Exhaust backpressure

[motocat12]

anyone ever measure the difference on exhaust backpressure from oem, aftermarket, baffled aftermarket??  I just found a spare gauge threads straight into my header.

[ReconRat]

Nope, but I've run design calculations on exhaust systems to see what is right and wrong. Typically Honda does it exactly right, per the book. Length, diameter, etc.

And I will say my one 919 had gutted baffles, and didn't run for crap at lower rpms. I replaced with used stock cans from ebay and it runs great.

The right amount of back pressure is tricky. It depends on restrictions, flow volumes and velocities, size of valves, cam duration and lift, compression, rpms, etc.

And the right amount will vary for various desired results.

[Tonik]

I would think that gauge is going to melt in a heartbeat.

[motocat12]

6 hours ago, Tonik said:

I would think that gauge is going to melt in a heartbeat.

My Italian bike's exhaust will melt metal and glass! How many heartbeats does it take to pressurize an exhaust? The fitting is closed off except for 1/8 opening. gauge threads are brass.  The worst part is I need to install my old 2 into 1 exhaust or find someone with the same bike to measure for comparison.

[motocat12]

6 hours ago, ReconRat said:

Nope, but I've run design calculations on exhaust systems to see what is right and wrong. Typically Honda does it exactly right, per the book. Length, diameter, etc.

And I will say my one 919 had gutted baffles, and didn't run for crap at lower rpms. I replaced with used stock cans from ebay and it runs great.

The right amount of back pressure is tricky. It depends on restrictions, flow volumes and velocities, size of valves, cam duration and lift, compression, rpms, etc.

And the right amount will vary for various desired results.

My SV definitely lost some torque with a shorty exhaust. I put a 5" extension in front of the can and improved it. SVs and RSVs have many saying they need a long exhaust. Now i'll start to get some science. I don't know how a dual 45 compares to a 2 into 1 60mm lengthwise. I also previously added 2 balance pipes on the old collector.

[ReconRat]

15 hours ago, motocat12 said:

My SV definitely lost some torque with a shorty exhaust. I put a 5" extension in front of the can and improved it. SVs and RSVs have many saying they need a long exhaust. Now i'll start to get some science. I don't know how a dual 45 compares to a 2 into 1 60mm lengthwise. I also previously added 2 balance pipes on the old collector.

In general, individual pipes and cans perform better at higher rpms and produce better horsepower.

Headers or collectors, combining into less cans tend to perform better at lower rpms and improve torque. Pipe diameter should increase in size from the collector back.

My basic rule, if high compression or high redline engine, go for the horsepower with the singles. If low compression, low rpm, torque engine, high displacement, etc type thing, go for the torque with a single or dual can setup. The cam design plays in too. The cam might be either high rpm or low rpm usage. Mix parts wrong and it won't work too well.

The other truth. When seeking performance of any kind, improve the electrical primary and secondary first. Then work on the rest. Performance changes can degrade the electrical quickly. Not to mention that if you do electrical last, you pretty much have to go back and start over on all the rest.

 

[Gixxus Christ!]

On 5/23/2019 at 10:46 AM, ReconRat said:

In general, individual pipes and cans perform better at higher rpms and produce better horsepower.

Headers or collectors, combining into less cans tend to perform better at lower rpms and improve torque. Pipe diameter should increase in size from the collector back.

My basic rule, if high compression or high redline engine, go for the horsepower with the singles. If low compression, low rpm, torque engine, high displacement, etc type thing, go for the torque with a single or dual can setup. The cam design plays in too. The cam might be either high rpm or low rpm usage. Mix parts wrong and it won't work too well.

The other truth. When seeking performance of any kind, improve the electrical primary and secondary first. Then work on the rest. Performance changes can degrade the electrical quickly. Not to mention that if you do electrical last, you pretty much have to go back and start over on all the rest.

 

You're almost always going to see better overall power out of a twin with a 2-1 because of the scavenging effect inherent in the firing order of most twins. 

[serpentracer]

btw, you can use an autotuner and it will do the calculations for the tune based on your header dimensions.