#6

[speedpro]

Weight comparison of old and new. A nice reduction in weight plus a shot of the finished setup on the bike. Still need to make a new stay arm.

[speedpro]

I machined up a couple of fancy end pieces, welded them to a bit of tube, and fitted it to the bike. After having a look at it I've decided that the arm is about 50mm too short which is a bit annoying. Fixing it isn't too hard. I'll machine down where the ends and tube are welded together and fit a longer bit of tube to the ends. I just want to get the geometry between the axle, arm, and swingarm mount correct. At the moment with the axle well forward in the swingarm it isn't too bad but if I move the axle back due to fitting different sprockets the geometry will be bad.

[speedpro]

The brakes as far as I'm concerned are finished. As expected it was simple to turn down the weld and the piece of pipe that fits over the endpiece extension. The welding, although still not flash, was markedly better than the first attempt. The geometry is way better and the axle can be moved back and it'll still be OK.

Also looks like a new rear tyre may be turning up. The one on the bike at the moment is of unknown age but it's only got two good features - it's round and it's black.

I have other gearing I want to try at Tokoroa so will be fitting those sprockets. Pretty sure I'll need another new chain but I can get DID chain at Westgate so not a problem.

[F5 Dave]

Always good to get brakes sorted and ideally easy wheel changes with captive spacers like RS have. Spent way too much frantic pit time juggling spacers and discs that needed swapping out to make a change to Wets work.

[Grumph]

These days, if a change to wets is needed, it's beer o'clock.

Can recommend the relaxed approach.

[F5 Dave]

To be fair I was at that stage. Younger me was all keen.

[speedpro]

Ready to go I reckon.

[speedpro]

Got the new Turbosmart fuel pressure regulator today at about 10:00. I ordered it at about midday yesterday so quite impressed. Tried it out and found that in comparison to the other cheapy one, that this one is very smooth to adjust. I also fed 1BAR of compressed air to it and the fuel pressure increased 1BAR. This is exactly what should happen and will allow the 4d fuel trim table to be deleted probably. It might even be time to up the boost. I'm kidding, it's always time to up the boost.

[speedpro]

Off topic, just trying to get an idea.

Just wondering if there is anyone interested in an old RS125 chassis and fairing. I had plans but you know how it goes. I think it's a '93. The suspension will need to be "tuned" and I have modified the front engine mount for the MB100 I planned to fit. No front caliper or master cylinder.

[speedpro]

Monday dyno session to dial in the fuel has been postponed. Hopefully it can be fitted in some time soon.

[F5 Dave]

Bet the plans didn't involve you trying to shoehorn yourself onto it!

Sigh. Great starting point.

[speedpro]

There was a lot more interest than I expected. Good news is that the RS125 has a new home.

[speedpro]

Dyno session is planned for Friday. All that should be needed is a reduction, or elimination, of the compensation for the old fuel regulator which did not increase fuel pressure at the same rate that manifold pressure increased. The ECU expects the fuel pressure to increase on a 1:1 ratio and calculates boosted fuel quantity based on it happening. We'll get a reliable horsepower reading as well.

There is no real plan to bump the boost up. The plan is to stick with what the current target, which from memory was 180kPa(absolute) or 11.6psi of boost. On the dyno doing short runs will yield a better result than on the track. At HD the intake air was hitting 100°C and the ECU backed timing off for safety. Intake air temp should be a lot less of a problem on the dyno. The temptation will be if we get ?8.9hp in which case a small tweak might happen.

Watch this space for the number

[speedpro]

I'm calling it 30hp which is a bit disappointing. There was a few things going on which don't show in the dyno graph with the AFR jumping up & down but not all the time. It looked like a bad wire but could also have been bubbles getting in the fuel to the injectors. Despite having a good fuel pressure regulator which increased the fuel pressure properly it wasn't looking a lot richer like I expected. The injector duty cycle was going over 92% if it pulled decent boost at high revs so, as setup, there isn't much left in the fuel system.
Through the gears if I didn't tap the rev limit it seemed really nice. I need to investigate getting boost sooner. I made adjustments to the boost control table but I think I will set it so the wastegate is never opened and see what happens. If there is no difference then it's a limitation of the little engine and this turbo.

It's strange but this engine does not sound like it's revving as hard as it is. It is only going to 17,000rpm where I really want 18,000rpm but it doesn't sound like it. something else to figure out.

Graphs are:
blue - from 4 years ago just before the previous engine stopped
green - through the gears today
red - 6th gear only

[speedpro]

I've had exhaust wrap for ages, maybe 20 years, just sitting in a bin of "stuff". I have always thought that the exhaust with the plenum chamber was not as efficient as it should be as it would lose a lot of heat from the gas before it got to the turbo. The reduction in gas temperature would reduce the gas volume and therefore the gas velocity through the turbine. It could very easily be contributing to the lazy way it comes on boost. I dragged it out and wrapped the exhaust as good as I could be bothered. The headers were wrapped as one. It's probably not the absolute best but it'll be better than before. Due to the odd angle the pipes enter the plenum and the tapered and turned plenum outlet, the wrapping is more a case of doing it in a way that shouldn't simply come loose. The end result is that most areas have at least 2 layers and there are more layers in a few places. Each end was left mostly uncovered simply due to the difficulty of wrapping it effectively and having it stay in place. Not shown in the photo is a shield that goes over the wrap on the plenum, which is held in place with a couple of hoseclips.

If you think this might be a waste of time, a simple experiment will illustrate the difference in gas volume with barely a 100°C change in temp. Get a 2L plastic milk bottle. Pour in a cup of boiling water and slosh it around to heat the air in the bottle. Quickly tip the water out and put the top on. Cool the bottle under the cold tap. The bottle doesn't just crinkle up a bit but completely collapses.