a bit more grunt

[whiskeyRichard]

I am looking to get a bit more grunt from my boat. I'd like to see 50MPH.

Right now, with a 15p Al prop, she has a ton of snap and tapers after 4k RPM and tops out about 43mph, but runs right where she should at WOT. I tried a 17p prop and still has decent snap, but runs about 200RPM shy of where it should be at WOT.....I did not check the speed but seemed a little faster than the 15p.

I have attached a picture of the boat. It has a hull that when it was built, was designed for performance and the boat is not too heavy.

I figure I need heads, intake, carb, cam and maybe exhaust.

I have a closed cooling system. The exhaust is early cast iron kodiak exhaust manifolds and risers and it goes through the y-pipe. I do run an exhaust tube instead of an exhaust bellows.

The motor is a 1980 Mercruiser 260 and has been rebuilt with about 200 hours on it now. I recently checked the compression and all cylinders were about 140+/-.

I don't mind pulling the motor to do the work as I was thinking about detailing the engine compartment and bilge area anyways.

I have read on here a few other people looking to do the same thing, but need a little more guidance regarding particular parts.

I was planning on getting an edelbrock carb and intake. Would the 1409 600 CFM be enough carb? Any advice regarding heads, head gaskets and cam would be great as well.

Thanks

 

[whiskeyRichard]

[No message]

 

[achris]

Vortec heads are worth about 20hp straight off the bat... You'll need a new intake for them too. the 1409 carb is good on that engine (350cid) to about 6000. See chart below. VE with stock heads on a normally aspirated engine is about 83%, so that's what's in. The 600cfm carb has volume to spare. You don't want to go much over 5500rpm as the drive won't take it. So cam to no more than that... But, and it's a big but... To increase speed by 7mph you're going to need a few more than 20hp, probably more like 60-80.... And that'll push you over the limit that an Alpha drive can handle.

Chris.....

 

[Scott Danforth]

make sure the boat isnt heavy (water logged foam). weigh it

as Chris mentioned, vortec heads help, however only add 20-30hp

other things that will help push up power to get to your goal
cam change (suggest an XM264H - depending on the head, may need spring pockets cut down )
rocker arm ratio change to 1.6:1)
add a 2" carb spacer

the above will get you to an honest 330hp at the flywheel

as long as you ease into the holeshot and dont get airborne the drive will be fine (you can make them last behind strokers)

 

[whiskeyRichard]

I've done a lot of poking (and some drilling) and my boat is dry and not rotten. The transom, stringers, floor and interior of the hull are exceptionally clean........especially for a nearly 40 year old boat.

There are a lot of options when it comes to the vortec heads. Runner and chamber size, and I read that I should make sure that the exhaust seats are hardened.

In my reading, since my 350 is an early model, it should have the flat top pistons. Does this help me determine which heads I should get?

I see that cam is listed as hydraulic roller......will that work in my engine?

Thanks

 

[kenny nunez]

Chris & Scott have your engine covered. Have you ever checked how much “hook” there is at the keel with a straight edge ?
A lot of boats have them to help the boat plane with less horsepower at slower speeds. When the drive is down and the boat is on the trailer how far down is the cavitation plate below the keel ? Performance sport boats usually have the cavitation plate either even or slightly above the keel. Most California style day cruisers were made for cruising and not so much for high top speeds. If your boat has the “hook” you can get it filled at a fiberglass shop. This may cause the boat to “porpoise” at certain trim angles but your speed on the top will increase especially with the engine modifications.

 

[Rick Stephens]

Seems to me that with the performance goal being pretty steep gain, you'd be better off both cost wise and in results by rebuilding with a 383 stroker bottom and Vortec top end. Swing a bigger wheel and go faster.

 

[whiskeyRichard]

Seems to me that with the performance goal being pretty steep gain, you'd be better off both cost wise and in results by rebuilding with a 383 stroker bottom and Vortec top end. Swing a bigger wheel and go faster.

Man, I would really like to do that, but the price difference between upgrading my engine (and probably falling a little short of my performance goals) and building or buying a new 383 is significant. It has been more than once or twice that I have been on summit racing with the 405 HP marine 383 in my 'cart' and just couldn't do it.

 

[Scott Danforth]

There are a lot of options when it comes to the vortec heads. Runner and chamber size, and I read that I should make sure that the exhaust seats are hardened.

all vortec heads have hardened seats. you will have to have the heads re-done anyway. they need to be modified for screw in studs and the seat pockets need to be cut.

In my reading, since my 350 is an early model, it should have the flat top pistons. Does this help me determine which heads I should get?s

Not really. your motor is a smog era motor. unless you put flat-tops in, there should be dished pistons. however vortecs work well with flat top heads

I see that cam is listed as hydraulic roller......will that work in my engine?

H not HR the H is hydraulic flat tappet. the HR would be a Hydraulic Roller tappet. I did mis-type. should be XM262H

http://www.compperformancegroupstor...=CC&Product_Code=12-236-3&Category_Code=HFTXM

 

[Scott Danforth]

Seems to me that with the performance goal being pretty steep gain, you'd be better off both cost wise and in results by rebuilding with a 383 stroker bottom and Vortec top end. Swing a bigger wheel and go faster.

Rick, if he didnt just rebuild the motor, that would have been my first suggestion.

Man, I would really like to do that, but the price difference between upgrading my engine (and probably falling a little short of my performance goals) and building or buying a new 383 is significant. It has been more than once or twice that I have been on summit racing with the 405 HP marine 383 in my 'cart' and just couldn't do it.

I have outlined on this forum many times that when building a motor, it is the same price to build a stock 350 as it is to build a 383. for about $3k you can build a new shortblock (new GM block, new GM heads, new SCAT rotating assembly ) for just a few hundred more than rebuilding a used motor.

 

[Rick Stephens]

Rick, if he didnt just rebuild the motor, that would have been my first suggestion.



I have outlined on this forum many times that when building a motor, it is the same price to build a stock 350 as it is to build a 383. for about $3k you can build a new shortblock (new GM block, new GM heads, new SCAT rotating assembly ) for just a few hundred more than rebuilding a used motor.

So the block and heads are pretty much cherry. What kind of HP gain dropping just the SCAT 383 rotating parts in?

And would that be cheaper than buying and modifying Vortec heads, new intake, new carberation, etc? Nice part with swapping in the 383 bottom, if you want more, add the heads and carburetor later.

 

[Scott Danforth]

Scat rotating kit is about $900 for cast crank, and hyper-e pistons. Requires clearancing the block, new bearings, etc. Set of vortec heads is about $400 (used and moded)

 

[QBhoy]

Hi. Is she an old glastron ? Looks similar to one of their models.
To get a gain of 7mph is a big ask, but if it is the glastron model I’m thinking of, there are others achieving 50 with the same set up.
Wont bore you too much on it, but you’ll be amazed at the difference a few bits on bobs on the boat will make to speed. Prop nicks will affect it. Stainless prop will help a few mph. Water in bilge or even the wife will slow you down. My boat will loose 5/6 mph min with a full tank of fuel compared to a quarter. Same if the hood is up. Same if someone sits in the bow. I could go on.

 

[achris]

.. or even the wife will slow you down. ....

That alone will restrict your top speed to about 15 knots...

 

[whiskeyRichard]

Hi. Is she an old glastron ? Looks similar to one of their models.
To get a gain of 7mph is a big ask, but if it is the glastron model I’m thinking of, there are others achieving 50 with the same set up.
Wont bore you too much on it, but you’ll be amazed at the difference a few bits on bobs on the boat will make to speed. Prop nicks will affect it. Stainless prop will help a few mph. Water in bilge or even the wife will slow you down. My boat will loose 5/6 mph min with a full tank of fuel compared to a quarter. Same if the hood is up. Same if someone sits in the bow. I could go on.

It's not a Glastron, but a brand called SKV. They made a small number of boats per year for a few years back in the late 70's. Very well built, tough boats.

Maybe instead of building my engine up, I should ask the wife to lean herself out a little bit.....LOL. I would be in deep sh*t if that sees this.

I do plan on getting a SS prop. Need to figure out what prop this motor will spin before I do that though.

 

[whiskeyRichard]

Looking at heads, I noticed there are a number of different chamber sizes. 64cc, 67cc, 76cc and so on.

Ho do I go about figuring out which I need to keep my compression ration where it is? My current plan is to read the casting number from my existing heads, see what those are and get the new heads with the same chamber size......legit?

I already got my new Edelbrock intake manifold, Edelbrock carb, EMI thunder exhaust manifolds and risers. Just need to figure out the heads and the cam.

I am going to route my exhaust through the hull at the water line below the swim platforms. If it is too loud, I will cut it up and build myself some mufflers, but I suspect having it below the swim platforms at the water line will keep it in check.

When I cut the holes for the exhaust, should I glass in around the opening to protect the wood? I do not see that most people do this, but it seems like it would be a good idea.

Thanks,
wR

 

[kenny nunez]

Since your boat is an SKV, Go on the Performance Boats site. There are people on that site that have a lot of experience with that style hull. Those hulls were also made under the Spectra and a few other names. You will find out how to get more out of the boat speed wise. SK stands for ski and the V stands for the hull shape. That is how someone described the name.

 

[H20Rat]

Maybe instead of building my engine up, I should ask the wife to lean herself out a little bit.....LOL. I would be in deep sh*t if that sees this

And he was never heard from again... Was hoping to see the end of this thread and if the OP went forward with his plan!

 

[Scott Danforth]

Looking at heads, I noticed there are a number of different chamber sizes. 64cc, 67cc, 76cc and so on.

Ho do I go about figuring out which I need to keep my compression ration where it is? My current plan is to read the casting number from my existing heads, see what those are and get the new heads with the same chamber size......legit?

I already got my new Edelbrock intake manifold, Edelbrock carb, EMI thunder exhaust manifolds and risers. Just need to figure out the heads and the cam.

I am going to route my exhaust through the hull at the water line below the swim platforms. If it is too loud, I will cut it up and build myself some mufflers, but I suspect having it below the swim platforms at the water line will keep it in check.

When I cut the holes for the exhaust, should I glass in around the opening to protect the wood? I do not see that most people do this, but it seems like it would be a good idea.

Thanks,
wR

pull the casting numbers of what you have..... either post here or look them up on mortec.com

you either have 76cc or 64cc heads. many of the boat motors were made with 64cc heads as they were spec'd for boats and didnt need to be SMOG compliant.

if you have 64cc, then switching to vortec heads (at 64cc) keeps your CR intact, however you now have the ability to run more base timing as well as the improved efficiency of the vortec chamber. vortec heads alone are good for about 30hp.

regarding cam, I can give you real world experience with what I posted earlier. the problem with small bumps in power is you want more. hence the reason I built up a BBC (simply go thru the link in my sig)

for the exhaust, you can simply use turn-down pipes. they sit below the water at idle, and come out as the boat comes on plane. AllDodge is running these on his 509. He has vids in his build.

however for a small block, not much to be gained with thru-hull exhaust for the cost unless you build the motor and do a bunch of other upgrades.

always a good idea to seal the edges of the wood on any thru-hull. and no, the factory or the initial rigging dealer wont do this, however nearly everyone on this great DIY site does.

a good read is project triple digits. however most people do not have the equipment available that RLC performance does. http://www.rlcperformance.com/images/projects/tripple_digits/project_trippledigits.html

 

[whiskeyRichard]

been away from this for a bit, but am back at it. Decided to pull the motor to do the work.

Why is it that the procedure for removing the motor has me take the lags out and completely remove the front motor mounts? Why not just back the top nut off and lift motor straight up and leave the mount on the stringer?

Thanks,
wR