4.3 2brl to 4brl Conversion Mod

[racer2c]

I did a quick search after I read fellow member Gazjen mention this in another thread and found some parts for anyone interested.

I'm very interested in doing this upgrade but I wonder if there are other things required such as the stock fuel pump. Do you think it can feed a 4brl? I imagine it would, especially a smallish 600cfm. Also, I assume I would need a different flame arrestor that would fit?
Anything else anyone can think of?

http://www.michiganmotorz.com/Holley...L+four+barrel)

http://www.michiganmotorz.com/4.3L+f...+(1996+-+2008)

[Gazjen]

Yep thats where I saw them, I would think the the standard fuel pump would be ok as its only low pressure and just refilling the carb bowl

I was also looking at the MPI manifolds they have and wondering about a EFI Conversion with a standalone ecu

Are you in the UK or the States?

[seapuppy]

the existing fuel pump should be fine....not sure the manifold will accept the 4bbl carb..may have to change out the intake to accept the carb....that needs to be checked out since if you stick a larger carb onto an existing intake ...it may choke it out rather than increase fuel flow.....it will definitly increase velocity thru the carb...better mixture and throttle response...may have to rejet the carb if it's too rich...watch for those when you order up the new carb...

just a few thoughts on the issue...

keep us informed...


SP

[racer2c]

Originally Posted by Gazjen

Yep thats where I saw them, I would think the the standard fuel pump would be ok as its only low pressure and just refilling the carb bowl

Are you in the UK or the States?

In the States.

Is the flame arrestor on the carb or does it go over the carb? Isn't that what makes it a marine carb vs auto carb?

[racer2c]

Originally Posted by seapuppy

the existing fuel pump should be fine....not sure the manifold will accept the 4bbl carb..may have to change out the intake to accept the carb....that needs to be checked out since if you stick a larger carb onto an existing intake ...it may choke it out rather than increase fuel flow.....it will definitly increase velocity thru the carb...better mixture and throttle response...may have to rejet the carb if it's too rich...watch for those when you order up the new carb...

just a few thoughts on the issue...

keep us informed...


SP

I would diffinilty do both the carb and the manifold. The two links in my original post are to both. Now the question...is $600 plus the time to install it worth 20hp. Hmmm. Probably not.
They say a High 5 prop will make it feel like 100hp nitrous shot out of the hole and I can get a used one for $250.

[Gazjen]

The flame arrester just attaches like a air filter

Not sure of the difference from automotive to marine

[Gazjen]

I think EFI and a little supercharger will be the way I go and a posh prop when I've read up

Plus I'd read up it was nearer to 35bhp extra

[Brit Rider]

I have run both the 190 hp 4.3 carb and the 210 hp 4.3 EFI - no noticeable difference.

I'd save your money and buy a boat with a bigger engine next year

[BKUMP]

Never thought about going with a 4 barrel carb but have thought about changing to MPI. A few times a year I run my 1900 sr3 at Shaver Lake and the altitide is 5500ft so my 4.3 carb engine runs pretty bad so I looked into Holley's conversion but they want $1500 to $2500, I'll buy a new boat before I'd do that. I talked to a prop guy and he said he had ran there before and told me to down prop so I bought a 19 pitch Black Max for up there and I'll stay with the 23 at the lower altitude. I doubt that this helps anyone just my 2 cents.

[Floatn Fun]

The difference between a automobile carb and a marine carb is that typically there will be tubes on the float bowl vents and the throttle shafts will be sealed, both of these changes are to prevent fuel spillage and leakage and the resulting fire. If you decide to go with the change to a four barrel changing the intake would get some additional performance. total cost for a Holley marine carb and an edelbrock performer intake is around the $600 mentioned above. You may be able to find a used carb and rebuild it, and you may be able to pick up a used intake on ebay.

[Argonaut]

Originally Posted by Gazjen

I think EFI and a little supercharger will be the way I go and a posh prop when I've read up

Plus I'd read up it was nearer to 35bhp extra

A small belt driven supercharger with 3-5psi boost would give an amazing boost.

I'm guessing that there must be plenty supercharger kits avail in the US ?

[seapuppy]

heck man...if your gonna go that route...why not a small turbine producing about 4oohp.....now that would be cool!!....

8)

[Argonaut]

Not sure what you mean by a turbine ? ... do you mean an exhaust driven turbocharger ?

If so the issues with these is that the turbine only spins up with exhaust power, and that means they are not that good form rest, and you get inherent turbo lag.
If you look at hp / rev graph the curve while it may be OK for a car, is wrong for a boat ... whereas a supercharger has the curve with the power band at low revs where it is needed ... and much flatter ... i.e more even boost.

3-5 psi boost requires almost no engine mods other than supercharger kit, whereas higher boost or turbo charger installs usually mean significant mods ... you can also have an electromagnetic clutch so you can switch on the boost only when you need it.
So if pottering around the bay with Grandma no need to have it running.
GMC 6-71 was one well respected supercharger

Different valves, reduction of compression ratio, re-jetting or upsizing carbs, inter cooler, anti backfire valves, lubrication etc.


If by turbine you mean something totally different, please let us know.

Also as I am not in US ... I know that there is a large 'tune it up' market in US, so you may well have more ideas .. kenn to know what works on a 4.3 .... for my own boat.

[seapuppy]

nah..I was just pulling your leg some about the turbine...I was talking about a small jet engine used in surplus helo's....saw some video's of some boats people converted from recip engines to a turbine...jet....they were awesome ..fast...quiet....but totally outragious.....


SP