Exhaust pressure and low-end torque issues

Joined
May 26, 2009
Messages
58
Location
Helsinki, Finland
Bike
ST1100AN
Hi all,

Maybe this is linked more to carb section but I have replaced my rotten OEM exhaust with Delkevic downpipes+collector and BSM cans. Combination is not the best match for the ST because downpipes wont fit very well, they need serious force when installed and those cans have too much flow, I guess. OEM silencers have an about 28mm hole in the end but these absorption-type cans have 48mm straight pipe through the whole can. My bike is quite noisy and it accelerates a bit slower in low RPM (1000 to 2500-3000) than a bike with OEM exhaust. It is a bit tractor-like, noise gets louder when I turn the throttle but acceleration is bumpy till 2500-3000 rpm, not smooth increase of speed like it usually is with ST's.

My plan is to take the bike to specified exhaust shop, I'm sick and tired in badly fitting aftermarket parts but has anyone made experiments with bigger jets etc in situation like this? Or has anyone ever faced similar problems with aftermarket cans and/or downpipes?

One fast solution is some kind of noise killers, too.
 

Blrfl

Natural Rider Enhancement
Joined
Aug 24, 2005
Messages
5,602
Age
55
Location
Northern Virginia
Bike
Fast Blue One
STOC #
4837
How your exhaust system and engine interact is a complex topic, but in some situations where the flow in the pipe isn't what the engine was designed for, you can end up with a loss of torque.

--Mark
 

Dale_I

Incorrigible Idealist
Site Supporter
Joined
Mar 23, 2005
Messages
893
Location
Spokane, WA
Bike
08 FJR1300/01 ST1100
2024 Miles
000209
STOC #
5341
Carb non-turbo gas motors dictate some of the flow through the cylinder with back-pressure in the exhaust. Gas motors burn an air/gas mixture and that mixture has now been changed to have a bit more air, which has made the mixture lean and less efficient.

You can re-set the exhaust back to more of a stock format and re-synch the carbs and you would probably be OK. Or, they can re-jet and re-synch for the additional flow. I would go somewhere that deals with this though. Mark is correct... it is a complex mixture of subsystems each doing their part to create a running motorcycle. When you stop to think about it... it really is amazing.
 
OP
OP
STonewall
Joined
May 26, 2009
Messages
58
Location
Helsinki, Finland
Bike
ST1100AN
Problem solved indefinitely, I literally glued aftermarket noise killers to can ends. Now sound is closer to OEM exhaust despite few leaks but engine become smooth and accelerations in slow speed are as luscious as they should be. I'm still not satisfied to my frankensteinish exhaust but experiments will continue in near future.
 
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