Is there any way of revving higher ?

[boo86]

Hi guys, what i mean is, is there any way of adjusting the rev limiter so it cuts in later. Maybe 500-1000 rpm later ? I know it'll probably be a black box swop but i can't find anything on tinternet. It's coming up to race/track day season and I've started tinkering.

Cheers,

[Sid Squid]

If you've got a Curvy 650 then the ECU from a 400 will fit and allows higher revs, can't remember how much though.

[ThEGr33k]

I cant say how unless you can re write the ECU (Can you easily?) but is it a good idea? :confused:

[jambo]

Fuel Injection and ECU's, Pah!

Sid Squid's quite right, the SV400 ignition control unit for the curvies (98-02) is a straight swap I believe, and will raise the rpm limit at which the unit cuts the spark to stop the engine revving higher. For a pointy 03+ bike you'd probably need a custom ECU to do the same thing.

Minor caveat on this: The rev limit's there for a good reason to limit the stress put on the engine, and the SV's engine probably isn't putting out much more power revving out higher unless you change the cams, exhaust etc.

Jambo

[rowdy]

As has been said there's not a great deal of point as the engine is more torque than power. As has also been said it will stress the engine more than desired.
Case in point, apparently there were a few k3's that slipped through the net with the rev limit set 1000rpm higher than should be (according to co founder of dynapro who dyno tested race bikes for the minitwin series) mine being one of these bikes (tested on dyno by said dynapro co founder) and after 5 years with the last few months of those seeing the bike reving towards 11500rpm more frequently than it should have to be honest, resulted in one snapped crankshaft. On the upside though the bike was capable of a speedo indicated 10mph more in top gear than before the race exhaust system was fitted, which allowed it to rev that extra 1000rpm in top gear. That said I don't think it is that great a benefit with regards to acceleration.

[Monkey_SDMF]

What's your end game here Boo? Are you trying to increase acceleration, or top speed, or just have the ability to hang on to a ear a bit longer before changing up?

For acceleration I would be inclined to drop a tooth on the front sprocket, and add a tooth on the rear sprocket (which means you don't have to faff about with the length of the chain). Although this will drop the top speed by about 10 mph. Depends where you are racing/trackdaying I suppose.

[Dappa D]

long time no spk boo, good luck for the season ahead! post some action pics if you get a chance mate

[boo86]

What's your end game here Boo? Are you trying to increase acceleration, or top speed, or just have the ability to hang on to a ear a bit longer before changing up?

For acceleration I would be inclined to drop a tooth on the front sprocket, and add a tooth on the rear sprocket (which means you don't have to faff about with the length of the chain). Although this will drop the top speed by about 10 mph. Depends where you are racing/trackdaying I suppose.

Race / track day bike, (race bike when finances are good), I'm thinking under minitwinrules a swop of a 400 box would be legal. It being from the same model allthough not the same deplacment. I just want to be able to hang onto any gear for slightlylonger. I think as my road bike is a zx9r it takes along time to get my brain back into twin mode for racing.

[boo86]

long time no spk boo, good luck for the season ahead! post some action pics if you get a chance mate


Woo @ work on saturdays !! Pics as requested. This years paint sceme is white. Pics asap. Hopefully I'll be able to pick up some sponsers.

[boo86]

Woo @ work on saturdays !! Pics as requested. This years paint sceme is white. Pics asap. Hopefully I'll be able to pick up some sponsers.

see pic, this damn R1 was in my way all day !!

[embee]

I have no idea what the relevant rpm cuts are at, but you obviously have to consider why the rev limit was set at the original value in the first place.

The main considerations are valve train and rods/crank. Valves will start to float (lose contact at peak lift) and then you start to get impacts which can break things.

The other, possibly more dramatic implication, is con-rod stresses.

Remember that inertia forces increase with the square of rpm, so going from 10k to 12k rpm increases the inertia forces by 44%, not inconsiderable and generally speaking probably more than the typical safety factor margin of the design. Con-rod bolts and the big-end eye will be the weak links.

The last major engine project I worked on included increasing the max rpm of a 4.7L V8 from 7k to 7.3k (about 10% inertia force increase), and the rods were breaking regularly at about 100hrs. The calcs said it was marginal but OK, real life and non-ideal material/machining etc said no. The big end eyes had to be redesigned.

[Spikenipple]

I have a feeling you're not allowed to change pistons under Minitwins regulations, but if you are you could get some lightened pistons to decrease the inertia?

[dual-power sv]

well ino on a tl you can put a rev limiter on that limits the revs to 5000rpm, not sure if you could use a similar principle to make it rev higher

[Alpinestarhero]

Is ther much point? IIRC, max power is before 10,000 rpm and the rev limiter cuts in at 10,500 (not that I have the guts to visit said limiter)