Ok sick fox.lets just all run around with open headers. Why try to figure out a cool exhaust when you can just uncap it
Stop Saying Car Exhausts Need Back Pressure
- Thread starter Noobz347
- Start date
Oh i remember doing that right after my first h/c/i swap. Had my buddy wait outside to see how far away he could hear me. Seemed like a good idea at the time 
Not the way I understand it, nor the way the video described it. You are describing resistance in you explanation, not back pressure, otherwise, agree.
Yes, not to be confused with resistance tho... and velocity is more dependent upon diameter of exhaust pipe. The back pressure you describe here is what you state in your last sentence.
Not sure about that... honestly, I have no idea... sounds right to me. ???
That wave that bounces back is known as back pressure.
100%
I don't think so.
Back pressure is not resistance, is the returning pressure that needs timed appropriately to match up with your desired power making window...
Resistance is just that, and as far as I know, the less of it the better.
Velocity will be determined first by the engine combination, but, then pipe diameter is used to dial the velocity in... pipe length is used to time the back pressure.
Here's a really interesting phenomenon I found on accident with my car.
I had Flowmaster 2 chamber mufflers on it... car has a nasty (for the street and 91 octane) solid cam in it. Car is n/a.
I started doing research about exhaust, and what nasty n/a cams really need.
Found out, the nastier the cam, the more it wants/needs/will benefit from - a straight through muffler.
Swapped in same size mufflers but with straight through design.
Prior, the car would pull to 7200rpm with ease.
Now, it screams to 7200rpm... betting it wants 7500rpm now.
Both my engine builder, and I "feel" the car is stronger above 4500rpm... pure butt-o-meter, but, if it's enough to "feel", there's gotta be a difference.
These - I am not surprised about.
No tuning changes have been made to the car.
Here's the accidental findings...
Prior the muffler swap...
It absolutely hated life below 2000rpm, and really wanted 2200 and up just to run right. and idled around 1200rpm.
Car will run along at 1750rpm now, and will lug as low as 1500rpm... prior the muffler change that was like asking to be bucked through the windshield.
Car now idles at 1050rpm.
Might be time to re-tune.
Had no idea mufflers would help the drivabilty... didn't see that coming.
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I didn' say I've never done it. It' actually pretty fun. But i wouldn' do it everyday
I would, add about 18" to the collector with a turn out so the sound don't bounce of the asphalt and ear plugs, really good ear plugs.
So on a truck they say dual chamber for the acupressure low end but what you just said about getting bottom end out of a single chamber muffler makes me wonder? I dont expect a truck answer on here just a comment. I' sure you all have trucks.most men do
cleanlx, you definitely understand physically what is happening, and this is semantics, but the pressure waves reflecting back and forth in the exhaust, and also in the intake, are not "back pressure." They are known as helmholtz resonance waves. There is a lot of math that comes down to adjusting length and diameter of your primaries to target a specific rpm band. However, "backpressure" works against resonance tuning and scavenging. It is just basic exhaust air pressure before the effects of resonance tuning and scavenging, and it is always bad. The smaller the pipe and longer the pipe, the more back pressure. At least, that is my understanding of the semantics of all of it.
Anyone that doesn't know Grumpys Toy needs return their man card.
Legend.
So, Grumpy... are you family of the famed and legendary Grumpy?
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Keep in mind it's the sum of all the parts that gives you what you want. Just changing a muffler on your truck likely would do little to nothing for torque, long tube headers will help the low end torque even if nothing else is done, stock induction, stock exhaust,
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Bill jenkins was from Pennsylvania and is hang'n with jim liberman, grumpy150 is from Michigan and hang'n with us
Aren't we lucky?
Aren't we lucky?
mikestang63
SN Certified Technician
Sorry, I really misstated that, I must not have eaten my Wheaties that morning. Basically what I was trying to describe what Noobz said, the venturi effect. Smaller diameter piping will increase velocity at lower RPM's which will help improve low end torque. That smaller diameter piping becomes a restriction at higher RPM (higher flow rates) and therefore has a negative effect on power.
And thank's for clarifying that @FastDriver. I really did a bad job at trying to explain it. I think we are all on the same page now.
