Toady1
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 posted on 24/8/07 at 11:03 PM |
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modded exhaust
I modded my exhaust today (remus end can) to have a 90deg 2.5" od tail pipe on it as ive fried my rear wheel arch a treat with it! However since
ive re fitted it i think its now down on power?!! Im guessing its because the gasses just cant pyhsically get out quick enough now having a bend to
accomdate too? anyone else had this? Im going to move the tail pipe closer to the manifold along the car 2mro, and chop my nice new mod in half so its
a 45 deg (cut with a slanted angle) as i think this will help? ideas anyone? its still fast but not crazy fast like it was, deffinately feels
restricted a bit! Ill get some pics up in the morning! and of my poor wheels arch!
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zxrlocost
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| posted on 24/8/07 at 11:37 PM |
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shouldnt do
as long as the pipe diameter is the same
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Ivan
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| posted on 25/8/07 at 07:41 AM |
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If the car sounds different it might just be a subjective thing as sound has a lot to do with a feeling of speed.
A 90 degree bend of the same diameter shouldn't make a noticeable difference.
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Toady1
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| posted on 25/8/07 at 07:49 AM |
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but it does though, if air has to travel through a 90deg bend the turbulence caused slows it down a great deal. Especially when a bike engine is
revving at 10k+ revs, i dont think it can get the gasses out quick enough like it couls before. Im going to get my mate to drive it today without me
saying anything, and see what he says.
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smart51
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| posted on 25/8/07 at 09:05 AM |
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It is harder for a fluid to turn through a radius than to go along a straight pipe. The tighter the radius and the longer the bend, the more
restriction it gives.
Cutting the 90° down to 45° will help.
What is the radius of the bend compared to the diameter of the pipe?
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zxrlocost
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| posted on 25/8/07 at 09:22 AM |
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sorry Im just imagining a curved tailpipe like most have got you got a pic
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ChrisGamlin
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| posted on 25/8/07 at 12:05 PM |
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Maybe your engine is running a bit rich anyway and the tiny increase in restriction is tipping it over the edge and making it less responsive
In theory a bend (or any addition in length, even straight) will increase restriction, but as long as there's no big blobs of weld etc blocking
it up, the difference really should be negligible so you either need to get your engine set back up, or as others have said its something you think
you're feeling because your head tells you its different.
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Ivan
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| posted on 25/8/07 at 03:00 PM |
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I still feel that the bend will make minimal difference to the power. In general when calculating pipe flows a bend is seen as the equivalent to a
length of similarly sized pipe of 2 or 3 times the length of the bend. And no - with a properly radiused bend the flow doesn't normally go
turbulent except for a small bit on the inside of the bend where at certain flow speeds (or Reynolds number) you might get turbulance. Also at the end
of the exhaust you are dealing with a significantly smaller volume of gas than at the Valves due to the cooling of the gas so the bend will have less
impact due to its location.
Even going from a restrictive standard exhaust system to a non restrictive after-market one will normally gain you only around 5% in power so 1 bend
extra is unlikely to cost you more than 1% to 2% (and most probably a lot less) and this is less than the difference in power made between a cool day
and a hot one.
I also doubt whether any driver could notice a 2% loss in power.
But if the loss is real to you, you will never be satisfied until you go back to what you had or test it on a Dyno (or against the clock) with and
without the bend and satisfy yourself as to what's realy happening.
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Toady1
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| posted on 29/8/07 at 09:09 PM |
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it seems to have got quicker again since driving it more?! Ive been told the engine has a self learning ecu (to some point) so it may have been
running a bit rich like was said, and has now learnt to lean itself back a bit? not sure, but im going to cut it down a bit when i mod it to fit a std
can for track, and see if there is any difference again.
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