CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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First, I have an AFB because it was cheap, and I heard that it was relatively easy to tune. This is my first carb so I didn't want to mess around too much.
Now that I've had some more experience, I'm ready to upgrade the motor, and perhaps the carb to a different brand as well.
I'm overall 85% satisfied with the Edelbrock AFB. The only gripe I have with it is that you have to remove the air horn to change jets. Otherwise the tunability seems ok as I have no experience with any other brand.
Right now I'm going to go with an AVS unless someone can give me some ideas.
Comments?
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The Edelbrocks are clones of old Carter designs that have gone nearly unchanged since the 50s. They're mechanically simple, but because of that they don't offer the tuning options that more modern designs do.
"Bad" isn't quite the right word. It really depends upon what you've got, what you'll be doing with the car, and how willing you are to learn how to tune a carb.
If you have a q-jet, keep it. Neither the Performer nor AVS is any better. The only thing the AVS adds to the Performer is adjustable secondary air valve (which the q-jet already has).
It really depends upon what you've got, what you'll be doing with the car, and how willing you are to learn how to tune a carb.
The new motor will be a 454 small block. The cam/heads will be fairly aggressive. I'm still debating on intake and carb though, but I don't think my 600 CFM AFB will be enough.
I would like to daily and roadrace. To me there is no real difference between the two applications. The vehicle has to be reliable and responsive to throttle input. I don't care about peak power numbers.
I am 100% willing to learn as much as possible.
Quote:
Originally Posted by five7kid
If you have a q-jet, keep it. Neither the Performer nor AVS is any better. The only thing the AVS adds to the Performer is adjustable secondary air valve (which the q-jet already has).
I would personally buy a Barry Grant Road demon/race demon depending on what you end up doing with your set up
If you have a cowl hood by a Edelbrock Victor Jr/Scorpion/Brodix Intake and a 750-800 DP holley or BG carb buy the carb new and you will do good with it. since you dont know much about them
On our restored Starsky and Hutch Torino, with a BB 460 Ford, we ran a really high Perf. RPM cam, this cause the metering rods in the edelbrock 750 to go nuts and dump large amounts of gas in at idle, it always reaked of fuel. The Holley hasn't been much better, found a piece of plastic in one of the float valves, but other than that, it's not bad.
The new motor will be a 454 small block. The cam/heads will be fairly aggressive. I'm still debating on intake and carb though, but I don't think my 600 CFM AFB will be enough.
I would like to daily and roadrace. To me there is no real difference between the two applications. The vehicle has to be reliable and responsive to throttle input. I don't care about peak power numbers.
I am 100% willing to learn as much as possible.
Auto or manual - I would assume manual for road racing. If thats the case, a mechanical secondary carb will suit your needs better - the throttle response is faster, and the peak power available should be a tad better as well than a vacuum secondary carb. A heads/cam 454 is gonna demand at least a 750cfm carb, and very possibly more depending on what agressive means to you.
Nothing wrong with the AVS carb, but on a stick-shift, maximum performance application, there is no better option than a mechanical secordary carb. I run an Edelbrock Performer carb on my 'lil 305 and that works quite well for that application - its got plenty of tunability for me, is the right size for the application, has an electric choke so my wife can manage the car if she needs to on a cold morning, makes very good power and has great throttle response, and returns fair gas mileage. If the car was stick-shift, there is no doubt there would be a mechanical secondary carb on there.
Do you know what size your afb is? If it is a 750 I think it will be fine for your new motor, and I think replacing it with a 750 avs would not be money well spent.I do believe that a q jet may be a better carb for a street car, with better gas mileage and throttle response. But I have heard they can be tricky to set up.
A holley or demon vaccum secondary is a great carb as well and are very easy to work on and tune. The vaccum secondaries are very forgiving and a little better on gas than there mechanical secondary(double pumper) cousins.
A holley or demon mechanical secondary is a great street/strip carb and is also very easy to work on, the secondary accellarator pump shot may take a little patience to get set right though.These carbs can be a little pricey and are probably the worst on gas.
So basically there is no bad carbs and it just comes down to your budget and priorities.
Then what's the difference between AFB and AVS? What brand/model would have mechanical secondary?
An AVS is just an Edelbrock Performer (AFB) with more gadgets - specifically the variable spring rates for the secondary air valve. Both are vacuum secondary - Edelbrock doesn't produce a mechanical secondary carb that I'm aware of. The names that come to mind for mechanical secondary carbs are Holley, Proform, and Demon.
Technically Edelbrocks are not "vacuum" secondary. Vacuum secondary carbs have a vacuum diaphragm to open the secondaries.
The Edelbrock AVS series offer an adjustable air valve (which I already said).
As mentioned, Holley, Barry Grant (Demon), and Proform, as well as Quick Fuel Technology and others offer new mechanical secondary carbs.
I'm pretty sure we played this word game before. Vacuum is what actuates the air valve in an AFB carburator. No, it is not a vacuum diaphragm secondaries carb, its an air demand carb, just like a Q-jet. What's another way of saying air demand with regards to this application - vacuum. I think it would be safe to say the motor-sports community would accept that an AFB would be lumped in the same category as a vacuum diaphragm secondaries carb.
I guess if we really want to split hairs, you stating that an AFB is not a mechanical secondary carb is false as well, because it does have mechanically actuated secondaries. I would say that's splitting hairs, and it isn't a mechanical secondary carb in function, even if it is partial by form. Kinda like saying an AFB isn't a vacuum secondary carb - maybe not exactly by form -although one could certianly make an arguement that secondary airvalves are the secondaries, and are directly controlled by engine vacuum - but certainly is in function.
Again, technically, it isn't vacuum that opens the air valve - it's air flow. Vacuum draws air into the cylinder (technically, the lack of pressure inside the engine and atmospheric pressure outside the carb is what drives the air flow), but the flap is really a mass air flow sensor of the mechanical sort.
Without the vacuum, you wouldn't have the air-flow to open the secondary air valve, I would still propose its fair to lump an air demand secondary carb in with the "actual" vacuum secondaries carb - they work on the same principals.
Regardless, we digress. You don't want a vacuum demand (or air-flow if you must) secondary carb for your high performance application, as this type of design does not react as fast to throttle inputs as a mechanical secondary carb can. They work reasonably well behind automatic transmissions because once you've made the initial hit, there is no lifting between gears so no snapping shut and then open at each gear change. With a stick-shift, on each shift the secondaries would close when you lift for a second to upshift, vacuum goes way up, they you reintroduce the load in the next gear, wack the throttle open, and the secondaries have to react again to a massive drop in vacuum. It happens reasonably well if the carb is setup right, but will never happen as fast as a mechanical secondary carb.
Also, with vacuum secondaries you've got one accelerator pump, not two, reducing the hit when you mash the pedal. That can be good if you've got an auto with long gears and a stock stall as at low revs it might drown the engine to some extent, but if you're driving stick, you have gearbox control, and can make sure the revs are up when the thorttles opened - taking full advantage of that hit.
1) They are a demand-based secondary type, which is less than desirable for performance applications. The standard Performer secondary air valve is not adjustable. The factory q-jet, which most people seem to remove to put a Performer on, is more adjustable, the computer version self-adjusts, gets better fuel economy, and has more power capability. If you don't have a factory q-jet, then that doesn't matter much.
2) They are based on an old design, with few updates.
3) Although they can be tuned, the they tend to be difficult when you have anything but a mild set-up.
Advantages:
- Easy metering rod changes (don't have to disassemble).
- Inexpensive.
I am looking for responsiveness and ease of tuning. I'll sacrifice some power if I can get response.
I get the secondary jets adjusted on the dyno and I adjust the rest on my own. I make a lot of fine-tune adjustments so the more adjustability and the easier it is to make these adjustments = thumbs up.
Quote:
Originally Posted by atc3434
Also, with vacuum secondaries you've got one accelerator pump, not two, reducing the hit when you mash the pedal. That can be good if you've got an auto with long gears and a stock stall as at low revs it might drown the engine to some extent, but if you're driving stick, you have gearbox control, and can make sure the revs are up when the thorttles opened - taking full advantage of that hit.
This sounds good, but how is the power delivery with respect to throttle position? Is there a snap of power when you open the throttle? Is the power delivery linear with throttle manipulation?
Again, I am looking for a linear relationship between the throttle and the response, and not necessarily maximum power output when the throttle is opened.
For example, I use the throttle to transfer weight. When I go from 0 to 1/2 throttle, I expect a certain amount of acceleration as is commensurate with 1/2 throttle. If the power delivery is too abrupt, I will have to back off the throttle to say 1/4. Then acceleration isn't enough then I would have to go back to 1/2 again. Back and forth until the power delivery stabilises.
This is my worst nightmare on my last engine. It was a small-displacement turbo engine with huge lag and huge kick in the pants. It was nearly impossible to maintain any linearity between throttle position and power delivery.
I would love for something to dump as much fuel as right foot tells it to, no more no less. Control is everything when I'm on the edge of traction, and every little bit of weight transfer can upset balance if not done properly.
i have a problem with my carb well more like a discomfort because it has like a 2 sec time from when the gas goes it to the engine actually revving. So in other words its got a slow throttle responce and this is on a edelbrock 600 or 650 been told either one...
i have a problem with my carb well more like a discomfort because it has like a 2 sec time from when the gas goes it to the engine actually revving. So in other words its got a slow throttle responce
It sounds like the step-up spring needs to be stiffened up. As I understand it, when you nail the throttle, the step up springs transition the metering rod from the cruise/lean profile to the power/rich profile. The stiffer the step-up springs, the more quickly the car will transition from cruise to power under light to moderate throttle.
If that doesn't work you need to change the metering rods and primary jets.
If that doesn't work then you need to richen the accelerator pump.
Any comments?
Quote:
Originally Posted by 84 camaro z28
this is on a edelbrock 600 or 650 been told either one...
The model number is printed on the body of the carb, left side when looking at from the front of the car. This number can tell you the exact model you have.
its a 1405 i believe and we changed the metering rods once because it was burning rich but now i think its lean and what would be the cause of the filter wreaking like gas.
we changed the metering rods once because it was burning rich but now i think its lean
You can't haphazardly change metering rods. The rods have to go together with the primary jets because the rod is a restriction inside the jets. The two parts have to work together to create the ideal restrictor size.
You need a wideband to see if you're actually lean or rich.
I suggest that you stay with one of the factory configuration for primary jets and metering rods. If you go outside of what's recommended you're on your own.
Quote:
Originally Posted by 84 camaro z28
what would be the cause of the filter wreaking like gas.
It's hard to tell what is normal and what is not in terms of fuel smell. Can you have a local mechanic look at this?
You can't haphazardly change metering rods. The rods have to go together with the primary jets because the rod is a restriction inside the jets. The two parts have to work together to create the ideal restrictor size.
You need a wideband to see if you're actually lean or rich.
I suggest that you stay with one of the factory configuration for primary jets and metering rods. If you go outside of what's recommended you're on your own.
I did have some help with the metering rods we put the right ones in for the jets thats in it so we did stay with factory settings for cruise to moderate power settings
I did have some help with the metering rods we put the right ones in for the jets thats in it so we did stay with factory settings for cruise to moderate power settings
What is the part number of primary jets and metering rods in the carb right now?
Did you get a wideband readout? You really can't tune the primary control system on the dyno. You need a street tune.
