2 barrell to 4 barrell on 5.7.....

[mavcar38]

Im thinking about upgrading from a 2 barrell to a 4 barrell on my 98 5.7 merc. Is this worth the money? I dont even know the cfm on my 2 barrell now? What carb and intake should I use if I decide to? Besides using more gas when the secondaries are in use will I get more power and speed? Is this an easy swap, just have to change the intake right? How bought the timing? Im currently at 55-57 at wot. Thanks guys for any help......

 

[MikDee]

Re: 2 barrell to 4 barrell on 5.7.....

Of course you'll get more power, & speed. It is an easy swap. a 4bbl is more efficient, then a 2bbl on a V6, or V8, engine. No need to change the timing.

 

[mavcar38]

Re: 2 barrell to 4 barrell on 5.7.....

Any suggestions on the intake or carb? Cfm size and so forth...I have no clue how big my 2 barrell is now. Thanks

 

[Maclin]

Re: 2 barrell to 4 barrell on 5.7.....

Later versions of the 2bbl 5.7's had a 4bbl intake and used an adapter plate for a 2bbl. You should be able to see this on the engine. If it is that configuration then I would not change out the intake. That would be a real easy swap if you stick to stock stuff.

In any case the fuel line entry point will probably be different, and the linkage usually changes positions as well. If it were me, and you need an intake because yours is only for a 2bbl, then I would try to get the same intake that a 4bbl 5.7 Merc uses rather than aftermarket. If you stick close to stock on the (new) parts then it should work out.

What size boat is this in? I have a heavier (and older) 22 foot cuddy with a 275hp 4bbl 5.7 and it will hit just over 53 at 4600rpm with the higher pitched propset and that is exactly what the prop specs say I should get. If your 55-57 at WOT means 55-57mph then that is pretty good performance already and you may end up causing more problems than it is worth until it gets sorted out (not to mention the downtime), I'm just sayin....

 

[John_S]

Re: 2 barrell to 4 barrell on 5.7.....

If its a mfg '98 5.7L 2brl, it should be vortec head. If it is a '97 in a '98 boat (which is common), probably non-vortec head. Need to know to make sure you get the right intake. Vortec heads have 4 intake bolts per side vs 6 per side on the older standard heads.

In general, you will gain about 30hp over the 2brl. As stated, you have some decent speed now, especially if that is gps measured. If so, you might break 60mph.

I was not aware that merc sold any 4brl manifolds with 2 brl carbs, like Volvo did. Merc does not have a 4brl carb on any of their vortec engines. MPI and TBI, and 2brl carb were the options. It worth a quick visual to verify though.

If you are raw water cooled and boat in salt or brackish water, you wll want a marine specific intake. Either cast-iron, or aluminum with a water jacket liner.

Report back on which heads you have along with cooling and were you boat. We will be able to give specific recommendations from there.

 

[Maclin]

Re: 2 barrell to 4 barrell on 5.7.....

I am probably mixed up between Merc and Volvo on this....

"I was not aware that merc sold any 4brl manifolds with 2 brl carbs, like Volvo did. Merc does not have a 4brl carb on any of their vortec engines. MPI and TBI, and 2brl carb were the options. It worth a quick visual to verify though."

(thanks John)

Just research research research to avoid problems like Imported_John has brought up.


or just enjoy it like it is....but not much chance of that I bet since you already ordered the CC exhaust!