Cycle World Two Stroke article

[Uniflow]

Nice bike, very clean and tidy, seems a pity to race as it's only down hill from there. This years Kiwi VMX should be a good one. Apparently entries are up on last year.

[SachsGS]

Hey Uniflow, why did you make the intake port timing variable as opposed to the exhaust port timing?

[lauterbacher]

Uniflow did you put the hole in the upper rod end of the crank? If so was it hardened and what did you use to do it. Thanks

[Uniflow]

The rod is a Hot Rod, to suit a Polarus trail boss. Five mm longer and I had to bore the crank flywheels out one mm. I offset the holes half a mm to get an extra one mm stroke. It is a much better rod than original. Piston is also Wiseco trail boss.
An exhaust power valve would be next on the development list.
I think this engine is as far as I want to go with development, I only did it to see if it could be done, EFI that is. I bought a YZF 250 to start the next development, throw the engine out and fit a 350 twostroke with EFI. This new water cooled engine will have a powervalve and I would like to use the vairable rotary valve again as it shows good results. Probably will run it on ethanol again as well. Trouble is, Meagan my daughter thinks the YZF is her's now and is using for trail riding. The new engine will probably take a little time to build up anyway.

[2T Institute]

Do you know Bill Doe the Taupo Tow truck king? Geez surely Wobbly would have knocked a pipe up for you? Nice to see Kiwi ingenuity is alive and well

[Uniflow]

2T Institute, you probably already know all about twostroke EFI, I'm teaching Wobbly, as if! I suppose what I'm trying to say here in general is, don't just sit there and wish for EFI, It''s a workable solution now. It works and works well.
Yes I know Bill, race with him. Lucky I'm not in his class though, because I'm not in his class. He is faster than me. So comes the relentless quest for MORE POWER!
Wobbly is involved with the new engine design, he is simulating the ports, exhaust and rotary valving at the moment. I have an onther set of YZF cases that I've clocked up in the mill. Usually we cut a pattern and cast cases but this time I might just cut from solid alloy, depends on cost. This way I can manipulate the new engine to fit the original frame mounts and not cut. I don't think people realise the damage you do to modern alloy frames by welding them. Frame goes soft and will crack! These frames are heat treated to probably T6 in the factory and can not welded without re heat treating afterwards. I'm even considering designing in a balance shaft to make it less stress on the alloy frame. Maybe?

[lauterbacher]

Well I'm trying to wrap my head around this and understand how it works, If the fuel is being placed in the injectors and not the rotary valve via a carburator.How does the rotary valve work in this application? Thanks

[SachsGS]

Some AL frames are 7000 series which is self hardening. You are right about the 6000 stuff, lose the T6 and it turns to silly putty.

[Uniflow]

7000 doesn't have good fatigue resistance. Bicycle manufactures have moved away from 7000 series now, 6000 heavier but lasts longer.

[Uniflow]

The rotary valve still organizes the air into the crankcase, just has no fuel with it. Oil is still deposited from the injected fuel around the crank case and rotary valve via deposits in the transfer ports. One of the problems with the Link computer is some it's twostroke injection timing software is not operational yet. I can change the start of injection timing to a given point with the "on time" moving away from this point. I'm injecting approx over 180 degrees at full throttle (180 degrees injector on time ), so I have to set the start at approx 20 degrees after TDC ( quite a way before transfers open) so that at full throttle there is no injection still happening after transfer closes. If injection occurs after transfer port shut the fuel mixture on the next cycle is not so accurate ( power loss ). This I have found. Best it to have a fixed shut time ( approx 30 degrees before transfers shut ) and have the injection start vary. This will bring max injector start time to about 30 degrees ATDC at full throttle. This is what is needed, as up to about one third throttle is happening as the transfer is occurring. This I have found gives best bottom end power. Clear as mud?

[Jeram]

If I ever get my bighorn project of the ground Ill have to look into your set up a little more. We were going to try and mount a 800cc twin snowmobile cylinder onto the bighorn bottom end to try and get more power.
One problem I found with the bighorn rotary valve was that it is difficult to increase the area of the inlet passage (at the disc) to equal that of a 44mm carb (or a 44mm throttle body). I found that you could increase the area to the equivalent of a 41mm throttle body via widening the inlet of the stock disc cover.
How did you overcome this? and what size throttle body are you running?

[2T Institute]

2T Institute, you probably already know all about twostroke EFI, I'm teaching Wobbly, as if! I suppose what I'm trying to say here in general is, don't just sit there and wish for EFI, It''s a workable solution now. It works and works well.
Yes I know Bill, race with him. Lucky I'm not in his class though, because I'm not in his class. He is faster than me. So comes the relentless quest for MORE POWER!
Wobbly is involved with the new engine design, he is simulating the ports, exhaust and rotary valving at the moment. I have an onther set of YZF cases that I've clocked up in the mill. Usually we cut a pattern and cast cases but this time I might just cut from solid alloy, depends on cost. This way I can manipulate the new engine to fit the original frame mounts and not cut. I don't think people realise the damage you do to modern alloy frames by welding them. Frame goes soft and will crack! These frames are heat treated to probably T6 in the factory and can not welded without re heat treating afterwards. I'm even considering designing in a balance shaft to make it less stress on the alloy frame. Maybe?

I know SFA about EFI. If Bill ever gets a bit cheeky ( ) about his riding prowess ask him what happened when he rode a TS400 at Classic Dirt    I'll see if I can dig up  the pic of him riding my TS 400.

Have you tried injecting a BDC that is when the pull from the pipe is strongest. 

[scotty dog]

It all sounds extremely confusing to me but it's good to see it can be done, good stuff

[Uniflow]

In a nutshell, the injection timing is important. I can see why it's probably a good idea to use a small and a large injector, staged. The Link software is not able to do this in " twostroke mode" . Also there is an option to nail down the injector finish time and adjust the start time, or a center and adjust either way from that point. Also not available in twostroke mode. These options are available in fourstroke mode. So next step is to call the bike a fourstroke twin, 360 degree firing ( I don't need to use the ignition as this is done with a separate unit), This will use two drivers ( switches ) in the Link unit to run each cylinder ( if it were a twin ). Both drivers can be hooked together to run my pair of injectors each 360 degree cycle. This requires a cam sensor, I'll use a circuit called a flip flop connected to the ignition trigger ( single pulse per rev ). This circuit ( flip flop ) will only allow every second pulse to be seen by the Link computer, as far as the computer is concerned, a cam sensor. This will trick the computer in doing what I need it to do. Now all these options will be  available. New Link soft wear will be available in eight months. I can't wait that long, I want it now.
That's a big nutshell.

[2T Institute]

I'll have to go the info pump on Wobbly all about this new engine