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Old 11-16-2004, 01:52 PM
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Which Carb Should I Choose

I HAVE A CHEVY 350 THAT I HAVE BORED 30 OVER , WITH A 525 LIFT ROLLER CAM, ALUMINUM ROLLER ROCKERS AND SOME TOP LINE PRO IRON HEADS WITH 2.02/ 1.6 VALVES. ALSO ADDED A 142 WEIAND BLOWER. AND INTAKE. MY PROBLEM IS THAT I STILL HAVE THE ORIGINAL HOLLEY 650 CARB. THIS CARB WORKED FINE WITH THE L98 IRON HEADS I HAD BEFORE, BUT I DONT THINK I AM GETTING ALL I CAN OUT OF THE NEW HEADS AND ROLLER ROCKERS. WHAT WOULD YALL RECOMMEND?

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Old 11-16-2004, 02:48 PM
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First off I recommend loosing the caps lock, no need to shout.
I would go with a Barry Grant Demon carb, all you have to do is call them up and they`ll recommend a carb for you. I run a road demon Jr and I`m very satisfied with it. A tech agent for BG is also a member of this site, aka Tech@BG, no other carb company is a member here and that says alot about them, and they try there hardest to make sure the customer gets all the help needed.
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Old 11-16-2004, 05:39 PM
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Thanks, for the info. My pc at work has to be in caps to run this old system we use called reynolds and reynolds. What size would you use though.
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Old 11-16-2004, 06:30 PM
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what carb?

CID X desired rpm divided by 3456 = CFM

example:
352 ( your displacement with 30 over) X 6000 rpm divided by 3456= 611 CFM.

While I prefer Holley carbs, they are all about the same in quality, I think, so your 650 should work quite well once you get it dialed in.
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Old 11-17-2004, 08:19 AM
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even with a 142 blower ontop of the 355ci motor? or should I add that in to the equation.
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Old 11-17-2004, 08:39 AM
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what carb

I would say thats all thats necessary. The formula I gave you is based on 100% efficiency of the engine and with a supercharger youre about as close to 100% as you are going to get.

You will definately need to jet up the carb some, runnning it on top of a huffer, but that is way past my expertice, as Ive never had any experience with running Roots type superchargers. The only experience Ive had was with a Paxton unit on a Ford 302, and we ran a 500 cfm carb with it and it was quite successful.
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Old 11-17-2004, 07:42 PM
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The above formula does not work when it comes to blowers. A blown engine will actually be over 100% VE.

I would probably run an 850CFM Holley blower carb (you might be able the get by with a 750). How many pounds of boost are you running? What kind of compression? You can over carb a blown engine and not suffer from it like you would a N/A engine. When I was building by blown engine, I was told on a 6-71 or 8-71 they wouldn't recommend running anything less that two 750's. If your engine is mild then I would go with a 750 blower carb. You didn't list the cam specs so I don't have that info to help me. I would definetly stick with a Holley or Holley style carb (stay away from the Carter/Edelbrock carbs for blown applications). If your car/engine is a little on the wild side I would suggest even running a 950CFM on it. My engine is only 33ci inches bigger that yours and I have 1500CFM worth of carb, my blower is larger so that makes a big difference too.

My engine is a little on the radical side, I run two Holley 750 DP blower carbs, 12lbs of boost, 8.47:1 compression.

I would also suggest you give www.allcarbs.com a call they have great prices and customer service. They proabably have a carb on the shelf that will fit your needs. See what they suggest.

Royce
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Old 11-17-2004, 07:47 PM
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blower vs turbo

Thanks for jumping in and bailing me out on the carb thing Camaroman.
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Old 11-18-2004, 09:40 AM
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Max Keith,
I just hope the info helps. That is what this board is all about. It's nice when people post back with results (good or bad) that way we all learn from it. If it wasn't a blown engine your recommendation would have been right on the money.

SIRIGGY,
Any info for us?

Royce
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Old 11-18-2004, 02:32 PM
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Man I really appreciate all the info. My engine has a mild cam dont really know the specs off hand but the lift is 525. Does any one have opinions on the Barry Grant carbs? I think I will go with a Road Demon 850. Any opinions? Thanks. I am trying to get my S-10 in the low 10's. Right now it is running 12.2's with the setup and 1 legged 3:08 's in the rear.
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Old 11-18-2004, 07:59 PM
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Barry Grant carbs are fine. I don't know if they have a blower specific version. The reason I like the Holley blower carb is because they have boost referenced power valves. Talk with BG and see what they offer. In any case you are under carb'd. Please let us know how it works out (even if it is 6 months from now).

Royce
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Old 11-18-2004, 09:08 PM
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It never hurts (too much) to over-carb. Slap a 750 double pumper on that dude
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Old 12-02-2004, 09:52 AM
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Over Carb!!!

It can easily hurt too much to over carb an engine. Carburetors work based upon the air velocity (pressure difference) drawn through them. Going with too large of a carburetor for an application can cause the engine to run rich at idle, and part throttle and lean at wide open throttle.

On a blown application you will want to use a carburetor that has been calibrated, and boost referenced for the blower. We've been setting carburetors up like this for over a decade.

Without knowing more specific information about the combination it would be impossible to make an accurate recommendation, but depending on the rest of your information we'd use either a 650 or 750 Blower Calibrated Mighty Demon carburetor.
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Old 12-02-2004, 01:52 PM
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The old formula for carbs raises its pretty little head again. It is used as a baseline, only. This subject has come up a hundred times, and it comes down to the same question: What is the intent of the motor?

Look HERE to see where actual testing was done with a NA 383 stroker. The end of the article states:

"Judging from the test results, we'd say that the 750-cfm carburetor seemed to provide the best power curve and throttle response. In the event that the engine made 50 hp or more and was dedicated for racing, we'd be willing to say that the 830-cfm piece with down-leg boosters might add a few extra horsepower and still be livable on the street."

This article has shown that with this particular engine combo that you could go with an 830 cfm, TUNE IT PROPERLY, and it could live on the street.
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Old 12-02-2004, 02:15 PM
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Dyno Testing vs. the real world

The problem with this type of test, is it doesn't take into consideration what will happen in the real world. They don't show you the acceleration rates to be able to determine how the HP will be used in the vehicle. Installing the same engine in a 2000 lb kit car vs. a 6000 lb truck would use a different carburetor to get optimal performance.
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