Upgrading mercruiser 350 v8 260 hp

[fabrimacator21]

Re: Upgrading mercruiser 350 v8 260 hp

stickers are usually worth 100hp.... ask importers.


I'm just wondering if your restricter plate theory is proven or if it's theory. Again, I don't see how log manifolds are much worse then stock manifolds on a truck. Matter of fact on a truck theres a muffler and cat along with more bends. I understand that whats behind the manifolds doesn't matter if the manifolds are maxxed out but I don't think thats the case.

Can of worms? ... it's pretty cut and dry. Heads and a manifold and he'll get 50 hp along with some much needed low end tq. Have a look at some stock vortec truck manifolds and tell me they're much better. Matter of fact they are almost a dead ringer for log manifolds. And yes I'm aware that heads require other work but it's nothing the weekend warrior can't do with some instruction. If he does it himself it can be done for much less then 1k. But if a shop does it labor costs make it sort of pointless. Lets not forget about "easy" power either. Port match the intake, roller rockers, and windage trays are great ways to get some easy power.

I'm not telling him to do either but having had this delimma myself(pay a grand for another 10mph or pay 5k for a bravo, and engine and maybe a few more mph) I think throwing a little money at the 350 isn't a horrible idea. When you look at the amount of money spent and compare it to how much mph your gaining and the amount of work it's a no brainer. (heads, manifold, and maybe a cam is the way to go... compared to a new outdrive and motor).

 

[n2ostroker]

Re: Upgrading mercruiser 350 v8 260 hp

stickers are usually worth 100hp.... ask importers.


I'm just wondering if your restricter plate theory is proven or if it's theory. Again, I don't see how log manifolds are much worse then stock manifolds on a truck. Matter of fact on a truck theres a muffler and cat along with more bends. I understand that whats behind the manifolds doesn't matter if the manifolds are maxxed out but I don't think thats the case.

Can of worms? ... it's pretty cut and dry. Heads and a manifold and he'll get 50 hp along with some much needed low end tq. Have a look at some stock vortec truck manifolds and tell me they're much better. Matter of fact they are almost a dead ringer for log manifolds. And yes I'm aware that heads require other work but it's nothing the weekend warrior can't do with some instruction. If he does it himself it can be done for much less then 1k. But if a shop does it labor costs make it sort of pointless. Lets not forget about "easy" power either. Port match the intake, roller rockers, and windage trays are great ways to get some easy power.

I'm not telling him to do either but having had this delimma myself(pay a grand for another 10mph or pay 5k for a bravo, and engine and maybe a few more mph) I think throwing a little money at the 350 isn't a horrible idea. When you look at the amount of money spent and compare it to how much mph your gaining and the amount of work it's a no brainer. (heads, manifold, and maybe a cam is the way to go... compared to a new outdrive and motor).

I have been through all this. It just isn't as easy as people think it's going to be. You won't pick up 10mph either. Big boat-small motor, it won't happen. Maybe 5 or 7 with heads, cam, intake, manifolds, carb tuning and the right prop. Assuming he gets his setup now dialed in. If you go the cam route which if doing the other stuff I would, you're talking about pulling the motor. Like I said, can of worms.
Port matching the intake would be a waste of time. a windage tray is bolted to the main caps(pull motor again)... and the Mercruiser 260 should already have one. Roller rockers= more money.
Have you ever replaced all the gaskets on a marine motor for doing a head change. Theres at least $150, oil/filter change $45, cap-plugs-rotor button $60, heads plus shipping $600, head bolts $50, other fasteners $25(they'll be rusted), then you have all the cleaning supplies and other misc crap that'll nickel and dime you.
If you're going to go through all that save money and buy a proven low maintenance set up with tons of torque to move a big boat.

 

[mylesm260]

Re: Upgrading mercruiser 350 v8 260 hp

Fuel injection does not MAKE power, that comes from the heads, intake, cam and exhaust choices.

That's simply not true.

A carb and Throttle body injection are about on par. Logically, they both work the same way.


Multi-point fuel injection however does offer an advantage over a carb (other than the obvious electronic control)


It is very difficult to keep fuel and air mixed (atomized) together properly. On a carbed system, the air/fuel must travel a long way from the jet in the carb to the intake valve. By the time it reaches the cylinder, some of the fuel has fallen, and is now a river flowing into the cylinder, rather than a mist.

(vortec engines are better in part because they swirl the air to help keep the fuel from separating from the air)

Also, because fuel weighs so much more than air, you end up getting different amounts of air and fuel to each cylinder. (some cylinders run leaner or richer than others)

Because of these factors, Carbed manifolds are extremely limited in how they can design their runners and their plenum.


This is why performance bike engines will have 1 carb for each cylinder, and tune them individually.


Multi-point EFI setups give you much better fuel atomization, and precisely the same amount of fuel to each cylinder. It also allows for better intake manifold and plenum designs, which leads to much more bottom end torque.


It's true that PEAK hp wise, a carb can get to within 90% or so of what EFI can, but at 50% throttle and 50% rpms (50% air velocity) the EFI system is far better.

 

[Bifflefan]

Re: Upgrading mercruiser 350 v8 260 hp

So the best way to find out my rpm is to go WOT while by myself and i should reach 4.8 rpm? I noticed that after or around 4 rpm, my tach gets all jumpy and screwy by going to 7 to 4 to 6 to 4 to 5 rpm very jumpy and so forth.. Why???

that is caused by spark jumping (or lack there of). Everytime ive seen this its a problem with the plugs, wires, or cap and rotor, or ever a coil. The faster you turn the motor the more power it takes to fire the plugs. therefor the harder it is to fire the plugs. sometimes the spark jumps around and feeds back and your tach picks this up and tries to read it.

 

[fabrimacator21]

Re: Upgrading mercruiser 350 v8 260 hp

When I said 10mph I was talking about my setup which will roughly be 100hp over stock... and I've heard the rule is 1mph for every 10hp.

As for a cam swap, (again this is MY boat) pulling the motor isn't necessary. Trim it down, support the motor and pull the trim bracket... plenty of room to pull the cover and cam.

Port matching is worth about 5-7hp... not alot but it's still 5-7hp and can be done in a few hours for free if you have a die grinder. Windage tray would be a PITA. Roller rockers are an easy 15hp up top for 170 bucks to your door... not to mention the ratio's actually all match unlike the factory stamped rockers.

Your prices came out to $780... to me thats not unreasoble when compared to $4k for a bravo II setup that is only rated at 100 more hp then his alpha drive.

I did some research on the big block setup and I was wrong... for a new outdrive your looking at $4K WITH NO MOTOR.

Price out a 496 or 454 and your looking at about 7 grand... so yeah 1k doesn't seem that bad for another 5-7mph.

 

[fabrimacator21]

Re: Upgrading mercruiser 350 v8 260 hp

That's simply not true.

A carb and Throttle body injection are about on par. Logically, they both work the same way.


Multi-point fuel injection however does offer an advantage over a carb (other than the obvious electronic control)


It is very difficult to keep fuel and air mixed (atomized) together properly. On a carbed system, the air/fuel must travel a long way from the jet in the carb to the intake valve. By the time it reaches the cylinder, some of the fuel has fallen, and is now a river flowing into the cylinder, rather than a mist.

(vortec engines are better in part because they swirl the air to help keep the fuel from separating from the air)

Also, because fuel weighs so much more than air, you end up getting different amounts of air and fuel to each cylinder. (some cylinders run leaner or richer than others)

Because of these factors, Carbed manifolds are extremely limited in how they can design their runners and their plenum.


This is why performance bike engines will have 1 carb for each cylinder, and tune them individually.


Multi-point EFI setups give you much better fuel atomization, and precisely the same amount of fuel to each cylinder. It also allows for better intake manifold and plenum designs, which leads to much more bottom end torque.


It's true that PEAK hp wise, a carb can get to within 90% or so of what EFI can, but at 50% throttle and 50% rpms (50% air velocity) the EFI system is far better.

This is true... EFI gives you much better off idle tq as well as throttle response... even TBI will give you a noticeable gain off idle.

 

[n2ostroker]

Re: Upgrading mercruiser 350 v8 260 hp

You have to drop the oil pan to do a cam on a Chevy.

 

[n2ostroker]

Re: Upgrading mercruiser 350 v8 260 hp

When I said 10mph I was talking about my setup which will roughly be 100hp over stock... and I've heard the rule is 1mph for every 10hp.

As for a cam swap, (again this is MY boat) pulling the motor isn't necessary. Trim it down, support the motor and pull the trim bracket... plenty of room to pull the cover and cam.

Port matching is worth about 5-7hp... not alot but it's still 5-7hp and can be done in a few hours for free if you have a die grinder. Windage tray would be a PITA. Roller rockers are an easy 15hp up top for 170 bucks to your door... not to mention the ratio's actually all match unlike the factory stamped rockers.

Your prices came out to $780... to me thats not unreasoble when compared to $4k for a bravo II setup that is only rated at 100 more hp then his alpha drive.

I did some research on the big block setup and I was wrong... for a new outdrive your looking at $4K WITH NO MOTOR.

Price out a 496 or 454 and your looking at about 7 grand... so yeah 1k doesn't seem that bad for another 5-7mph.

Do all this to your boat, add all the receipts and come let us know how much you spent. ALL your receipts. Then let us know your gains. This isn't your mom's Oldsmobile.

Also the OP's boat is A LOT longer and heavier. All speed guesses are out the window. I added 70-80 hp to my boat and have struggled to get 5-6mph after trying 5 props because of the hulls limits and what I have to overcome. Holeshots like crazy, just hits a wall up top.

Good luck if you think its as easy as your posting.

 

[fabrimacator21]

Re: Upgrading mercruiser 350 v8 260 hp

Yup hull has a big effect on how much mph you gain....

$780 for a head swap seems fair... and you said you've been through all that so I don't know why your asking for my receipts. That was YOUR estimates, not mine.

And that was being generous with head bolts and miscellanious hardware.


I'm not trying to butt heads with you here. Just trying to hammer out nickel and dime costs of those mods...

If you know anymore hidden costs PLEASE post them up. I could use the info and I'm sure others could.

However like I said, when you compare spiffing up your current motor to buying a bigger CID engine with the price of a new I/O setup it's small beans.

Your talkign 1k-1500 compared to $7,000. Tq is definetly a factor with a big boat but a warmed up 350 will do the job just fine. Even after you spend 7k on a new I/O and motor setup you won't gain much mph compared to a warmed 350. Price per mph goes WAY up with a new I/O and motor.

 

[fabrimacator21]

Re: Upgrading mercruiser 350 v8 260 hp

You have to drop the oil pan to do a cam on a Chevy.

Bond-o was saying the same thing.... why is this? Seems like a new gasket and rtv on the timing cover would do just fine. I've seen a few shows where they swapped cams without pulling the pan.

 

[ringmaster72]

Re: Upgrading mercruiser 350 v8 260 hp

No, you do not have to drop the pan. It would make reinstalling the timing cover much easier but in can be done without dropping it. if you plan on doing any more cam swaps, it would pay off to get a timing cover that you can take the cam out without removing the whole cover.

Tim

 

[Cptkid570]

Re: Upgrading mercruiser 350 v8 260 hp

Not to change subject, but I think you should prop it right before doing anything.

I'd try a 15x15, 3 blade prop and see how the boat performs with that.

 

[n2ostroker]

Re: Upgrading mercruiser 350 v8 260 hp

Yup hull has a big effect on how much mph you gain....

$780 for a head swap seems fair... and you said you've been through all that so I don't know why your asking for my receipts. That was YOUR estimates, not mine.

And that was being generous with head bolts and miscellanious hardware.


I'm not trying to butt heads with you here. Just trying to hammer out nickel and dime costs of those mods...

If you know anymore hidden costs PLEASE post them up. I could use the info and I'm sure others could.

However like I said, when you compare spiffing up your current motor to buying a bigger CID engine with the price of a new I/O setup it's small beans.

Your talkign 1k-1500 compared to $7,000. Tq is definetly a factor with a big boat but a warmed up 350 will do the job just fine. Even after you spend 7k on a new I/O and motor setup you won't gain much mph compared to a warmed 350. Price per mph goes WAY up with a new I/O and motor.

I don't want all your receipts. I just don't want misinformation spread. You brought up cam, heads, intake and other things thinking you're going to pick up 100hp and 10mph and it just won't happen. You're hidden cost are what ifs and stuff you don't think about till you need it. Sealants, parts that break from age and rust upon removal, cleaners, etc. Head bolts and miscellaneous stuff are necessary and not being generous. If anything I'm still on the conservative side. They need replaced. I don't think someone wants to pull a head gasket because of a couple of reused bolt stretched. I don't. This stuff adds up in a hurry. Also no one ever said a brand new 454 and Bravo drive. You could probably pick up used stuff and do the whole swap for $4500 or less. You also can't compare a small block to a big block. Two totally different beast. A 350 will NEVER make the torque, especially on the low end that a big block makes. I don't think the OP is so worried about top speed as much as all around performance either. So price per mph isn't a deciding factor overall.

Your also talking about $800 for just a head swap and nothing else. I'd bet you'd be lucky to pick up 20-25hp from that.
Then you're still stuck with an alpha drive behind a big heavy boat.

Marine exhaust isn't like a car. It is water cooled. Take a log manifold cool it then throw water in the exhaust stream and all the sudden you have zero scavenging. Then you're left with each cylinder fighting one another and killing power. Throw a cam in and things get worse. You may not get water reversion but there will be exhaust gas reversion into the cylinder meaning now your left with hot oxygen depleted gas in you combustion process. It's all bad.

As for the timing cover. It will come off fairly easy without lowering the pan but will be a PITA to get back on if you get it back on. Then most likely won't seal worth a d***. There is a lip that wraps around the front of the pan that the front seal is on then rides up against the block. They make a cover that is 2 pieced and the front unbolts so you can remove the cam cover easily without disturbing the pan seal.

If you want to check out performance stuff go over to speedwake.com or offshoreonly.com and see what some of these guys do to gain speed and power. It isn't easy in a boat. On some dyno test they may lose 20-30hp going from a dyno header to their high dollar wet headers let alone a 20-30yr log.

 

[knightowl]

Re: Upgrading mercruiser 350 v8 260 hp

that is caused by spark jumping (or lack there of). Everytime ive seen this its a problem with the plugs, wires, or cap and rotor, or ever a coil. The faster you turn the motor the more power it takes to fire the plugs. therefor the harder it is to fire the plugs. sometimes the spark jumps around and feeds back and your tach picks this up and tries to read it.

I installed my plugs last year, since i only taken the boat out like 2-3 times last year, i didn't bother changing the plugs this year (i know bad knightowl bad!)

As for top cap, it is from last year also. I do have a few year old coil on their though.

So given the info, which one should i replace? The coil is the oldest thing out of all of them. (if you do say coil, is their a nice heavy duty one i should look out for to maybe get bigger spark?) (MSD?)......

Another key info. Ive notice my engine IDL kinda shaky every maybe 10 seconds or so even after engine warm up... Example, sounds like it squirted bad gas into one of the cylinders or one of the cylinders didn't get a big enough spark to combust so the engine shakes real quick (like almost died but then comes alive). Ive though about my plugs being old, but when pulled one of them out, they look good. (i think my IDL is set somewhere between 700 and 750. )

--------------------------------

As for upgrading the engine, like mentioned in other post, ive decided to fix my tach and do a couple of speed test to figure out best prop for my boat before any upgrades. I think i will try a 3 blade 15" dia 14 pitch or depending on what you guys recommend and the prop specialist recommends after my testing are finshed.

Interesting debate between you two though. Reading it and loving what im hearing from both of you. Keep in mind engine is about 2 years old and ran only about 10-20 times on the river. Im the type of man that if i see a bad bolt, i would probably replace if i feel like my massive arms might brake the thread when tightening down ...If its some what nice and shiny i will leave it alone.

 

[n2ostroker]

Re: Upgrading mercruiser 350 v8 260 hp

I would definitely do a full tune up. I put a brand new distributor cap on mine last Oct. When I took it out this spring(~march) I had a small miss. Pulled the cap and it had corroded on the contacts with maybe 3hrs use. Moisture does bad things to ignition parts and fuel. Thats why its recommended to do a tune up at the beginning of the yr.

Find a shop that'll let you try a couple of props. You might not find a 3 blade 14p since most 3 blades are an odd pitch. Do the tune up then try a 3 blade 15-17p stainless. After that you may be satisfied for now with the performance.

 

[Cptkid570]

Re: Upgrading mercruiser 350 v8 260 hp

Knightowl,
You have done a wonderful job on your restoration and your boat looks great, but to be honest, for some of the costs to upgrade your good running solid engine to more hp (and then risk tearing up your outdrive), you may want to keep an eye out for a cheap 24' boat that needs an engine package and trailer and then throw your engine/transom assembly/outdrive into the 24' boat and stick it on your trailer.

Thats what I did when I wasn't satisfied with my underpowered 26' boat and I actually upgraded to a newer boat that I like more.. Just a thought..

If you get your boat propped perfectly, you may end up happy with what you have though..

 

[knightowl]

Re: Upgrading mercruiser 350 v8 260 hp

Yes that's what im hoping for. I will clean my rotor and cap (probably get a new cap) and then do a test run with my current prop and then exchange it for the one i need. Thanks.

 

[knightowl]

Re: Upgrading mercruiser 350 v8 260 hp

actually i just remembered something interesting. Another day i was at the lake and my boat had trouble starting. i checked my connection at the battery terminal and made sure i had a solid connection. Boat still didn't fire, just CLICKED... So kept following my connection and came to the battery SWITCH. Since i have two battery's on my boat, i got one of those switches "1" "2" "ALL" . I notice a crack running through one of the terminals on the switch. I moved the connection around on that switch and found one positive terminal loose. I tighten it as much as i could but its still loose... Its good enough to start the boat but still a loose connection.. you can move the wire back and forth.


I picked a new Perko switch today. Going to install it............. but could have caused my tach to flip out and become all jumpy around 4,000 rpm? sounds like it could, but still gonna look at the rotor cap.

 

[fabrimacator21]

Re: Upgrading mercruiser 350 v8 260 hp

I don't want all your receipts. I just don't want misinformation spread. You brought up cam, heads, intake and other things thinking you're going to pick up 100hp and 10mph and it just won't happen. You're hidden cost are what ifs and stuff you don't think about till you need it. Sealants, parts that break from age and rust upon removal, cleaners, etc. Head bolts and miscellaneous stuff are necessary and not being generous. If anything I'm still on the conservative side. They need replaced. I don't think someone wants to pull a head gasket because of a couple of reused bolt stretched. I don't. This stuff adds up in a hurry. Also no one ever said a brand new 454 and Bravo drive. You could probably pick up used stuff and do the whole swap for $4500 or less. You also can't compare a small block to a big block. Two totally different beast. A 350 will NEVER make the torque, especially on the low end that a big block makes. I don't think the OP is so worried about top speed as much as all around performance either. So price per mph isn't a deciding factor overall.

Your also talking about $800 for just a head swap and nothing else. I'd bet you'd be lucky to pick up 20-25hp from that.
Then you're still stuck with an alpha drive behind a big heavy boat.

Marine exhaust isn't like a car. It is water cooled. Take a log manifold cool it then throw water in the exhaust stream and all the sudden you have zero scavenging. Then you're left with each cylinder fighting one another and killing power. Throw a cam in and things get worse. You may not get water reversion but there will be exhaust gas reversion into the cylinder meaning now your left with hot oxygen depleted gas in you combustion process. It's all bad.

As for the timing cover. It will come off fairly easy without lowering the pan but will be a PITA to get back on if you get it back on. Then most likely won't seal worth a d***. There is a lip that wraps around the front of the pan that the front seal is on then rides up against the block. They make a cover that is 2 pieced and the front unbolts so you can remove the cam cover easily without disturbing the pan seal.

If you want to check out performance stuff go over to speedwake.com or offshoreonly.com and see what some of these guys do to gain speed and power. It isn't easy in a boat. On some dyno test they may lose 20-30hp going from a dyno header to their high dollar wet headers let alone a 20-30yr log.

Misinformation? I said 1500 for head, cam, and intake. 780 for the head swap, 150 for the cam, 120 for the intake. Thats $1,050 Carb would be another $300. Now we're at $1,350. Add in a cam installation kit(70 bucks) and it's 1,420. If I'm missing something it can't be much... within a few hundred or so is pretty decent IMO. Also you can sell the old, heads, carb, intake, and MAYBE (big maybe) the cam for a 1-200 bucks.

When I said your where being genrous with the head bolts and hardware I meant your price was a little high... not that you should re-use your old ones. Head bolts are 30 bucks... and hardware is easy to clean up if you have a bench grinder with a wire wheel. Either way thats small beans.




This combo produced a 370hp 305 using headers. Granted it was at a high rpm peak but at 5k it ought to be pretty close to 300hp with log manifolds. (was 340hp at 5k with headers) So I don't think 280-290hp with that combo and log manifolds is unreasoble... they weren't using roller rockers either (I may go roller rockers). http://www.popularhotrodding.com/en...hrs_305_chevy_engine_blocks/dyno_testing.html



Knightowl.... your on the right track, get your tac working, try a few props and go from there.


I found a good article a while back on warming up a merc 260.... made somewhere around 350hp with stock manfiolds. I'll see if I can find it again. If nothing esle it's a good reference point.

 

[mylesm260]

Re: Upgrading mercruiser 350 v8 260 hp

You're tach is driven off the coil, directly, (or the signal to the coil more specifically) so a bad cap-rotor would not effect it.


It IS possible that you're bad battery switch was to blame. Batteries are an important part of an electrical system. Not only do they store power, but they also help dampen any voltage spikes and drops (caused by all number of things, including a change in alternator RPM, or a sudden increase or decrease in amperage draw)

If the connection between you're alternator and you're battery was intermittently breaking (possibly related to engine vibration (@ RPM) or rough water. Then that would trow off the reference voltage to the tack, and could cause it to jump all over the place.