[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

What I was thinking about is if it charges for, say, 300V then maybe it doesn't improve anything because you will have lower voltage which could lead to more misfires.

I do agree that 1J would be  too much and probably 400V 1,5 uF is already enough (if you would be able to reach that at high rpm).

Ferrite has low conductivity (reduces eddy currents) and has high magnetic permeability so it should not reduce your magnetic field too much.
It is very commonly used in transformers so if you can find or make it I think that would be the way to go.

Yes you are right, but even charging more than what we already had it was no change in performance (I tested it on 1 engine, like I said before, not hard enough) I need more squish velocity to test this I think...

What I can tell you for sure is that I going to give it another try :)

I have some ferrite lying around from scrapping electronics, I am going to try it when I finish the axial generator (like the polini one, because is for street use, I need lights and other things) Thanks for sharing your knowledge and ideas with me, and your time, our most precious asset.

Happy Birthday Jan!

Replacing 400V/1.5uF by 800V/3.3uF would not give you more energy. Unless you change its charging method.
The capacitor should be seen as a tank. Having a bigger tank is useless if you don't fill it.

The spark energy is comming from the capacitor charging system. The capacitor and final coil are only "transformers of energy" from "continous low voltage" to " sudden high voltage".

What is charging it? If the charging system is limited in available energy, time to charge or current, the new capacitor would be charged at lower voltage (low level in your tank).

The final coil is working as a transformer to produce a high voltage for the spark, so the target is to charge the capacitor at same or higher voltage. You would have misfire if the voltage is lower.


Angelo

Thank you Frits, I had a very happy birthday

And we wish you a lot of happy birthday

I no longer know the correct place to post something like this (and regret having to do this yet another time!!).

My sympathies and condolences to the gallant citizens of France for the Bastille Day horror in Nice.  What absurd irony that the nation whose people have so long insisted upon individual freedoms for all should suffer these outrages.

I was hoping to get some opinions on a diesel application, specifically on the scavenging side of things. The engine in question is very similar to a two-stroke Detroit Diesel and features a supercharger and turbo so there is a lot of air moving through it. I've been contemplating the port design and if geometry similar to the RSA's could be a good route to go?

One could force a lot of air through the engine but scavenge the cylinder poorly due to the port geometry. This would by definition leave a lot of residual exhaust gas in the cylinder. Perhaps to a point that is detrimental to performance.

On the other hand optimal scavenging geometry could be utilized to move the exhaust gas out of the cylinder as best as possible.

Or perhaps a certain amount of residual exhaust gas would be beneficial in a diesel application as it would help warm the incoming air and fuel.

I'm leaning towards scavenging as efficiently as possible because I believe the temperature of the compressed air will be hot enough for good combustion and because fuel is being sprayed directly onto hot combustion chamber surfaces, both of which will aid combustion. Any thoughts or differing perspectives would be appreciated!

A small part of exhaust gas is generally used to réduce or kill the NOX. All diesel engines have now an EGR valve lay-out to do that because diesel run generally lean.
Dan

Jan or Frits. I know you dislike air cooled engines but I am building an engine for the World Champipnship vintage snowmobile class and I need some advice. The engine is a piston port 440 cc twin cylinder 59.6 stroke x 68.5 bore with 115 mm rods. It is a free air running on leaded VP c12 fuel. What is the maximum compression ratio should I target. I know the liquid cooled engines live with 16.5-1 but a free air would surely overheat with that much compression. I was thinking 13.5-1. The port timing is as follows: Ex opens 79ATDC Transfers open 115ATDC Intake duration is 194 degrees. Ignition timing retards to 12 degrees btdc at 9500 rpm. 9500-10,000 rpm is my target rpm. Carbs are VM44 round slides.

Howard Gifford a écrit:

Jan or Frits. I know you dislike air cooled engines but I am building an engine for the World Champipnship vintage snowmobile class and I need some advice. The engine is a piston port 440 cc twin cylinder 59.6 stroke x 68.5 bore with 115 mm rods. It is a free air running on leaded VP c12 fuel. What is the maximum compression ratio should I target. I know the liquid cooled engines live with 16.5-1 but a free air would surely overheat with that much compression. I was thinking 13.5-1. The port timing is as follows: Ex opens 79ATDC Transfers open 115ATDC Intake duration is 194 degrees. Ignition timing retards to 12 degrees btdc at 9500 rpm. 9500-10,000 rpm is my target rpm. Carbs are VM44 round slides.

There are two aspects to be considered regarding compression ratio.
The higher this ratio, the more the burnt gases in the cylinder expand before exhaust opening. This means cooler gases flowing through the exhaust duct, hence less heat transfer from these gases to the cylinder. In other words: a higher compression ratio yields a cooler cylinder!
But the pistons and combustion chambers of aircooled engines are unavoidably hotter than their water-cooled cousins, which increases the risk of detonation. This severely limits what you can do with your compression ratio. Use a relatively rich mixture (that will give you some 'internal liquid cooling') and an effective squish, which will speed up combustion.
Fast combustion has a twofold effect: less detonation risk and less heat transfer to the surrounding metal.
A 13,5 ratio may work but I would prefer 12. This lower ratio may even give more horsepower.

Probably not the place to post this, feel like a tadpole in a lake full of sharks but what the hell!! If it's only way to get those in the know's attention.

Erm, so I'm a massive noob who hasn't a clue what 98% of what I've read on this thread was about, but want to learn how to port my RG125F (road use LOL), could someone advise me on a the best kind of dremel carbide/diamond/polishing kit I could get, preferably not silly money? if this is to be deleted could u advise me where to post it? thanks *skulks off out of Rossi's pit garage red faced*

marlow a écrit:

     but want to learn how to port my RG125F (road use LOL), could someone advise me on a the best kind of dremel carbide/diamond/polishing kit I could get, preferably not silly money? ...

Hi marlow, have a look at dental burs, e.g. on ebay.

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how are they so cheap? Thought diamond cutters would cost alot. You'd think there'd be a perfectly made kit for everything u need to for port barrels eh... What are the names of the handhelds that drive them? Only things I'm finding are big fat things unable to get down bores etc...

edit: ah I didn't realise the link had good info on it ha thanks alot

marlow:
Here is a link you should look at.
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I've used 3 of these over the past 45 years. They really work well.

His prices are ridiculous when you compare with $15 dentist kits

The prices are NOT ridiculous. Some of these units are NAKANISHI'S , the very best quality in the world. NSK made. Superior Japanesei industrial quality. If you want to go for cheap Ch....e junk that does not last at all, just proceed. Before making a comment please use your brocking fains ( if present) and do your home work, my dear pommy friend

I'm sure they're WORTH the money (to rich pros not piss porr novices looking for help and receiving very little) I didn't say they weren't. When the pioneers of 2-stroke tech are talking about using cheap dental tools then I assume they don't spend this type of money on cutting ports. I could be wrong. cheers for the insult though. Aren't the Dutch meant to be passive? What did you use as a beginner? Or were you born into a rinking stich family? Attitude suggests so :)

As a rule of thumb , one get what he gives , and going that way you may gonna get nothing more here



.

(Sorry, duplicated advice given above, don't know how to delete this)

Jan, I think you mentioned before that you made a radius on top of the exhaust port on the Aprilia cylinder, correct? How large shall I do this radius on a typical 125cc cylinder, something like 2-3 mm? Of course this would change the port opening timing, so I need to lower the port roof a bit, right?
Juergen

Jan, Frits or anyone who knows :

who was the first to come up with the idea of putting the rotary inlet disc behind the cylinder ? I ask because I came across a picture of a similar KTM (125 ?) in a dutch magazine from july 1982 (no, not yours Frits, but in "Motor", but after going through a similar decade of "Motor" and "Moto 73", the 73 was clearly my favourite ) :

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Jawa did the same in 1983 on a 125 cc motocross experimental engine, it seems that your picture JanBros show the first engine with such a system back in 1982.

Rotax used also such a system on its engine type "454" I don't know the year.

The interesting point is that CZ patented this idea back in April 1960..

Here is the CZ 125cc MX engine with rotary valve.     Could well be that this is the same engine as the Jawa that was previously mentioned.

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Exactly, here is CZ' s patent dated 6 April 1960.

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