LeonV

We dyno tested our FSAE engine back in college ("homemade" water-brake dyno), before and after making new intake and exhaust tracts. I've also dyno'd my 260Z before/after exhaust modifications and written "reports" about it on another forum (here). That's probably as far as my relevant practical experience goes.

TougeHorseman

It was actually a loose measure of power based on an average of several runs on a "closed course". Basically a time trial.

pingels

Cool story bro

TougeHorseman

darkfalcon

http://www.youtube.com/watch?v=PfQbUBeImBg

Sound review of the UK exhaust mod.

TougeHorseman

Great sounds.

Trustd_1

nice clip. thanks for sharing. i like the 44mm. the ap2 w/out mufflers sounds gross at start up & idle. not sure how i feel about it at cruising speed. i definitely wouldn't run w/out cans on an NA car tho, esp the street.

andrewhake

I agree with your first sentence, but a pipe of smaller diameter connected into a larger diameter pipe isn't the path of least resistance. The path of least resistance has nothing to do with distance to the end goal. There is a lot of pressure built up in the exhaust by the time it arrives that the "short circuit" and there is nothing at all that says the path will suddenly change just because that is the shortest distance to the exhaust exit. The exhaust gas doesn't know that though does it? It's not as if the exit of the exhaust is drastically different pressure and forcing gasses through the shortest measured distance is it? It is just a fluid doing what fluids do, following smooth bends that lead into the largest possible openings, not narrow ones at harsh 45 degree angles. Smooth out any part of this exhaust mod so the "short circuit" is actually the path of least resistance and maybe it would actually be more than an extra piece of piping hacked onto an engineered twin loop muffler. Even doing that though, without actually blocking off the other parts of the muffler and completely smoothing out the bend into the 'short' (at which point you should just get a different exhaust, I say you are doing more harm to the exhaust flow than good. But again, I am no fluid dynamics engineer.

Say you just punched a small hole in the piping instead of adding the mod piping, not all of the exhaust gases are going to just change direction and exit through that hole before the muffler. But it will cause quite a bit of turbulence and disrupt the regular flow. Take a crazy straw blow air through it, the air might take some time to get to the end of the straw, but the flow always remains consistent. Punch a small hole before the "crazy" bit of the straw, and air should still make it's way to the end of the straw, but in a very inconsistent way with bits of it escaping through the hole.

The reason the mod "works" and makes the car slightly louder is because it is f@#king with the frequency of the exhaust pulses by f@#king with the pressure slightly and not allowing the muffler (which was engineered to work with a specific frequency of pulses) to do it's job in the way it was designed. This in no way means the rate of flow is increased though. It's just different, which will change the way the sound waves can travel through it. Just like having a hole in your muffler or exhaust piping.

Annnnnyway though. All that bullshit aside, the rear section of an exhaust is pretty minor compared to the overall size of the piping when it comes to performance isn't it? So I would say any negative effect the mod could have on the exhaust flow is negligible anyway. And as others have mentioned, it is all about tuning the sound anyway so mod away. I just say get more creative with it is all. It isn't my intention to stop anyone from doing this mod, I was just interested in the discussion. For the record, my favorite exhaust has all sorts of extra stuff slapped onto it.



To me the mod gives the stock muffler a 'hacked' sound rather than a specifically tuned one where the ASM Circuit Siren and EVS 70SSP give a tuned sound in the way a Ferrari exhaust sounds tuned. So for me in the question of OEM tuned sound $0, Mod 'hacked' sound $80, or tuned sound $1000~, I choose OEM tuned sound with intention to spend money on better tuned sound.

All this has got me curious though. I wonder how adding an additional capped pipe at 90 degrees off the main pipe near the rear section of the exhaust would change the sound. I think an additional capped pipe coming 90 degrees off the main piping (like the one already on the stock exhaust) would still give the change in sound without creating a maze for the exhaust flow. With it connecting to the main piping and the twin loop piping the flow is being disrupted twice instead of a single minor time.

macr88

Holy typesalot

That hole must really screw things up disrupting flow and all

TougeHorseman

In for Mac to put a "crazy straw" exhaust on his car!