Base Valve:
Why is a base valve shock better or is it? As you know, I have always been for it in ours shocks, and when I say ours, I mean BSB. As I have always said, not all base valves are the same, and they are not. We are not going to cover that, just want to make that statement to clear that up for 1st time readers.
The Base Valve, what is this thing we talk so much about and what is it doing. Well, here is a picture of it in a tube so let’s explain it, and its function and why it is so good to the car.
This is the base valve; it is a piston that is fixed in the tube (solid) as not to move up and down. It has shims on each side of it and they regulate pressure that is created in the tube by the main piston. It also converts the high pressure made by the piston into low pressure allowing the divider piston to handle it with less gas pressure.
Now to understand the base valve better we must understand what is going on in the shock and what we want to happen in the shock. We will look at these items to understand what is happening.
· Activity in the compression stroke:
· Divider piston function without a base valve:
· Pressure in the oil column:
· How it effects the car:
Let us start with Pressure in the oil column and why it is there. The pressure is made from the main piston as it controls the force that is being applied to it. This pressure is on both the compression and rebound side of the piston. The rebound side pressure is absorbed by the seal head (seal head is the object that the shaft comes out of), this allows all of it to be directed back to the piston and forced. Some oil may bypass the piston, but the rebound stroke is strong because of the seal head. The pressure on the compression stroke is being held in place with the divider piston and gas pressure, as you increase the gas the divider will work better in holding the oil column in place. The divider has a tuff job to do and fails at doing it in many ways, therefore we have shock problems that are hard to determine the origin of the problem. The divider is holding the oil column in place as it is slowly moving in the opposite direction of the pressure being applied to it. This is often when the failure happens, as the car hits a bump on the track it overloads the divider with pressure that the piston cannot process thru the shim stack and pushes the oil column up the tube.
More info on base valves.
Added note: All twin tube shocks have a base valve in them, this is what allows them to work under pressure, it is also what makes them fail. Although they work on the street they are not the best for the race track. Maybe in a different world the twin tube shock would be good to race on but until than we will not.
Divider holding oil column in place during compression stroke. The divider moves up and down in the tube because of displacement of the shaft. As the shaft goes inside the tube it displace oil volume and this makes the divider move up and down. The shaft diameter and the bore of the shock will determine the amount of movement in the divider piston.
Figure 2 Stroke line with activity.
Let’s look at a stroke in compression without a big bump on the race track and say it is moving 3 inches in travel. This is not one solid move in that direction but a bunch of little moves back and forward as it moves in the compression stroke. This is what we call activity in the stroke and the divider must deal with it flawlessly to make grip at the tire. This is a hard task to mange and where most failure start and grows from. With out this task being performed the shock goes into cavitation and the load at the tire is wiped away at this point. This has been seen here lately in a soft spring setup, as the cars have more grip in them because the spring adds activity to the shock because of its lighter rate.
Okay so we have covered Pressure, divider function, and activity, so now we need to look at how the base valve when in its proper stage will increase the grip at the tire. The Base valve in its fixed position will hold the oil column in place, much like the seal head, this will force the oil to be process thru the main piston increasing grip at the tire. It will decrease the need for the divider to super sensitive to small moves and make the main piston active in its function. The base valve also performs another function as it decrease the internal pressure made by the main piston turning it into low pressure. This allows the gas behind the divider to be lower in pressure because it is now not controlling as high of pressure as it was. Most people consider this to be the best function of a base valve as lower gas help increase feel for the driver, but the improved base function is responsible for the biggest increase in feel and grip at the tire.
Remember this, that all base valves are not created equally so the function of them will also differ. I feel that our base valve performs very well in all conditions (smooth to rough) allowing the car to perform. This is our main goal, to increase grip at the tire and we have seen that the base valve is one of the main items in doing this in our shock. We also have other items we use to increase grip levels but our goal here is to understand better the function of a base valve and how this tool works in conjunction with our car.
Gofast and God Bless: Jay Neal
Update from the video:
Link to video: https://youtu.be/sK0aHcg3Td4
Key Themes and Concepts:
Shock Anatomy and Mechanics:
Standard (Non-Base Valve) Shocks: Consists of a piston, oil column, divider piston, and gas column.
The divider piston separates the oil and gas, moving up and down as the shaft displaces oil.
The divider piston in non-base valve shocks has a "very difficult job" managing both oil column pressure and compression forces, making them prone to failure.
Gas pressure is crucial to control compression and the amount of gas is directly related to the compression.
Excessively low gas pressure in a standard shock can lead to performance issues.
They rely on the divider piston and gas pressure to control the compression stroke.
Standard shocks create more "rod force" due to higher gas pressure.
Base Valve Shocks: Include all the components of a standard shock, plus a fixed base valve located within the tube before the divider piston.
The base valve has shims on both sides, providing a solid point to push against for the pressurized oil, as opposed to the divider piston directly in non-base valves.
The base valve system separates the high pressure oil (before the base valve) from the low pressure oil (after the base valve, going towards the divider).
The divider piston in a base valve shock has less gas pressure.
Base valve shocks need less gas pressure to operate properly than a standard shock.
Rod Force and its Impact:
Definition: Rod force is the force created by the gas pressure within the shock, which resists compression.
Issue: The speaker states, “Rod force is something that we're trying to uh eliminate we're trying to get away from it because it hurts feel in the in the shock and it hurts feel in the race car."
Standard gas shocks typically generate around 25 lbs of rod force at full open using 100lbs of gas.
Base valve shocks significantly reduce rod force, often to around 10 lbs.
Lower rod force is considered desirable because it improves the driver's feel for the car's suspension and handling.
Gas Pressure Management:
Standard Shocks: Require higher gas pressures, often around 100 lbs in the right front, but some run lower amounts.
Base Valve Shocks: Require significantly lower gas pressures, typically 35-50 lbs, to enable the divider piston to function properly and have the shock operate effectively.
Gas volume within the shock is manipulated by some builders to cheat gas pressure and alter shock performance, which the speaker discourages and argues it is not ideal.
Zero gas pressure shocks are not recommended for racing because the divider piston may not return.
The divider piston's free movement is critical for the shock's performance, particularly in base valve shocks.
Base valve shocks sometimes won't "shaft out" upon being compressed due to the lower gas pressure and are not necessarily defective.
Stroke Length and IMCA Rules:
Most shocks have a 7" stroke but are limited to 6" strokes in IMCA.
A "base valve nut" can be added to further limit stroke by 3/8" on rough tracks.
Body lengths have been increased to make IMCA legal shocks easier to use.
Advantages of Base Valve Shocks:
Reduced Rod Force: This is the most common selling point for base valve shocks, but it is not the primary advantage in the opinion of the speaker.
Instant Pressure/Zero Lag: The main advantage the speaker discusses is the "instant pressure" created in the oil column by the base valve and that there's “no delay.” The oil is ready to work and provides instant feedback to the driver. The base valve allows the oil to be compressed and immediately react to a change in force, which provides better feedback and makes the car more responsive.
The lack of lag is more important because it improves car control and performance. "It just makes the car work and it makes it work right now.”
Specifically, in a left rear shock a base valve is a better option due to this advantage of instant feedback and pressure.
Valving and Application:
The speaker walks through several example shock packages for specific positions on a race car. Examples are given for a "AOD," a "USR" car, a "stock car," and a "street stock."
Valving recommendations are not "one size fits all." They depend on the car, driver preferences, track conditions, spring rates, and other factors.
Consultations with the shock manufacturer are used to develop a custom valving setup for each customer. The quote used to support this is, "we're going to sit down and have a phone conversation about your car your setup your spring rates your driving style and your motor package and your tire package and then we're going to determine the valving we need."
The "elite" series combines a base valve and an SRT shock.
"GF" is the name of the gas shock series from ARS.
"SRT" is the name of a shock series.
Company Background:
The manufacturer (BSB) has a long history with base valve shocks going back about 5-7+ years, although they no longer offer them in their 20 series.
The company is focused on continuous improvement and product development.
The company emphasizes customer education and consultation to optimize shock performance.
Key Quotes:
"Rod force is something that we're trying to uh eliminate we're trying to get away from it because it hurts feel in the in the shock and it hurts feel in the race car."
"The biggest Advantage is that base valve sitting in there and that oil column has instant pressure and there's no delay so it instantly loads up on the base valve and it creates a zero leg time and that lack of leg is instant feel to the driver so it just makes the car work and it makes it work right now."
"we're going to sit down and have a phone conversation about your car your setup your spring rates your driving style and your motor package and your tire package and then we're going to determine the valving we need."
Conclusion:
The transcript emphasizes that while base valve shocks are known for reduced rod force, their primary benefit is the elimination of lag time through the base valve providing instant pressure in the oil column and a more responsive and predictable feel for the driver. A proper understanding of gas pressure, divider piston function, and valving is critical for optimal shock performance. The speaker advocates for consultations with the manufacturer to tailor shock packages to specific racing applications and setups. This document provides a framework to understand the advantages and the technical details of base valve shocks and how they can benefit a race car program.
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