The Taylor made exhaust is shit.
2x this - I bought the Taylormade, sold it damn near immediately. Looks good - and that is about the most (only) positive thing I can say about it.
Honestly it all depends on the type of riding/racing you're doing. On the track, the 4th gen can still hold it's own. If you're slow there, then in most cases, you need to look at setup, suspension and possibly what you may be doing that is holding the bike back. I can flog the hell out of my 4th gen just as well as my 5th gen.
But if you're simply doing highway pulls, sorry to be the bearer of bad news - the only way you're going to be able to keep pace with a 17 ZX10R and/or 17 S1000RR on a 4th gen is by opening the motor. They are just too strong of bikes. Maybe paired up with another 4th gen and/or 2010-2014 S1000RR you'd likely have better luck with. Even with the S1000RR it's going to be a rider's "race" or a question of who is the lighter rider and/or the better set up bike.
In any event, here is a list of things to look at... (not a fully conclusive list by any measure).
* I always say the full is worth it, having had multiple slip ons before going with the full system on my 4th gen (5th gen went right to the full). Depending on where you're starting your run from, you could be looking at a double digit difference in torque/horsepower.
* Head is terrible on the 4th gen, so that should be addressed. Once it is though, then the OEM header becomes a bottle neck. At which point you'll then want to switch out to a full system to get the max benefit of a better flowing head.
* Degree the cams (don't waste the money on the KRT ones)
* Knife edge the crank (APE does good work)
* Aluminium rear sprockets and lighter chain. I have even seen titanium front and rear sprockets (something I want to try this season). EK 3D 520GP (the 520GP, not just the 520, 520GP
) is the best chain out there in my opinion.
** Gearing will be key depending on what you're racing for; either all out acceleration or top speed
** Further reducing rotational mass one can look at a lightened rear rotor similar to MMR
* Lighter wheels
* Lose weight where you can on the bike - I have replaced nearly every bolt on my 4th gen with aluminium or titanium fasteners. Lightweight battery will help too.
* If the bike is ABS, remove the hardlines and run your own braided lines instead
* Change out the front rotors for fully floating rotors in an attempt to reduce parasitic drag
* Have the bike tuned, tuning/data logging at speed is key and correcting the fueling per gear will help too
* Quickshifter of course will help as well preventing the bike from slowing down on upshifts (our hands are not as fast or faster than electronics)
* Tune per cylinder (the first 11-15 ZX10R we did picked up nearly an extra 10HP)
* Better air filter, I recommend MWR WSBK filter but it requires extensive tuning (see above; at speed, per gear and per cylinder) to get the best out of it as it's not just a drop in instant power adder
* Higher quality fuel or even race fuel
* At higher speeds aero becomes extremely important - so if you have a shaved down windscreen or one that is hard to get behind, physics is working against you. Even your mirrors can hold you up.
At this point, it may behoove you to either swap in a 5th gen motor, ECU, harness/electronics and throttle bodies to get a little extra boost in power. Or possibly future proof yourself, at least for a little bit as nothing is future-proof in this industry, and look at a newer model with some upgraded tidbits. Personally, the Ducaca V4 S
eņor edition is calling my name this spring.