| northwind |
30-08-05 06:54 PM |
The rule of thumb for SVs is, more or less, 85bhp at the rear wheel before you end up significantly increasing the risk of a bottom end failure in the short term. Pretty much any power boost you do will reduce the lifespan of the engine in some way, but it's at that point the crank and rods are said to be no longer able to deal with it in the short-medium term and failure is considered to become when, not if. So the question is, what are you going to do with it? And what cost in reliability and price are you willing to pay?
IMO with this drawback in mind, serious extra power is just not reasonably achievable without spending a ridiculous sum of money. But you can still do a lot… Cams, breathing, maybe a little headwork can get you within spitting distance of that 85bhp. Mine I think will be bubbling just under the 80 mark with around £500 spent on power mods, with nothing too clever going on.
IMO, going further into the engine for a street SV isn’t too clever. I think I’m going to fit hayabusa pistons (lighter, not much more power) and deck the heads for higher compression but that’s taking it beyond the point where it really makes much sense. I just like mucking about with bikes.
An SV can be taken so much further than anything JHS have on their website, by the way... Some of the US bikes are kicking out ridiculous power figures. But that's a total engine rebuild, new crank and rods, bigbore, cams, FCR carbs... Total loss charging too generally, and race fuel. Combined with serious weight reduction, and you have a ridiculous machine…
JHS have a lot of good options, but IMO most of the more dramatic gains are pretty impractical. Big bore or the high comp pistons have a lot of potential for problems in "later life"- they're both much heavier pistons in the first place and so stress the rods and crank beyond that which you’d expect from the power gain. Likewise, flatside carbs and pod filters would give you a big boost in response and power- but they're pretty much impractical for a daily runner- no choke!
There's a bit of disagreement on how great these risks are- James Holland claimed to me that there were absolutely no servicing or lifespan (or even warranty!) issues with the 700cc pistons, which was the point at which I simply stopped trusting his advice. (I still have this email if anyone doubts me.) On the other hand, some people maintain it's sudden death for the engine, which likewise is unreasonable. The trust lies somewhere between I think.
Likewise the Stage 2 cams- they're very effective, but you're paying a heck of a lot for it. You can get probably 9/10 of the benefit with the K3 intake cam/carbed intake/exhaust cam swap for £130, since a home tuner's not likely to be able to make effective use of the adjustable cam sprockets. I
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