650 or 750 Edelbrock on 340

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I know I will get flamed for this.
Dan Nothing wrong with Champion plugs.
And
Dan a carb will only flow what is demanded by what it is on.
Putting to large a carb will not be better but can be made to work.
Say you need A 600cfm putting a 750 DP will not be good. But a 750 vac secondary like 3310 will work better out the box tgan a DP.
You gotta play with a way to large carb to get it to work.
He'll you gotta play with the right size carb some.
Are the rear blades open at idle? Right jets?
And as far as Holley goes best street strip carb to get working easy is 3310. It is more forgiving on wrong app. As is easy to swap springs and jets and is vac sec.
Much better than a 4779 in wrong app.
 
Dan I ran a single plain with Holley 4777 on my auto trans 340 driver with A/C
you have to tune a carb.
 
Think of the money the carb companies could have saved by putting 1050 Dominators on everything. Unit cost would be low because of the huge quantities bought. Parts inventory cost low because of reduced number of parts that needed to be kept on the shelf......

But they didn't.....
 
340six said:
Dan I ran a single plain with Holley 4777 on my auto trans 340 driver with A/C
you have to tune a carb.
Click to expand...
He said that he tuned and tuned that carburetor and still ran poorly, all I know is that going from that 1050 to a 750dp made a huge difference
 
The volume of air the engine ingests is the same for [a] the cyl capacity & [ b] the rpm.
A 400 Chev that is turning 4531 rpm ingests the same volume of air as a 400 Chrys turning 4531 rpm....around 500 cfm. Doesn't matter what the CR is or how big the cam is...it is the same.

CFM [ cubic feet per minute ]. It is a volume measurement. Not weight or density.
What changes is the air density, & therefore the mass of air ingested into the engine. More mass, more HP.
 
I'm not saying that yourself or others haven't had good luck with champion plugs, when I was a teenager they would foul out pretty quick. For my car's use autolite copper. For 2 cycle equipment, my lawnmower, quadrunner I only use NGK. My lawnmower is going on 11 years old and when I pull the plugs at the end of the season they look great. My equipment always starts right up and they run great.
 
The roadrunner I spoke of earlier, I don't know how much cam he had, it had a noticeable idle to it. I don't know what the compression ratio was or what was done to the cylinder heads. All I remember is that it was a dog off the line and he lost a few times to sbc and sbf. Like I said earlier that I suggested that he get rid of his 1050 dominator and single plane intake. He did go to a holley 750 DP and a dual plane intake, I'm not sure but I think that he went with a Weiand. After he did the carb / intake swap I didn't see him again, I had heard that he had sold the car but I don't know this as a fact.
 
Bewy said:
The volume of air the engine ingests is the same for [a] the cyl capacity & [ b] the rpm.
A 400 Chev that is turning 4531 rpm ingests the same volume of air as a 400 Chrys turning 4531 rpm....around 500 cfm. Doesn't matter what the CR is or how big the cam is...it is the same.

CFM [ cubic feet per minute ]. It is a volume measurement. Not weight or density.
What changes is the air density, & therefore the mass of air ingested into the engine. More mass, more HP.
Click to expand...
Thousands of dyno test show even though that carb calc shows a 340@6000 rpm needs 501cfm street 649 cfm race back to back test the 750 carb makes more power.
The direct connection 10 11 12 13 second builds calls for bigger carb but i guess the factory race teams are clueless
 
I wonder how much of this comes down to bad tuning then over carbed?
 
273,
Doesn't matter how many times you explain it, guys like a-bodyguy will never get it.....
They are fixated on carb cfm.
 
273 said:
I wonder how much of this comes down to bad tuning then over carbed?
Click to expand...
I really do not think someone who builds engines and dynos them has trouble tunnng a carb its pretty easy
and they have all the readings to do it
 
Bewy said:
273,
Doesn't matter how many times you explain it, guys like a-bodyguy will never get it.....
They are fixated on carb cfm.
Click to expand...
So the dynos lie do they bewy?
Iam not fixed on anything but results
I happen to run a 650 dp on my 340
I have a 2nd 650 dp in the garage next to a holley trick kit
If ever buy a new carb for a stock 340 it will be a 750dp
But that wont happen next engine will be a stroker and it will have 950 on it
Guys like me know what the 340s made for real power and raced a 1968 gts all stock
 
Every single domestic automaker from the muscle era proved that a spread bore carburetor is best for the street. Best mix of MPG and performance and also very forgiving from a small engine to a large one. The Thermoquad was the best. Then the Quadrajet, the Ford 4300 series I think there were one or two more.
 
a-bodyguy said:
I really do not think someone who builds engines and dynos them has trouble tunnng a carb its pretty easy
and they have all the readings to do it
Click to expand...
Wasn't talking about them, talking about guy who buys a used who how was tuned before or even new say 750 throws it on some mild engine do little to no tune then decide it junk.

Just speculating where this fear of over carburation came from, not saying you can't but it seem way more for giving then some make it out.
 
273 said:
Wasn't talking about them, talking about guy who buys a used who how was tuned before or even new say 750 throws it on some mild engine do little to no tune then decide it junk.

Just speculating where Thats spotthis fear of over carburation came from, not saying you can't but it seem way more for giving then some make it out
Click to expand...
thats the most likely cause for sure
there is a member on fabo has the 360/380 crrate motor gears the whole chabang
But questions 340s running low 14s stock because he is running something like 14.6
 
The Rochester QJ with 1 3/8" primary bores. Rated at 750 or 800 cfm, depending on which book you read....

Used on a 1967 Pontiac 230 cu in inline 6 engine....455 Pontiac [ double the cubes ]....500" Cadillac....& heaps of others.
Do you think the QJ air valve on the 230 ever opened? Probably rusted shut from non-use....
 
Bewy said:
The Rochester QJ with 1 3/8" primary bores. Rated at 750 or 800 cfm, depending on which book you read....

Used on a 1967 Pontiac 230 cu in inline 6 engine....455 Pontiac [ double the cubes ]....500" Cadillac....& heaps of others.
Do you think the QJ air valve on the 230 ever opened? Probably rusted shut from non-use....
Click to expand...
Horse crap. Mama had one on a 67 Tempest and Daddy used hit 90 on the way to Fernandina Beach when we went on vacation growing up. That quadrajet would make that big old Poncho hood shake when it opened up. And it DID open. lol
 
Bewy said:
The Rochester QJ with 1 3/8" primary bores. Rated at 750 or 800 cfm, depending on which book you read....

Used on a 1967 Pontiac 230 cu in inline 6 engine....455 Pontiac [ double the cubes ]....500" Cadillac....& heaps of others.
Do you think the QJ air valve on the 230 ever opened? Probably rusted shut from non-use....
Click to expand...
BMW makes a Q-jet intake for the M30 I6 motor! they also make one for the B190 6 cyl marine motor too!

wild stuff
 
RustyRatRod said:
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.
Click to expand...

RustyRatRod said:
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.
Click to expand...
Heavily worked 71 manifold

IMG_4058.jpeg
 
JY Hero.
Do you have any pics? First I have heard of QJ being used on non US cars.
 
Bewy said:
JY Hero.
Do you have any pics? First I have heard of QJ being used on non US cars.
Click to expand...
let me dig around a little. i don't think they *came* with QJ's but i've seen them mounted and the manifold flange is 100% for a spread bore. i've stumbled across two at the yard, one had a QJ and the other had a small holley on it with an adapter which seems the more common set up due to the inability of the general public to tune a carb.

anyway here's one for sale with a solex that looks like a long lost QJ twin:

www.ebay.com

Used 1971-1974 BMW E3 E9 3.0CS Bavaria M30 Intake Manifold w/ Solex 4A1 Carb | eBay

Find many great new & used options and get the best deals for Used 1971-1974 BMW E3 E9 3.0CS Bavaria M30 Intake Manifold w/ Solex 4A1 Carb at the best online prices at eBay! Free shipping for many products!
www.ebay.com

heres a bare one (pic from another forum):
20170221_152234.jpg


the M30 motor can be built pretty stout and if i was gonna do it, 100% i'd throw a TQ on there just for that BBBWWWWAAAAAAAA when the 2ndaries tip in.
 
Bewy said:
Wow, thanks for that. Very interesting.
Click to expand...
considering the the stock set up is twin zeniths, i can certainly see the appeal!

i was quite surprised when i stumbled upon that setup and to learn about the widespread use of it. but basically everybody converts to stock FI from later models or twin webers, though.
 
750 Eddy on my 340 .030 over with a mopar purple .509 cam along with 3500 stall and a 9" ford 389 gear set. The 750 works great with this set up. Oh I may add that I also have a Holley Blue electric fuel pump with psi regulator set at 7psi
 
junkyardhero said:
let me dig around a little. i don't think they *came* with QJ's but i've seen them mounted and the manifold flange is 100% for a spread bore. i've stumbled across two at the yard, one had a QJ and the other had a small holley on it with an adapter which seems the more common set up due to the inability of the general public to tune a carb.

anyway here's one for sale with a solex that looks like a long lost QJ twin:

[/URL]

heres a bare one (pic from another forum):
View attachment 1716217303

the M30 motor can be built pretty stout and if i was gonna do it, 100% i'd throw a TQ on there just for that BBBWWWWAAAAAAAA when the 2ndaries tip in.
Click to expand...
That's interesting. I was just looking at 3.5 litre BMW coupe from the late 1970's or early 80's yesterday but it was injected.

You wouldn't happen to know if that Solex is a divorced Idle design?
 
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