new boat, some questions on 5.7 mercruiser

[idleRelaxation]

5.7 mercruiser/alpha 1 in it. it currently has a 23 pitch prop, first time out at WOT it was hitting maybe 40mph at 3200 rpms but wouldnt go above, distributor was loose as timing is off and i would have to adjust in order to idle/throttle up smoothly so it does need the timing adjusted with an actual light gun.

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

Welcome aboard idleRelaxation!! I moved this to non-repair as it doesn't really sound we have an issue as much as general discussion. No biggee, but maybe we can suggest additional thread locations for you when we narrow down a few things. Doing a little research and then I'll be back . . .

In the meantime, can you help with some more info. Speed? Sounds like a guess, anything to back it up? GPS would be best. Also tell us more about your prop. Blades? Model? Material?

 

[Don S]

Re: new boat, some questions on 5.7 mercruiser

What igntion system do you have? You really need to set the timing to spec and confirm the advance timing is working. I would even go so far as to say a compression check is needed. If you have to keep moving the timing for different speeds, it's hard to say what's wrong without some checking.

Also need to verify you tach is accurate.

 

[81 Checkmate]

Re: new boat, some questions on 5.7 mercruiser

Be sure that the spark arrester (AKA - Air cleaner) is marine spark aproved.

Not sure from the pic, but thought i would mention it.

Good luck with your new boat!

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

I find two 5.7s available from Merc in 92 - 93; very possible it has a '92 in a '93 boat. Happens a lot. Anyway, the 5.7L was rated 235 at the propshaft and the 350 Magnum was rated 250. Both 1.5 ratio drive.

I agree with Don, tach may be off, but really depends on your speed too. I am always suspect of data showing low WOT RPM, and not hearing a planing complaint. With a 23 and low WOT RPM I would expect this to be a dog out of the hole. More info needed for sure.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

I find two 5.7s available from Merc in 92 - 93; very possible it has a '92 in a '93 boat. Happens a lot. Anyway, the 5.7L was rated 235 at the propshaft and the 350 Magnum was rated 250. Both 1.5 ratio drive.

I agree with Don, tach may be off, but really depends on your speed too. I am always suspect of data showing low WOT RPM, and not hearing a planing complaint. With a 23 and low WOT RPM I would expect this to be a dog out of the hole. More info needed for sure.

yes, definitely a dog out of the whole, maybe 5-10 sec of simply seeing the bow and not planing

propeller has 3 blades, will get more details later today

tachometer is working correctly, speed estimate based on friend on another boat

anyway to tell between the 350magnum vs other?

i believe intake manifold/carb are aftermarket as you can see in pic (possible even cam)

id think compression too, but no symptoms besides low rpm, which i can more easily attribute to either prop/carb tuning/timing mix

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

Be sure that the spark arrester (AKA - Air cleaner) is marine spark aproved.

Not sure from the pic, but thought i would mention it.

Good luck with your new boat!

how would i check this for sure? just from looking at it myself it does not seem like it is, will check when i get home and take pics while getting model number (believe its a 1409) of edelbrock carb

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

tachometer is working correctly

How do you know this? Not being argumentative, but has to be dead on for us to use it. Your hole shot comments makes me think maybe the tach is right. The numbers actually add up as "possible", but I always want perfection in the numbers. How was your buddy's boat's speed tracked?

Externally the Mag had Stainless exhaust elbows. No way for us to know if those have been replaced. Yes, the carb and manifold are aftermarket.

All of the stuff on your list can contribute to low WOT RPM. Need solid data to start, and then look here for more ideas and help: http://forums.iboats.com/showthread.php?t=295070

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

How do you know this? Not being argumentative, but has to be dead on for us to use it. Your hole shot comments makes me think maybe the tach is right. The numbers actually add up as "possible", but I always want perfection in the numbers. How was your buddy's boat's speed tracked?

Externally the Mag had Stainless exhaust elbows. No way for us to know if those have been replaced. Yes, the carb and manifold are aftermarket.

All of the stuff on your list can contribute to low WOT RPM. Need solid data to start, and then look here for more ideas and help: http://forums.iboats.com/showthread.php?t=295070

will post again this weekend with more info, just wanted to post and see if my initial notions were leaning towards correct.

 

[KyHeadhunter1]

Re: new boat, some questions on 5.7 mercruiser

What size is your boat? It looks like the Sprint was available in many different lengths.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

it is a 18' sprint

 

[Scott Danforth]

Re: new boat, some questions on 5.7 mercruiser

that air cleaner is not a marine unit.

borrow an optical tach and verify the tach on the boat is accurate.

make sure the ignition system is up to speed and timed properly as Don mentioned.

 

[KyHeadhunter1]

Re: new boat, some questions on 5.7 mercruiser

it is a 17' sprint

Ok, According to Iboats' specs page, your boat is "This inboard/outboard runabout is 18.25 feet long and weighs 1860 (pounds dry). This weight does not account for passengers, fuel, or gear. The beam of this craft is 84 inches. "
and came with either a 3.0 or 3.0LX.

My first thought is, this boat is going to be DANGEROUSLY fast if you get it straightened out and if its your first boat, PLEASE be careful!!

Second, you may have other issues besides your timing. Your boat is very light for its size, a full 1000 pounds lighter than my Baja of the same length. I can't imagine a 350 struggling to get your boat out of the hole with a 23 pitch prop no matter what drive is on the back. Your boat has been modified probably more than you realize and in order for these guys to help you, you will need to identify your drive's gear ratio also. My 1995 Alpha 1 has the gear ratio printed on the sticker that wraps around the upper drive. On the passengers side of the boat, look at the multi colored sticker on the upper drive and see if yours is printed there on the lower left corner, under the M in Mercruiser. If not, you will have to ID it by its serial number.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

Ok, According to Iboats' specs page, your boat is "This inboard/outboard runabout is 18.25 feet long and weighs 1860 (pounds dry). This weight does not account for passengers, fuel, or gear. The beam of this craft is 84 inches. "
and came with either a 3.0 or 3.0LX.

My first thought is, this boat is going to be DANGEROUSLY fast if you get it straightened out and if its your first boat, PLEASE be careful!!

Second, you may have other issues besides your timing. Your boat is very light for its size, a full 1000 pounds lighter than my Baja of the same length. I can't imagine a 350 struggling to get your boat out of the hole with a 23 pitch prop no matter what drive is on the back. Your boat has been modified probably more than you realize and in order for these guys to help you, you will need to identify your drive's gear ratio also. My 1995 Alpha 1 has the gear ratio printed on the sticker that wraps around the upper drive. On the passengers side of the boat, look at the multi colored sticker on the upper drive and see if yours is printed there on the lower left corner, under the M in Mercruiser. If not, you will have to ID it by its serial number.

my thoughts exactly when i saw the boat listed, but for the price i couldnt pass it up, even as a first boat, though i do have experience with fast cars (completely unrelated i can imagine but experience nonetheless)

i figured the drive ratio might also be a problem but was hoping one of my three mentioned possible problems would come together to explain the problem as a whole. I will be trying to make time from work to get more into the boat and provide you guys with more info ASAP. will also post some pics in a bit so you guys have an idea

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

only took the boat out once besides sea trial, will be trying to solve problems before next trip out

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

idle vid

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

Ok, According to Iboats' specs page, your boat is "This inboard/outboard runabout is 18.25 feet long and weighs 1860 (pounds dry). This weight does not account for passengers, fuel, or gear. The beam of this craft is 84 inches. "
and came with either a 3.0 or 3.0LX.

My first thought is, this boat is going to be DANGEROUSLY fast if you get it straightened out and if its your first boat, PLEASE be careful!!

Second, you may have other issues besides your timing. Your boat is very light for its size, a full 1000 pounds lighter than my Baja of the same length. I can't imagine a 350 struggling to get your boat out of the hole with a 23 pitch prop no matter what drive is on the back. Your boat has been modified probably more than you realize and in order for these guys to help you, you will need to identify your drive's gear ratio also. My 1995 Alpha 1 has the gear ratio printed on the sticker that wraps around the upper drive. On the passengers side of the boat, look at the multi colored sticker on the upper drive and see if yours is printed there on the lower left corner, under the M in Mercruiser. If not, you will have to ID it by its serial number.

i will get back to you with my findings this afternoon

 

[TilliamWe]

Re: new boat, some questions on 5.7 mercruiser

I/you can see the "custom motor mount" that had to be added to the stringer on the starboard side of the engine. Not sure I would trust a piece of angled aluminum with nothing under it for support. But that's what they had to do, since the boat was never intended to have anything but and inline 4 cyl engine installed.

Something is very wrong, because even if the engine was stock (which it isn't) it should get out of the hole quickly and run at possibly dangerous top speed. The outdrive ratio would have been 1.81 from the factory, but it would need A LOT more than a 23 pitch prop to compensate for that. It had to be changed at some point. But even a 1.47 ratio, with a 23 pitch prop, behind a 5.7, in an 18' boat should turn 5000 rpms, easy.
As mentioned above, this boat has been modified. Make sure the carb and ingnition system are all marine rated, or you are looking at some serious danger/liability isses. And then when you get it running properly, be ready for some possibly dangerous handling characteristics. Good luck.

 

[idleRelaxation]

Re: new boat, some questions on 5.7 mercruiser

I/you can see the "custom motor mount" that had to be added to the stringer on the starboard side of the engine. Not sure I would trust a piece of angled aluminum with nothing under it for support. But that's what they had to do, since the boat was never intended to have anything but and inline 4 cyl engine installed.

Something is very wrong, because even if the engine was stock (which it isn't) it should get out of the hole quickly and run at possibly dangerous top speed. The outdrive ratio would have been 1.81 from the factory, but it would need A LOT more than a 23 pitch prop to compensate for that. It had to be changed at some point. But even a 1.47 ratio, with a 23 pitch prop, behind a 5.7, in an 18' boat should turn 5000 rpms, easy.
As mentioned above, this boat has been modified. Make sure the carb and ingnition system are all marine rated, or you are looking at some serious danger/liability isses. And then when you get it running properly, be ready for some possibly dangerous handling characteristics. Good luck.

recommended WOT rpm is 4600 for this motor or am i wrong? either way ill probably keep it well below that unless its a relatively calm day in the bay.

i believe drive ratio is 1.5 though i will double check this afternoon

there is more support for motor, just cant see in picture, will try and snap one later aswell

 

[QC]

Re: new boat, some questions on 5.7 mercruiser

recommended WOT rpm is 4600 for this motor or am i wrong?

Actually we don't know, but I would guess the range is either 4200 - 4600 or 4400 - 4800. Hard to tell as we don't know how it was built . . .