Back in 1998 when I bought my first Fazer I was one of PDQs regular customers .Also at the time they were the main agents for Dynojet in this country and Larry ( the boss) asked if they could have my bike once it was run in to develop Dynojets kits for that model, in return anything they fitted I got to keep gratis. The general conclusion was while improvements were possible they werent massive without serious airbox/intake mods. Memory is a bit hazy but I think they ended up offering Stage 1 and Stage 3 kits , Stage 1 was just a K and N filter for use with standard pipe, Stage 3 was a filter and slightly different needles to clean up the power curve when using a more open pipe.
I still have the dyno graphs and they do show good improvements in the mid range ( not massive bhp increase but much smoother with less dips in the torque curves) and about 3bhp increase but right at the top end.The mid range improvements were very noticeable.My bike ended up with a K and N and a Remus can with no baffle
At the time Larry said it would be unlikely Dynojet would offer a Stage 7 ( full fat, needles, jets, filter ) kit as the other mods needed to make it work were un-reversible and could leave Dynojet open to litigation for blown motors .If they do offer that now maybe more research has been done so it could be worth doing. At the time the conclusion was Yamaha had done a good job and aftermarket firms could do little but make small gains to clean things up a little
As an example of some one not doing such a good job,PDQ also used my new 1991 750 Zephyr as the development bike for Dynojets kits and sfter initial runs gains could be made.It ended up with a Kerker pipe, full re-jet and serious but reversible mods to airbox that gave 15bhp increase throughout the rev range.I still drool over those graphs and have very fond memories of that bike howling as it came on pipe coming out of Alpine hairpins and yes I still own the bike ( currently undergoing full restoration)
So if youre looking at Rejetting talk to PDQ , theyve been doing it for years and know their stuff.I really should get back down from the frozen north one day and pay a visit to Taplow and chat to the guys ( used to live in Slough and spent many hours at the workshop shooting the shit )