Re-powering Cierra 2855

[TonyBal]

I am re-powering a 1998 Bayliner Cierra 2855 that had a 7.4 MPI w/B3 drive. I am keeping the drive and transom assembly and totally replacing the engine. Two separate estimates to rebuild the old engine are leading me to either new or remanufactured. I am considering a new 6.2 MPI or a remanufactured 383 MPI. Fresh water cooling is a must. Has anyone delt with anyone online that they could recommend.

 

[Bondo]

Re: Re-powering Cierra 2855

Ayuh,... Welcome Aboard,....

You're going to be Disappointed going from a BBC to a SBC,....

There Won't be a fuel savings,+ the lack of Torque, Will be noticable....

I haven't used them, but many members here Have,+ They mention Rapido out of Fla. alot,..
Talk to Raul...

 

[HT32BSX115]

Re: Re-powering Cierra 2855

That is a BIG boat. You may not be happy with a 383.

Also, your drive ratio may not be correct for the 383 (which likes to turn a little faster than a 454 usually.

I could be wrong but I think the 383 wants to turn about 5000 and the 454 is 4800 or less. (My carbed 454 is 4600)

You drive ratio might be wrong with your current props. (24P maybe?) Your drive ratio is probably 2.0:1 or even 2.20 .....Your current props will probably have to be pitched down with the (320hp) 383. Isn't that 7.4MPI rated at 350hp?


I have to fall in line with everyone else..... I think I'd rebuild/replace the current engine. (btw, I'd LOVE to have a "core" 7.4MPI to rebuild/replace my carbed engine......Are you in the NW?.....maybe you should switch to a 383)

 

[QC]

Re: Re-powering Cierra 2855

I don't agree on the BBC vs. SBC discussion in this case. The 7.4 MPI is 310 bhp (propshaft), Bravo 3's do not have hole shot issues, and the 6.2 and 383 both have more ponies at 320 and 325 respectively (propshaft). I am very supportive of this plan. I bet she will plane as well or better and she'll be slightly faster.

Will need pitch change though as the 6.2s are rated between 4800 - 5200 RPM . . .

 

[QC]

Re: Re-powering Cierra 2855

This test example is very eye opening as this is a 350 MPI mag 300 vs. the 310 7.4 MPI . . .

http://www.stingrayboats.com/products/reviews/tb2_99.html

Yes, the BB went 0-30 faster than the small block . . . 6.2 vs. 6.7 seconds with a Bravo 1. Every single other spec favors the SB; cost, fuel, lower RPM plane and top speed.

 

[mkast]

Re: Re-powering Cierra 2855

This test example is very eye opening as this is a 350 MPI mag 300 vs. the 310 7.4 MPI . . .

http://www.stingrayboats.com/products/reviews/tb2_99.html

I would have no problem in the 23 footer, 2200+ LBS.
1998 Bayliner Cierra 2855, a tad heavier.
A stroked small block in a barge???

 

[QC]

Re: Re-powering Cierra 2855

Why would the size of the boat negate a horsepower and weight advantage?

 

[HT32BSX115]

Re: Re-powering Cierra 2855

1998 Bayliner Cierra 2855, a tad heavier.

A 2855 is not just a "TAD" heavier it's more than 3 TIMES heavier at around 7000lbs.

I'm not saying a 6.2 would not work or that it wouldn't plane the boat, I am saying it wouldn't be better. It would certainly be more money than just rebuilding the 7.4MPI and a prop change would absolutely be required to get the 5200 RPM at WOT.....possibly to 22 or even 20p props.

That TB article also mentioned that a BB is probably a better choice for a "cruiser"

If we want to pop a heavily loaded cruiser on top with a minimum of fuss and strain, the big-block is the answer. In such applications, there truly is no substitute for cubic inches............

I would also bet that the 6.2 would have the same fuel burn as the 7.4MPI at the same cruise speeds....
( I didn't try to find it but I'll bet the BSFC for both engines are very close)

So what would the advantage be that would justify the additional cost?
(the weight difference is a little over 150lbs..... a small percentage of the total weight of a cruiser)

 

[QC]

Re: Re-powering Cierra 2855

Because first off, Horse power has nothing to do with it, its all about the low RPM Torgue and thats where cubic inchs has the advantage.

Horsepower has EVERYTHING to do with all speeds. Why do you think you like high peak torque? It's because it delivers more horsepower at lower speeds. I promise you I understand this as engine applications has been my entire 30 year career. Particularly high peak torque, and high torque rise engines . . .

With a Bravo 3 and less weight I believe the low end performance will be very close . . . Yes the 7.4 MPI has slightly more torque than the 5.7 in the test, that's why there is a piddly point five second difference in 0 - 30, but the 6.2 will have more low end than the 350 Mag AND the Bravo 3s are exceptionally good at hole shot. I am standing by my assersion and believe it strongly.

Listen, I am not that nuts to think that there is no place for big blocks, I think in this example the performance will be slightly, if at all, affected at the low end. It should have improved top speed, and better efficiency at cruise. Yes, BSFC at full load would be similar, but with the same required cruise hp for say 26 MPH and lets say 217 bhp (hypothetical numbers pulled outta me arse), the lower displacement engine will usually get better fuel efficiency if the engines are at a similar level of technology (they are). I have posted data. I am not trying to fight here, but many of our closely held beliefs prove to be wrong when the numbers are actually crunched. The case for big blocks makes absolute total sense to me at 400 bhp, but not at 300. Annnnnd, all of you guys over emphasise peak torque value in marine applications. With the exception of tug boats and ski boats and people that like snappy hole shot, higher low end torque is not that big o' deal. If any boat planes OK as is, then higher peak torque will not make that big of a difference to you. If a boat struggles to plane, then absolutely higher peak torque will make things better. Because? It results in more low end horsepower to get the job of planing done . . . BTW these assertions are not opinion, they are math.

The only issue on which I will concede is prop pitch for this application to reach the 5200 top end of the WOT range. I'll even go so far as to say if you prop to 5200 she'll have better hole shot than the big block in there now.

Cost? Well the OP said that rebuild quotes are why he decided on repower. If that is false, then this is a stupid discussion.

 

[HT32BSX115]

Re: Re-powering Cierra 2855

Cost.

Of course some of us are thinking DIY installation.

The local machine shop that did my Ford Y-block told me he'd "Longblock" my OMC 460 for about $2000......my 454, for about the same. (not including manifolds/riser-elbows)

I did a little searching around for 6.2L MPI 320hp complete engines and I found new ones for about $9k (retail about $12K)


I do not think a 150lb reduction is going to make the same difference in a 7000lb cruiser as it made in a 2200lb ski boat.(In fact, I think it'll make NO DIFFERENCE) But hey, Try it! (and if you're in the NW I'd like a shot at your "core" 7.4L MPI engine for my old Four Winns Liberator!!)

 

[chiefalen]

Re: Re-powering Cierra 2855

Never saw it discussed in a more informative, professional, manner.

What this guy needs is 2 motors pushing a 28 foot hull.

Hah double the trouble.

 

[QC]

Re: Re-powering Cierra 2855

Try this. Your sitting in the water at idle, you dump the throttle and the engine jumps to say 2000 RPM. Now what is the torque of the SMB at that RPM compared to the BB . . . In a small (light weight) boat it makes little difference because its going to pick up speed quickly and RPMs will build. That is not true when you triple the load (weight) of a crusier.

I have not asserted anything different. What I have posted is that the minor difference will not be significant with a Bravo 3 and less weight.

In a small (light weight) boat it makes little difference because its going to pick up speed quickly and RPMs will build. That is not true when you triple the load (weight) of a crusier.

You guys seem to think that the 23 footer with the data makes the math irrelevant, it doesn't. That's with the same gear ratio and propeller, so it is even easier to say that propped correctly they will be even closer in low end performance annnnnd if you add in the increased displacement of the 6.2 vs. the 5.7 they get even closer . . .

The bottom line here is that no matter what you do to it, the smaller CI engine will never have the low end Torgue of a big block. (If they could, no one would build a big block. )

That is kinda false. The easiest is blowers, so a better way to say it might be: equally optimised, the higher displacement engine will put out more power, both torque and horsepower. However, the whole point is that an optimised 6.2 can be stronger than a conservatively rated 7.4 . . . I would not even have this discussion if it was the 454 Mag MPI at 385.

Now lets look at other expence of going to a differnt block. If he rebuilds his existing block, everything simply bolts back together. Change the block and that will not be true. (Always "something* that isn't the same.

I have not suggested that this is an econmically sound plan, that's his problem

Also consider wear and tear. If the big block is running say 2800 RPM at cruise speed, you can be certain the small block will have to spin faster to hit the same speeds. (Will probably require a shallower prop or a different gear ratio in the drive.)

Nobody wears out pleasure craft engines, they break them . . .

Finally, assume he wants a bit more power. The big block has LOTS of potential for more power, the small block has pretty much been pushed to the limit (if durability is important) in a boating application.

Totally agree . . .

 

[HT32BSX115]

Re: Re-powering Cierra 2855

Just found this example on ebay..and 2 more.. (MerCruiser 357/325HP MAG Bravo with a "Buy it Now" of about $4500+ shipping)

If the HP number can be believed, it could be a good alternative I suppose.

I considered a similar thing for my 454.

Using a tricked out 383 with aluminum heads, manifolds, risers, the weight advantage over a cast iron 454 is significant even for my 4000 lb Lib211 .

That might be a pretty good difference.

I would still not expect much difference between that engine and the 7.4L MPI he has now in his 7000+ lb cruiser.

I still think he's "money ahead" by having a local machine shop "long-block" his current engine....

Nobody wears out pleasure craft engines, they break them . . .

Absolutely true.... I ran my dads old 66 Marktwain (150 Mercruiser) up to the 39 year point and it still didn't wear out (or break) I think the guy that bought it is still running it!


Regards,


Rick

 

[a70eliminator]

Re: Re-powering Cierra 2855

When in doubt, go with the bigger hammer! and get the job done.

 

[HT32BSX115]

Re: Re-powering Cierra 2855

Yanmar now has their own dual prop drive behind their diesels too!! (they look a lot like a Bravo under that plastic))...... but the problem would be you'd have to take out a second on your house to pay for a package like that!!!!

 

[chiefalen]

Re: Re-powering Cierra 2855

Heres a nice diesel option.

http://www.transdiesel.com/Engines/MARINE/Pleasure/Lombardini-13hp-150hp.asp

 

[chiefalen]

Re: Re-powering Cierra 2855

I think they make bigger?? Can"t remember who just came out with a light diesel 150.

 

[thatguy]

Re: Re-powering Cierra 2855

I would love to put a little turbo diesel in the pursuit.

There is a guy that re powered a bayliner 24 hardtop in my area, he said that its ran about the same as the gas for cruise and top speed, but was only burning about 3gph @ 22mph. that would be awesome!

Its just alot of money to swap over, not easy on the budget.

Tom

 

[krisnowicki]

Re: Re-powering Cierra 2855

http://www.transdiesel.com/Engines/MARINE/Pleasure/Lombardini-13hp-150hp.asp#JMT Series 1

 

[HT32BSX115]

Re: Re-powering Cierra 2855

Well,

back to reality.....He could put a Cummins Mercruiser diesel engine in it......

Big bucks. There's also the 6.5L Peninsular Diesel rated at 340hp. But all these require a much higher ratio diesel Bravo drive. The regular Bravo's will not survive long behind a diesel.

Bring LOTS of money to this party!