5.7 IO merc

[Stormy1]

I've got a 92 19'celebrity with the 5.7 merc in it with only 252 hours. I've been through all the prop changes but am still disappointed. Is there anything that can be done to the motor to enhance performance such as different exhaust, etc.? It does run good but.... Thanks

 

[rabidfish]

Re: 5.7 IO merc

You got a 19ft boat with a 5.7 & you're dissapointed??? If that engine is running properly then you are one hard dude to please! Consider an SST120 tunnel boat!

 

[Stormy1]

Re: 5.7 IO merc

I might be one fussy dude who at 52 still wants to water ski. I am desperate for a better hole shot. Like I said, I've done the prop thing and its better but... I'm new to this forum Rabidfish,<br />thanks, I think I'll change my display name to Fussy!

 

[L Christopher]

Re: 5.7 IO merc

Stormy1<br />What prop are you running now, what MPH & max RPM range? Have you tried 4 blade prop, have you tried 5 blade prop?

 

[Doug Durako]

Re: 5.7 IO merc

If you've got the right prop on that rig, it should be hard for you to hold on to at full throttle out of the hole!<br /><br />I am 6-3 and about 210 and mine pops me up on a slalom ski with no problems.

 

[Stormy1]

Re: 5.7 IO merc

Thanks for the reply, the best prop I've tried is a four blade 20 pitch. It would get me out of the hole 'OK' and top out at 44 mph and 4200 rpm. When I got the boat it had a 21 pitch Alum three blade and it was really slow out of the hole but toped out at 50 mph and 4400 rpm. To get back to my orginal question, is there anything that can be done to the motor? What about the external exhaust or whatever it is called. I've heard that the exhaust is very restrictive on a I/O so to me it would only make sense to me do something there. Maybe a different cam? I'm sure that efi would be very expensive. The Chevy 350 is the most built motor there is and I can't seem to find anything on the web or elsewhere for the boat people!

 

[Bondo]

Re: 5.7 IO merc

Well Stormy1,<br /> There's A Whole Lot that can be done to the SBC to build Real Power.....<br /> It's the Most Hot Rodded Motor Ever.....<br />I'd suggest you go to amazon.com,+ Buy yourself a copy of "Small-Block Chevy Marine Performance" by Dennis Moore.....<br />If you've got Questions, Dennis Has the Answers....<br />I'm putting 1 together now, that'll be pulling just a shade under 400hp.... And, will Idle(trolling) All Day Long....

 

[rabidfish]

Re: 5.7 IO merc

If you want a better holeshot, then try the mercruiser Alpha 4 prop. It is aluminum 4 blade that runs close to stainless performance. Based on the info you have given, try the 18 pitch version. You would be better served to get your WOT RPM's up close to 4600. That is max but in the range. I'd be happy to sell you one. if you're interested email me directly. It runs $195.00 plus shipping.

 

[Doug Durako]

Re: 5.7 IO merc

Guess I should have asked you to define performance. You said "desperate for hole shot" then you also talked about top speed.<br /><br />For speed, find a quality 3-blade stainless prop that can give you your maximum wide open throttle (4800 rpm?). No, you can't run all day at that rpm but that is the top of the recommended range. Get a hand-held gps to log your true top speed. My guess is with the right prop, your boat will run about 54-56 on a calm day, trimmed out, with only you in it.<br /><br />Then, you have your baseline and know where you stand converting your current horsepower to the water. How else will you know what your motor enhancements will do for you?<br /><br />Otherwise, you might spend $2000 on the motor and end up with about 2 additional miles per hour.

 

[Doug Durako]

Re: 5.7 IO merc

Hey, Bondo----you're not going to stick and Alpha drive on that monster, are you? I would think 400 hp would destroy an Alpha.

 

[Bondo]

Re: 5.7 IO merc

Weeelllll.........<br />I've Got an Alpha1 laying around........<br />Besides, I'm only going to use the 1st 300hp.....<br /><br />With a Torque- Shift Prop, of course....

 

[Stormy1]

Re: 5.7 IO merc

ddboater, I'll think about that offer. Why doesn't anybody mention the above water (external) or whatever its called, exhaust? It sounds good (my wife would hate it) but does it add any horsepower?

 

[John Carpenter]

Re: 5.7 IO merc

The thru hull exhaust is a waste of time and money except for the cool factor. I have had a couple with the Captain's Call exhaust, where you flip a switch to change back and forth from thru hull to thru prop. I could tell very little difference in performance....does sound good though

 

[Ralph 123]

Re: 5.7 IO merc

If hole shot is what you're after the right prop, good trim tabs and hydrofoils are what you're after.<br /><br />I found changing my props to cupped SS props and adding hydrofoils made an enormous difference in my hole-shot.<br /><br />If you get the book Bondo talked about you'll get all the info on all the possible mods including thru-hull exhaust.

 

[denniz]

Re: 5.7 IO merc

Relentless nailed it . there is No difference unless you have a previous prob. But it sounds good!!!Thru hull exhaust makes no difference. Any one who thinks it does is a IDI#T.WILL NOT MAKE 1 MPH DIFFERENCE.But it sounds great

 

[magster65]

Re: 5.7 IO merc

I disagree, the stock Y pipes on some of these packages are way too small. There is performance gains by 'opening up' the exhaust... usually it requires a carb. jetting adjustment to optimize the change.

 

[Ralph 123]

Re: 5.7 IO merc

Moore seems to agree with Relentless & Rod if the engine is stock. From Moore's Book "SBC Marine Performance"<br /><br />"The biggest roadblock to making performance with a marine engine is the exhaust. Because a correctly designed ehaust system can create such a dramatic increase in horspeower on a V8 engine, extreme amounts of research, testing and development has been done in this area"<br /><br />[The performance difference in exhaust systems comes from using headers rather than manifolds.]<br /><br />"Through-the-prop exhaust systems... manufacturers have claimed for years that through-the-prop exhaust systems actually improve horsepower [due to the vacuum created by the prop sucking the exhaust out]. I don't doubt that claim, but I believe it has to be said that it will only oncrease horspepower on small four and six cylinder engines that do not have large volumes of exhaust gas."<br /><br />Most high performance marine engines will need a straight shot out of the boat for the exhaust. This is called through-the-transom exhaust"

 

[Bondo]

Re: 5.7 IO merc

Thru-hull Exhaust ,By itself, Isn't a performance gain.... But, It'll pave the way for other Improvements to work Much Better......<br /><br />For What you're looking for, the Land&Sea Torque-Shift Prop would No doubt give it to you...... It takes a bit of Tuning to get it Right, But When you Do, It'll allow your boat/motor to just about Rip your arms from your shoulders......With No Loss, at WOT....<br />It Improved my boat at both low-end,+ WOT....

 

[EPK]

Re: 5.7 IO merc

Stormy1, I've been in (and still have) the same situation as you, i.e., how to best improve performance other than upgrading. <br />On a VP-5.7-Single, originally had a SS 14.5x19 3-blade. Hole-shot sluggish but WOT good (for a cruiser). Topping-out at 37mph @4200-rpms. Economy around 1.5, distance of 100-nm on 60-gal. Downsized to a 15x17 Alum 3-blade. Now, WOT only 34mph but in operating range, around 4500-rpms, but, hole-shot amazingly better. Also, going around 130-nm on same amount of fuel.<br /><br />Its the same ol, story. Lower pitch gives better hole-shot but lower WOT. Higher pitch is vice-versa. This has been my experience.

 

[Ralph 123]

Re: 5.7 IO merc

Bondo, got a link where I can learn more about those props?