MILD THUNDER

iTrader: (3)

Been doing a little research on this topic lately. It seems the general consensus is, more pressure, should mean more fuel flow. But does it?

First started looking into holley needle and seats. We have the basic ones, like .097 , .110, .120, .130 diameter. Naturally, a larger orifice will flow more fuel at the same psi. The needle & seat, is basically the last stop from a pressure creating standpoint.

Lets just pretend there are two scenerios. You do a dyno pull, (a long dyno pull), with a single carb and .097 seats. You see a solid 7psi of fuel psi on your gauge. You then remove the .097 seats, and install a .130 seat. You now see the fuel pressure drop during the pull, from 7psi, to 5psi. You may think you are starving the engine for fuel, when in fact, it may be quite the opposite. As we know, psi is resistance to flow.

Then the topic may come up, that dropping from 7psi, to 5psi, is no good, because the float may shut off the needle and seat. But, then there is the argument, that "area" comes into play. While the pressure may be less, there is also more "area" with a .130 needle & seat. This is generally why the large needle and seats, dont tolerate as much fuel psi as a smaller one. The pro stock guys and big alky guys, run around 4psi of fuel pressure, obviously making gobs of HP. A .097 seat, might take 8-9lbs of pressure without lifting, while a .130 might only take 6-7lbs before lifting.


We all pretty much know that pressure, isn't what we need with carbs, its volume. Yet, so many , focus on psi. Like say a guy plumbs an electric pump, with a dead head restrictive regulator. He is restricting flow, to get psi to increase. While his gauge tells him his pressure is good, that doesnt mean his engine is getting the volume of fuel it needs to survive. The bypass regulator is a much better idea for a carb setup.

the entire idea, is to keep the fuel bowls full at all times. It seems the general consensus from some race engine builders and carb experts, is lower pressure with a larger N&S, is better than higher psi, with a smaller N&S. Mainly, because, the higher psi , can really aerate the fuel , and cause other issues.

MILD THUNDER

iTrader: (3)

Thought this video was kinda cool. There was another one on the web somewhere, that shows how much there is going on inside the bowl.

https://www.youtube.com/watch?v=JedC0ocBQYY

sutphen 30

I'll let them explain it.

https://en.wikipedia.org/wiki/Bernoulli%27s_principle

Mbam

You need to add in the G factor of a boat running in less than flat water. Every impact tries to sink the float giving an extra shot of fuel in the bowl. This creates a "soggy" response on re-entry. More pressure/bigger seat aggravates this problem. So there is a fine balance between the seat diameter and fuel pressure.

I used to run a max of 5 psi, but I don't remember the diameter.

We did some work with clear bowls back in the mid 90's and yes it is wild in there! Finally wound up running float bowls with dual needles on some big engines we built at the time.

vintage chromoly

iTrader: (3)

Had a long conversation with Dale Cubic about this.
My carb is set up with a bypass regulator with a -6 return line.
PSI will be set at 5.5.

Pressure vs. flow rate and volume is probably one of the most misunderstood concepts in hotrodding.
It certainly can get a bit confusing.

MILD THUNDER

iTrader: (3)

Very true Marc. It seems that the majority think 7psi is a magic number, but theres much more to it. Probably something to consider today, where guys are running single carbs on some engines making big numbers.

I remember my buddy had a blow thru 4150 carb on his procharged engine. It kept going lean at the end of the dyno pull. Mike Tkach sat next to the engine during a pull with his bifocals on and a flashlight, and sure enough, the bowls were being emptied . Dual needle and seat bowls were the fix. Even though fuel psi looked good, it was starving for fuel.

MILD THUNDER

iTrader: (3)

From another site ,

FOR GASOLINE

118 - .101V Viton Stock Holley. For use
in low output motors, 450 HP and below,
using 4-barrel carburetor. Useful in
preventing high RPM enrichment on
speedway motors with restrictor plates.
Flow capacity 125#/hour @ 7 p.s.i. and
.25" float drop.

118 - .110V Viton Stock Holley. Used in
most applications, up to 650 HP with
4-barrel and to 400 HP with 2-barrel.
Flow capacity 175#/hour @ 7 p.s.i., .25"
float drop.

118 - .120V Viton Stock Holley. Used in
most applications, up to 775 HP with
4-barrel and to 500 HP with 2-barrel.
Flow capacity 215#/hour @ 7 p.s.i., .25"
float drop.

118 - .120RV ProSystems Carburetion
modified to produce higher discharge,
600-800 HP with 4-barrel. 225#/hour @
7 p.s.i., .25" float drop. Also useful on
lower horsepower motors that will not
maintain sufficient fuel pressure at high
RPM.

118 - .130RV Largest Viton needle and
seat available. Recommended for high
output 2-barrel motors and single 4-barrel
motors producing over 750 HP. Will flow
275#/ hour @ 7 p.s.i. and .25" float drop.
Will not hold idle pressure above 8 p.s.i.