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Old 02-17-2004, 01:40 AM
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too much cfm?

ok, im still looking into buying a carb for my 305, i want to get a Barry Grant, i emailed them and asked what would be the best carb for my application they suggested the speed demon 575 but the road demon 625 should work fine also but not as good as the speed demon. now this is my big question, what would running a 650 speed demon do to my 305? i know its too big. the reason i want this carb is because i have a 350 that will eventually go in my car in a year or maybe 2 after i do a mild performance build up on it, it may even become a 383, and i would need the extra cfm for that engine. plus the 575 and the 650 are the same price. to turn my question around, how would the 575 speed demon perform on a mild performance 350 or 383?

thanks very much.

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Old 02-17-2004, 01:49 AM
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Get the 650, it may not be as bad as you think on the 5.0L.
plus thats one less thing you will have to buy for the 350/383.



Shane.
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Old 02-17-2004, 01:53 AM
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Use an 1850, 600 cfm vac. sec carb until you build your bigger engine. You can get them for $20 sometimes on Ebay.

By that time there may be more BGs on Ebay for cheap.
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Old 02-17-2004, 04:00 PM
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would i have to rebuild it? and how would it perform?
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Old 02-17-2004, 04:05 PM
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The smaller carb would be a more responsive carb on your engine.
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Old 02-17-2004, 05:15 PM
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I've used both a 600 holley and edelbrock on my 305. I've found that the holley carbs tend to have better fow velocity and better low end torque. There are a bunch of rumors about tuning with holleys, but I think that's old news, I tuned it once and it works great. The edelbrock, don't get me wrong here, is a good carb too. Great bolt on and go carb. You could probably use the 625, it wouldn't hurt your performance too much.

K
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Old 02-17-2004, 06:00 PM
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thanks killerformula. what about the 650 speed demon? would that be too much? and would the 575 be too little for a mild 350 or 383?
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Old 02-17-2004, 06:46 PM
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the 575 is def. to small for a 383 my buddy runs a holley 750 and it runs mint . but think about the weight of your car also. and stall speed. he runs a 3000 stall .
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Old 02-17-2004, 06:52 PM
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Super Chevy- If you are going to build a 350 the 650cfm Speed Demon is probably a real good choice. It is what I am using on my biult 383 and it is a perfect fit for me as I want it to perform well on the street but I do not intend on racing it. You'll want to factor in stuff like manifold style, cam lift and duration, compression ratio, valve size and also what you intend to do with the car when the engine is built. Will you be racing it every now and again or do you want good street performance? A 650 cfm Street Demon will be too much carb for a stock 305. You could detune it to a degree but it would probably be better to buy something a little milder for your current 305 if you intend on driving it hard. Talk to the guys in the tech department at BG, Edelbrock and Holley for good advice. These guys really know the applications. Mike
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Old 02-17-2004, 07:23 PM
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Quote:
Originally posted by johns79ta
the 575 is def. to small for a 383 my buddy runs a holley 750 and it runs mint . but think about the weight of your car also. and stall speed. he runs a 3000 stall .
my car weighs around 3400lbs and its a 4 speed.

Quote:
Originally posted by mike bryan
Super Chevy- If you are going to build a 350 the 650cfm Speed Demon is probably a real good choice. It is what I am using on my biult 383 and it is a perfect fit for me as I want it to perform well on the street but I do not intend on racing it. You'll want to factor in stuff like manifold style, cam lift and duration, compression ratio, valve size and also what you intend to do with the car when the engine is built. Will you be racing it every now and again or do you want good street performance? A 650 cfm Street Demon will be too much carb for a stock 305. You could detune it to a degree but it would probably be better to buy something a little milder for your current 305 if you intend on driving it hard. Talk to the guys in the tech department at BG, Edelbrock and Holley for good advice. These guys really know the applications. Mike
i will be racing it every now and then but its also gonna be daily driven in the summer. as of right now my future 350 or 383 is still a dream. i haven't started collecting parts and i don't know what parts im even gonna use (diff companies etc...). my main focus right now is to just get the car on the road. my 305 has a mild cam, edelbrock performer eps intake, ho heads, long tube 1 5/8" headers, so it isn't totally stock. i have talked to the guys at bg and they told me to either go with the 575 speed demon for higher performance or the 625 road demon for better drivability. i just really want to buy the right carb once. how do u think the 625 road demon would perform on a mild 350 or 383?


thanks for all the help guys
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Last edited by Super Chevy; 02-17-2004 at 07:23 PM.
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Old 02-17-2004, 07:39 PM
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575 or 650 Speed Demon

Super Chevy,

The Road Demon series carburetors are designed for engines with a maximum cam duration of 220 degrees @ .050". For what you're doing the Speed Demon series carburetors will give you much better overall performance.

You've got two options as far as the Speed Demons go. You can use a 575, and send it back to the factory to be converted into a 650 (for about $50) when you switch engine packages. or You can use the 650 Speed Demon, and install a 4-Hole carburetor spacer betwen the carb and intake on the 305 to help make up for the fact that the carburetor is a touch too big for the small engine.
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Old 02-17-2004, 07:46 PM
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Re: 575 or 650 Speed Demon

Quote:
Originally posted by Tech @ BG
Super Chevy,

The Road Demon series carburetors are designed for engines with a maximum cam duration of 220 degrees @ .050". For what you're doing the Speed Demon series carburetors will give you much better overall performance.

You've got two options as far as the Speed Demons go. You can use a 575, and send it back to the factory to be converted into a 650 (for about $50) when you switch engine packages. or You can use the 650 Speed Demon, and install a 4-Hole carburetor spacer betwen the carb and intake on the 305 to help make up for the fact that the carburetor is a touch too big for the small engine.
Thank you very much! that should work out perfect, i am glad we have someone like you on this forum! now i have 2 more questions for you and then im done. 1) what would you do? get the carb converted or use the space? and 2) what size spacer would i use if i did choose that route?

thanks again, you made my day.
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Old 02-18-2004, 07:34 AM
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575 or 650

Either way will acomplish the same results. The first criteria for what I would do, would depend on a few things. First does your engine compartment have enough room to install a 4-hole spacer between the carburetor and intake manifold, and second how long into you're realistically going to change engines. If you're going to change engines by the end of the year, and your have the room for at least a 1" spacer I'd go with the bigger carb. If not I'd stay with the smaller carb until the new engine is ready to go in. As with most projects that are that far off what we plan, and what we end up with are usually different.
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Old 02-18-2004, 03:57 PM
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the engine is probly gonna stay in for over a year, unless something happens to it. i also dont think i couls fit anything over a 1" spacer anyway, so i think ill just get the 575 and have it converted when the time comes.

thanks for your help.
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