To crossover or not?

I’m getting some new silencers for my loop. My V7 Special has got very loud Norton type pea shooters on at the moment without a crossover and I’m fed up with the noise and that’s with good ear plugs! Â Armours give me the choice of with or without crossover. Â Now it’s going to be easy to just change over silencers without crossover. Â To add the crossover will mean I’ll have to disturb header pipes! Â So I would like to know the actual benefits of a crossover? Â Your thoughts would be appreciated.
Thanks Ian.Â

I think the crossover is to aid tickover and low speed stuff.
If you don’t need one why bother?

Well this is my thinking its just that I don’t know what i don’t know! I’m definately edging towards no crossover because I haven’t got the tool for the header pipes. Cheers IanÂ

Why would you need to disturb the header pipes? On my 850GT (with original silencers) the crossover is fitted to a stub on the silencer not on the downpipe.

I also think the crossover helps with balance and is good for smoothness at low revs - surely the best thing about a loop. I know when mine is all freshly set up, carbs balanced etc it will pull virtually from idle.

Regarding disturbing the header pipes, as I’ve never taken the exhaust off I just presumed I’d have to loosen the header pipes to wiggle the crossover and silencers on.  From past experience I’m always nervous of fine alloy threads and steel nuts! If their is an advantage to the crossover I will definately put it in, it’s only a £20.00 difference so if it’s going give me smoother low down running that’s a big plus. Â
Thanks for your advice.

And going for the cross over just increases the chances of Armours providing stuff that don’t fit.

Well now this hadn’t croseed my mind, might make fiddling with header pipes a necessity. I thought this would be easy apart from parting with the money!

I have Armour’s pipes on my Eldorado (a full set) with cross over pipe. There is a slight interference with the cross over and centre stand, but only a smidge and not enough to worry me - but it’s there never-the-less

The original crossover has 2 dents in it to clear the stand. Do a trial fit and mark it up and give it a squeeze in the vice or similar. Should be able to sub-assemble the silencers and crossover loosely and offer the whole lot up to the bike, if you’re far enough off the floor with the back wheel.

Have run mine without crossover for 7 years or so: ever since I fitted the MAC pipes from “Yooessay”. What with fuggin’ great flywheel, not sure if much difference. Very easy to tune each carb to it’s own exhaust too!

According to a tuning book I’ve got at home, a crossover pipe actually causes a break in the continuous diameter of the exhaust downpipe, which in turn causes a negative pressure wave to be reflected back to the exhaust port. This is because the pipe has a resonant frequency, like an organ pipe, and the resonant frequency is determined by its length. At a certain r.p.m., the moment when this negative pulse arrives at the exhaust port coincides with the next opening of the exhaust valve, in other words it helps scavenge a bit more exhaust gas out of the combustion chamber by literally sucking it out, than would normally be expelled by the piston alone. More exhaust gas out means more fuel and air can go in, in other words, it boosts top-end b.h.p.

Double crossover pipes like e.g. Le Mans’ have got make for two r.p.m. points where this occurs. Interestingly my R80 also has two crossovers!

Well thanks all for your input, on reflection I’ve decided to order the crossover version from Armours, I’ll post when fitted and road tested. Cheers Ian.

Miko…you is just too bloody clever…x

I can add to this discussion from experience (& graphs if required) a cross over will aid for a flatter torque curve. I have had my Le Mans dyno’d with two different sets of pipes. A set of Lafraconis with a balance at the headers & before the silencers & the custom set that I have now.Â

+1 on the torque (curve) principal.
Interesting to see the positive effect on EVs of fitting a Tonti balance pipe instead of the OE box.
Just a thought…If balance pipes were unnecessary why would manufacturers like Guzzi go to the expense of fitting them?
All the best

Eau contraire, the book sez … I merely regurgitate …