needle and seat flow testing

[tuffxf]

Gday
That makes perfect sense!
Cheers
Paul

[mag2555]

If memorie serves me right even a .136" will flow over 65 GPH @ a lowly 6 psi.

[Dave Koehler]

again, not a carb guy but do you fellows line up the NS window with the fuel flow direction even if it means you are not "perfect" on your float position?

You have to do some digging but there are other float bowls besides what Holley offers out there.

[cjperformance]

I went through this exercise recently for a bike engine on methanol. The thing that really stood out to me was the relationship between pressure, seat area and flow. The actual fuel flow through the seat doesn't increase in direct proportion to pressure; it's not even close. It does however increase roughly in direct proportion to seat area, so in other words you'll get much greater gains using a big seat at low pressure than a small seat at high pressure. You'll probably also get less fuel agitation with the low pressure and big seat combo. The limit for both these factors is the ability of the float to shut off the fuel flow.

Yes exactly !

[John Wallace]

The float needs to be taken into account, it's what seals the needle/seat when full?
Bigger seat diameter, the less the pressure has to be to keep from overpowering the float?

And as Dave said, they have different needles to let the fuel come out without disturbing the surrounding area?

Easier with mechanical fuel injection.
(why I went that way over the carbs on methanol)

[Dave Koehler]

Food for thought: Assuming a constant pressure, If the engine pulls as much fuel through the main jets as the NS can provide you have a stalemate or a power limit.
In a perfect world a single .150 NS hole could just support 2 .141 main jets in the above scenario.

You have to do some digging but there are other double NS float bowls besides what Holley offers.

At higher pressures the fuel in the bowl gets beat into a froth. Makes me think that there needs to be a baffle built in to those bowls to give the fuel half a chance to settle.
Any bowls like that?

[JDR Performance]

A belt driven fuel pump works well with methanol, and nearly all oval track racers running methanol use one. This allows the floats to be set higher since idle fuel pressure is low but it ramps up with rpm and of course fuel consumption. It's something drag racers should consider doing, or at least the use of a ball valve style bypass would be good if an electric fuel pump is the only option they'll consider. If not, the idle fuel pressure is much higher than needed and the needle and seat has a hard time shutting off the fuel. It's common to see carburetors come in from drag racers that have the floats ran down almost to the bottom of the fuel bowl. If there's no room for the float to drop, there is no room for the needle to completely fall away from the seat. It is problematic at idle and at w.o.t.

[jmarkaudio]

I'm going to blow out some of the responses here. A larger bowl is a BAD idea, with the exception of dual N&S bowls when used for methanol on forced induction applications. Larger bowls may look great on the dyno but will allow for too much slosh and the resulting foaming that makes metering fuel correctly an issue. Assuming the fuel system will supply sufficient volume at any pressure, the restriction point is the N&S. Running the largest N&S you can with the lowest pressure is the best idea. Take a bucket, start filling it with an open hose end and watch the foaming. Then watch it when you put your finger over the end to increase pressure, you get lots of bubbles. You want to avoid that. With gas I use a .140 viton N&S from BLP, I've run them with C45 in a 2.800 throttle blade billet carb making over 1200 HP. With methanol I use .164 BLP Ti nail head N&S, .170's in some cases. I've run .164 with about 5 psi of pressure and an electric Magnafuel pump and deadhead regulator with methanol, running 5.0's in the 1/8. A larger N&S will pass the same fuel with less float drop as a smaller N&S, keeping the jets covered. And if you can control fuel pressure even lower BLP has a low pressure bowl, using a custom .250 N&S. BLP has run passes in the 6.70 1/4 mile range with pressures under 2 psi thru the traps.

[Walter R. Malik]

Use a correctly designed, large diameter fuel log with the correct size fuel entry and exits to help remove the aeration ... not the fuel logs they sell within the aftermarket which don't do anything but, disperse the fuel.
SO, you'll need to fabricate it.

[pamotorman]

when I used bowl extensions I fitted the open areas with fuel cell foam to prevent sloshing of the fuel

[tuffxf]

A belt driven fuel pump works well with methanol, and nearly all oval track racers running methanol use one. This allows the floats to be set higher since idle fuel pressure is low but it ramps up with rpm and of course fuel consumption. It's something drag racers should consider doing, or at least the use of a ball valve style bypass would be good if an electric fuel pump is the only option they'll consider. If not, the idle fuel pressure is much higher than needed and the needle and seat has a hard time shutting off the fuel. It's common to see carburetors come in from drag racers that have the floats ran down almost to the bottom of the fuel bowl. If there's no room for the float to drop, there is no room for the needle to completely fall away from the seat. It is problematic at idle and at w.o.t.

Gday Jdr,
All good reading, say you had an oval track / speedway car that is running laps on end with the foot buried.
Engine making 700 hp , single needle and seat 4 barrel , belt pump . methanol
What size and brand needle and seat and what top end fuel pressure would you have it set up for?
If you dont mind?
Thanks very much!
Paul

[oldjohnno]

Why don't we just get rid of the damn N&S altogether? We could replace it with a prox. sensor or reed switch actuated by the float, and this would operate an inline solenoid valve. There'd be no more problems handling flow or pressure and the entry into the bowl would be gentle via a full width log using multiple holes or a slot. The log could be submerged as well.

Such an arrangement would be trivially easy to build and might eliminate a lot of fuel supply issues.

[cjperformance]

I'm going to blow out some of the responses here. A larger bowl is a BAD idea, with the exception of dual N&S bowls when used for methanol on forced induction applications. Larger bowls may look great on the dyno but will allow for too much slosh and the resulting foaming that makes metering fuel correctly an issue. Assuming the fuel system will supply sufficient volume at any pressure, the restriction point is the N&S. Running the largest N&S you can with the lowest pressure is the best idea. Take a bucket, start filling it with an open hose end and watch the foaming. Then watch it when you put your finger over the end to increase pressure, you get lots of bubbles. You want to avoid that. With gas I use a .140 viton N&S from BLP, I've run them with C45 in a 2.800 throttle blade billet carb making over 1200 HP. With methanol I use .164 BLP Ti nail head N&S, .170's in some cases. I've run .164 with about 5 psi of pressure and an electric Magnafuel pump and deadhead regulator with methanol, running 5.0's in the 1/8. A larger N&S will pass the same fuel with less float drop as a smaller N&S, keeping the jets covered. And if you can control fuel pressure even lower BLP has a low pressure bowl, using a custom .250 N&S. BLP has run passes in the 6.70 1/4 mile range with pressures under 2 psi thru the traps.

Yes totally agree on less pressure & more n/s area.
What you say about larger bowl volumes is spot on, yes, just more fuel to slosh around , airate and affect what the engine is trying to pull thru the jets.

[cjperformance]

Why don't we just get rid of the damn N&S altogether? We could replace it with a prox. sensor or reed switch actuated by the float, and this would operate an inline solenoid valve. There'd be no more problems handling flow or pressure and the entry into the bowl would be gentle via a full width log using multiple holes or a slot. The log could be submerged as well.

Such an arrangement would be trivially easy to build and might eliminate a lot of fuel supply issues.

With a well baffled bowl and fuel entering below the fuel level as well, deairate the fuel prior to entering the bowl, sounds like a project!

[smeg]

A belt driven fuel pump works well with methanol, and nearly all oval track racers running methanol use one. This allows the floats to be set higher since idle fuel pressure is low but it ramps up with rpm and of course fuel consumption. It's something drag racers should consider doing, or at least the use of a ball valve style bypass would be good if an electric fuel pump is the only option they'll consider. If not, the idle fuel pressure is much higher than needed and the needle and seat has a hard time shutting off the fuel. It's common to see carburetors come in from drag racers that have the floats ran down almost to the bottom of the fuel bowl. If there's no room for the float to drop, there is no room for the needle to completely fall away from the seat. It is problematic at idle and at w.o.t.

Gday Jdr,
All good reading, say you had an oval track / speedway car that is running laps on end with the foot buried.
Engine making 700 hp , single needle and seat 4 barrel , belt pump . methanol
What size and brand needle and seat and what top end fuel pressure would you have it set up for?
If you dont mind?
Thanks very much!
Paul

Is this a super sedan? We do a lot of these, using a BLP belt drive pump and set up at 9 - 10 lbs at 8000, over 700 8000 + rpm with no problems for years in multiple cars we do the engines for.