Which carb what to do

badbowtie

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May 18, 2007
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I have a 85 wellcraft with a built gm 350 in it. It has bored out and I installed a very mild marine cam. It has a Edelbrock carb 1405 It is only a 600 cfm carb.
I am thinking about putting a bigger carb on it. I know years ago I had a stock 350 car and it ran 2 seconds quicker when I went from a 600 cfm two a 750 cfm
carb. I am thinking of the Edelbrock 1410 but am open two other suggestions.
 

180shabah

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Re: Which carb what to do

First things first,

GET RID OF THAT 1405 before you kill yourself or others, it is not a marine carb.

I doubt you need any more than 600CFM (which would be the 1409, marine version) on your engine, even with the cam upgrade. As for the 2 second increase on your car, there are too many variables to make a valid comparison.
 

John_S

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Re: Which carb what to do

Yep, get the 1409. It will fit your plumbing and throttle with no changes. It will be jetted for the SBC. The edelbrock 750 marine is jetted for BBC and you will have to change it. Under 5K rpms, you wont use all of the 600cfm.
 

Bondo

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Re: Which carb what to do

Ayuh,.......... a 750 is Too Big.........

You'll be more apt to Loose power, than Gain Anything.......
 

SuperNova

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Re: Which carb what to do

If you are running a 350 with a dual-plane intake you can easily run a 750 because each cylinder is only able to draw off half the carb at any given time, unless you run a carb spacer. Most rochester q-jets are 780 cfm and up to almost 900 cfm on some of the big blocks. As far a jetting goes, all carbs are jetted for airflow, not engine size. Some retuning can definitely optimize them for any particular application, but that is a trial and error kind of thing. The only thing you may notice is some loss of very low rpm response and a little poorer fuel mileage, but I even doubt that will be noticeable and if it is it'll be because the 600 was restricting airflow into the engine so badly. Less airflow= less fuel flow. Just my .02. Just make sure it is a marine carb.
--
Stan
 

badbowtie

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Re: Which carb what to do

I know I have to get rid of the auto carb That is why I am here so you guys are suggesting stay with edelbrock and I do have a dual plane edelbrock intake.
 

Coors

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Re: Which carb what to do

Any marine spreadbore with vacuum secondarys is hard to beat.
Hard to beat one one a car, too, unless full-bore wide open, with the cam ready to install the charge, and not idle under 2000rpm.
 

Bondo

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Re: Which carb what to do

Ayuh,......

Not to start Another P!ssing Match,.......
But,.....
If you Do the Math,....... A 350 can only move alittle over 500cfms at 5000rpms........
Going to a 750cfm will just cause a loss of vacuum signal at lower rpms......
The only thing you may notice is some loss of very low rpm response and a little poorer fuel mileage,

And That's reason enough for Me to stick with the 600/650cfm carbs on a 350....
Even a Chevy 400cid would be hard pressed to use That Much Carb........

Btw,....... The Rochester Carb is a horse of a different breed,..... And Not a Good Comparison....
 

SuperNova

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Re: Which carb what to do

You are absolutely right bondo, but the equation doesn't take into account the type of manifold used or whether or not there is a spacer plate in use and if there is a spacer plate is it open plenum or divided into halves or is it four separate bores? I think it assumes an open plenum or single plane type manifold where the engine draws off both sides of the carb. My belief is if you are running a divided plenum, then each cylinder can only draw off half the carb -one primary bore and one secondary bore- and therefore can stand a little larger carb than an engine with a single plane intake or a large,open spacer.

I also agree that I don't want to start a pissing contest. All I want is a discussion and a presentation of ideas or theories. That is after all, how information is exchanged and upgraded. I don't come on here to start arguements, either.

P.S. I also run 600-650 cfm carbs on my marine 350's, for the same reasons as you. The extra bottom end punch and the increased fuel efficiency.

--
Stan
 

Bondo

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Re: Which carb what to do

I'll buy that Nova,.....

But,........

Marine Motors are generally Choked by their Exhaust Systems,.........

Trying to pump in more air, Just Ain't gonna Happen, by adding a Bigger Carb.........

There aren't many of Us willing to drop a Few Thousand Bucks on True Headers..........

Which brings Us back to the Fact that the 600/650cfm Carb is the Best Bet for a SBC.........
 

SuperNova

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Re: Which carb what to do

You're right about the exhaust for sure!lol. He didn't say what he was running exhaust-wise and I didn't think to take that into account! Can't draw it in if you can't push it out.
--
Stan
 

John_S

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Jun 21, 2004
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Re: Which carb what to do

Personally, I think the dual plane manifold info is reverse of that, but thats just me.

No normally asperated intake manifold will get above 100% Volumetric Efficiency. A 355 at 5K w/100% VE is still only 514cfm.
 
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