500 cfm carb too little?
Thread Starter
Racer
Joined: Jan 2002
Posts: 488
Likes: 0
From: Woodstock GA
500 cfm carb too little?
Hey one of the guys at Jeg's is telling me that their 500 cfm Edelbrock carb is better for my vette- it's set for 'performance' rather than fuel economy- than the 600 cfm Edelbrock.
I've got a mild crate 350 with headers, duals, and flowmasters- and getting a Edelbrock performer intake to go with a new carb. :-)
So what gives? This dude on the wacky tobacy or is he telling me straight?
Thanks!
I've got a mild crate 350 with headers, duals, and flowmasters- and getting a Edelbrock performer intake to go with a new carb. :-)
So what gives? This dude on the wacky tobacy or is he telling me straight?
Thanks!
Drifting
Joined: Nov 2003
Posts: 1,410
Likes: 0
From: chicago IL
Re: 500 cfm carb too little? (Tom73)
500 cfm, what is he talking about 
, if i were you i would go get myself a brand new 650 cfm speed demon, i have one and i LOVE IT, it looks cool 
, runs great, easy to modify, and is very reliable. Just my .02 
, if i were you i would go get myself a brand new 650 cfm speed demon, i have one and i LOVE IT, it looks cool , runs great, easy to modify, and is very reliable. Just my .02
Thread Starter
Racer
Joined: Jan 2002
Posts: 488
Likes: 0
From: Woodstock GA
Re: 500 cfm carb too little? (killervette666)
Mechanic says that the Qjet won't fit under the hood with Edelbrock intake. The Qjet had been giving me problems, so I was going to get a new Edelbrock carb to go with it...
The stock QJet is a 750 cfm carb? Get out! Really?
Anything I need to get to with a speed demon to fit an Edelbrock Performer intake?
The stock QJet is a 750 cfm carb? Get out! Really?
Anything I need to get to with a speed demon to fit an Edelbrock Performer intake?
Drifting
Joined: Nov 2003
Posts: 1,410
Likes: 0
From: chicago IL
Re: 500 cfm carb too little? (Captain_Kaboom)
I have a speed demon 650 with a performer RPM intake, all under a stock 79 l-48 hood, all you need is a drop base air cleaner, you can find them at your local pep boys, at least i did, they look cooler, and will let you run that setup no problem. The only other problem i had was that with the speed demon you need a dual inlet fuel line for the fuel bowls, and i dont know how the egr is setup on the performer intake, but on my stock intake the line wouldnt fit and would run into the egr and the coolant line to the heater. Thats is why i decided to get the performer rpm, no emmisons c*ap and lets me run the carb the way i want to, if you know of another way to run a speed demon feel free to chime in, i use a mr gasket dual inlet line with fuel pressure gauge built in.
Race Director
Joined: Apr 1999
Posts: 15,156
Likes: 477
From: NM
Re: 500 cfm carb too little? (Captain_Kaboom)
Mechanic says that the Qjet won't fit under the hood with Edelbrock intake. The Qjet had been giving me problems, so I was going to get a new Edelbrock carb to go with it...
The stock QJet is a 750 cfm carb? Get out! Really?
The stock QJet is a 750 cfm carb? Get out! Really?
All Q-Jets used on the Vettes can flow 750 cfm, but due to the design it will flow whatever you engine can handle but not more. So if you can just used 600 cfm then that is what it will flow.
tom...
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Melting Slicks
Joined: May 2002
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From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Re: 500 cfm carb too little? (Captain_Kaboom)
It depends on max RPM you plan on turning the engine and what the engine is capable of turning. According to this formula a 350 CID engine will require only 516 CFM at 6000 RPM. CID * RPM / 3456 * 0.85 = CFM required. This formula assumes that you engine is 85% efficient. I believe that 85% is a little on the high side for a factory motor.
Neal
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Neal
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Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Re: 500 cfm carb too little? (Captain_Kaboom)
You would probably be fine. The 600 is said to be Holley's biggest selling carb, the min. a hotrodder would put on, good for more later.
The Q-J 750 rating is not relevant.
The Q-J 750 rating is not relevant.
Burning Brakes
Joined: Apr 2004
Posts: 814
Likes: 2
From: WESTLAKE LA
Re: 500 cfm carb too little? (Wamplet)
IMHO more money is wasted on too large a carb than anywhere else on engine upgrades. people would rather say they have a 750 double pumper than a 600 single line.waste of money and fuel.i went thru all kinds of articles and websites before deciding all i needed was a 600cfm( i went with holley). i'm running the basically the same setup as you are. 
[Modified by COMMANDER370, 9:41 PM 6/24/2004]
[Modified by COMMANDER370, 9:41 PM 6/24/2004]
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Re: 500 cfm carb too little? (Wamplet)
No, you do NOT want a carb that is too big, nor too small. Kinda like Goldilocks...it's gotta be JUST right. A 600 to 650 cfm square bore Holley or Edelbrock is good.
The QJet is a unique design due to its secondary air valves, so the cfm equation does not apply to it.
IMHO, a Lars-tuned QJet is the best street carb money can (or cannot) buy
The QJet is a unique design due to its secondary air valves, so the cfm equation does not apply to it.
IMHO, a Lars-tuned QJet is the best street carb money can (or cannot) buy
Intermediate
Joined: May 2004
Posts: 44
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From: Houston TX
Re: 500 cfm carb too little? (page62)
^ :o lol, for a good laugh, check my other thread out. 
Thanks for the info, by the way. You've been a big help to me all this time. 
I am SO glad I saw this thread and another cfm thread. I would have been in big trouble when that new carburetor got here, if i hadn't cancelled it.
I am gonna try to email Lars on my other email account and see if he can do his magic.
I still say 795 cfm would definitely be too much for my car, because it's a small block and stock. No cam or anything fancy in there. :o
Thanks for the info, by the way. You've been a big help to me all this time. I am SO glad I saw this thread and another cfm thread. I would have been in big trouble when that new carburetor got here, if i hadn't cancelled it.
I am gonna try to email Lars on my other email account and see if he can do his magic.
I still say 795 cfm would definitely be too much for my car, because it's a small block and stock. No cam or anything fancy in there. :o
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Re: 500 cfm carb too little? (Wamplet)
So is the cfm rating more or less a non-factor/irrelevant, as long as you have a cfm carburetor that is above what you need?
The GM solution
Q-J- Small primarys w/ huge secondary.
With the spreadbore the small primarys allow velocity, response & fuel economy while the huge sec. provide capacity. Designed by RPD of GM w/ basically unlimited budget & then used on nearly all GM V8s w/ 4 bl. since.
From about 300 C.I. to 500 C.I., so the Q-J sizes itself to the engine & the 750 rating is not really relevant on a stock 305, 350 since it is not using all it's capacity.
A modified 350 can use 750 for example. 750 minimum for 454.
Remember a carb is a responsive device.
[Modified by Ganey, 5:57 PM 6/24/2004]
