OzVMX Forum
Marque Remarks => Suzuki => Topic started by: oldfart on November 22, 2008, 02:53:20 pm
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Just spent the last hour measuring and comparing the 2 barrels and there seems to be no difference .
Ports sizes and positions are within .5 mm of each other
Or is there one and I have over looked it .
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with the PE's its the barrel fining and rubbers that are the main differences, but also look at HP figures. 81 and 82 PE have suposedly got more HP than the T. im yet to be able to view/print my 250 z microfiche card but i would like to see the barrel part number on that one.
i think your onto something here. i reckon the X and Z PE 250 could use the T model RM barrel. that would explain the HP difference maybe? hmmm but the MX porting wouldnt be right for a enduro bike?
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Lieth you have read me well, trying to suss out why the Pe have that little extra gain over Rm set up , disregarding the fly wheel
I have traced the ports on both barrels and done an over lay , there's nothing in it.
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The timing is of more importance, then ports were all pretty crap back then anyway. An easy way to look at Time/Areas is to do a rubbing on graph paper and count the squares.
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ive got port maps for PE 175 T/X and RM 125 T and possibly N as well as RM 250 B and PE 250 B, but i dont think i have any on RM 250 N/T or PE 250 T/X/Z
there are higher compression ratios amongst all this too. i was looking at this the other week. They bumped the compression up on later PE 250's. i think the 80 was a little lower ghan X/Z, this was just done by different head gasket thickness.
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timing , as in stator base plate adjustment or CDI unit
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i think he means port timing, (and not port size) and when the piston opens and closes the ports
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have you measured the PE -X barrel and compared to measurements of PE-T barrel?
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I have about 10 barrels on the bench Rm 250 N-T Pe T-X and there is SFA difference
Rods and Pistons are the same .
Getting back to the Institute - Just measured stroke centres and there appears to be 3mm difference
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never under estimate the difference 0.5mm makes in a 2 stroke port. Of course there is the pipe to consider. Tuning is always a combination of ports/ pipe/jetting and how you hold your mouth.
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how the hell do you port a engine with a porting tool and get into those tight, difficult to reach spots to tollerances .5mm or less i will never know. must be an art to it. how do you get in there and measure with calipers/ruler etc and measure this accuratly?
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I used a piece of cardboard rolled up to form a cylinder , dropped it in one bore and rubbed it so as it left an outline of ports. Spent half an hour to cut the holes so they matched up perfectly with the one I had traced , then tried it on all the others with pretty much the same results ;)
I'm stuffed if i know how you would get a die grinder into those reed tranfers .
Not one of my barrels has had any port work done . Most of the work has been on the intake and base ports ( what ever they are called ) ???
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That's like sealing the shocks ,a trade secret Leith, and why I command the big $$$ ;D ;D ;D. Half a mm is production tolerances nothing more and any affects (if at all) depend on rod and stroke length. A thing to look for on ported cylinders is a knife edge on the transfer dividing fin which indicates the hands of an amature at work.I always work in mm from top of the barrel and use the sine rule to calculate degrees from that.
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why does a knife edge at the edge of fin between the transfers indicate amature work?
was boost ports the term you were looking for oldfart?
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Because it shows that whoever did it has NO understanding of gas dynamics.Show me a pic of a LEADING surface/edge of a chopper rotor, plane wing, open wheel race car wing, push bike helmet or anything else that goes fast(besides a boat bow) that is sharpened to a point.
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compare these then
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Up until 1980, from 1977, I know the PE & RM 250 ran the same bore and stroke of 67mm bore and 70mm stroke. I reckon the PE 250 T/X are way underrated as a vintage/twinshock motocross engine. I have an RM250 T and sometimes put my PE pipe on to mellow it out- and it does help. I am going to try and drop the whole motor into the RM this summer for a test run- give me bottom end and mid anyday for MX.
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81 and 82 PE250 was also 67x70.
its a bit like the PE 400 which actually has mor HP/torque than the RM 400. this was discussed long ago on the old forum.
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a plane wing or chopper prop isn't a good comparison Loz as all the above mentioned use the edges to create turbulance thus creating lift. A rocket is pointy and it's designed to travel as fast as practically possible the 2 stroke is an air pump, the faster the air can pass through it the better it will go (in theory) ;) sharpening the tranfers and inlet bridge is par for the course in near any ported 2 smoker barrel I have seen. Doesn't make it right I suppose but it's overwhelmingly standard practice.
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i was thinking the same as you Doc and became confused by this. Arent plane wing edges tapered to a point????? they are not square and block shaped because its not aerodynamic.
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Wings generate lift because they are flat on the bottom, thus the air passing over the wing travels further and faster than the air going under thus giving lower pressure on top of the wing=lift.Trailing edges are sharp and a track cyclists helmet is the perfect example. Rockets are super sonic and that changes everything.Gas flows in engines are never super sonic and knife edges don't contribute to gas speed at all.Gas speed is created by bigger and faster pressure drops, in the cases/cylinder and pipe. Knife edging and case stuffing has long fallen out of favour with any serious/professional engine builder or factory. A KTM 125 makes 43HP out of the box, same for a TZ and RS 125's but there around 50HP no knife edges to be seen. As I said amature work. ;D
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guess you have to move with the times, but knife edges used to be a given, like carbon reeds and cutting that little spirally thing out of your PE muffler.
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Mr Lozza ... I have been scrathing me head all day over this ( just about gone bald ) The Oldfart has come to the conclusion - cranks are not the same , Pe wieghs in at 3.9kg and the Rm 3.5kg internal - crank case volumes are different - both share the same crank Daimeter, but Pe measures 62mm across where as Rm is 58mm rods the same length - share the same piston - and the barrels ARE THE SAME . Difference is chamber - stator - CDI ? Pe has a 6 speed box ( and much stronger ) Rm = 5 speed and has a tendancy to wear gears ( split 3 today and all had the same problem )
NOW ON THE HUNT for a decent gear box set for a Rm 250 T
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so the PE has higher crankcase compression?. are the cases the same and the larger mass of the PE crank webs reduces the crankcase volume air space giving more compression? so if you think the barrels are the same, why does RM 250 T and PE 250 T have different part numbers? i wonder
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:o Lozza! are you saying my TM isn't supersonic!! :D now you're really pulling my leg ::) not arguing the fact but there are many other contributing factors to be taken into consideration when comparing a 2008 125 to a 70's technology item. 2 of these considerations being the powervalve and digital ignition which means they can build the motors to pump out mega HP without the dramatic loss of low end power the early models suffered. You could get over 30HP from the old too but it became unusable unlike the new generation stuff which is infinately adjustable. :P
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Not too sure about extra volume ,crank holes in PE = 28mm Rm 30mm case volumes should be the same??? . Tolerances each side of crank when in cases are similar . Cases are NOT interchangable due to the fact of extra gear and 4 mm difference to accommodate crank.
Lozza ! I'm more a 4 stroker man than a 2 smoker ...... im my language are we talking about Duration versus lift
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I had some RM & PE stuff a few years ago & I compared the barrels, I think they were C models. The barrels & ports were identical except for the exhaust port height being lower on the PE, this would be enough for different part No's.
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yep, I'd reckon even the rubber blocks in the fins would call for a new number. The factory didn't want us thinking they'd simply used an RM barrel. Takes me back to an old article in a Trail and Track from 'RM250N Gone Enduro' remember this pic? 8)
(http://osysga.bay.livefilestore.com/y1pLqEtWYXtAaHqto8TrWxM5WwdnyRmIHGu2l6ibeLAVqy5svWW5HL2Ij2oe0RyybkVIONqBWEfaFw/1979%20RM250N%20Enduro.jpg)
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Proving it's not to hard to confuse a plumber ;D Case volumes in the PE will be smaller, lower case volumes bring the engine into phase lower down the rev range. A great engine would be the heavy PE crank in the RM cases with an adjustment in case volume, would rev and be very tractable/forgiving and very fast around the track.What am I supposed to be looking at with the barrels Stew ???
Pipes and ports account for most of the performance Doc a 70's 125 typicaly ran a 32/34mm carb a 08 mx 125 has 38/39mm carb.The engine does the pumping not the ignition.
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ok i think ive worked this out. if the ports of RM T and PE T are the same then its must be the barrel rubbers giveing reason for differnt part numbers
the RM had none but the PE did
i say this because ive seen an optional sound kit availble for RM 250 T in the parts book which included a spark arrestor, barrel/head rubbers and a different air box lid, all to quieten things down for offroad use in USA.
but just as i write this im wondering were replacment PE barrels sold with the rubbers fitted? when you find NOS barrels, do they have the rubbers already fitted?
if they dont that throws my theory out the door.
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I know new cases come with the screws ;)
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Barrel on right has had some sort of Knife edge port work, note that there is a taper from barrel all the way down port . RHS has a flat step on barrel . From what I read this means SFA
So I'm off down stairs to check volumes ::)
Lieth , I'm thinking the same as you with barrel rubbers being the only difference.
That is srews and gasket :)
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oops..srews and gashget I meant sorry oldfart ;) :D
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The PE barrel has grooves cut into the fins to allow the rubber blocks to engage/sit in properly ,the RM does not. The other rubbers were small round discs that you pushed into the fin gaps to help absord a bit of vibration/engine noise.
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thats the X/Z 250 PE barrel that has those slots in the fins for the TS style square rubbers. most T model PE barrels i have seen have plain fins with no slots like the RM 250 T and the barrels look exactly the same as RM 250 and the round rubbers just squish in between the fins.
on one of my PE's i thought it had a RM cylinder when it just had plain fins and round rubbers, but more research just told me the early PE barrels were like that. but now going by this topic it looks like the Rm and PE barrels are the same anyway. its still a bit strange as the early PE/RM 250s had different porting and i have port maps side by side to show that from suzuki tech bulletins.
i also checked the RM 250 T parts book and theres definitely no small barrel rubbers fitted as standard like the 1980 PE barrel. they were only optional in the offroad sound kit.
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What's the plan? How insanely powerful you want it?
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Insane ::) just getting old :D Lozza- I was just curious to see if there was any difference or not, as I had done the swap barrel exercise and found no differrence . Having said that there was a noticable change in power with the knife edge ports :)
Yes I had a plan and that was to Rm a Pe motor ( much stronger box , six speed plus a shit load of parts available still )
Going the other way I recon the G/ boxs arn't up to it
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Where's your spirit of adventure? Surely you didn't leave it behind at Coffs? The rubbers make the difference......................... ;D
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yes Loz, and not only do the rubbers make the difference the placement and sequenc of these rubbers is Feng-Shooooo and most infinately adjustable to suit individual requirements! Very misunderstood and underestimated the importance these rubbers have on outright performance and inner harmony I'd reckon ;)
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I must admit Doc that when I was in the process of fitting the little rubber discs it become a lot like decorating a Xmas tree- a couple here, a couple there and then stand back and stare a while and go and change a couple and so - on.
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Rubbers!!! what are you blokes talking about . I refuse to use them ...literaly ;D