Carb Swap

[Guest]

Anybody Swap a 4BBL for the 2BBL on the 90s 5.0 in there 2452

[itsabowtime2]

Why are you considering a swap from a 4 bbl to a 2 bbl? 4 bbl should yield better fuel economy.

[Guest]

itsabowtime2 wrote:
Why are you considering a swap from a 4 bbl to a 2 bbl? 4 bbl should yield better fuel economy.

Have 2BBl looking to see if any body has swapped to a 4BBL and what there difference in performance, fuel economy and difficulty in install.

[2850Bounty]

over40pirate wrote:
Anybody Swap a 4BBL for the 2BBL .......................

Phil, I read that as you did, and I could not understand the reasoning either.

Looks like the swap is [SIZE]3 wrote:
from[/SIZE] a 2 Barrel [SIZE]3 wrote:
to[/SIZE] a 4 Barrel !

[bhawes]

x3 but....

I had considered swapping my 2 bbl to a 4 bbl on my 4.3 to pick up the extra 30 hp that the 4 bbl version has. I've learned that to achieve the extra 30 hp, a cam swap is also required, (as well as the manifold and carburetor) so that killed the idea. I can live with the 190 hp that I have now.

[Guest]

Have 2BBl looking to see if any body has swapped to a 4BBL and what there difference in performance, fuel economy and difficulty in install.

I did it on a 2001 5.7 2455. Not the same but fairly similar. All the parts would be the same. I picked up 500 RPM at the top, improved fuel economy by 20% (I have flow meters, it was easy to measure accurately), and the hole shot was hugely improved.

You need:

Carb (Holley 650 marine)

Manifold (Edelbrock Marine Performer)

New fuel line

New mount for the throttle cable

Larger spark arrestor

Misc small parts

The carb and manifold cost me around $900 and the mount was custom-made in trade for my old carb. The same shop traded spark arrestors with me. This of course includes no labor, and it's a few hours for an experienced mechanic.

OH...BIG QUESTION... Do you have Vortec heads on that old engine? If not, the flow will not improve much with the carb, it will still be limited by the heads.

[Guest]

SwampNut wrote:
I did it on a 2001 5.7 2455. Not the same but fairly similar. All the parts would be the same. I picked up 500 RPM at the top, improved fuel economy by 20% (I have flow meters, it was easy to measure accurately), and the hole shot was hugely improved.

You need:

Carb (Holley 650 marine)

Manifold (Edelbrock Marine Performer)

New fuel line

New mount for the throttle cable

Larger spark arrestor

Misc small parts

The carb and manifold cost me around $900 and the mount was custom-made in trade for my old carb. The same shop traded spark arrestors with me. This of course includes no labor, and it's a few hours for an experienced mechanic.

OH...BIG QUESTION... Do you have Vortec heads on that old engine? If not, the flow will not improve much with the carb, it will still be limited by the heads.

Don't know if I have Vortec heads or not but doubt it.

[boatworkfl]

To give you an idea of the difference, the gm 350 truck crate engine, a 4 bolt main non vortec engine, the only difference in the 270 hp and the 290 hp is the cam.

Installing a 4 bbl carb should be a bit better on the gas consumption issue, and is a simple swap, manifold and a new Holley carb, if using a quadrajet manifold, Holley makes a 650 cfm for that manifold. Do not use a non marine carb. I do not know how efficient it will be on a 302.

[Guest]

boatworkfl wrote:
To give you an idea of the difference, the gm 350 truck crate engine, a 4 bolt main non vortec engine, the only difference in the 270 hp and the 290 hp is the cam.

Installing a 4 bbl carb should be a bit better on the gas consumption issue, and is a simple swap, manifold and a new Holley carb, if using a quadrajet manifold, Holley makes a 650 cfm for that manifold. Do not use a non marine carb. I do not know how efficient it will be on a 302.

I did it once on my 2150 Volvo Pinta but just the carb with adapter plate. It diffidently had more power.

[Guest]

SwampNut wrote:
I did it on a 2001 5.7 2455. Not the same but fairly similar. All the parts would be the same. I picked up 500 RPM at the top, improved fuel economy by 20% (I have flow meters, it was easy to measure accurately), and the hole shot was hugely improved.

You need:

Carb (Holley 650 marine)

Manifold (Edelbrock Marine Performer)

New fuel line

New mount for the throttle cable

Larger spark arrestor

Misc small parts

The carb and manifold cost me around $900 and the mount was custom-made in trade for my old carb. The same shop traded spark arrestors with me. This of course includes no labor, and it's a few hours for an experienced mechanic.

OH...BIG QUESTION... Do you have Vortec heads on that old engine? If not, the flow will not improve much with the carb, it will still be limited by the heads.

Speaking of air flow I saw a picture on this forum of someone who had diverted the exhaust from thru outdrive to directly thru hull by putting elbows just past risers. I tried contacting to see if that worked well but he did not answer. I'm an old hot rod builder so I like all that header stuff. But not at the price these marine companies want.

[itsabowtime2]

over40pirate wrote:
Have 2BBl looking to see if any body has swapped to a 4BBL and what there difference in performance, fuel economy and difficulty in install.

OK, now I get it.

There have been many talks about this. Here is one:

http://www.baylinerownersclub.org/forum/showthread.php?65543-Upgrading-Merc-5-0L-2bbl-to-4bbl&highlight=2bbl+4bbl

[Guest]

We have a '97 2355 w 5.7 alpha 1 gen II. Boat would do about 34 mph@4500 rpms WOT when we got it in '99. It did not have vortec heads (they came out in '98, 2 yrs after they were introduced on the Chevy small and big block engines). Around 00' we did the carb upgrade first including a new intake manifold to handle the larger throat of the 4 bbl. Like Carlos, we used a Holley 4160 marine carb. The linkage for the secondaries is mechanical. Ours switches at around 3500-3600 rpm. W didn't change the cam.. That upgrade netted us around 300-400 rpms. We increased prop pitch from 15" to 17". So hole shot did not improve but top end did (about 5 mph to around 39 mph), and cruise rpms @30 mph were reduced to around 3500 rpm. And yes we have to cruise at around 27 mph min (30 is better) to comfortably stay up there.

A year or two later we did the Vortec head upgrade. Had to get a second new intake (as well as the Vortec heads). used the same Holley 4160 carb & prop. Still no cam change. Hole shot improved and top end increased to around 43 mph @ 4600 rpms.

We're very happy with all that and frankly, if the boat could do 50 mph it might not be stable. 43mph seems pretty fast & one has to slow down for any wake or waves to avoid slamming.

That said, we did it on a 3 year old boat with 80 hrs on the engine. I am not sure doing it on a 16 year old motor is cost effective (you might have some other undetected problems as wel)l. You could buy one of the new engines from someplace like Michigan motors & it would have all those upgrades plus the cam.

Don

[Guest]

I do not know how efficient it will be on a 302.

Wait, this motor is a Ford?? Or was that just a typo and you meant 305?

I did it once on my 2150 Volvo Pinta but just the carb with adapter plate. It diffidently had more power.

This is very inefficient and ineffective. Don't do this.

I'm no expert on the older heads, but twice now I've upgraded boats to 4-barrel carbs and every time I've discussed it with experts the first thing they ask is whether I have Vortec heads, then go on to tell me that's good. So I assume the older heads are simply not going to flow well enough, but I don't know if it completely makes the 4-barrel worthless.

[Guest]

SwampNut wrote:
Wait, this motor is a Ford?? Or was that just a typo and you meant 305?

I did it once on my 2150 Volvo Pinta but just the carb with adapter plate. It diffidently had more power.

This is very inefficient and ineffective. Don't do this.

I'm no expert on the older heads, but twice now I've upgraded boats to 4-barrel carbs and every time I've discussed it with experts the first thing they ask is whether I have Vortec heads, then go on to tell me that's good. So I assume the older heads are simply not going to flow well enough, but I don't know if it completely makes the 4-barrel worthless.

My mistake when I did my swap it was just 4BBl to 4BBl the adapter plate was to fit the Holley. Thus the reason for the thread since I have not done a 2 to 4 swap

[Guest]

hi thear is a adaptor to fit a four barel to a two barel manifold whot the performance would be like would not like to say