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Everything posted by numbhands

  1. I have a bit of a noise issue with mine. If you are curious as to the effect of using a silencer similar to those on super bikes, why not pick up a cheap OEM muffler from ebay from say a gsxr 750/1000 and adapting it to fit your pipework? would give you an idea if the concept worked, allthough the resonant chanbers inside wouldnt be tuned correctly to damp all the noise from a big single. In theory a gsxr can would flow enough air for 180 hp on the 1000, so shouldn't plug up the engine too much.
  2. Hi there, just had a read through this, and from what I've read in the past a good result can be had from injecting water to supress detonation, but the volumes of water need to be be tightly controlled and proportional to fuel air/flow. With this in mind, have you considered setting up some a programmable ecu, along with fuel pump and injectors as per a fuel injection system, and then running a water/methanol mix? The only issue i could see would be if the fuel pump would suffer from running water (corrosion, lubrication issues). That way you would have a fully mappable water injection system, where you could closely control water volumes and injection timing at all throttle and rev conditions. Just an idea.... I also have a vague memory of water injection being injected into the exhaust port, with the main intention of this being to cool exhaust gasses at certain parts of the rev range. The cooler gases act to change the speed of reflected pulses in the expansion chamber, and therefore give you a means to effectively change the tuned length of the exhaust system, meaning the power band can be moved up and down the rev range. In a clever system the water could be metered out according to the rpm, and thus keep the system "on pipe" for much longer, like an infinite powervalve....in theory! could be quite interesting to get working
  3. Good work there! I like the way you made up the cone section, never really occured to me to use hydraulic forming to get a nice tapered section, would be a good way to make tapered headers... Got me thinking now! What did you use to generate the pressurised water to expand the welded together sections, and what sort of pressure did you have to get up to? You'll have to let us know what happens to the power delivery, I've never used a megaphone design like that so would be interesting to see some powercurves vs the previous design.... Looks smart with all the welds ground down and tidied up though, and is a super tidy install
  4. I think thats the valve guide boss isnt it? helps to guide the air flow round the valve guides.
  5. I've always taken it as the heat value of the plug dictates how hot the plug electrode gets, not the engine. I cant see how the spark plug would affect the temp of the engine itself, given its comparatively tiny surface area compared to the combustion chamber. i might be wrong, what are your reasons for saying that?
  6. Hi all, After gaining a few horses from switching the pipe on my pegaso engined rs 125, my thoughs naturally turned to what the next step was to get me over the magic 50 hp at the back wheel. A bit of digging on various forums made look at the twin bst 33 carbs that I use for fuelling, which I had assumed would be ok for that kind of power. looking at my valve sizes (3 x 30 mm) with valve throats at 25.5 mm gives a cross-sectional area of 1531 mm sq .The bst 33's , taking into account the 4mm thick butterfly spindle give a total area of 1444 mm sq. So I plugged in the figures into lotus tuning software, and sure enough the power from 4000 rpm upwards goes up by around 3 hp. I think this why the engine has such a flat torque curve , keeping 40 ftlb between 3500 and 6200 rpm and without the increase in torque i was expecting around 5000 rpm... the engine wants to but runs out of induction past 4000. So.... with all this in mind I start looking at aftermarket carbs, the universal nod seems to go to FCR carbs, which flow more due to flat slide /no butterfly. However I dont have the best part of £800 quid to spend on carbs, and the 33mm I need seems to be rare and not crop up on ebay, and the ones I have seen crop up are 39 mm which I think is massive overkill for this engine. I'd love to have the money to be able to spend 800 quid to test a theory, but sadly not... Thinking OEM (cheap) I instead looked at 36mm CV carbs, which doing the maths gives me 1746 mm sq taking the butterfly into account which I think will be more than enough. Fleabay came up with the goods, with some BST 36 s from a 98 triumph speed triple. I went for these in the hope that being the same model of carbs the external dimentions would be the same, and would let me use the spacers etc from the 33mm BSTs . these turned up yesterday, and a quick look confirms that 36 mm is simply a bored out version of the 33. Brackets all fit, I had to make a plug for the fuel rail, shorten one of the butterfly spindles, block off the inside float bowl vent lines and unblock one of the outer ports to allow pipes to be fitted. All I need to do now is sort out how the choke mechanism, and I have a set of bst 36's that will bolt straight into the existing carb inlet boots: I've simply swapped over needle jet, needle , spring , main jet and idle jet to get me in the ballpark with jetting, but no doubt it will be miles out, so will sort a trip to PDQ's dyno again to get evrything set up right. I must be their best customer by now! Will report back with results.....
  7. 30 mm intake is right, but remember I've got 3 intake valves so the valve area is about the same as 2 36mm valves? ignition pick up is fixed, but I can probably find a way to move it a few degrees each way... I think the next step is to bump up the compression to 10 - 10.5 , but I'd have to deck the block to do that. The squish at the moment is so large as to be useless ( 2.3mm), but decking the block would close that up to around 1.4 mm (thickness of the gasket). Then I'd have to slot the cams to let me time them in again, make sure I had enough clearance from valves to piston (its tight!) and maybe get the piston pockets machined a little deeper. I have a spare mule engine in pieces, so I'll put that together and get the modeling clay out I think. Performance isn't too bad, but I'm used to a 636 Ninja so its all comparative! I've got the weight down to 149 kgs without fuel, so without making carbon fibre fairings I think thats it I think. Allthough I did buy all the gear I need to do that so maybe if I get bored enough...!
  8. I think you're right there! No airbox, just a foam filter covering both carbs. I know the cam timing is conservative, timing figures are IN open 5 BTDC close 40 ABDC (225 deg) EX open 47 BBDC close 47 ATDC(234 deg) Valves are fairly small, Inlets are 3 x 30 mm and exhaust are 2 x 32mm Compression is low, 9:1 Not fiddled with ignition timing, I'd need a programmable CDI for that but on the to do list, especially if I change the compression ratio.. Not sure if the slides are opening all the way! the air filter was on for all the power runs, but I did swap the slide and spring from the old carbs, so assumed they would open all the way... not sure about that now! If I'm honest I'm happy enough for now. I think more power now = major engine surgery, which means taking the engine out which in my case is an epic adventure! I'll do something with it over winter I guess
  9. As grey racer said above, the iridium plug wont give you more power per se, but its finer point will allow the spark to jump the gap more easily under difficult conditions, ie Higher compression ect. So you only see an increase of power if the standard plug is struggling because of any mods, i doubt a standard engine would need it. Having said that I use one, because my plug is an absolute swine to change and because the iridium tends to last longer than a standard plug i dont have to change it as often. My alfa 156 v6 used platinum plugs for that very reason (manifold off etc) I also believe the imprezza uses them for the rear plugs only because they're difficult to change... Fronts are normal plugs.
  10. Spent 2 hours at PDQ this morning setting up the new carbs and trying spacers, and I'm a little dissappointed with the results: Net result is 1 hp more, and an engine that holds on to peak power longer, with no losses anywhere, and a snappier throttle response. Peak is now a fag paper under 49 hp. The red trace shows what happened with 20 mm spacers, a very minor boost in the midrange, not worth the issues it gives me with relocating the wiring to run the bike like that in my opinion... Never mind, You have to try these things to see what happens! Am running the bike with standard intake length which is the green trace, and I added the blue trace which is the original 33 carbs with standard length for comparison. Still havent reached the magic 50 hp, which is a shame, but spring is here and hopefully the weather will pick up soon, so thats it for now until winter (unless I blow it up) quick vid, filmed it the wrong way so oops. Will do you a fly-by engler when I find a volunteer to stand there while I ride at them. Saw 114 mph with more to come on way home, which was nice...
  11. Got the last spacer made, this is how they sit on the head so ready for tomorrow. The inner one needs blending a little to match the port completely, but no worse than the original carb rubbers so happy with them for now. Might give them a little work at a later date, because it'll bother me other wise! post results tomorrow!
  12. Yup, I'm a metric boy! not that cold really, i'm just a wuss...
  13. Machined up some 10 mm spacers today:- I've built in a O ring to each, so when I make the next two they'll be "stackable" and simply clamp together using longer bolts in the existing holes that currently hold the carb rubbers to the head, that way its a quick swap to check the effects of +10 +20 mm. Hope it warms up a bit for friday, -1 at the mo...
  14. Redline is 7500, but it's shaking so hard by then I dont like to go there too often!
  15. Thanks for the info englert! Since I have a limited amount of room to space out the carbs to lengthen the inlet tract, I've done the maths for an increase of +10 and + 20 mm as well as what I have at the moment. With my current length of 265 mm, the second harmonic is only effective at 8542 rpm ( way above my redline ) and this only drops to 7943 at 285 mm so will be tuning to third and four harmonic. 275mm gives me a ram peak 3 at 6423 rpm with the wave working against me at 7190, which is ok as the torque is rapidly falling away by then anyway, and the 4th ram peak helping at 5176 and hindering at 5612. With 285 mm peak 3 is at 6198, trough at 6860 , peak 4 at 4994 and trough 5415. My thinking is to try the standard length (265) with new carbs, get them set up and get a baseline reading before changing any lengths.... booked in for the first of march, so I'll try to get the spacers I need machined in time, otherwise it'll have to wait for another session. I shall post results! Tanks again for the help, everyday is a school day,
  16. Apologies, I've been a bit busy with work and stuff, but have managed to run it up with the new carbs. Oddly enough it feels ok, idles fine and seems to be a bit revier at the top end ( took it to 8000 rpm by accident, oops! and no rev limiter it seems...) Not had time to take to the dyno yet, I've just fitted some adjustable maxton forks to replace the crappy standard ones, and that meant new brakes and some new brackets to fit the the old mudguard. Will get to it in a week or so hopefully! Thanks for the theory on intake tuning guys , much appreciated! Does anybody have a fomula for working out the correct intake length? I've looked at a few online calculators, but I'd like to know the maths behind whats going on. I have had a play at working it out , assuming the shock wave is moving at the speed of sound and reflects once for the first harmonic, then (and this is where I get unsure) three times for the second and 5 times for the third...is this thinking along the right lines? Anyway tuning for 6000m rpm I seem to be getting a length of 490 mm for the fourth harmonic,686mm for the third, 1.143 mm for the second and 3430 mm(!) for the first....Can anyone check these figures for me to see If I'm near or if I've got the concept completely wrong! Cheers guys,
  17. Yield strength of a few materials... Mild steel 250 Mpa 6061-0 55Mpa 6061-t6 241 Mpa 7075-0 145 Mpa 7075-t6 434 Mpa Mild steel isnt particularly strong, but there isnt really a way to tell if thats what you have in your current linkage, it may be a stronger higher carbon steel or alloy of some kind, in which case it could have a much higher yield point than 250. So in my opinion 7075 t6 is the one, giving you a bit more room for error.Unfortunately it is a bit more difficult to machine and any welding would reduce it back to annealed state (0)... Having said that the bottom linkage in my ninja is a cast alloy design, so with the right design alloy is up to the job! Good luck mate,
  18. That does make sense! so what we're talking about arent really what i think of as harmonics of the fundamental resonance frequency ( ie multiples of the main wave frequency), but numbers of reflections of the main resonant frequency that have had time to occur in between inlet valve events? In that case, in answer to your original question, I still have no idea! but now i think I have a handle on what I need to work out... So in theory, a shorter intake tract would give more points to tune to, provided i could offset the negative effects from the negative reflections, but I assume there is a payoff with a shorter tract length of less inertial ramming at the end of the intake cycle when the piston is on the start of it journey back up the cylinder? Am I thinking along the right lines? I'll sit down down with my calculator and boys book of maths and see what comes out, and then plug the figures into the simulator to see if i confirms what i work out... Thanks for the explanation, its hard to find someone who can explain the fundamentals of what going on clearly Will report back. PS, have machined up an adaptor for the choke, just need to strip down and clean the carbs to make sure no swarf etc is anywhere it shouldnt be, then I'll fit them and we'll see whats what!
  19. Hi all, as you may or may not know i've recently added a new pipe to my pegaso 650 engined rs 125, and got the power up to nearly 48 hp at the back wheel. http://www.thumperta...ust-dimensions/ I suspect I may be running into the top limit of what the 2x mikuni bst 33 cv carbs I have are capable of supporting, and I'd like to take this engine over 50 hp if I can, with some valve work and a boost in compression and some work on the induction side. First of all, am I right in thinking I should change the carb to something that would flow a little more air? And If I do, what should I change them to? My current thinking is to change to a flat slide type carb of the same diameter (33mm) as this matches the rest of my induct and as such would be easier to install. The only problem is that the only carbs I looked into so far are the keihin fcr's and these would be around £600 for the pair new.... so I'm wondering if anybody knows if anything like these has been used on a production bike that I could pick up cheaper, and if so which bike? Lastly, my understanding is that the flow rate difference between cv and flatslides is mostly due to the butterfly in the cv? If I'm right, has anybody experimented with slimming down the butterfly spindle, and how much of an increase in flow could you expect from doing this? Lots of questions I know, but would appreciate the benefit of peoples experience with these carbs as I have very little! Cheers for any advice you guys may have.
  20. I think thats the drain hole for the spark plug tunnel? Its there to allow any water that finds its way into the plug area to drain away. If the rocker cover gasket is leaking in that area, any oil collecting there would drain out too. have a look down the plug hole and see if its oily in there...
  21. numbhands

    welding a swingarm?

    Think it depends on the alloy being used, some need heat treating to restore strength, some dont, and the temper of the original alloy before welding, ie if it was t6 alloy before welding it wont be in the region of the weld afterward... thats assuming you need the extra strength from T6. no problem if the part is overengineered to compensate,
  22. numbhands

    exhaust dimensions?

    I currently have 2 x 33mm bst 33 mikunis, but I'm not sure how these compare in flow to an 31 mm keihin FCR? I do know slipstream tuning do a set for the SZR 660 that are 39mm , which seems huge to me! I presume they're for a full race tune 80-90 hp... Am thinking of a total induction length of 300 mm, up from 265 mm which i have now, and this would come from spacers between the carb and head since I cant fit extra length as a bell mouth because of the existing entry on the carb. If I'm honest I'm not sure what you mean by which harmonic I'm tuning to? My understanding is the intake resonates (at the correct RPM) at a fundamental frequency dependent on the length, setting up a standing wave in the intake with constructive and destructive interference occuring at various points, the aim being to generate max amplitude of the wave at the intake valve as it starts to open. From what you say are there multiple resonant frequencies for a given intake length? Still learning this stuff so bear with me! Have found out why the simulation was wrong which is helpfull. I inputted the induction area based on my carb diameter rather than the actual size of the intake ports, which oddly are larger. The extra port diameter holds up peak torque around the 5000-6000 mark instead of 4000-5000 letting the engine rev out better, but at the cost of torque further down. I think that explains why the bulge in torque never materialised as I expected, and it also makes me thing the port is a little on the large size. Strange for aprilia to do that on an engine designed for bottom end and midrange, but it helps me so not complaining! It does however mean gas speeds stay a bit low until the engine really gets going, so I dont think the extra length of intake will make as much of a difference as I first thought.
  23. Hi all Quick intro, I'm living in the southeast of the uk, and have been building an Aprilia rs 125 with a Pegaso 650 engine shoe horned into it... Not a dirt bike I know, but I need abit of advice on big single cylinder engines as there doesnt seem to be a lot of info out there, especially the pegaso engine (rotax 655) Finally got the bike dynoed to sort out any fuelling issues as the bike engine runs with pod filters and a weird exhaust I made up to look like the rs250 twin pipes, and found a very flat torque curve but no real top end.Looks like this for info: The existing exhaust takes a tube from each exhaust port to an individual silencer through what I now know to be a too small diameter 1.25 inch bore pipe, same dia for the whole length. I'm wondering, first of all is the power figure overhead in the right sort of ball park for this engine? If not what sort of gains could I by making a new system with 25" long 1.5 " dia headers into a collector and maybe a 2.5" link pipe to a single silencer, which from what I've read might bias the power a little further up the rev range? Sorry for the mega post.... I need to get out more! cheers for any info and any opinions welcome,
  24. numbhands

    exhaust dimensions?

    Think so, going to start making them tomorrow! I think I might need to refine the simulation a bit to make sure I get the length right, the graphs dont quite match up between real life and what I get on the PC. Dont want to waste a lot of time making something that I'm not sure will work... Am pretty happy with what I have so far in any case, dyno operator said most pegasos hes done get around 44 at the back wheel, so nearly 48 aint bad! would be nice to get the magic 50 though....