Kodokan_4

I've heard that some engines make more power with a muffler that is not a (straight through) race type. In other words, the engine needs more backpressure.

I've seen enough dyno results to know that most aftermarket exhausts for the Honda S2000 give a small increase in HP. So this backpressure thing doesn't appear to be true for the S.

I'm actually trying to find out if the same holds true for the engine in my Scion xA (without buying a lot of parts and testing).

I thought a more free-flowing exhaust would ALWAYS produce more HP than a more restrictive one.

Can anyone enlighten me on this topic?


-Pete

blown_xa

yea I can tell you that the engineers at Toyota have a MUCH larger budget than any aftermarket exhaust company. Just think about that. Usually you will only see noticable results with exhaust if you have messed with intake air consumption also (Turbo, Nitrous, Supercharger, intake).
I can tell you from personal experience that when I first put my Turbo kit on, I had a good exhaust leak from the downpipe to the cat, and when I fixed it... I had a really really noticable power increase.

stangdude22

yeah, having a less restictive exhaust will mean more HP, but less restiction = less back pressure = less low end tourque. Look at the same dyno charts, they will have less torque below 3k. chambered mufflers tend to give gain up top without sacrficing bottom end, but the Hp gains arnt as great. but lets face it. A muffler isnt going to make that big of a diff either way.

But if you take out the cat, be prepaired for a loss in bottom end...

Kodokan_4

Thanks, guys!

I also searched for some info and now have a little better understanding of what you guys are saying.

The diameter of the exhaust piping is crucial to attain the best velocity of exhausted gases. If the piping is too small, it will create increased backpressure, causing the engine to work harder, and lose HP. If the piping is too large, the velocity will be decreased, and also HP will be lost.

On the issue of backpressure itself, I think the lower it is, the more HP will be attained. I read that most of the backpressure issues are with dated technology.

In older cars with carbs, when backpressure was decreased, it caused increased fresh air intake. The carbs wouldn't automatically adjust for this, causing a lean condition and decreasing HP, leading to a loss of low-end torque.

I think most modern injection systems are able to compensate for lean and rich conditions, so backpressure is not really an issue.

Obviously, if I go to FI with the Scion, I will need a larger diameter piping for the exhaust, but it becomes more difficult to determine when to go with larger piping for a "built" NA engine.

-Pete

guitarguru44

for N/A go 2.5, turbo or supercharger go 3 if its a lot of power... I cant imagine running wider than a 3 inch on this car..

guitarguru44

oh and you want the bends to be limited to the least possible and the most freely flowing designs..

vintage42

Yes, there was a lot of engineering put into the stock muffler, and it's not likely that a louder muffler can do everything that the stock one does:
Scion xB Engine Features (posted in 2003, taken from unknown source):
"... Unique features of the Scions are its variable backpressure muffler and ...."
https://www.scionlife.com/forums/viewtopic.php?t=1685