600 cfm on a 3.0 merc

[sippi]

I want to replace my old ragged out carbatooter with a new one. When I got online to see how much they are I coundnt believe that it is over $500 bucks for the original two barrel(as soon as you put marine in front of the name the price seems to double)not that I would run a none marine carburator or anything ...but dang thats a lot for simple little 2 barrel!
So anyhow I am thinking of maybe trying to run a edelbrock 600cfm marine with a 2 to 4 barrel converter plate and 2" riser, any of you guys ever try somthing like that ? The factory carb is 500cfm I believe and I have just had the motor rebuilt with a comp cam kit so I think it might work!

 

[deerslayer303]

Re: 600 cfm on a 3.0 merc

I have alot of experience with carbs from drag racing, I think you will probably be alright, worse case you might have to drop a jet size. Now I've seen dyno charts from engines with adapter plates on the intake like you are talking about, the plates are just not that efficient. But you probably wont notice it much on your boat. Us drag racers try to wring out every last stinking pony. lol

 

[Polar_Bus]

Re: 600 cfm on a 3.0 merc

I want to replace my old ragged out carbatooter with a new one. When I got online to see how much they are I coundnt believe that it is over $500 bucks for the original two barrel(as soon as you put marine in front of the name the price seems to double)not that I would run a none marine carburator or anything ...but dang thats a lot for simple little 2 barrel!
So anyhow I am thinking of maybe trying to run a edelbrock 600cfm marine with a 2 to 4 barrel converter plate and 2" riser, any of you guys ever try somthing like that ? The factory carb is 500cfm I believe and I have just had the motor rebuilt with a comp cam kit so I think it might work!

I would not put that carb on a 3.0L engine. A 600cfm 4V on a 181CID engine is WAY over carbing. Your engine at WOT only requires about 210 CFM . You will never get that engine to run clean nor will you ever get reasonable fuel efficiency. It's better to slightly "under carb" than "over carb" in most normal engine situations..

 

[CharlieB]

Re: 600 cfm on a 3.0 merc

Over carbing a motor isn't recommended.

The reduced air speed thru the carb requires LARGER jets to compensate for the reduced pressure differential across the venturi, thus larger fuel droplets, poorer atomization, less efficient combustion. Poorer performance.

A smaller carb increases air speed, better fuel mixture, yada, yada, yada.

Marine engine performance is a careful balancing act to achieve best engine performance throughout the operating range of the motor.

While it may be possible that a larger carb could give more HP at WOT, HOWEVER, the power LOST at lower RPM may not allow the boat to accelerate and possibly not even get to the higher RPM.

 

[Phantom_II]

Re: 600 cfm on a 3.0 merc

I've never tried them myself, but you might want to look into http://www.marinecarburetor.com for a rebuild or have them rebuild your old carb.
Their prices are about half of what you mentioned.

 

[Don S]

Re: 600 cfm on a 3.0 merc

I have just had the motor rebuilt with a comp cam kit

For some reason I have this feeling we are going to hear from you again, about water in the cylinders due to reversion.

 

[MikDee]

Re: 600 cfm on a 3.0 merc

IMO, If you already put a comp cam in the motor, it should perform better with the stock carb. There's no reason to put a carb that large on that motor, you'll just lose all your low end torque, & response, for maybe just a little improvement at top end.

 

[sippi]

Re: 600 cfm on a 3.0 merc

Thank you all for your input. I never really thought about the air speed thing before on a carburator but I wouild think if the secondaries are closed the air speed at idle would still be the same.
Mr Don S. ??? exacty what is this reversion thing you speak of ???? Do I need to run they exaust out the back above the water line???...........Your scaring me

 

[Tail_Gunner]

Re: 600 cfm on a 3.0 merc

Reversion is a product of all engine's..it's just that in marine engine's it's very bad or can be. Simply said using a cam with with some valve overlap creates a mech situation where both the intake and exhaust valve are open at the same time...and it just so happens that your piston is now on the down stroke....That creates a temporary vacum in the exhaust stream and yes water get's sucked back in the engine. Small amounts but when a motor is running at idle there are a lot of those pulses going on.

In marine motor's or cam's there is a mininal if any valve overlap. I will post a pic of the exhaust chamber and cooling system it is all in one design..Now you can buy a dry system..but i doubt is there is one made for a 4cyl...i couldnt find one for the 4.3...but you can build one.. But that will take a few weeks of research..It's really quite simple when your all done.

 

[sippi]

Re: 600 cfm on a 3.0 merc

Wow! the cam I put in the motor is recommended for marine applications so I am hopeing I won't have to worry about it sucking water.
Hmmmm ....not sure if I need to worry about a new carburater or a new exhuast system at this point!

 

[MikDee]

Re: 600 cfm on a 3.0 merc

Sippi, Clean up your old carb, get your boat going, get the motor broken in, and see how it goes, you probably won't even need that big carb

By the way, I'm curious about that marine cam, where you got it? and the specs?
And, I'm interested to know how you make out with that Mighty Mouse sewing machine motor! Keep us posted

 

[Gary H NC]

Re: 600 cfm on a 3.0 merc

If you decide to replace the carb try these guys...i have always got great service from them...about half the price too..

http://marinecarburetor.com/?gclid=CJq99rvutpoCFQIwxwod1xgVvA

 

[sippi]

Re: 600 cfm on a 3.0 merc

I talked to the motor builder about a posable reversion problem and he assures me that as long as the lobecenters are no closer than 110 degrees I won't have to worry about it.
I was thinking of going to the redline carb from weber, until I looked at the website Gary posted "Gary thankyou sir!" that looks alot more resonable and "plug N play" is always more fun!!
The only after maket stuff I have done is the cam kit(cam,lifters,valvesprings,retainers) SS valves ,and roller tipped rockers.
I wasn't trying to build a hotrod four banger or anything I just figured I would go see what kind of after market stuff was out thier.
Here is a link to the cam specs
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=54&sb=2

 

[Kovah55]

Re: 600 cfm on a 3.0 merc

260 dollars on e-bay right now for a carb. New. No reason not to try to rebuild the one you have now. I think the real reason you want to go with a bigger carb is speed, and trying to get more hp out of the motor. Ain't gonna happen.

What will happen is what MR. Don S posted. That motor builder you using, he does marine motors ? He also suggest to put a high recovery oil pump in also ?

What will happen if you do, you will suck the pan dry and blow up the motor !

Do what you want. your gonna anyway. I'm new here but have been reading this, and other forums for a long time, we will see you back here again, or on another forum, asking how to fix what you did now.

 

[MikDee]

Re: 600 cfm on a 3.0 merc

I talked to the motor builder about a posable reversion problem and he assures me that as long as the lobecenters are no closer than 110 degrees I won't have to worry about it.
I was thinking of going to the redline carb from weber, until I looked at the website Gary posted "Gary thankyou sir!" that looks alot more resonable and "plug N play" is always more fun!!
The only after maket stuff I have done is the cam kit(cam,lifters,valvesprings,retainers) SS valves ,and roller tipped rockers.
I wasn't trying to build a hotrod four banger or anything I just figured I would go see what kind of after market stuff was out thier.
Here is a link to the cam specs
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=54&sb=2

Hey, That is a NICE Cam! That should really bring that 4 banger to life, without over doing it! With specs like that, it is similar to having a truck cam in a V6, or V8. I hope you didn't over do it by changing the stock rocker ratio on those roller tipped rockers??? Anyway, Be sure to break it in right, and let us know how it goes.

 

[sippi]

Re: 600 cfm on a 3.0 merc

The rockers 1.7 and the stock ones were 1.75 so the lift will still be slightly bigger and the duration will be slightly longer than the stock configuration. I am just trying make the thing run a little more efficient maybe last a little longer.
I am definatly going with the stock rebuild for the carb! Now all I have to do is get the motor back in the boat!
And no I am not running a high volume or high pressure oil pump

 

[MikDee]

Re: 600 cfm on a 3.0 merc

The rockers 1.7 and the stock ones were 1.75 so the lift will still be slightly bigger and the duration will be slightly longer than the stock configuration.

What? That's less lift then the stock rockers??? Meaning you'll have less lift, & duration then if you had the stock rockers

 

[sippi]

Re: 600 cfm on a 3.0 merc

The duration will be the same as advertised but the lift will be about 6 to 8 thou less than advertise. Whitch is still more than the stock cam

 

[MikDee]

Re: 600 cfm on a 3.0 merc

So be it

 

[MikDee]

Re: 600 cfm on a 3.0 merc

Hey Man, How are you doin? I'm real curious as to how that camshaft is working out?