2bbl to 4bbl...

[John_S]

Re: 2bbl to 4bbl...

thats exactly the question i was wondering, thank you. its alot cheaper just buying a 4 barrel, than buying a carb and intke. wish you knew the exact thread for that swap. i think the merc manual shows going from 210hp to 260hp, thats alot i think. ours is a merc

I missed the 5.7L in your earlier post, since this thread was on 4.3L, jumped over that. If you have the standard head 5.7L 2brl it is rated at 210hp @ prop. Going to a 4brl will get you 240-250hp @ prop.

I'd recommend a bigger jump, by changing to vortec heads. The heads and 4brl will put you at 280hp @ prop. I made these exact change, a few years ago.

If you want to discuss in detail, recommend starting your own thread.

 

[jkust]

Re: 2bbl to 4bbl...

I missed the 5.7L in your earlier post, since this thread was on 4.3L, jumped over that. If you have the standard head 5.7L 2brl it is rated at 210hp @ prop. Going to a 4brl will get you 240-250hp @ prop.

I'd recommend a bigger jump, by changing to vortec heads. The heads and 4brl will put you at 280hp @ prop. I made these exact change, a few years ago.

If you want to discuss in detail, recommend starting your own thread.

If Dvandsm's 5.7 is a 1997 it will have vortec heads already. If you can find the article I mentioned it talks about the procedure as well as the results.

 

[John_S]

Re: 2bbl to 4bbl...

If Dvandsm's 5.7 is a 1997 it will have vortec heads already. If you can find the article I mentioned it talks about the procedure as well as the results.

In'96 and '97 merc offered both heads, but 2brl was only standard head. Vortecs had "gen+" in name. In '98 merc had all vortec head sbc offerings. But, a '98 boat can easily have a '97 engine. It is easy to check which heads, anyway.

I am familiar with the article but it appears to have been removed from its original source.

 

[jkust]

Re: 2bbl to 4bbl...

In'96 and '97 merc offered both heads, but 2brl was only standard head. Vortecs had "gen+" in name. In '98 merc had all vortec head sbc offerings. But, a '98 boat can easily have a '97 engine. It is easy to check which heads, anyway.

I am familiar with the article but it appears to have been removed from its original source.

Thanks imported_John, I always thought it was 96 that could go either way and assuming his 97 has a 97 engine, he was safe. Didn't realize any non- vortecs made it into the 97 model year line-up (meaning not a nos non-vortec 96). What ever year it is Vortec is pretty clearly marked.

 

[Aloysius]

Re: 2bbl to 4bbl...

Heads with the vortec combustion chambers require less total timing advance because the flame front spreads faster.

 

[John_S]

Re: 2bbl to 4bbl...

Heads with the vortec combustion chambers require less total timing advance because the flame front spreads faster.

The 5.7L 2brl has a very mild base timing curve, not like the LX and 350 Mag. About 32 degrees total advance. Nothing to worry about with going to vortec heads.

 

[Aloysius]

Re: 2bbl to 4bbl...

That's perfect for a vortec! good call.

 

[John_S]

Re: 2bbl to 4bbl...

Even the LX and MAG are only another 2 degrees wot advance. On those models with T5's they have a knock sensor to retard timing if it does become too much. It was a concern of mine when doing the intial reasearch. I saw some volvo 350 vortec timing curves, and they were basicly the sane as old LX.

My conclusion was, even though the vortec head info indicates not as much timing needed, most stock boats were already conservative enough. If this was a performance car, you might have to dial it back a coupe/few degrees.

 

[Aloysius]

Re: 2bbl to 4bbl...

The automotive system for vortecs will allow over 40 degrees total advance, depending where you are on the map. Older Chevy performance curves would often go to 38 degrees. I hold vortec stuff to 32 degrees or so.

Often the curve used is a default ignition curve used in "limp" mode.