ESE's works engine tuner

[F5 Dave]

I've only had 3 RV bikes and 2 were road spec discs, but every reed valver was like 2 steps and drop the clutch, at least when hot.

[husaberg]

That is of course true.The only experience Honda had with 2 strokes stemmed from reed valved MX bikes, Miyakoshi himself was project leader in the development of many of these.So of course they would use tech they were familiar with,given that unlike with the NR,this time they had to succeed quickly.

Still,it would be interesting to know if reed valved 2 strokes are fundamentally easier to start than disc valved.

Honda did arround that period have the two disc valved bikes the 1981 RC125 and the RS125T.
http://i155.photobucket.com/albums/s...07/30_1024.jpg
I do have something written about the NSRs that i have neever posted that suggests the engine characterstic of theese two bikes were the reason they stayed reed.
prior to the introduction of the big bang motor the engine design was through open to anyone at HRC.
Four options were chosen, two were developed, One option was the big bang, the other i believe was a similar set up to the Swiss auto.
the other two i have no idea about.

It should be noted that Kawaski KR250 were also pretty successful also suzuki and yamaha did a lot of Disc valve bikes from the 60's right up to the mid 80's.

re the starting i have no idea, but they are both easier to start than a simliar output piston port.

[oldjohnno]

This is what Kevin Cameron had to say in "The Grand Prix Motorcycle"

Another advantage of the NS was that its reed valves made it a much quicker push-starter than any disc-valve engine. The disc-valve engine's piston was only 10mm into its 54mm up-stroke when the intake opened, creating very little "pop", or suction signal, with which to start fuel flowing in the carburetors. By contrast, the stiffness of the reeds - which has to be high enough to enable them to keep up with the engine at 11,000rpm - prevents opening until a stronger vacuum has been pulled on the crankcase. When the more sudden pop from this hits the carburetors, they deliver fuel promptly.

[husaberg]

This is what Kevin Cameron had to say in "The Grand Prix Motorcycle"

Another advantage of the NS was that its reed valves made it a much quicker push-starter than any disc-valve engine. The disc-valve engine's piston was only 10mm into its 54mm up-stroke when the intake opened, creating very little "pop", or suction signal, with which to start fuel flowing in the carburetors. By contrast, the stiffness of the reeds - which has to be high enough to enable them to keep up with the engine at 11,000rpm - prevents opening until a stronger vacuum has been pulled on the crankcase. When the more sudden pop from this hits the carburetors, they deliver fuel promptly.

Sometimes the reeds signal works far too well, which is why cagiva had to put in spacers under the reeds so the reeds never completely closed.

[Frits Overmars]

The only experience Honda had with 2 strokes stemmed from reed valved MX bikes.

This is an MX bike. It's rotary. And it says Honda. Categorical statements are always risky...

Sometimes the reeds signal works far too well, which is why cagiva had to put in spacers under the reeds so the reeds never completely closed.

Reeds need a pressure differential before they will open, and the bulk of that differential is provided by the suction effect of the exhaust system.
When you close the throttle, combustion stops, all pipe effects stop, and the reeds stay almost closed. When you open the throttle again, exiting a corner, nothing happens because there is not enough igniteable mixture in the cylinder. So you open the throttle a bit further, and a bit further still, and at some time the cylinder contents are igniteable again. So combustion starts, the pipe chimes in and it's two-stroke business as usual. But now your throttle is wide open and the next thing you'll experience is a highside.
Cagiva put spacers under the reeds in order to make sure that they never completely closed. It cost power but it helped lap times and saved bikes and riders.
The spacers killed the 'pop' that Kevin Cameron mentioned, so carburation became less than responsive, which inspired Cagiva to experiment with fuel injection.

[husaberg]

This is an MX bike. It's rotary. And it says Honda. Categorical statements are always risky...


Reeds need a pressure differential before they will open, and the bulk of that differential is provided by the suction effect of the exhaust system.
When you close the throttle, combustion stops, all pipe effects stop, and the reeds stay almost closed. When you open the throttle again, exiting a corner, nothing happens because there is not enough igniteable mixture in the cylinder. So you open the throttle a bit further, and a bit further still, and at some time the cylinder contents are igniteable again. So combustion starts, the pipe chimes in and it's two-stroke business as usual. But now your throttle is wide open and the next thing you'll experience is a highside.
Cagiva put spacers under the reeds in order to make sure that they never completely closed. It cost power but it helped lap times and saved bikes and riders.
The spacers killed the 'pop' that Kevin Cameron mentioned, so carburation became less than responsive, which inspired Cagiva to experiment with fuel injection.

They had the similar powered 125 gp bike as well. I was also told they also had a tandem twin that they played with. but i have never seen a picture of it.
Erv Kanemoto was once told by an HRC technican that he was never to mess with the cutaway shape on the NSR, when he asked why? he was told that the shape had taken 6 solid months of work to get right.

[Frits Overmars]

Erv Kanemoto was told by an HRC technician that he was never to mess with the cutaway shape on the NSR, when he asked why? he was told that the shape had taken 6 solid months of work to get right.

I bet the next thing Erv did was try a different cutaway. I know I would have. Getting a good advice is fine, but one also wants to know the background .

[husaberg]

I bet the next thing Erv did was try a different cutaway. I know I would have. Getting a good advice is fine, but one also wants to know the background .

imagine going home to the mrs and answering that yes you were working on the cutaway for 180 days in a row

[2T Institute]

Talking of exhaust mfg, here’s something of interest. It’s about a place in Italy (Elto Racing) that mfg the multi piece KZ style exhausts. https://www.youtube.com/watch?v=Da-g7LTsGWM

Have a look at this one and you can see they do a lot of exhausts for lots of customers, inc TM. http://www.eltoexhaust.com/en/

As to the rolling, where Elto use the 2 roll principle (steel top roll and urethane bottom roll), this joint supplies them. https://www.acrotechinc.com/art-of-bending/ A shitload better than mucking about with the 3 rolls and gets the rolling very close to the edge.

Maybe there is an opportunity for you ingenious & recourceful kiwi guys, other than sending up satellites. Over here in Oz, there is a saying in the karting industry: ”You can make a small fortune out of karting, as long as you start out with a big one”.

great stuff Ken

[ken seeber]

Cool Lozza.


I do know in karting that reeds start (& idle) so much easier than piston ports, as Husa has pointed out. At starting speed, effectively due to their passive shutting off, reeds do offer a positive displacement principle. A piston port, at very low rpms will provide a net inlet flow of zero.

Dunno about rotary valves, but must be a function of the crank angle position at the time of closure. Fletto’s variable timing disc valve system could help here, although I can’t remember whether it controlled opening or closing.

[Jannem]

2Ts are hateful things but do in the end respond to some sort of logic.
The ceramic coated piston was a disaster,but change the coating so that only the dome is insulated,and the squish area is left stock - then the deto instantly goes away.
One has to assume that the heat that isnt absorbed by the piston has to go either into the combustion gas, or a % of it is transferred into the water via the insert.
When I tested this the egt did rise,about 1/2 a jet size,so not really significant,but if you coat the combustion chamber ( not the squish area ) the temp rises another
whole jet size and the pipe then reved on a worthwhile amount.
As it turns out, i prefer now to mirror polish the piston ( much cheaper than ceramic ) and that works even better.
But you have to keep on cleaning it as oil burns onto the surface.
The coating in the chamber is a real "hidden trick " and doesnt cost much at all.
It increases the combustion gas heat retention and the water temp drops, a win win.

Have a think about the process and what is needed by different parts of the enclosed combustion space.
We want to keep heat out of the piston and in the gas - so polish the piston so it reflects the heat back.
We want to keep heat out of the water - coat the chamber.
We want to effectively cool the plug body - get water right up to the threads.
We want to keep the squish area boundary layer and thus the trapped end gases cool - you work it out, I have but aint telling.

Re the TM Ex duct - I have the cylinder CAD file so I remodeled the duct,reducing the height and added the ears all the way down the side right thru the spigot to the header.
The exit area is smaller again than the C model, and as per usual it made best power in the sim at 75% of the effective total Ex port area.
Franco has the file,and has promised to make the special sand cores for a cylinder in the next manufacturing batch - " just to make me happy ".
As Jan said,I think he will be surprised, but for me it enables a bigger scope of new pipe design critera with alot more front side power and overev capability.

Thank You for sharing this. Still lot to be learned...

[breezy]

Frits, wobbly,Jan,

is their any kind of rule of thumb regarding the compression pressures above and below the piston on a two stroke engine which are deemed relevant for two stroke engine rpm?

[wobbly]

Peak combustion pressure exceeds 80 Bar, peak case pressure is under 0.5 Bar.

[jonny quest]

Why would a shorter exhaust duct hurt power? Is it because the cast shape can be more organic?

[wobbly]

Why would a shorter exhaust duct hurt power? Is it because the cast shape can be more organic?

A short duct allows more of the over-scavenged air/fuel mixture to be subjected to the uncooled spigot/header surface.
This heated mixture is than shoved back in past the closing port.
Any heat added to the trapped combustion gases within the cylinder reduces its density and directly affects power.
Of more concern is that if its overheated enough, it causes detonation.
As Jan stated, they tried a shorter duct and longer header at Aprilia and it was useless on the dyno and the track.
He also stopped water from accessing the bottom of the duct, and that lost power and detoed like hell as well.