650 or 750 Edelbrock on 340

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Divenut

Divenut

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Hey Folks,

In the process of putting the top end of the 340 back together. 72 Duster, 340, J-Heads w 2.02 intake, 727 w/RMVB, 3500 stall, 4.30 gears. The motor has what appears to be a decent cam (Unknown grind but really comes alive as the rpms increase), .30 over KB 1267 10.2 pistons, swapping Edelbrock 60779 closed chambered heads and ported the old Torker intake.

The car ran really well with the 650 Edelbrock carb before deciding to go with new heads, but I'm thinking a 750 might be better suited.

I've seen/read folks running both with success but was hoping any FABO members with similar build will chime in!

Thanks in advance!
 
700 to 750 cfm carburetor will work fine. My suggestion would be to read your plugs after a few miles, or get a AFR gauge. It will take a bit of tuning in order to get it right.
 
Thank you both for the quick replies. Much appreciated! I will definitely will be running an AF gauge to take away some of the guesswork.

Be well,
Pat
 
I’m going to make you an offer you can’t refuse.. Swing by and pick up my 750 Holley competition #0-937 9 dp with annular boosters and choke horn milled. You can try it out this summer.

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Hey Mike, @EL5DEMON340

That's friggin awesome. I may just take you up on that offer! If nothing else, I can check out all the changes you've made to the Demon since we saw each other last. And gotta check out the work on the heads too. Thinking of doing some work on these new Eddys.

I'll bring the beer. :)

Pat
 
Divenut said:
Hey Mike, @EL5DEMON340

That's friggin awesome. I may just take you up on that offer! If nothing else, I can check out all the changes you've made to the Demon since we saw each other last. And gotta check out the work on the heads too. Thinking of doing some work on these new Eddys.

I'll bring the beer. :)

Pat
Click to expand...
if its tuned to your setup you will get a 750 dp for sure
 
I don’t think I have ever put a bigger carb on a healthy small block and had it not pickup.
One exception was an 1100 dominator wasn’t any faster( and was more trouble) than a 1025 race demon I had..and foolishly sold later on.
 
Run the one you got and if it's pulling a lot of vacuum (restrictive) then decide on upgrade.
 
a-bodyguy said:
650 settlebrock loses 20 lb ft to a 750 dp@ 3000 rpm
its not close
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Well then he'll get to notice the enjoyment when trades up :) I don't care what the OP does but he's already got carb doesn't hurt to try it, or not.
 
Either or will work more cam needs more carb . My experience is Holley is a gas guzzler but whos actually watching ...? Ihave a 750 Eddy on my 340 now but car is in forpaint. When I get it back on the road I have a 650 eddy,the 750 eddy on it now, a 600 and 750 Holley to swap around see what it likes.
 
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So many just don't get it........
That is it is just not about the carb cfm rating. 340s came with a 625 cfm Carter AVS carb...& a 800 cfm Thermoquad. Which do you think was faster?
In Roger Huntington's American Super Car book, he lists about a dozen pony cars that were tested. Equal fastest was 14.6 for the 1/4, 340 Cuda & 428 Mustang. The Cuda had a 3.23 diff, Mustang had 3.50.
The 340 was the only engine that the estimated HP was greater than the adv HP, 290 v 275. The 428 Ferd adv 335, est 320. Yep, all that with a little ol 625 AVS. And it didn't have annular pri boosters either!!!!I presume the Ferd used the POS 715 cfm Holley.

In Jan 1969, Car & Driver tested the Econo racers. Two Ford 428s, Chevelle, 426 Road Runner, 383 Super Bee. Tests were strictly controlled to production specs. The Pontiac entry was disqualified for cheating.
1/4 mile times. Hemi was quickest 13.54.
Next was 428 Cyclone 13.94
S/Bee & 428 Mustang were equal @ 14.04........both had 3.5X axles. The Cyclone had a 3.91 axle.
Here is the Dodge getting an equal 1/4 time with 45 less cubes....with a little ol 625 cfm Carter AVS...
 
A carb is a restriction if we were running fuel injection you'd want zero restriction, but a carb needs some restriction (vacuum) to operate ideally you want to run the least amount restriction for the carb to operate as intended. That why I say run what you got and see how much vacuum it pulls during a full throttle run and go from there.
 
Bewy said:
So many just don't get it........
That is it is just not about the carb cfm rating. 340s came with a 625 cfm Carter AVS carb...& a 800 cfm Thermoquad. Which do you think was faster?
In Roger Huntington's American Super Car book, he lists about a dozen pony cars that were tested. Equal fastest was 14.6 for the 1/4, 340 Cuda & 428 Mustang. The Cuda had a 3.23 diff, Mustang had 3.50.
The 340 was the only engine that the estimated HP was greater than the adv HP, 290 v 275. The 428 Ferd adv 335, est 320. Yep, all that with a little ol 625 AVS. And it didn't have annular pri boosters either!!!!I presume the Ferd used the POS 715 cfm Holley.

In Jan 1969, Car & Driver tested the Econo racers. Two Ford 428s, Chevelle, 426 Road Runner, 383 Super Bee. Tests were strictly controlled to production specs. The Pontiac entry was disqualified for cheating.
1/4 mile times. Hemi was quickest 13.54.
Next was 428 Cyclone 13.94
S/Bee & 428 Mustang were equal @ 14.04........both had 3.5X axles. The Cyclone had a 3.91 axle.
Here is the Dodge getting an equal 1/4 time with 45 less cubes....with a little ol 625 cfm Carter AVS...
Click to expand...
And the 71 340 with the 800 cfm t-quad makes more HP than the 625 AVS, OH…. and the 340’s with the 1350 cfm Holley 6 pack ( 950 actual cfm) make even a little more !!
 
I'd probably try one of the new 750 Street Demons. Very Thermoquadish.
 
EL5DEMON340 said:
And the 71 340 with the 800 cfm t-quad makes more HP than the 625 AVS, OH…. and the 340’s with the 1350 cfm Holley 6 pack ( 950 actual cfm) make even a little more !!
Click to expand...

They measure 2V carbs at 3 inches of mercury and 4V carbs at 1.5 inches. So three 2V carbs do not flow 950 CFM if measured at the same pressure drop as a 4V.
 
a-bodyguy said:
650 settlebrock loses 20 lb ft to a 750 dp@ 3000 rpm
its not close
Click to expand...
Why would you compare a 650 Edelbrock to a 750 4150 style carb, that isn't the question? Furthermore, wouldn't a direct comparison between the 650 Edelbrock and 750 Edelbrock be more inline if trying to decide on cfm requirement for a given engine? For those that like the 4150 style carbs, a comparison between the 650 dp and 750dp would likely tell a story also.

On the dyno, my W2 408 made significantly more power with a Quickfuel Q950, vs same model carb in 850cfm version. That to me is a relative comparison.

I sure see a lot of guys running stock, and superstock that can go really fast, making big power with the AFB, AVS style carbs.
 
EL5DEMON340 said:
And the 71 340 with the 800 cfm t-quad makes more HP than the 625 AVS, OH…. and the 340’s with the 1350 cfm Holley 6 pack ( 950 actual cfm) make even a little more !!
Click to expand...
If the user can tune it optimimally.
 
cpearce said:
Why would you compare a 650 Edelbrock to a 750 4150 style carb, that isn't the question? Furthermore, wouldn't a direct comparison between the 650 Edelbrock and 750 Edelbrock be more inline if trying to decide on cfm requirement for a given engine? For those that like the 4150 style carbs, a comparison between the 650 dp and 750dp would likely tell a story also.

On the dyno, my W2 408 made significantly more power with a Quickfuel Q950, vs same model carb in 850cfm version. That to me is a relative comparison.

I sure see a lot of guys running stock, and superstock that can go really fast, making big power with the AFB, AVS style carbs.
Click to expand...
You like them i dont
I wouldnt run a 625 650 vacuum secondary of anything ever again ive had them
I have a tuned 650 dp on my 340 its pretty stock ive had that carb on 4 motors in 35 years call it a keep sake
750 dp or a t/quad
750 avs2 i guess
Q950 is what should be on a stroker
340s should have 750s
I guess they put the 800 cfm on in 71 340 for a reason it added 30 hp over those chit 625s that flowed 600 if they were lucky
 
a-bodyguy said:
You like them i dont
I wouldnt run a 625 650 vacuum secondary of anything ever again ive had them
I have a tuned 650 dp on my 340 its pretty stock ive had that carb on 4 motors in 35 years call it a keep sake
750 dp or a t/quad
750 avs2 i guess
Q950 is what should be on a stroker
340s should have 750s
I guess they put the 800 cfm on in 71 340 for a reason it added 30 hp over those chit 625s that flowed 600 if they were lucky
Click to expand...
For the sake of clarity for others reading, AVS and AFB carbs are not vacuum secondary carbs. The butterfly valves on the secondary side open with application of throttle, beginning about 65% of primary opening, and are fully opened together. Air flow through the secondary side is controlled by air valves, either weighted or spring loaded.

Not intending to be a wise guy to your post, just clarity for others reading.
 
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