So, following on from the earlier post re’ de-catting my 2022 v85tt. Satisfied with the noticeable decrease in running temperature with the Chinese (AliExpress) Y pipe, we yesterday compared my de-catted v85 with Elaine’s 2021 model with cat still fitted. Both of us felt there was a definite increase in mid range power and the engine felt much more responsive throughout the rev range without the cat. Whilst the exhaust note (standard silencer) was deeper and more throaty, it wasn’t a whole lot louder. The AliExpress Y pipe was then put on Elaine’s bike and a Mistral version was put on mine. Given that the AliExpress version was £250 delivered as opposed to the nearly £700 for the Mistral, any difference in performance between the two is, quite frankly indistinguishable and I think it would require a dyno to tell the difference The quality of the Mistral setup however is quite frankly amazing, it’s a work of art, is it the £450 difference worth of amazing? Honestly, I think not. Today I fitted the Mistral v boost, literally a 10 minute job. It has definitely made a difference to the throttle response, it hasn’t got rid of the hiccup at low revs but it is much improved with the bike running smoothly down to 25mph in 5th gear. Mid range is a different story altogether. I would say it has transformed the midrange power delivery. It is smoother and makes overtaking effortless. On our test ride today we overtook slow moving vehicles heading up Garrowby Hill and hit 3 figures without effort. The exhaust note has also deepened a little with a nice growl under acceleration. Tomorrow Elaine and I will ride both our bike back to back and see if we both come to the same conclusion. If we do then Elaine’s bike will get the v boost as well.
Great testing, my wife and I also have v85’ s interested to see how this ends up
Thanks for posting this up. I am running a 23 plate bike with a Storm can fitted. I have a V boost ready to be fitted and have just ordered a decat pipe of ebay. I am still contemplating ordering the ali air box funnel. Looks like I’m going to busy over winter. Lol.
Does “decat” mean removal of the catalytic converter? If so, isn’t this illegal in the UK, and how will the bike pass its next MoT?
I have a 23 bike too, and im wondering if i can get the cat out of the downpipes without damage. Would save me a bit if money and hopefully get me nearer smooth running at low rpm 
According to google, it is not illegal to remove the cat’, it is a device designed to ensure the exhaust gas falls within certain boundaries. It is therefore possible but not guaranteed that the bike could fail an MOT on emissions. (My 1971 Land Rover has a 30 year old 200tdi engine fitted an yet passed the current emission tests even though it isn’t required to). As a matter of interest I will see if one of my local MOT testers will put our bikes on the emissions tester and see what the readings are with the cat’s removed and report back. As an aside, for me the benefits of a cooler running engine with a smoother power delivery more than makes up for the 25 minutes it takes to swap the system over once a year (and that’s only if it proves necessary). That is without mentioning the not inconsiderate increase in power which is not the primary reason for me trying the various mod’s.
My concern with doing this would be if the bike then fails its MOT on emissions, you could not then replace it for the test. Currently on both our bikes , every single mod’ is quickly and easily reversible.
MoT makes no specific mention of the cat. See MOT inspection manual: motorcycles - 6. Structure and attachments - Guidance - GOV.UK. I can’t see emissions on such a lean running engine being an MoT issue (Update: As others have said, emissions not tested as part of the MoT for ‘bikes)
I have recently decatted my E4 v85tt using a Y pipe from Muzzi Moto, which looks very much like a Chinese item (I couldn’t justify the cost of the Mistral version.) Fits fine, and quality looks ok, tho’ a rubber bush on the rear mount would have been nice. Done to address heat/pinking and it runs much better tho’ I still get the occasional pink when the engine gets very hot (stuck in urban traffic on a hot day - so it rarely happens…). K&N fitted at the same time. The exhaust note is barely any louder which is good, just a bit more of a Guzzi rumble (a Grumble??). Fuel consumption the same (65-70mpg) .
Max isn’t due MOT for quite a while, so im more than happy to swop it all back. But as stated im not sure on the legal requirements of the MOT and cats.
Hi. Temp5848, Since you asked about how a de-cat might effect a mot I did a bit of fishing. If you take your standard exhaust, cut out the existing cat and refit the exhaust, you are breaking the law. If however you buy a replacement exhaust that never had a cat built in and fit that in its place, you are perfectly legal as long as the exhaust bears the BSAU 193 stamp. Pretty much every aftermarket decat’ “Y” pipe that is advertised as road legal will bear that stamp. As for MOT compliance, unlike cars, the actual emissions from the exhaust are not tested. The exhaust must not have any holes or damage that would effect its use, it must be secured properly and not be loose. With regard to noise, it is down to the tester to decide if it is excessively loud. Most testers in my experience would put an advisory on the test certificate if he suspects it is too loud, this covers him if the ministry were to ever get involved. Obviously, a straight through pipe spitting flames and bursting eardrums is unlikely to pass! 
I hope that clarifies the situation.
i have put bikes with cat removed through mot, it’s fine
From the replies to my earlier question it just go to show the Law is an ass! We all (manufacturers and consumers) have to put up with ever more restrictive rules and regulations regarding noise and emissions. Then we, as motorcyclists can fit noisy exhausts and remove catalytic converters with no consequence. The World has gone mad!
Whilst I agree with you to a point, I prefer the present system to the more draconian alternative, imagine a situation where faceless ministers who have never even sat on a bike were to impose a set of rules based on whatever lobby group had paid the most in donations. Total type approval where you can’t even change a tyre because it wasn’t fitted originally. Vehicles not designed to run on the new e10 fuel to be scrapped, etc etc. the present system is flawed without a doubt but some of the alternatives are frankly terrifying mate.
I think Germany doesn’t allow any modifications whatsover after a certain date. that’s why any custom bikes over there use very old frames to build with. also why M sport and AMG make type approved ‘modified’ versions of bmw and Mercedes-Benz