Exhaust Back Pressure: how to choose the correct exhaust pipe diameter

Comments (3) Guides

On most vehicles, the exhaust system’s sole job is to lead gases out of the engine.

But if you drive a performance vehicle, your exhaust system will play a bigger role in determining your engine’s performance and power.

To set up optimal exhaust system, you need take into account your engine’s power band, its maximum usable RPM, as well as back pressure.

And we get a lot of questions on how to reduce back pressure in the exhaust system…

But back pressure shouldn't be eliminated altogether - you actually really need it!

BACK PRESSURE- GOOD OR BAD?

Back pressure exists all around us.

The term refers to the atmosphere which pushes down on your exhaust system. And back pressure generally has a very negative effect on your engine’s power output.

When your engine works at the top of its power band, it creates a lot of spent exhaust gases.

And if the exhaust pipe diameter is too small and it generates too much back pressure, these exhaust gases will be heavily restricted from exiting the engine.

The amount of generated exhaust gases will be greater than the amount of exhaust gases that are able to leave the engine.

And this “surplus” of exhaust gas will contaminate the cool and fresh air-to-fuel mixture on the next intake stroke.

Engine power and performance will be reduced.

If it reduces power - why do I need it?

If back pressure reduces your engine’s power and performance.. why do you need it?!

Flow Velocity

If you equip your ride with a super large exhaust pipe to eliminate back pressure, you will also reduce the flow velocity of exhaust gases.

And you need higher flow velocity.

Why?

A high flow velocity aids the complete expulsion of burnt gases. And it increases the amount of the air-to-fuel mixture being drawn into the combustion chamber.

How?

When exhaust gases exit the engine with a higher flow velocity, they create low pressure behind them. And this low pressure continues to suck out exhaust gases at an extremely high rate, creating a valuable cycle.

Waste of Air/Fuel Mixture

Your engine’s exhaust port opens up to expel exhaust gases from the combustion chamber. And it remains open for a short time once they’re out.

During that time, unburned air/fuel mixture can escape directly into your exhaust.

And this wastes fuel, and needlessly creates pollution.

And the only way to prevent this waste is if the back pressure at the opened exhaust port is greater than the pressure in the cylinder.

So it becomes clear that too much back pressure is bad. And too little back pressure is bad.

You need just the right amount.

WHAT EXHAUST PIPE DIAMETER IS BEST?

Don’t be fooled into thinking that a bigger pipe is always better for power and performance.

To strike a balance between low back pressure and high gas flow velocity, you need the correct pipe size.

The industry has developed a table to be used as a general guide. It tells you the proper pipe diameter based on your vehicle’s engine size and horsepower.

table

But what if your engine is putting out more than the numbers shown in the table?

Just give us a call or drop us a comment below and we’ll help you figure out what type of exhaust system is best for your vehicle!

3 Responses to Exhaust Back Pressure: how to choose the correct exhaust pipe diameter

  1. My little brothers car runs well but has an exhaust system that is rusting out. He is looking to get a system, but he isn’t sure what kind of pipe he should go with. He originally thought that getting a big old pipe for it would be the best way to go, but this points how that is not always the case. This has a great chart that can help him see what kind of pipe will best fit his car.

  2. Dob Chem says:

    Hi!I’m driving a Nissan Murano 3.5L petrol engine. With a horse power of 235hp.
    Can you please let me know what is the right size back pipe for my exhaust sistem!

  3. Rocco Abbondandolo says:

    that is some great info and should be more like this at easy access.. any way i drive a 1999 ls1 camaro with 305hp and 320tq rating… which headers should i use? and i do plan on doing more mods asap…right now i just have gears and a shift kit with k&n cai but headers exhaust and intake and throttle body are all next… let me know plz and thank u

Leave a Reply

Your email address will not be published.