Air supply :: Tank spacers :: Other methods
 

The difference between using tank spacers on a correctly setup airfilter and jets is significant. I took my make shift ones out today and went from 130mph to 90mph! Mid-range is bad too. So if anyone thinks there is little difference, I beg to differ.

However I'm not decided on whether tank spacers are the way forward. They effect the petrol warning light (not that mines working at the moment) but more of a concern to me as a winter rider is how it exposes more of the mild-steel underneath the tank to the weather.

Now I've had one of my ideas (oh god!). What about feeding two largish rubber tubes from the bottom of the airbox to the top near filter intake? This would cut down the airbox volume and increase air supply to the top of the filter.

And if it messes up I patch it very easily. Who thinks it would work?

From what I understand you are saying- you would be making a cold air feed to the airbox. It wouldnt have the effect of ram-air as the airbox wouldnt be pressurised. However if you did make a ram-air box jetting would be a bugger to set up. With this cold air feed you have described, you would have the benefit of fresh clean air being supplied to the engine- which increases volumetric efficiency and hence gives you a bit of a boost in power and more importantly response.

There are negatives tho- in these cold winter months the colder supply of air may increase the likelyhood of carb icing- but if it does you could allways take the tubes off. They should work well in the summer tho.

Bottom line is- give it a go and see, just dont do anything too permanent, and have a go at different positions of the tubes.

After trying all of this over the years, its really not worth the effort. You end up making the bike run lean at the bottom end, and only really getting top end power. Fine if thats how you ride, but a lot of effort for nothing. How about putting spacers at the rear of the tank, that way the tank will be level.

If I understand, you're talking about putting the pipes right over the carb intakes?

Tank spacers do a totally different job to what you're describing of course, since all they do is reduce the restriction between the airbox top and the tank... Have you scraped out the foam on the bottom of the tank yet? It's right in the narrowest point of the intake and reduces clearance between the tank and airbox top filter to not very much at all.

I saw pics of an airbox someone had modified by reducing the height by about a cm, which would have the same effect without tilting the tank but would obviously cut the size of the airbox.

Have you actually tried spacers? They made a huge difference to me with the rene airkit, since they gave me just enough additional clearance for the filter to not foul the top of the tank. I couldn't say for a fact that they do help, never done a with/without dyno run or anything, but it's a very popular mod after all.

For the fuel pickup, wouldn't worry about it at all, it means I get the fuel lights about half a litre before but you get used to that after about 2 tanks. You could raise the seat end slightly to reduce that if you wanted, but I found that to be a hassle when doing maintenance and it mate the tank feel a little loose.

As for exposing the tank underside, even with big spacers like Chewy's I don't think it'll make any real difference...

Northy, with correctly set-up jets the difference is massive, like I said I've lost 40mph! This is with a BMC Race RS. K&N users won't see much difference because as people generally know the filters are more restrictive at top end. I've been improvising with some longer bolts and form to see what difference it makes.

I need to explain my idea better. This will be one or two tubes leading from the top of the airbox next to the filter top to the bottom of the airbox.

Currently the tank blocks air-flow to the filter top as Northy says. I shall be funnelling an extra supply of air to the filter head from the bottom/left-right of the airbox. When the filter can't get enough air from under the tank it'll feed from the extra funnels whatever 'top-up' air it needs.

Making the airbox have a different height is also an option, possibly by heating up the top and squashing it down a bit.

[quote="andrewcharnley"]Wrong Northy, with correctly set-up jets the difference is massive, like I said I've lost 40mph! [quote]

You've misunderstood me there, I said that with spacers it shouldn't make any difference to the exposure of the underside of the tank to the elements, which was one of your concerns about spacers. Like I said, I use spacers- Chewy's in fact- because I needed them to give the rene filter the clearance it needed. Whether or not they make any difference with any other setup, I couldn't say for sure, but personally I'd say it does, and also I'd say it gives me no noteworthy downside at all.

Of course having properly setup jets makes a massive difference, the difference between melting your cylinder bores or not if you get it really badly wrong... I ran the RS filter with my Rene kit jetting for one day and the bike ran so lean it was actually dangerous to ride... Terrible engine response, power losses at unexpected times. Teach me not to do a test ride after a modification.

Still not really clear where you're planning to run these pipes to and from, your description leaves a lot to the imagination :)

Had rectified my post but you were too quick. Tubes would run from the top of airbox to the bottom. Filter top would suck air through bottom tube, up to top of tank and into air filter. Hopes this makes sense!

Nah, I read your clarification, it just didn't clarify much ;) So are you talking about cutting through the bottom and top of the airbox and running a pipe right through it, from bottom to top?

Exactly, hurrah! :roll: :lol:

Guys. I have tried Ram air on an sv and made it run very lean, even with large jets and such like. For it to work properly, you will need to change the volume of the airbox itself. If you really want to know what has been done, and can be done, the go and have a look at SVrider. I believe that you can even get a ram air carbon airbox for the SV.

At the end of the day, youa re talking 2hp max anywhere in the range. If you want serious power gains, then you need to start looking at engine mods. At which point, id say, get a different bike.

Its all about having what you have got, set up right by people that know what they are doing. Tank spacers, in my trials, actually made the bike unstable, as the airflow got under the tank too much.

By all means experiment, but as the Mk1 SV has been around for sometime, i am sure that someone somewhere has, to coin a phrase, been there, done that.

Mike1234, will tell you, that there is only so much power you can extract from the std engine with any matter of carb/filter setups.

You have to look at the pound per BHP value 1st!