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Author Topic:   Carburator question's
vosevichs
Member
posted July 31, 2003 08:00 AM
Holley 4412 500 cfm 2 barel

What size needle and seat? .130 or bigger?

30cc or 50cc accelerator pump?

Does anybody use those circle track floats?

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Scott Vosevich


KPLugnut
Member
posted July 31, 2003 08:13 AM
unless you're running alcohol, there is no reason to use anything larger than a .110 needle/seat.
If the carb is on a v8 motor (typical stockcar), then a 50cc pump setup will be needed as to eliminate hesitations when the throttle is nailed quickly.
We use oval track floats in all our gas carbs, but brass works well too.

Any other questions on specifics, just ask.

Hope that helps,
KPLugnut


vosevichs
Member
posted July 31, 2003 09:13 AM
I've been seeing these ads for race carbs with .130 needle & seats and 30cc accelerator pumps. The bigger needle & seats are to keep the carb from starving from fuel. And the 30cc accelerator pump for better throttle responce out of the corner. This is what they claim. Any input on that?

Yes it is on a 350 SBC.

We are running a stock 4412 holley with bigger jets. It works, But it can be better. I have an extra carb that I want to play with and try some things.
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Scott Vosevich.

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[This message has been edited by vosevichs (edited July 31, 2003).]

[This message has been edited by vosevichs (edited July 31, 2003).]

[This message has been edited by vosevichs (edited July 31, 2003).]

KPLugnut
Member
posted July 31, 2003 10:24 AM
The flaw in that needle/seat thinking is that a .110" needle/seat can easily flow all the fuel that almost ANY gas 2bbl will ever consume. It is NOT the needle/seat that is the point or cause for fuel starvation by any means.
And I'd like to see a 4412 with a 30cc pump and small pump cam that does NOT have a BIG ol' flat spot in both the fuel curve and in throttle response if you nail the throttle from idleon a V8 racing engine.....It has been my experience both on the track and in the dyno room here that there is NO such animal since the high demand for a big pump shot as the motor gulps a relatively HUGE amount of air is most definitely above what a 30cc pump can deliver.
The application where a 30cc pump and small black pump cam IS usefull and preferred is on 4cyl motors where the 4412 (or 7448) is mandated by rule. In that application, there is actually too much carb (as opposed to not enough when using the 4412 on a V8). Detuning the pump shot helps because the motor is not requiring nearly as much fuel as a V8 does when the butterflies open.

A heavily modified 4412, such as our Outlaw Gold series where airflow tops 700cfm out of that 2bbl body, is one case where I'd say the use of at least a .120" needle/seat is recommended. I've found the lbs/hr of fuel to be high enough at WOT that I feel more comfortable using the .120 seat.

Hope that helps, and let me know if you need more.

KP

vosevichs
Member
posted July 31, 2003 10:34 AM
Thanks KP Any suggestions on putting together a nice 4412 carb for a 350 SBC?

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Scott Vosevich


tilley88
Member
posted July 31, 2003 10:48 AM
Don't the Dorton 4412's have 30cc pumps?


vosevichs
Member
posted July 31, 2003 10:54 AM
They advertise a 30cc pump on the 350 cfm carb. But don't say anything about the pump on the 500 cfm carb.

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Scott Vosevich


KPLugnut
Member
posted July 31, 2003 11:10 AM
I believe the Dorton 4412's have 50cc pumps just like stock 4412's now do. Years ago, the early 4412's came with 30cc pumps and you could buy a "kit" to increase pump capacity to 50cc (and even 76cc was available at one time).

Hope that helps,
KP


stockcar5
Member
posted August 02, 2003 11:27 AM
i have a c&s 890cfm 2bbl gas carb and c&s said .110 needle and seat is plenty even for that big of a carb.

luke

KPLugnut
Member
posted August 02, 2003 01:45 PM
That is true about the .110 needle/seat, but for that "890" carb, keep in mind it is not ACTUALLY flowing that much cfm. They are in the low 700's in reality. That 890 number is for advertising purposes only.
And it goes without saying that one needs to remember that 2bbls are rated on flowbenches at TWICE the pressure drop as a 4bbl carb is rated. That means about a 40.8" of water pressure drop for 2bbl's and a 20.4" drop for 4bbls. If one was to rate a 2bbl at only 20.4" of water, the actual numbers are MUCH less.
But anyway, enough rambling. The flow capacity of a .110" needle/seat is a lot higher than many racers think.

KP


66jj
Member
posted August 02, 2003 08:23 PM
kp, whats a imca legal 350 going to set me back from you?? are you just working on a 7448 and adding the new plate with air bleeds??

I do need one in the future, I have a 406 and 2 383s. I plan to turn 6200 max rpm.

Thanks jeff

KPLugnut
Member
posted August 03, 2003 07:41 AM
$350 plus shipping. I build them from absolute scratch starting with bare castings. We final machine everything including the bare metering block castings.
Boosters are installed the way I want them, and our final tuning package is put in last.
They're not a "stock" carb that's just been tweaked a bit by any means. And the most important part is they are always legal.

Feel free to contact me directly either by PM, in email, or check the website and hollar at me by phone.

Thanks for asking,
Dayton Umholtz, owner
Kinetic Performance


stockcar5
Member
posted August 03, 2003 03:32 PM
your right kp about the pressure drop. mine was rated at 20.4 and flowed alot less....645cfm

luke

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