Muffler delete on MBRP race catback exhaust?

[stannypack]

I have the MBRP race catback exhaust, and was wondering if I straight piped these 2 mufflers would that affect emissions/require a tune and pass inspection? Love the rumbly sound as is but seeing if I could wake it up even more since I'm not going with a downpipe for now. Also would it trigger a CEL since I read the backpressure changes could?

Sponsored

 

[XFactor7889]

While I can't say for sure, I don't think it would impact your emissions. My understanding is limited, but I do think it'll negatively impact the back pressure these cars require, idk if it would trigger a CEL though. So, that may make a tune required regardless if you went that route. That said, given the design of the mbrp resonators, I'd be shocked if you liked the sound without them more. There's a good chance you'd lose the rumbly note you mentioned with very little impact to the volume, given what resonators are designed to do.

 

[K4fxd]

First off no engine requires back pressure. Ok someone is going to point out 2 strokes, but they only like it for starting. Once running you want a good scavenging expansion pipe.

Your car's ECU doesn't care what happens after the cat, neither does the emissions police. The noise police might be different.

It will probably sound like crap so make sure you can put them back if you don't like it. I do believe the MBRP race mufflers are straight through.

 

[Buldawg76]

MBRP race mufflers are just a glass pack which is straight thru with no baffles at all just tiny louvers to help direct some of the flow/noise into the packing. No effect on emissions testing or backpressure/engine tuning will be encountered. Exhaust noise/note may or may not be improved to your liking.

I have that same cat back on my car and like the sound very well.

Backpressure is a useful tuning tool for both 4 and 2 stroke engines and is a must for two strokes to run properly which is why they have expansion chambers to create backpressure/reversion in exhaust to keep fuel/air charge in cylinder for combustion. 4 stroke only benefits from 0 backpressure if operated at WOT constantly for drag racing.

BD

 

[K4fxd]

You are confusing back pressure with pulse wave tuning.

Most high performance 2 strokes have a butterfly valve near the exhaust port. It closes when not running, this helps the engine start. Once running it opens and the expansion chamber creates a vacuum at the exhaust port.

The back pressure myth will never die it seems.

4 Strokes benefit from pulse wave tuning in both intake and exhaust. This is why header tube length and intake runner length matters to peak Tq and HP RPM.

 

[babrams3]

Sheesh, cant imagine what this will sound like. I'm still a little irritated with rasp straight out of the box. Post a video if you choose to go this route!

 

[Buldawg76]

You are confusing back pressure with pulse wave tuning.

Most high performance 2 strokes have a butterfly valve near the exhaust port. It closes when not running, this helps the engine start. Once running it opens and the expansion chamber creates a vacuum at the exhaust port.

The back pressure myth will never die it seems.

4 Strokes benefit from pulse wave tuning in both intake and exhaust. This is why header tube length and intake runner length matters to peak Tq and HP RPM.

Its been many years since I raced 2 stroke dirt bikes and Yamaha never used any valve in the exhaust but rather used reed valve/piston port fuel transfer in the intakes and backpressure/reversion tuning in the chambers to help keep fuel charge in the cylinder from being sucked out the exhaust before the piston closed the ports in the sides of the cylinders. You cannot have reversion without backpressure since they work in unison to help tune the intake/exhaust pulses as you state above in four strokes also.

You answered the question with your last statement on pulse wave tuning, that is exactly what backpressure is all about.

BD

 

[K4fxd]

I'll run my exhaust as close to zero back pressure as I can and you do what you think is best.

A 2 stroke makes no vacuum. The expansion chamber in the exhaust pipe creates negative pressure at the port in the designed power band to help pull air and fuel into the cylinder. These pipes look like a megaphone.

Not all 2 strokes used a butterfly valve in the exhaust. These were mostly 440 CC and above single cylinder, this is to aid in pull starting.

If you think back pressure is good weld a washer with a 1/2 inch opening at the end of your exhaust system. How does the car run?

 

[XFactor7889]

First off no engine requires back pressure. Ok someone is going to point out 2 strokes, but they only like it for starting. Once running you want a good scavenging expansion pipe.

Your car's ECU doesn't care what happens after the cat, neither does the emissions police. The noise police might be different.

It will probably sound like crap so make sure you can put them back if you don't like it. I do believe the MBRP race mufflers are straight through.

You're right. My mistake, like I said, my understanding is limited on the topic. I shouldn't have said they required backpressure, but rather that I've learned that the wrong exhaust setup can negatively impact the back pressure (aka- allow back pressure that otherwise wouldn't be there with the current cat back).

 

[Buldawg76]

I'll run my exhaust as close to zero back pressure as I can and you do what you think is best.

A 2 stroke makes no vacuum. The expansion chamber in the exhaust pipe creates negative pressure at the port in the designed power band to help pull air and fuel into the cylinder. These pipes look like a megaphone.

Not all 2 strokes used a butterfly valve in the exhaust. These were mostly 440 CC and above single cylinder, this is to aid in pull starting.

If you think back pressure is good weld a washer with a 1/2 inch opening at the end of your exhaust system. How does the car run?

I never said backpressure is a good thing at all in a 4 stroke, but it is inevitable that any exhaust will have some backpressure even open headers have some backpressure if there is any bend in the pipes, even straight pipes off the head have some resistance to flow.

A 2 stroke does make vacuum just very little compared to a 4 stroke with intake and exhaust valves. The expansion chamber does not create negative pressure at the exhaust port but rather allows for a positive reverse pressure wave to arrive at the exhaust port just before the piston moves past the transfer ports to seal the fuel/air in the combustion chamber to keep the mixture from being sucked out the exhaust post. I raced a 74 Yamaha SC 500 single cylinder 500cc MX that had the balancer and kick start activated compression release removed on purpose to get the most power from the engine. It was a 105 MPH 4 speed 210 pound bike with 45 HP on the ground at the rear tire. It was a reed valve piston port design just as all 70s/80s model Yamahas were as well.

I have no experience with the butterfly valve 2 strokes or the Suzuki rotary valve style 2 strokes at all.

I know exactly what a 2 stroke expansion chamber looks like and modified mine several times on my 500 to get the best powerband possible from it when racing it. It also could be tuned for where the powerband occurred by adding the silencer on the end of the pipe or adding just a different length stinger to the end of the pipe. All of which I used depending on the track i was racing one at the time. My 500 would do 80 MPH wheelies with just the twist of the throttle with no clutching or bouncing the front end in 4th gear.

BD

 

[K4fxd]

I'll just add this. The expansion chamber does both. It sends a pulse to the port. This pulse timing is based on pipe length and is only good for 15 to 2000 RPM. Same as a 4 stroke. The megaphone design causes the gasses to expand resulting in a low pressure area starting at the port and following the expanding gasses.

One main reason we no longer see many 2 strokes is due to raw fuel entering the exhaust system. They are very powerful for their size but are very dirty as far as emissions.

I used to race snowmobiles. I've broken pipes before and there is a 2 or 3 foot stream of flame.

 

[Jaymar]

It's an Ecoboost, all turbo cars have a giant muffler in them in the form of a turbine that has a great benefit in boost. It's the cost of doing business, it will never be as loud as a naturally aspirated or supercharged V8 moving raw combustion out the pipes. Personally, I liked the sound of mine with a resonated system on it giving it that nice, low hum that I associate with a turbo car.

I think the great back pressure myth is created in part because of an oversimplification of exhaust scavenging which is exactly as said above how 2 stroke expansion chambers work, properly sized header primaries and well designed intake manifolds. The momentum behind a stack of gas moving at velocity will continue to move air, adding a restriction won't do anything but make it flow like crap.

 

[Buldawg76]

I'll just add this. The expansion chamber does both. It sends a pulse to the port. This pulse timing is based on pipe length and is only good for 15 to 2000 RPM. Same as a 4 stroke. The megaphone design causes the gasses to expand resulting in a low pressure area starting at the port and following the expanding gasses.

One main reason we no longer see many 2 strokes is due to raw fuel entering the exhaust system. They are very powerful for their size but are very dirty as far as emissions.

I used to race snowmobiles. I've broken pipes before and there is a 2 or 3 foot stream of flame.

We can agree on all the above except for the narrow range the expansion chamber works in since that is dependent on the length and diameter of the chamber section. I had my SC 500 chamber tuned for a powerband of 3 to 9K rpm with no silencer or stinger on it and if adding the silencer or different length stingers could adjust the power band up or down by 1000 to 1500K rpm range.

My 500 piston was the same size as a 283 chevy small block and was a single ring piston that was only ever made by Yamaha, Wiseco or any other piston manufacture never made any pistons for the SC 500. It was only built by Yamaha 1.5 years from mid 1973 thru 1974.

BD

 

[K4fxd]

It is the pulse tuning that is a narrow range, that is defined by physics. Length of the pipe determines the time it takes for the pulse to hit the port. It will only hit the port at the correct time over a narrow RPM range.

The expanding gasses in the mega phone works at all RPM's.

 

[stannypack]

Sheesh, cant imagine what this will sound like. I'm still a little irritated with rasp straight out of the box. Post a video if you choose to go this route!

I like it, is louder has more pops and crackles, didn't have any drone either driving an hr back

Sponsored