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Bonneville, Thruxton and Scrambler Easy Airbox Baffle Removal

The airbox baffle placed in the airbox of the Bonneville, Thruxton and Scrambler has no positive effect on the twins other than to be the second line of defence against induction roar, with the airbox cover snorkel being the primary line of defence. With these two items in place, the induction roar is more of an induction whimper which is great if you have to pass noise emission tests, but once a bike leaves the showroom, the induction roar isn't a concern for many owners or vehicle testing centre's.

So, you've had your bike for a while and you're maybe thinking about about releasing some or all the available power that would have been on offer from the factory if you'd bought your modern Triumph twin in the 60's or 70's. By removing the OEM silencers, airbox snorkel and airbox baffle and installing free flowing silencers, performance air filter and Breathe high flow airbox intake cover you will gain between 10 and 25% more BHP, but more importantly release between 25 and 33% more mid range torque which you will use every time you ride (power increase figures are model dependant). These mods will be the easiest and cheapest release of power and torque you will ever achieve from your bike, bar none.

Dyno of 790 OEM bike, modded 790 with TTP Breathe and airbox baffle and without airbox baffle

The graphic on the right shows two dyno graphs, the first is a comparison of a 790 Bonnie in three states of tune:

  1. As it came out of the factory, less the AI system.
  2. With a TTP Breathe high flow airbox intake cover, DNA filter and with the airbox baffle in place (Stage 1).
  3. With a TTP Breathe high flow airbox intake cover, DNA filter and with the airbox baffle removed (Stage 1.5).

You can see the power and torque improvement by just removing the airbox baffle. The second dyno is a comparison of the same 790 Bonnie:

  1. With a Breathe high flow airbox intake cover, DNA filter and with the airbox baffle removed.
  2. With DNA pod filters fitted.

This dyno shows that by installing the TTP Breathe and DNA high performance filter, that the engine is very close to the power and torque figures achieved by fitting pod filters, you even gain a little torque and power up to 4,750rpm. (as with all dyno's, disregard the trace upto 2.5 - 3,000rpm as this is determined by how quickly the throttle was opened on that particular run and generally changes from graph to graph)

Back to the job in hand!

Removing the airbox baffle takes between 1 - 1.5 hours from start to finish. It is not a particularly hard job, but can be fiddly at times. The idea of this exercise is to remove the right hand side of the airbox so the baffle can slide out, and then put everything back together.

Please click on the picture to the right for a slide show of the process. (sorry for the dirty bike, but it was a hard working Scrambler)

List of tools required for the job:Rear mudguard electrical connector.

  1. 3, 4 & 5mm Allen key/socket.
  2. T30 TORX key/socket.
  3. Large flat head screwdriver.
  4. Large cross head screwdriver.
  5. 8 & 10mm socket/spanner.

Strip Down Steps

  1. To remove your seat, remove the two hex head bolts underneath the rear of the seat. 4mm or 5mm Allen key/socket required (model dependant).
  2. Remove rear mudguard and light, this is easier than it first looks. You will need to disconnect the electrical connector for the rear light and indicators and then remove 3 of the 4 x T30 TORX bolts holding the mudguard to the frame, then remove the 4th bolt while supporting the mudguard and then gently slide the mudguard from under the frame. T30 TORX key/socket required.
  3. Remove both side covers by removing the large head bolts and then gently lift them off. Large flat head screwdriver required.
  4. Remove the airbox air intake cover/snorkel by removing three 8mm bolts and then pull out the air filter. 8mm socket required.
  5. Remove battery rubber strap and then the battery by disconnecting the wires from each terminal. (ensure you make a note of which wires connect to which terminals) 10mm socket or cross head screwdriver required.
  6. Remove 4 x 8mm top of airbox bolts. 8mm socket or spanner required.
  7. (Bonneville & Thruxton) Remove fuse box and rear brake master cylinder and tie them out of the way. 5mm Allen key/socket.
  8. (Scrambler) Remove fuse box and side cover bracket and tie them out of the way. 5mm Allen key/socket required.
  9. EFI bikes, disconnect electrical ambient air sensor connector from sensor. Carb'd bikes, disconnect the ambient air sensor from the wiring loom, but DO NOT try and remove the sensor from the airbox side cover, the clip that holds it in place is very brittle and WILL break.
  10. Loosen clamp bolts on airbox to carb/throttle body rubbers. 3mm Allen key/socket required.
  11. Remove 12 x screws from airbox side cover. 10 of these screws are easily accessed but number 11 & 12 are high up and to the rear and will need the airbox moved about to access. Large cross head screwdriver required.
  12. Break the seal between the airbox and the right hand side of the airbox. This generally isn't a problem, the factory uses a sealant that seals well, but once there is a little pressure between the airbox and side cover, the seal breaks quite easily.
  13. Weedle the right hand side of the airbox out between the frame and airbox.
  14. Pull the airbox baffle out of the airbox.

Build Up Steps

  1. Put the tiniest bead of silicone sealant in the groove of right hand side of airbox.
  2. Weedle the side cover back in between the frame and airbox and then locate it in place.
  3. Insert and screw in the 12 x airbox side screws.
  4. Connect airbox rubbers to carbs/throttle bodies while manoeuvering the airbox, this can be quite fiddly, but very important that they are fitted evenly around the rear of the carbs/throttle bodies. Once the rubbers are in place then insert the four 8mm bolts in the battery compartment of the airbox and secure the airbox in place.
  5. Ensure the rubbers are still in place around the rear of the carbs/throttle bodies and then tighten the two clamps on the rubbers.
  6. Reconnect the electrical connector of the ambient air temperature sensor.
  7. (Bonneville & Thruxton) Replace fuse box and rear brake master cylinder.
  8. (Scrambler) Replace fusebox and side cover bracket.
  9. Install battery and rubber strap.
  10. Replace the air filter and air intake cover/snorkel with a DNA High Performance air filter and TTP "Breathe" air intake cover. :-)
  11. Replace both side covers.
  12. Replace rear mudguard and light.
  13. Replace your seat.
  14. Have a nice cold beer or whatever your poison, and relax. :-)
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