ESE's works engine tuner

[peewee]

1kg of red Vinamold arrived today. Will last for every possible duct I will ever want to mould.
Will be interesting to see how bad especially the transfers are.

hey i just ordered some also. hope to see it by friday. 2kg but maybe i only needed 1kg. oh well i guess ill have plenty of extra if i need it

since i never used vinamold before, what type of oil or grease do you apply to the duct wall so the vinamold can be removed easily ?

[seattle smitty]

The problem with a long slow angle rear cone is that it returns a pulse ( though of low amplitude ) over a very wide band.

.

Okay. And that would seem to match the effect of the long, skinny, low-angle diffuser cone. Both ends of the pipe have a long duration, low amplitude effect. Which would seem like the right thing for a very broad range, moderate power street motor. Why have one end of the pipe with a mild effect, and the other end with an on-off switch effect?

Wobbly, have you ever encountered anyone who wanted a "mild" RD, for commuting and just tooling around? I never have seen this idea offered up anywhere. Everybody else wants a rocket.

About the Vevey pipe: Was Vevey a brand name, a pipe manufacturer, or just the name of the person who came up with a baffle cone with lots of holes? It's hard to tell from googling (and BTW, Bell referred to it, but had no pix or drawings). More important to me, since you say it's a good deal for my purposes, are there any guidelines to making one? Your drawing appears to be of a rather short, somewhat steep-angle cone, with (my guess) 12mm holes all over the aft 2/3 of the cone. It looks like a good thing from the standpoint of noise reduction even before one comes up with a silencer.


Dave, I knew about the motorcycles, and omitted mention of them because there were few, whereas Konigs were used in sidecars for a long time, as I understand. Another German bike racer, Helmut Fath, built his own engine with a similar layout, and had some good runs. After Konig was killed, all the racing parts and tooling were bought by someone in the Czech Republic, and new and (I hear) improved versions of the 500 and 700cc fours are being sold under the name Konny.

[seattle smitty]

Question for anybody, have you seen a good discussion of the property of "over-rev" in the power curve as applied to 2-stroke engine and pipe design for motorcycle applications? In my ignorance (you know, dumb welder with useless liberal arts degree), my notion is that this is NOT a useful property for racing outboard motors. My assumption is that one picks a prop that loads the engine to stay at the power peak. If the boat takes a bounce and the prop comes out of the water, I don't want the engine winding to the moon, I want a rev-limiter, or an engine and pipe with a rev-limiting effect, a relatively long power curve (because I have no transmission), BUT one that drops like a rock after passing peak power rpm . . . .

Well, don't I ?????

Where has over-rev been talked about at length? I want to know (I think)(??) how to "design it OUT." In other words, IF I do not need this particular property, maybe I can make design tweaks to improve other characteristics of the engine/pipe combo slightly, at the expense of a property that bikers need but my outboards don't.

(EDIT-EDIT-EDIT) WHOA, there, Wobbly, you've been holding out on me!! I just got to page 350 of this mega-thread and see that you have done pipe work for Rossi/GRM engines. For the factory, for somebody in Europe, for somebody Here??? Anyway, talk to me!!

[chrisc]

(EDIT-EDIT-EDIT) WHOA, there, Wobbly, you've been holding out on me!! I just got to page 350 of this mega-thread and see that you have done pipe work for Rossi/GRM engines. For the factory, for somebody in Europe, for somebody Here??? Anyway, talk to me!!

Welcome to the ESE thread

[dark art]

.

Okay. And that would seem to match the effect of the long, skinny, low-angle diffuser cone. Both ends of the pipe have a long duration, low amplitude effect. Which would seem like the right thing for a very broad range, moderate power street motor. Why have one end of the pipe with a mild effect, and the other end with an on-off switch effect?

From my experience, rather low for instance, a pipe with good ressonance will produce high torque figures at the ressonant speed. As Wobbly as described in over-rev and low rpm will be inferior to one pipe not so ressonant. The more ported the cylinder is, the higher the initial pulse from exhaust port down to the pipe and the more ressonant the system becomes. But the higher the dips in torque be as well.

The ressonant speed may be low rpm or high rpm for good power peak. Even inside the "powerband", or "in-the-pipe" you can move the torque peak around. If eventually the torque peak is right after the "pipe-hit" you get a hard hit followed by loads of over-rev and little power. For me this is a engine that is not a pleasure to drive, either more in high cc bikes, due the hard hitting power-band. But it sures lift the front weel easy...
That is what very shallow diffuser angles tend to do...

Now, if you eventually design a pipe that kills ressonace deliberately, the torque peak is not so high, but anywhere from 0 rpm to the peak the torque area will be superior. If the engine allow correct breathing, even in over-rev will have more power... Actually I´ve saw systems like Wobbly described, the vevey system, to get more peak power than a poorly designed, true ressonant, system. Usually there is a very flat, predicatable and wide torque curve. Is usually more easy to get the carburation right as well, without any flat spots.

Does the flat plate in the pipe has some big bleed holes? If yes, the flat plate becames a natural "ressonance killer".

Does that make any sense?

[wobbly]

You missed the point I made that well outside the nominal tuned length rpm,the flat plate has virtually NO effect.
The long slow angle rear cone has a BAD effect, over a very wide band above and below the area where it does have the positive addition to the powerband width.
Thus the flat plate makes alot MORE power at the extremes of the useable range - it makes this power by doing nothing,and or killing resonant tuning as mentioned above.
The plate in the kart pipe was a square - the pressure bleed rate was done thru the gaps.
And yes the Vevey sytem helps to smooth out big variations in the fuel curve - my first kart pipe had a "proper " long rear cone with no mid section, and it was impossible
to tune out the very rich/lean spots even with all the variables available in the pumper carb.

The Vevey design is a generic name I believe, like Biro pens.
The drawing is not a good indicator of relativity - here is a pic of the fastest kart pipe on the planet, the floor squares are 12", and the holes in the rear cone are 1/8" - on varying
centres to widen the torque curve.
And no there are no generalities in the design process.It took me months of full time dyno, weld,cut,dyno weld,cut to develop the very best for the KT100, and that was
made somewhat easyer in that I had 10 existing designs as a baseline.
Now we have EngMod, that can model the whole system - it will take a year to learn how to use it, and a week to design an RD pipe.
2:1 header designs are a real compromise affair in that to work even 1/2 correctly they need an EPO near 80* - completely counter-intuitive and then super difficult to get
resonance to work positively for your end use.
One way to help is to cut the front of the pistons of the twin such that the Ex port is open with the piston at TDC.
This creates another Helmholtz system that works havoc on the carburation - but when that is sorted it makes a heap of very wide band power.

Yes I have done alot of work on Hydro outboard pipes - but I would have to stab you in the eye with a fork immediately after revealing the names.
But the only "mild" design work I have done is for that twin cylinder aircraft engine ( derived from a fan cooled snowmobile ) and that worked best with the Vevey system.

Killing overev is easy, wind in some advance past peak,crank up the com, use a very steep rear cone, use a tight stinger,use a combination of port timing and pipe length
that has NO superposition resonance past peak.
All will make the powerband drop heavily after peak power, either by lowering the pipe temp or reducing pipe/port efficiency.

[lodgernz]

Here is a pic of a "Vevey" type pipe as modelled in EngMod, and this system works supremely well in exactly the scenario you are looking at.
I made several for Yamaha fan cooled engines used in small aircraft, with a 2:1 header - tuned to just 6000 rpm.
They need a very wide torque curve to enable them to spool the prop up, and then overev when needed.
A very similar end use to pushing a prop thru water, and having trouble reaching planing speed.
Also a pic of the drone pipe as I called it - with a nice stainless racebike pipe for comparison.

Wobbly, is the "box volume" part of the Vevey pipe empty, or stuffed with muffler packing?
Enjoyed meeting you at Hampton Downs. Nice to put a face to the name.

[wobbly]

No, the rear tube is empty,the high frequency harmonics of the snap port opening are attenuated to hell by the holes
and the rear box volume.
The small stinger as such can have some packing, but in a back to back with the Kart Federation noise meter it made no difference to
the DbA reading at all so I never added any in the pipes I built.

Yes good to meet someone I would never have apart from participating here.
I had a major success in finally getting the 71Yr old teenager to agree to use tyre warmers - only because he was spitting the dummy about getting second.
Too far back in a 4 lap race to catch up once the tyres came in.

[lodgernz]

I had a major success in finally getting the 71Yr old teenager to agree to use tyre warmers - only because he was spitting the dummy about getting second.
Too far back in a 4 lap race to catch up once the tyres came in.

Feisty old bugger was riding like a kid. Great to watch.

[lodgernz]

OK Wobbly, I have to ask this, even if the answer makes me cringe:
Why wouldn't I use a Vevey system in my 50 and 91cc buckets that need lots of midrange rather than peak HP?

[wobbly]

Because the system reduces the peak power dramatically,and the only applications where the huge increase in low rpm power and bandwidth is of
any use whatsoever is direct drive - no gears.
The KT100 needs to be able to haul off a hairpin at 8000 rpm and then spin to 16,000 to be able to only use 1 gear.
In this case the torque multiplication of the very short gearing enabled by the peak rev capability makes the system workable.
With a bucket ( basket ) case you have a pile of gears to play with and only need to find the best compromise between powerband width and peak, to enable the least amount of gearchanges per lap.

[lodgernz]

Thanks Wobbly. Clear now. Had to ask.

[morini155]

Great thread, very useful information about exhaust design. My question is : the vevey exhaust type its aplicable to a fixed gear engine with centrifugal clutch or a conventional design is best?
Thanks.

[wobbly]

Clutch pipes only have to be used between the lockup rpm at peak torque, usually 10200 in a KT100 and max rpm of, at most, 15,000
on a sprint track, and 12500 on road racing.
Thus a normal rear cone works just fine as no large amounts of power are needed well outside the tuned rpm range ie at 8000 and or 16000.
I did build several test clutch pipes using the Vevey system, but just as I was starting to make serious dyno power, and beginning to be faster than the conventional
pipes from RLV and Nunnley etc in the USA, clutches were banned in NZ due the idiotic cost of maintenance and even costlier upgrades at regular intervals.

[Gigglebutton]

Thomas thanks, this has 2 B the best 2T tuning thread in the world .... ........