Corbs

What carb will work best for a N/A 540 with a Dart intake. Will be propping for WOT at 5800 RPM. I plan on using a Holley 830 CFM (Part No. 0-9381) but am now concerned it may not be big enough. Does this 830 actually flow 830 CFM or something less. Thanks for your input.

Vinny P

I would suggest talking to Nickerson. They set me up with a worked 1050 for my NA 540. It has been flawless so far.

Wobble

The sea demon by BG is rated at wet flow so it should have a higher dry flow than other carbs that are rated by dry flow. "Rumrunner" here on oso is head of technical services for BG and could help you spec the right carb for your motor. The sea demons are CG approved which should be a consideration also.

I don't know if they make a marine dominator type carb. They do make a 850 though, available on Jegs I think

SB

Corbs - please give us details about the rest of the build up. This will give us a better idea of what your engine will require for airflow.

razor1115

Basic rule of thumb for dry flow:

cu. in. X max rpm X vol. eff. / 3456 = cfm

in your case 540 x 5800 x 1.00 (assumption and it's hard to get to here)/ 3456 = 906.25 cfm.

You may want to look at a 950HP from Holley if it can be marinized. Someone else may have some insight on a re-worked carb to acieve the flow numbers you are needing. I ran the 950HP on my N/A 540 with no issues.

Zack

HARDCORE A/O

I would say the best all around performance and C.G. certified carb for your application (at a reasonable price) would be a 850 Mighty Demon Marine. You can also get this carb w/ annular discharge boosters. I have one of the annular booster versions that I used on my 509 and it ran flawlessly out of the box. The Annular boosters produce a much stronger booster signal at low RPM/ heavy-load situations and this is just the ticket for smooth planing and better off-idle acceleration, in my view.
I intend to use this carb on my new 540 for N/A use. All Barry Grant / Demon carbs are wet-flowed (which is how a carb actually flows air, isn't it?) and so this would compare to a larger Holley carb, as Holley uses the dry flow formula that Razor posted above.
A really neat feature on these carbs is the EZ-Idle idle-air adjustment which allows for idle speed adjustment without have to move the throttle plates around which tends to expose too much of the idle slot. The carb comes with an instructional DVD and clear simple written instructions as well. You can get one from Jegs for around $550.00 (if my memory is correct).
BTW: If you were running a Holley before you will need to order a new fuel inlet line/fittings which are I believe a 9/16x24 thread (check w/ a sales rep to be sure).
I like these Mighty Demon carbs so much that I now have three of them, a 750 General Competition version, an 800 Annular Blow Thru (for my Procharger setup) and the 850 Annular Marine Version.
Just my 2 cents. Hope this helps you make a decison. Good luck.

DrNautica

I run a highly customized 540 (bowtie based block) at 5750-5800 RPM and use a Barry Grant (Demon) 1000 CFM Drag Race carb. It has been absolutely flawless. Other than minor rejetting and power valve change by my builder, it is stock. I also use a 1" phenolic spacer on a Brodix HVH single plane intake. This motor makes 686 HP naturally aspirated.

KAAMA

About 5 years ago I had my 540cid engine with Dart intake on Tom Earhart's dyno with an 830cfm HP Series Holley carb with annular discharge and a hydraulic roller cam. I specifically remember Tom saying to me that in all the 25+ years of dyno testing engines he has never seen a carb "follow" as well on a naturally aspirated engine as what mine did on that day. "Follow" meaning the power curve was extremely good for the application and usable RPM range my engine was being used for. Heck, I have heard of some guys using a Holley 800cfm on a 540cid marine engine with excellent results!

BUT, we did run a 950hp Holley bact to back vs the 830hp just for comparison. Didn't really see a noticable difference until about 5400rpm. Here's the diff in HP/TQ we experienced...

RPM
3000 592TQ 338HP 830cfm
3000 614TQ 351HP 950cfm

3500 598TQ 398HP 830cfm
3500 598TQ 399HP 950cfm

4000 662TQ 504HP 830cfm
4000 662TQ 504HP 950cfm

4500 694TQ 594HP 830cfm
4500 692TQ 593HP 950cfm

5000 688TQ 655HP 830cfm
5000 684TQ 651HP 950cfm

5250 664TQ 664HP 830cfm
5250 658TQ 658HP 950cfm

5400 646TQ 664HP 830cfm
5400 655TQ 673HP 950cfm

5500 636TQ 666HP 830cfm
5500 651TQ 682HP 950cfm

SB

'Too small' a carb will start to go rich when it starts becoming a sizeable restriction. If you jet for top end a/f ratios, then the low/mid rpm will be too lean.

'Too big' a carb will not have enough airspeed thru the boosters at low rpm to pull enough fuel. Thus, low speed will be lean and unpredictable. If jetted larger for low rpm to give proper a/f ratios, the top end (now having proper air speed) will go far rich.

So, this can be quite a balancing act, especially with out of the box carbs.

Enter modifiers like Nickerson, Quick Fuel, etc,etc,etc. They'll try to shape the fuel curve ie: a/f ratio to be correct for all load + rpms.

Now, with a 540cid and small plenum intake (like 4150 Dart) airspeed really isn't a problem at all with low rpm's . The Dart intake, cyl heads (assuming atleast decent one's), rpm's, and very large cid's will want massive amounts of airflow at higher rpm's.

Enter the reason / need for a good quality transitional piece between this type of motor and a Dominator carburetor. Here's HVH's 4500-4150 Super Sucker made for this.

or 'Funnel Ram Intake' by Reher Morrison that ports both a spacer/adapter along with an intake manifold. Manifold choices are 4150 Dart or Vic Jr.



Here's an extreme example: many SBC's in the 434 to 454cid range create enough air speed at idle/low rpm/mid rpm's that these now too can benefit from the use of a Dominator. No, not just high winding one's.

Pressure drop should be looked at also - not just carb rated cfm, especially since most carb manufacturers, tuners, modifiers, don't test them (some don't even test them ) the same.

A/F ratios all across the load / rpm graphs can be more important than the cfm . However, if we can get both correct we got a winner.

mrhorsepower1

The 830 Holley will most likely make more power on your combo Steve. I just wish we had more hatch clearence. Getting closer to getting it together bro! Lifters showed this morning and will be assembling top end today.

Dean