Forum whore
TZ or was it Thomas? whatever, on the ESE thread page 66 I think, one of them posted a link to a SAE paper from Yamaha that showed the sweep of the transfer passage was the second most important factor.Originally Posted by F5 Dave
And it had a significant effect on power and torqe, the larger the sweep the better more or less. Follow the link and the paper can be downloaded and printed out, its worth a look.
Forum whore
So who is the biggest dick then?
(Extracts From Wikipedia) "A study published in the September 1996 Journal of Urology concluded that average erect length was 12.9 cm (5.08 in) (measured by staff) Erection was pharmacologically inducedin 80 physically normal American men (varying ethnicity, average age 54). It was concluded: “Neither patient age nor size of the flaccid penis accurately predicted erectile length"
"Erect circumference was an average of 12.6 cm (5.0 in)."
"A study published in BMC Women's Health, surveyed women's preferences concerning penis size and concluded that width rather than length is a more important factor of sexual stimulation."
Great stuff mines bigger than average
Yes it sure is silly...... But ........ how do you measure up?
Bucket Racer/Crasher
from post #63
So. . . . . How did that crank work? I'm expecting a report of lots of vibration above idle. So much in fact that you probably wouldn't run it up to check power differences. I'm keen to know though.
Forum whore
Quite acceptable vibration actually....
42% factor..... not much, but very little I can do to change that (with-out Tungsten)
Small Frame Vespa engines are of course Rubber mounted, so that does help.
Of course like I said, I am trying to find minimum values for primary compressions, and how you increase the volumes of your crankcase (to lower the ratio) is up to whoever is doing the job (removing material from the cases is one option, but in this scenario is not really feasable, and since I wanted to lower the blowdown time of the transfers (by removing 1mm from the case faces) I had actually INCREASED the ratio, so removing material from the crank was my only real option)
If, as is (SOMETIMES) the case (depending on the cylinder and it's intended purpose) you need to space the cylinder up....therefore increasing the crankcase volume (and lowering the ratio) by default.....in this instance spacing the cylinder up was the exact opposite of what I needed to do.
Like I say the vibration level is totally acceptable (I am sure the rubber mounts are doing their job well!)
If it was a solid mounted engine, possibly it would be a problem.
The following attachment is the "first finished run".... (I previously posted a picture of a "plug and play" run ....16.8 PS).......Shortly (when the customer is ready) I would like to run a few degrees higher on the exhaust, and change to another exhaust (just for comparisons), as I expected a bit longer flatter peak power...this is quite acceptable, but that could well be due to the exhaust.
28mm dellorto PHBH28 (possibly the most basic carb on the market)
Prototype exhaust
Retarding Ignition
Port timing and primary compression ratio specs as per my previous posts
One big problem we have all found over here with exhaust designs is a resonance issue in the midrange, which took a bit of solving last year (the exhaust I used on this engine was designed to eliminate this (quite well actually), but it appears that it does come at the expense of the "length" (and amount) of peak power.
I am pretty sure with some changes to certain aspects of the engine I could run ALMOST the same dimensions as last years pipe, which has proved time and time again to have the most PEAK power (and longest spread), but unfortunatly required changes to engine set up that wasn't expected.
That will have to wait, as I have 2 more to build now.
But I am confident with the other exhaust system I would see 25 PS no problem.
It does also appear that I was correct in my thoughts that the high blow down times on the transfers was a major contributing factor in the poor performance of these cylinders, (by poor performance, I mean a narrow power band, and no bottom end to speak of, coupled with a surprisingly low peak power figure for an air cooled 125cc aluminium cylinder)
Which is most likely because this particular model of cylinder was "adapted" from a Kart sport cylinder, (which typically have blow down times approaching revs more like 15,000 RPM, as well as a narrow RPM range. Which clearly does not match the exhaust port height the cylinder was produced with,( the original transfer times would suggest an exhaust port time area over 200 DEG), which would then require "power valves" to be useable.
Basically, the transfer ports where too high, hence removing 1mm from the crankcase, then raising the exhaust port height to suit. I would still go a few degrees higher on the exhaust port, it clearly can handle it, as even though they are lowered, the blowdown times are still more suited to a slightly higher exhaust port.
If I was to attempt to make a lot more power (more like 28PS,), I would approach the whole job differently, but such an engine, while very exciting to ride, has proven to be less fun that a torquey engine. (particularly when you are limited in your available gear ratios)
But, like I have stated previously it would seem there is a direct correlation between:-
exhaust design, carb size, intended RPM range, available gear ratios , ignition design and type and primary compression ratios.
Simply "one set up for all" is not correct.
Change one (particularly exhaust design) and if all the others are unsuitable for such a design, then you will most likely go backwards, rather than forwards, and perhaps notice no change at all, when if the engine was set up correctly you would otherwise see tangible gains.
But I still maintain it is vital to put accurate values on all changes you make, as clearly there is finite values for everything you do, not a "more or less" attitude (unless you find it important to keep some values to yourself, in the interest of competition!)
Forum whore
This arrived in my email just now...... A very clever guy, a series of runs he did last week, same type of cylinder, (heavily heavily modified), now experimenting with a new exhaust..... he didn't say what size carb, retarding ignition..... Same crankshaft cutting as the picture I posted......
Quite a lot of work, (made 2 exhausts just for the testing) but the results speak for themselves....
now where's some dirt!
Woah that is crazy, you are getting within the realms of a RS125 engine there!
One thing I've been meaning to ask is what do you guys use these engines for? Is it just for rich scooter boys or do they race them over there?
Forum whore
While most of our customers are from Germany (at I guess the majority of these guys could be considered "wealthy", as to build an engine of this type complete with exhaust, carb, ignition, machining and labour is quite high, although some customers will save all year for an engine that will put out "more than 23 PS and 20 NM")
I do have a few jobs occasionally from France and recently England.
Predomanantly these are for the road!
(quite frightening really, but all pass the tough TÜV regulations, so are legal), but I now get more and more enquiries from guys who race them, and it is clear that for the A grade class, 30 P.S AND 24 NM is the standard.
2 years ago 20 PS was the standard, just goes to show how things improve with competition!
Bucket Racer/Crasher
Just looking at it I expected more like 70-80%. At 42% it would actually get better at the upper end, and further, of the engines rev range. You need to track down a bit of Mallory metal.Quite acceptable vibration actually....
42% factor..... not much, but very little I can do to change that (with-out Tungsten)
Small Frame Vespa engines are of course Rubber mounted, so that does help.
Forum whore
These big Hp Scooter motors are more than 125cc.
We need the cc's and Hp to make a comparison but from what I've seen, in realitive terms, Speedpros Bucket seems to be in the same ball park.
.
Hardcore Biker
42% REALY!!!!!
SS90 as cranks are traditionally balanced to 60-65% and your so fond of dumping on people maybe a "BOY" like yourself can explain how removing material from the big end area of the crank reduces the balance factor to 42%.
Me thinks you’ve got it wrong, and don't realy understand how balance factors are determined, which is surprising for a self confessed Ace Engine Tuner.
Forum whore
No, these graphs are from 125cc engines.
There are indeed 140cc (aircooled) engines (quite a few), the following graph is from one.........
However, they don't last very long at all (see second picture), as with the longer stroke cranks used piston speeds start getting too high.
Setups like this really are only for quartermiles, and parts like crankshafts, pistons bearings don't last very long at all.
It's just a matter of which one breaks first.
But like I say, 30PS 125cc aircooled engines are an everyday occurance in Europe now
A small few have 140 (some 150cc) 35PS 25NM engines
I think the reason so many clever guys over here get into it, is because with the tough (E4) emmission laws, there are pretty much no road legal "performance" two strokes allowed on the roads in central europe anymore (that will change in the next 5 years, I am certain)
The exception being any "classic" vehicle (which is totally exempt from emmissions and noise testing), so that provides a platform for tuning that would otherwise be impossible.
Yes, certainly 35 PS on a small frame Vespa is completely dangerous, they handle like turds, but it's the only vehicle you can ride that's been modified.
The best power is obtained from the "scootermatic" boys (huge industry), but as they are subject to emmissions testing, they can't be ridden on the roads and are limited to use at quartermiles.
Forum whore
Really? 60-65% ?
Maybe it's because I am on the other side of the world, but I was under the impression that 50% was the norm for such applications.
Is that not correct?.
The crank I modified was an "old school" designed "full circle crank", that are an after market part, designed only to increase the primary compression. nothing else.
In fact, full "circle cranks" completly destroy the balance factor, and the engines vibrate terribly.
The second picture attached is of an original crank (designed for disc valve), the other is a "full circle" (designed to be used with a "piston induction (reed valve conversion) cylinder.
Notice the amount of material around the pin? the other side of the crank is only like that, because it is used as the "disc valve" portion of the engine (quite different to a Japanese engine) if that was not required, the crank webs would be symmetrical.
Basically, the "full circle" cranks have a terrible balance factor, and in so far as tuning goes, they have proven their best use is only as a "blank" to enable you to make your own.
These where originally designed from the "old school "raise the primary compression", however, they raise it it 1.6:1
Original cranks are closer to 1.48:1
I'm quite happy with the fiqures I posted.
Remember that the "full circle cranks" are not original.
Forum whore
I got the idea these big Hp Scooters were bigger than 125 cc from the link you posted http://www.lambretta.it/eddy/edmonds.htm posted page 5 of the “Two-stroke performance tuning?” thread.
Where Charlie Edmonds talks about his 225cc 37Hp 07 BSSO Championship winning scooter and the “Vespa 180 VE Small Frame” tag on the dyno charts you posted. And amongst all the Scooter hot-up cylinders I’ve seen while following your Posts, they all seem to be “Big-Bore” and about 200cc or more and in the so called 30+ Hp range.
The 125 scooters you build, are they using the traditional 56mm bore or the more modern 54mm bore?
The Charlie Edmonds article was a very interesting read. I see he has trouble with heat in the air-cooled engines and this limits the power output. To help with cooling he uses air ducts and a Yamaha MX head with a head insert, I bet he wishes he had thought of using a copper head gasket/fin like Thomas, ESE’s Engine Tuner has.
Hardcore Biker
Or possibly from another Planet!!!
Hmmmm that full circle crank looks pretty much like most mid capacity Japanese 2-Stroke Cranks, but, what the heck, what would they know.
Forum whore
There is a lot of talk about "Balance Factors", folks how about putting some numbers to the talk and a small explanation about how they are calculated from someone who knows what they are talking about.
If SS90, FastFred or someone else can't do it I will ask Thomas to write something for us, he's bound to come up with something interesting.
.
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