abecedarian

basically says that backpressure is a factor, but not the only one. so myth still ????

chrisbnaz

I'm kind of tired of the backpressure "myth."

The butt dyno can be decieving. I've had electric cutouts on a couple of my cars. The camaro has an electric cutout. Making back to back passes, one with the cutout open, and one with the cutout closed it was consistently worth .2 in the 1/4 mile. I've done this multiple times with several different cars. The results are pretty consistent across the board.

An engine is an air pump...Faster/more air you get in, and the faster/more air you get out the more power you will make.

I'm thinking that the backpressure myth is so common among people with smaller engines because when they experience it, they experience the torque band not disappearing but moreso moving up in the rpm range.

Me for instance, the cars I have run back to back with the cutout open/close have been V8 cars, 2 with Nitrous, 1 without so obviously, these cars are pushing alot more air through the combustion chambers than your typical 22re in a 20 year old truck with 250k miles.

Different effects on different cars, but I can promise you that you're not losing power. If the torque band moves too much, that could obviously make your vehicle slower due to being out of a usable rpm range that your vehicle is setup for. Peak power is not always better...I'll take a smooth flat torque curve and 20hp less over a choppy torque curve that has a few more peak hp.

91Toyota

Just saying my truck feels slower and I can't go up hills without flooring it for some reason. Now I can steadily climb hills and I somehow reached 100mph today. Don't know why or how...but I like the muffler on

abecedarian

Everything I was taught was that the backpressure enhances the scavenging of the cylinders by allowing the acoustic pulses to travel better in the exhaust, similar to how a 'tuned port' intake manifold works. Without the backpressure, an exhaust pulse moves across the next fired cylinder's manifold pipe too quickly and fails to create a sufficient negative pressure pulse at the timed properly to assist the exhaust valve opening. Do a little research into venturi effect and you'll understand a bit better.
Add in the slowing of velocity caused by the cooling of the exhaust gasses as they travel the pipe and the effect of pipe cross-section on back-pressure and such becomes more evident.
Too much backpressure and obviously things back up, too little and exhaust pulses are battling against dead flow gasses, just enough and it flows fine.
Turbo'd engines have an entirely different problem, and positive displacement supercharged engines don't require as much if any backpressure due to positive pressure in the intake and cylinders from the blower forcing exhaust out during valve-overlap conditions.

saitotiktmdog

I totally understand what your saying but I think some things need to be clarified. The pulse timing of the cylinders has more to do with all the header tubes being equal length mor so than the size (diameter). It not so much the size as it is the equal lengths. But as far as backpressure its really about volumetric flow rate. Too big of an exhaust equals a huge pressure drop, a decrease in velocity and less volumentric flow. Too small of an exhaust equals high pressure and increased velocity but less volumetric flow due to less cross sectional area. You need the best ratio to optimize flow rate. this then can affect the lean rich condition as explined in the link in my previous post.

But I guess you could change the size of the individual header tubes to offset for the different lenghts and achieve the same results, or add baffles. That would be a neat experiment.

gary96360

I've noticed that glasspacks make your vehicle lose power. my dodge ram has a gutted cat and a glasspack and i can feel that i lost tons of low end torque off the line. i can still chirp tires in 1st 2nd and 3rd but not good as before. what are good mufflers for a 3.0 v6 yota that sound alright but without that ricer sound?

Belize Off Road Team

I run a resignator and no CAT.:


I have no problems with back pressure. i get maximum performance from my 3.0L and great fuel economy. including some nice rumble at idle

When i get around to putting the 3.4L in I'm going to run pipes out the side in front of the rear tires from Downey headers.

If you want more info PM me

rusche

I run a setup to Belize
From an LC header to a Delta 40 was way too loud (no cat)
Threw a resonator in front of it and it quieted it down, and to people who dont really know what they are talking about, the resonator even looks like a cat!

Belize Off Road Team

Not my resignator, it looks like a muffler from a scooter. It looks like a long, skinny cylinder.

bigt

my toyota dsiesel only has a reonator thats it.. dont know too much about diesel engines yet..
but i love JUMPING on it the TURBO screams and the black smoke rolls!!!!

Belize Off Road Team

Down With Black Smoke

abecedarian

black smoke from a turbo diesel? what's up with that? you shouldn't have hardly any smoke if the injection pump is tuned properly to the increased airflow provided by the turbo. black smoke on a diesel is the tell-tale sign of a rich fuel mixture (too much fuel, not enough air) on a diesel.

but like I mentioned above, turbo's have different exhaust requirements than naturally aspirated engines. the turbo itself is plenty of backpressure for the engine so the exhaust behind the turbo needs to be as open as possible, but for maximum performance, the exhuast pipe should not be so large that it creates turbulence in the exhaust pipe after the turbo that causes backpressure to the turbo and wastegate (if equipped).

I had a vw quantum turbo diesel that barely smoked at all even full throttle climbing I-15/Cajon Pass.

Belize Off Road Team

mostly, turbo's will smoke in alot of problems, or lack of exhaust system parts such as CAT.'s or some seals go.

abecedarian

I'd have to disagree. Maybe the way you use the glasspack(s) can hurt you, but not the glasspack itself.
Case-in-point:
1981 VW Scirocco, 1.7l 8v. I replaced the exhaust from the converter back with 2", into a 14" glasspack installed backwards, then 2" pipe (crush bent at the muffler shop) up and over the rear suspension into a 12" glasspack mounted normally into the exhaust tip (mentioned below). Granted, not a horsepower monster by any means but without any other mods to the engine it went from being the economy vehicle it was (35+ mpg on the highway) to CRX killer (well, up to about 90 mph). 3rd gear tire chirps were no problem for it.
I originally had an 18" glasspack mounted normally where the 14" listed above was mounted and then 2" pipe into a dual 'monza' resonator tip (wow... 80's reference?). Took it back to the shop because it was too loud. So we looked at things and decided to go down to a 14" pack in reverse and add the 12" in front of the monza tip. Got it back and it was all nice and growly, nearly ricer, but without that tounge-between-the-lips-and-blow resonance... sounded more like a modern ducati motorcycle than rice-rocket... and actually performed better.

abecedarian

...nudge...nudge... I used to be a certified diesel mechanic for heavy equipment (OTR trucks and construction tractors) on cummins, detroit and caterpillar engines....

it's normal to get black smoke when going from light to full throttle, but once the turbo spools there should be enough air being pumped in by the turbo to burn the fuel supplied by the injection pump thus causing the smoke to abate.

91Toyota

diesels smoke because of excess fuel into the engine. Honestly it looks pretty cool When I get my diesel I'm putting a stack on that biatch...should have it in a couple of months

93toyrunner

I know you already have a glasspack on but another cheap good sounding muffler is the cherry bomb turbo it is about $20 fleet farm, Auto Zone, advance, any where. It is cheap and sound really nice. I have a small high flow cat though.

91Toyota

Well maybe I'll give it a try...I actually kinda like my glass pack though...definitely thanks for the suggestion!!!

Belize Off Road Team

Well, the last 8 diesels i have driven never blew any black smoke. and they where all turbo'd. a 01' ram 2500, 5 05' ram 3500, 1 91' f250, and a 95 f250.

The only time i saw black smoke was when a rubber seal finally gave out, the entire rear panel and bumper of the 01' Ram was BLACK. and when i drive a diesel...i drive foot to the floor.

saitotiktmdog

abe is right. Black smoke is power you can see but not use. As least thats how gale banks put it from banks performance. According to him what happens when a diesel puts out tons of black smoke is due to improper intercooling, and too much fuel. With the right size intercooler, etc the black smoke can be eliminated. I wonder however if this is only to a point. Because all diesel pulling tractors smoke and trucks as well. It may be like on a gaser turbo where when you run 80 psi you dump extra fuel through to protect against pre ignition etc. But I am not sure on this.