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TURBO TALK – FUEL PART 1 – PUMP GAS
At KMS Performance, I receive many questions thru phone and emails that pertain to “turbo”. We have turbocharged many small engines since 1998 and have made many mistakes in the process. With every mistake, came an opportunity to make something better. Trust me when I say: “LEARN FROM MY MISTAKES!” We would analyze every failure to get to the real truth and make the necessary changes. Essentially, we break things so you don't have to. So, thanks for reading and let's make performance FUN!
Let's first break fuel down into 3 major groups : Pump, Race, Diesel, and Alcohol. These 4 are the primary animals that pertain to a reciprocating engine (4 stroke, 2 stroke, and Forced Induction versions). For snow applications, alcohol and diesel is not a good choice due to cold starting issues and overall temperature complications. We will focus on the Pump and Race gas for this topic (if you do have questions on alcohol based fuels, diesel fuels and other fuels, such as propane and nitro please ask away). This week we focus on Pump Gas.
Pump gas: This is the stuff you put in your car and commute with (unless you drive a diesel). The octane choice is what matters here. For our performance needs, there is only one: High test. The only button your push is the most expensive one. Depending on your region, the highest available octane available may change. So, for this we will say 91 octane is the bare minimum (the higher the better). The brand of pump gas is also of huge importance. You want a fuel that is manufactured to withstand the worst of the worst. Here are a few great choices: Chevron, Shell, and Quicktrip. If you are unsure of a brand, look for Top Tier Ratings and compare them to Chevron or Shell.
Pump gas is only good for a specific level of mean cylinder pressure (BMEP). What is that? That is the average amount of pressure your combustion chamber produces while making power. This pressure goes up as you make more power. Here are some examples:
Naturally aspirated spark-ignition engines: 850 to 1050 kPa (this is where your 91 octane lives)
Boosted spark ignition engines : 1250 to 1700 kPa (this is where your 91 octane dies)
Top Fuel dragster engines: 8,000 to 10,000 kPa (you would be insane to even try)
Pump gas is only good for about 1100 kPa. So how can you make a pump gas turbo work, you lower the pressure thru compression ratio. This will lower the overall pressure in the engine, thus allowing more boost. Trust me when I say this: “Science will always win here”.
Kelly, I know a buddy who runs a turbo on his bike at low boost and he never has any problem. How can that be?
The answer lies with conditions. The 2 biggest conditions that play into this math is elevation and load. If you are at a high elevation, the air pressure is lower. This condition lowers your BMEP, thus cheating the math. The second one also plays with cylinder pressure. The more load the higher the cylinder pressure. Why? The load slows the engine down during the power stroke, allowing the flame that generates the pressure more time, thus making more pressure. In other words you may be completely fine with a short track, however if you install a long track your stuff may explode.
Race gas is really expensive and hard to get. I really want to use pump gas. How do I do that?
You do it the right way. LOWER YOUR COMPRESSION! Trying to cheat this is like playing Russian roulette. Here are some examples of what many turbo system builders are saying:
Just run low boost....This is easy for them to say in order to “close the sale”. There is no additional cost to you and you get a warm fuzzy feeling inside, but there is a dark side. Question 1: How much boost is safe? Well, you will find out that answer when your engine is scattered on a hill side. Question 2: You told me “X” of boost was safe; I ran what you said and my engine popped....Generally they will say you ran too much boost and it's your fault. Here is my question....So, I'm buying your turbo system and in order to be safe I have to....drive it slow? That does not sound like much fun to me and, for the most part, is ridiculous.
Use head or base gasket shims....This is a cost effective way to lower compression, however it does present some problems. If you shim over 0.055” of squish on a four-stroke, the power falls off dramatically. This will cause significant bottom end power loss and most of the boost applied will only be used to make up for what you lost. Does it work, yes. Does it make your stuff run slower, yes.
Use octane booster.....Don't. This may suppress ping, but it is like putting duct tape on a sinking ship when talking turbos.
The bottom line on these “pump gas solutions” is that they want your deposit, however when something goes wrong you will be the one paying for the damage:
This was $4200 worth of "just lower the boost and everything will be ok" - makes me angry...
I'm OK with the lower compression piston, now how much boost can I run with that?
In most snowbike applications, 12+ psi. You get to keep low end performance, your boost is being used for more power (not making up for what you lost), and allow the turbo to “stretch its legs”. There is a question however, what about load. Changes in load, hard pack vs. deep snow, can make a happy turbo pump gas engine very sad. The real answer lies with a specific event...PING. When ping, or pre-ignition occurs, your octane is pushed to the limits. The best device to detect this is a knock sensor. These have been around and used for a very long time, however most products integrate with either an ecu or a data log system. We wanted something simple. A light that lets the rider know if his bike is pinging due to load, bad gas, or whatever. The concept is simple. When the light goes off, you need to do something different. Lower the boost, add more fuel, reduce ignition timing, kick your wife off the back....just something different. This light will come on long before your engine pays the ultimate price and we make them EXTRA BRITE. It is easier to stare at the sun than this thing, making sure it gets your undivided attention. So, if you're trying to squeeze out 15 psi on a turbo pump gas situation, this little knock sensor has “got your back”.
Thanks for reading and questions are always appreciated
At KMS Performance, I receive many questions thru phone and emails that pertain to “turbo”. We have turbocharged many small engines since 1998 and have made many mistakes in the process. With every mistake, came an opportunity to make something better. Trust me when I say: “LEARN FROM MY MISTAKES!” We would analyze every failure to get to the real truth and make the necessary changes. Essentially, we break things so you don't have to. So, thanks for reading and let's make performance FUN!
Let's first break fuel down into 3 major groups : Pump, Race, Diesel, and Alcohol. These 4 are the primary animals that pertain to a reciprocating engine (4 stroke, 2 stroke, and Forced Induction versions). For snow applications, alcohol and diesel is not a good choice due to cold starting issues and overall temperature complications. We will focus on the Pump and Race gas for this topic (if you do have questions on alcohol based fuels, diesel fuels and other fuels, such as propane and nitro please ask away). This week we focus on Pump Gas.
Pump gas: This is the stuff you put in your car and commute with (unless you drive a diesel). The octane choice is what matters here. For our performance needs, there is only one: High test. The only button your push is the most expensive one. Depending on your region, the highest available octane available may change. So, for this we will say 91 octane is the bare minimum (the higher the better). The brand of pump gas is also of huge importance. You want a fuel that is manufactured to withstand the worst of the worst. Here are a few great choices: Chevron, Shell, and Quicktrip. If you are unsure of a brand, look for Top Tier Ratings and compare them to Chevron or Shell.
Pump gas is only good for a specific level of mean cylinder pressure (BMEP). What is that? That is the average amount of pressure your combustion chamber produces while making power. This pressure goes up as you make more power. Here are some examples:
Naturally aspirated spark-ignition engines: 850 to 1050 kPa (this is where your 91 octane lives)
Boosted spark ignition engines : 1250 to 1700 kPa (this is where your 91 octane dies)
Top Fuel dragster engines: 8,000 to 10,000 kPa (you would be insane to even try)
Pump gas is only good for about 1100 kPa. So how can you make a pump gas turbo work, you lower the pressure thru compression ratio. This will lower the overall pressure in the engine, thus allowing more boost. Trust me when I say this: “Science will always win here”.
Kelly, I know a buddy who runs a turbo on his bike at low boost and he never has any problem. How can that be?
The answer lies with conditions. The 2 biggest conditions that play into this math is elevation and load. If you are at a high elevation, the air pressure is lower. This condition lowers your BMEP, thus cheating the math. The second one also plays with cylinder pressure. The more load the higher the cylinder pressure. Why? The load slows the engine down during the power stroke, allowing the flame that generates the pressure more time, thus making more pressure. In other words you may be completely fine with a short track, however if you install a long track your stuff may explode.
Race gas is really expensive and hard to get. I really want to use pump gas. How do I do that?
You do it the right way. LOWER YOUR COMPRESSION! Trying to cheat this is like playing Russian roulette. Here are some examples of what many turbo system builders are saying:
Just run low boost....This is easy for them to say in order to “close the sale”. There is no additional cost to you and you get a warm fuzzy feeling inside, but there is a dark side. Question 1: How much boost is safe? Well, you will find out that answer when your engine is scattered on a hill side. Question 2: You told me “X” of boost was safe; I ran what you said and my engine popped....Generally they will say you ran too much boost and it's your fault. Here is my question....So, I'm buying your turbo system and in order to be safe I have to....drive it slow? That does not sound like much fun to me and, for the most part, is ridiculous.
Use head or base gasket shims....This is a cost effective way to lower compression, however it does present some problems. If you shim over 0.055” of squish on a four-stroke, the power falls off dramatically. This will cause significant bottom end power loss and most of the boost applied will only be used to make up for what you lost. Does it work, yes. Does it make your stuff run slower, yes.
Use octane booster.....Don't. This may suppress ping, but it is like putting duct tape on a sinking ship when talking turbos.
The bottom line on these “pump gas solutions” is that they want your deposit, however when something goes wrong you will be the one paying for the damage:
This was $4200 worth of "just lower the boost and everything will be ok" - makes me angry...
I'm OK with the lower compression piston, now how much boost can I run with that?
In most snowbike applications, 12+ psi. You get to keep low end performance, your boost is being used for more power (not making up for what you lost), and allow the turbo to “stretch its legs”. There is a question however, what about load. Changes in load, hard pack vs. deep snow, can make a happy turbo pump gas engine very sad. The real answer lies with a specific event...PING. When ping, or pre-ignition occurs, your octane is pushed to the limits. The best device to detect this is a knock sensor. These have been around and used for a very long time, however most products integrate with either an ecu or a data log system. We wanted something simple. A light that lets the rider know if his bike is pinging due to load, bad gas, or whatever. The concept is simple. When the light goes off, you need to do something different. Lower the boost, add more fuel, reduce ignition timing, kick your wife off the back....just something different. This light will come on long before your engine pays the ultimate price and we make them EXTRA BRITE. It is easier to stare at the sun than this thing, making sure it gets your undivided attention. So, if you're trying to squeeze out 15 psi on a turbo pump gas situation, this little knock sensor has “got your back”.
Thanks for reading and questions are always appreciated
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