500 AVS2 or 650 AVS2 ???

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gtxdude

gtxdude

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As some of you know, I've been throwing carbs at my 65 Dart 318 for a couple of years. Have a 600 Eddy on there right now, not bad but looking for a change (don't ask me why). Long story short, looked at posts going back a few years about carb sizes for 318 and everyone's thoughts. It's a 318 with 230hp at the crank, about 180hp at the wheels, 8.25 3:23 posi. As some of you know we do a lot of cruising, long trips ( Route 66 a couple of years ago, awesome trip)
It's going to be AVS2 500 or 650 I really want the 500 for mpg but I'm leaning toward the 650 to make sure I have enough carb (never been over 4500rpm ) My question is, can I calibrate the 500 up or am I better calibrating the 650 down to be a little bit more fuel efficient? I pretty much know who's going to respond and I appreciate all of your guys input.
For what ever reason Summit just knocked $90 off there AVS2 650 so that's what has my asking, Tilly :)
 
Measure manifold vacuum on a full throttle run and see how restrictive the 600 is 1st. Go from there.
 
Primary bores are the same but secondary is slightly larger on the 650. Jetting is different. I would guess you could tune either for a 318 street engine….experts may beg to differ
 
I'm running an AVS2 on my '63 Riviera. It's fine, but it feels no better than the Edelbrock 500 AFB on my Mustang. I don't think I'd spend the money to upgrade, personally, but I've spent a lot of money on carbs in my life, too, just to see how they work.
 
gtxdude said:
As some of you know, I've been throwing carbs at my 65 Dart 318 for a couple of years. Have a 600 Eddy on there right now, not bad but looking for a change (don't ask me why). Long story short, looked at posts going back a few years about carb sizes for 318 and everyone's thoughts. It's a 318 with 230hp at the crank, about 180hp at the wheels, 8.25 3:23 posi. As some of you know we do a lot of cruising, long trips ( Route 66 a couple of years ago, awesome trip)
It's going to be AVS2 500 or 650 I really want the 500 for mpg but I'm leaning toward the 650 to make sure I have enough carb (never been over 4500rpm ) My question is, can I calibrate the 500 up or am I better calibrating the 650 down to be a little bit more fuel efficient? I pretty much know who's going to respond and I appreciate all of your guys input.
For what ever reason Summit just knocked $90 off there AVS2 650 so that's what has my asking, Tilly :)
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Well, you're thinking isn't exactly right here. You cannot really tune "up or down" regarding carburetor SIZE, but rather rich or lean and that's about it. However, using the AVS makes that a little different, since they are regulated on the secondary side by an adjustable air door. So you can actually back off on the flow on the secondary side some. Since the more the door opens, the more fuel is pulled in. By making the door more difficult to open and also limiting the opening, you can back off the total flow of the carburetor some. I would use the 650, because I believe it will be easier to limit IT rather than try to make the 500 match up. Just one peon's opinion.
 
Post #3 claims the pri bore size is the same on the 500 & 650. Since you cruise [ fuel economy ] on the pri bores, either carb should give the same economy.
 
Bewy said:
Post #3 claims the pri bore size is the same on the 500 & 650. Since you cruise [ fuel economy ] on the pri bores, either carb should give the same economy.
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I'd have to get the dial calipers out on that one.
 
Every body has there own opinion. Sounds like you may be a cruiser and not a full throttle guy.
From my own thoughts I favor the 500 for a street use car because of better throttle response
and drive ability. I played the carb game and used a 500 on a 451 stroker for Power Tour .
The car had OD and I got a real 20 MPG during a 5,000 mile round trip. Now I will admit
that I have a AFB 600 on my 318 car now.Reason is I had it sitting on the shelf. If buying new it would be a 500.
My 2 cents.
 
If you never go over 4500 rpm, the 500 cfm is not going to be a limiting factor of anything in your combination and should return better fuel economy with less fooling around. With that level of engine build, you are picking fly poop out of pepper. The return on any change is going to be very difficult to discern without instrumentation.
 
Is there any proof that a 500 automatically gives better fuel mileage ?
 
gzig5 said:
If you never go over 4500 rpm, the 500 cfm is not going to be a limiting factor of anything in your combination and should return better fuel economy with less fooling around. With that level of engine build, you are picking fly poop out of pepper. The return on any change is going to be very difficult to discern without instrumentation.
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It could be, IF the engine needs more on the primary side. If the 500 and 600 have the same throttle bore and venturi size, as eluded to in previous posts, then you're probably right......but I'd have to measure it for myself. I find it difficult to believe they have the same size throttle bores and venturi.
 
I think the 500 has smaller primaries [ than the 600 ] because it has 086 pri jets v 100 for the 600. So the 500 would be expected to give better economy.
 
Bewy said:
I think the 500 has smaller primaries [ than the 600 ] because it has 086 pri jets v 100 for the 600. So the 500 would be expected to give better economy.
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Maybe. It depends. In my situation, I believe a bigger carburetor will win out with MPG. On this Ford 400, with the Street Demon 625, it runs out of primaries real quick and I get into the secondaries pretty quick and I don't have a lead foot. I tried this Edelbrock 750 and when I had it running "good" I could tell a WORLD of difference on the primaries. But, it was not meant to be, because I just could not make the Eddy work well. I think if I am able to get the Street Demon 750 I will see a difference in fuel economy, since with the bigger primaries, I won't be into the secondaries "as much". It's a theory at least. I know beyond a shadow of a doubt now that it does need the bigger carburetor. So mileage or not, that's what it will eventually get.
 
273 said:
Measure manifold vacuum on a full throttle run and see how restrictive the 600 is 1st. Go from there.
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A modded 600 only pulled 1.2 or 1.7 inches at the top end on a 360 that ran mid 12's
 
Hysteric said:
A modded 600 only pulled 1.2 or 1.7 inches at the top end on a 360 that ran mid 12's
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My point is why guess which to go when you can measure what you got and make a more informed decision.

1.7 is fairly restrictive so can be 1.2 depending on application. Pumping loss can kills hp, mpg etc.. also.
 

How does it affect performance?​

Vacuum is actually a measurement of the engine’s inefficiency. Higher vacuum indicates that the engine is working harder to breathe. This limits performance. However, it is necessary. Restricting the airflow and creating vacuum helps slow the engine down and limit rpm.

The vacuum created by the piston pulls air from outside, through the intake, into the cylinder. The throttle blades create restriction. This reduces the amount of air/fuel that goes into the cylinder. With less air/fuel, the engine cannot turn as fast.

As the throttle blades open, restriction and vacuum are reduced. This allows more air/fuel into the cylinder and rpm increases. With the throttle wide open, airflow is maximized and vacuum is at its least.

When you let off the throttle and the blades snap shut, rpm is still high. This creates a spike in vacuum. The restriction starves the cylinder of air/fuel. The result is falling rpm and vehicle deceleration.
 
273 said:
My point is why guess which to go when you can measure what you got and make a more informed decision.

1.7 is fairly restrictive so can be 1.2 depending on application. Pumping loss can kills hp, mpg etc.. also.
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Sorry checked the data log it was 0.7 @ 6K
 
Frank Mopar said:

How does it affect performance?​

Vacuum is actually a measurement of the engine’s inefficiency. Higher vacuum indicates that the engine is working harder to breathe. This limits performance. However, it is necessary. Restricting the airflow and creating vacuum helps slow the engine down and limit rpm.

The vacuum created by the piston pulls air from outside, through the intake, into the cylinder. The throttle blades create restriction. This reduces the amount of air/fuel that goes into the cylinder. With less air/fuel, the engine cannot turn as fast.

As the throttle blades open, restriction and vacuum are reduced. This allows more air/fuel into the cylinder and rpm increases. With the throttle wide open, airflow is maximized and vacuum is at its least.

When you let off the throttle and the blades snap shut, rpm is still high. This creates a spike in vacuum. The restriction starves the cylinder of air/fuel. The result is falling rpm and vehicle deceleration.
Click to expand...
You don't say? I wouldda never guessed. :realcrazy:
 
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