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Post by rallyrrr on Aug 11, 2008 22:51:59 GMT -5
In my quest for more top end power from my modified Derbi Atlantis I decided to remove 1" from the belly (dwell,parallel section) of the Technigas Next R pipe I was using on the scoot. This action, of course, places the midpoint of the baffle (converging) section closer to the piston/exhaust port juncture. This distance determines the effective rpm at which the baffle produces its cylinder stuffing effect as the exhaust port is closing. The shorter the distance the higher the rpm at which the baffle "hits" and conversely, the longer the distance the lower the rpm at which it is effective. Rough calculations told me that this would move the operating point of the baffle about 1000 rpm up the scale to around 10,000 rpm.
What I found upon opening up the pipe were more opportunities to improve wave action. Specifically, there was a 1/2" overlap of the headpipe into the diffuser and expanded (mesh) metal lining the inside of the baffle. I summarily attributed the overlap to half-fast (or the similar word) assembly and the expanded metal to efforts to achieve sound deadening.
Anyway, I ground/broke the tack welds loose and removed the expanded metal (I found there was no overlap at the baffle/bleedpipe juncture ). Also I ground away the overlap of the headpipe using a conical rotary stone on an extension in a high speed electric drill. This overlap had to be affecting positive and negative wave action to a significant degree as they entered the headpipe. The expanded metal no doubt was fracturing pulses impinging aginist the baffle and thereby reducing the reflective sharpness and pulse strength of the return wave.
I removed the 1" section from the belly, rewelded the pipe and refitted it to my bike. There was a discernable increase in power throughout the rev range and at about 8000 rpm the engine smoothed out and really began to pull well past the mid tens. It was running out of steam at about 9500 before. A cop pulled me over and said I shouldn't be doing 65 on a no tag scooter!
The pipe, however, remains a weak link in my power system as it is of insufficient volume to produce good pulling in the 5000-8000 rpm range.
Other modifications beside the pipe mods include:
installed digital tach
replaced 25w headlamp w/35w
rollers drilled to 4.5g
yellow torque spring
lightened clutch shoes
Airsal 47.6mm T6 single ring kit
raised exh. port 1mm (approx. 180 degree exh. duration)
raised boost ports to open first by about 1.5mm
carefully chamfered and polished all ports
Top Performance carbon fiber reeds in flow-profiled cage
Delorto 21mm PHBG w/115 main
K&N air filter
No head gasket (Coppercoat only)
0.55mm squish
Removed oil pump (premix Amsoil 50:1)
Amsoil gear lube
93 octane
NGK iridium plug indexed
converted oil tank to auxillary gas tank
clear fuel hose
removed vacuum fuel tank valve
Gosh, scooter tuning sure is fun. Wished I still got 70 mpg though (40mpg now). She's up to 30 in about 100 feet though and almost wheelies on takeoff (ideal really) without pulling on the bars.
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Post by Karl on Aug 11, 2008 23:06:21 GMT -5
Rally, excellent write up and nice job on the Tecnigas Next R!
What do you suppose your compression ratio is now?
You'll have to post some pics when you get a chance. ;D
Karl
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Post by 90GTVert on Aug 11, 2008 23:09:53 GMT -5
Awesome. Glad to see someone that really knows the workings of a 2 stroke and enjoys modding. Even taking it all the way with the plug indexing. Sounds like a nice and beefy scoot you've got there. Pics/vids?
I always hear all this great stuff about the Technigas pipes. It usually comes from the general public, and the people that appear to be more well-versed in 2 strokes aren't impressed. Not that my MRP pipe is some gem either. I'd love to check out one of those high dollar Polini, Yasuni, Roost pipes that cost $5-700 and see just what it is that makes them so special, if anything.
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Post by rallyrrr on Aug 12, 2008 1:56:03 GMT -5
I don't know my compression ratio. I just know it is too high for all around driving. I melted a piston recently on the highway at speed going up a steep hill. The air was dry and cool. Haven't torn it down yet but it has no compression. This is not the first time I've done this but I've had issues with my rubber intake developing cracks, leaning out the mixture and well, melting pistons. They don't hole, just collapse enough to trap the ring in it's land causing compression loss. I need to have my combustion chamber depth increased into the head to maintain my 0.55 squish clearance and drop my c.r. Unless I stand the scooter almost vertically on its rear tire or remove the engine/tranny I cannot measure the c.r. using the burette/light oil method. I've seen evidence of detonation (pitting) on the exhaust side of my pistons. I am unemployed and money is tight so scooter tuning is on the back burner right now.
My scooter is not very pretty. It's been down hard twice and the once pretty chrome pipe shows it's surgical scars. I may try to post some pictures sometime though. It is a Red Bullet Special Racing Edition (cosmetic with checkered flag decals from the factory). It is an '02. I've had it for over three years. It's had a hard life under me. Almost 6000 miles. Had 800 on it when I got it.
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Post by lbo on Aug 12, 2008 10:52:03 GMT -5
Good write, thanks for the info. There is a video somewhere in internet land showing someone cutting up this pipe. Technigas really gets pounded hard over in the UK as general crap pipe. However one of the sites over there did a dyno comparison with several pipes, the Technigas Type R was right in the top-mid range in terms of horsepower out of about 10 pipes. Unfortunatly there isn't much to choose from here in the States for a Kymco engine..... would love to see LeoVance, Laser Pro, and some of the other better pipes available.
The "word" is the new Technigas RS II pipe is suppossed to be head and shoulders above anything else they have produced and will breath a lot better providing better RPM's as well. I am waiting for a distributor in Florida to get more in stock so I can order my upgrade kit (73 airsal t6, 19mm carb, said pipe) soon.
Good info, thanks for the post.
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Post by rerun2 on Aug 12, 2008 12:20:10 GMT -5
You are right, you should not be doing 65 on a little scooter!! Those things get squirrelly at anything over 50, and dang out right 'interesting' anywhere above that!! Great write up and it is obvious you enjoy doing the most to get the most!
Post some pics so we can forward them to your local po-lice!! ;d I probably shouldn't say stuff like that even in jest!
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Post by rallyrrr on Aug 12, 2008 12:41:38 GMT -5
With all due respect, sir, my Derbi is rock solid at these speeds. Not scarry at all. Thanks.  |
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Post by rallyrrr on Aug 12, 2008 13:05:00 GMT -5
My understanding about the Next R pipe is that it is really a 50cc pipe. I would love to design, cut, roll and weld my own pipe. I guess you might call this a pipe dream. LOL! Building a proper tapered headpipe, I understand, is pretty much a nightmare though and I would probably use the headpipe from my stock pipe or the Next R.
As a slight aside...when I had a really hard crash on gravel and badly dented my pipe a machinist/tuner in Texarkana suggested filling the pipe with water and freezing it to push out the dents. It worked pretty good but ripped a weld at one spot. You stroker dirt riders have probably heard of this though. Huh?
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Post by 90GTVert on Aug 12, 2008 14:45:37 GMT -5
Someone needs to make a DIY expansion chamber pipe kit, kinda like the kits you can buy for building automotive headers, with different tapered pipes and such. I don't even know if you can buy tapered pipes, unless you find them for some other purpose. One thing that I thought would be cool, but have not seen in scooter pipes, is a pipe with interchangeable stingers. I had one on a pocketbike and you could tune the pipe to better suit your needs by simply swapping out stingers. Very quick, worked well, and made the bike more fun in most conditions. Of course the pocketbike didn't need any silencer so it was a little simpler than it would be on a street driven scoot.
Never heard of the ice trick, but it makes sense.
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Post by lbo on Aug 12, 2008 15:37:20 GMT -5
the ice trick works on small RC tuned pipes for Nitro engines..... those pipes are aluminum though but I guess the same principle applies..... definatly easier to fit in the freezer too.
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Post by Karl on Aug 12, 2008 20:23:48 GMT -5
As a slight aside...when I had a really hard crash on gravel and badly dented my pipe a machinist/tuner in Texarkana suggested filling the pipe with water and freezing it to push out the dents. It worked pretty good but ripped a weld at one spot. You stroker dirt riders have probably heard of this though. Huh? Indeed I have! My bro-in-law tried it and his split at the weld, too. But it was a small split and nothing to fix. |
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Post by ashtonisdrugfree on Aug 29, 2008 20:29:06 GMT -5
technigas is mostly for all around pep. acceleration and what not. I've got a biturbo exhaust on a tomos targa lx and the top end went up about 9 mph over the technigas, but the accel is very poor, now.
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Post by motomech on Sept 3, 2008 5:43:05 GMT -5
From an archived post; <<<<In 1990, I bought a new Honda NS 50 with the intent of going racing. I had been eying mini racing, but I didn't want to go with a YSR, mostly because I didn't fit(6'0" and a svelte 170# at the time), but also I didn't think much of it's antiquated power plant. The project was inspired by an article I saw in a Japanese Mini-Moto magazine that some thoughtful person in Japan had tossed in a box of Kitaco big-bore kits I had ordered. The text was in Japanese of course, but the photos showed an stereotypical Japanese technician in a white lab coat standing next to two disassembled engines layed out on a bench. But the two engines were named in English, NS 50 and a CR 80. I was intrigued, and took the article to the local university's language department for translation. When I went back, the person who did it wasn't there, just a note that said, "no fire". Hummm... Well, I knew one thing though, the CR 80 was air-cooled and that nailed down the years down to a couple of mid '80's models. With the two engines layed out on my bench(minus the lab coat), it became apparent that there was a lot of interchangeability. The 80's close ratio tranny and internal rotor ign(including CDI) bolted right on/in the NS. The ported cylinder was bored to fit a KX 60 piston, which with the stock NS crank came to 57cc's. The class limit for modded 50's was 61cc, to accommodate the stroker YSR's. The cylinder head's combustion chamber was reshaped on a lathe, adhering to the 1/3 squish band rule. The squish was real tight, .010" to .015", if I recall right. All this came together real quick, but the carb and pipe took some development time. The first try was the CR 80 bits, because I had them. The 28 m/m round slide fitted ok, but cutting and rewelding the CR's up-pipe was a challenge. Lot's of carbon and I didn't have a wire-feed. Anyhow I got them on and while the Frankenpipe was not pretty, it worked well. Too well. The bike was a rocket from the git-go, until I seized it(ever notice that two stokes run best right up to the point they seize?). Attempts to jet it safe proved fruitless and I came to understand that the pipe wasn't going to work, It was too fat, creating a negative wave pulse that the carb couldn't deal with. Next try at a pipe. I ordered some cones from Air Cone and tried to make my own from scratch. Easier said than done as I discovered the problem that plagued all pre cad-cam pipe designers. To make the center cone the diameter I wanted, the cone angles became too steep and became counter-productive. At least the metal was clean and I could get some decent welds. With a serviceable pipe, it now became clear that the carb was too big and a 26 m/m round slide Mikuni was fitted..... .......I did meet a guy who built me a pipe, a beautiful hydro-formed number that really woke the motor up........ ........A Kiehin 28 m/m flat slide(PWK) was installed and when I finally got it dialed in, it was like adding a supercharger! It was in this configuration that I was clocked at 74 m.p.h.(By radar) on the slight uphill starting straight at the Streets of Willow track(It was never dyno'ed, I think 15 h.p. at 15.000 r.p.m. would have been close..... .....>>>>* Removing part of the center section reduced the overall tuned lenght of the pipe and may have created a "negitive pressure spike" that the carb can't deal with like the one I experienced by using a shortened 80 pipe on a 60cc. hence the seizure. When designing and building expansion chambers, I found it very difficult to change one aspect(cone angles, center section lenght, tuned lenght, etc)without adversely effect another tuning aspect. It's always a compromise, that's why I never had a really good pipe on that bike until I aquired that Hydro-formed unit. *Full post here; scootdawg.proboards59.com/index.cgi?action=display&board=general&thread=3067&page=1 |
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Post by rallyrrr on Sept 4, 2008 16:48:53 GMT -5
Mototech, could you explain what your statement means:
"Removing part of the center section reduced the overall tuned lenght of the pipe and may have created a "negitive pressure spike" that the carb can't deal with like the one I experienced by using a shortened 80 pipe on a 60cc. hence the seizure."
Thanks,
Reg
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Post by motomech on Sept 5, 2008 9:50:52 GMT -5
It's risky to generalize about specific results due to changing one aspect on an expansion chamber's design because there is a complex inter-relationship of all the elements, but...
Overall tuned length mainly effects the spread and intensity of the negative pressure pluses. Shortening narrows the period and increases the amplitude.
Decreasing the internal volume tends to move this scavenging effect up in the R.P.M. scale.
Intensify and focus this enough and no amount of taper on the jet needle can deliver enough fuel and the result is a momentarily lean condition.
This is exactly the dilemma the engineers at Yamaha faced with their World-beating TZ250 racers in the late '70's.
In an effort to achieve absolute peak H.P., pipe development though the D, E, and F models has moved from long, small diameter center section chambers to the hard-hitting "fatty" pipes.
Their brilliant and elegantly simple solution, introduced on the G(1980)models was the Power-Jet carburetor.
Utilizing the intense period of neg. pressure at the "mouth" of the carb., extra fuel is siphoned, via a sm. tube, from the float bowl, directly into the venturi.
This break-though helped the "Tuning Fork" Co. extend their dominance in the GP250 class well into the '90's.
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Post by w8tlftr on Sept 25, 2008 9:06:37 GMT -5
Pretty impressive info, I have to admitt this is pretty far over my head , I have an older version tecnigas next muffler non chrome, I set my bike up around the muffler , but cant imagine makeing mods to the muffler , very impressive. I am glad to hear some good things about a tecnigas muffler though, being where my scooter is from in Italy , they seem to hate a tecnigas Muffler, claiming its very cheap and not made to last.I was advised when my Tecnigas falls apart to get a Giannelli Reverse or a Giannelli Extra ,but this may best installed on my particular scooter a Piaggio Typhoon 50, now a 70cc Malossi, I understand that differant pipes have differant compressions and changes the engine curve somewhat. But just the same very cool post and informative.
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