jjwithers wrote:This has got to be the longest topic on boxerworks...ever! and i love it. I've learned a ton.
What about the idea of adding a baffle to 'tune' your exhaust on a BMW? Can it be done?
I ask for those running aftermarket short pipes, or straight pipes without mufflers. I'm wondering if you can install a baffle in the header pipe, or somewhere else to tune the flow a bit. There are dozens of baffle options out there.
I would certainly not advise stuffing a baffle of any sort into a "header pipe".
As reason to dismiss such a concept,
let's start with the (now) accepted practice of
increasing primary pipe diameter throughout it's length
in order to boost torque output throughout the RPMs.
Seems to me that adding a baffle into a header pipe
effectively reduces both the diameter and effective length (volume) of the system ...
To achieve what desired result ?
Greatly simplified basics:
Primary pipe diameter determines the RPM point at which torque peak will be produced.
This RPM becomes the "fulcrum" about which the torque curve pivots with changes of primary length.
Lengthening the primary pipe adds torque above that [established torque peak RPM]
and removes torque below that [established torque peak RPM].
Shortening primary pipe length adds torque below the RPM peak and removes it from above.
Hence, dragsters that operate at or near redline
ONLY
will use large diameter short pipes.
Torque peak will be fixed at or near redline,
and torque delivery will be needed at those RPMs used before that torque peak / redline.
Road-race MCs typically run at high RPMs.
Torque peak will be tuned to
BE THERE at these higher, most used, RPMs.
Primary length will be adjusted accordingly, and, typically,
with shorter primaries than will be found on a street MC
which typically needs to be able to operate at a range of lower RPMs ...
So, what works on an old air-head ?
Pretty much what the factory did:
38 mm diameter primary pipe to put the peak at a streetable RPM
and pipes long enough to balance torque delivery throughout usable RPMs –
and crossovers to fine-tune that torque curve.
At the risk of being redundant again ...
Any vehicle exhaust system will need to be
designed and engineered for it's intended use.
The operative term may well be "engineered" –
The trick was to avoid getting too close to the back of a road train! Hard way to learn.