More HP Top end for 96 5.7 mercruiser

[jared_blown5.0]

Who here has modified there top end and what power did you see with what combo? I have a 96 baja 20 outlaw with this engine and want to get in the 70's mph range with it.

 

[180shabah]

Re: More HP Top end for 96 5.7 mercruiser

Can you be more specific about what your are currently running?
EFI? Carbed? 2bbl or 4bbl? with or with out vortec heads?

 

[mtnrat]

Re: More HP Top end for 96 5.7 mercruiser

Also what is your current WOT gps speed and correct RPM? As well what engine, drive and hp combo are you currently running?

 

[Limited-Time]

Re: More HP Top end for 96 5.7 mercruiser

You'll need a lot of modifications (read $$$$$$) to get a single 5.7 to push a 20' fiberglass planing hull into the 70's....................even the low 70's. I'd start with a 383 Stroker..........and remember your looking for a 5000 RPM engine max.Something like this for starters.

 

[Bondo]

Re: More HP Top end for 96 5.7 mercruiser

I have a 96 baja 20 outlaw with this engine and want to get in the 70's mph range with it.

Ayuh,....

Basically,... That just Ain't gonna happen......

 

[Mkos1980]

Re: More HP Top end for 96 5.7 mercruiser

See sig. Thats before tuning and props. I hope to be about 66-67 when I get done tuning. With your hull you may hit 70.

The day I bought the boat it did 47.7 with an aluminum 19P prop and 5K rpms. It was a stock 260HP 5.7 I added a Laser II 21P and the rpm's dropped to 4400 and got me 52.1 I was surprised how many rpm's fell with a performance prop. Added the Mag bowtie intake, timed it at 34 total 12* initial and aluminum hi-po manifolds and was able to pull 55.1. I then updated the motor to a hyd roller setup (which you already have) and tossed in a Crane Compu cam 214/220 450/465 112 cam and got 57.3. Added Corsa's quick and quiet and moved up a hair to 58.1-58.3 At this point I bought a set of "rebuilt" vortec 906 heads, added beehive springs, comp retainers and machined locks, LT4 hotcam 218/228 525/525 112 , GM's bowtie 1.6 Aluminum rockers, Edelbrock Airgap RPM intake and pulled 62.3. Believe it or not, the boat idles so smooth and runs perfect. This was all with an off the shelf 1409 Edelbrock carb, conservative timing 30* total and the same Laser II prop. Upon my last test which was tongiht I moved the timing to 32* and tossed in a 4% richer metering rod set. RPM's rose 150 to 5300 RPM's but I couldnt verify a speed as I forgot the GPS at home. Water speedo was violently moving back and forth in the mid 60 range. I have a Laser 23P coming in next week to try that. We'll see what happens! I tossed some vids on YouTube of the combo running but not boat runs with the combo. I just have one run posted up before the top end upgrade.

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

You;re either gonna need a good trailer (that'll handle runnin that fast safely ) or a downhill lake....

I'm kidding of course - no condescension intended whatsoever!

Seriously:

I've got a single smallblock pushing a smaller i/o well into the 70's. So far have hit as high as 77 on gps and have it propped down a little now and only push it to upper 60's, but it handles great for pulling skiers, etc... even with a boat full of people. I have another carb and one more prop to try... thinking I'll try to hit 80 on a cool day late this fall with some light chop, a little more carb and the mufflers removed... maybe a little bigger cam (it idles too smooth now.. ). As was noted above, when i started on this - and this was confirmed in first 5 min of talking with the experienced marine engine builder i wound up using - a 383 is a very good option so that's what we built. My boat is a good bit lighter than yours (17 1/2 ft, 1400 pounds without power), to get into the 70's you're probably going to need something approaching 500 horsepower...

In order to make it last in a marine applicatoin if you're going to run it, you're talking all forged internals and built by an experienced marine engine builder, a good oil cooler with a thermostat and a strong enouhg drive to hold it all together. say 6 or 7 k for the engine. you can build one with good manners... turn it as high as 5500 or so, and use yours as a starting point, but it isn't trivial.

ie. 9.5:1 compression, steel crank, good rods, forged dished pistons, GOOD heads (afr 190's), something like comp 270 or 276 cam, decent single plane or dual plane intake, 750 carb, and some careful tuning. Add good after market exhaust - minimum emi or imco... and you're off to the races...

where is it now in terms of speed? there are a lot of things that can be done that will make a difference - and a lot of folks on here that can help you figure out what you want to do. Hope this is helpful.

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

Sorry guys... I am running a turbo 21pitch ss prop, 5.7 350 not the mag (260hp) it has and edelbrock performer intake and a 600 cfm edelbrock 4bbl carb. Other than that it is stock. I can run 60 on gps currently on a light chop at 4800 rpm that was with 2 ppl and half tank of gas and a cooler full of beer hahah.

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

Sorry guys... I am running a turbo 21pitch ss prop, 5.7 350 not the mag (260hp) it has and edelbrock performer intake and a 600 cfm edelbrock 4bbl carb. Other than that it is stock. I can run 60 on gps currently on a light chop at 4800 rpm that was with 2 ppl and half tank of gas and a cooler full of beer hahah.

That's running really fast for that hull! You're making more than 260 horsepower - based both on the intake and carb as well as the speeds you're getting. You've got really good slip numbers, etc... the only thing to do to make it significantly faster (I'm talking 5 mph +) is to add horsepower and torque. it is probably about the same hp / weight ratio as my boat was with the v-6 in it (healthy, tight vortec set-up, non-balance shaft 4bbl intake and carb, etc...). when I swapped engines, I went from the 4.3 v-6 to a strong 383 stroker motor. In other words, I likely added at least 200 horsepower, a commensurate amount of torque (that's probably conservative) and have seen 15-17 mph speed increase.

I'm assuming you're running an alpha drive, which means with a heavier boat, you'll likely frag it with the kind of hp / tq you'll need to get into the 70's. That means bravo drive... unless you REALLY like the boat, it might be better to look for a similar sized set-up that already has a healthy big block and bravo drive. The other thing you might consider is that from a speed / acceleration performance standpoint in shorter boats, you simply can't beat a light hull and a worked outboard. Even for light stern drive boats we're in great shape in the 60's, really doing well in the 70's and there are only a small handful that (honestly) run into the 80's or more. The lighter outboard boats from companies like Allison, STV, Checkmate, Baja. where we talk about 60's and 70's that crowd talks about 90 and 100... and the faster ones are into the 120's or 130's...

with what you've got now, you could arguably pick up a little bit by adding good after market heads, cam and depending on what you're going to spin it to, a bigger carb. The problem with that is that you'll lose some torque and to get your hole shot back up to par are going to have to prop down or play with vents, etc...

All that being said, there's a guy that runs the river near me that has a blown small block pushing a 20 or 21 foot Mariah into the upper 80's and of course there are others that go faster. obviously can be done, just costs $$$ and in many cases reduces reliability... also always the issue of fuel cost and being able to carry enough fuel to make a good day on the water without constantly worrying about how much fuel you've got left.

final note. I'm no expert, more of a backyard hack who loves to play with my "toys" when I get the chance....

Just my two cents... perhaps worth about what you paid for it...

 

[mtnrat]

Re: More HP Top end for 96 5.7 mercruiser

I needed 150+ hp to get my boat from 48 at 4500 to 60 mph at 5200(engine design and cam WOT 5350. Previously had a weak 200hp 350. I built a 383 all forged, Quench pistons with .035 quench and 9:1 compression, engine quest 200 heads, roller retrofit custom ground cam .510 in .480 ex, 112 separation. Air gap and 750 Qjet. My boat is heavy with a 18' deep V, so it is not the fastest hull. I figure I can get 5+ more out of it with tuning and removing the antifouling and applying 2 part polyurethane. It cost $$$$ and I did everything except the machining. Have 26 hours on it since Aug 1. The cam gives an excellent idle at 650 and I could likely get more there but I do a lot of skiing, boarding and tubing with it. I am likely losing a couple of mph due to the duoprop, but without it, the prop torque made it undriveable over 4000 rpm. With the DP, one finger steering. I am also a backyard hack so take what I say under advisement. Just what my results were. The key to performance is researching and properly matching all your components. I got advise from a number of experienced engine builders. The end result was an engine that has good dock manners and accelerates like a scalded cat.

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

I've seen your build stuff before, nice set up. what are your cam duration numbers? am curious because of the drop in exhaust lift relative to the intake. was the cam designed for a stock exhaust and thus have a longer exuast duration and lower lift so that the valve is open far enough that the manifold is the bottleneck, but no further than needed so limits chance of reversion?

just curious... and am thinking very seriously about a more agressive cam...

I needed 150+ hp to get my boat from 48 at 4500 to 60 mph at 5200(engine design and cam WOT 5350. Previously had a weak 200hp 350. I built a 383 all forged, Quench pistons with .035 quench and 9:1 compression, engine quest 200 heads, roller retrofit custom ground cam .510 in .480 ex, 112 separation. Air gap and 750 Qjet. My boat is heavy with a 18' deep V, so it is not the fastest hull. I figure I can get 5+ more out of it with tuning and removing the antifouling and applying 2 part polyurethane. It cost $$$$ and I did everything except the machining. Have 26 hours on it since Aug 1. The cam gives an excellent idle at 650 and I could likely get more there but I do a lot of skiing, boarding and tubing with it. I am likely losing a couple of mph due to the duoprop, but without it, the prop torque made it undriveable over 4000 rpm. With the DP, one finger steering. I am also a backyard hack so take what I say under advisement. Just what my results were. The key to performance is researching and properly matching all your components. I got advise from a number of experienced engine builders. The end result was an engine that has good dock manners and accelerates like a scalded cat.

 

[mtnrat]

Re: More HP Top end for 96 5.7 mercruiser

Duration @.050 are 212 in and 218 ex
Duration @.006 are 260 in and 272 ex
The cam was designed for the stock volvo 280 thru prop exhaust. I just hate noisy pleasure boats. Yea...umm...Yea... what you said . Good manners was more important to me than max hp and that is what I told the cam designer. I do not know enough about the exact intricacies that is why I went to a custom design for my components, instead of off the shelf.

I've seen your build stuff before, nice set up. what are your cam duration numbers? am curious because of the drop in exhaust lift relative to the intake. was the cam designed for a stock exhaust and thus have a longer exuast duration and lower lift so that the valve is open far enough that the manifold is the bottleneck, but no further than needed so limits chance of reversion?

just curious... and am thinking very seriously about a more agressive cam...

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

Ok guess a better question is what is a good proven h/c/i combo for a 96 5.7 350 4bbl carburated.

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

Ok guess a better question is what is a good proven h/c/i combo for a 96 5.7 350 4bbl carburated.

Honestly it depends on what you want to accomplish and how much you want to spend. Not intending to be a smart alec at all. There are many combinations that will "work".

Probably the best way to get a real appreciation for it is to go to the library and get a copy of small block marine performance, by Dennis Moore. It's out of print so you'll have to get the librarian to borrow it from another library.

I'm sure folks will probably chime in and suggest some particular combos. I'll add some tomorrow if you really want to give it a try (just tired tonight and would have to look through some of my notes for specifics so i don't screw you up). I doubt you're going go get the kind of speed increases you're looking for without a complete top to bottom build, but you can make some difference - especially if you go with good heads.

Do you boat only in fresh water? or get in saltwater or brackish once in a while?

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

that would be great... and strictly fresh water

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

ttt

 

[mtnrat]

Re: More HP Top end for 96 5.7 mercruiser

I'll take a stab.
dart, engine quest etc. 180 cc runners
Performer RPM air gap intake, qjet 750cfm
Comp cams XM262H or custom grind.

It is really a tough question without knowing the pistons you are using, etc. Need that to get compression ratio so can figure out the combustion chamber size. My advise is to spend a couple months reading, reading, searching and searching. Search here, offshore only, speedwake, hotrodders bulletin board, speed talk etc. There is no correct answer, but there are a lot of wrong answers. Talk to engine builders near you. Chances are without doing the bottom end, matching all components and balancing, you will not get the 350-375 hp and flat 400 lbs torque you will need to get that 10mph. To go 70 your rpms are going to be over the 5200rpm range and your engine needs to be built to take those kind of rpms As you go faster it takes more and more hp to get each extra mph.

 

[John_S]

Re: More HP Top end for 96 5.7 mercruiser

That 5.7L would have the dished pistons (-10cc) and probably flat hyd cam. The heads would be 64cc center-bolt style non-vortec heads. It was converted to 4brl, and would have about 240-250hp @ prop, vs 210 stock 2brl.

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

Reason I ask is because I am used to auto engines where anything under 500 hp you can get away with cast parts instead of a forged setup. However I realize the rpm/ load range of a boat is way different than a car. Also Im big into mustang 5.0's and a few companies (Edelbrock, Holley, Trick flow, AFM) sell dyno proven complete bolt on top end kits. Basically if you have this engine bolt it up an tune as stated then you will have xxx HP... Thats something I was looking for anyone know of a kit like this? I found one on jegs made by edelbrock and they told me it was for a 350, but when I called edelbrock that said those were BB heads no SB. Thanks guys I am new to boatiing.

 

[mtnrat]

Re: More HP Top end for 96 5.7 mercruiser

Creating hp numbers is one thing. Combining that with torque that comes in low and stays throughout the power band is another. That usually means a change of piston to a flattop with larger combustion chambers or a D dish with smaller combustion chambers. For a boat that sees alot of pleasure use, 9:1 is a good compression ratio to shoot for. That can be bumped up some with an aluminum head (not good for salt water or raw water cooled engines). Now you have the pistons and good heads picked out(about 180 cc for a 350) you can go onto adding an intake that will give good torque (dual plane). Get a carb, ( I like the Qjet, others will differ). Once all of those parts are chosen get a cam that will work with those parts. Nothing to radical or you will not idle worth crap and or get reversion. Like wca_tim recommended read Small Block Chevy Marine Performance by Dennis Moore. It is a little out of date but covers the topic very well.