2 barrel vs. 4 barrel carb.

[lunchbox1671]

Just curious, what's so good about the holley 500cfm 2bbl?

[AMC-J/20]

Its the largest 2bbl Carb, Iys also been the most reliable I have had many 2bbl's most of which got replaced the by the holley 500 even a few Quadra pukes got ditched for Holley 500 2bbls

Mike

[will e]

So a 500cfm 2bbl is comparable to a 387cfm 4bbl. (Flow wise)

[lunchbox1671]

Oh, ok. Why not put a small 4bbl on, like a 600 or 650? I would think the primaries would be smaller than a 500 2bbl....

Sorry if it sounds like I'm knocking on your build, 2bbl carb upgrades are just new to me. Excellent build, by the way. I've been following closely!

[AMC-J/20]

Flow wise 500 vs 387 type ? I was told a 500 2bbl = 300 4bbl ? ? So technically you'd be losing flow, but the 500 2bbl on an SBC got up went quicker n smooth to me . . .

The quadra jet's I ran when smashed down had this loud bogging sound and slowly started to pull, With the 500 2bbl on the same engine it pull harder off the line about the same on the top side.

I always thought it was better anyway, Aren't they ? ?

Mike

[Ristow]

Originally Posted by AMC-J/20

Flow wise 500 vs 387 type ? I was told a 500 2bbl = 300 4bbl ? ? So technically you'd be losing flow, but the 500 2bbl on an SBC got up went quicker n smooth to me . . .

The quadra jet's I ran when smashed down had this loud bogging sound and slowly started to pull, With the 500 2bbl on the same engine it pull harder off the line about the same on the top side.

I always thought it was better anyway, Aren't they ? ?

Mike

i said this was incorrect earlier,i was backward in my comprehension of what you said. it is correct,the lesser rated 4 barrel would match the higher rated 2 barrel due to the cfm calculation differences. how the two compare flow wise i don't know.

2 barrels are flow rated at 3" vacuum,and 4 barrels are flow rated at 1.5" vacuum.

that means a similar rated 4 barrel will significantly outflow the 2 barrel. the 4 barrel will typically get better economy as well due to better velocity through the carb.

[will e]

Originally Posted by will e

So a 500cfm 2bbl is comparable to a 387cfm 4bbl. (Flow wise)

Whoops, my bad, I was thinking 2.5" vs 1.5"

4bbl is typically measured at 3"?

So then it is square root of (1.5/3)) * 500 or 353.

So a 500CFM Holley 2bbl would be equivilent to a 353CFM 4bbl.

(Unless I am wrong and then Ristow will let me know... )

Me? I prefer to see my 500cfm 2bbls framed with a couple of 350CFM's. I will post a pic later.

[AMC-J/20]

Ya I've asked about the 2bbl vs 4bbl before got many different explanations, Yours seem more Tech based then opinion.

Could you explain to me why the when I would swap the Q-jet for the 500 2bbl it seemed like the vehicles always got/felt "quicker" on off the line so to speak ? Always wondered that . . .

Mike

[Ristow]

yea,the smaller rated 4 barrel would flow similar to the higher rated 2 barrel. at what point they intersect i don't know.

[bigun]

I know that when my 390 Ford had the Holley big 2 barrel on it I could spin the tires in low gear no trouble I changed to a Holley 604 barrel and the truck couldn't get out of it's own way

[AMC-J/20]

I think the Big 2bbl is good for lo end Torque in slow reving engines, Like them big 6s that max out at 3200-3600rpm . . . V8-Setup for a 4500rpm peak . . . It seems like about every 1.5-2.5 ton truck with Gas engines were all fed by a 2bbl Carb.

There has to be a reason why opt for the 2bbl over a 4bbl.
Mike

[babywag]

Originally Posted by lunchbox1671

Just curious, what's so good about the holley 500cfm 2bbl?

It's a bolt on power maker, easy to rebuild, usually pretty easy to tune.
However it will decrease your mileage.

That being said, I have one on my '88, and I love the power it makes.
I can break loose 33" tires on pavement with it, could never do that with the stocker MC2150 carb.

Some say they're junk offroad, but add a spring loaded float, and offroad needle/seat and they do just fine.