RZ/RD 350 & Misc. 2-Stroke Tech BBS

Greg, I ran the reed spacers ahead of the reed valves, between the cages and the cylinders. I was told that you can run them behind the cages to raise the power higher in the rpms.
As far as pulling to 10,500, I'm running Allspeed pipes and they pull well past the 9500 rpm range and I can feel the power drop after 10,000-10500 range. I can not say anything about the Toomeys, I have no experience with them( although I have 2 sets of them) I have only seen graphs of them and they show pulling past 10,000 also.

2bang wrote:

T.RexRacing wrote:

Properly sized boost bottles will do the same thing as an airbox. Reference Harry Barlow for that one.

So what is "properly sized"?

According to the aforementioned Mr. Barlow.

Wow, I'm not an engineer, just a racer/street rider/motorcycle mechanic.

Air boxes in the eighties were crude, and rapidly developing entities. Yamaha had hp claims, that were calculated at the crank. They ranged from about 53-65, again at the crank, not the rear wheel.

My take? Pipes and pods with jetting. Pods must be K&N, as others just choke...dyno proven. My bike hits hard and is reliable. The only mods? Pipes and pods, oh, and fibreglass bodywork, fibreglass tank, lighter F2 parts.
My bike dyno's at 56 RWHP. Off Roads, 60 with other mods, shaved head, Y intake, Zeel + unknown. Those are the two fastest RZ350s that I've ever ridden. They pull really hard and rev nicely.

Getting back to air boxes. The RZ had snorkels used to help control emissions and tame the bike a bit. The early F1 pipes were also not as good for flow as the F2s.
Current air boxes are harmonized works of art. They are not to be tampered with at all!
For the RZs, make them breathe. Jet them, and don't err on the side of rich. If your jetting is spot on for wide open riding, you WILL have to alter the jetting for street riding. I had to. Leaned out the pilot, which I never had to touch on my LCs, and leaned out the needle by raising the clip and dropping the needle one notch. That is what is working for me in Edmonton right now. No more fouled plugs.
The ultimate air/fuel mixture is 14.7-1. It just happens to be 1 atmosphere. Numbers do not lie. You want to get as close to that as you can. The sniffer on the dyno allows that. Once you have optimum jetting for wide open racing, it's time to alter that for whatever your purpose is. In my case, a squirley street commuter.

That is my $0.02.

14.7:1 is the ratio that will achieve the most complete burn-at sea level. Great for heating your home however it's lousy for making power.

T.RexRacing wrote:Great for heating your home however it's lousy for making power.

I wouldnt run any 2 stroke on street fuel at 14.7 ratio as it wont last long at all. 2 strokes like 12-13:1

Years ago I made a spreadsheet to calculate boost bottle volume based on several variables and the RPM it was to be effective at. The math came from Yamaha's SAE paper for YEIS (Yamaha Energy Induction System), but is basically thanks to Mr. Helmholtz. Yamaha call the effective RPM, or 5K stumble, as the "trough of torque". I cut a connecting tube in half to attach them, one for each cylinder, and tried a couple of different configurations. There was definitely a noticeable effect, but without dyno work it was just 'different', although their research showed clear benefits. Unfortunately I could never find anything explaining how the variables are affected by having both cylinders connected. The one shown by T-Rex is both smaller and has far shorter connecting pipes compared to what I used, makng it far more practical to install.

T.RexRacing wrote:14.7:1 is the ratio that will achieve the most complete burn-at sea level. Great for heating your home however it's lousy for making power.

I'm pretty sure my dyno info has me close to 13:1. I'll confirm tomorrow what it showed.

the "5K stumble" is directly related to the expansion pipe. Any expansion-pipe will create a bad point in the power-curve at 2/3's of rpm of max torque. just because the pulses do more bad than good at that point.
carburation, boost bottle, airboxes,... can do little about that, small improvements yes, but they can not cure it. What does help is progrmmable ignition. By more advance, the burning takes place sooner, so the gases entering the pipe are colder -> the speed of sound drops making the pipe longer.

The 5k stumble is carburation related. Fitting a 4H16-2 jet needle and a 345/0-6 needle jet off an early Canadian RD350LC into the later power-jet carb fixed it completely on my RZ.

Kenny hit it on the head. I'm running a 13:1 air/fuel mixture on the dyno with a sniffer.