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What would be the best carbs for blown 440

Posted By: 440dustr

What would be the best carbs for blown 440 - 03/13/12 09:03 PM

Hi everyone
I have a 70 440 duster with an 871 bds blower. I have a pair of 600 edelbrocks on it now. Runs pretty good just having and issue after I drive it a while it tends to stall when i am at a light and go to take off, or if i am coasting slow then go to go and once in a while when I drive up an incline. I checked the floats they seem correct. I am wondering should I look into a better carb setup for my car. Its main intent is just crusing around locally.
what are your recommendations?
Posted By: DaytonaTurbo

Re: What would be the best carbs for blown 440 - 03/13/12 09:04 PM

You should be able to make those carbs work. Others are running similar carbs on blown 440's. If it was me, with a blown 440 I would run a pair of holley 3310's.
Posted By: 440dustr

Re: What would be the best carbs for blown 440 - 03/13/12 10:34 PM

any other suggestions
Posted By: Clanton

Re: What would be the best carbs for blown 440 - 03/13/12 11:42 PM

maybe it is boiling the fuel so it needs a insulating spacer under the carbs but on my car i found the fuel pressure to be too high when that happins.
Posted By: Anonymous

Re: What would be the best carbs for blown 440 - 03/14/12 01:02 AM

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Posted By: Cab_Burge

Re: What would be the best carbs for blown 440 - 03/14/12 02:43 AM

Check the springs under the step up rod pistons idling in gear to see if they are pulsing up and down or staying down like they should If pulsing trim one coil off of the spring at a time until they stay down
Posted By: DARTH V8Я

Re: What would be the best carbs for blown 440 - 03/14/12 02:55 AM

PREDATOR CARBS
Posted By: John_Kunkel

Re: What would be the best carbs for blown 440 - 03/14/12 07:33 PM

Quote:

Check the springs under the step up rod pistons idling in gear to see if they are pulsing up and down or staying down like they should If pulsing trim one coil off of the spring at a time until they stay down



Any Carter/Edelbrock carb on the top of a blower should have the metering rods blocked full up....(or removed)
Posted By: Cudajon

Re: What would be the best carbs for blown 440 - 03/15/12 12:37 AM

Don't know about removing the springs but it sounds to me like as the blower heats up you losing pressure so the signal to the carbs is changing. I would play with the springs in the metering rods when the engine is hot, this is something you can do on the side of the road. I would go for a heavier spring. Edelbrock recommends the orange at 5".
Quote:

Two model #1405 carburetors should be used on engines with positive displacement superchargers, such as GMC 6-71 blowers or equivalent. The following calibration changes make an
excellent starting point: Primary Jets - .101" (#1429); Secondary Jets - .101" (#1429); Metering Rods - .070" x .042" (#1450); Step-up Piston Springs - 5" (orange, stock); Needle & Seat
assemblies - .110" (#1466). This calibration has been tested on engines ranging in size from 350 c.i.d. Chevys to 440 c.i.d. Chryslers with good results.

Posted By: Clanton

Re: What would be the best carbs for blown 440 - 03/15/12 12:55 AM

any pics?
Posted By: Cab_Burge

Re: What would be the best carbs for blown 440 - 03/15/12 03:06 AM

Quote:

Quote:

Check the springs under the step up rod pistons idling in gear to see if they are pulsing up and down or staying down like they should If pulsing trim one coil off of the spring at a time until they stay down



Any Carter/Edelbrock carb on the top of a blower should have the metering rods blocked full up....(or removed)

Why would you do that Why render that metering circiut useless
Posted By: chrisf

Re: What would be the best carbs for blown 440 - 03/15/12 05:53 AM

i ran 2 750 eddy's on my blown 383 worked great. only problem was at the end of the 1/4 at 130mph it blows fuel all over the windsheild. i think if you read it says those carbs are not designed to be outside of the hood.
my buddy has eddys on his 440 and it works

youtube
Posted By: John_Kunkel

Re: What would be the best carbs for blown 440 - 03/15/12 07:31 PM



Why would you do that Why render that metering circiut useless



On a normally aspirated motor, vacuum drops off to near zero at WOT and the metering rod springs push the rods out of the jet to richen the mixture but a blower will create plenty of vacuum at WOT...at high vacuum the metering rods will descend into the jets and lean the mixture at a time when the most fuel is needed; in many cases this will cause a lean backfire through the blower or might burn pistons...AMHIK.

In the AFB/Edelbrock there is no separate "metering circuit" as in the Holley, the metering rod merely increases/decreases the area of the primary main jet to control the mixture.

Stiffer springs will only delay the descending of the metering rods, if enough vacuum builds at high RPM it will overcome the springs and lean the mixture then.....POW!!!! BTDT and have the busted parts.
Posted By: Cab_Burge

Re: What would be the best carbs for blown 440 - 03/15/12 09:29 PM

John, I have not seen any vacume at WOT on the engines I've dyno tested between the carbs and the blower rotors , same thing below the blower when at part throttle going to full throttle before boost is made It would (vacume signal)read vacume at part throttle in the blower intake and then go to zero and then start making boost This was with two 650 Holleys, two 1050 Dominators and two 750 carters, I have not dyno tested a roots blown motor with a single carb so I don't know if they wll make vacume under the carb at the upper RPM or not
Posted By: DARTH V8Я

Re: What would be the best carbs for blown 440 - 03/15/12 09:38 PM

Quote:

I have not dyno tested a roots blown motor with a single carb so I dino't know if they wll make vacume under the carb at the upper RPM or not


We did (4-71, single Holley 900), the answer is (in our app anyways) no vac. below the carb.
Posted By: John_Kunkel

Re: What would be the best carbs for blown 440 - 03/16/12 09:01 PM

Anecdotal experience varies, my 15% overdriven 6-71 would pull enough vacuum to close 6.5 power valves on a pair of 780 Holleys...Carter/Edelbrock works on the same principle.

From the Holley tech page:

"QUESTION What is a Manifold Referenced Power Valve?

ANSWER Nothing will kill a blower or Nitrous engine quicker that a lean condition. You want plenty of fuel available for the engine to use. There is a thing you need to know about the power valves on a roots style blower engine. The power valve is installed to keep the engine from loading up and running rich at an idle. On a normally aspirated engine the engine vacuum at idle will hold the power valve closed. When you step on the gas the throttle plates open and the engine vacuum drops as you accelerate. When the vacuum drops below the rating of the power valve , it snaps open and richens up the main system. On a blower with the carb mounted above the rotors there is constant vacuum all the time even under wide open throttle. The power valve will never open and you will have a lean condition. To remedy this there is a modification you can have done that is called manifold referencing the power valve. You plug the vacuum feed hole in the baseplate for the power valve. Then you drill a hole in the side of the main body into the hollowed out vacuum chamber for the power valve. You then insert a vacuum nipple in this hole. You will run a vacuum line to the lower intake manifold from the new vacuum nipple. Now you will have vacuum on the power valve at an idle, and when you hit the gas as the boost builds, it will force the power valve to open and richen up the main system. This can be done by most carb modifiers or even yourself. We offer quite a few different size blower carbs with this already done. Consult you local Holley dealer or our Techline for the correct application.
"
Posted By: VZCharger

Re: What would be the best carbs for blown 440 - 03/17/12 12:48 AM

I had a pair of 750 Mighty Demon boost referenced carbs on mine until I went with EFI. They worked great, motor was 440 with a 8-71. I had a pair of edelbrocks on there before that and they were always a touch lean under full boost.

Matter of fact just reminded me I have to get rid of them
Posted By: Rug_Trucker

Re: What would be the best carbs for blown 440 - 03/17/12 05:10 AM

Quote:

PREDATOR CARBS



Never got into specifics with a blown 392 owner with a set of these. Said it ran like crap, Went back to his Eddies.
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