Tunning Dual Carbs

[shelbydoug]

      Here's a curve Doug. IF you had a two inch tall "box" made to bolt onto your Weber manifold you could run two Webers and make more power than you do now with four. The ability for all eight cylinders to "feed" off of a common area makes a huge difference.

Stop it. You will push me over the edge. I've been dangling there for years.

[1109RWHP]

Would my combination work better using two 390 cfm carbs instead of the 600's? I was wondering about this before I spend a lot of time messing with the 600's. The only thing I have done so far is install the secondary diaphragm covers with the vacuum fitting to tie them together and replaced the secondary metering plates with ones you can install normal jets in.

[shelbydoug]

Would my combination work better using two 390 cfm carbs instead of the 600's? I was wondering about this before I spend a lot of time messing with the 600's. The only thing I have done so far is install the secondary diaphragm covers with the vacuum fitting to tie them together and replaced the secondary metering plates with ones you can install normal jets in.

Depends on what you mean by better. I don't think so. I think the 600's are just about right. How hard it pulls depends on the gearing. I'm running a Richmond 5 speed, 3.27 first gear, 3.50 rear.

I don't know about the flow numbers but it makes one heck of a racket and its hard to see over the hood until the nose comes down. It pulls very hard from any rpm in seemingly every gear. I do not think it is over carbed.

It's a perfect example of how you can do everything wrong and turn out so well. Pulls very much like a big block.


Actually Randy presumes that my Pantera never ran anything but Webers. Not so. It ran the Ford Motorsports version of the Edelbrock Torker, aka, the 341-a, and a Holley 4779, 750 dp. It wasn't even close to the Webers. Kind of like an electric golf cart going up hill by comparison.

Sometimes I think things like flow numbers are just for the nerds to argue over and just load into their data forms? As Randy points out, no one races a flow bench. So of the results just seem to defy logic at times?

[2112]

I bet throttle response will be better with 2 smaller carbs but top end numbers may take a hit.

[shelbydoug]

I bet throttle response will be better with 2 smaller carbs but top end numbers may take a hit.

It will be all done by 3500

[1109RWHP]

Ok, I will go with what I have.

[jerry merrill]

I have a 347 with dual quads that are 390 cfm and I could not be happier, it doesnt stumble or hesitate and pulls like a frieght train cleanly past 6k, i have the carbs mounted backwards like 67 gt500. Mustang and Fords issue a few years back got the highest HP with the 390's over 460's. I didnt think they would work that good but I was wrong.

[2112]

It will be all done by 3500

Nope

[shelbydoug]

It will be all done by 3500

Nope

By comparison to 600's it will.


This all depends on what your set up is. Size of engine. Type of transmission. Gearing. Camshaft, not to mention type of linkage and is about the same discussion as selecting any of that criteria.

Run what makes you happy and how you like it.


As far as relying on what some of these magazines investigate I've taught more intelligent and insightful  high school tech classes. I haven't seen one yet where they can even select a matching camshaft for what they are going to test.

They are good reading for filling your spare time in study hall.



If you want to argue, go tell your wife that her hair cut  sucks and slug it out with her. I'm not interested. I learned not to do that 50 years ago.

NO ONE is going to write a prescription for what you should take. This is largely what you like.

[2112]

I am not arguing. You made a blanket statement and I responded.

I have compared a very similar small carb combo to a big carb combo on a common plenum intake (very high end build) no other changes were made and my experience was greatly improved throttle response with a small hp loss at 6500rpm. It certainly didn't fall off at 3500.

[427heaven]

Not unless its a 6 banger...

[shelbydoug]

I am not arguing. You made a blanket statement and I responded.

I have compared a very similar small carb combo to a big carb combo on a common plenum intake (very high end build) no other changes were made and my experience was greatly improved throttle response with a small hp loss at 6500rpm. It certainly didn't fall off at 3500.

I don't care if you are arguing or not. I'm just not going to. I too am not a novice on this and am just offering guidance.

This is like offering $20 to the homeless guy and he kicks you in the balls because you are a cheap bast ard.

Simply put. It don't matter to me. Figure it out yourself. 

[gt350hr]

Would my combination work better using two 390 cfm carbs instead of the 600's? I was wondering about this before I spend a lot of time messing with the 600's. The only thing I have done so far is install the secondary diaphragm covers with the vacuum fitting to tie them together and replaced the secondary metering plates with ones you can install normal jets in.

    The factory  T/A "regular" Holley intake used 720 cfm center squirters. ( 660s weren't invented yet) Going to a 390 carb is a waste of time. When I ran the Shelby intake at the drag strip ( back in the late 70's) , I ran 1850s and just a jetting change up to 70s in the primary but I had Eelco plates in the secondary and used regular Holley jets ( 71 by my note book) I had the diaphrams connected too. It was worth about a tenth of a second and 1.5 mph in trap speed over the H&M manifold and 850 DP I normally ran. Yours should be similar jet wise. Quick Fuel makes secondary jet conversion plates now and they are superior to what I ran.
     Randy

[gt350hr]

I have a 347 with dual quads that are 390 cfm and I could not be happier, it doesnt stumble or hesitate and pulls like a frieght train cleanly past 6k, i have the carbs mounted backwards like 67 gt500. Mustang and Fords issue a few years back got the highest HP with the 390's over 460's. I didnt think they would work that good but I was wrong.

     Jerry,
        Every engine is different and the same goes for carburetors and manifolds. Your combination works well for you no doubt but it would hurt the performance of my 331 drag race engine. I know because I have tried them.
    Randy

[1109RWHP]

I have the secondary plates already and the vacuum units connected.