Actually, they are 1350cfm@3"Hg, & ~[email protected].
650 or 750 Edelbrock on 340
- Thread starter Divenut
- Start date
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Both the 340 & 440 engines with the 6-pack set up make 15 hp more than the 4bbl. One has a 625 cfm 4 bbl, other has a 750 4bbl....but still 15 hp difference for each.
The 6-pack intakes are true high rise intakes [ compared to the 4 bbl ]. Smoother bends, less restriction. So how much of the 15 hp increase is due to this?
The 6-pack intakes are true high rise intakes [ compared to the 4 bbl ]. Smoother bends, less restriction. So how much of the 15 hp increase is due to this?
EL5DEMON340
Well-Known Member
Factory underrated all 340’s at 275hp the 4 speed cam, the t-quad with the better intake in 71, AVS 340’s around 300hp, 71 340’s closer to 315 and 6 pack a little more. NHRA pegged the actual HP back in the day. 340’s and Hemis were underrated, 383, 440, and 440 + 6 were a lot closer.
Newbomb Turk
Well-Known Member
Are you saying they measure the 2V carbs at 3 inches and convert it down? If that's true what I was told decades ago is wrong. And it may be. Now I have to go look up the venturi and butterfly sizing.
I guess you did
69 340 nhra hp factor 295 hp based on trap mph turned
71 340 nhra hp factor 325 hp fastest stock 340 based on trap mph turned
70 340 six pack hp factor 315 hp nhra
That is how nhra factors hp for class ratings
pretty simple
AVS2 800 carbs
If this hasn’t been posted, and for anyone who is interested: I called Edelbrock yesterday and was informed that, yes indeed, there is an 800 version of the newer AVS2 carbs on the way. Annular booster AVS, and they are taking pre-orders now. Shipping soon I’m told. :thumbsup: ( public...
www.forabodiesonly.com
and even though this thread gets off track at the end, read what Hysteric Rumble and Bewy discuss about the 750 as made by Edelbrock.
750 Edelbrock issue
I am in the process of tuning my 340 with 750 edelbrock. It will idle at 800 rpm and then the idle gets low, if I rev the throttle it returns for a while then does it again, this is sitting in neutral in the garage. I am suspecting a problem with fuel pressure, however I am wondering if anyone...
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One of the early lies I read in multiple rags, was that the 440 6bbls were 1350cfm, & the 340 6bbls were 1050. Once I actually had the Holley books & real 340 carbs in My hand, it was BS, but they are different in jetting/bleeds, etc. The other difference is the PVCR's in the center carb are staggered for upper/lower plane, & the SB & RB(at least the iron ones) have the planes reversed.
The outboards are 500cfm@3"Hg, & the center is 350cfm@3"Hg, as You stated tho'...converted to 1.5" it is lower...but it is a-plenty for a 340..
They are good carbs, have one on my Duster nowNo street demon love?(i know how this will go)
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My dream engine has always been to build a blueprinted 71 340 using the 68 4 speed camshaft. Stock cast iron intake, Thermoquad and all. Maybe hang a set of good headers off it. A body, 4 speed with 3.91s.
You need to elevate your engine dreams. lol ode to mighty 340
junkyardhero
Well-Known Member
276,284 .444, .453. 4spd (1968)
268,276 .429, .444 AT (all other 340)
there is some literature showing slight deviations such as 445/455 and 430/445 but those are the generally accepted numbers. i *believe* they were all ground on a 114*. that was advertised duration and it's acknowledged that they have pretty healthy @ 50 numbers.
Frank Mopar
Well-Known Member
Calculate CFM of Carb from Vacuum
Calculate CFM from actual vacuum reading of carb
www.wallaceracing.com
So a 750 @ 1.5 = 750, @ 1 = 612, @ .5 = 433
A 600 @ 1.5 = 600, @ 1 = 490, @ .5 = 346
Say your engine only displace 500 cfm of air, a 750 @ .65 = 494, 650 @ .85 = 489,
Both carbs are basically a 500 on your engine and obviously the larger is less restrictive but the question it that enough vacuum to get your carb to run the way you want to.
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Swinger 340
Well-Known Member
I have the 68' 4-speed cam in my 69' 4-speed Dart. It runs well, with a nice thump. Don't forget the Thermoquad carb needs the later intake, as a 71'. I had the 3.91 and sold it but went back to the 3.23 as a street driver. It all depends on what you are looking for in a application. No maybe on the headers, do it. It's all in the package.
ir3333
Well-Known Member
Late to this party... responses all seem to be based on max HP. For 1/4 mile the big carb
but for a strictly street driven car, the 650 could be the ticket.
but for a strictly street driven car, the 650 could be the ticket.
My point was the Edelbrock 1407 as manufactured is flawed. Its not fair to draw any conclusion about the design or whether the extra cfm/lower restriction is a demonstrateable advantage or disadvantage.
If @Divenut wants to use the 750, then fix the flaws an it should be OK. Just looking at the build in the first post I'd say do a new baseline with the 650. Get the best mph and ET you can tune it to. Then go try something else. Less restriction should pick up some power - depending on fuel distribution etc. Tires weren't stated but I assume its close to peak power rpm at the finish. If after tuning for best et and mph their not both better than with the Carter 650, its time to figure out why. Maybe that engine doesn't have great fuel distribution. Maybe the intake velocity slows down too much. Anyway thats for later only if it doesn't work out.
If @Divenut wants to use the 750, then fix the flaws an it should be OK. Just looking at the build in the first post I'd say do a new baseline with the 650. Get the best mph and ET you can tune it to. Then go try something else. Less restriction should pick up some power - depending on fuel distribution etc. Tires weren't stated but I assume its close to peak power rpm at the finish. If after tuning for best et and mph their not both better than with the Carter 650, its time to figure out why. Maybe that engine doesn't have great fuel distribution. Maybe the intake velocity slows down too much. Anyway thats for later only if it doesn't work out.
Divenut
Well-Known Member
Thanks for all the input everyone. I'll definitely try a couple different carbs to see what it likes. Ultimately the car will be enjoyed on strip/street rips and leisurely backroad cruises.
Not many made. Even the Hot Rod magazine tests in '68-'69 were with the automatic cam that became the only cam.
Why did they drop it? I have no idea. Cost vs. sales? Emissions? Technical Issues? My guess it was production and accounting reasons.
No true replicas either.
Ken at Oregon Cams has a copy that is pretty close but he's said himself its not quite the same.
Cam craft might have had the scoop.
We would need to put a real one on a cam doctor or very carefully degree one to really understand its ramps and valve openings and closings.
The factory shop manual specs are not .004/.006 as previously discussed.
The one guy that has the dope and is or was willing to repop was given a hard time here, which seems to have discouraged him from making a run.
The ticket is a 71 intake 800 cfm t/quad its not close
smaller primaries so it has better part throttle response then 625 650 plus better mpg plus the most torque and hp
Dan the man
Well-Known Member
I'll admit I have very little experience with carburetors, but I do remember years ago that a guy who raced at MAR, had a '68 roadrunner with a warmed up 383, he had a Holley 1050 dominator on it and it was pretty much a dog off the line. I heard him complaining about how poorly his car was running and I said get rid of that wash tub carburetor and single plane intake, and use anthing other than those champion plugs and go with a 750 dp and a good dual plane intake manifold. He did just that and his cars performance greatly improved.
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