ESE's works engine tuner

[Flettner]

So the slower/later timing softened the " hit " making it easier to control tire spinup, and the shorter gearing made it accelerate faster due to the torque multiplication.
A better set of compromises, in that application.
Yes, MX is a special case with a special set of requirements to be fast, but you gotta realize the vast majority of members on here don't give a monkeys what happens well under the pipe.

I give a monkeys,

[jonny quest]

Wobbly, I know you know power off the pipe is always beneficial. Always.

The moral to my story (which was brought up because of Airstriker mention) mechanical gearing advantage in my case trumped all out power.

Bottom end power, strangely, is more beneficial the bigger an engine gets for faster lap times.

[F5 Dave]

I know I was dribbling on about Enduro bikes before which are largely used below peak, off pipe. Yesterday I was out on the Trials bike. Still good clean 2 stroke fun. . . but I don't think it has any on-pipe power

[Larry Wiechman]

Wobbly, I know you know power off the pipe is always beneficial. Always.

What if my monkeys think like kart racers and use a slipper clutch that gradually engages just before peak torque? On a small displacement motor (Freetech 50 or Bucket), that would help cover up gearbox ratio gaps and the power dip at 2/3 RPM.

[jonny quest]

What if my monkeys think like kart racers and use a slipper clutch that gradually engages just before peak torque? On a small displacement motor (Freetech 50 or Bucket), that would help cover up gearbox ratio gaps and the power dip at 2/3 RPM.

Every motorcycle with a gearbox and clutch has a slipper clutch. It's your left hand. Good offroad riders constantly slip clutch in corners.

[diesel pig]

KTM used Keihin carbs from MX Suzuki RM 250 for semi mass production Red Bull cup, when they was on the right way with 2T Al frame 125. Original PJ and TPS, but working must be different from MX.

Of couse. The Red Bull bikes were mean to be all the same ( I am sure some here would let us know if that was actually true or not) So they all should here been giving up the same amount of power with all them having the same bad carburation. So what Wobbley posted still holds water I think.

[ApolloMotoMoto]

Every motorcycle with a gearbox and clutch has a slipper clutch. It's your left hand. Good offroad riders constantly slip clutch in corners.

1000X this.

My Single-Speed Direct-Drive Kart track racing machines have a manually operated friction clutch. A carefully manuplated clutch hand converts this into a slipper clutch. All the fastest racer are apply controlled slip in certain areas around the course to maximize drive and generally keep the engine within its useful power-delivery band given my use has NO TRANSMISSION of any kind.

Yeah I care about "under the pipe" features, but only because our engines and vehicles are not yet really optimized for the use case.

We keep changing gearing to shift the RPM range relative to vehicle speed "UP" such that we can get the bike "above the torque hole" comming out of the slowest corners.

As it stands right now, we still have to use RPM's that are below 2/3rds of the torque peak, which means accelerating through the 2/3rds torque hole.

Everything that addresses while still requiring the vehicle to operate in this band is mostly a band-aid.

Really, gear ratio must be such that the vehicle never drops into that 2/3rds of peak torque "torque hole" band, with an effective power range wide enough for the application;

That means in my case, if I am going to make peak torque between 9-10k PRM in a ~90-100cc engine, I cant really be using RPM's below 7k RPM's, and with a required power range for single-speed direct-drive of 3.0+ (ideally more like 4.3-3.6...) that means this engine needs to have usable over-rev to 20k RPM's, or I am going to be forced to use the dreaded "torque hole" range.

As it stands right now, our setups are not optimized, over-rev to 15k is barely consistently achievable, engine RPM comming out of the slowest corners is 4-5k RPM's, and there is a LOT of 'manual slipper clutching".

Its mildly interesting how much of a race is decided on "cltuch games" VS. the other elements of the competition; clear evidence that the setups have quite a bit more optimization required.

It can be deceptive how much better a bigger rear sprocket can be. You think you are going to give up terminal velocity, be the way the engine is loaded will allow over-rev to extend further than intuitionally expected when you slap the bigger rear sprocket on the bike, and the torque multiplications wins everywhere else can produce an unexpected range of ideal gearing if these larger rear sprockets are never fully explored.


This is a persistent argument within my own race team and across the paddock, and everytime we put a new "biggest ever used" rear sprocket (or smaller front sprocket, or anything else that drives the ration in this direction) lap times come down, and we dont loose the terminal velocity we would expect to loose given the change.