35mm PWK VS. 39mm PWK

[530grafix]

Whats everyones experiences with 35s vs 39s on a 4mill cub. Just wanting to know if its worth switching carbs. I drag at sand mountian, nv 50% and Dune 50%..

[Bansh-eman]

stick with the 35's... the 39's will give you more power on the VERY topend but you wont have any bottom end for the dunes.

[530grafix]

stick with the 35's... the 39's will give you more power on the VERY topend but you wont have any bottom end for the dunes.

Thanks, thats what i kind of thought but wanted a second or more opinion!

[flotek]

39's will give a solid 4 or 5 more hp everywhere (not just topend)o n a ported 4mill cub over the 35pwks

...wha t your thinking makes sense ,but cubs love huge carbs and if i hadnt seen the dyno graphs that show this i wouldnt belive it either ,i would say the bigger carbs are worth the expense on your setup

[_Hex*]

Thanks, thats what i kind of thought but wanted a second or more opinion!

 

 

nooo noo no definately 39's you will run them dry if you dont set them up right for the hill, and as far as not having bottom end on the 39? haha ive taken out a 20mil trex (yes i know its not all that great but still) on alky and override with a 4 mil cub stock tranny. and yes the t rex was running good not shitty. stick with the 39's you cant go wrong

[dajogejr]

39's all the way since you drag 50% of the time...

Hex is right...if you're running a long distance, billet float bowls and a dual feed fuel outlet is probably a good call...

 

I can hook you up with the billet bowls, hit me up if you need a set.

[moneybags]

Swiching from 35's to 39's is like night and day. You could always get some velocity accelerators.

[Dave I.]

if you want to try alky again i got some 39s :biggrin:

[FireHead]

39's will give a solid 4 or 5 more hp everywhere (not just topend)o n a ported 4mill cub over the 35pwks

...wha t your thinking makes sense ,but cubs love huge carbs and if i hadnt seen the dyno graphs that show this i wouldnt belive it either ,i would say the bigger carbs are worth the expense on your setup

That's not what I have seen on my dyno with in-frame pipes on my 4mil running race fuel. If you are running alcohol, then the larger carbs make sense. Otherwise, they do not................. :geek:

[flotek]

That's not what I have seen on my dyno with in-frame pipes on my 4mil running race fuel. If you are running alcohol, then the larger carbs make sense. Otherwise, they do not................. :geek:

 

yes it was a gas 421cub with shearer sb inframes ,it makes sense

[FireHead]

yes it was a gas 421cub with shearer sb inframes ,it makes sense

BS.............. Mathematically speaking, a 421 cub with air flow increased 50% over the as-cast capability of the cylinder, will not reach mach 1 flow speed through 35mm carburetors, let alone 39mm carbs. If you were effectively able to come up with a way to move the air volume requirted with that setup, then the small bore pipes you are using will become a limitation.

 

If you make more power with that setup with 39mm carbs than with 35mm carbs, then your 35mm carbs/intake are setup incorrectly or you have ported the cylinders for peak air flow at such a high rpm that your torque output is not what it could be (there is no "free lunch," to quote John Judd when it some to horsepower vs. torque with a given engine displacement).

 

Maybe you have a problem with your dyno or dyno techniques? :ermm: