5.7L Mercruiser Vortec Head Swap

[StevNimrod]

I wrote a nice long post and it got deleted (beginner's luck, I suppose), so here it goes again...

I have a 1994 Wellcraft Excel 26SE powered by a 5.7L carbureted GM motor. The motor serial number is OF276159.

I'm considering getting my hands on a pair of the 906 Vortec heads (with matching intake) and doing a swap. Are there any issues I should be aware of in doing this?

The previous owner told me that the guy he bought the boat from did some engine work and made it a "roller" engine. I've called a few local shops and there is some dispute as to whether or not this is even possible on this motor. Is it possible or not? It's hard for me to tell on the phone which shops know what they're talking about and which don't. I also would like to know if there is any way for me to find out what cam this guy put in, or do I have to pull it out? I figure that while I'm doing the heads I might as well...or maybe the engine will get pulled and I can do it in the comfort of someone else's garage.

Also, I've been reading a bit about having to modify the rocker studs (changing them from press-fit to screw-in) and keeping an eye out on the lift, etc. Anyone have any experience with how big (or small) of a PITA this type of stuff is?

One more thing...

I can currently turn the engine up to 5200 RPM (based on the tach on my timing light, not the dash tach) with a 15.25 x 15 3-blade aluminum prop. I don't know if this was the idea of the engine build from two owners ago, but it got me thinking that either it's underpropped or he built it like he was building a car engine (top end HP rather than low end torque). There is also a Stainless Marine thru hull exhaust system (manifolds/risers/etc) installed as well as an Edelbrock Performer intake and I can still only get 32 MPH at WOT vs. the 38 MPH advertised in the boat's owners manual. I'm not a speed junkie by any means, but thought it suspect that all of these add ons have lost 6 MPH. Is this even possible, or did someone get it wrong somewhere along the way?

As an aside, there is a faint white smoke trail out of the thru hulls at WOT or when I accelerate hard, but the smoke dissipates rather quickly. I also leave a small fuel sheen on the water at the dock when I first start the boat up to leave my slip (but not when I come back in at the end of the day and let it idle at the dock). I'm not burning oil (or otherwise consuming it), and I'm fairly sure the sheen is fuel (smells rich). Compression numbers are all within 10% of each other or so. I don't have the actual numbers with me, but from what I recall they were all in the 140s range. Any ideas on what the culprit could be (I recognize that "a million different things" is probably one correct answer, but I'm looking to get a few knee jerk responses on what it could be based on experience)

Lastly, how much time can I expect to tie up doing the head swap? Are there any other parts I'll need, so I have an idea of how much I'm going to get nickel-and-dimed?

Sorry for the long, rambling second attempt at posting, and thanks in advance for your input.

 

[Maclin]

Re: 5.7L Mercruiser Vortec Head Swap

Regarding the WOT rpm and speed and pitch something is not quite right somewhere.

If the gear ratio is 1.5 then the speed should be above 40 even with 10 percent slip. To get only 32mph at that rpm and prop pitch then the gear ratio would be more like 2.0, or prop slip is REALLY bad. Maybe on that big of a boat they did have a higher ratio installed on single engine applications.

If the gear ratio is in the 1.5 range then 5200rpm with a 15p prop would be hitting 44 mph with 10% slip. Only 32mph would be 35% slip, so if the prop is in good shape then some of your numbers do not jive OR the gear ratio is out of bounds with what I am thinking it is.

Here is a link to a web page with a simple prop calculator and fair amount of explanation that seems to have a good amount of accuracy built in....:
http://www.rbbi.com/folders/prop/propcalc.htm

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

Maclin,

Thanks for the response!

I agree that something is wrong. My theory is that the second PO didn't do something correctly when he did the "engine work". I've gone to every imaginable prop calculating tool and they all came back with the numbers you gave me.

I have the drive off (Alpha 1, Gen 2) and can confirm that the gear ratio is 1.5. The speed is by GPS so I don't think I'm going to get better numbers there, and the RPM has been confirmed numerous times with a timing light.

One of my theories (and like most other theories of mine, this one was pulled out of my...) is that whatever work was done resulted in some undesired valve operation (intake valves not open long enough, open too late, etc., or something with the exhaust valves) because I don't think it's putting out the power it's supposed to.

I suppose I'll know more when I get the heads off. Is 35% that unreasonably high for a 27' boat?

 

[krisnowicki]

Re: 5.7L Mercruiser Vortec Head Swap

If you are reaching 5200 rpms and only getting 32 mph you are wasting horsepower somewhere. You ratio is or maybe wrong. If thats not it then your prop has a bad hub or needs to be bigger. You should probably be between 4200-4600 rpms, some one will chime in with the exact number. the general rule is 1 inch in pitch equals 200 rpms. So for you to get down to 4600 drop 2-4 inches. I would try a prop swap first before doing all this work. If the hub is bad and you put a 17p that is good it could save hours of time and hassel all to have the same problem when you finish.

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

krisnowicki,

I agree that I'm wasting horsepower. Earlier in the season I match-marked the hub to the prop with a marker and after a month the mark hadn't misaligned so I'm pretty confident that it's not an issue with the hub. Things could never be that easy.

4200-4600 rpms is correct per the manual, but I'm not sure if whatever work was done prior to my owning the thing allows it to be run at higher RPMs. Either way I'd prefer to come down a bit since it's just wasting gas and we all know how that worked out for us this summer.

I contacted the manufacturer and the 15.25 x 15 prop was what came with the boat. Incidentally, the engine was rated at 235 HP when it left the factory. That said, I'm sure with the intake, exhaust, and mystery engine work the HP numbers are higher and the prop is probably small on pitch.

That said, my original thinking was what you said -- get the prop situation improved first. I did that earlier in the season (put a deposit down and borrowed a few from a local prop shop) and the changes were marginal at best -- in some cases it helped (gained one or two MPH, dropped a few RPMs with a 17P) to hurting (getting caught in my own wake, etc. with what I think was a 16x16 or some other oddly sized prop). That said, I know I'm a bit underpropped, but my fear is that the engine itself isn't putting out. If this is the case, I'd have to re-work the prop again post engine work.

I've come to accept the fact that it's looking like I'm about to step into quite a big repair bill...or I'll just deal with knowing there's a problem and hope it doesn't hit the fan while out on the Lake (which I'd rather not do).

 

[Bondo]

Re: 5.7L Mercruiser Vortec Head Swap

I did that earlier in the season (put a deposit down and borrowed a few from a local prop shop) and the changes were marginal at best -- in some cases it helped (gained one or two MPH, dropped a few RPMs with a 17P) to hurting (getting caught in my own wake, etc. with what I think was a 16x16 or some other oddly sized prop). That said, I know I'm a bit underpropped, but my fear is that the engine itself isn't putting out. If this is the case, I'd have to re-work the prop again post engine work.

Ayuh,....

But What happened with the RPMs,+ WOT Speeds,..??
That quote really means Nothing for diagnostic purposes...

I'm considering getting my hands on a pair of the 906 Vortec heads (with matching intake) and doing a swap. Are there any issues I should be aware of in doing this?

Nope,... Not within itself...

The previous owner told me that the guy he bought the boat from did some engine work and made it a "roller" engine.

Ayuh,.. The Block is Roller Lifter usable,.. Whether it's equiped with Roller Lifters has to be Checked,.. But it probably Is...

I also would like to know if there is any way for me to find out what cam this guy put in, or do I have to pull it out?

Ayuh,... With Mics,+ a Degree Wheel it's measurable, In the block...

Also, I've been reading a bit about having to modify the rocker studs (changing them from press-fit to screw-in) and keeping an eye out on the lift, etc. Anyone have any experience with how big (or small) of a PITA this type of stuff is?

Ayuh,... It's a Easy 1 for a Machine Shop,.. It's Not a DIY thing though...

I also leave a small fuel sheen on the water at the dock when I first start the boat up to leave my slip (but not when I come back in at the end of the day and let it idle at the dock).

Ayuh,... When it's a Cold Start,.. The Choke is activated,+ it over fuels slightly,....
Perfectly Normal...

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

Bond-o,

As far as the RPMs and WOT speeds:

What more do you need regarding RPMs/WOT speeds with the props I tested? With the 17P prop (I think the diameter was 15) I gained about 2 MPH and brought my RPMs down a couple hundred. It seemed to be a bit slower getting up to plane, and it's already slow to plane with the factory 15.25 x 15. The 16 x 16 he gave me was even worse to plane so I didn't even bother with any WOT figures. The point of the quote was that despite my testing numerous props, the fastest the boat has EVER seen with me at the helm is 34 MPH, which is low given the available calculators I've used (like the one Maclin included).

Thanks for the other information and confirmation about the fuel sheen at startup. This was my first season boating so I'm still getting used to what is considered "normal" on a boat so my apologies in advance if some of the things I reference are obvious to those with more experience than myself.

 

[chiefalen]

Re: 5.7L Mercruiser Vortec Head Swap

First may i say welcome aboard.

Ok that one big boat to be pushing with a single 5.7 motor.

That being said i read your post carefully.

Did i miss what kind of carb you got on it ? 4 barrel i assume, but i have learned here not to assume anything here. Make also please.

That motor should be putting out closer to 260 hp ideally. And could be modified to put out 30-40 more hp.

But is it gonna push that boat over 40-45 mph dunno.

You did check to see that you don't have water hiding in the bilge or elsewhere in the boat. Maybe foam soaked it up and is adding a ton of weight.

And the bottom is not dirty correct ?

You are turning to many rpms, and must go up in pitch, you tried a 17p and it didn't help ? You should be turning rpms between 4200-4600 recommend rpms, keep going larger with the props till you are. And then verify with the gps the speed.

How mush fuel you have onboard when your doing all this testing usually the factory tests with 1/2 tank of gas. Makes a big difference.

You carrying a ton of gear on the barge ?

As i posted that is a large barge to push with a single motor.

Good luch and keep us posted.

 

[Bondo]

Re: 5.7L Mercruiser Vortec Head Swap

Bond-o,

As far as the RPMs and WOT speeds:

What more do you need regarding RPMs/WOT speeds with the props I tested?

Ayuh,....

While it appears you have Something going on that Isn't Right.....

Prop Testing is gaged by RPMs at WOT,.. Along with Seat of the Pants feelings....

We can't Feel the feelings, so the final #s are rather Important....
If you Test Props,+ return with No #s,.....
It doesn't give Us much to work with....

That's All...

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

chiefalen,

Thanks for the welcome; glad to be aboard.

I've always thought it was pushing the upper limits for a single screw, and using a small block at that.

Sorry, I original post I wrote got deleted so what is now showing as the original post is actually a trimmed version of what I first wrote (if you can believe that).

The carb is an Edelbrock 1409. It was rebuilt this summer, even though it ended up not needing it (I'm a bit picky about certain things and randomly determined the carb was the first thing to get checked out).

I'm still not sure how Wellcraft managed to dress the motor only to 235 HP, but I've been in touch with them twice and that's what it's equipped with.

I'm not necessarily looking for speed, I was just figuring that if something is mechanically suspect it might make more sense to do repairs that also happen to be upgrades. I've personally never been convinced that this thing can see much over 40 MPH, but I've made a few friends at the marina with similar setups (single 350, similar weight, and capacities, etc.) and several of them get in the 40s. The one's that didn't either didn't have a working speedo, or simply don't care to pay attention.

That said, I do have water hiding in the bilge. About 3 or 4 gallons I'd estimate. If I suck it out with a wetvac I don't get any appreciable change in speed. That said, if I'm sitting at the dock bored one night and decide to suck the bilge dry, the water will be back by the next day. It's always three or four gallons, no more and no less. Still haven't figured that one out, and was finally convinced by my dock neighbor that it's pretty common to have a wet bilge. Other than that, there's no water hiding anywhere that I've search and I've been over the thing stem to stern.

Bottom is clean, always. It's painted and I pull it out every few weeks to spray it down.

The 17P helped, but not much. I think I'll end up going to a 19P prop, but currently the debate within my inner circle of friends (who, for people who admittedly know little about boats, have all the answers when it comes to picking random propellers for me to try) is whether or not going down to a prop in the 14-14.5 diameter range will be enough to push that much tonnage.

I've tested the boat under every conceivable condition I could magic up. Full fuel, half tank, almost empty. I've done this with a full tank of water (22 gallons), and no water whatsoever. I'll say that I can tell when I'm running a full tank of gas with a full water tank (that puts me down in the high 20s MPH).

As far as gear goes:

All I carry is the required USCG safety equipment, spare prop, fluids, two fishing rods and tackle, my tool box (50 lbs or so), a few miscellaneous bottle of donated alcohol I'll never drink, and the future-ex-wife.

Other than that, I'm at a loss about the lack of speed (whether it's normal or not) and, now that you've mentioned it, that mystery 4 gallons of water that reappears. I've done everything I've been told to track it down -- mirror and flashlight, load up on trailer and back the tail end of the boat into the water then spend an hour looking at nothing, and all I ever get is that water is getting in...nothing as to where.

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

Ayuh,....

While it appears you have Something going on that Isn't Right.....

Prop Testing is gaged by RPMs at WOT,.. Along with Seat of the Pants feelings....

We can't Feel the feelings, so the final #s are rather Important....
If you Test Props,+ return with No #s,.....
It doesn't give Us much to work with....

That's All...

Bond-o,

Ok, I see what you're saying. I think I posted all of the numbers I kept in my last response.

That said, I can try to help with the seat of the pants feelings.

I've been on a few similarly set up boats and the biggest difference I've noticed with mine is that it seems to "load up" when I hit the throttle hard. And by "hard" I mean taking anything less than 5 seconds to travel full throw on the stick.

Actually I can count about 2 or 3 seconds until I notice that seat of the pants feeling. And that's also the 2 or 3 seconds where the white smoke seems to be most rampant. The carb was rebuilt (new accel pump and all the goodies) this summer and there's still the white smoke.

Also, if I slowly take it up to about 2500 RPMs, then drop the hammer, the response is basically instant.

 

[chiefalen]

Re: 5.7L Mercruiser Vortec Head Swap

Maybe it's a fuel issue, maybe the fuel pump is lazy, maybe the filters are clogged.

You check the pressure the fuel pump is giving you?

You cleaned out every filter and know where they are ?

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

Maybe it's a fuel issue, maybe the fuel pump is lazy, maybe the filters are clogged.

You check the pressure the fuel pump is giving you?

You cleaned out every filter and know where they are ?

Chief,

It's a mechanical fuel pump but I haven't checked pressure or volume. Replacing it is near the top of my "to-do" list for next season anyway. That said, from what I've read a fuel pump issue would also include hard starting, and stalling...neither of which I have.

I found out the hard way where every filter was. I think I originally had two -- the fuel/water seperator, and a strainer in the carb -- and I added an inline filter mid season (which didn't change anything).

Also, I used marine gasoline all season, ran several cans of SeaFoam through it, and pulled the carb apart to make sure there was nothing in the float bowls that shouldn't be there.

 

[captmello]

Re: 5.7L Mercruiser Vortec Head Swap

A couple details i noticed.

Compression in the 140's seems a little low for this "Rebuilt motor"

I think your running the wrong prop (as you know) and shouldn't expect a hole shot from a boat that size. Its a cruiser.

Vortecs give how much more power? 30 hp?

Wonder if the boat came with a 2 barrel carb originally.

Sounds like you need a bilge pump.




Just had to throw in my .02.

 

[chiefalen]

Re: 5.7L Mercruiser Vortec Head Swap

Last one for me till we get some numbers on the 19 pitch.

Maybe this is all there is, ain't gonna get no more, learned that with my ole girl.

There is a limit with the hull design and hp.

And you will have to live with that limit unless you want to throw mondo big bucks into it.

Me i'm happy with doin 20-25 all day long, once in a while i goose it.

Some ain't happy till the drive grenades, or they blow there motor.

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

A couple details i noticed.

Compression in the 140's seems a little low for this "Rebuilt motor"

I think your running the wrong prop (as you know) and shouldn't expect a hole shot from a boat that size. Its a cruiser.

Vortecs give how much more power? 30 hp?

Wonder if the boat came with a 2 barrel carb originally.

Sounds like you need a bilge pump.




Just had to throw in my .02.

captmello,

I agree with your take on the compression numbers, which is why I'm really starting to wonder about the depth and quality of this mystery engine work.

Thanks for the confirmation on the holeshot. That was the influence of many of my friends who are running 350s in boats almost half the weight. I got into boating not expecting performance in the cruiser class (can't have your cake and eat it too), but I'm new at this and, frankly, a bit impressionable.

As far as the OEM carb, that is a question I cannot find an answer to.

And I do have a bilge pump. The issue is that the fore and aft bilges are "connected" by a hole (which appeared to be purposely placed) in the bulkhead aft the fuel tank, so an inch or so of water occupies a bit of volume. That and the fact that my automatic float doesn't kick on until I've got about 2.5" of water (measured from the very bottom of the V in the bilge).

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

Last one for me till we get some numbers on the 19 pitch.

Maybe this is all there is, ain't gonna get no more, learned that with my ole girl.

There is a limit with the hull design and hp.

And you will have to live with that limit unless you want to throw mondo big bucks into it.

Me i'm happy with doin 20-25 all day long, once in a while i goose it.

Some ain't happy till the drive grenades, or they blow there motor.

Chief,

I hear that. Unfortunately the 19P is going to have to wait until spring since the lake is not very calm these days and the boat is tied up getting a new camper built.

The more I think about what everyone is saying, the more I start to think you're right -- this may be all there is?

Like I said in other posts in this thread, I'm new to this and I raise an eyebrow when things aren't up to what they're advertised. That said, I do realize that this is a 14 year old boat and engines are designed to wear.

The future-ex-wife taught me the "ain't gonna get no more" lesson...I was hoping to avoid it with boating

I pulled the "throw mondo bucks at it and things will change" trick this year...and learned to save my money. Things change, and in the process you find new stuff to tinker with...and spend more money on.

That said, I've talked to two local mechanics (one of whom I trust by virtue of the fact that he's got grey hair, which I was always taught is a sign of wisdom...usually...and he seems to be a straight shooter) and he advised simply pulling the engine to see what's going on.

So now the issue still remains as to whether or not to bother with the Vortecs. You're content with doing 20-25 so I'd guess you'd vote "no"?

 

[captmello]

Re: 5.7L Mercruiser Vortec Head Swap

he advised simply pulling the engine to see what's going on.

That seems a bit unnecessary at this point. You don't need pull the motor to install those heads either. Unless the motor sits way down below the floor.

I'm one of those guys running a 350 in a boat half your size. I could probably get up to 60 mph with the right prop but I'd lack the hole shot and I might lug the motor at cruising speed. Mrs. Mello won't let me run WOT anyway.

 

[Maclin]

Re: 5.7L Mercruiser Vortec Head Swap

I think the Vortec heads would be just an OK upgrade. They do not seem to hurt low end and do definitely give more HP past 3000rpm with the same cam and stuff. I think that the full 30HP peak is at about 5200 though, so a realistic 20 hp in the operating range (4400-4600) is all you would net.

Having typed that, I would want to determine where the error is in the calculations first.

In my opinion, when assuming the RPM and speed and prop pitch are accurate as given and then "toggling" between an arbitrary 10% slip value and 1.5 ratio, the prop calculator is showing either 1.) 35% prop slippage with a 1.5 ratio or 2.) A 2.0 drive ratio with 10% slip. To me this indicates a problem with the numbers being supplied.

You seem to be confident in the RPM figure, and since you are pretty sure the prop is ok then the drive ratio may not be what it "should" be, or the prop is still suspect. I would be interested in making triple sure the RPM as given is correct.

And about the water "holding" at that level (and if you are sure you do get all of it with the wetvac), is the auto bilge pump system keeping it at tyhat level? Or does it really quit coming in after a time?

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

That seems a bit unnecessary at this point. You don't need pull the motor to install those heads either. Unless the motor sits way down below the floor.

I'm one of those guys running a 350 in a boat half your size. I could probably get up to 60 mph with the right prop but I'd lack the hole shot and I might lug the motor at cruising speed. Mrs. Mello won't let me run WOT anyway.

I agree that it seems a bit unnecessary at face value, but when I consider that his labor rate is $45/hr and he usually writes off the time he spends on things that don't end up solving the problem, it's a better value than any of the other guys who are charging from $85/hr to $115/hr and bill you 1.5 hours if a job goes one second over an hour flat. The motor is pretty easy access, but trying to work in the compartment is a bit weird -- his thinking was that it'd be more convenient for him (since he's pushing 60) to have it out of the boat rather than trying to bend and twist around. At 45 bucks I'm not about to argue with the man. Lest he fracture a hip.