Diaphragm shutter on inlet

Bernhard · Jun 20, 2016

Anybody ever come across a Diaphragm shutter on the inlet manifold on an internal combustion engine :?:
they were sometimes fitted to the Ducati 888 (and others) works WSB engine to increase the rev range ;

https://en.wikipedia.org/wiki/Shutter_% ... gm_shutter

A diaphragm or leaf[1] shutter consists of a number of thin blades which briefly uncover the camera aperture to make the exposure. The blades slide over each other in a way which creates a circular aperture which enlarges as quickly as possible to uncover the whole lens.

This seems like a good idea for those of you who want to fit ridiculously large carbs but don’t want to lose the low down power :!: :idea:

grandpaul · Jun 20, 2016

I played with a design for iris carb apertures many years ago but had no equipment with which to fabricate prototypes. I have the CAD drawings somewhere...

acotrel · Jun 21, 2016

I use 34mm MK2 Amals on my 850. However the inlet ports are tapered for the first inch and are standard diameter after that. It is about maintaining gas speed, any sharp step in the port should probably be avoided.

Bernhard · Jun 22, 2016

Re: on inlet

acotrel said:
I use 34mm MK2 Amals on my 850. However the inlet ports are tapered for the first inch and are standard diameter after that. It is about maintaining gas speed, any sharp step in the port should probably be avoided.

I’m not thinking of changing the size of the Commando inlet tracts;/ports, merely asking about the possibility of using larger than standard bore inlets ( upwind of the cylinder head!) controlled by a Diaphragm type shutter- like the start of the 007 James Bond films- the leaves open and close like a camera leaf shutter.
A diaphragm or leaf shutter consists of a number of thin blades which briefly uncover the camera aperture to make the exposure.

In the world superbikes Ducati used one on their works machine, but of course it was fuel injected- but after a few searches on the internet I can find no information about it.

mikeinidaho · Jun 25, 2016

Maybe make it some variation on a reed valve, mounted in the intake tract? Reed valves have been used on piston port two cycle engines for quite a while. They allow timing the intake event for top end power and still have reasonable low speed running characteristics. A reed valve mounted between the carb and the intake valve would cut down on reversion pulses, making the airflow through the carb more even.

acotrel · Jun 28, 2016

The inlet tract on most bikes actually makes a noise. So what happens within it is probably sonic. Have you ever seen photos of the air waves coming off the models in trans-sonic wind tunnels ? What you THINK you might get with the diaphragm might be considerably different from what you actually DO get.

acotrel · Jun 28, 2016

Do reed valves on two-strokes make the gas flow more even ? I suggest they flutter like crazy.

grandpaul · Jun 29, 2016

acotrel said:
Do reed valves on two-strokes make the gas flow more even ? I suggest they flutter like crazy.

No joke, especially when spinning at 20K RPM!

Danno · Jun 29, 2016

acotrel said:
Do reed valves on two-strokes make the gas flow more even ? I suggest they flutter like crazy.

Reed valves on two-strokes prevent combustion from blowing back into the intake. The charge is pulled into the crankcase as the piston rises and blown into the chamber via transfer ports as it begins it's descent. There is a time period in which the intake port is not yet covered that the charge can reverse flow, but the reeds prevent that.

Nater_Potater · Jun 29, 2016

Honda played around with reeds during the mid-80's on their big four stroke singles in attempts to allow a more aggressive cam while helping with reverse intake flow during low rpms. An aftermarket company made a plate that would allow you to do away with said reed block. I did so with my 600, and, after some minor jetting, never regretted getting rid of the reed block. I didn't notice any loss in bottom end tractability, and it made a noticeable improvement at the higher rpms.

As for the iris variable-area venturi, the Brits had a similar item (I think) on the Rolls-Royce V12's during WWII. Rather than an iris, it was a rectangular-throated carb with two opposing moveable sides shaped like the top surface of a wing. The fuel spray bar lay directly in front of the wings. The opening between the wings was governed by intake manifold vacuum. The idea was to keep a constant velocity across the spray bar, thus a more uniform mixture delivered.

From Chandler's 1938 patent:

Nathan

acotrel · Jun 29, 2016

I think reed valves were used on the Yamaha TZ750 to get more bottom end and remove peakiness in the power band. Without them the bike would probably have been a killer. The RD350 had reed valves, however the TZ350 had none. A TZ350 is very easy to hi-side it you don't get it upright before it comes on song. A lot of these things come down to rider ability, however a later TZ250 would probably be a faster ride than the TZ350 of the 70s, simply due to the better use of reed valves.

Danno · Jun 29, 2016

At higher rpm, charge inertia keeps some of the potential blowback going in the right direction, but a lower revs, power gets anemic without the reeds. Two-smokes don't have a lot of grunt in the best case. Similar to the effect of large overlap in a 4-stroke, the rpm has to catch up with and pass the velocity of the charge to make good power.

concours · Jun 29, 2016

Variable exhaust ports help a lot. My current project, RZ350

Bernhard · Jun 30, 2016

acotrel said:
I think reed valves were used on the Yamaha TZ750 to get more bottom end and remove peakiness in the power band. Without them the bike would probably have been a killer. The RD350 had reed valves, however the TZ350 had none. A TZ350 is very easy to hi-side it you don't get it upright before it comes on song. A lot of these things come down to rider ability, however a later TZ250 would probably be a faster ride than the TZ350 of the 70s, simply due to the better use of reed valves.

The first bikes were TZ700 (2x TZ350 Barrels ) this was a very peaky engine, like the TZ350 was and the TZ700s was soon adopted by the chair boys. The tz 750 with the reed valves was more solo rider friendly after the complaints of the TZ700 powerband.

Re” A TZ350 is very easy to hi-side it you don't get it upright before it comes on song.”
Or….more likely slide off when you hit the powerband while banked hard over, don’t me how I know as I got caught out once- but this can happened with almost any bike that has the power in the engine.

acotrel · Jun 30, 2016

I don't think the TZ700 was ever purely piston port on the inlets. I understand there was one guy in Victoria who tried a TZ700 with two sets of TZ350 barrels and the bike tried to get out from under him, so he gave the idea up as a no-go. A TZ350 is enough scare on it's own for most people. It is quite easy to build a bike which will scare you shit-less, particularly with two-strokes. My latest project involves an H1 Kawasakii bottom end fitted with RD350 barrels with the reed valves. I've bored the crankcase mouths, moved the studs and machined the bottoms of the RD barrels. It has ended up at 600cc with TZ750 port timings. The frame is an Egli copy and most of the running gear is RG250 Suzuki. It is sitting rotting away in my garage because whenever I start working on it, the minor problems twist my brain.

acotrel · Jun 30, 2016

lcrken · Jun 30, 2016

acotrel said:
I don't think the TZ700 was ever purely piston port on the inlets.

I believe you are correct, Alan. The TZ700 was a development of the TZ500, and had the same 7-port cylinders and reed valve intakes.

I owned a late monoshock TZ750 for a while. It wasn't really that terrorizing. The chassis was flexy, compared to modern bikes, but as long as you didn't push the handling limits, it wasn't all that bad to ride. The previous owner, who had restored it, managed to get it registered for the street in California, complete with license plate. No lights, mirrors, etc., but a current license plate. I tried it out on the street, and it would not have been too bad as a Sunday play bike if it had lights and such, and a starter (and maybe a silencer!). I sold it to pay for a new Miller TIG welder and part of the cost of a milling machine, and never really regretted it. I've got way more use out of them than I would have out of the TZ. I sold it to a British dealer, who was in the US to buy British bikes to take home. He said he wanted it to put in his display window.

Ken

acotrel · Jul 1, 2016

The frame for that silly bike I've built (in the photo) was copied from an original Egli which was used to build a faster TZ700. My friend used to own it and in the hands of Graeme Muir, it won a round of the Australian Swann Series. I watched it on TV and Graeme simply rode around the other TZ 750s. The bike is still here in Melbourne unraced and there is a matter of disputed ownership to be resolved. It would cost an arm and a leg to race it again. And these days in historic races, the morons put TZ750s on the grid alongside four cylinder superbikes. Such a bloody waste !

acotrel · Jul 1, 2016

There is only one superbike in this race - have a look at what happened to it :

https://www.youtube.com/watch?v=VxzOmI2zat0

Bernhard · Jul 5, 2016

acotrel said:
I don't think the TZ700 was ever purely piston port on the inlets. I understand there was one guy in Victoria who tried a TZ700 with two sets of TZ350 barrels and the bike tried to get out from under him, so he gave the idea up as a no-go. A TZ350 is enough scare on it's own for most people. It is quite easy to build a bike which will scare you shit-less, particularly with two-strokes. My latest project involves an H1 Kawasakii bottom end fitted with RD350 barrels with the reed valves. I've bored the crankcase mouths, moved the studs and machined the bottoms of the RD barrels. It has ended up at 600cc with TZ750 port timings. The frame is an Egli copy and most of the running gear is RG250 Suzuki. It is sitting rotting away in my garage because whenever I start working on it, the minor problems twist my brain.

Really :?:

I had a early tz700 barrel on one of my tz350s-defeninely no reed blocks,
You could fit TZ750 barrels onto a TZ350 if you opened the crankcase out :shock:

From;
http://global.yamaha-motor.com/showroom ... ing_tz750/

“This was the Formula 750 production racer developed simultaneously with the YZR500. The concept was the same as well and the engine was created on the idea of connecting two blocks of the 2-stroke, liquid-cooled, in-line 2-cylinder TZ350 engine together to make a 700cc in-line 4-cylinder engine and mounting it on a newly designed high-tensile steel pipe double cradle frame. “

Diaphragm shutter on inlet

Similar threads