Forced Induction Custom FI Setup Questions

Motorcycle exhaust questions.

Old 07-17-2013, 02:43 PM
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Default Motorcycle exhaust questions.

Hi everyone, I'm a new member but have been reading the forum for a while now.
Unfortunately my first posting is an introduction plus a question!
I've recently completed fitting a Garrett T25 turbo to my BMW K100, it's an oldskool draw-through set-up using a HIF 44 SU carburettor with the T25 turbo modified for draw-through.
The turbo is mounted on top of the engine, carburettor towards the front, exhaust outlet rearwards.
The problem is excessive exhaust noise.
The turbo, with built-in wastegate, has a 50mm outlet for the exhaust pipe, I've used stainless steel tube with an I.D. of 57mm. The oulet exhaust pipe is about 1m long, it finishes behind the pillion peg on the left of the bike.
I've seen numerous photos of road-going turbo-ed bikes with just a very short, (300mm), exhaust from the turbo, no-one has complained of excessive noise.
Thanks in advance for any imput!
In desperation I made an absorption type baffle for the outlet of the exhaust pipe, 200mm long, I.D. 43mm, which is a bit quieter, but after testing the bike this evening, it doesn't have the power delivery I was expecting, 130-140bhp at the rear wheel, (the K100 makes about 90bhp as standard, the turbo
has a 7-8psi activator).
Has the baffle killed the tubos performance, (which I'm beginning to suspect!).
Also, it's been suggested to me that a long exhaust pipe can be louder than the very short pipes because it allows the pulses to re-form, is this true?
Apologies for such a long first post, it's my first turbo installation and it's a steep learning curve!

Last edited by Mickymoto; 07-17-2013 at 03:00 PM.
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Old 07-18-2013, 08:49 AM
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It seems unlikely that pulses would re-form in a longer pipe unless the pipe happened to accidentally be tuned for a frequency that's making it through the turbo. I'd probably try using a high flowing sport bike muffler, or maybe even a 2" automotive glasspack.
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Old 07-18-2013, 02:20 PM
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Thanks for the reply.
I 'phoned a motorcycle turbo installer in England this morning, so I now have a few answers!
The baffle is a no-no so I've removed it, power has increased by 15% ish, and the bike pulls rapidly to the rpm limiter easily.
Apparently the short pipes are no quieter than my longer system, the owners just don't care about the noise output!
So that's the build finished except for the intallation of a 60mm bore absorption-type silencer.
Would I build another one? Winter's on it's way.................!
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