More power to heavy cruiser, is it worth it

[alldodge]

Have a 1994 Formula 27PC which weights in around 10K pounds (sig below). Currently has a single 502MPI and moves it OK with B3 drive. Having a few minor issues which I want to fix so while the engine is out I'm looking into increasing the HP and changing the outdrive. Reading a few threads on OSO about increasing the HP and still being able to run on 87 octane. Haxbyspeed (OSO see below) has a good thread on pumping up the 502. It did loose a bit of HP when changed to Holley fuel injection but that was top end. Currently my cruiser gets a bit loose at WOT but I need to replace my gimbal ring and pin this year. My thought is to pull the Merc MPI off and go with the Holley EFI setup. Change out the cam, install roller rockers then replace my standard B3 drive with a B3XR setup all new transom. From what I have been reading on HP rating, the X and XR have the same rating, don't know what else the differences are. I run 89 octane all the time because

More Power http://www.offshoreonly.com/forums/...tarts-me-thinking-more-power.html#post4171672
Haxbyspeed post 502 MPI upgrade http://www.offshoreonly.com/forums/do-yourself-boating-budget/248779-502-mpi-upgrade-results.html

 

[alldodge]

Well was hoping there was a couple ideas. Got about the same from OSO, they just said get rid of the boat and buy go fast. Got a smile out of that one

 

[haulnazz15]

Well, since no one gave a response (amazing considering how this forum used to be before the vBoard f-up) I'll give it my .02. I don't know if the X/XR drives are a necessary expense. It would be one thing if you were pushing up above 55mph+, but I don't think your cruiser will do that without forced induction and I don't think you want to see that fuel bill, either. If the cruiser runs fine as-is, why mess with it? If you were having trouble getting on plane or staying on plane with a heavy load, I wouldn't discourage trying to get a little more out of it.

I guess it just depends on what you are trying to accomplish by changing out fuel-injection systems and drives. As for myself, I'd rather leave this boat alone and get a Nordic or other performance boat if I wanted to mess with going 65+. It would just take an inordinate amount of cash to make any major performance differences on a 10K lbs. boat with a cruiser-style hull.

 

[alldodge]

Well, since no one gave a response (amazing considering how this forum used to be before the vBoard f-up) I'll give it my .02. I don't know if the X/XR drives are a necessary expense. It would be one thing if you were pushing up above 55mph+, but I don't think your cruiser will do that without forced induction and I don't think you want to see that fuel bill, either. If the cruiser runs fine as-is, why mess with it? If you were having trouble getting on plane or staying on plane with a heavy load, I wouldn't discourage trying to get a little more out of it.

I guess it just depends on what you are trying to accomplish by changing out fuel-injection systems and drives. As for myself, I'd rather leave this boat alone and get a Nordic or other performance boat if I wanted to mess with going 65+. It would just take an inordinate amount of cash to make any major performance differences on a 10K lbs. boat with a cruiser-style hull.

Thanks, appreciate the comment. Probably should add one clarification of the question "is it worth it". This comes from that I currently have 415HP and thinking about going to 500 to 525HP. So by another 100HP what can be expected of coming out of the hole and cruise. Could go from B3 to B1 but this would effect coming out of the hole. Current B3 is 2.00:1, would a different ratio help? Don't really care about top end

Merc says the B3 is good for 400HP, the X and XR appear to be the same at 525HP. Go figure if I go with the B1 XR it's good to around 650HP

 

[Scott Danforth]

If your only looking for another 100hp, I would look to add a supercharger and get you to the 525hp range. your top speed would be a bit more than what you have now. your fuel bill will be about double. There are also people that tweak the factory fuel tables on the mercruiser MPI http://www.azspeed-marine.com/peecuca.html

 

[alldodge]

Don't want to go the super charger route, don't have the clearance for it and just want a bit more power. Starting to show some wear on my current B3 setup so this is why I'm thinking of the upgrade. Need to do some more this winter anyway. The link above at OSO Haxbtspeed took a standard 502MPI, added a slight bit higher lift cam, roller rockers, and had the MPI remapped and pulled out 497HP and 501 torque running 87 octane gas. He later removed the Merc EFI system and installed the Holley EFI and lost some top end HP but not much. So I'm really thinking hard about going through my motor anyway do to some other issues which have no bearing on the more HP question. So while I'm refreshing everything, maybe pump a few more ponies out and get rid of my Merc VST system.

 

[funk6294]

I would think staying with the b3 would be best as it will hook harder to get that boat up and out of the water. As for upgrading the hp output, if you have it out then why not. Since it's a 502 you might look to the merc 525 parts list and use that to help guide your build.

 

[haulnazz15]

I wouldn't be as worried about the max HP rating on the B3 you have unless you tend to just hammer it from a dead-stop a lot, or run WOT through heavy chop causing shock-loading on the prop/gears. If you are smooth on the throttle and mainly cruise around, your B3 will hold up just fine. Same as the guys running 350-400HP a stock Alpha I when it's only rated for 300HP. It's the high load torque that kills 'em, not the high horsepower itself. Nothing wrong with adding a cam/etc to grab an extra 80-100HP. Was the 497hp/501tq flywheel or propshaft HP? What is your 415HP rated (prop or flywheel)? I probably wouldn't mess with changing out the Merc FI system if it's only for a small gain, as opposed to re-mapping it.

 

[alldodge]

I wouldn't be as worried about the max HP rating on the B3 you have unless you tend to just hammer it from a dead-stop a lot, or run WOT through heavy chop causing shock-loading on the prop/gears. If you are smooth on the throttle and mainly cruise around, your B3 will hold up just fine. Same as the guys running 350-400HP a stock Alpha I when it's only rated for 300HP. It's the high load torque that kills 'em, not the high horsepower itself. Nothing wrong with adding a cam/etc to grab an extra 80-100HP. Was the 497hp/501tq flywheel or propshaft HP? What is your 415HP rated (prop or flywheel)? I probably wouldn't mess with changing out the Merc FI system if it's only for a small gain, as opposed to re-mapping it.

Thanks, some good points. Have a buddy which has a single engine 600HP fountain and it had the standard B1 installed. He babies this thing and still after a few years it destroyed the drive. My cruiser is so heavy as compared to other cruisers of the same size. My cruiser weights as much as the older twin engine 29 searay. Another guy at the dock has a newer 270 rinker cruiser with 496HO and he weights in at 8600. Knowing my luck I would need to get back to the dock in a hurry and floor it and the drive would come apart

The 8.2MPI is at the flywheel and the one upgraded is at the flywheel. The links in my first post show the dyno results

 

[achris]

Just remember that any increase in top end HP may also result in a decrease of low end torque. And it's that torque you're looking for. That's what gets up out of the hole and staying on plane at lower speeds.

 

[alldodge]

Just remember that any increase in top end HP may also result in a decrease of low end torque. And it's that torque you're looking for. That's what gets up out of the hole and staying on plane at lower speeds.

Good point, but wouldn't you say if I add 75HP I should be able to increase the low end torque some?

 

[achris]

It's a bit of a trade off. Usually (and this is only a 'rule of thumb') an increase at the top end requires an improvement in the engine 'breathing'. That's achieved by increasing things like valve overlap and duration. Low end torque in improved by the exact opposite, decreased overlap and duration (within reason).... The only real way to increase both is with forced induction.

I would start by talking to engine builders... Talk to them as if you're looking to buy a new long block, and see how they would handle the issue.

 

[Scott Danforth]

you have room for this supercharger http://www.cpperformance.com/p-12416-procharger-marine-m-1-intercooled-kit.aspx

 

[alldodge]

you have room for this supercharger http://www.cpperformance.com/p-12416-procharger-marine-m-1-intercooled-kit.aspx

Not really, I currently have to lay across the intake upside down just to change the impeller. Good thing I have the MPI intake or this would be a bit harder, If I go with the Holley EFI setup the intake would be lower but then there is the throttle body which resembles a carb.

Original MPI intake which was shortened by an inch and went through porting and polishing. ECU was remap


Removed the MPI unit and installed an untouched Vic Jr. and a Holley 900cfm TBI unit (note rpm went to 5500)

 

[Walt T]

I would build the crap out of it if I had it out. I have never built a 502, not sure that's the best choice motor. I'd be looking at blown and stroked 454 (496) for a boat that size. B3 is not the best choice for top speed but is definitely a good solid drive. B1XR would be a top speed choice simply because the B3 props are more drag. But quite frankly the difference isn't all that big, so if you like the bite of the B3 which obviously your boat needs, by all means stay with it. The XR will stay together and give more top speed, and you can rev higher with it. It's simply built stouter. If you don't want forced induction, then stroke out a 454 to 496, keep compression below 10, use vortec with mirror pistons and 100 hp and at least 100 ft lbs at low rpm is possible. You should definitely feel that. 87 octane should be fine but you should keep 104 in the boat as you just never know what you're getting at marina pumps.

 

[alldodge]

I would build the crap out of it if I had it out. I have never built a 502, not sure that's the best choice motor. I'd be looking at blown and stroked 454 (496) for a boat that size. B3 is not the best choice for top speed but is definitely a good solid drive. B1XR would be a top speed choice simply because the B3 props are more drag. But quite frankly the difference isn't all that big, so if you like the bite of the B3 which obviously your boat needs, by all means stay with it. The XR will stay together and give more top speed, and you can rev higher with it. It's simply built stouter. If you don't want forced induction, then stroke out a 454 to 496, keep compression below 10, use vortec with mirror pistons and 100 hp and at least 100 ft lbs at low rpm is possible. You should definitely feel that. 87 octane should be fine but you should keep 104 in the boat as you just never know what you're getting at marina pumps.

Thanks Walt appreciate the input. Everything I read the 502 will out perform the 454 but even if your right, buying another motor is adding more expense. Leaning toward a slightly modified cam, bore it to ,010 over, remove the Merc VST MPI, add the holley 900 cfm with new intake and the B3XR drive including the new transom. Also use a MSD ignition setup. Figure by the time it's all done if I can get 75 to 100HP more it would work out pretty well.

So far as 104 octane gas, I've never seen it other then race tracks and aviation fields. Paying 439 a gallon for 89 octane now, but do understand your point

 

[Bondo]

I would build the crap out of it if I had it out. I have never built a 502, not sure that's the best choice motor. I'd be looking at blown and stroked 454 (496) for a boat that size. B3 is not the best choice for top speed but is definitely a good solid drive. B1XR would be a top speed choice simply because the B3 props are more drag. But quite frankly the difference isn't all that big, so if you like the bite of the B3 which obviously your boat needs, by all means stay with it. The XR will stay together and give more top speed, and you can rev higher with it. It's simply built stouter. If you don't want forced induction, then stroke out a 454 to 496, keep compression below 10, use vortec with mirror pistons and 100 hp and at least 100 ft lbs at low rpm is possible. You should definitely feel that. 87 octane should be fine but you should keep 104 in the boat as you just never know what you're getting at marina pumps.

Ayuh,.... SBC, or BBC, that's a solid combo for a boat motor,.....

I ain't done much Big blockin',.... Small blocks, that, 'n a long stroke is Wicked,...

So far as 104 octane gas, I've never seen it other then race tracks and aviation fields. Paying 439 a gallon for 89 octane now, but do understand your point

Where's home,..?? 'round here, that's 'bout what 91 ethanol free is goin' for,.....
I run it in my barge, 'n All my small motors,....

 

[alldodge]

Where's home,..?? 'round here, that's 'bout what 91 ethanol free is goin' for,.....
I run it in my barge, 'n All my small motors,....

I'll send a PM to ya to give the exact, but not on the forum. I will say I'm far south and to the center of KY. In town 87 with ethanol is running 3.38. I run nothing but 87 when I can find it because that's all that Merc and everything else I own calls for, that is other then my diesel truck and equipment. I run the 89 in the boat only because it's ethanol free and it's the lowest grade I can get on the lake. Not having any detonation issues, just way to rich right now. So the rich running issue, worn gimbal got the ball rolling about refreshing everything, and that got me thinking about a total different power options.

 

[Walt T]

900 cfm carburetor is useless. Unless you're planning on 6000+ rpm stick with a good 700-725 cfm. Why complicate things?

 

[alldodge]

900 cfm carburetor is useless. Unless you're planning on 6000+ rpm stick with a good 700-725 cfm. Why complicate things?

The Holley EFI system appears the lowest is 950cfm these days. Could also use the FAST system but have not checked into the system as much