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Does changing mufflers and deleting resonators give you more horsepower?

36K views 32 replies 20 participants last post by  SFCR  
#1 ·
I put on some super 40s. I listened to it with the resonators on and I didnt notice a difference so I deleted the resonators. Sounds pretty good. Big question. Does this give you more horsepower deleting and adding new mufflers?
 
#3 ·
Some guys have dynoed b4 and after what you did and lost hp in the low to mid ranges because of lose of back pressure. I have always keep the stock exhaust on my jeeps and have ran pretty good and infact faster than some with modded exhaust.
 
#5 ·
Where do people get the idea that loss of back pressure hurts performance? You want the exhaust exiting the cylinder at maximum velocity to help with 2 factors, 1.) scavenging (evacuating the cylinder) and to help refill the cylinder when the intake valve opens before the exhaust valve closes (the negative vacuum caused be the reversion wave) which is why you tune your exhaust for your engine's RPM range. Loss of velocity can hurt but if you have back pressure your exhaust is trying to flow in the wrong direction.
 
#4 ·
most EVERY owner is swapping/modding exhausts for nothing more than a subjective improvement in sound. Never heard one single person say "I don't care how crappy the exhaust sounds all I want is better straight line performance".
 
#6 ·
I have actually see race on the street 2 identical chargers rt same year 2013 one bone stock one with straight pipe no mufflers no resonators , the stock charger pull ahead 4 out of 4 times.
 
#7 ·
Exhaust too long and losing the "scavenging effect" of the mufflers? I don't know open up an OEM muffler, what does it look like inside. What people used to do was install long tube headers and a piece of pipe to the collector, drive the car (down the drag strip) a few times (test and tune night) and cut the pipe off where it turned blue and voila you tuned your exhaust to your engine. (old street racer's tricks are like old wive's tales)
 
#10 ·
No gain in HP, but a drop in torque due to loss of back pressure.
Only gain is sound.
If you change your exhaust and then go for a tune, you might be able to pick up a few ponies,
but mostly because of the tune.
Went through this with a bunch of bikes over the years.
 
#13 ·
Maybe I read it wrong, but he states that just increasing flow without matching it to the rest of the system causes power loss. So in reality, it's not a myth.
If you change only part of your exhaust system and don't get your motor tuned, you're not going to get any benefit.
 
#18 ·
Finally somebody is getting that people are confusing the words backpressure and flow/velocity.

Any backpressure is back...it is a restriction or blockage....no OEM would let an exhaust design in this day and age to create a blockage to flow.

Now velocity and total flow...different story....you can tune flow to help increase velocity and the scavenging effects and to reduce reversion (not as much an issue on long exhaust)

of course that all changes on something like a turbo car... with a turbo anything after the turbo does not really effect power as much as an NA/supercharged car.


Example of backpressure vs velocity. I once had a customer with aa supercharged mustang and a MAC catback...one of the mufflers broke apart internally and block the right side....that created back pressure....ran like crap and the numbers at the boost gauge went up as it was stopping airflow.

Velocity...another custmoer has 2 1/4 pipes on a bike with 1200cc....lost all velocity...low end tanked....peak number was up but it was a slug below 5k
 
#19 ·
I agree with you guys, but without re tuning the motor, either adding back pressure or increasing flow will cause the motor to run like crap.
Too many people think that just by changing their exhaust system they are going to gain power. They completely forget about air/fuel ratios.
This is where the problem is.
 
#20 · (Edited)
It is applicable to jet engine science, and rocket exhaust science

Maybe in a way it is (exit velocity and pulse vacuum) but really rocket science is not really that difficult either.[/QUOTE said:
Good post by the way. Anyway, the V1 Buzz Bomb used a Pulse Jet motor that depended on the principles we are discussing. https://www.google.com/search?q=why+does+the+exhaust+of+X1+rocket+show+pulses&biw=1680&bih=902&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMIzuHg2-TsxwIVhY0NCh1X7wK1#tbm=isch&q=why+does+the+exhaust+of+V1+rocket+show+pulses&imgrc=IInXtdx2Abor8M%3A


I do believe a slightly bigger diameter exhaust can add more power if tuned...
 
#21 ·
My understanding is that some BP is purposely engineered into exhaust systems because those BP 'pulses' that travel in waves back to the combustion chambers (and the low pressure areas that follow them) help to scavenge the combustion chambers, leading to a better intake charge in the next cycle. Sorry to perpetuate the myth.
 
#22 ·
so wouldn't removing the resonators increase the velocity of the exhaust gases? even if just a minimal amount, since you would be removing a part of the exhaust system that creates a restriction in flow. im not talking about making more power because if your not doing headers & a tune then were talking about +/- 5-10 hp. I just removed mine for the sound, any benefit in power is just a bonus!
 
#25 ·
I did the resonator delete with new mufflers (Flow Master copies) and then had a dyno done. The car (5.7)came out with 375 hp . So there was no increase in HP. Does sound alot better !! Guy told me to do a tune and I will see probably up to 50 HP more with the right tune.
 
#28 ·
Well, with experience with my 13 RT (straight pipes, no muffler, no resonator, cai, cai spacer, ported throttle body, diablo tune) and a 15 RT (stock exhaust, cai). When we pulled up, he definetly pulled ahead for fora second until I started going through RPMs. Did 4 pulls and got him every time, but the same beginning result.
 
#29 ·
Notice the mod list. The mods that allowed you to pull ahead was the ported throttle body with the tune. straight pipes/no muffler and CAI's don't add anything.

So basically ported throttle body + tune car vs a stock car. Of course you're going to pull ahead every time.
 
#30 ·
My 1980 Cutlass had a wormed over 307 with intake, cam, headers full duel exhaust 2 1/4" with no cats, ran a 16.2 at the tack. I needed to put cats on the car because the police were handing out huge fines at the time, so I added 2.5" exhaust with cats and good mufflers. Tail pipes were still on order but I took it to the track with out them and ran 15.6 Once I had added the tail pipes I took it to the track the final time it was running 15.2 and that was in the hottest month of August. I thought that with adding the cats it would slow me down, so I was surprised when I was going faster with cats.