Which Eddy for me?

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demon322

demon322

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Yes, I know there are a ton of threads on here about this topic. I have read many of them. I was just curious about opinions for my specific setup.

Also, I know many of you prefer/swear by Holleys, but I have decided to go Edelbrock.

I am leaning toward the AVS 2 650. Just wanted to make sure that would be "enough" carb for me. A few old school guys I run with are from the bigger is better school and are heavily recommending the 800 Thunder series.

'68 340, performer rpm manifold, mild cam (unknown specs, was in the engine when I bought it), headers.

90% street use, occasional trip to the local track. Streetablity is very important but want the performance there when I need it. It feels like the 650 would be all I'd need. Not sure if the 800 would be 'too much' or not.

Thanks all.
 
I got a 800 eddy on my 360 works good.
A 650 will work but your probably giving up some hp but like you said you care more about driveability. So it will give a slight advantage there.
 
What trans,what gears, what TC?
With a manual trans;
A short stroke engine with tall gears, works better with a mechanical-secondary carb, due to the lack of TM in the TC. Saddled with hiway gears, and an AVS-type carb, the secondaries might be slow to open, and you will be tempted to speed them up, and then run into a bog or hesitation.
That same engine with a performance rear gear will hardly care what type carb is on it.
The AVS-type carb sometimes has a mind of it's own, delivering the wrong amount of power for a given situation, in accordance with the amount of throttle-opening you have commanded, and has put me out-of-control, more than a few times. For this reason I prefer the mechanical secondary, the power is more consistent.
Autos
are more forgiving,especially as the stall goes up

As to size; on the street,favoring streetability, pretty much any street carb will work, cuz the primaries of even the biggest ones are just about the same size as a big 2bbl. If you choose too small a primary for your driving style, then you will be into the secondaries a lot of the time.
But if the car spends a lot of time on the hiway, then a spread-bore with tiny triple booster primaries is the way to go. I really like those with autos. I love the old small-primary TQs, and their counterpart, the QJs

But really the rear gears are a really big factor. If your engine can spin the tires hard on take-off, or if she lights 'em up at 30mph on the downshift;then not-so-much.

BTW; below your engines peak torque, it almost doesn't matter what size 4bbl carb is on her, cuz the engine will only pull what it can pull.. In other words if the engine can only pull about 450cfm, then only a carb smaller than that is gonna slow her down.And if you bolt an 800 on her, it's still only gonna pull about 450 thru it; that is the mechanical limit of the combo. If you increase the mechanical limit with a cam or heads or compression, and then she pulls 550cfm, then an 800 is still not gonna make much more power over a 550.
And finally; for a streeter with 3.23s and an auto, you are only gonna hit peak rpm once on the way to 65mph, and you'll probably still be spinning into second. If you can do that with a 550, then there would be no point in the 800.
 
Buy a 650 you will never know if 650 was enough. Buy an 800. your covered. I run a 1050 Quik-Fuel on a built 340 small block. I run a 650 Edelbrock on a bone stock 318.
 
The Ede 650cfm Thunder Series will be the perfect carb for your 340.
Great manners on the low end and top end for what you are doing.
Even the Ede 600cfm works well on the street, with great signal, only giving away on the very top end.
Lets be honest, unless you are going to the track regularly, how often are you going to
be all full throttle, rung out on the street ?
The Ede 650 will suit you just fine.
 
demon322 said:
Yes, I know there are a ton of threads on here about this topic. I have read many of them. I was just curious about opinions for my specific setup.

Also, I know many of you prefer/swear by Holleys, but I have decided to go Edelbrock.

I am leaning toward the AVS 2 650. Just wanted to make sure that would be "enough" carb for me. A few old school guys I run with are from the bigger is better school and are heavily recommending the 800 Thunder series.

'68 340, performer rpm manifold, mild cam (unknown specs, was in the engine when I bought it), headers.

90% street use, occasional trip to the local track. Streetablity is very important but want the performance there when I need it. It feels like the 650 would be all I'd need. Not sure if the 800 would be 'too much' or not.

Thanks all.
Click to expand...
 
I ran an eddy 750 single pump on a 340. I got the 750 new for a good deal. It ran ok with it. My car's with Holleys ran much stronger. Really research the eddy carb reviews first if buying new.
 
AJ/FormS said:
What trans,what gears, what TC?
With a manual trans;
A short stroke engine with tall gears, works better with a mechanical-secondary carb, due to the lack of TM in the TC. Saddled with hiway gears, and an AVS-type carb, the secondaries might be slow to open, and you will be tempted to speed them up, and then run into a bog or hesitation.
That same engine with a performance rear gear will hardly care what type carb is on it.
The AVS-type carb sometimes has a mind of it's own, delivering the wrong amount of power for a given situation, in accordance with the amount of throttle-opening you have commanded, and has put me out-of-control, more than a few times. For this reason I prefer the mechanical secondary, the power is more consistent.
Autos
are more forgiving,especially as the stall goes up

As to size; on the street,favoring streetability, pretty much any street carb will work, cuz the primaries of even the biggest ones are just about the same size as a big 2bbl. If you choose too small a primary for your driving style, then you will be into the secondaries a lot of the time.
But if the car spends a lot of time on the hiway, then a spread-bore with tiny triple booster primaries is the way to go. I really like those with autos. I love the old small-primary TQs, and their counterpart, the QJs

But really the rear gears are a really big factor. If your engine can spin the tires hard on take-off, or if she lights 'em up at 30mph on the downshift;then not-so-much.

BTW; below your engines peak torque, it almost doesn't matter what size 4bbl carb is on her, cuz the engine will only pull what it can pull.. In other words if the engine can only pull about 450cfm, then only a carb smaller than that is gonna slow her down.And if you bolt an 800 on her, it's still only gonna pull about 450 thru it; that is the mechanical limit of the combo. If you increase the mechanical limit with a cam or heads or compression, and then she pulls 550cfm, then an 800 is still not gonna make much more power over a 550.
And finally; for a streeter with 3.23s and an auto, you are only gonna hit peak rpm once on the way to 65mph, and you'll probably still be spinning into second. If you can do that with a 550, then there would be no point in the 800.
Click to expand...

727 with what I was told is a close to stock TC. 3.91 sure grip out back.
 
I have been doing a lot of reading on CFM to cubic inch needs. I ran across a formula that calculated theoretical CFM needed, but that didn't include the Volumetric Efficiency (VE) of the motor. Most good running street cars have a VE in the range of 80% - 85%. Higher performance cars might be 90% efficient. It is virtually impossible for a naturally aspirated engine to have a VE greater than 100%. That has to be factored in to get the true CFM need in the end.

The calculation factored in cubic inches times the preferred max RPM range then divided by a constant of 3456. I don't remember what the constant was driven by, but basically it was a calculation to convert the combination of cubes and RPM down to CFM. you then take that times the estimated VE of the engine. I think I get it, but may be wrong, but I think it is a conversion from cubic inches to cubic feet, then doubled because you have two full strokes for every compression stroke.

Anyways,.... For instance.....

340Cubic inches x 6000RPM / 3456 = 590.28 cfm (theoretical)
Take the theoretical cfm x VE (.85) to get actual required CFM, so,....

590.28 x .80 = 472.2 cfm
590.28 x .85 = 501.7 cfm
590.28 x .90 = 531.25 cfm
590.28 x .95 = 560.76 cfm
590.28 x 1.0 = 590.28 cfm


Like someone said above,... a 600 - 650 cfm carb would likely do what you want it to do. Bigger gets to be a waste. Keep in mind that fuel is drawn in by the velocity of the air rushing through the venturis of the carb. A larger carb has larger venturis, so with a given vacuum draw from the motor, the velocity of the air going through the bigger carb will be less, which will draw less fuel. It IS possible to run too large of a carb on a motor. Performance sucks, mileage sucks, and you will constantly be battling Air/fuel issues.

Bigger ISN'T always better.
 
You got it and for a streeter I usually tone it down for that fact that over 98% of the time, the engine will NOT be at max rpm, or max VE. So at a more common 3600, and a VE of say 65%, she will need 230cfm. Where have we seen that number before? Oh, yes, that is the standard Carter 2bbl rating. Just saying,lol.
 
You also mentioned the AVS 2. I havent had the chance to try one of these out yet, but definitely like the idea of the new Annular Booster design. In theory, these should work better then the original Edes.
 
Last edited:
Regarding the AVS2, and it's annular boosters.

I have the Summit M2008 carb. It is 600 cfm and has annular boosters. I have problems with icing under specific atmospheric conditions. I do not know if it is a function of the boosters creating smaller droplet size, the size and shape of the venturi or some combination of that and/or something else. I am at sea level. When I get icing the temps are between 40 and 60. Icing would occur after car had just been started and warmed up for five minutes AND also when it had been running for 30+ miles. Usually at engine speeds over 2000 rpm.

I would suggest that you wait a year for lots of other people to test out the new annular boosters AVS2 carbs.

My annular booster experience was on a 318 with an eddy performer and 1968 675 heads.
 
Oldmanmopar said:
Buy a 650 you will never know if 650 was enough. Buy an 800. your covered. I run a 1050 Quik-Fuel on a built 340 small block. I run a 650 Edelbrock on a bone stock 318.
Click to expand...

This right here ^^^^^^ covers it.
 
Frnknsteen said:
I have been doing a lot of reading on CFM to cubic inch needs. I ran across a formula that calculated theoretical CFM needed, but that didn't include the Volumetric Efficiency (VE) of the motor. Most good running street cars have a VE in the range of 80% - 85%. Higher performance cars might be 90% efficient. It is virtually impossible for a naturally aspirated engine to have a VE greater than 100%. That has to be factored in to get the true CFM need in the end.

The calculation factored in cubic inches times the preferred max RPM range then divided by a constant of 3456. I don't remember what the constant was driven by, but basically it was a calculation to convert the combination of cubes and RPM down to CFM. you then take that times the estimated VE of the engine. I think I get it, but may be wrong, but I think it is a conversion from cubic inches to cubic feet, then doubled because you have two full strokes for every compression stroke.

Anyways,.... For instance.....

340Cubic inches x 6000RPM / 3456 = 590.28 cfm (theoretical)
Take the theoretical cfm x VE (.85) to get actual required CFM, so,....

590.28 x .80 = 472.2 cfm
590.28 x .85 = 501.7 cfm
590.28 x .90 = 531.25 cfm
590.28 x .95 = 560.76 cfm
590.28 x 1.0 = 590.28 cfm


Like someone said above,... a 600 - 650 cfm carb would likely do what you want it to do. Bigger gets to be a waste. Keep in mind that fuel is drawn in by the velocity of the air rushing through the venturis of the carb. A larger carb has larger venturis, so with a given vacuum draw from the motor, the velocity of the air going through the bigger carb will be less, which will draw less fuel. It IS possible to run too large of a carb on a motor. Performance sucks, mileage sucks, and you will constantly be battling Air/fuel issues.

Bigger ISN'T always better.
Click to expand...


That formula is a little misleading. I see an engine as static and dynamic displacement.
A 340 static displacement would be 340, its dynamic displacement would be 1,020,000 cubic inches per minute or 590.28 cfm. Thats what that formula tells you the actual engine volume at rpm. And when used with the right VE its fairly accurate guesstimating how much air your engine can displace per minute .

But the problem using it to pick a carb is the cfm of a carb and that formula are two different levels its not a apples to apples comparison. You wouldn't use that formula to pick a head. 590 cfm divide by 8 equals 74 cfm. You'd be hard to find a intake port to match that at the standard we use.

From a performance point of view Its the not cfm that matters but the vacuum level (restriction) at wot that matters. A full out race car can get away with very little wot vacuum hence very large unrestrictive carbs. A street car is very different cause wot is not our biggest concern.

But really we don't need any formula we already know what works with sb. Basically stock-mild under 350hp 600-650 is your carb can be put on higher output engines but your sacrificing hp for nothing. Over 350 hp 700-800 cfm is your carb which also can go on lower output engine if tuned right but not necessary. And race anything that gives the best time.
 
Last edited:
Frnknsteen said:
I have been doing a lot of reading on CFM to cubic inch needs. I ran across a formula that calculated theoretical CFM needed, but that didn't include the Volumetric Efficiency (VE) of the motor. Most good running street cars have a VE in the range of 80% - 85%. Higher performance cars might be 90% efficient. It is virtually impossible for a naturally aspirated engine to have a VE greater than 100%. That has to be factored in to get the true CFM need in the end.

The calculation factored in cubic inches times the preferred max RPM range then divided by a constant of 3456. I don't remember what the constant was driven by, but basically it was a calculation to convert the combination of cubes and RPM down to CFM. you then take that times the estimated VE of the engine. I think I get it, but may be wrong, but I think it is a conversion from cubic inches to cubic feet, then doubled because you have two full strokes for every compression stroke.

Anyways,.... For instance.....

340Cubic inches x 6000RPM / 3456 = 590.28 cfm (theoretical)
Take the theoretical cfm x VE (.85) to get actual required CFM, so,....

590.28 x .80 = 472.2 cfm
590.28 x .85 = 501.7 cfm
590.28 x .90 = 531.25 cfm
590.28 x .95 = 560.76 cfm
590.28 x 1.0 = 590.28 cfm


Like someone said above,... a 600 - 650 cfm carb would likely do what you want it to do. Bigger gets to be a waste. Keep in mind that fuel is drawn in by the velocity of the air rushing through the venturis of the carb. A larger carb has larger venturis, so with a given vacuum draw from the motor, the velocity of the air going through the bigger carb will be less, which will draw less fuel. It IS possible to run too large of a carb on a motor. Performance sucks, mileage sucks, and you will constantly be battling Air/fuel issues.


I went thru this when I was building my last 3 hotrods. I always wondered about dyno operators showing "over" 100% volumetric efficiency !
-------------------------------------
I went a little bigger than the formula figured out, but w/ 1200 cfm a throttle body, w/ 8 injectors in it. Still farting around w/ leaning it down. So far so good.
Click to expand...
 
Eddie Haskell

Eddie_Haskell.jpg
 
lol @ the different eddy's. Definitely opened myself up to that one.

Lots of good info. I appreciate that. Seems to be a split here. Some say the 650 should be plenty. But others mentioning I will always wonder if I had enough if I opt to not go with the 800.

I'll admit I am no carb expert by any means. Say I went with the 650. How would I know if its not enough? Does it not get enough fuel under a heavy load? Like are we talking a possible miss during a high rpm situation?

Those suggesting the 800 - is the thinking here that its better to have too much than not enough? And that the 800 could be better tuned to my needs? Future plans include a different cam (mainly so I will know what exactly I have) but I probably will keep running the same (X) heads.
 
Johnny Dart said:
You also mentioned the AVS 2. I havent had the chance to try one of these out yet, but definitely like the idea of the new Annular Booster design. In theory, these should work better then the original Edes.
Click to expand...
Yessir. I have been doing a lot of reading about them and that annular booster setup really seems like a cool design. Unfortunately, the 800 isn't out yet (even though they mention it in their own video on their site) so if I go AVS 2 right now I'm locked into the 650.
 
Ottmundr said:
Regarding the AVS2, and it's annular boosters.

I have the Summit M2008 carb. It is 600 cfm and has annular boosters. I have problems with icing under specific atmospheric conditions. I do not know if it is a function of the boosters creating smaller droplet size, the size and shape of the venturi or some combination of that and/or something else. I am at sea level. When I get icing the temps are between 40 and 60. Icing would occur after car had just been started and warmed up for five minutes AND also when it had been running for 30+ miles. Usually at engine speeds over 2000 rpm.

I would suggest that you wait a year for lots of other people to test out the new annular boosters AVS2 carbs.

My annular booster experience was on a 318 with an eddy performer and 1968 675 heads.
Click to expand...
Thanks for the info. I will look into that for sure. I was not aware that summit also offered an annular booster carb. I have read everything I could find about the edelbrock version but this is the first I have heard about this issue.
 
demon322 said:
lol @ the different eddy's. Definitely opened myself up to that one.

Lots of good info. I appreciate that. Seems to be a split here. Some say the 650 should be plenty. But others mentioning I will always wonder if I had enough if I opt to not go with the 800.

I'll admit I am no carb expert by any means. Say I went with the 650. How would I know if its not enough? Does it not get enough fuel under a heavy load? Like are we talking a possible miss during a high rpm situation?

Those suggesting the 800 - is the thinking here that its better to have too much than not enough? And that the 800 could be better tuned to my needs? Future plans include a different cam (mainly so I will know what exactly I have) but I probably will keep running the same (X) heads.
Click to expand...

When people say its not enough, it don't mean after 650 cfm is gonna stop flowing fuel and air. It just will be more restrictive over an 800 cfm could cost you some hp for the choice. Think of it like headers 1 5/8 vs 1 3/4, even if 1 3/4 is the optimal choice 1 5/8 gonna give you 80-90% of the performance and probably better at low rpm and way better than manifolds. Same with 650 vs 800 you got 80-90% of the performance and way better than a 2 bbl :) You maybe only losing 0-20 hp maybe a little more.
 
Definitely not limited to a 650 or an 800. Plenty of 670 and 750’s to choose from too that could give great street ability and plenty of track punch but I know lots of guys sware by the Holley 4150 with a drive train in line with yours.
Holley’s website has an easy to use choice finder and plenty to choose from. Might be worth a look to get you closer to your range.
 
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