also, why do headers work off of scavenging, and why a tuned exhaust works better, using sound waves to extract exhaust gasses?

im just sayin things i've heard, please comment

 

Try running your car without headers and see what happens, and a tercel should have a muffler no matter what, its a tercel for christ's sake.......

 

Do it, your exhaust valves will love you for it.

 

Here's one the Mazda guys can understand



Lets’ say that Max puts a 3-inch system on his normally aspirated car. He soon realises that he has lost power right through the power band. The connection is made in his throbbing brain…. put on 3" pipe = loss of backpressure = loss of power. Max erroneously concludes that you need backpressure to retain performance. He has ignored the need for exhaust gas velocity to get that scavenge effect.



If Max had chosen a 2 1/4" pipe he would have achieved better performance in the mid- to high-RPM power band. You need the combination of the least positive (close to zero) backpressure possible with the highest gas velocity achievable to create performance. The diameter of the pipe (and smoothness of internal finish and bends) will strongly influence if your exhaust change is going to create performance or lose power.

As a general rule, a normally aspirated MX-5 will get better high RPM performance with a 2 1/4" exhaust system (2 1/2" or above is just too wide to retain exhaust gas velocity for street driving). The general consensus is that a 2 1/4" system is for mid to high RPM petrol heads. Your mechanic should be able to advise you what exhaust system will best suit you driving style and needs.



Forced induction (turbo or supercharged) MX-5s perform better with the high volume pipes (2 1/2" to 3"), but that’s another story. The choice of a 4 into 2 into1 or a 4 into 1 header to exhaust set is yet another story.



Safe journey



Rob (Techno) Spargo

Mazda MKX-5 Club Victoria

 

Nope your right, thats why F1 teams would use variable length exhausts (and intake runners) if the FIA didn't ban them.

Get your exhaust design right, and you can actually achieve over 100% volumetric % just on the scavengeing effect alone.

 

I think thats where alot of people get screwed up, they are thinking gas velocity is backpressure. Back pressure is bad, gas velocity is good.

 

how are they different?

if your exhaust gas is going out faster then the engine is putting it out, there would be negative pressure on the system, and no backpressure right?

 

Well, backpressure is just that, pressure in the exhaust system. Velocity is just that, velocity. Run a pipe too big and you'll lose exhaust velocity.

 

Think of it like this.

Get a straw and blow in it. Its easyer for you to blow out the whole straw since its so small that all the air you put it in feels it up quickly and it goes out faster.

Now take a paper towel tube and blow in it. its harder to blow fast due to having such a large space to fill and the air to go out.
Same concept. You have a smaller pipe(2 inch) the air can move quickly out of it sine the air is filling it up faster. Instead of a big pipe (3inch).

Instead of moving in the big pipe the gas just kinda lingers around when it gets farther from the engine.

 

I don't feel like reading the whole thread, but what series motor is in the tercel? If it's a 5efe, than one of the reasons could be the TPS, another common prob for the efe series is the fuel reglator. IDK hope that helps. I had a bud w/ a tercel had the same prob. replaced the TPS, and it was fine . . .