Carb issues
 

I took my new 496's (stroked 454's) to the dyno and had trouble with the 750 Holley's (4010). First the idle and starting is crap... it was this way when they were 454's but I thought we could tune them better when hooked up to an EKG... nope! We hooked up a carb they had laying around (850 Holley) and it purred like an angry kitten. Started up without having to pump it several times... AND pulled 25 more HP. The best CFM i got from the 750 was 715 while the 850 let it pull in 757 cfm (both at 5800).

So I'm now hunting new carbs. I decided to read everything there is about carbs here on oso and started my search with ProSystems and Barry Grant.... and just like e v e r y t h i n g else there are 10 different answers for 10 different questions. BG tells me I MUST use annular boosters, PS tells me I MUST use Dog Leg Boosters because I have big cubes with a dual plane intake (Edelbrock RPM). PS says they wet flow their carbs to match my engine needs, BG says run from anyone that claims they can tune your carb off the engine.

All I want is a carb that after the first start of the day, will start at the flip of a switch (without pumping and pumping and holding your face just right). One that will ease into the throttle without stumbling and dieing or catching and snapping necks (or parts).

Here are the specs I gave them... can I get some opinions which carbs to get please? I'm dizzy.

Vehicle Weight: 34' scarab heavy
Engine Cubic Inches: 496 twin
Compression Ratio: 9.3
Intake Manifold Brand: Edelbrock RPM
Cylinder Head Type: Chevy 049 ported
Intake Valve Diameter: 2.19
Exhaust Valve Diameter: 1.88
Engine HP (or Estimate): 530
Fuel Type: 93
Fuel Pump: Mechanical
Fuel Pump GPH rating: 130?
Type of Camshaft: Hydraulic Roller Lifters
Camshaft - Intake Duration @ .050: 228
Camshaft - Exhaust Duration @ .050: 238
Camshaft - Intake Lift at valve: .585
Camshaft - Exhaust Lift at Valve: .612
Lobe Separation: 112

454 Mags....

I have Barry Grant 850s and they are awesome. They fire instantly, hold steady idle instantly even when cold. Zero hesitation. Never load up. I can idle at no wake zone speeds for hours on end without issue. The throttle response is rediculous. They are coupled with BG electric fuel pumps.

Very happy with the entire set-up.

http://i209.photobucket.com/albums/b...t/IMG_0045.jpg

Thanks! love real world input!!

Did you get the Speed Demon or Mighty Demon? BG told me the mighty demon would be too rich for my idle?

Honestly, I don't know. They were installed by the previous owner. My metering blocks do not say 'Demon' on them like most BG carbs do. These are circa-'96 or so. I just had them rebuilt with BG Master kits this spring. I don't think they needed it, but I did it anyway.

If I make it to the boat this weekend I would be more than happy to get the serial #s off them so BG can identify exactly what they are.

Holley 800cfm carbs, just like what is used on the HP500, should work just for what you have. Your engine specs are fairly close to the HP500 specs.

Patrick @ Pro Systems is a DAYUM good carb guy!!! We have two from him the gas works PERFECT........ the alky not as good.

Another good carb guy Willy Krup http://www.willyscarbs.com/
We have had prolly over 10 Willy's carbs thru the years and NEVER had a problem BUT he is EXPENSIVE.

Pro systems is prolly the best bang for buck JMHO:drink:

I agree with Griff....Buy a new set of Holley 9022's...they are 800 cfm carbs. Easy to work on...easy to tune...and they are pretty close right outta the box. Your gonna spend way more cabbage buying from the other guys, and the few hp you MIGHT get, you wont feel. Merc used them on the HP500...so I think you can trust their judgement. :drink:

Thanks guys!

I was happy with the results of the 850 at the Dyno... it idled very nicely with a very crisp response. I think the Holley 9022 is the smart choice, with tons of user base. But to be honest I'm leaning towards the BG Mighty Demon Marine 825. It's not that much more than a 9022. Stupid mistake??

The BG 825 should work fine as well.

I used Quick Fuel 950's on my 496's. Very nice pieces and work great. I dumped the old 800's for these, mine were also junk. They will install J tubes on request.
BC