Recently I have been trying to find the posts that talk about pipes and collate and edit them. There is heaps of it and pages 620 630 640 650 660 670 and 680 have un edited collections of raw material. If your interested in expansion chambers they are worth a look.
Pages 610 600 590 580 570 ..... 100 etc all have links lists to other stuff, then there is the Thread-Tools View-Thread-Images option that also helps to find the interesting pictures and posts.
http://www.underdogsracing.com/fospipe.html
509
Originally Posted by wobbly
Before you get all out of control, consider a couple of factoids.
Turning the cylinder around has alot of advantages in pipe shape as well as allowing easy forward movement of the whole engine - remember the RSW is better than the RSA for that reason alone..
Secondly, I have shown conclusively several times to disbelieving audiences that using a PV can double the power of a highly tuned 2T at the bottom of the useable range.
So - imagine the single exhaust GP125 with double the power at say 6000, then draw a straight line up to its 31 Hp peak at 12500.
A ATAC system can achieve a similar result, the trombone is capable as well, this system has been used in hydro racing forever ( remember Konig and the Kiwi ).
So getting a 4T killer setup is staring everyone in the face, you - meaning Rob et al, just need to commit to one approach and develop it.More questions for the wise ones,
How good does the seal around the butterfly need to be : should there be clearance to allow for expansion of the flap ??
How critical is it to have the butterfly open into the ex, stream? ( mine is going to be about 5mm from the inside wall of the header when open and close to 10 when closed )P513I am not wise but if you have a look on Ebay Cr125 about 1986 there are plenty. Remember it opens Parallel to the flow as well not into it.
The throttle plate or whatever you design must seal well.
I did a sliding flat plate with a hole in it design like they use in fuel injection throttle plates, that worked well on Champ winning jetski, as this got the plate real close
to the header and there was very little flow disruption when closed.
A small leak into the cavity will kill power real quick with an ATAC system.Using the det sensor with lights makes it dead easy to shape the curve to suit the engine, you dont need a brake at all.
You can dyno load cycle the engine as fast as you like, and for the short period it may deto, in a small band of rpm - the lights go off like a Xmas tree.
Takes a bit of fiddling with sensitivity to get in the ballpark and read actual deto - not normal noise, as the det frequency is
determined by the bore diameter.
Just make sure the M8 bolt thru the Bosch sensor is tightly fixed to the head or case, with no washers to crush etc.
Data logging the sensor output against rpm is the trick way to go, but simply watching the revcounter and the lights to see where deto is happening during a pull, is easy.
Works just like the deto warning when running EngMod - see the warning and fix the excess advance before a rod comes thru your screen, your choice.
In this case we are dealing with an aircooled scenario - remember two things here, Avgas loves com to make power, and the pipe loves retard to get heat for revon power.
Whenever you have high com or lots of advance a larger % of the heat of combustion is directed out from the chamber into the finning, via mainly the ring contact with
the bore, reduce either or both and more heat ends up in the pipe, making it appear shorter due to the increased wave speed..
Thus when you are thermally limited by the finnings capability to reject heat, you must reduce the heat input by limiting the com.
This then means more heat is available in the pipe, so more power can then be made by upping the advance - just another balancing act.
Its a Catch 22 when there is high dynamic com - ie, when the engine is on the pipe,there is danger lurking, but below that point - the cylinder filling is so piss poor the only way to get good
throttle response off slow corners is to pile in plenty of advance - its safe as houses as there is very little effective com.
This engine has no powervalve so the cylinder filling efficiency comes on slowly, so you roll of the advance slowly, then pull it out quicker as the system starts to work well.
With a powervalve its the opposite - as soon as the valve starts to lift the efficiency increases dramatically, so the advance needs to be pulled out much quicker and sooner.
Any well set up race engine will love 28* below the pipe when running Avgas.
In one of the World Champ skis I did we had 35* of mid advance, as the only time it was in that band was at full throttle from a standing start.
It would jump real hard using that advance to generate cylinder pressure - but troll around on part throttle at that rpm and it would kill the engine by loosening the barrel nuts with rampant deto.P547You must take into consideration the fuel being used, and how the factory engineers approached the problem.
Unleaded ( FIM that needs gloves and a respirator ) will go to 15:1 but must be run VERY rich to achieve best power with that level of com.
Leaded was run up at 19:1 in GP engines and at the end of the day the result was that the advance curves changed very little.
The big advance was in using the powerjet solenoids.
The unleaded scenario uses BIG powerjets ( 60 + ) to turn off the rich mixture past peak power.
The leaded setup was very lean at peak power, so only needed small ( 35 ) powerjets to keep the pipe temp up, over the top of the pipe.
Later of course that bastard Thiel came along and did the clever thing of PWM controlling the powerjet, thus even closer continuously matching the A/F ratio to the pipe
temp needed for max power.
Makes me sick just thinking about how clever he was, and how advanced the results became.
We are all just wankers floundering around in the mire of a mediocratic 2T wasteland - buckets.
P547Re coating pistons with ceramic - the cool boundary layer in the squish helps suppress deto of the trapped end gases.
The ceramic surface is HOT, the alloy underneath is COOL.
Coating the piston or head in the squish CAUSES deto.
HPC have done dozens of pistons and heads for me with a spray mask, to keep the coating in the middle only.
Even doing a clear ceramic for classes where coatings are illegal - woops didnt say that.
And I got the Britten Ex ports coated to help stop the thing boiling on the grid - worked a treat and made more power as well.
Except the first time it was done the valve seats all fell out from the baking process.
found this it is from Rob Tuluie from what i understand used to be head of R&D at Renualt F1 and was a Rocket scientist so i guess he is reasonably clever or has good PR. Edit he did this all before turning 39 .
he also designed the frames above.
its about Detonation i haven't actually read it yet.
http://www.motorcycle.com/how-to/wre...tion-3420.html
http://www.motorcycle.com/how-to/wre...tion-3420.html
fuel
http://www.motorcycle.com/how-to/wre...-gas-3417.html
P552So, I might have read more into it than there was, anyway, this is the post I was thinking about.
Originally Posted by Frits Owermars @ Pitlane
In theory enclosed cranks are good. Jan Thiel did some experiments at Aprilia with a kart engine that had its reed valve at the front: the incoming mixture had to move against the direction of crank rotation. And although the crankcase stretched over the crank webs, reversing the direction of rotation brought another HP. So the crankshaft does have an influence.
But in practice, if you reduce the distances between crankshaft and crankcase walls to less than 1 mm, the viscous friction of the mixture between the surfaces really costs power at high rpm. And if you make the clearances so tight that lubricating oil can no longer reach the big-end and crankshaft bearings, it will also cost engines
Another negative aspect: any volume with a narrow 'entrance' between the crankshaft and crankcase surfaces acts as an hydraulic damper on the Helmholtz-resonance in the crankcase.
Aprilia has avoided this by making the space between the crank webs as wide as the big-end bearing. As a result the crankcase volume of the 125 cc RSA engine at TDC is about 650 cc, so the exhaust pipe really has some volume to breathe from.
So much for the fairy tale of high crankcase compression
There might be more on this subject over there, will look around a bit more, if I find more I'll add it to this post.
I havnt constructed a stock RZ EngMod file but from the numbers given I can say outright the design wont work well at all.
The RZ has 50mm in the duct, and assuming no spigot on the cylinder ie the pipe fits flush on the cylinder face, then the header length is 36% - way too long.
Then the diffuser end is 58% and way too short.
The header angle at 2.35* is way too shallow, and the rear cone setup with 19* then 15.8* is back to front, and is a disaster on the dyno - been there ,tried that - no free lunch.
The stinger is way too big for anything but a full race setup,and the body at 116 dia is simply too fat, and will drag on the ground no matter how well the pipe is tucked under the bike.Sorry,yes i forgot the 50mm in the cylinder with the diffuser end calc, its 678/1083 = 62%, a very old fashioned number..
For a street setup the longer header and longer diffuser expand the powerband width, but as it has a powervalve this changes everything,due
to the very low blowdown area when the valve is down.
Normal range for header = 30 to 33%, and for the diffuser = 64 to 68%, so I would be shooting for the longer on both for a stock add on pipe.
The longer diffuser gives better max case depression around BDC,later in the cycle, thus boosting mid scavenging efficiency.
Very long - 36% headers only work on piston port engines - like say TZ350,as this then allows a steeper initial diffuser angle, boosting power in the limited band the piston port can operate within.
There is no case for a header angle under 3* incl and dual angle rear cones are best with shallow then steep angles.
The main effect here is to increase the belly volume, thus smearing the wave amplitude over a lower, wider band.
Its always a combination of compromises, but helps you if the basic geometry suits the application,and the physical limitations presented..... turned your equations to an online calculator a few months back. It's here: http://www.underdogsracing.com/fospipe.htmlThe large cone angles come with high piston speeds and short exhaust timings. I can only guess at the exhaust timing you used, but aiming for max. power above 10,000 rpm in a twofifty is definitely provocative. I don't think the time.areas will be up to it. But like I wrote: try it and you'll find out.
Cone angles in themselves have little meaning, especially when reflector cones are dealt with. Short pipes tend to have steep cones and there is nothing wrong with that. The longer a pipe, the more the reflected wave is developing a steep front on its way back to the cylinder and the greater the risk of it developing into a shock wave that is very inefficient in shoving back washed-through fresh mixture.
One last word of advice: I would not build the second pipe in the above drawing. You succeeded in making it look like an Aprilia pipe, but those many cones just require too much cutting and welding. My overall rule of thumb: keep it simple.Keep it simple, Ief. That ratio should be exhaust volume divided by cylinder volume. 30 is a good value, but it's not critical (and you probably won't be able to achieve it on an RD350; not if you want to keep some cornering clearance).I could babble on forever about pipe specifics but here are a few pointers.
Rear cone ( single ) max out at around 28*,the multi angle setup used by Aprilia can be equalled simply by a single cone set at around this angle.
In a 250 it is counter-productive shooting for the same swept/pipe vol ratio as a 125, you need to be aware that there is a finite amount of energy in the wave
running down the pipe, and huge diffuser angles dumping into a huge mid section will loose more of this energy than will create a bigger depression around BDC,or a bigger
plugging pulse heading toward EC from a very steep rear cone..
I have found the best compromise is at around 135 dia.
The very over square engine will theoretically rev harder, but you will by default a have a very heavy piston, plus needing big timings to create the STA necessary for power over 10,000
means any perceived advantage is lost in reality.Many combinations will "work " just as well as a myriad of others, when you are offsetting the negative effect of one element by overriding it with the positive effect of another.
That isnt clever, its just using knowledge to mitigate the necessary down side of some one else's arbitrary decision, that was wrong.
Simply put the best way forward, is to limit the down sides,and implement as many truly clever elements as you can, to synergistically work together.
For example , the proven need for huge case vol in a full house race rotary valve engine, isnt even close to being a positive element in a stocker reed valve engine with
seriously crap transfer ducts.
Quite the opposite will produce better power in that scenario.
The smaller case vol gets the flow going sooner and more effeciently when the duct geometry is compromised , but then of course peak power
cant be the object of the end game, with that upsetting mechanical limitation.
Its been proven a hundred times in Jetsjkis etc that have won world titles with ease, due to combining the best effects to limit the inherent issues preventing a better result.Diffuser positioning is a very hard variable to pin down,but experience has shown that moving the steep part of the flare closer to the header
helps to pump up the power higher in the rev range.
Up to a point though.
Early versions of Aprilia pipes had the steep cone connected directly to the header.
But later ( more powerful ) versions had a short additional section that pushed the steep cone further out, but increased its angle.
This gave a deeper depression closer to BDC, even though it started later.
The other idea that works well also for many designs is the use of a shallow,short,end diffuser.
This increases the main diffuser angle again, and also increases the belly volume.
You have to be careful though with this clever stuff when dealing with crap transfer ducts.
Very effective and well timed diffuser action, can easily create so much depression around BDC, that the compromised transfers cant keep control
over the scavenging stream integrity.
Alot of the fresh charge disappears out the pipe, without clearing out the remnant exhaust residuals.
Fat pipes dont work on things like RDs - even if you could fit them in.P556Old, cast Rotax cases,make better power than CNC billet replica ones as the rough cast surface sheds heat more effectively.
Even where both are watercooled.
On the dyno the CNC cases heat fade very quickly.
Very very little transfer flow is created due to case com, except in your lawnmower,its all to do with the diffuser depression around BDC.
And there is a Catch 22 happening with the piston.
Transfer flow needs to attach to the crown to cool it, but this heat transfer affects the volumetric efficiency badly.
Cant have one without the other, but the piston simply isnt able to shed heat fast enough, just thru the ring and skirt alone to the cylinder wall.
In a 125 engine at 50 Hp, raising the head exit temp from 50 to 60* looses a couple of Hp instantly.
The deto sensors are connected one wire to earth, the other to the guage.
A good direct connection to the guage and chassis earth is essential.
In the units I have tested with two wires I havnt seen any connection of the sensor body to either of the wires and polarity doesnt seem to matter - except where there is a shield
strap.
Flowing the wrong way between Transfer Open and BDC is not the result of a too-early returning exhaust pulse, but of insufficient blowdown time.area.
What I meant was the instant just before Transfer Closure. The stuffing pulse from the exhaust should not arrive at the cylinder just yet, but at rpms under the powerband it will, raising the pressure in the cylinder while the transfers are still open. So the fresh charge gets pushed back into the crankcase, leaving little of it in the cylinder. And on top of that, just after the transfers close, that stuffing pulse reverses sign and direction, and sucks what little charge is left in the cylinder, out...
Loss of heat should be avoided all right, but if you want power, it is more important to avoid detonation. The part of the exhaust duct where washed-through fresh charge temporarily resides, should be kept cool to avoid heating up that charge. And it is much simpler watercooling an exhaust duct that is part of the cylinder, than cooling a duct that is part of the pipe.
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- anyone tried Acousta-fil ? - I've been using it myself for a couple of years for our TZ350...
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