Merc 540 575hp build heads cam ect..?

[SickSation]

Pulling my merc 540 575hp n/a to freshin it up. Just to clarify, this isnt a bully dog motor. I know most people arent aware that merc made a 540 575hp n/a motor, but they did in the late 80's. Tall deck. anyhow, I put it in at the end of last season and only put about 10 hrs on it. I'm going to put new rings, heads, cam, and bearings (if needed). I havent got into the motor yet, but supposedly it has corrila rods and a crowler crank. Sorry if i mispelled the the brand names. It has cast rect port heads. Ls6 heads #6272990. I put a 1050 dominator on it as well. victor s/p intake. The motor came out of a 42ft searay. the problem I had last season was getting rpms out of it reguardless of prop size. Im assuming someone put in some bottom end torque cam for that giant boat. It was a stump puller in my 25ft sunsation to say the least. I want to put some different heads on it and a higher rpm cam. Naturally I would like to find the best bang for my buck to to speak. I want to have a high horsepower N/A motor. Anyone have any good suggestions? Thanks in advance. Has stainless marine manifolds with custom risers i made. Dont know if i will need to go to headers.

[jrz]

I had one, used it stock a few times, then added merlin heads ported at Champion in Eikerts old building, Crane hyd roller (not sure of the grind anymore), new valves, springs etc, etc. It actually showed a slight dyno improvement running 1qt low on the oil, a reliable source said windage issues.

[SickSation]

I had one, used it stock a few times, then added merlin heads ported at Champion in Eikerts old building, Crane hyd roller (not sure of the grind anymore), new valves, springs etc, etc. It actually showed a slight dyno improvement running 1qt low on the oil, a reliable source said windage issues.

Did you see much of an increase in hp form swapping out heads?
I know this motor came with stellings headers. Im afraid these stainless marine manifolds arent going to flow enough.

[MILD THUNDER]

Your stainless marine manifolds will work fine. As for heads, there are several options. I like the CNC dart pro 1 325CC for your 540CI. A custom spec'd hyd roller from bob madera along with the morel hyd roller lifters would be the way to go. I would think 650HP is doable with that package.

on a side note, you stated you couldnt get rpm out of it, regardless of prop size. Are you sure you werent hitting the rev limiter?

[SickSation]

Your stainless marine manifolds will work fine. As for heads, there are several options. I like the CNC dart pro 1 325CC for your 540CI. A custom spec'd hyd roller from bob madera along with the morel hyd roller lifters would be the way to go. I would think 650HP is doable with that package.

on a side note, you stated you couldnt get rpm out of it, regardless of prop size. Are you sure you werent hitting the rev limiter?

Thanks for the info. I wasnt on the rev limiter. I just found a spec sheet a few hours ago on the motor. It says 4800-5200 rpm range with peak 575hp at 5000. I was able to get 5000 out of it, but that was with a 24p 3 blade. I was turning that with my stock 310 hp 454mpi. I went all the way up to a 32p and spun it at 4600-4700 if i remember correctly. The confusing part was no matter what prop i turned, the speed was within 2 mph of each other..

[jrz]

Did you see much of an increase in hp form swapping out heads?
I know this motor came with stellings headers. Im afraid these stainless marine manifolds arent going to flow enough.

At 540 CI and naturally aspirated, a longer primary exhaust (around 32" to 34") will work better.

[SickSation]

At 540 CI and naturally aspirated, a longer primary exhaust (around 32" to 34") will work better.

Found some old CMI tube top headers for pretty cheap. Are they going to be that much better than my manifolds?

[jrz]

Found some old CMI tube top headers for pretty cheap. Are they going to be that much better than my manifolds?

Thats what Merc used after the Stellings.

[WETTE VETTE]

Found some old CMI tube top headers for pretty cheap. Are they going to be that much better than my manifolds?

The tube tops are great headers for that motor. If you are willing to turn some RPM (6000ish) they will likely out perform the manifolds.

[MILD THUNDER]

Thanks for the info. I wasnt on the rev limiter. I just found a spec sheet a few hours ago on the motor. It says 4800-5200 rpm range with peak 575hp at 5000. I was able to get 5000 out of it, but that was with a 24p 3 blade. I was turning that with my stock 310 hp 454mpi. I went all the way up to a 32p and spun it at 4600-4700 if i remember correctly. The confusing part was no matter what prop i turned, the speed was within 2 mph of each other..

Sounds like something is going on there. Something strange. Scientifically, it does not make any sense. If you can turn a 32P to 4700RPM, and a 24P 3 blade to 5000, and speed doesnt change but 2 mph, something is seriously wrong.

I would check into some basic stuff like making sure your tach is correct. Then be sure your carb is opening all the way at full throttle. I'd also make sure your fuel system is up to par. From the size of the pickup in the fuel tank, hose to the fuel pump size, fuel pump output, and carb jetting. Make sure your timing is advancing as it should. Take a close look at the valve springs, making sure none are broken, cracked, etc.

IF your speed didnt increase spinning higher pitch props at the same engine rpm, I am baffled. Especially a 32p compared to a 24p.

[SickSation]

Sounds like something is going on there. Something strange. Scientifically, it does not make any sense. If you can turn a 32P to 4700RPM, and a 24P 3 blade to 5000, and speed doesnt change but 2 mph, something is seriously wrong.

I would check into some basic stuff like making sure your tach is correct. Then be sure your carb is opening all the way at full throttle. I'd also make sure your fuel system is up to par. From the size of the pickup in the fuel tank, hose to the fuel pump size, fuel pump output, and carb jetting. Make sure your timing is advancing as it should. Take a close look at the valve springs, making sure none are broken, cracked, etc.

IF your speed didnt increase spinning higher pitch props at the same engine rpm, I am baffled. Especially a 32p compared to a 24p.

I have been very confused as well. Ive been a wrencher my whole life, but Im no pro when it comes to making big HP. Here is a few links to threads i posted last year. Maybe some of it might make sense. I guess bottom line is, I need to get the motor out and tear into it and see what ive got.

http://www.offshoreonly.com/forums/g...questions.html

http://www.offshoreonly.com/forums/g...g-540ci-n.html

[SickSation]

Ok, got the motor down to bare block. Heres what i have..


carrillo H Beam rods
crower 4.250 crank
10.2 bow tie block 4.5 bore
BRC flat top pistons


The cam is what im not sure about its a Reed cam. Not familiar with them and i couldnt find any info on the cam.
------------------------------
CAM
Reed
Ch288-98-10A3
------------------------------------

What im looking into is Mahle 4.530 dome pistons
dart single plane intake
cam- Not sure yet..?
trick flow 340-360 heads

Any suggestions or opinions are welcome.

[jeffswav]

Before you do anything talk to Bob "RMbuilder" Marine Kinnetics. He will point you in the right direction.

[SickSation]

Before you do anything talk to Bob "RMbuilder" Marine Kinnetics. He will point you in the right direction.

I sent him an email yesterday,. Hoping to hear back from him soon.

[MILD THUNDER]

Ok, got the motor down to bare block. Heres what i have..


carrillo H Beam rods
crower 4.250 crank
10.2 bow tie block 4.5 bore
BRC flat top pistons


The cam is what im not sure about its a Reed cam. Not familiar with them and i couldnt find any info on the cam.
------------------------------
CAM
Reed
Ch288-98-10A3
------------------------------------

What im looking into is Mahle 4.530 dome pistons
dart single plane intake
cam- Not sure yet..?
trick flow 340-360 heads

Any suggestions or opinions are welcome.

I dont think REED is still in business. I think your motor came from merc with solid flat tappet lifters.

Just a guess here, but i would assume that cam is a 288-298 Advertised duration, on 110* LSA, and its a Hyd lifter cam.

stock 540/575HP was a solid lifter motor. Cam was a 292/300 duration with 618/638 lift. Used the GM Iron square port heads. Stock compression was 8.75:1. They used aftermarket forged cranks, rods, and pistons, not the standard GM forged stuff. Stock carb was a 1050 dominator. Jetting was 90 Front and back. Base timing was 10* at the crank, and 34 total i believe.

With all that being said. I'd go with a modern hydraulic roller cam spec'd by bob madera, with the morel roller lifters, with a nice pair of dart 325CC pro 1 heads. I'd leave the compression alone, as long as you dont need new pistons. With the crappy fuel we get these days, you'll have plenty of safety margin with that compression and aluminum heads. plus in a year or two, you can always bolt a blower on it, and make some serious power. With the new heads and cam, i dont think you will have a problem making 650HP, and be reliable. Of course you can go solid roller, bigger cc heads, but to gain your gonna have to really spin that motor around 6000rpm or faster.

Im not familiar with Trick Flow heads in the marine world. Most of the big name builders stick with what works, mainly dart and brodix. And when it comes to heads, bigger isnt always better.

[ROGUE]

Thanks for the info. I wasnt on the rev limiter. I just found a spec sheet a few hours ago on the motor. It says 4800-5200 rpm range with peak 575hp at 5000. I was able to get 5000 out of it, but that was with a 24p 3 blade. I was turning that with my stock 310 hp 454mpi. I went all the way up to a 32p and spun it at 4600-4700 if i remember correctly. The confusing part was no matter what prop i turned, the speed was within 2 mph of each other..

I have loaded all this information into my supercomputer and it said "the trailer must have still been attached to the boat" LOL. Sorry, Couldnt help myself.

[SickSation]

I have loaded all this information into my supercomputer and it said "the trailer must have still been attached to the boat" LOL. Sorry, Couldnt help myself.

lol. I think the cam was the limiting factor. Starting from scratch so it should be a beast.