73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

Joined
Jun 18, 2012
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Ok so here is what I have been dropped into my lap:
Originally this was my uncles boat: 73' Sleekcraft with a MerCruiser(not sure which model)
My uncle decided to buy a 351W HO SVO crate motor to put into it. It ran great 8 years ago, would do 55 mph on the water no problem. His health issues and various things the boat sat in a storage yard and raccoons ate through the cover and totally destroyed the interior of the boat. Was sold to my cousin and she replaced the whole interior and was having a hard time getting the 351 to run. While trying to get it back to running, she flat spotted the cam when a lifter stuck. The cam was replaced with a Crane Cam that was comparable. The carb was gone through and cleaned and new seals. A new fuel pump was installed. Motor was timed and in the driveway it revs up smooth and quick, sounds great. Well on the water it barely has any power and wont rev above 3k rpm. The only thing that has been changed with this motor since it did 55 mph was the cam and lifters, but Crane gave a comparable cam. Any Idea's? I have tried to play with the distributor out on the water with no success. its getting frustrating. I have called local shops and basically tell me since it's an aftermarket motor they cant and basically aren't willing to help. I will try to post the crate motor sheet and the cam that was replaced in it. I am a Chevy guy and more of a LSX motor/new school tuning with a laptop kind of experience. So this is all new.
 
Joined
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Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

Here is the motor and cam specs
 

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Bt Doctur

Supreme Mariner
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19,092
Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

firing order maybe.

Windsor (289, 302, 5.0, 5.0HO, 351) Firing Orders Have you ever needed to know what the cylinder firing order on your windsor motor is? Fear not, as we have the cylinder numberings for pretty much all windsor combinations out there!


289 1-5-4-2-6-3-7-8
302 (Pre-82) 1-5-4-2-6-3-7-8
5.0 1-5-4-2-6-3-7-8
5.0 HO 1-3-7-2-6-5-4-8
5.0 Truck 1-5-4-2-6-3-7-8
351 1-3-7-2-6-5-4-8


Cylinder numbering The table below covers the positions and numbering for all cylinders on a windsor motor. Generally, it can be summarised as follows: When looking into the engine bay the number one cylinder should be on your left hand side (left bank) at the front of the engine. The number eight cylinder is on the rear right (right bank) up against the firewall.

Firewall
4 8
3 7
2 6
1 5
Front bumper
 
Joined
Jun 18, 2012
Messages
7
Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

firing order maybe.

Windsor (289, 302, 5.0, 5.0HO, 351) Firing Orders Have you ever needed to know what the cylinder firing order on your windsor motor is? Fear not, as we have the cylinder numberings for pretty much all windsor combinations out there!


289 1-5-4-2-6-3-7-8
302 (Pre-82) 1-5-4-2-6-3-7-8
5.0 1-5-4-2-6-3-7-8
5.0 HO 1-3-7-2-6-5-4-8
5.0 Truck 1-5-4-2-6-3-7-8
351 1-3-7-2-6-5-4-8


Cylinder numbering The table below covers the positions and numbering for all cylinders on a windsor motor. Generally, it can be summarised as follows: When looking into the engine bay the number one cylinder should be on your left hand side (left bank) at the front of the engine. The number eight cylinder is on the rear right (right bank) up against the firewall.

Firewall
4 8
3 7
2 6
1 5
Front bumper

I used the 1-3-7-2-6-5-4-8 firing order that was suggested on the Crane cam sheet.
 

haulnazz15

Captain
Joined
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Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

Have you verified that the ignition timing is advancing as it should when accelerating?
 
Joined
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Messages
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Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

Have you verified that the ignition timing is advancing as it should when accelerating?

Yeah we pulled the vacuum off and had it about 4 degree's initial, then up around 30 with the vacuum advance. This was all done in my driveway without load on it. It runs and idle's great, just under load it is being a POS
 
Joined
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Messages
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Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

I have already torn down the motor to the timing chain, and it is set at 2A TDC on the crankshaft, which the Crane cam said it needed in the specs.
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,092
Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

only other thing is to put the Degree Wheel on and see exactly what the cam timing is.
 
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Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

only other thing is to put the Degree Wheel on and see exactly what the cam timing is.

And that I have not done, just would make me wonder why they have put that much time into making a keyed crankshaft with everything from 0 to 2R - 8R and 2A - 8A on it.
 
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Messages
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Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

only other thing is to put the Degree Wheel on and see exactly what the cam timing is.

The cam that cam out of it required 2 degrees of retarded timing on install and that key was sitting at 2R on the crankshaft, so I guess i'm assuming that since this newer cam needed 2 degrees of advanced then sitting the key at 2A would suffice.

I was hoping there were some external problems that I could troubleshoot without tearing right back into the motor again. :facepalm:
 

cruzn

Cadet
Joined
Feb 10, 2011
Messages
8
Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

The cam that cam out of it required 2 degrees of retarded timing on install and that key was sitting at 2R on the crankshaft, so I guess i'm assuming that since this newer cam needed 2 degrees of advanced then sitting the key at 2A would suffice.

I was hoping there were some external problems that I could troubleshoot without tearing right back into the motor again. :facepalm:

Assuming this is a merc stern drive, have you determined the gear ratio? Is it original drive? What prop pitch/style is on it? Maybe it's just trying to push too much prop to be able to reach max rpm.
 

haulnazz15

Captain
Joined
Mar 9, 2009
Messages
3,720
Re: 73' Sleekcraft w/ 351W HO swap wont rev above 3k rpm? Idea's?

I don't know the 351w HO numbers, but the regular 351w uses 10-BTDC for initial timing and something like 32-36 degrees of total timing on the advance curve.

Also, there should be no "vacuum advance". If there is a vac-powered distributor, then you have an automotive unit and that is not marine-rated (could cause explosion). Get a full-mechanical distributor. Also, there is a high liklihood that if you have a non-marine dizzy, you have a non-marine carburetor on there which is an even bigger explosion hazard.
 
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