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what carburetor?

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solowookie

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I'm trying to plan out a 383, and I'm wondering what CFM carburetor to get? will a higher CFM carb decrease my fuel mileage?

I''m seeing a couple cheaper cheaper options at summit racing which include a 600 CFM carb, and a 750.

I know absolutely nothing about carbs so I'm way out of my league here.

also - one of these has an electric choke, but only the 600 CFM has that option it appears.
 
Ehhh carb size has nothing to do with motor size rather how much torque and horse power your making really. For a mild 383 I'd start with a 650-750. Alot of people really over carb motors...

Your better off on a generic chevy site for something like this. Thirdgen.org is always a good place for fuel deilvery and motor questions.
 
cam quest shows very little difference between a 600 CFM, and a 750 CFM (like 3-4 HP & 1-2 TQ)), but the cost of the parts would be a lot more for a 750 CFM if I were go after an electric choke.

I've been on thirdgen, but it has been several years.
 
I'm not very versed in carbs. All I can tell you is from watching build discussions on thirgen people tend to think their car needs more carb than it does which richens everything and wastes gas.

When I said estimated HP and TQ with give a rough estimate of carb size I meant whatever the guess for motor number power wise will be a good clue as to what carb to go with. 275-325hp I would guess in at a 600cfm range. 325-360 I would say is a 650cfm, and so on and so forth. My number might be wrong but i'm saying picking the right carb goes like that and ever then you might go too small or big.
 
There is a formula for figuring out carb size:

Required Carb CFM = VE% x [(CIDxMax RPM)/3456]

VE=Volumetric efficiency. Most stock and mild performance motors will see 75-85%

I'll assume you're using good parts. Heads, intake, headers all improve the VE% So I'll use 85% And guess that you want a max RPM of 6500.

.85x[(383x6500)/3456]
.85x[2489500/3456]
.85x720=612

Now no one makes a 612cfm carb. A 600cfm would work, or a 650cfm. Moving the peak RPM's up or down will affect the size predicted.

Bigger carbs will work better at higher RPM where there is a better signal to them. Small carbs will give better throttle response.

That being said, I say find a Q-jet and learn to tune it.

Edit: A 750cfm can be made to work, possibly even better than a one of the smaller choices. It all depends how much time you want to spend tuning it in.
 
I'm going to be spending as little as possible lol. probably Dart Iron Eagle S/S, 6" rods, and will be stock manifold for now. later I will change out to short headers, and a new exhaust. I'll be running comp cam w/ a 206 & 206 RPM range 800-4800 RPM #12-205-2[49].

last engine I did was a cam that went from 1k - 5k RPM, and I wish it would of had a bit more grunt about 200 RPM's lower. this suits the way I drive it in the mountains a bit better.
 
I am not a carb expert by any stretch, but , I agree that most people tend to "over carb" their engines. For your application I would think that a 600 cfm carb would be plenty for your app. I know some guys here hate them but I have had good luck with the Edelbrock performer carbs, I put the "offroad kit" in the last one I had on a mild 350 and I never really had any problems to speak of. Just my $.02 , hope it helps :D


Oh, those carbs can be found used for cheap and the rebuild kits are approx $35 in Summit and pretty easy to install.
 
jt512 said:
I know some guys here hate them but I have had good luck with the Edelbrock performer carbs,
Click to expand...

honestly I've only heard good things about the Edelbrock carbs. from what I hear the Holly's take a lot more upkeep, and you can get the Edelbrocks tuned it, and don't have to mess with them. since I have never messed with a carb that sounds like the type of setup I need! :waytogo:
 
FWIW the Edelbrock carbs are easier when it comes to jet changes and metering rods. It is also really easy to mess it up when it comes to the jet and rod combo as there are more factors involved. Holleys on the other hand can work on lower fuel pressure, changing afr is just a simple jet change. In a holley the power valve takes the place of the metering rod system in a edel. I think that you can get both carbs tuned to perform the same but in my opinion the edelbrock will take less effort when it comes to change jets. But you can also make more mods on a holley.
 
is it normal to do that jet changes & all that? i want as simple of a setup when it comes to a carb as possible (whatever that is lol)
 
you will always get the best performance out of a carb by tuning it to the specific engine rather than bolting it on as is, and most manufacturers include a section about tuning in their owner's manuals. (I would know b/c the edelbrock 600cfm i swapped over from the old engine it was tuned for to my new 350 runs way rich, etc)
 
I got a few guys locally I think can help me tune it when it comes time... I can't get them for much of the project, but everything else I can handle by myself.
 
solowookie said:
I got a few guys locally I think can help me tune it when it comes time... I can't get them for much of the project, but everything else I can handle by myself.
Click to expand...


I am coming late to this discussion but I will add:
Qjets are the best when you don't really know what size to get, they are great up to 750CFM, meaning the same carb acts like a 600 with part throttle and when pushed will open up to 750CFM.
That is why it's so great on fuel since it's flexible, although if you need bigger CFM's then you need to go another rout.
The other thing about carbs you need to tune them to your altitude mor ethan to your engine at least for the Qjets.
I have had edelbrocks, holleys and Qjets and the Qjets n my book are still the best.
 
vac. secondaries are the way to go, the engine will draw the secondaries open as it needs the additional flow. Although that can be altered too.
 
I think my vacuum lines have opens in them all over I need to work them over. I wonder how much better this truck will run when it actually has a properly functional carburetor with vacuum also?
 
solowookie said:
I think my vacuum lines have opens in them all over I need to work them over. I wonder how much better this truck will run when it actually has a properly functional carburetor with vacuum also?
Click to expand...

Oh if you have all the vacuum lines fixed it should run much better.
If the carb isn't messed up a stock Qjet runs real nice and gets great mileage.
If yours is no good I have a good rebuilt and modified for off road. :D
 
when I'm done I'm going to have to get a sticker that says "build from recycled imiceman44's par4s"...

I'll let you know how it all works out I'm going to be working on it tonight.
 
Transmission proble

Hi have a 1986 K5: 350/700R4/33"
I pay a guy to rebuild my transmission and I have the problem that when I start using the truck every thing’s fine but after 10 minutes the transmission STOP working, I don’t know why, I wait 30 minutes and the transmission works again for another 10 minutes.
Any Idea
PLEASE HELP!!!
 
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