Performance not as strong after new downpipes

[stoneman86]

Hey guys,

I recently had the misfortune of smashing my exhaust into a gate and therefore snapping the downpipes, i had to ride it a couple of times (My only way to get to work at the time) after this had happened and the bike just made an awful noise and had an obvious drop in power. I managed to buy some second hand pipes off an L1 (mines an L8) when replacing them, they fitted no problem, however i noticed the L8 pipes had a connection between pipes 1 - 4 and 2 -3. The bike now starts fine and the noise is much better how ever the performance hasn't really returned, I was just wondering if any one could tell me if its because the L1 dont have the connection or theres just "another" problem with the bike?


Thanks

Stu

[parby81]

I do believe, and any one can correct me if I'm wrong and I won't have a hissy fit like lewisdale, the connecting pipes aid the removal of exhaust gases and introduction of fuel air mix in altering the way the back pressures work. I believe this aids in the mid range slightly. Therefore with them removed the midrange is slightly down on what you are used to, but again, I believe that with the connecting pipes gone the top end is supposed to be better. Though on these torque laden beasts I would not have thought that the difference would be immense. Most aftermarket downpipes you buy get rid of these connecting pipes, but then most people want better top end power as in this world peak power seems to be what people like to brag about, though in real world riding its usually the mid range that counts.

[zimm]

im not sure whether the link pipes are open or closed on OE systems .. anyone know for sure ?

either way, ive never noticed a massive difference swapping from one OE exhaust to another

sure its firing on all 4 ?

[Mori Man]

Commonly known as balance pipes, they ignite any unspent fuel ensuring that the next expulsion is going into a clear header.

Most systems generating good torque have them , however not essential depending on the header design - you find that tapered headers don't have these as the exhaust gases are dragged down the tube quicker and the fuel evaporates quicker.

It goes along the line of reversion , if the expelled gases meet a "wave" from a pre-explosion then power will drop. As the hot gases are expelled you have a heat wave in front of the actual expulsion - this wave then ignites any dormant fuel which in turn sets up a shock wave which prematurely causes back pressure into the bore.

Or words to that effect

[cargo]

SUCK

SQUEEZE

BANG

BLOW


It's only fuel and air..............

[Mori Man]

Nope - fluid dynamics , wether that be liquid or gas

Had a lovely talk with an exhaust engineer at the MotoGP in Oz , when I threw in a few idea's he was off on one !

A straight through exhaust is the worst design as none to little reversion at all (Even your race "straight" through isn't as it will have outer baffling and harmonic padding in the can) - slash cut's on chops run toad and are fuelled way rich. Only way to run pipes like that is with DFI and again you'll be drinking fuel like it was priced in the '70s

[Mori Man]

Also Ti pipes don't retain heat as well as Steel and Stainless so most of them also have these balance pipes to keep HP up.

[zimm]

Also Ti pipes don't retain heat as well as Steel and Stainless so most of them also have these balance pipes to keep HP up.

ackcherrly ... on the subject of Ti v Steel ..

its all about resonance, egt and tuned length, timing waves to arrive back at the exhaust port at the right time in the firing cycle to help scavenge the combustion chamber etc etc .. due to the fact that the speed that sound travels through a gas is related to to both the temperature and pressure of that gas in that as temperature/pressure increase, sound speeds up, so you need a longer pipe to arrive back at the same "timing" compared to when the exhaust is cold. This variance is a BAD thing.. either wrap the headers, (or ceramic coat them) to keep the temps up, or make an exhaust that sheds heat quickly (Titanium).. doesnt really matter which, the aim being to maintain as consistent a temperature as possible and optimise the tuning within a temperature range that can be maintained.