Better Performance Output

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Raul

Raul

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Mukilteo/Marysville, WA
I Have a mild build on my 340 '68 Barracuda fastback with Summit Racing intake, 650 cfm double pumper, Pro Comp Heads, roller rockers/lifters, Speed Daddy headers with 1.5 inch tubes,. It ran 13.58 in the 1/4 mile with 3.55 gears. I had it Dyno'ed @318 HP to the wheels and roughly 300 ft-lbs of torque. I've upgraded to Edlebrock RPM Airgap intake which notably Increased throttle response/power and also switched out headers to Doug's with 1 5/8 tubing. Would a better carburetor help? What size is typically used on upgraded mild builds? Is 650cfm sufficient? Would a 750 produce more or be overkill, ....I noticed it ran rough with the intake manifold change and plan on another dyno tune.
 
A 750 is fine. What about the engines cam, compression etc.
 
Raul said:
I Have a mild build on my 340 '68 Barracuda fastback with Summit Racing intake, 650 cfm double pumper, Pro Comp Heads, roller rockers/lifters, Speed Daddy headers with 1.5 inch tubes,. It ran 13.58 in the 1/4 mile with 3.55 gears. I had it Dyno'ed @318 HP to the wheels and roughly 300 ft-lbs of torque. I've upgraded to Edlebrock RPM Airgap intake which notably Increased throttle response/power and also switched out headers to Doug's with 1 5/8 tubing. Would a better carburetor help? What size is typically used on upgraded mild builds? Is 650cfm sufficient? Would a 750 produce more or be overkill, ....I noticed it ran rough with the intake manifold change and plan on another dyno tune.
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You don't need anything bigger than a 750 cfm carb with the proper camshaft, rear gear, and stall converter. A stock 340 4 barrel cam is a actually a decent cam. 65'
 
Im doing something similar with my 73 340 dart. Just a bone stock engine right now. Im adding air gap intake, AVS2 650 carb and tti 2.5 exhaust. In my case I dont think anything more than a 650 carb would help. Im staying with the stock exhaust manifolds so thats going to be a bottleneck.
I think your build could handle a 750. You didnt say what cam your running, is it stock?
 
If I went with a 750, what brand carburetor is better with throttle response? Holly, Edelbrock, or are they pretty equivalent?
 
20170921_183748.jpg


This is before the intake/exhaust upgrade
 
Install a vacuum gauge.
And see what your pulling at a full throttle run. Then go from there. If its higher than 1.5 you definitely want a bigger carb. Just make sure it aint the breather holding it back. If your more like 1 its debatable.
 
Deep-6 the open airfilter and go with cold air intake tubing.
The open filter element pretty much cancels out the benefits of the Air Gap manifold.

Also ditch the solid mounted flex fan for a thermo-clutch with a factory fan with aluminium blades.
A fanshroud would take care of any hot idling issues.
 
273 said:
Install a vacuum gauge.
And see what your pulling at a full throttle run. Then go from there. If its higher than 1.5 you definitely want a bigger carb. Just make sure it aint the breather holding it back. If your more like 1 its debatable.
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I basically agree. Even around 1.5" I'd say its a crapshoot whether there's much to be gained. Depends a bit on the quality of the fuel distribution. Up around 2" Hg at the end, I totally agree. Just make sure your throttles are fully open with the pedal at the bottom when you do the test. (forgive me if that sounds basic, but its often overlooked)

Raul said:
If I went with a 750, what brand carburetor is better with throttle response? Holly, Edelbrock, or are they pretty equivalent?
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Which ever one your most comfortable tuning. Honestly, I'd look for an old school Carter or Holley (pre 1990s) like a 4779 with a low - revision number. Less likely to have problems (and new carbs aren't cheap). Since you're running a Holley style now, there's the slight advantage of keeping the same fuel lines.

All that said, might want to experiment further tuning with your current setup. Working with initial timing, see if more vacuum can be developed at idle (in drive if an automatic). On the dyno, make sure the fuel curve is flat, and at the track, finalize jetting (and total timing) for best mph.
 
70aarcuda said:
Holley 750 Double Pumper if you want performance
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And so long as the rest of the drivetrain can handle a sudden wide open throttle hammering.

273 said:
Install a vacuum gauge.
And see what your pulling at a full throttle run. Then go from there. If its higher than 1.5 you definitely want a bigger carb. Just make sure it aint the breather holding it back. If your more like 1 its debatable.
Click to expand...
On mild 360’s, your looking at approximately a 10hp gain. This is a very variable number. It could very well be greater.

BigBlockMopar said:
Deep-6 the open airfilter and go with cold air intake tubing.
Click to expand...
I don’t understand how this applies.
The open filter element pretty much cancels out the benefits of the Air Gap manifold.
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Totallly disagree th this!!!!
The better the air filter is, the better the intake can shine. To cancel any benefit the intake has, install a crappy air filter.

Raul said:
If I went with a 750, what brand carburetor is better with throttle response? Holly, Edelbrock, or are they pretty equivalent?
Click to expand...
Throttle response is directly related to the size and state of tune of what ever carb you run. PERIOD!
State of engine tune is also included with this. But for the moment, let’s assume everything about it is in mint tip top shape. And the only variable is the carb.
 
rumblefish360 said:
And so long as the rest of the drivetrain can handle a sudden wide open throttle hammering.


On mild 360’s, your looking at approximately a 10hp gain. This is a very variable number. It could very well be greater.


I don’t understand how this applies.

Totallly disagree th this!!!!
The better the air filter is, the better the intake can shine. To cancel any benefit the intake has, install a crappy air filter.


Throttle response is directly related to the size and state of tune of what ever carb you run. PERIOD!
State of engine tune is also included with this. But for the moment, let’s assume everything about it is in mint tip top shape. And the only variable is the carb.
Click to expand...
Ok, I decided to try a Holly 750 Double Pumper but noticed there are many models to choose from, which model would perform best? Would the aluminum holly be a good performance gain? I would definitely need one with an electric choke. And I would be opting to tune the carburetor while it is on a dyno.
 
Raul said:
Ok, I decided to try a Holly 750 Double Pumper but noticed there are many models to choose from, which model would perform best? Would the aluminum holly be a good performance gain? I would definitely need one with an electric choke. And I would be opting to tune the carburetor while it is on a dyno.
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67200 is the Proform number. I personally wouldn't use a 4779 Holley as they came with a fairly rich tune up and the last I knew they don't have replaceable airbleeds etc.

A few days ago a guy had a Proform 750 for sale here in the FABO for sale section with a pretty righteous price.

FWIW I also don't run carbs with a choke. Other than a fast idle the choke is just a pain in the ***.
 
Raul said:
Ok, I decided to try a Holly 750 Double Pumper but noticed there are many models to choose from, which model would perform best? Would the aluminum holly be a good performance gain? I would definitely need one with an electric choke. And I would be opting to tune the carburetor while it is on a dyno.
Click to expand...
This I somewhat answered in the private message you sent me. I’m not going to repeat it here. You could always do yourself a genuine favor, and call quick fuel. (AKA Holley.)
 
If it was mine, I would make sure the combo that's THERE is in optimal tune FIRST, before changing anything. Often times, when one does not run to the potential the owner thinks it should, it's simply a case of not having the best tune. "I" would try that first. It may pick up the gains you're looking for.
 
rumblefish360 said:
I don’t understand how this applies.
Totallly disagree th this!!!!
The better the air filter is, the better the intake can shine. To cancel any benefit the intake has, install a crappy air filter.
Click to expand...

Just like he did yes.
Not sure what you don't understand here; He installed a cheap $5 airfilter with a $10 China filterhousing, sucking in hot engine bay air.
 
RustyRatRod said:
If it was mine, I would make sure the combo that's THERE is in optimal tune FIRST, before changing anything. Often times, when one does not run to the potential the owner thinks it should, it's simply a case of not having the best tune. "I" would try that first. It may pick up the gains you're looking for.
Click to expand...
Wish I knew how to tune them or where to go to get it tuned....The last tune before I changed over to the Air gap intake cost me just over $600.00 They did an optimum tune with jet/metering rods and changed out the weights for timing advance. They did an awesome job with its performance, but the tune cost me as much as a new 750 double pumper....thinking of getting both carbs tuned to the engine and just using the 750 on the track
 
BigBlockMopar said:
Just like he did yes.
Not sure what you don't understand here; He installed a cheap $5 airfilter with a $10 China filterhousing, sucking in hot engine bay air.
Click to expand...
Are you suggesting cutting my hood to add a taller Air filter element and inducing cold air through an aftermarket hood scoop?
 
rumblefish360 said:
This I somewhat answered in the private message you sent me. I’m not going to repeat it here. You could always do yourself a genuine favor, and call quick fuel. (AKA Holley.)
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As I looked through my records, the carburetor I currently have is in fact a Quick Fuel Carb. So these are actual Holly Carbs as well?.. So much information and so much to choose from...Are the Quick Fuel Carbs just as good as the Holly Carbs? The Quick Fuel 650 I currently have required extensive tuning and clogged up easily as the car went through its cosmetic restoration of over a year. I had to rebuild it at $250.00 just to get it going again. It performs awesome when optimally tuned on the dyno.
 
I love the information on our forum And I Thank you all for responding and trying to help me with my build and restoration.
Merry Christmas to all of you.

Raul
 
Quick Fuel used Holley carbs.
Holley purchased Quick Fuel.
Competition eliminated.
 
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