5.7L Mercruiser Vortec Head Swap

[StevNimrod]

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?

I'm starting to agree that they would be just an OK upgrade. Since our first exchange I've actually been able to call a few places, and what I'm hearing is that there are a few things that should be pressure tested first (exhaust manifolds, the existing heads, etc.) to see what the cause of the smoke issue could be, then move forward with any potential swap after that. Considering this, and adding the amount of back and forth I'd have to do, etc., it's crossed my mind more than once that it might just be less hassle to go with a Rapido longblock...if it comes to that.

As far as the Vortec peak, I agree with that number, and found a post where someone said something to the effect that 20 HP on a boat is worth about 1 MPH. That still puts me a long way from home.

Trust me, the numbers have been checked, re-checked, and re-checked again. I spent all summer not understanding how they could possibly work. To my eye, since the prop was known good (unless it's flexing an insane amount under load) and there are no drive issues, that only leaves the engine as the weak link.

I'm sure that the water is holding. The funny thing is that if I suck the water up completely, it'll be back the next day, but it won't rise enough to trip the bilge float over the rest of the week (spent a week straight on it and it never tripped the bilge). Very weird.

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

For a rebuilt engine those compression numbers are too low.

They should be closer to, or in, the 160's...right?

 

[FreeBeeTony]

Re: 5.7L Mercruiser Vortec Head Swap

I read most of this thread but never saw the weight of the boat.

Here are some numbers for comparison:

Boat: 24' grady White
Weight: ~4000#
Engine 350SBC w/ Vortec heads, roller cam and Edelbrock 1409 carb
Outdrive: Mercruiser Alpha 1 gen 1 w/ 1.5:1 ratio
WOT ~4600RPM @ 34MPH (GPS)

Generally cruise @ 3600RPM 29-30MPH.

I am attributing my low speed @ WOT to the weight of the boat.

Another thought..........are you trimmed properly?

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

I read most of this thread but never saw the weight of the boat.

Here are some numbers for comparison:

Boat: 24' grady White
Weight: ~4000#
Engine 350SBC w/ Vortec heads, roller cam and Edelbrock 1409 carb
Outdrive: Mercruiser Alpha 1 gen 1 w/ 1.5:1 ratio
WOT ~4600RPM @ 34MPH (GPS)

Generally cruise @ 3600RPM 29-30MPH.

I am attributing my low speed @ WOT to the weight of the boat.

Another thought..........are you trimmed properly?

Good catch!

The dry weight of the boat is 4100 lbs.
Half tank of fuel (~38 gal. @ 6.25 lbs/gal) adds about 238 lbs.
I add 265 lbs.
My girlfriend adds, well, let's say 150 lbs...and if you guys don't see another post from me, send out a search party.
I estimate that with gear, other misc. stuff., and the few gallons of water I carry in the bilge, I'm adding no more than an extra 300 lbs.

Which brings us to a grand total of 5053 lbs.

So I'm coming in about 1000 lbs heavier than you, so my speeds now seem very reasonable. Since you have the exact setup I'm contemplating, what do you think about the Vortec heads?

And yes, I am trimmed properly. That was another one of those "oh, that's what that button does" moments of the season.

 

[Bondo]

Re: 5.7L Mercruiser Vortec Head Swap

Trust me, the numbers have been checked, re-checked, and re-checked again. I spent all summer not understanding how they could possibly work. To my eye, since the prop was known good (unless it's flexing an insane amount under load) and there are no drive issues, that only leaves the engine as the weak link.

Ayuh,....

Those #s say it's Not the Motor.... It's pulling to 5000+rpms....

Are you Sure that you've been weighing the Anchor during these Tests,..??

These #s say the Hull is Dragging,.... Badly.... 35% Slip is Ridiculous...
Or,... Something is Slipping, Really Bad....

 

[krisnowicki]

Re: 5.7L Mercruiser Vortec Head Swap

you will be surprised I bet even if you add the vortec heads. You will get 30ish hp which may only translate to about 3-6 mph. Is it worth it?

 

[Maclin]

Re: 5.7L Mercruiser Vortec Head Swap

Freebee, what is that prop pitch?

 

[FreeBeeTony]

Re: 5.7L Mercruiser Vortec Head Swap

Forgot about the prop.......it's a 16" pitch 4-blade aluminum.

From where I am sitting you might be OK..........my ~4000# number is coming from an old Grady White catalouge........doesn't include any gear or anything.

I like the Vortecs.........not sure I would go through the expense/bother if your current set-up is OK.........I would try the 19" prop any see what happens first.

 

[FreeBeeTony]

Re: 5.7L Mercruiser Vortec Head Swap

Here is a thread I started a while back you might find interesting........

http://forums.iboats.com/showthread.php?t=280773

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

I'll try to hit everyone at once...

Bondo-

I'm sure the total weight is accurate, at least to within a reasonable number to prevent error. From what I'm reading on other posts, 35% is high, but depending on hull design may not be as crazy as it sounds. That said, I have a fresh coat of bottom paint lined for the upcoming spring.

krisnowicki-

3-6 MPH may not be worth it, unless only the heads have to come off...at which point it really wouldn't be adding too much to my costs. If that's the case I'll probably go for it.

FreeBeeTony-

Good suggestion on that post. I'm starting to lean towards your thinking -- it's not a speed boat, but I'd still like to optimize.

Bubba-

I think you're spot on with rechecking the compression test. I've read quite a few posts where people have had compression gauges that weren't accurate (or flat broke). That coupled with my lack of skill could mean I didn't do something correctly.

As far as the valves go; I'm not getting white smoke at cold start, I'm getting it when I accelerate hard or when I'm at cruising speeds. Does this also jive with overly tight valves.

The compression test, unfortunately, will have to wait until we're out of the 20 degree temperatures here.

 

[Maclin]

Re: 5.7L Mercruiser Vortec Head Swap

The engine gets to 5,200 rpm under load, sounds like it is in pretty good tune to me. Improper valve lash would not let it get past 4,000. I'm just sayin'....

 

[mylesm260]

Re: 5.7L Mercruiser Vortec Head Swap

I think you are putting the horse before the carrage here.

First of all, the 30-50 HP that the vortec heads will add will do absolutly nothing for you, if you are already maxing out at 5200 RPMS. The only thing they would do is help you out of the hole a little bit.


Before you do anything, you have gota to nail down your gear ratio, prop pitch and hull type. IF your engine is hitting 5200 rpms, than something is clearly not correct.

You can always pull the spark plugs, and spin the engine by hand while in drive to figure out your gear ratio. just use White-out and mark the prop against the drive, and the crank to the water pump, then slowly spin the crank and have someone tell you when the prop has gone one complete revolution.


I would tend to think that your engine is running fine as it is. It sounds like your carb could use a little tunning for bottom end torque and throttle responce but other than that, it's sounds like it's making HP.


When is the last time you had a look at your engine coupler? I've heard of them slipping before, maybe that's part of the explaination.

Also, go take a picture of your hull, and post it here for the guys to look at. There are guys in here that have had many many years of experience, I'm sure they could look at your hull type, and tell you exactly what kind of prop slip you should be expecting.


From what little experience I've had with non-vortec to vortec engine swaps, if you are turning 5200 rpms with a non vortec and a 15P prop, then you are going to need like a 21P prop or higher to get the desired 4400-4600 rpms with the vortec heads.


Physically verify your gear ratio, and post pics of your hull type, and maybe ask the guys in here if the rubber couplers can slip, and go from there.


Also guys, here's a thought.

Why would someone change to a rollerized valve train, and go with different risers?

Sounds to me like the previous owner went with a hotter cam. The valve train was to work with hot cams, and the risers could be to prevent water from sucking back into the engine. This would totally explain the low compression numbers.

This might also explain your hard to pin down performance issues. The hot cam would give you more top end, but less bottom end, and make finding the right prop very difficult.

Because you have less bottom end torque, too high of a prop pitch, and you woudn't have enough mojo to get on plane.


I'm sure many people would disagree with me here, but I would recomend grabbing the the cam, the valvetrain and the heads off a vortec 5700 from a truck when you do your swap. Sounds like your boat is pretty big, and those truck cams are very very similar to the marine cams, just slightly colder. The "colder" truck cams will give you a little bit more bottom end, which, given the size of your boat, would be a good thing.

 

[bolo78910]

Re: 5.7L Mercruiser Vortec Head Swap

very intrested tread i am following this one, i also have a heavy boat push by a 5.7 and iam not happy also, with four guys 90 gallons of gas gears i get 20 miles per gps at 3700 rpm 15x15 ss prop alpha one. good luck you are on the right forum. my carver dry weight is 5,300 lbs . keep posting

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

You can always pull the spark plugs, and spin the engine by hand while in drive to figure out your gear ratio. just use White-out and mark the prop against the drive, and the crank to the water pump, then slowly spin the crank and have someone tell you when the prop has gone one complete revolution.

I would tend to think that your engine is running fine as it is. It sounds like your carb could use a little tunning for bottom end torque and throttle responce but other than that, it's sounds like it's making HP.

When is the last time you had a look at your engine coupler? I've heard of them slipping before, maybe that's part of the explaination.

Also, go take a picture of your hull, and post it here for the guys to look at. There are guys in here that have had many many years of experience, I'm sure they could look at your hull type, and tell you exactly what kind of prop slip you should be expecting.

From what little experience I've had with non-vortec to vortec engine swaps, if you are turning 5200 rpms with a non vortec and a 15P prop, then you are going to need like a 21P prop or higher to get the desired 4400-4600 rpms with the vortec heads.

Physically verify your gear ratio, and post pics of your hull type, and maybe ask the guys in here if the rubber couplers can slip, and go from there.

Sounds to me like the previous owner went with a hotter cam. The valve train was to work with hot cams, and the risers could be to prevent water from sucking back into the engine. This would totally explain the low compression numbers.

This might also explain your hard to pin down performance issues. The hot cam would give you more top end, but less bottom end, and make finding the right prop very difficult.

Because you have less bottom end torque, too high of a prop pitch, and you woudn't have enough mojo to get on plane.

I'm sure many people would disagree with me here, but I would recomend grabbing the the cam, the valvetrain and the heads off a vortec 5700 from a truck when you do your swap. Sounds like your boat is pretty big, and those truck cams are very very similar to the marine cams, just slightly colder. The "colder" truck cams will give you a little bit more bottom end, which, given the size of your boat, would be a good thing.

I can do you one better...I have the drive off of the boat and in my living room (admittedly not the best place to replace a water pump, and I learned the hard way that "drain the oil" means just that...did a pretty good job oiling the carpet) so I can spin the driveshaft by hand and count the number of propeller turns no problem. I can do that tomorrow morning and post results.

Does anyone with the Edelbrock 1409 on a large boat have any suggestions as to the best setup with the rods, etc.?

As far as pics of the hull...that's gonna be a bit of a problem. The boat is over an hour away getting the canvas re-worked. If I'm feeling particularly motivated I'll make the trek. Otherwise it may have to wait until the weekend.

WRT the cams, I have absolutely no clue what went on. Yesterday I called the PO and he didn't know what the guy before him did. So, being anal, I'm tempted to find out for myself. Which, obviously, I know nothing about

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

very intrested tread i am following this one, i also have a heavy boat push by a 5.7 and iam not happy also, with four guys 90 gallons of gas gears i get 20 miles per gps at 3700 rpm 15x15 ss prop alpha one. good luck you are on the right forum. my carver dry weight is 5,300 lbs . keep posting

Glad to see I'm not the only one. I've been monitoring these posts since I got out on the water in April but nobody really had anything about having the 5.7, a heavy boat, and unimpressive numbers. Let's not even get started with a full tank of fuel and a couple of buddies. I was hoping that finally joining and posting about it would bring some guys out of the woodwork and we can all compare notes.

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

Ok, here goes...

Since I have the drive off, I (triple) check the ratio. Spinning the U-joint one and a half times rotates the propeller exactly once.

The weather didn't cooperate as far as me getting down to get hull pics, but here are pics I found online of the same boat (make, model, year...the only difference is they have a Volvo drive and I have a Merc) for those who can tell what slip I should be expecting from this hull. Per the owner's manual the deadrise is 20*.

 

[Gazza1]

Re: 5.7L Mercruiser Vortec Head Swap

I'll put my 2 bits in.. One problem that I had with my boat 213c Haines Hunter (an Aussie built that weighs 2.25 ton built Originaly built with 260hp mercruiser 1979) was water leaking into the bilge and after destroying 2 transom mounts blaming the bellows found the shift cable bellows was leaking. duh. speed wot was only about 38mph.. After rebuilding the engine the hole shot was heaps better but wot didn't improve.. I fitted an 86 corvette efi/mpi and walla, the hole shot improved by at least 300%, fuel consumpson dropped by 150%+++. The carb that was fitted to this engine, I could never get it to run on the plane without the secondarys opening at least half..
On your engine, I think I would pull it out strip it and see what is really wrong with it. 140 compression sucks, it should be at least 160+. I think that you will find several broken rings and or maybe some leaking valves.. If you go with the Vortec head, remenber that they crack very easely if over heated, but are lighter.. The genuine mpi intake is about 50 to 60 lbs as it is cast iron.
If you are in a positio to be able to buy a new 5.7 mpi Alpha/Bravo, I would do it then you would know what you have.. Mods that suit cars don't suit boats, remenber a boat is going up hill all day and does not go down hill like a car.
I hope I could help in some small way.
Cheers and good luck.
Gazza

 

[mylesm260]

Re: 5.7L Mercruiser Vortec Head Swap

I congradulate you sir, for running an automotive EFI setup in a boat.

I did the same thing in my boat, and people in this forum were not very impressed.

I'm running a 2001 AWD astrovan engine in my boat with the automotive EFI.

And just like you, WAY better hole shot and WAY better fuel consumption. I also have way more top end, but that's because I was going from an old 2bbl non vortec engine to an EFI vortec engine.

I have about the same hole shot with my 23P prop and my new motor that I did with my 19P prop and my old motor.

And even with the bigger prop, I'm turning MORE RPMS at WOT, I can hit 4900 rpms with just me in the boat..... 63 MPH GPS.

On your engine, I think I would pull it out strip it and see what is really wrong with it. 140 compression sucks, it should be at least 160+. I think that you will find several broken rings and or maybe some leaking valves..
Gazza

Remeber, that hotter cams cause lower compression numbers when you do a compression test, If the previous owner did in fact put in a hot cam (remember he also modified the exhast and added rollerized valve train) that would explain it.

His compression numbers are also consistant, which would indicate a good engine.

 

[chiefalen]

Re: 5.7L Mercruiser Vortec Head Swap

Very nice a 86 mpi motor ? Out of a corvette? What motor was that precisely?

And what manifolds did you use ?

And what drive in that boat ?

And you just dropped it in the boat ? With no modifications ?

The last thing i remember this guy got a carb .

So you want him to sink what into this boat money wise, maybe 10 grand probably more with a bravo 3.

 

[StevNimrod]

Re: 5.7L Mercruiser Vortec Head Swap

I'll put my 2 bits in.. One problem that I had with my boat 213c Haines Hunter (an Aussie built that weighs 2.25 ton built Originaly built with 260hp mercruiser 1979) was water leaking into the bilge and after destroying 2 transom mounts blaming the bellows found the shift cable bellows was leaking. duh. speed wot was only about 38mph.. After rebuilding the engine the hole shot was heaps better but wot didn't improve.. I fitted an 86 corvette efi/mpi and walla, the hole shot improved by at least 300%, fuel consumpson dropped by 150%+++. The carb that was fitted to this engine, I could never get it to run on the plane without the secondarys opening at least half..
On your engine, I think I would pull it out strip it and see what is really wrong with it. 140 compression sucks, it should be at least 160+. I think that you will find several broken rings and or maybe some leaking valves.. If you go with the Vortec head, remenber that they crack very easely if over heated, but are lighter.. The genuine mpi intake is about 50 to 60 lbs as it is cast iron.
If you are in a positio to be able to buy a new 5.7 mpi Alpha/Bravo, I would do it then you would know what you have.. Mods that suit cars don't suit boats, remenber a boat is going up hill all day and does not go down hill like a car.
I hope I could help in some small way.
Cheers and good luck.
Gazza

This is very helpful. At this point I'm seriously considering pulling the motor and tearing it down...just to have a look see.

I've heard that about the Vortec head -- that they crack -- and one of the machine shops I called told me that you MIGHT get one overheat out of them before they're done.

I think I'd be more likely to buy a bigger boat than go full EFI. One of the problems I've identified in my personality (at least as it relates to owning a boat) is that I don't seem to have the ability to just let things be as they are. That said, if it comes down to having to to the EFI route I'll probably just get something bigger with twin screws.