Best Carburetor

Just dreaming again....maybe.

The rodders at work tell me to dump the Qjet and go with a double pumper like a Holly, BG, or other.

They say that a Qjet is not the best for a manual trans. We are talking from a pure power standpoint. They have no argument that for street cruising there is probably nothing better than a well tuned Qjet in terms of carbs. Talking Carbs not FI.

So, I've been looking at various carbs. Holly is where I get the most info and interactive selection for the application. So I looked at the 4150. They state that it is ok for 3100lbs or less manual. Guys at work say BS. They are good for more weight than that.

The double pumpers are mostly square bore, so an adapter would be required amongst other things. So, from a pure power off the line standpoint, is a double pumper that much better than a Qjet?

Right now, the vette is probably 3500 + lbs with me in it. Then engine pulls 532lbs torque and around 480HP. The Qjet is tuned quite well. Instant power, no transition lag, etc. AFR at 12.5 to 13.0 at WOT.

The Holley is better for more power, at the cost of economy. However, carb size has jack shit to do with car weight.(Where do they get this crap)?

CID X RPM X Volumetric effeciency / 3456 = CFM

IE, assume VE of 100%, 350x7000rpmx1/3456=709CFM

For best results, not economy, vacuum secondaries with auto, mech. secondaries with manual. (Although you can use a vacuum secondary with manual for a little more economy). However, it wont be as fast.

It just depends on what you want the car to do. On the last tour, Darrow's BBC and Scotty's SBC were far faster than me on acceleration. However, due to the curvy roads, with me in the lead, they could barely keep up.
I used 1/4 tank all day. They filled up twice. I had more than enough power to drive at the brink of "unsafe."
NOW, at the drags, they would clean my clock in a heart beat. I know, I have driven Scotts car.
Speed = $$$. How fast do you want to go?

big2bird said:

The Holley is better for more power, at the cost of economy. However, carb size has jack shit to do with car weight.(Where do they get this crap)?

CID X RPM X Volumetric effeciency / 3456 = CFM

IE, assume VE of 100%, 350x7000rpmx1/3456=709CFM

For best results, not economy, vacuum secondaries with auto, mech. secondaries with manual. (Although you can use a vacuum secondary with manual for a little more economy). However, it wont be as fast.

Click to expand...

Right off of the Holly interactive carb selector when picking vaccum secondaries or a double pumper.

SmokinBBC said:

big2bird said:

The Holley is better for more power, at the cost of economy. However, carb size has jack shit to do with car weight.(Where do they get this crap)?

CID X RPM X Volumetric effeciency / 3456 = CFM

IE, assume VE of 100%, 350x7000rpmx1/3456=709CFM

For best results, not economy, vacuum secondaries with auto, mech. secondaries with manual. (Although you can use a vacuum secondary with manual for a little more economy). However, it wont be as fast.

Click to expand...

Right off of the Holly interactive carb selector when picking vaccum secondaries or a double pumper.

Click to expand...

I never heard that one before.:footmouth::confused2:

Jeff, I hadn't either until the drag guys here brought it up. But they all have auto's with drag set-ups except one guy who has a 69 Camaro with a built 402, 5 speed MT. He uses a holly double pumper. I can't imagine his Camaro is any lighter than my vette. I'll have to get more details from him. However, his Camaro is a friggin ball buster.

My BB came with a 800CFM Qjet from the factory. When I calculate CFM per your calculation, I get around 760CFM using a 95% VE (460*6000*.95/2456=758). If I use 100%VE I come closer to 800CFM. How do you "guess" what VE that you might have? Or, is there a set of variables that you need to consider?

of ALL the freeking carbs I have dealt with, seen on friend's cars, been around with for a long time....I love the Original CARTER AFB's or it's knock off the AVS....they work, don't leak, take about 6-8 lbs fuel pressure without flooding, I understand they don't do well in violent turns while racing....fuel slosh....never had a drag strip problem though...and I never had a issue on any street car.....I drive fairly quickly, but not as fast as many others....

:crap::nuts:

From the Doug Roe book:
Different engine types produce various VE percentages. Ordinary low performance engines have a VE of about 75% at maximum engine speed; about 80% VE at maximum torque.(WOT). High performance engines have a VE of about 80% at maximum speed; about 85% at max torque.(WOT)A full race engine, 90% at max speed;about 95% at max torque.(WOT)
A highly tuned engine,intake,exhaust,head combo CAN attain 100% at the engines tuned port speed.

I would use the 80% factor. Overcarb the engine, and it will bog. (Quite common) If you do not have enough vacuum, the venturis cannot do their thing.

big2bird said:

From the Doug Roe book:
Different engine types produce various VE percentages. Ordinary low performance engines have a VE of about 75% at maximum engine speed; about 80% VE at maximum torque.(WOT). High performance engines have a VE of about 80% at maximum speed; about 85% at max torque.(WOT)A full race engine, 90% at max speed;about 95% at max torque.(WOT)
A highly tuned engine,intake,exhaust,head combo CAN attain 100% at the engines tuned port speed.

I would use the 80% factor. Overcarb the engine, and it will bog. (Quite common) If you do not have enough vacuum, the venturis cannot do their thing.

Click to expand...

Yup, all of the above is the way I remember it too....

I still love the AFB types....they never leak....easy to tune, run like a charm....I kept a AFB on a pontiac for years after they were outta production....kept switching manifolds....

:hi:

big2bird said:

SmokinBBC said:

big2bird said:

The Holley is better for more power, at the cost of economy. However, carb size has jack shit to do with car weight.(Where do they get this crap)?

CID X RPM X Volumetric effeciency / 3456 = CFM

IE, assume VE of 100%, 350x7000rpmx1/3456=709CFM

For best results, not economy, vacuum secondaries with auto, mech. secondaries with manual. (Although you can use a vacuum secondary with manual for a little more economy). However, it wont be as fast.

Click to expand...

Right off of the Holly interactive carb selector when picking vaccum secondaries or a double pumper.

Click to expand...

I never heard that one before.:footmouth::confused2:

Click to expand...

Well, actually, weight and gearing is what I use to detemind the carb (type)along with CI and cam.


That's why I have 1000 cfm on my 400.