Hardcore Biker
Excuse my misconception then.Originally Posted by SwePatrick
You sure know better Frits.I was thinking about high-er header/baffle angles and port timings. Wouldn't those add peak power at the expense of power spread?
Forum whore
No.
Port timings and pipe shape of a state of the art competition two-stroke are just that: state of the art. I think I already tried to explain why steeper cones and higher port timings won't do any good. I just can't find it back (silly search option!) so you may have to do some searching yourself.
Hardcore Biker
Is that where you explained that and why the ideal exhaust port timing is about 190 degrees?
Was worth a crack
SwePatrick, you seem to be taking on thoughts, advice and general ramblings as personal attacks. Im not sure why but I am sure it will limit what you can gain from this thread/forum.
Forum whore
I think we are getting lost here due to misconceptions of approach.
If you take a RD250 and lift the Exhaust 3mm it will narrow the powerband and raise the peak power.
Take a RSA250 and raise the Ex by 3mm and it will make less power, alot less.
Same with trying to use steeper cones, the RSA approach pushes the limits of energy being able to be used to increase the charging and trapping efficiency.
Combined they create a very high Delivery Ratio, and I would say there were very few avenues left to explore that would increase the current value.
If your engine hasnt got SOTA anything then sure, making any changes that move toward the RSA system will be a good thing.
But thinking that simply carrying on that approach to the extremes is faulty logic.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Hardcore Biker
Yeah, I realised that after going back and seeing the word 'racing' in Frits' pre-previous post. He meant that 'state-of-the-art racing' two stroke.
The thing is most of us have little to no access to materials, experiments and parts of this perfection. (I skipped the 'knowledge', thanks to you)
Forum whore
132cc 40 crank hp 1/8 mile racing moped ..... it should be possible, anyway I like the idea.
Forum whore
Ha Ha he really told you Green!
Weekend cruiser
OK, firstly please forgive me if this has been spoken about here before... I have searched and havent found any references to it... nor do i recall reading about it here, but maybe i have missed it.
Several years ago i was rebuilding a friends 2007 RM250 MXer which was previously used by an Australian offroad champion. The engine was incredibly strong, possibly the fastest 250 I have ever ridden. It had great bottom end and revved to the moon without any hesitation. When I opened it up the engine was essentially stock other than a crude angle cut along the exhaust port roof at the bore edge... the angle was close to 50 or 60* and was slightly radiused into the port. I forget the stock exhaust opening but the angle was probably 3-4mm high and raised the duration to the mid 190's (196* rings a bell but dont quote me on the figures as i wasnt in the habit of keeping good notes back then). Overall it was done in a very rough manner but it seemed to work incredibly well and i spent a long time thinking about the effect it would have until i eventually forgot about it before really coming up with any answers.
I was recently re-reading the entire pit-lane thread on the RSA125 an noticed a brief mention by Jan Thiel of the radius that the Aprilia cylidner has at the exhaust port roof to improve flow... there are also two differnt durations mentioned for the RSA exhaust, one is 202* the other states "196* without taking the radius into account", or something to that effect... I instantly remembered the crude RM250 mod and have been thinking about it ever since. To be honest i can't fully explain the effect of the radius... I think increased blowdown and increased flow out of the port but how would the leaving and returning exhaust wave act??... Hmm, still thinking about exactly how the radius would act.
Going by the RM i rode it seemed to keep the stock bottom end and add significantly to top end and over rev...
The other day i tried to sim it using Engmod. I started with a stock 2012 KTM300 file and raised the exhaust port only by 1mm, 2mm and 3mm... the graph shows the stock and +2mm power curves and if you combined the best of both lines this is pretty much what i felt on the RM... the +1mm and +3mm graphs are intuitively obvious...
I have also seen some patents relating to this idea but no explanation as the the exact effects it has.
Has anyone tried a back to back comparison between a 'standard' port and a radiused port to explain the real world effects it has?
Once again if this has been spoken about before then just ignore this and ill retreat back into my cave...
Hardcore Biker
I don´t think i do.
What upsets me is that people are reading my posts as the devil reads the bible.
And that expression 'geez' is to me an expression we use in Sweden when people are really really dumb.
I do not judgement people until they have proven themself dumb.
But in certain cases i might reconsider my rules from here on.
I´ll tell you a little bit of my 'history' and where i´m coming from to clearify that i´m no rookie:
I´m born 1970
started to tune my first moped, a Puch 'florida' at 12years of age.
I got that to run at the impressive speed of 40Mph, not bad for a guy that wasn´t even a teenager.(and only tuned 1hp products)
At 13years of age i ported and flowed my first FORD V4 heads.
Those became running so good that they were used in an Rallycar(SAAB 96)
Then it became a Zündapp, at 15 years of age, tuned that one to the point where the std conrod couldn´t take it anymore.
It revved REALLY hard with my bored out BING22mm carb, (bored out to 24mm)
this was 1985.(with homemade pipe)
Several engines has passed my fingers since then.
Snowmobiles,Rallycars,Offroads, all with good results.
In latest 10years i have been concentrated to port and flow different dragracing cars heads.
Often Audi 5cyl 2.2litre.
Which i have tuned to about 1100hp in engine.(Exactly 1132hp)
And often with MUCH broader powercurve than others.
I had myself an Opel(vauxhall) Kadett GTE wich i had converted to 4wd with an specially built turboengine from my theories.
This was quite cool,, i settled for about '700hp' as maximum and then finetuned everything to work as good as possible.
This ended up in the most hard running 2.3 litre(4cyl) engine i ever driven.
full boost already at 3000rpm, and had it all the way up to 8000rpm.
Boost was almost instant, no lag, at any rpm between 3k and 8k.
Latest acheivment is an Audi 80 quattro 1984 wich had a topspeed of 214.2Mph on standing kilometer,(1000m)
But somehow i got tired of all this hogging out 4 stroke heads, so i picked up 2stroke tuning again.
Now with skills i wish i had when i was 15 years old.
Through all this years of tuning, i have never used a flowbench. i often have to 'fight' with internet trolls that people CAN be born with talent, but i´m always loosing the keyboardwar *lol*.
With that said, i just wanted to say i got about 30years of experiance in enginetuning in my spine.
Rgds
Patrick
Low personal B.M.E.P.
Relax Patrick, you're not under attack....The Kiwi sense of humour and some of our colloquial expressions are often hard to interpret...
Frits seems to have it covered though - I hear he may have family here in NZ which would help.
With your background in performance cars you'd fit in well here in NZ, it's a large part of our culture.
Just be thankful it's not an Australian site...
Carry on the good work.
Hardcore Biker
I´m calm.
But i know of experiance that many people reacts strange when a 'newbie' on different forums is waving the big hammer.
I just wrote the last post to clearify that i am not dumb
And this thread with Frits many many tips and pictures have made me more certain of my work as i can see a lot of similar thoughts and similar ways to design different things on a twostroker as my own ways.
Rgds
Patrick
Hardcore Biker
Could you please tell us more about this radius, maybe draw a picture so I can understand it. Thanks.
Forum whore
I have just completed a back to back test on the Ex port radius in a TM 125 kart engine.
The cylinder from the factory was a special "tuned "expensive part number, and I was given a stock one to modify.
For sure the two were very different, the stock one being alot lower timing.
This was fortuitous,in that it enabled alot of room to be used to move ports.
First test was the stock cylinder with the main EX at 194, I put a big radius on the roof giving effective timing at 196.5 ( the trick cylinder was the same at 196.5 )
This instantly picked up power everywhere from 8000 to 14000, with alot better overev power, being 6Hp up at 14000
The next test involved dropping the cylinder,removing the chrome and regrinding the ports to the reverse stagger layout.
The A port being the lowest, to allow alot bigger Aux ports.
The main Ex port now opened around 192,with effective at 195 but the Aux opened at the same time, giving better blowdown area, as well as the flow enhancing radius on all 3 ports.
With the reverse stagger giving better transfer area ( as the B,C ports being high with alot of width compared to the previously high A port ) the engine now made 2 Hp or more than the factory trick cylinder
but was now 8 Hp up at 14000 and gained 400 rpm of usable overev, as previously it dropped dead at 13800 on track.
This setup proved to be quite insensitive to jetting and timing changes, allowing alot more static advance giving much better off corner power without killing revs as this would normally do.
Thus the enhanced blowdown flow of the radius at low port openings,allowed those much lower timings to be used effectively, enhancing power everywhere, but most importantly in the overev,where blowdown is most needed.
Frits is right when he says that the Italian factories are 3 years behind,as they still havnt started to use much of the technology developed at Aprilia even now.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Weekend cruiser
Thank wobbly, very interesting info... Seems my bum dyno wasnt telling lies on the RM. I'd love to do a series of tests of radius vs different port heights to determine a loose relationship between radius and 'equivalent' duration (based on normal right angled ports)... I guess it gives the BD of a high port but does the exhaust system more or less act like a lower port setup giving improved spread?? Maybe with the right port durations (similar to the aprilias) it allows the superposition effects of a ~19X* port (and exhaust) with the blowdown advantage of a ~20X* port for extra overrev. I'll keep thinking... and testing!
Out of interest when you dropped the cylinder in the second test did the port floors end up below the piston at bdc? And if do did you bother correcting this with epoxy to avoid flow separation and improve cooling?
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