Question for the engineers

[idb]

So the inertia of the gas is creating a low pressure area behind it which helps to build the inertia of the inlet charge [conductence ?].

Question is, the zorst gas is under pressure (because its being pushed out, rather than being sucked out as is occuring to the inlet charge which is not under pressure). So I thought that would have an impact as well. Perhaps the piston is now slow enough so that the dwell at tdc is starting to have an effect as well.

I wonder if its to perform attenuation of the inlet port in the same way as the megaphone is used to attenuate the zorst port ?

Yes, the inertia of the exhaust gases helps 'suck' in the fuel charge.

But wait, there's more.....
Pulses of low pressure are sent back through the exhaust gas column from the end of the header pipes.
These pulses help to scavenge the exhaust gases from the exhaust valve as well.
Peak efficiency is reached when the low pressure pulse arriving at the exhaust valve coincides with that valve opening.

[Motu]

whats stopping manufactures using rotary valves on a 4 stroke? Can they not handle the combustion pressure or is lubrication their biggest issue (hence why they only seem to be doing big things on 2 stroke engines). It just seems better, not having anything upsetting the flow of air into the chamber ie the valve itself.

Shit,a whole page of posts went up while I was doing my reply,making it redundant! This thread must be more interesting to some than the bitch sesions going on elsewhere....

Ralph Watson,one of this countries great unknown engineers,has made a working rotary valve (Ralph Watson built the Lycoming Special) There is a very limited edition book about him (into second edition),I got mine hot off the press from the author,printed by one of my customers.Ralph's lifetime work,like Burt Munro,but oh so smarter,was his BSA Special,using a V twin engine.Finaly he had built the whole engine himself,including crankcases,cranks,rods,pistons and cyls - then he made his own rotary valve heads.By the time Ralph was confined to a wheelchair suffering from Parkinsons disease he had put more than 30,000km on it (I'll check my book tonight) He beat all the so called problems with rotary valves...the motor is a work of art.

[TwoSeven]

Yes, but remember that a tuned header length is generally only effective at a certain engine speed. The trick is deciding where you want your power to be and making sure inlet length, valve timing and exhaust design all conspire to make it so. Classic example is yamahas EXUP valve that effectively changes the tuned length of the exhaust thus giving a broader spread of power.

In a 4 pot engine, not only is the length of the header important but you need to make sure the collector and muffler are correctly dimensioned.

http://www.carcraft.com/techarticles/0304_merg/

Oh heck the 'net is full of it...

Once you start tuning an engine nearly everything becomes a trade off. I'll sacrifice a little power and torque here to gain a whole lot there... Street bikes usually require a broaded spread of power hence all the trickery...

You need to have a plan and stick with it. Just bolting a bunch of shite on is likely to make the bike run slower....

I've already chosen and 'fixed' my parameters. Am using 12.5k rpm where the old peak power was. My goals are to increase dynamic power (but not a priority) and modify the torque cuve and move peak torque closer to peak power (only to make the bike slightly more agressive). I'm not interested in increasing overall power. I could just buy a new bike for that.

On the design styling side I would like to also make an underseat zorst (which is changing my zorst length and diameters - if done much of the math just seeing now if the engine will like it or not). I'm thinking of changing the 4-1 into two 2-1 on each side.

So far I've not had much of a need to look at the carbs because it seems that the flow rate is more than enough from the 36mm to cover stuff (although i might look at the jetting closer a bit later).

My trade off is that I'm taking everything from below 5.5k rpm and a little from above the 14k range (but I think I might need that bit back).

[Paul in NZ]

If you look at some of the pictures of the single cylinder racers of the 60's you may see some with honking long tubes on the carb intakes. A foot long in extreme cases. Theory was these acted to attenuate the inlet flow, as you say. Dunno if it ever actually worked, mind.

I have played with extended inlet manifolds on triumph twins and there are gains to be made in torque but i suspect, not in BHP. Isolating the carb from the vibrating engine helped a little as well but there was a distinct $$ limit and mechanical limit beyond which I could not go....

(snif)

[Brian d marge]

We on the Enfield site, have done a lot of work to get these thing running with modern power outputs with enfield reliability

Charles Fayette taylor ; The internal combusion engine

wood ; SAE Journal no 50 June 1942 - Airflow through intake valves

Livengood and Stanitz ; The effects of inlet design size and lift on air capacity and output of a four stroke engine
SAE Journal 915 November 1943

Eiichi and Watanabe ; An Analysis of the Volumetric Efficiency using mean index Mach number
SAE 790484 March 1979



Also see the Temp Entropy diag below and the pressure Volum dia for an otto cycle

It will give you grey hair nutting all that out but the maths is all there and so is the answer ....

Stephen

[Paul in NZ]

Shit,a whole page of posts went up while I was doing my reply,making it redundant! This thread must be more interesting to some than the bitch sesions going on elsewhere....

Ralph Watson,one of this countries great unknown engineers,has made a working rotary valve (Ralph Watson built the Lycoming Special) There is a very limited edition book about him (into second edition),I got mine hot off the press from the author,printed by one of my customers.Ralph's lifetime work,like Burt Munro,but oh so smarter,was his BSA Special,using a V twin engine.Finaly he had built the whole engine himself,including crankcases,cranks,rods,pistons and cyls - then he made his own rotary valve heads.By the time Ralph was confined to a wheelchair suffering from Parkinsons disease he had put more than 30,000km on it (I'll check my book tonight) He beat all the so called problems with rotary valves...the motor is a work of art.

Now thats something I'd like to know more about....

I remember a quote from Phil Irving regarding the Sarich (sp) orbital engine - "That engine will never go into serious production' or words to that effect...

Sealing a rotary valve at high rpm would probably be the issue I suspect.

Some days I seriously wonder if we are on the right track at all. Perhaps the research should have gone into transmissions and we could have stuck with a fixed speed engine to get optimal operation.

[Kickaha]

Wow. Great answers guys.

Could you control valves with electromagnetics? Or is it just not fast enough?

I think I read somewhere that they are used in F1 engines.

Renault F1 have experimented with this in their quest for infinitely variable valve timing but as yet they have not been able to make it work

[willy_01]

Renault F1 have experimented with this in their quest for infinitely variable valve timing but as yet they have not been able to make it work

haha are you sure? Renault have come from nowhere in the last 2 years.

I saw a very cool engine about 2 years it was a 36 cylinder (3 v12's) supercharged 2stroke desiel (well i think), i cant remember what it was called so cant find anything on in again but that was a true piece of engineering art, has anyone else seen this thing?

[TwoSeven]

It's actually quite complicated, because you can't think of it in static terms. Remember this is all happening about 50 times per second.

I'm doing both static and dynamic calculations.

[TwoSeven]

We on the Enfield site, have done a lot of work to get these thing running with modern power outputs with enfield reliability

Charles Fayette taylor ; The internal combusion engine

wood ; SAE Journal no 50 June 1942 - Airflow through intake valves

Livengood and Stanitz ; The effects of inlet design size and lift on air capacity and output of a four stroke engine
SAE Journal 915 November 1943

Eiichi and Watanabe ; An Analysis of the Volumetric Efficiency using mean index Mach number
SAE 790484 March 1979



Also see the Temp Entropy diag below and the pressure Volum dia for an otto cycle

It will give you grey hair nutting all that out but the maths is all there and so is the answer ....

Stephen

I've been trying to do some of the thermal stuff already. Biggest problem at the moment is trying to calcuate the temperature changes. I've just been using fixed values (25degC), but want to be able to calculate stuff inputting a measured air and fuel temp. Recon I might have it in about 5 years time

[TwoSeven]

haha are you sure? Renault have come from nowhere in the last 2 years.

I saw a very cool engine about 2 years it was a 36 cylinder (3 v12's) supercharged 2stroke desiel (well i think), i cant remember what it was called so cant find anything on in again but that was a true piece of engineering art, has anyone else seen this thing?

Take a look at the new Audi R10 Le Mans racer then.

[Brian d marge]

I've been trying to do some of the thermal stuff already. Biggest problem at the moment is trying to calcuate the temperature changes. I've just been using fixed values (25degC), but want to be able to calculate stuff inputting a measured air and fuel temp. Recon I might have it in about 5 years time

the sae papers deal with air flow through the valves

woods sets out a methos to determine flow at various valve lift/ valve head dia

from memory watanabe deals with the dynamics of the flow


Stephen

Methos ..is like a mentos but different
The older sae papers are free , someof them are anyway !

[Motu]

I've got some photo's here of Ralph Watsons rotary valve heads....and I'm a bit scared about posting them.They are from the book ''Ralph Watson Special Engineer'' by T R Sheffield.It was put together for Ralph to clear up discrepancies about his work,and to cronicle what he's done.The photos are from Ralph's personal collection - I really hope I don't upset anyone,but I think everyone needs to know a bit more about this guy...after all,a film was made about Burt Munro.If you think I shouldn't put them up,take a peek,than I'll delete them.We are just tucked in the corner of some obsure forum anyway...

[riffer]

You must spread some Reputation around before giving it to Motu again.

I'm enjoying the read...

[Ixion]

I've got some photo's here of Ralph Watsons rotary valve heads....and I'm a bit scared about posting them.They are from the book ''Ralph Watson Special Engineer'' by T R Sheffield.It was put together for Ralph to clear up discrepancies about his work,and to cronicle what he's done.The photos are from Ralph's personal collection - I really hope I don't upset anyone,but I think everyone needs to know a bit more about this guy...after all,a film was made about Burt Munro.If you think I shouldn't put them up,take a peek,than I'll delete them.We are just tucked in the corner of some obsure forum anyway...

Hm. The valve appears to be pure rotary, not reciprocating rotary like a Knight valve. How does it cope with deposit buildup . It's one thing to produce something like that which will run fine under racing condition, pulled apart every couple of thousand kilometres. Another matter to make it reliable for 250000 untouched miles.

That's always been the Achilles heel of rotary valves. Good as, to start with. 50000 miles later , oh dear.

I'm not knocking his work, just Devil's advocating. I've always hated the poppet valve myself, it offends my sense of engineering fitness.