ESE's works engine tuner

[bjorn.clauw.1]

I would like to believe that moving the rear Aprlia studs and then pulling back the rear wall would have a positive effect if that
operation reduced the backward lean of the B duct ie getting rid of the two dimensional bending of the flow around the corner into the port..
But as you say Frits this would upset the scavenging pattern by increasing the B port flow regime, but if the extra space gained was used then to increase the A port
flow area, this may then restore the balance - and gain an overall increase in transfer Cd.
That would then maybe allow slightly lower timings, to increase the all important ( and ultimately power limiting ) blowdown STA.
We started this discussion when it was suggested we look at ways of "improving " what Jan had achieved, but unless the same effort was put into restoring the leaning tower
geometry, then failure would be more than likely.
As we know well, several geniuses in R&D had a go at improving what Jan had done,as of course its obvious the crank needed cheek plates to reduce the case volume - only
to find the bikes thus delivered to the teams were somehow slower.
As it stands the only really optimistic direction of improvement would be to try my Ex duct length/area recommendations that work so well in the sim, and
maybe to improve the Ex duct cooling by having water all the way up to,and around the back of the spigot that I know works well in KZ2 engines.

Hi Wobbly, by cooling the spigot in kz2's, does it help by cooling (/not heating as much) the fresh mixture that's in the spigot before it gets pushed back by the pipe?
About port geometry, I have been looking for an answer about 100cc kart engine port layout to no avail.
Namely what gives these engines their long powerband (and what has to be compromised to do so) and why most have only 3 transfer ports.

[TZ350]

First time on the roller for my spx/m50 creation. It's fierce on the pipe, and dead below it. I'm excited!

I love it, please keep us posted as your project progresses.

[wobbly]

Re cooling the spigot in KZ2 engines - yes, this idea if done by milling slots thru the flange face on the cylinder allows water
to cool right around the duct to the face, then also the steel spigot face is cooler as well if you cut the slots thru the gasket material.
I can touch the tapered spigot on the engine after a hard dyno pull without being burnt.
As you say this keeps the trapped mixture in the cylinder duct much cooler,and the egt further out in the header dropped as well.
I can run at least 2 jets leaner to get the egt back , without getting into deto using that system.
The pic is an early testing one, now the slots go right thru to water,top and bottom.

The 100cc engines really wide power band is down to the pipe design, with its series of bleed holes in the rear cone.
This pulls down the peak power and adds plenty at the bottom, and in the overev area.
Take that pipe and remove the rear cone holes,and it becomes all but impossible to tune the pumper carb properly,and the power band is basically 1/2 as wide.
OK for a slipper clutch setup on direct drive, no good at all without the clutch set to peak torque rpm.
The 3 port system has plenty of STA for the power produced, and the scavenging regime has been slowly developed over time to enhance the band width as well.

[marsheng]

Bet he's using the avgas available at Ruapuna....

I'm not sure if this could be the reason but, when on the dyno after a fresh rebuild, it wouldn't run without the choke. On stripping the carb the ElF HTX 909 had turned to gum. We washed it out, drained the tank and used fresh 100+ octane from the Challenge station. Probably only ran for 10-15 seconds on the old stuff.

[marsheng]

I'm stumped again on this one. As you may be aware I have had a few issues with KR150 cold seizing.

My guidelines are Top End Rebuild by Gordon Jennings.

66x64 mm 2 stroke engines made 33 bhp with pistons with .002- inch piston/bore clearance. The same engine made 30 with .004 and 27 with .006 and then seized,.

So in doing rebores, I have tried to stick to the minimum recommended clearance.

On the Macio (67mm bore) the recommended clearance is 0.07 mm (.0027mm) for my first build I used this clearance. After 20 min of running, the barrel flange broke. On measuring the piston, it was now 0.06 mm smaller than original but still had the teflon coating and the bore was good.

On the second rebuild, I used a new piston and same clearance and raced it for almost a year. This piston also "shrunk" by 0.06 mm but looked perfect did so did the bore. So this running piston/bore clearance was 0.12 mm or .0047.

This last rebuild I decided to use the original piston of 20 minutes and bore to its new size plus clearance. I bored to + 0.08 mm. I did a few good heat cycles and took it very gently on the track for 2 x 5 laps.

Still being gentle but with a bit more power, I felt it start to slow down on the main straight and then 2 corners later it nipped up. On cooling it freed up.

So the question is, was Gordon using a cast piston ?

On the track, should forged pistons be given bigger clearance. ?

Or do I have something else wrong ??


Thanks Wallace

[wobbly]

Yes, 909 will settle out in AvGas after only a few minutes of mixing it up - did exactly that to me on the dyno.
We tested for probably 20mins,stopped for a cup of tea,and it would not restart,I could see straight oil in the bowls of the Lectrons.
But add a cup of acetone in 5L and no issues after that.
Motul Kart GP does not do this in Avgas, I have had some mixed , sitting in the kart dyno plastic tank for weeks to test this.

Modern forged pistons made by Wossner run the same sort of initial clearances as cast ones.
In my TZ400 the 66mm Wossners run at 0.06mm,they get 2 - 5min heat cycles then thrashed.
After 1 race meeting they had shrunk by 0.02, and at 580Km I replaced them as they were now with 0.04 extra ie they were at 0.1mm in the bore.
This is with a 58 stroke spinning to 11200 in every gear, and topping out at 11800 in 6th.
They looked like brand new on the skirts, but I thought why take a chance.
As it stands I wouldnt use a Wiseco if they gave them away.

[chrisc]

Bet he's using the avgas available at Ruapuna....

I thought the avgas at Ruapuna was decent? I'm assuming you'll tell me it's just old stuff from the airport?

[wobbly]

There is no such thing as "good" Avgas at any place but an airport tank.
In those tanks it has to be checked constantly for volatility and water content.
At Ruapuna - Philip Island is even worse, the tanked fuel is absolute rubbish as it sits forever,flashing off all the good front ends in no time at all.
A small aircraft crashing due to fuel related engine failure simply isnt allowed,full stop.

[peewee]

Just stripped my Macio after a day's of testing and I have this strange carbon build up on the piston. It has had around 30 min running time.

It looks like the frying pan after cooking honey bacon. (Now I feel hungry)

It has these miniature hills and valleys. Any suggestions ?

Thanks Wallace.

not sure if I have the photo anymore but I had a piston with weird stuff like that on the top. was heavy black gum or carbon with divets like golf ball. castor at 6% with Sunoco is what I was using. my thought was it must of been partially separated in the tank and continued through the engine that way

[Grumph]

There is no such thing as "good" Avgas at any place but an airport tank.
In those tanks it has to be checked constantly for volatility and water content.
At Ruapuna - Philip Island is even worse, the tanked fuel is absolute rubbish as it sits forever,flashing off all the good front ends in no time at all.
A small aircraft crashing due to fuel related engine failure simply isnt allowed,full stop.

Agree 100%. particularly given we've had 30 plus degree days for what seems like weeks now. I'd be surprised if there were any good front ends left at all by now. Your avgas ex challenge, Wallace, is probably just as bad.
I've been using the BP 98 pump gas - bought from a station with a high turnover. It isn't avgas but likes a lot of advance - and it's consistent.

[Grumph]

I thought the avgas at Ruapuna was decent? I'm assuming you'll tell me it's just old stuff from the airport?

When they put the tank in, they swore, up, down and sideways that it was going to be topped up every time the tanker went to the airport. On the way to the airport they said - so fresh...
BUT as it turns out, the fresh stuff costs more - so it's back to overage delivered on the way back FROM the airport....

What pees me off is that they were going to carry E85....but don't.

[JustHarry]

I've been using the BP 98 pump gas - bought from a station with a high turnover. It isn't avgas but likes a lot of advance - and it's consistent.

what about putting an octane booster into the 98 to bring it up to more av gas levels. so a consistent fuel with a high octane.
the kr150 got a bit noisy on 98. av gas seemed to fix it

[marsheng]

Modern forged pistons made by Wossner run the same sort of initial clearances as cast ones. In my TZ400 the 66mm Wossners run at 0.06mm,they get 2 - 5min heat cycles then thrashed..

Does it make a difference being a water compared to air cooled with piston/cylinder clearance ?

Could the cold seizing be not enough retard at the higher RPMs? Ie more heat in the combustion chamber heats the piston very quickly and it expands too fast for the liner ?
My thoughts are, more heat in the combustion chamber could heat the piston by XX degrees or so over its working temperature etc but the plug and carbon temperature may still be at a low enough to not show any signs of overheating.

Thanks Wallace.

[TZ350]

Bacon. It is a superfood don't you know?

Hey 10 more posts and we'll be at #22222.

Looks like CrispyBacon took line honours for post 22222

[MotleyCrue]

As it stands I wouldnt use a Wiseco if they gave them away.

I've heard this a million times from different sources but I haven't heard a good explanation. What is the reason they suck ? They have been in business a long time and still sell lots of pistons, is it just certain applications they aren't good for ?