340 Advice

[Mopar4Speed]

Is the Avs II eddy as good as everyone is raving about or is it all just hype?

 

[rumblefish360]

Here’s your electric choke! 2-800 TQ’s!

 

[Challenger340]

I like a 440 AVS and a big TQ!

Yep.... either works really well

 

[RJRENTON]

Is the Avs II eddy as good as everyone is raving about or is it all just hype?

As I previously mentioned, the Edelbrock AVS 2 (or AVS II, if you prefer), is a hermaphrodite, or a combination of the old Carter AFBs, that used counterweighted velocity operated air valves above the secondary butterfly valves but were below the secondary booster venturi. The "new" AVS 2, removed the velocity operated air valves and added the "old" Carter AVS air valve blade, but maintains the secondary booster venturi below the air valve blade. Notice the clearance slots in the back edge of the AVS 2 air valve blade...that allows the air valve blade to clear the booster venturii fuel delivery tubes when it opens.
True...the PRIMARY BOOSTER VENTURI's annular feature is a great improvement over the origional Carter design. This feature allows for better atomization of the fuel, resulting in more even fuel distribution and significantly better off idle transition to the main fuel. But with modifications to the origional Carter design's off idle/transition circuit similar results can be achieved....IMO.
One additional factor to consider, for the Carter TQ proponents, consider the Holley Spread Bore design. It uses the time honored Holley designs, BUT the 4165 model never achieved great popularity as a Quadrajet replacement.
To answer your origional question, re popularly of the AVS 2, you'll only hear about the good aspects but seldom or never the bad results .... its only human nature to suppress our failures or mistakes.
BOB RENTON

 

[Sparky Anderson]

I run a holley 3310 750 vacuum secondary on my 340 with 4:30 gears and gets out of the hole real strong and surprises a lot of big block cars.

 

[Green72]

Ever consider TBI?

 

[JC Boatguy]

Now I gotta jump in. I owned a 340 with 284 duration cam 445 lift and ran a 650 Holley spread bore double pumper mechanical secondary and that carburetor was unbelievably efficient and had absolutely instant off the line throttle response and top-end. It had a 10cc secondary accelerator pump chamber which made absolutely Wicked throttle response, also a 4 speed car.

 

[72sunroof]

Hi all,

To all those that replied or viewed my previous thread on my 318 issue, I ended up just getting a 340 for the extra cubes and power potential.

Just wanted some advice on what the correct pushrods would be for my 340. I was able find a beautiful like new set of original 273 adjustable rocker arms with the original banana groove shafts. The stock 340 stamp steel rocker pushrods measure approx 7.5" tip to tip. I read somewhere that people have luck with the Sum-g6420 (7.389") pushrods on La's with hydraulic lifters and adjustable rocker arms. Comp cams also makes some pushrods for this application (cup and ball 7.389") but they have pressed tip whereas the summit ones are welded for less money. Should I upgrade the carb or if the 600cfm is enough for my setup? Was leaning towards the the new Avs2 eddy.. Let me know your thoughts/opinions..

Specs of the engine are:

1969 340 block bored 0.030" over
Mahle Powerpak Forged Flat Top Pistons & balanced to crank
MP high volume oil pump and full groove main bearings
MP purple cam P4452992 280/.474
Original Forged 4 speed crank with factory windage tray
Pocket ported X heads, Manley Stainless valves, Comp 901 springs, Hardened locks & retainer
Tti Headers 1 5/8 step to 1 3/4 with x pipe 2.5" duals
Edelbrock Air gap intake
Edelbrock 1406 Carb
Petronix Billet Distributor with Ignitor 3
Edelbrock dual roller timing chain

I would give it a 1407 Edelbrock 750 cfm carb and let that 340 cid eat! 440'

This 1000%. I have a similar build and l run a 850 Thermoquad with 100 primaries and 147 secondaries. It pulls to 6500 rpm.
They sell an aftermarket electric choke for thermoquads. Or Get the biggest Street Demon 750 i believe.

 

[rumblefish360]

They sell an aftermarket electric choke for thermoquads.

Really? I’d like to see that. Link please.

 

[72sunroof]

Really? I’d like to see that. Link ple@ase.

https://www.carburetor-parts.com/cu1245.html

I use the Mopar time delay module hooked up to the choke with heater wire.

 

[rumblefish360]

https://www.carburetor-parts.com/cu1245.html

I use the Mopar time delay module hooked up to the choke with heater wire.
View attachment 1192103

Wow! I have fiddled with my own version a long ways back by bending up my own tin bracket and making use of an Edelbrock choke. This is much nicer. I had no idea this was available at all. Glad your here & thanks for that link!

 

[JC Boatguy]

As I previously mentioned, the Edelbrock AVS 2 (or AVS II, if you prefer), is a hermaphrodite, or a combination of the old Carter AFBs, that used counterweighted velocity operated air valves above the secondary butterfly valves but were below the secondary booster venturi. The "new" AVS 2, removed the velocity operated air valves and added the "old" Carter AVS air valve blade, but maintains the secondary booster venturi below the air valve blade. Notice the clearance slots in the back edge of the AVS 2 air valve blade...that allows the air valve blade to clear the booster venturii fuel delivery tubes when it opens.
True...the PRIMARY BOOSTER VENTURI's annular feature is a great improvement over the origional Carter design. This feature allows for better atomization of the fuel, resulting in more even fuel distribution and significantly better off idle transition to the main fuel. But with modifications to the origional Carter design's off idle/transition circuit similar results can be achieved....IMO.
One additional factor to consider, for the Carter TQ proponents, consider the Holley Spread Bore design. It uses the time honored Holley designs, BUT the 4165 model never achieved great popularity as a Quadrajet replacement.
To answer your origional question, re popularly of the AVS 2, you'll only hear about the good aspects but seldom or never the bad results .... its only human nature to suppress our failures or mistakes.
BOB RENTON

Bobs right! Holley spreadbore is EXCELLENT!!! MY 340 had one and it really is the best of both worlds, great economy and gobs of power when needed, absolute INSTANT throttle response.

 

[rumblefish360]

Anyone use the 4011 spreadbore Holley?

 

[HawkRod]

I know this is an old thread, but I built a stroker 340 with 416 cubic inches. I put an 850 Carter Thermoquad from a 400 on it.

I know the Thermoquad is often an afterthought to other carburetors, and it was in my mind too. ...UNTIL I put one on my 416 stoker motor.

A Thermoquad really is a great carburetor. First of all, the small primary bores give you great throttle response as well as optimal fuel economy. But then the massive secondaries give you the power when you put your foot in it. In addition to that, the secondaries only open based on demand from the car, so you really can't over carburate your car, unlike for example, a traditional Holley.

 

[6PKRTSE]

I have run both 650 and 750 carbs on my 340 engines as well as 1407 Eddy carbs depending what was done to them with no issue with either.