Spitfire Scrambler Mufflers/Silencers

[RDfella]

The idea open pipes give more power ain't necessarily true.
I recall the Hillman Imp I had in the early 60's. Handled a dream and had a noisy exhaust (as bought). But was forever being pulled over for excessive noise, so I fitted a standard silencer. Much quieter, and the car actually performed better.

[muskrat]

Gday RD.
Yes there is a fine balance between performance and noise.
Depending on cam timing no or little restriction is best.
Short warm up, low revs to get out of the neighbor hood then let'er rip.
Cheers

[berger]

the solution is let them know it's loud then they are warned

[Superarnie]

I watched a short video on YouTube dealing with the subject of exhaust back pressure and it dealt with the science around it. It concluded that a little back pressure is a good thing.

I think stuffing restrictions up the back pipe will have an overall effect on speed/performance but I will only be using the bike in the summer months to pootle to work, so not too bothered about the performance unless it starts coughing and generally running poorly.

[BSA500]

I have Hornet pipes on the A7 with the short baffles shoved in. Makes a little difference to the noise not much, the best thing is not to wring its neck when pulling away it can be quite genteel on a whiff of throttle until you are clear of the nieghbours. Then you can let rip

[thackero]

i have 2 x 6" long baffles inserted into my 61 Spitfire pipes and during low revs they do reduce noise. Once I am out of our neighborhood I can give it sum welly. It still sounds superb and no power loss. Timing and carbs were not touched.

[Superarnie]

Hi Thackero,
I have bought the 6 inch inserts, did you wrap them in exhaust wadding prior to fitting them?

[thackero]

No wadding .

[Superarnie]

Update - hi everyone, sorry for this rather late update but other matters have gotten in the way.
Before I put the DB Killers in each exhaust, I used a decibel app on my phone to establish how load it was. The result was 90 dB (at idle) I then inserted the baffles (with fibreglass wadding) into the exhausts and re-checked the decidels; the sound was definitely reduced and hovered around the 86/87 decibel Mark. That doesn't sound much, but it is a marked reduction. I then took it for a ride in our local area and the bike is struggling to make its usual high speed. It's OK on initial acceleration but upper speed limits are reduced and the bike coughs a bit. One of you posted and predicted that I might need to lean the fuel out. Can someone confirm if this is the case and if so, why? Presumable the adjustment will be made by dropping the needle valve by a slot or two?
Many thanks
Gary

[limeyrob]

Early (ie 1950'60's) VW Beetles had chrome tail pipes that were lined with perforated steel and acted to cut high frequency noise.  I recall fitting one on the tail pipe of my BSA and it worked.  They still seem to be available and quite cheap but it not clear whether the modern replacements still have the sound deadening lining.  They are straight through with no baffles.

If you have more restriction on the exhaust (or inlet) you will have less airflow. The carb can correct for this a bit but you may need to drop the fuel flow at wide throttle openings so try one size down on the main jet.  Proceed carefully and check the plugs as you don't want to go weak.