Hitchcocks Forum

Hi all

I got a 5 month old EFI B5 Bullet and changed the rear silencer to this one off ebay

http://m.ebay.co.uk/itm/391225727781

Anyway I did it for mainly looks and sound, but then the bike would only get to about 72mph, my mate suggested changing the front pipe also, which I did last night with no difference. Will getting it remapped bring the performance back or do I need to ditch the rear silencer??

"Getting it remapped" would mean the Dynojet Power Commander V (PCV), mapped for "free-flow exhaust and K&N air filter", from Hitchcocks, because other vendors do not provide this mapping.



The stock ECU is capable of running a more open silencer without the PCV but not all silencers are suitable. The EFI does need some back pressure or it will seriously lack mid-range power. Most of this engine's performance is from its torque which is in the mid-range. There are replacement ECUs in India but I wouldn't advise touching one with a long stick.



Top speed of these bikes is realistically only about 80mph and that probably drafting traffic on a motorway; this is mostly down to the gearing, it hits max power/revs around 83mph. The sit up and beg riding position doesn't help but I can and have cruised at 70-75 sitting bolt upright. I have fitted the 50s free-flow system 91130 and K&N and PCV to my C5, and have fitted the Dynojet AT-200 wide-band O2 sensor system on top of that. The latter component is not commonly added and is a work in progress but the torque increase is astonishing.



A wide-open pipe is for racing where the motor is running at max revs most of the time, it produces maximum power at high revs. On the road this is pretty useless because without back pressure we do not get mid-range power for acceleration and drivability, especially this engine which is a slow revving slogger - it need back pressure from baffles and such.

Some megaphone silencers do work on the EFI but it may very well be that the type you have bought is the 'wrong thing' for the job.



Two options: go the whole hog and tune the bike up like wot I done, not cheap, or fit a more sympathetic silencer like p/n 91080. Phone Hitchcocks for other options and advice.

Looks fairly restrictive in the sound deadening department, have you removed the baffle (or just the wadding) to see if that makes any difference.

Something else I have found that may limit top speed is the spark plug gap. If the gap has increased much beyond 0.7mm then there is a tendency to miss at high revs.



The stock two-electrode WR7DDC4 is nigh impossible to clean and adjust. Consensus seems to be NGK BP6ES/BPR6ES. Personally I found the stock HT cap to be rubbish, it was not properly connected to the HT lead which created missing, and then it fell apart. I switched to the rubber non-suppressor Champion HT cap and a NGK BPR resistive plug.



Swapping the silencer may alter the air-fuel mix which can soot the plug up. Missing will produce unbrunt fuel which can soot the plug up.



It is worth checking the plug to see if anything is amiss there.

Fit 91080 from our hosts - I know it works (without remapping), I fitted one to my 2016 B5. Highly recommended.

What do you think to the noise level, nigelphoto? And did you notice any difference in performance?

91080, the 50's silencer, is quite noisy but the neighbours say it sounds good. It sounds very proper but it is not quiet, an understatement, it barks opened up; it sounds like a big single should. Short adjustable baffles, which do not do much to reduce decibels. I can't speak for its performance on its own since I have the complete system and other goodies thrown on top.



This is a video with that silencer but the sound is from an Olympus PCM recorder slung in the pannier right above the silencer. Apart from being in a leather pannier, the microphones are also in a soft bag, so it sounds like it was recorded from inside the sock drawer, but you'll get the idea. I can never remember how to post videos, you may have to follow the link.

https://www.youtube.com/watch?v=Ti2_n5p ... UNL37OSD5G

Thack, its not noisy just a little louder than the mouse phart sounds emitted by the standard silencer. In terms of performance I'd say the engine revs a bit freer and its a little easier to get a slower and smoother tick over. Whats also helped my B5 a great deal is that I torqued all the engine mounts properly which the dealer forgot to do at PDI . . . actually he didn't PDI it all, but that a another story for later on! Its now done 1100 miles and its very smooth with clear mirrors all the way up the rev range. Here's a link to a snap of the 91080 on the bike for you (sorry, I'm too stooped to be able to put snaps on here!) https://www.flickr.com/photos/nigelphot ... 541953073/

@jefrs

Many thanks for you well explained reply. Today I have put on the 91080 tailpipe and there is absolutely no difference to the top end speed of 70mph, but the mid range is far better runs far smoother. Just could do with that extra 5mph!

Thanks

Harty, I assume the bike is run in Do check the spark plug, HT cap and HT lead. I suggest gapping a BPR6ES to 0.7mm (28-thou) because I have have found if it is too wide (0.9 to 1.0mm) it will start missing at high revs, and if it is less than 25-thou it won't run nicely at low revs (I had a session experimenting with plugs). One other cause of missing is plug not actually connected to the HT, so do check the HT lead is properly connected to the HT cap (mine was not).



I probably have a few extra horses from the Power Commander but the top speed is not increased, that is down to the gearing. The extra ponies probably get it there quicker but don't make it go any faster. Realistically top speed is about 80mph, maybe 85mph on a motorway flat out and drafting. I can and do cruise at 70mph sitting bolt upright; bullets can normally cruise at 65mph.



What mileage have you done? It is possible that at 5 months it is not fully run in yet, some seem to take 1200 miles to loosen up and yes, they do get quicker.



There is a rubber flappy thing over the intake to the air filter. Check it is not closing the inlet at high suck. It shouldn't do so but things are squeezed in around the back of the box.



Sooty plug? These bikes can go through a spate of sooting the plug up. Mine did (hence plug experiment), I got rid of the soft soot by running double the prescribed dose of RedEx through two tankfuls of petrol, a cure not for regular use.