Engine Power theory

[Pinoy84]

I have noticed that on the powerband its makes a good amount of torque at 3000 rpm but as it closes to 3500-4500 it has a dip in torque. I think the honda engineer's purposely did so as when crusing shifting at 3000 through the gears would be possible due to the decent torque output but the dip was programmed into the fuel maps so when crusing on the freeway (70-90 mph) the rpm would be around 3500-4500 so reducing power would yield more fuel econmony(26 street mpg - 30 highway mpg).

[JSIR]

you could be right, but the power charts you see normally see are run at WOT, what happens at part throttle such as highway cruising conditions is only really known by the engine manufacturer through their testing. That dip you see in a powr chart run at WOT may not necessarily be a dip when you run the car at 12% throttle (typical throttle % for a Honda) - crusing on the highway. There may actually be a hump in power when running at part throttle, hard to say. But more torque means you can use less throttle for a given speed at cruise conditions, which = less fuel consumptions.

So it is quite possible that they tuned the engine and it's components - small midpipe, somewhat restrictive intake, and okay header to work best at highway cruise conditions making good broad torque - part throttle driving. This may be why many guys get worse fuel economy when changing to aftermarket parts - me included. The power charts look better at WOT, but we dont' really know what's happening at part throttle driiving, we may be losing a bit of torque with aftermarket mods which causes us to use more throttle (say 15% throttle instead of 12% as an example) in cruise conditions to maintain the same speeds we were used to driving in stock form. More throttle = more fuel consumption. Just a theory but I think it is plausible..

[JoshSI]

Originally posted by JSIR

The power charts look better at WOT, but we dont' really know what's happening at part throttle driiving, we may be losing a bit of torque with aftermarket mods which causes us to use more throttle (say 15% throttle instead of 12% as an example) in cruise conditions to maintain the same speeds we were used to driving in stock form. More throttle = more fuel consumption. Just a theory but I think it is plausible..

EXACTLY!
I completely agree with you. Puting less restrictive parts on your car does free up some power at WOT at high rpms becuase it can get that air moving alot faster. BUT you sacrafice some street driving power which is low end torque. Smaller pipes equals more back rpessure which in return gives you more torque. Its more or less like a trade off.

[JSIR]

Backpressure is a by-product of smaller sized exhaust components, it ( backpressure ) doesn't necessarily increase torque on its own. Smaller sized exhaust components that exhibit higher backpressure at WOT and high rpms are usually found to have good bottom end torque characteristics at low rpms and part throttle driving because they keep velocities higher under such conditions. They can start to choke up at high rpms and WOT as gas volumes increase thereby creating backpressure.

Bottom end torque and part throttle power is all about getting exhaust gasses to flow at high velocities, with intake air flowing at good velocity in proper quantity as well. Keep in mind that at part throttle driving you only have a percentage of the gasses flowing through the exhaust and sucking into the intake, maybe 20% of amount that you would have at WOT. Adding a bigger exhaust pipe or intake under these conditions can kill the velocities of the exhaust and intake flow. So the trick is to keep these gasses and air flow moving quickly when there is lower volume. So they install a narrower midpipe, smaller primaries on the header, smaller intake, and non-straight through muffler. These parts keep the gasses and air flow moving quicker at low rpms and part throttle driving. Resonant effects caused from these parts move the peak torque lower on the rpm band.

If the parts are too small you get backpressure at high rpms and WOT, which hurts power under such conditions. So it is a tradeoff for sure, Honda attempted to get the most driveability and bottom end power at lower rpms and part-throttle driving without overly-restricting the top end. There is still some restriction in the top end on a stock Civic as we have found, so you try to open up the top end without killing the bottom end and part throttle driveability.

What you see on a dyno chart under WOT conditions is far different than what you experience at part throttle daily driving on the street. While my car is making 17whp more than stock in its current condition, I think the the stock setup felt more peppy in daily driving conditions such as lane changes and general part throttle driving in the city. My current setup is definitely quicker when I open up the throttle and push it to higher rpms though, as well as highway driving conditions.

stuff to consider when modifying your beast !.

[chunky]

Originally posted by Pinoy84
I have noticed that on the powerband its makes a good amount of torque at 3000 rpm but as it closes to 3500-4500 it has a dip in torque. I think the honda engineer's purposely did so as when crusing shifting at 3000 through the gears would be possible due to the decent torque output but the dip was programmed into the fuel maps so when crusing on the freeway (70-90 mph) the rpm would be around 3500-4500 so reducing power would yield more fuel econmony(26 street mpg - 30 highway mpg).

that's a faulty hypothesis.

The reason for the dip in the torque is b/c of the single runner intake manifold setup. The airflow resonates at roughly 3000rpm, and then again at 5000rpm. It's a well documented phenomena. The resultant torque plot looks like the back of a camel.

Honda motors with dual stage intake manifolds do not exhibit this camel back torque plot.

But it is entirely possible that Honda engineered the intake to resonate at a lower RPM, but my guess is that they wanted the 5000rpm resonance more than the 3000rpm resonance as on most of your upshifts, the rpms fall to just above 5000rpm. Generally you want your torque peak to occur at roughly the rpm where the revs fall to on an upshift.