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Thread: ESE's works engine tuner

  1. #26326
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    Re the GRM case volume - as I have said a dozen times I have never been able to get better power going under 1.3 case ratio with a reed engine.
    Any bigger and you have to run the reeds so soft,they loose control at higher rpm and power drops - the exact opposite of what a big case should be capable of.
    In a KZ10B TM kart engine I cut 5mm of the reed face on the case.
    This needed stiffer reed backups to get the power back, but that lost too much mid power capability.
    Adding a 10mm spacer ( making the reed 5mm further out than stock ) needed the reeds so soft that the small amount of mid gained
    from them was completely lost by a huge drop in overev power.

    Re the KTM exhaust duct - yes they are stupid huge and adding ears to try and promote the Aux blowdown flow is very overwhelmed by the fact that
    you have just made a huge power loosing duct, an even bigger liability.
    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.

  2. #26327
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    Quote Originally Posted by jasonu View Post
    How does a company like KTM with presumably huge resources and cash get something like this wrong?
    To be fair, they may not get it so wrong, it's a auto-clutched direct driven motocross bike for 8/9 years old kids. Most minis seem to have a huge exhaust duct, including 85's

  3. #26328
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    Quote Originally Posted by jasonu View Post
    How does a company like KTM with presumably huge resources and cash get something like this wrong?
    Quote Originally Posted by dark art View Post
    To be fair, they may not get it so wrong, it's a auto-clutched direct driven motocross bike for 8/9 years old kids. Most minis seem to have a huge exhaust duct, including 85's
    KTM have no real competition in the mini MX market
    The older Beta powered KTM50's 02- 08 were actually faster in a straight line drag, but slower where it really counts arround an tight MX track.
    The 09 onwards ones with KTM's own engine however had a clutch that was much lower maintainace, which is a boon for MX dads.
    AS no engine mods are allowed in most kids MX, its irelevent if moding the engines vex duct makes it faster.
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  4. #26329
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    Quote Originally Posted by jasonu View Post
    How does a company like KTM with presumably huge resources and cash get something like this wrong?
    and if they been lurking around here like some have suspected, then theres no excuse for getting anything wrong. heres what I think. theyre 250 engine has been around 45-47hp for a lot of years and really you don't want more than that for motox so why spend a bunch of time with the ports, if anything I think they been trying to smooth it out, mostly with crappy head designs like what they did in '14 when the put a huge radius on the transition from band to bowl. I think that head went in the scrap pile the following year because they have a new design now. its seems theyre more focused on mainly suspension/chassis and rightfully so. they have been doing some work on making the cooling system even more efficient which is never a bad thing but the ports in the very newest cylinder doesn't look much different than years ago
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  5. #26330
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    Looks like KTM knew a decent head design back in the 80's;
    http://www.ebay.com/itm/KTM-250-Cyli...5Y8RZ7&vxp=mtr

    http://www.ebay.com/itm/KTM-250-KTM2...1Yzuxq&vxp=mtr

    Maybe the marketing department had a different idea later on..

  6. #26331
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    Quote Originally Posted by wobbly View Post
    I will be logging egt and deto level in acceleration testing at the same rate as the engine is run on track.
    Its my opinion as well that a shorter duct ( thus longer header ) would indeed make the header temp react faster.
    But is that what is needed.
    As you exit the corner at well less than peak power rpm, a cooler pipe will for sure give a wider dynamic power range, and its thus my belief the duct should be longer
    due to this effect.
    I have already track tested this by in effect cooling the back of the spigot by allowing water right around the duct and up to the flange back face.
    I also concurrently cut Aux ears right thru the spigot, so the drop in track time by 3/10s cannot be attributed to one or other of the changes directly.
    The Aux ears did not affect low end power on the dyno at all, but on track the driver, and the datalogger said it hooked up and drove out noticeably quicker - as well
    as the big increase in overev power the dyno showed conclusively.
    The pic shows the ears, and the slots.The red line is the new duct exit being cast at the factory now for testing as well.
    with the ktm 2wheeler mostly finished I reckon ill start back on the twin that's been sitting in the corner for ages. added my own exh cooling and a wee bit more material for large aux passages . its got a 4spd clutchless gearbox with manual 6th and 1st gear removed. crankshaft is skf roller bearings all the way across with ktm rods. should be a fun time
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  7. #26332
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    Quote Originally Posted by wobbly View Post
    Re the KTM exhaust duct - yes they are stupid huge and adding ears to try and promote the Aux blowdown flow is very overwhelmed by the fact that you have just made a huge power loosing duct, an even bigger liability.
    Thanks for confirming my hesitations Wob. No doubt another reminder to me that improvements in isolation of other required factors often aren't improvements in a 2 stroke engine at all

    Quote Originally Posted by Frits Overmars View Post
    The standard KTM 50SX exhaust duct diameter is way too big, and so is the 65SX header diameter. Below left a standard 50SX duct, right and a sleeved-down duct.
    This is still a dry sleeve; a much cooler-running wet sleeve with extended aux ducts is on the drawing board.
    Attachment 331452
    As always Frits, you show your skills at being both very informative and very alluring. Thanks! I have to ask now, is that your SX50 cylinder? Please excuse my ignorance but was the duct machined out and a sleeve press fit into it? At least that's what my initial thoughts are on what a "dry sleeve" would be.

    I see the file name is from September 2013. Am I able to see more of the work done to it? If so, where? There's some limited discussion on pitlane on the SX50 but I haven't seen that cylinder before.

  8. #26333
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    Quote Originally Posted by wobbly View Post
    That then is the problem with the AM6.
    If you have holes in the skirt above the small end that connect the Aux and the A transfer,then it will run rich,and will not respond at all
    to jet changes.
    The seemingly rich mixture in the Exhaust is caused by the short circuiting, not by rich jetting, so you go leaner and nothing happens.

    A file I have of a fully tuned TZR50 that puts out 18Hp Crank at 13,000 with triple Exhaust ports and this has a spigot exit area equivalent to 22mm.
    This is 78% of the Exhaust effective area, and gives a Mach of 0.8 , absolutely fine.
    Going slightly bigger in displacement or making more power than this would put the exit velocity close to sonic, so yes this may well be an issue as well.

    The case com ratio is a very important element, guessing or not measuring it correctly isnt an option.
    PS - you have a worn out piston available, drill a hole in it.
    Sorry for a late reply. I wanted to reply with correct measurements and atleast some results..

    Crankcase volume, measured as accurate as possible (drilled a piston I could no longer use and filled the reedvalve with vinamold so it would be fully sealed) .
    It is 300cc @ TDC with the "new" cylinder (has slightly smaller transfer ducts than the previous one), so the crankcase compression ratio is 1.224.
    Too low, as you have said.

    There are a few ways I could reduce it.. but not much.. larger reedvalve could take away some volume but I don't like it (the current already has enough reed area..it is the same as KTM 65SX VForce 3), and filling the crankcase below cylinder skirt or shorter connecting rod (94mm to 90mm) so I would get rid of the 5mm aluminium spacer.
    The crankcases haven't been grinded that much, only transfer entries have been matched to the cylinder.

    The previous cylinder had a very bad quality nicasil coating. It started flaking after the first failed combustion chamber o-ring seal, and got in extremely bad condition while using it (couldn't find an used aluminium D50B0 OEM cylinder..this one was a copy cylinder, made in Taiwan).
    That caused loss of power too, of course. But so did the 2-ring piston with large 'holes' above piston pin (short circuiting.. you (wobbly) were 100% right about this to cause the problem).

    After I found an used D50B0 OEM aluminium cylinder (though it had quite bad scratches...of course the seller did not get me any good quality pictures, so I could have not seen them before buying), and did some minor porting (approx. 190 degress timing + large radius for the exhaust port and also radius for the transfer ducts..and got started porting 1 aux exhaust port and 1 main transfer port...until my 90 degree mini grinder broke, so I left it as it was).
    Then I did some testing. Didn't take long till the flywheel side crank bearing failed (probably was a 'pirate' bearing..because it failed so quickly), so I replaced both bearings (FAG 6204/C3 and 6303/C3 + new NBR70 oil seals (yes, I know, they are bad..and also made in Taiwan or China. No Viton seals were available off the shelf).

    Now I've reached 13,3hp@11,500rpm and max. 14,160rpm (on 4th gear, 6th gear it'll rev up to ~13,900rpm).
    This is a GSF Dyno result, and can be repeated. Previously the best result has been 13,5hp@11,500rpm.
    It has reached almost 14hp@11,300-11,500rpm too, but it cannot be confirmed 100%.

    I know the results cannot be compared to a real dyno.. but on dyno day it did 9hp on GSF Dyno, and 12,5hp on Fuchs dyno (ran way too rich).
    This was almost 2 months ago, outside temperature had been less than 10 celsius degress, and I had no time to adjust it on dyno.

    It is interesting to see, how much the piston itself made a difference and only small modifications.
    When I get a new 90 degree mini grinder, I can start porting the cylinder a bit more.. it is clear it's lacking mostly blowdown area.

    ----

    Something interesting I found during fixing a GasGas 125cc engine..
    It had problems with E98 fuel (gas), and produced very low power. On E85 it was a different engine (originally was meant for E85 fuel, so combustion chamber had less volume).

    It did 31,3hp@12,437rpm on dyno (running way too lean, because carb bowl got empty when 'riding' it on 5th or 6th gear at high revs).
    And max rpm was ~13,300. (quite a lot for an enduro engine)

    So, after fighting with multiple problems, I found out the carb (PWK38 air striker) had a bad seal on jet block and the engine sucked extra fuel from there (explained why it wanted a lot smaller jets).
    I couldn't get a new seal, because it was weekend, so I took my Keihin PWM 40.5mm carb and threw it in (some random jets, that I thought would work fine there) and emptied the fuel tank and filled with E98 fuel + Castrol Power1 (4%).

    After I got it running and idling, I went testing.
    Suddenly the engine had woken and had more power than ever on E98 fuel. About as much as with E85 fuel!
    (I had jetted it on previous carb to work fine on higher rpm's and got some power back)

    Best power I got on E85 + PWK 38mm was ~28hp@12,300rpm. On PWM 40.5mm + E98 max. ~28hp@11,400rpm.
    Previously on E98 + PWK 38mm only 20hp@10,140rpm (after jetting it) - simply had no power. These are GSF Dyno numbers.

    I could not belive the carb made such a huge difference.
    And I'm not sure if the seal could have affected so much.. because the fuel mixture was not too rich at high rpm's after jetting.
    Is it possible that a 125cc 2-stroke engine would actually prefer that large carburetor ??


  9. #26334
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    Quote Originally Posted by chrisc View Post
    As always Frits, you show your skills at being both very informative and very alluring. Thanks! I have to ask now, is that your SX50 cylinder? Please excuse my ignorance but was the duct machined out and a sleeve press fit into it? At least that's what my initial thoughts are on what a "dry sleeve" would be. I see the file name is from September 2013. Am I able to see more of the work done to it? If so, where? There's some limited discussion on pitlane on the SX50 but I haven't seen that cylinder before.
    Thanks or the flowers Chris. You are right, the duct was machined and the sleeve was pressed in. The cylinder isn't mine, it belongs to my friend Jan Schäffer (the German giant who wins 50 cc races). He is quite open about his engines and chassis, but he publishes most of his work on a closed forum, so I do not feel at liberty to show much of it here. But you may find some info on his company website https://langtuning.de/Shop2/Startseite-1 and on http://www.simson-rennteam.de

  10. #26335
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    Been there done that with Airstrikers.
    The stock 38 PWM will flow more air and make way better power than the same 38 PWK with Airstrikers.
    The Airstriker design is specifically designed for better response off low speed corners, but the mess it makes of the airflow down the venturi
    and into the carb body looses a heap of power at higher airflow numbers in the mid range to peak and beyond.
    Wouldnt use an Airstriker if you gave it to me.
    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.

  11. #26336
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    Quote Originally Posted by Grumph View Post
    Did you check for dribble at steep angles ? I mocked up my pair the other day and found that even with the tracts dead vertical there seemed to be no weeping from the pilots...I'll be using mine with the top covers pretty well horizontal - so back a bit from full vertical downdraft.
    Yes, I found the same, none of my carbs dribble on my angle jig, even at steep angles. However, I suspect they would in real life when braking for a corner.
    The TA carb is already at 45º downdraught with the float bowl perfectly level, so it's unlikely to dribble.

  12. #26337
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    Oh no!

    Quote Originally Posted by wobbly View Post
    Been there done that with Airstrikers.
    The stock 38 PWM will flow more air and make way better power than the same 38 PWK with Airstrikers.
    The Airstriker design is specifically designed for better response off low speed corners, but the mess it makes of the airflow down the venturi
    and into the carb body looses a heap of power at higher airflow numbers in the mid range to peak and beyond.
    Wouldnt use an Airstriker if you gave it to me.
    That's worrying Wobbly I use a 36 PWK on my 100cc bucket for the TPS and solenoid powerjet, Would the PWK Airstrikers be messing up the carburation on it?
    I take it the Airstrikers are these fences on the bottom of the bellmouth?
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    Compare Pornography now to 50 years ago.
    Then extrapolate 50 years into the future.
    . . . That shit's Nasty.

  13. #26338
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    Yeah I have 35 airstrikers on my 496 CPI . so? Snap end off with some pliers?

    Mind you its a roadbike which is why only 35s.
    Don't you look at my accountant.
    He's the only one I've got.

  14. #26339
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    Quote Originally Posted by F5 Dave View Post
    Yeah I have 35 airstrikers on my 496 CPI . so? Snap end off with some pliers?

    Mind you its a roadbike which is why only 35s.
    Its easy enough to grind off the ramps, but the PWM has a different intake bell shape as well and that is also able to be replicated
    so you get the performance as well as the PJ and TPS.
    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.

  15. #26340
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    Quote Originally Posted by wobbly View Post
    Its easy enough to grind off the ramps, but the PWM has a different intake bell shape as well and that is also able to be replicated
    so you get the performance as well as the PJ and TPS.
    out of interst what carb did nigel run an RGV TM mikuni or a Keihin shorty TPS Solinoid PJ.
    That's the other advantage of the TPS ELectirc PJ MX Kehin (ie 98ish KX125)they were about 25-30mm shorter than the av Keihin.
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

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