Power tuning the Excelsior triple

[steven mandell]

I am looking for all information that would allow a wide band of highest power to be reliably extracted from Excelsior triple engines.
Al has come forth in typical fashion with very pertinent suggestions as to adding a tickler to the center cylinder's carb, as well as grooves along the sides of the piston for helping hold on to same, so as to lower the risk of scuffing a piston on long downslopes that provide little cooling fuel to the cylinder that is devoid of a side breeze.
Use of a fan focusing on the center cylinders head dome is an obvious to do .
Al also suggested having the crankshaft indexing and consequent balance checked, as it is subject to user indiscretion.

As far as I know, there are none of the newer innovations in 2 stroke technology present in this engine.  I.e. no rotary or reed valves, but I believe that expansion pipe exhaust tuning was in its infancy in the days that these first came out and were raced.
I therefore wonder what wonderful effects of exhaust system supercharging effect combined with  appropriately involved modifications of port shapes and locations, as well as possibly different piston crown configuration and possible other improvements could be effected through the vantage point of an additional 50 years of two stroke research and innovation.
As Al pointed out, the Dynastart's constantly engaging brushes, as well as considerable inertial mass and the crankshafts sections only being held in proper index by tightening nuts, argue against the typical narrow band of power at highest rpm approach.
However, I believe that an expansion chamber and port configuration could be chosen to provide its maximum enhancement at mid and lower rpm ranges just as well.  The peak horsepower always being a product of the multiplication effect of highest rpm, means that the highest theoretical power output would remain unachieved.  But better to have a more wide and useful power band, with less tendency to self destruct- especially when street use is the desired outcome.

[AndyL]

Really excellent book on Two strokes-

http://www.dragonfly75.com/motorbike/2StrokeDesign.pdf

Very technical, but a lot of valuable information in there I haven't seen elsewhere.

[richard]

hi steven ,the twin engine that i sold apparently had rare " sport" pistons they had 2 or possibly 3 extra grooves around the piston similar to ring grooves . how this made it sporty i have no idea - i am sure others would . i imagine it would be nigh on impossible to buy any now though -  my memory was at fault , i have found a photo that shows the grooved pistons they are much lighter than ring grooves and i now think they ran the whole length of the piston - but why ?
sorry making a meal of this but i found my last and final photo that might help - blowing up the last pic shows the grooves quite clearly and i hope helps i  will pm you the berkeley engine guru's address he MAY help you ? it was him that explained to me about the " sport" pistons

[Big Al]

Used together with a bevel edged bottom of the piston favouring the cylinder it hold more Fuel/oil mixture close to the interface between piston and barrel. Thus both additional cooling by evaporating charge, and by the extra oil left in contact with the metals increasing lubrication with no need to increase oil to fuel ratio. So 'sport' in that those were for extra revs and a darned good thrashing over and above the standard pistons, at least.
I believe these pistons are no longer available, and would need to be converted from standard by machining. I do not know if the porting is different. They are what I was telling Steven about and, as I understand it, standard fitting for the triple mid cylinder.

[Rusty Chrome (Malcolm Parker)]

I guess you guys have already read this. "Tuning the Excelsior Talisman 328cc and 492cc Engine"

http://www.pearsy.co.uk/Manual/BerkeleyTuningNotes.pdf

[Big Al]

Not sure I ever saw that doc. But then I never wanted to tune my Berk. However, lucky someone has published it. You no longer have to Berk in the Dark, as it were. BEC produced a lot of these fact sheets over the years. A great resource. Thanks.

[steven mandell]

Thanks Malcolm,
I read through it all with interest.
A few considerations that remain to be dealt with:
1) These are the modifications that were in vogue some 55 years ago when expansion chamber, and many other technologies related to two stroke performance were essentially not discovered yet.
2) Drawings and descriptions are certainly helpful, but I would feel a lot better seeing pictures of finalized modified parts, before I would feel secure enough to go merrily filing away any irreplaceable original metal to the degrees proposed.
3) Similarly no mention is made of modern ignition systems that can incorporate both advancement and retardation of spark timing, as the hardware did not exist for these engines to do this at that time.  Now a days it is known that higher performance can be wrung out by finely tuning spark timing to vary through both retarding and advancement to differing degrees depending on engine speed / loading, and there are electronic ignition systems available that allow one to accomplish this whilst doing away with troublesome contact breaker points.
4) All the advancements in performance technology probably need to be considered and decided upon as a package deal, as I consider it most likely that choice of one option should effect the viability of other options to correctly coordinate with it in a most effective manner.  E.g. The supercharging effect of an extractor exhaust system can be so influential, and variably tuned to produce more h.p. at differing engine speed ranges, that it is hard to imagine that this variable tuning strategy wouldn't need to be decided upon before performing many of the porting and piston modifications proposed.

[steven mandell]

hi Steven ,the twin engine that i sold apparently had rare " sport" pistons they had 2 or possibly 3 extra grooves around the piston .
My last and final photo that might help - blowing up the last pic shows the grooves quite clearly and i hope helps i  will pm you the Berkeley engine guru's address he MAY help you ? it was him that explained to me about the " sport" pistons

Thanks Richard
This is just the kind of visual proof that I need, in addition to exacting specs,  to feel secure enough to make irreversible modifications on possibly non replaceable parts.
Unfortunately the email address of the guru that you p.m.ed me still isn't allowing me to establish a connection with him.

[steven mandell]

Really excellent book on Two strokes-

http://www.dragonfly75.com/motorbike/2StrokeDesign.pdf

Very technical, but a lot of valuable information in there I haven't seen elsewhere.

641 pages!
I asked for it, and now I have it...too much information.
I will make an attempt to glean through it all, pausing on points of particular pertinence.  It does look interesting.
But probably would be best advised by someone who has already sucessfully applied all the best and most appropriate modern strategies to the Excelsior Talisman triple-  if indeed this has yet occured.

[AndyL]

It makes excellent bedtime reading! 

In all seriousness, that book has all the theoretical material you need. A thorough understanding of unsteady gas dynamics is needed if you really want to make informed choices on how best to tweak an engine for power.

Sadly it's also a real brain burner.

If you want to have a go at engine modelling, Lotus supply a free version of their engine sim tool. It's for single cylinder engines (handy for bubble cars and other micros with single pot engines), but it will work with multi cylinder engines if they use discrete carbs/throttle bodies and exhausts (e.g. no shared plenum's).

https://dl.dropboxusercontent.com/u/26682374/lesoft/LES_insert.pdf

https://dl.dropboxusercontent.com/u/26682374/lesoft/freeware_software.exe

https://dl.dropboxusercontent.com/u/26682374/lesoft/freeware_documentation.exe

A tool like that was the stuff of dreams for engine designers back in the 50's.

I had a go at modelling the Isetta engine in it. It came back with 15hp output- I didn't add the restrictive intake and exhaust system, which I reckon must cost 10-15%, so it's pretty accurate.

[Big Al]

Two stroke tuning is a course in applied physics. Very good for the grey matter. Even a computer is really only a tool to shortcut modelling of differing ideas. The human brain still out performs the machine, if it is allowed to. Trouble is often it is the owner of the brain that refuses the challenge.

I am tempted to study the book. I have a similar tome on forced induction. A far more complicated matter than it looks for optimum returns, but a possible mod for the amateur non the less, as it can add huge increases in engine power delivery, even if it is not greatly efficient. It all depends what you are trying to do, of course.
 
Does the Lotus program include two strokes? Not seen this. My computer bud will be interested as he likes these diagnostic type programs.

Fiddling with Sachs and Heinkel, it is clear that Carb technology has improved. Fuel has also changed its spec. So some mods there. Matched with some refinement in induction tract and you have immediate improvement without even going inside the engine itself other than the head off. Ian found some 2 2/3rds BHP on the Sachs, but crucially over a longer rev range. It was made available as a bolt on kit. That equates to an increase of near 25%. The mainstream Schmitters rejected it. Few more kits are available, if any, then that's it. Interestingly these are probably mods the factory would have done had they carried on trading. This does not have to mean the car is faster, but it would be more tractable, climb better and therefore its a to b times greatly improved. That drivability given a better brake performance, again increases the potential of the KR200 and brings it into focus as a genuine option for use. However it does not resolve the weak clutch and small gears which are going to wear faster in that application. Ultimately only an engine change can remove those issues and a fifth gear is the obvious addition. So we have John Bannell's car as that logical extension, adding a few more cc into the bargain.

I am not sure such a track record exists for the Excelsior Triple. We will have to see what turns up.

[AndyL]

Whilst the human mind will out perform a computer in terms of imagination, computers are experts at performing calculations over and over again with perfect accuracy. Something the human brain isn't so good at, and something you really need to do when working out optimum engine parameters.

It also has to be backed up with dyno testing, which gets expensive.

The chap who wrote the book I linked to was one of the best authorities on engine technology in the world. he consulted for major companies and backed it up with practical application too, so it wasn't all algebraic equations.

He also wrote a great book on four strokes (which he was less keen on), although much of the underlying theory is the same.

The Lotus program works with two strokes as well as four strokes, compression ignition and spark ignition. You can also add things like turbos and superchargers, so not just restricted to naturally aspirated.

[AndyL]

The biggest improvement to two strokes is direct injection. Totally transforms them, and massively improves torque- tests showed about 40% improvement over carburettor based engines, and with improved economy and clean exhaust.

Being able to inject the fuel once the exhaust port is closed is a massive advantage. Wouldn't be an easy conversion though, commercial units are thin on the ground, with much of the development work either gone into small displacement engines (e.g. Aprilia SR50 Ditech) or restricted to marine engines or skidoos (Mercury, Evinrude and Rotax).

[Big Al]

In relation to Sachs, the record breaker was meant to give 17 bhp. That will have been more via revs, probably, as we are talking prior to modern equipment. The tuning used was never disclosed officially. The engine failed not long after 24 hours. However it had done its job. So a standard engine offering 15.5 bhp sounds like big trouble to me. One mod saw a Husquvarna 400 barrel mounted onto a Sachs bottom end. This was a powerful unit and could take out a Tiger. Unfortunately the torque was so great it sheared the primary gear layshaft.

Other engines will be different. All have their weak points. Retrofitting power is a tricky game and no amount of knowledge can be enough. 

[AndyL]

Here is an article that some will find interesting reading- http://www.jawamania.info/Files/tech/223903/Design_of_a_Direct_Injection_Retrofit_Kit_for_Small_Two_Stroke_Engines.pdf

Another-

http://www.skyshorz.com/university/publications/Gitano_04SETC89.pdf

and one more-

http://www.orbeng.com.au/technical-publications/464-2001-01-10-siat/file.html