4.3 mercruiser with a 2brl

[m_87]

hey i have a 1988 chris craft that i am restoring. it has a GM 4.3 with a 2 brl carb i think its rated for like 170 hp.

had a few qestions like i wanted to put a 4brl carb on it.. how would it afect my fuel economy? i would want to get a 4 brl intake and how much power would i gain? would it be worth it? i would be happy with an extra 20 horses but maybe i am dreaming. let me know if anybody has come accerost this issue


o and also where would i find the carb and intake? best bet junk yard? do most the years line up? thanks to any replies.

 

[zbnutcase]

Re: 4.3 mercruiser with a 2brl

The 4bbl manifold was marine (and industral engine) specfic, so if you mean a boat junkyard, maybe you will find one. And you can't use an Edelbrock, as the t-stat housing outlet is in a different location, and the Merc t-stat housing wont fit.

 

[paultjohnson]

Re: 4.3 mercruiser with a 2brl

Another factor to consider is if it came stock with a 2BBL the drive ratio is 1.84:1 stock w 4BBL 1.65:1 Acording to my owners manual. I have heard NOT SURE that a 4.3 with a 4 BBL had a diff cam then a 2 BBL

 

[Cpt D]

Re: 4.3 mercruiser with a 2brl

Well, I've got an 86 4 Winns, 4.3L and it has a quadrajet on top of a eldebrock aluminum intake. The cover over the spark arrestor says it's 185hp. I'm sure the intake wasn't stock, but it was on it when I got the boat. I've never really looked at the details with the thermostat, but it works perfect. It's also a freshwater only boat, so not worried about the aluminum. My boat runs perfect and sounds real good with the secondaries opened up. It will suck a lot of gas like that also. If I keep it below 3500 rpm's it does fantastic on fuel. I burn a little less than 3 gallons an hour this way. I've been told that I gain a lot for hole shots with the four barrel. I have no idea since my boat had the 4 barrel the day I got it. I will say I'm not interested in changing it to a 2 barrel. My best guess would be a 10 to 15 horse increase. Also, my gear ratio is 1.84/1.

 

[paultjohnson]

Re: 4.3 mercruiser with a 2brl

Captd Hmm A have an 86 thundercraft with 4.3 2 bbl My engine cover also says 185 hp 99% sure its all original. The 4.3 with a 4 bbl is rated 205 in my merccruiser bible Do you know what your drive ratio is ?

 

[Cpt D]

Re: 4.3 mercruiser with a 2brl

Cool, maybe I have 20 horse more than I thought!!! Don't really care though, just want it to keep running good.

 

[paultjohnson]

Re: 4.3 mercruiser with a 2brl

Also keep in mind that Whippin that old engine will probably start more, earlier assosiated mechanical issues. will start moaning ang groaning. leakn....tickticktick got time and money? JUST some thoughts Ive had my 86 Thundercraft 2 bbl 185 hp since 1990 and wanted to go 4bbl .. Got bad vibes about it from my boat wrench buds. Or go 4 it and go like hell !!! GD LK !

 

[Cpt D]

Re: 4.3 mercruiser with a 2brl

I generally don't go like hell, but it's nice to know it's there if I want it. I actually think at cruising speed I do better on fuel than I would with a 2 barrel carb. Like I said before, I'm told it also increases the hole shot which makes it nice for waterskiing and wakeboarding.

Happy boating!!

 

[m_87]

Re: 4.3 mercruiser with a 2brl

awesome thoughts guys! i am not sure what me gear ratio is i guess i will look it up acording to the serial number from the adults only section..

thanks again good stuff

 

[Aloysius]

Re: 4.3 mercruiser with a 2brl

The only place you'll notice any power difference is wide open at top rpm..no power difference below 4000 rpms will be obtained. Fuel economy may actually improve at cruise if you use a quadrajet and keep the secondaries closed.

The cost of a new manifold and marine quadrajet will be substantial, and hardly justify the meager return in power. spend the money on properly tuning what you have, including dialing in the timing advance and total timing.

 

[BAproject]

Re: 4.3 mercruiser with a 2brl

if it ain't broke, don't fix it , you could introduce a whole slew of different problems....

 

[Cpt D]

Re: 4.3 mercruiser with a 2brl

The only place you'll notice any power difference is wide open at top rpm..no power difference below 4000 rpms will be obtained. .

I don't agree with you. I can hear the secondaries open up very well at about2000 rpm's at full throttle coming out of the hole. I think you're confusing carbs with valves. If I went to larger intake valves I would only notice a difference above 4000 rpm's.

 

[fossill]

Re: 4.3 mercruiser with a 2brl

A few posts on here on those who converted the 350 and 305 to a 4bbl. No noticeable gains from their experiences. I'm sure the same applies to the 4.3. Waste of time and money.

 

[m_87]

Re: 4.3 mercruiser with a 2brl

it runs great now. im just woundering why they switched from the 2 brl to the 4??? probably cause it gives out more power. the engine may not run at its full potential right no and would be better off with the 4 brl.. i kinda think the same scenario as fuel injection.. but not as big of a difference.

my drive has a 1.84:1 gear ratio and i would probably be buying the intake manifold and carb from a boat salvage.

might look into an eldeborck manifold.

 

[Aloysius]

Re: 4.3 mercruiser with a 2brl

Just because the secondaries open doesn't mean you're getting more air at 2000 rpms..the 2 bb. doesn't become flow limited until about 4000 rpms, and even then the pressure(vacuum) differential is slight. A 262 cu.in. engine only requires about a 350 cfm carb at 4000 rpms..at 2000, i'ts 1/2 that, or about 175 cfm.

If your secondaries are opening at 2000 rpms, they're opening way too early. Atomization will be compromised because the air flow through the venturis is too low.

 

[Cpt D]

Re: 4.3 mercruiser with a 2brl

it runs great now. im just woundering why they switched from the 2 brl to the 4??? probably cause it gives out more power. the engine may not run at its full potential right no and would be better off with the 4 brl.. i kinda think the same scenario as fuel injection.. but not as big of a difference.

my drive has a 1.84:1 gear ratio and i would probably be buying the intake manifold and carb from a boat salvage.

might look into an eldeborck manifold.

All I can tell you is that I love the 4 barrell on my v6 and it is apparently not stock. They did put them on these motors stock, so I don't think putting one on is going to make it fail prematurely. I don't agree with Aloy at all on this matter. A 4 barrel carb will pull you out of the hole faster than a 2 barrel carb. I wish some of the more respected people of this forum would post their opinions on this.

 

[Danny Mc]

Re: 4.3 mercruiser with a 2brl

Boat is 93 Regal SC 206 Valante. I just swapped a 93 4.3 for a 2001 4.3 vortec with 96 S10 4whd cam, Edel 2114 intake and the 93 Weber carb with SB to SQ adapter. I had to go from stock 21p prop to SS23 prop. Acceleration much stronger, WOT went from 45mph to 54 mph. Now will replace the 600cfm Weber with 650cfm Holley Marine carb to get rid of adapter plate.

 

[wire2]

Re: 4.3 mercruiser with a 2brl

Many years ago I had a '66 Mustang 289 3 spd. It was rated at 200 hp with a 2 bbl. I put a Rochester quadrajet and Edel alum intake on it, I swear it added 40 hp. It made a HUGE difference. Tires suddenly wore out faster.

 

[m_87]

Re: 4.3 mercruiser with a 2brl

great guys thanks for the input. im going to start looking for a setup!

 

[bigdan1]

Re: 4.3 mercruiser with a 2brl

I generally don't go like hell, but it's nice to know it's there if I want it. I actually think at cruising speed I do better on fuel than I would with a 2 barrel carb. Like I said before, I'm told it also increases the hole shot which makes it nice for waterskiing and wakeboarding.

Happy boating!!

this is the nice point with quadrajet 4 barrel carbs

great torque ,fuel response and fuel economy on normal cruise ,due to high velocity in small venturies ......and ,power on 4 barrel