Cold air bends valves?

[dichotomous]

Originally Posted by Christ

If that's true, how are cat-back manufacturers and tuners alike showing off dyno runs where a cat-back exhaust system outflows stock and nets 5-15 HP gains?

cause they are also pairing it with a retuned computer and cold air intake system. and thats cat back. he said muffler. just the muffler is about the least restrictive part on most automobiles. the exhaust gas is cool and lost its velocity by then so its not as big a deal. the headers and midpipe are where you make your best gains. and everyone knows that claims of 5-15hp for an exhaust (catback) are completely bogus anyways, its laughable

[guudasitgets]

dich; stole my thunder, well put

[dichotomous]

and I know all this for sure BTW, my car has a full custom exhaust from the engine back (tuned for high RPM racing) and a shortened "cai" (its not but is, very trick to actually categorized, but its custom). and combined they probably give me 30hp to the crank, maybe 20 to the wheels. I could make 30-35hp more to the wheels (than stock) with this setup if added the hondata kpro engine mangagement chip to my computer and tuned it right. but that can extend the rev limiter to 8000rpm (instead of 6700), dial in the most power from cam angle, ignition timing, vtec activation, fuel additions.....

[Christ]

I wasn't saying anything about that for a project, I was just wondering how they can get away with showing those gains if they're not true... not paying attention to the fact that they've re-tuned the ECU for those specific mods.

Oddly, that's the first thing I tell people tuning Hondas (what I work on mostly), and I still forget it when I ask a question.

"You're not doing anything good if your ECU isn't programmed according to your setup."

Although, technically, my ECU isn't programmed for my engine either, and it still works better than stock... 35-ish mpg for the most part, and a fully open exhaust (not too loud though), the ECU is from a 1.6, the engine is a 1.5.

Oddly, it runs slightly rich... and still gets better mileage than it did before I did the changes.

MY DD isn't a project anymore, I just fix stuff as it breaks.. I find more and more lately that I'm not even willing to do that, I just want to get rid of it most days.

[Christ]

Question though, since we're on it, is there a way that I could manipulate exhaust flow to lower the peak torque of an engine?

[dichotomous]

Originally Posted by Christ

Question though, since we're on it, is there a way that I could manipulate exhaust flow to lower the peak torque of an engine?

yes, especially for lower rpm torque, make the exhaust bigger. I lost a noticable amount of lower and midrange torque with my raceheader and larger midpipe/muffler. I did not go all the way to 3" or bigger, and 2.25 seems about right for my engine, but it makes its power higher in the RPM band. should give me better milage at lower RPMS, and a good screaming power at higher, just the way I like it, have my power and eat it too

[IndyIan]

Originally Posted by dichotomous

and I know all this for sure BTW, my car has a full custom exhaust from the engine back (tuned for high RPM racing) and a shortened "cai" (its not but is, very trick to actually categorized, but its custom). and combined they probably give me 30hp to the crank, maybe 20 to the wheels. I could make 30-35hp more to the wheels (than stock) with this setup if added the hondata kpro engine mangagement chip to my computer and tuned it right. but that can extend the rev limiter to 8000rpm (instead of 6700), dial in the most power from cam angle, ignition timing, vtec activation, fuel additions.....

If you don't dyno it or race at a drag strip its hard to say how much extra hp you are getting. A true racing header might get you there but not without tuning like was said above. I imagine in general its hard to get a Honda performance engine to output 25% more and still be good for daily driving.
In some solo racing classes where they can't touch the engine internally they do headers (for hp) and the shortest exhaust pipe possible out behind the driver (to save wieght).
Ian

[guudasitgets]

IndyIan same goes for Formula Fords, all your allowed to do is put a header on it.

[bclark89]

Thank you all for your help.

I've decided to stick with my current muffler for now. I want to replace it with a stock type eventually but I'll probably wait until spring so I can monitor my change in FE.

[Christ]

Originally Posted by IndyIan

I imagine in general its hard to get a Honda performance engine to output 25% more and still be good for daily driving.

Ian

Some guys that I mess with working on their cars add a nice combo of boost and excess amounts of fuel to get 200+ from their D16Z6's... normally these engines produce a modest 118HP.

The same can be done for a DOHC ZC engine, it can easily make 200+ at the crank, again, on boost.

The nice thing about them is that they're still plenty streetable... b/c the stock clutch can hold all that power, for the most part, if not, a stage 1 will, and isn't that much harder than a OEM, the stock axles are good for about 300 or so if you're not using slicks, and as long as you upgraded the rods in D-series engines, you're good to go. (They're pencils.)

So, that said, 25% more power is nothing.. in fact, my car has 25% more power just based on estimates from 0-60 times than it did stock. Counting my car's weight loss, I still say it's not quite 25%, but I'm sure I went from 92HP to around 115-120 at least, considering that I can beat a stock CR-X Si, but only by a few feet.