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Discussion Starter · #1 ·
I got a runabout that I use for commuting around on close runs and it has a 4.3 in it. The carb needs to be rebuilt but I thought about just upgrading and getting one of the H.O. throttle boddies to bump it up a little. I also thought about taking my boat thru hull.

Questions 1) Are these aftermarket 4.3's carbs and good or just a joke? Im not sure what a stock flows and is jetted etc....I can dig and find that info when the time comes but I just wanted to know if anyone has beffed up their 4.3 at all. By the way it is a 89 model in a baja sunsport 17.5ft.

Question 2) I have read a ton of stickys on here about thru hull on v6's and to be honest this is the only thing I have ever owned with a V6 in it in my life (I got a steal on the boat). Is there a muffler set up or anything for a 4.3 that would allow this thing to sound decent? I know most v6's sound like a pissed off bumble bee fighting a weedeater or a v8 with the flu.
 

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If its a 4BBL manifold already run the Edelbrock 1409 with the 4.3 calibration kit.

As for thru hull.. Your description about sums it up with a 4.3L

There is however a guy on youtube that has thru hull on a 4.3 and it sounds good, but he has a radical V6 with heads and a healthy cam.
 

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Discussion Starter · #5 ·
After some review I think I will first get a decent speed prop and let my race car boys run through the carb a little.....switching to 4bb seems to be bad when I can already turn 4700 rpm on my 21pitch. I will also be doing some research on TRIM TABS....Heard smart trim is really good and saw that they even have some on here. Looks like alot lower dollar fix and the better way to go after reading some aerodynamic portfolios on boats......as far *** thru hull I dont think I will do it...I may however upograde motors if I get bored sometime and if I do trim tab and prop upgrades now they wouldnt be a TOTAL waste of money in the long run.
 

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going by what the previous owner said, my 17.5 88 checkmate would go 50 with the original 2bbl in it.

the reman longblock I4.3 I put in it, with vortec heads, aluminum intake and 4bbl, it'd run 60...
 

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I really think the 90* v-6 sounds great. It makes an exhaust pulse more offen than an sbc, so it sounds more like a flat 8 than a v-6 to me. It depends.... most guys are running a v-8 so they don't like the smoother sound of the 4.3.... but on the other hand it is still turning the same size lungs.

It is an open disscusion to say the least.

my 4.3 has #772 vortec heads, alum. edelbrock manifold, 4bbl, hi perf GLH exhaust alum manifolds, 1.6 roller rockers, slightly hotter cam than the merc marine cam, and will be 4" thru-hull.

:bandit: It will sound baddazz!!! :winker: At least to me it will. What does it matter what everyone else thinks of YOUR boat. If you like it....do it! It will make a difference in power and you will get some more speed with a few smart moves.

BTW..... unless you have some good ported vortech heads and a hot cam.... the 4.3 will not like anything as big or bigger than a 600cfm 4bbl. stick to a reman rochester 4bbl for now. They are cheap and reliable. You can always move up from there
 

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a couple points of contention:

independant of whether you like the sound or not, there is little if any power to be gained for a 4.3 in changing the exhaust to through hull - my impression is that until you start getting well above 300 horsepower, the factory exhaust flows pretty well. cam duration and dry riser length (volume?) is a different story in the context of reversion.

a v-6 fires 6 times per revolution and so actually makes an exhaust pulse at 3/4 the rate of a v-8... less often than a v-8.

I know a number of people, including myself that have or do run 600 cfm carbs with the factory cam and stock vortec heads on a v-6 with great results. The key is to get the jets / metering rods dialed in. the 600 cfm Edelbrock marine carb (mod 1409) is cheap at only a little over $300 new... and is easy to set up.

glm aluminum manifolds are well worth the coin for the weight loss alone in a light boat, but are only going to add a very small improvement over stock in terms of engine performance / power.

Finally, since you don't have a ton of torque on the bottom end with a 4.3 to begin with, and you still have the issues of idling down to shift into gear with an alpha drive (unless you want to bypass the switch and start in gear.. kind of silly for a 50-60 mph boat), things that all become an issue if you start opening up the heads and increasing cam duration very much...

if you want a lot more out of it, hands down easiest, cheapest and most effective way to get there is a cheap (marine) 350.

food for thought...




sprint18 said:
I really think the 90* v-6 sounds great. It makes an exhaust pulse more offen than an sbc, so it sounds more like a flat 8 than a v-6 to me. It depends.... most guys are running a v-8 so they don't like the smoother sound of the 4.3.... but on the other hand it is still turning the same size lungs.

It is an open disscusion to say the least.

my 4.3 has #772 vortec heads, alum. edelbrock manifold, 4bbl, hi perf GLH exhaust alum manifolds, 1.6 roller rockers, slightly hotter cam than the merc marine cam, and will be 4" thru-hull.

:bandit: It will sound baddazz!!! :winker: At least to me it will. What does it matter what everyone else thinks of YOUR boat. If you like it....do it! It will make a difference in power and you will get some more speed with a few smart moves.

BTW..... unless you have some good ported vortech heads and a hot cam.... the 4.3 will not like anything as big or bigger than a 600cfm 4bbl. stick to a reman rochester 4bbl for now. They are cheap and reliable. You can always move up from there
 

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a v-6 fires 6 times per revolution and so actually makes an exhaust pulse at 3/4 the rate of a v-8... less often than a v-8.
"food for thought"....
evenfire 4.3 = bang every 60*
standard sbc = 2 bangs every 90*

independant of whether you like the sound or not, there is little if any power to be gained for a 4.3 in changing the exhaust to through hull
so what your saying here is that merc underwater exhaust flows the same as open thruhull?..... Maybe this would be true for a bone stock v-6... but then again I think even 5hp is an improvement. Isn't it? besides, unless your goal is to make noise... thruhull is only a real option for modified engines.... ie; cam, heads, porting, high flow carb or port injection. Like mine. I'll tell you what. I'll go get a good dyno run with thru-drive and thru-hull and see what it yields with a modified 4.3 since that is more or less my arguement.

I know a number of people, including myself that have or do run 600 cfm carbs with the factory cam and stock vortec heads on a v-6 with great results.
Yeah but my bet would be that there is NO difference in power between say 3/4 throttle and wtfo. That was my point anyways, if u didn't understand where I was coming from :rolleyes: Even a sbc will lose throttle response with a 600 on a stock block and sh*tty heads. Those of you with 91-up 4.3 have great flowing heads. the 772 heads I have flow around 250 per port without touching them. for reference the turbocharged 4.3's out of the typhoon flow only 160cfm. My heads will move more air than a standard BBC casting.

glm aluminum manifolds are well worth the coin for the weight loss alone in a light boat, but are only going to add a very small improvement over stock in terms of engine performance / power.
Again.... Only true for a bone stock 4.3

Finally, since you don't have a ton of torque on the bottom end with a 4.3 to begin with
I'd say 250ft/lbs at 2800rpm is plenty for a 262ci.... at least thats what my truck puts out on the dyno. (It sure is nice having a Land & Sea 4k lb roll at my brothers house) I'm willing to say that the 4.3 I'm building with top that by 10% around the same rpm. We'll see when I'm done.

if you want a lot more out of it, hands down easiest, cheapest and most effective way to get there is a cheap (marine) 350.
Too bad most boats under 18ft can't take the extra wieght of a sbc..... otherwise we wouldn't need to build V-6's huh. Alum sbc blocks are as expensive as my whole rig, so that blows that one outta the water too. Not all of us want a sbc otherwise we wouldn't bother asking.

please don't knit-pick my words until you think about them for at least 2 minutes. :winker: Thank you
 

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nitpicking?

primarily intended that original poster got representative information in answer to his questions. note that I'm smiling a friendly smile while typing this...

"food for thought"....
evenfire 4.3 = bang every 60*
standard sbc = 2 bangs every 90*
2 "bangs" every 45 = 1 "bang" every 45 on average...
45 is 3/4 of 60, which is what I said...

so what your saying here is that merc underwater exhaust flows the same as open thruhull?.....
no, I intended to convey that the merc through-prop exhaust is not a power limiting bottleneck until you get well above 300 horsepower, most people don't see a difference until closer to 400 horsepower if at all. that goes for smallblocks and bigblocks. if you take a look at volumetric efficiency and power production, the amount of exhaust gas producted for a ballpark level of horsepower is going to be in the same range... so unless your modifying a 4.3 to make say 350 or more horsepower - there is no benefit in power production for the through hull exhaust. If you like the way it sounds, go for it, I'm the last one to tell anyone what they should do with their rig. let's just be honest about what really makes a difference.

Yeah but my bet would be that there is NO difference in power between say 3/4 throttle and wtfo. That was my point anyways, if u didn't understand where I was coming from Even a sbc will lose throttle response with a 600 on a stock block and sh*tty heads. Those of you with 91-up 4.3 have great flowing heads. the 772 heads I have flow around 250 per port without touching them. for reference the turbocharged 4.3's out of the typhoon flow only 160cfm. My heads will move more air than a standard BBC casting.
the original poster asked if the aftermarket carbs were any good and add any performance. The answer is yes. is it overcarbed for a "stock" 4.3, sure, but jetted right it'll work great and put out significantly more power than the stock set-up. definately a much better option than rolling the dice on a reman quadrajet (can be good carbs, but not that many people know how to build one right these days... )

Again.... Only true for a bone stock 4.3
Here you were disagreeing when I said the glm aluminum manifolds weren't going to be good for much if any power increase... My answer had nothing to do with the specs for the engine they were on, they won't make much if any more power because they're very similar in flow to stock... just lighter! I think the EMI's flow a little better on the v-6, but havn't personally run them and so can't comment on this one from experience.


I'd say 250ft/lbs at 2800rpm is plenty for a 262ci.... at least thats what my truck puts out on the dyno. (It sure is nice having a Land & Sea 4k lb roll at my brothers house) I'm willing to say that the 4.3 I'm building with top that by 10% around the same rpm. We'll see when I'm done.
not bad considering that a new, bone stock gm / merc vortec marine engine with a 4bbl carb puts out 267 ft lbs at 2800 rpm and 223 hp at 4800 rpm...

Too bad most boats under 18ft can't take the extra wieght of a sbc.....
a (marginally) fat chick in the boat weighs more than the difference between a 4.3 and a 5.7. There is only a difference of 100 pounds between the two engine packages. it drops to more like 40 pounds if you put aftermarket aluminum manifolds on the v-8. If a boat is designed to handle the weight of a 4.3, it can handle a 5.7. Having the space and whether the boat will be safe with the increased torque and speed is more important. Is it the best thing to do? maybe in some cases yes, in others no. depends on the boat and what you want to do...

I've got no bone to pick if you want to hot rod a v-6 that's great, they can make cool toys. Hell my lawn mower would probably have a cam, ported aftermarket head, high compression piston and forced induction if I knew where to buy the parts.

for my current, 18 ft boat, i went the v-6 rounte to about 240 horsepower or so, still wanted (a lot) more so instead of pushing the v-6 to the edge with hard to find parts, went with a smallblock for over 400. and it's still a put put compared with a lot of the rigs people on here have...
 

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Wow
I was just gonna say that all the work and effort (and $$) might be best directed at a small block 350 or even stroker. I don't think anyone is going to argue that $ for $ that would be best. If you got a v-6 and love it, cool. But the swap would certainly be easier ind cheaper overall.

I have had daydreams of working over my Volvo 4.3 ... then woke up. :D
 

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Big Flame Arrestor
600cfm Holley or Edelbrock
4.3 Edelbrock RPM Vortec
4.3 96+Vortec heads
Comp Cams 215 or 220 HR with .500" lift 112LSA
9-9.5:1 Compression

Let it fly.

Enough talk. Go do it ! :laugher:
 

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a (marginally) fat chick in the boat weighs more than the difference between a 4.3 and a 5.7
:laugher: :laugher: :laugher: That's good!

I can only speak for my package on the wieght topic. I've been told numorous times that the sbc would make my ride overall uncontrollable. I of course would like nothing more than to hear that beautiful sound when I turn the key. But I fear it would be the wrong choice. And I can'r afford to do things twice. I think their is a good future for smaller power plants. And performance mods for them shouldn't be viewed as futile. Every little bit helps. maybe he won't get 20-30hp out of a carb and exhaust swap (or maybe he will) but for a small boat that is in the 2000-3000lb range it will certainly make a difference. My hull is 1100lbs. so a 950lb engine would be overkill I think. Going up from my 3.0lx to a 4.3 is about all that hull will eat. I believe the math worked out to about roughly 30 more lbs than the 4cyl with alum manifolds and thru-hull. Thats about 2 30 pks ....lol Twice the power though!!! :winker: :winker: I'm definately excited to do this :D

I appologize wtfo for sounding a bit nippie, but as I've found several times before it's truely hard to convey emotions and tone of voice through words on a screen.

2 "bangs" every 45 = 1 "bang" every 45 on average...
I was under the impression that 2 cylinders on a sbc actually fire at the same time every 90*. That is why they sound so lumpy right? Also why my truck (4.3) sounds like it runs much smoother than a v-8...??? If so then that was my piont. Sorry for the misunderstanding :winker:

most people don't see a difference until closer to 400 horsepower if at all.
That sure is alot of air to move through that 2.5 x 1.5 opening on the drive gimbal. Why does it make so much of a difference on an auto and not on a boat? I would think with the fact that your mostly into the throttle on a boat that the extra air and lack of heat in the exhaust would give an ideal situation for flow improvement. Insite?
 

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Jees i have been all over this topic for about a year or so.....4.3 are about as strung out in a marine version as you can get..

But a 5.7 takes little mods huge torque gains and very little cost....for about 4000 i could drop a a new 5.7 that is lighter than a 4.3 and producing 400 hp and 400 lbs of touqre....it would take far more than than that to get a 4.3 even close to that performance
 

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Hey sprint18; I wrote a response last night and then hit the back button and erased it (****).

I'll try again...

Definately no worries on any perception of attitude... and I hear you loud and clear on emotions conveyed with typing... I really tried to insult / piss someone off at work yesterday and they thought i was kidding... if they coulda seen my face they wouldn't have smiled at all.

I have a 383 in my 17 1/2 foot checkmate.. it weights about 1300 pounds without engine and drive according to mfg's original spec. Balsa cored, padded v-hull and with stern lifting and neutral props is very well mannered well into the 70's (fastest so far is 77 gps and still working on set-up, also going to try a differtent carb and taking the mufflers off here in a week or so. It is making over 400 hp and even more tq. Somewhat mild numbers for a 383, but it's built to run and run hard and last. and it idles down to 500-600 rpm without dying... I spent more than 4k, but it's built with all forged internals and to tight (marine) tolerances, etc...

I'm NOT trying to talk you into a 5.7 - a well built 4.3 will probably make that boat fly and especially if you go with good aluminum manifolds, intake, etc... should be light and nimble, etc... I eard the emi v-6 msanifolds actually flow pretty well. not sure if the longer risers you would need for a cam profile much over stock will bolt on. would really suck to spend a bunch of time and money on an engine only to fill the damn thing up with water...

the nice thing about a smallblock is the availability of a wide range of cheap parts. probably one of things that cinched my thoughts the most. know where you can order a forged steel crank? really strong rods? balanced rotating assembly? blower that'll fit? sure, it is possible, but the options are scarce and expensive - especially once you try and get into more power than is easy with simple head, manifold, carb, etc... as in much over 250 horsepower. I will say that my 4.3 ran really strong and would runw tith or outrun a lot of the guys i know who have (stock) 350s in their boats and that it was clear the factory roller cam was running out well before 5000 rpms. It and the same heads on it as yours touched up a little (wink), a little higher compression (ca. 10:1) an edelbrock performer intake and 600 cfm carb, etc...

lots of people told me I would be unhappy with the result, that it would be uncontrollable, that, blah, blah, blah... it couldn't be further from the truth. It is great! sure, without the trim tabs on it if you give it some gas out of the hole, it'll stand up on end (grin), but if you don't drive like an idiot it handles just fine. My 13 year old daughter can drive it fine.

on the exhaust, couple of things, remember that boat exhaust has water cooling. The volume gas decreases rapidly with cooling - requires less space to get pushed out. Second, the way the prop and drive segment of the exhaust is designed, when you're going fast, there is a low pressure zone created right behind the prop which creates somewhat of a vacuum helping pull the exhaust gasses through the lower portion of the drive and y-pipe, and 3. remember that we're talking about a marine engine. Think of an engine likean air pump, the amount of gas pushed out, is proportional to the speed / rpm of the pump. a lot of the sizing we think about for car engine exhaust is based on hitting say 7,000 or more rpms... you're not going to turn any regular type of marine engine for much over 5000 for long... remember also that the two sides of the exhaust are connected in the y-pipe and so the exhaust pulses alternate between sides... that helps some because it lets the pressure pulses from one side be distributed somewhat into the volume of the other side of the exhaust. all these factors combine to make it a reasonable set-up for near stock small blocks and anything with that horsepower level or below... or at least that's my current understanding... it's really a well designed system.

on firing spaced out evenly... since the distributer turns off the crank, and the engine fires when the rotor passes a plug wire terminal, and the plug wire terminals are evenly spaced out, then the firing is evenly spaced... ever notice how a bone stock small block, like an old beater with the tailpipe off sounds? blah, blah, blah, blah... even and crappy? unless of course way out of tune or have dead / dying cylinders... the lumpy idle for more performance based engines is only from the cam duration / overlap...

hope that's helpful... not an expert, but have some experience learned mainly from breaking things, making mistakes, and once in a while hitting wood on one... have a great one!

sorry bout the book... type too fast for my own good!
 

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the nice thing about a smallblock is the availability of a wide range of cheap parts. probably one of things that cinched my thoughts the most. know where you can order a forged steel crank? really strong rods? balanced rotating assembly? blower that'll fit? sure, it is possible, but the options are scarce and expensive - especially once you try and get into more power than is easy with simple head, manifold, carb, etc... as in much over 250 horsepower. I will say that my 4.3 ran really strong and would runw tith or outrun a lot of the guys i know who have (stock) 350s in their boats and that it was clear the factory roller cam was running out well before 5000 rpms. It and the same heads on it as yours touched up a little (wink), a little higher compression (ca. 10:1) an edelbrock performer intake and 600 cfm carb, etc...
Yeah I'm not really looking for more than 250hp... I would love to tell you that I have plans (and money) to pop on a 4-71 and some bowtie alum heads...ect. But I think I'm going to have to go with my pop on this one and just put a nicely warmed over fresh V-6 like the boat was made with from the factory and be happy with some new paint and vinyl. Besides 60mph will be good enough to make it to hamlin beach or sodus for a few drinks in a reasonable amount of time. Not many people out on ontario actually have a boat that will do 60+..... and if they do then chances are it does over 80, so I won't have to worry about putting and green backs against them anyways.

i mostly just want enough power to hop over the bigger waves and some more speed to smooth out the ride a bit. With such a small hull I fall into every hole out there. plus I like airtime!!!

plus it would be nice to cruise around at 40 without breaking 3/4 throttle or 4000rpm. Hence the 1.50 gears I got. With any luck I will get a healthy 260 horse and a sweet spot between 2500-4500.... Higher than 5k and I'd be afraid I'd be swimming back. H-beam eagles are only 400 for the set thought.... and the crank is good for 6k/500hp I hear. Bumstick choice will have to be spot-on. I have to try this one out on the desktop dyno and see what it thinks I should try.

I'll be looking at a 25ftr soon anyways. I'll finish this one up and enjoy it for the next 2-3 yrs first though huh.

Next ride will have a mid cabin/ open bow. I like those nordic's. I also watch for advantage 25'ers. I like those too. There is a powerplay 27 for 22k for sale around rochester. has a 502/415hp. Clean! My options are open. Need to find a new truck first though if I go bigger.

sorry bored at work, shifts almost done. L8r
 

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ot many people out on ontario actually have a boat that will do 60+.....
in my experience, most people that have boats that will go 60+... don't, they lie.

sounds like you've got a good plan for your boat. that's a fast hull, you should be able to hit 60 with what you're planning and not spend a huge amount of money on it. I've still got the v-6 that came out of mine on the carport and there are days I look at it and wonder if I should have left it in there... it made good power and didn't use quite as much fuel as the bigger one... fuel prices have really put a damper on people's boating around here as well we the industry around here.

oh, the manifolds I was thinking about weren't EMI they're the imco's (Thumperpower). powder coated cast aluminum. with different water jacket gasket between the manifold and riser. They're about 1000 for the complete set with gaskets, but I've seen them on ebay a few times for a good biut less. you might get lucky.

Have you decided on a carb yet? going with a quadrajet or??? do you have one? What else do you need that you don't have?

good luck with your project(s) and have fun...
 

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I have a rochester 4bbl for a 350 mag.... needs a tune I'm sure. I still need a 4bbl manifold and risers. I'm going for the GLM manifolds for $189 each and probably going to order some 304 for the risers and bring it right down to the thru spigots. I've had plenty of sanitation welding practice since I work in the kitchen at the place that makes all of the tostitos salse and con queso and most all the red sauses except prego. I'm sure you have eaten some salsa that went through my welds...lol :winker:

Other than that i have

block
heads
y pipe, 90*'s
carb
rear bellhousing
flywheel
coupler
fuel pump
harness
starter
serpentine pulleys
power steering pump/bracket
1.50 gears
gimbel repair kit/ bellows/ hoses etc

still need...

4bbl manifold (buying edelbrock 2104)
bumpstick
exhaust manifolds/ risers (GLM alum. and 304 risers... eventually)
sparky
distributor (found a sweet one from patriot performance...one wire hei)


what am I missing?
 
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