from 34-39. At the time of putting the motor in my boat I also added stainless marine performance exhaust manifolds.

After I broke the cam in on the outer springs. I used a leakdown tester to prevent the valves from falling down when inserting the inner and didn't notice anything out of the ordinary. (didn't take actual readings)

When I ran the boat for the first time, after getting all the carb jetting good, I couldn't get the boat to turn more than 4200rpm with the same prop GPS at only 57mph. I'm running pretty large carb 950, I've tried another carb, a 650 and slowed down. At one point I had dropped 400rpm and couldn't get it back to where I was. (collapsed lifter)

I did a compression test and had 125psi on all but one cylinder, it had 25psi. So, I pulled the engine and did leakdown tests on all. Most were 10-15%, there was one that was 25%, 28%, and the one with low compression was BAD. The piston with low compression (#5) had a collapsed exhaust lifter.

I pulled #5 piston and couldn't see anything wrong with the piston, rings, or head/valves. The whole engine looks very clean and there is actually very little cylinder wall wear.

I ended up putting my original engine back into the boat and regained my 63mph speed at about 4700 or 4800.rpm



So leading up to my question:

What is the true cause of my lack of power? Would it be worth my efforts to hone and replace piston rings? I would hate to go through the efforts of all of this and end up with the similar results.

Should I ditch the 427 and build a 489 over the winter? (I know the answer to this, but please be in mind that I would like to spend as little as possible, just like everyone else)

Thank You if you actually read all of this...

 

[kct11]

Look for bent valves, bad valve job, bad head gaskets. The air is leaking some were..a collapsed lifter, or worn lobe will yield higer cranking pressure then the other cylinders in a "sound" engine.

 

[JeffCh48]

I have the heads off now and all the valves look good, none of them have been hit or look bent. The chamber in #5 was excessively dark, I think from oil, but can't prove this.

The head gasket looks great.

I'm not sure I understand how a collapsed lifter would cause high cylinder leakdown, I do understand it could cause low compression numbers.

 

[corey331]

I personally don't agree with the whole "no replacement for displacement" mantra. I am personally ditching my 454 for a small block in my Convincor. That being said, you are obviously losing power somewhere. Looking at your cam specs, it seems to be very undersized to me. I'm far from an expert, but it seems to me that something a little more aggressive might help you gain some rpms. I think the 950 carb might be a little too big as well, especially since you aren't spinning the motor very fast. I learned that lesson at my engine builders shop when they were dynoing my buddy Brent's 565 marine motor. It made almost 25 more horsepower with a 750 than it did a 950, and that was at 6000-6200 rpm. Also, if I remember correctly, that intake is a dual plane intake? Those tend to not work well on marine motors from what I have been told. I had originally planned on running a dual plane on my new motor as the power band seemed to be in my rpm range but my engine builder turned me away from that real quick and I bought a victor jr.

If you have any aspirations of changing the cam, I very highly recommend a call to Bob Madera at Marine Kinetics. I went through him for the cam in my new motor and he is super easy to work with, really knows his stuff and is very reasonably priced. I got a custom grind cam made just for my application for the same price or less than most off the shelf cams.

Keep us updated on what you find and decide to do!!! Also, where are you from?

 

[JeffCh48]

Hey thanks for the advice

I'm from around Lancaster, Ohio. (I just updated my profile to show that)
I boat on the Ohio River around Pomeroy, OH.

I did try a smaller carb that was jetted right and dropped about 200rpm and regained them back when switching to back to my original one. With my cam, I couldn't go too aggressive as this isn't a very high compression motor. From my calculated estimates its about 8.7

Yep, that is a dual plane intake, I've seen some articles describing how this is the best intake for engines who's RPM's that don't reach over say 6,000

 

[corey331]

Oh ok, I know right where Lancaster is. If you decide to have the motor taken apart and checked, I have an engine shop here in Ohio I very very highly recommend. Its in Piqua, Ohio which is probably 2 hours from you, but they are great. They are all boaters, so they know marine motors inside and out. They have done quite a few motors for people on the board here. One of my buddies came from Mansfield to have them do his motor work. Heck, my buddy Ron drove 6 hours from Michigan to have them work on his motor. They are building my motor and did the 565 in my buddy Brent's checkmate. They are a wealth of knowledge and can make very simple motors run very well. Might be worth a call!!!

 

[JeffCh48]

I will definitely keep that place in mind.

I do have the engine apart, but I am just not seeing anything seriously wrong.
In the meantime I'll keep researching and thinking about what my next move is.

 

[corey331]

Sounds good, keep us updated on what you find.

Also, to the forum. You should make an introduction post and we are all picture whores, so we would love to see your boat!!!

 

[kct11]

A smaller cam profile will make for more cranking compression. It bleeds off less then a larger cam. Take a motor with the spark plugs in it, turn it my hand, then back off all the rocker arms and then givit ta try.

To check your valve job spray brake clean in the ex and in ports and if it leaks through it bad.

 

[JeffCh48]

I don't think that my cam is too big. Although 125psi compression does seem low to me.

A sprayed brake cleaner in the head of a cylinder (one that leaked down badly), enough so that it puddled on top the valve. There was dampness around the seat of the valve, but not enough to cause even 1 drop.

My only thought is weak/worn rings..

I will work on creating an introduction post. Including pictures

 

[JeffCh48]

Just some pictures to share with everyone.


Cam Card:



Broken lifter that caused the 400rpm drop:




Engine Pictures:






My boat isn't the one in the background in the engine pictures. That's a Scarab, my boat is the red and black enforcer on the left.

 

[ckaluger]

So were you swimming in the algae?

 

[corey331]

Very sharp boat!!! Is that blue persuader next to it solid blue flake? If it is, I have a new favorite boat!!!

Also, with that 112 degree LS, you might want to watch for reversion. That's the same LS I am running on my new cam and I had to run dry exhaust.

 

[JeffCh48]

I was swimming in the algae, and I'm still alive lol.
Right where we were at in the picture it wasn't bad. This pic was actually taken on labor day weekend. There were some very green patches though. Little green specs floating..

Yes, that Persuader is a 21.9 ft and it is actually my dad's boat. It's all blue flake except for the silver flake stars haha

When I took the manifolds off one side didn't have any water, but one side did. My assumption is that it was only getting water back in because #5 ex lifter collapsed.

 

[corey331]

I was swimming in the algae, and I'm still alive lol.
Right where we were at in the picture it wasn't bad. This pic was actually taken on labor day weekend. There were some very green patches though. Little green specs floating..

Yes, that Persuader is a 21.9 ft and it is actually my dad's boat. It's all blue flake except for the silver flake stars haha

When I took the manifolds off one side didn't have any water, but one side did. My assumption is that it was only getting water back in because #5 ex lifter collapsed.

If he ever wants to sell that boat, PLEASE let me know!!!

 

[JeffCh48]

I will let you know. Recently he was starting to think about selling that to buy a bigger boat. I'll let you know if he does get serious about it though.

I actually ended up looking at the valves again and discovered that #5 intake doesn't seal well. I used a sharpie and spun the valve just a little bit, the valve had a good ring around it, but the seat does not. I'm not sure if you can see it in the picture:




The machine shop will warranty this for me. So, I'm taking the heads back to him to have them checked. I'm also taking this opportunity to hone and put new rings and barrings in the bottom end since I feel it is old and could use "freshend up".

 

[ezstriper]

pro-comp heads have been known to be absolute junk, also look closely at the cam, being a flat tappet and they are prone to wiping very easily, after you get back together really need to run a wideband 02 to dial in whatever carb you end up with..otherwise its a crapshoot.

 

[Gimme Fuel]

39 degrees is a TON of timing for a marine motor. You really shouldn't need anything past 35-36 degrees. That would cause detonation issues and give problems. I hope you were running premium fuel. Also, I see you have a 112* centerline cam. I can't tell what your exhaust riser length is from pictures but if they are short, you may have reversion issues that would quickly take out your valve jobs as well.

 

[Skip 7750]

Just a couple of thoughts

Did you check push rod length? With different heads the length will probably need to be different.

Are you sure your cam is in correctly? I have seen cams installed 1 tooth retarded and it still ran, but was way down on power.

Make sure that the cam did not go flat. Only takes a second or two to wipe out a flat tappet cam.

Check to see if the timing marks are correct on the balancer. The outside can spin and your timing mark will be way off.

If it was me, I would throw those heads in the rubbish bin and buy some AFR, Edelbrock, or Dart heads. Why, because they work and will not cause you problems down the road.

Make sure that you have correct fuel pressure and there are no obstructions in the lines and nothing is blocking your carbs air intake.

Don't give up, it will be worth it when you get it running right!

 

[Jimway]

Add installed spring height and pressure at rest and full lift to the list of things to check (spring bind too). The broken lifter tells a story.