ESE's works engine tuner

[bucketracer]

Fawk me does this guy know what he's doing or what!

[speedpro]

For the RM125 pipe specs see Page 76..........http://www.kreidler.nl/artikelen/per...raham-bell.pdf

Note the method used on page 15 to calculate compression ratio.

It is correct to adjust compression ratio down if it has previously been optimised for a less than ideal engine configuration which is now corrected resulting in improved pumping through optimised porting, pipe resonance, etc. What is regularly overlooked is the crankcase volume which may also need to be increased to supply the volume of gas to the transfer ports in the optimised engine.

[Bert]

Nice Work TZ. Thanks for sharing all this useful bits and pieces, keep it up (It would make a useful web page or addition to some of the other ones around the place).
I could only wish that i had access to all that equipment & labour to make my bucket sing.

So it should go well then,,, see you on the track at taupo as you go past me.

Bert

[Skunk]

Nice Work TZ. Thanks for sharing all this useful bits and pieces, keep it up (It would make a useful web page or addition to some of the other ones around the place).

There's room at http://www.bucketracing.co.nz

[TZ350]

What is regularly overlooked is the crankcase volume which may also need to be increased to supply the volume of gas to the transfer ports in the optimised engine.

.
Hi Speedpro, I remember you explaining to me how crank case volumes had become to small and how its easier to get a cylinder full of air/fuel from a larger crankcase volume than a smaller one. Your advice made sense, check out the 12mm cylinder spacer under the barrel. I rememberd that fitting the longer RD400 rods to a TZ was the trick setup years ago.
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[F5 Dave]

Fawk me does this guy know what he's doing or what!

I'd say 'or what', but only to be controversial.

Measuring compression with a gauge is a rough stick. Far more accurate to measure the actual combustion volume with liquid (fork oil works well). Maybe he did.

I’d only ever use a gauge to check the engine after a rebuild & take that as a point to compare later to. If you were too lazy to take the engine apart.

One of my bikes I measured it as 196psi with fresh piston & ring & a base gasket removed. I then machined the head & got . . . 196psi. Same german gauge, same technique (kick it an awful lot of times with throttle wide open till it stops moving) but a very real difference in combustion size.

Oh & the high number? Just peachy for the bike’s application, watercooled trail bike with a wide spread pipe.

The correct compression ratio is the one that best matches the bike, there are other compromises that in isolation may appear best, stinger size (or steep baffle), general pipe, ignition, head shape to name a few.

Primary compression is another compromise & which way it is approached has different benefits, the Honda or the Yamaha route (some way back) was high crankcase compression for more pumping efficiency (the crankcase is afterall just a pump) or more volume & let the pipe do the work.

[TZ350]

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So some one does read this.

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[speedpro]

only for a laugh

[TZ350]

Note the method used on page 15 to calculate compression ratio.

Translated for Thomas.


Thats a good point Speedpro. Using the total swept volume of 125cc uncorrected compression ratio is 15:1 using the volume above the exhaust port for the corrected ratio is 8:1 different approaches.

For those who want to know:- R = (CV+SV)/CV
Where R=Ratio, the compression ratio.
CV=ClearanceVolume, the bit in the cylinder head.
SV= SweptVolume, the cc's of the whole cylinder or the bit above the exhaust port, however you want to do it.

If you know the compression Ratio you want and the SweptVolume you have (total or corrected) then by transposition.

R = (CV+SV)/CV
R = CV/CV + SV/CV
R = 1+SV/CV
R-1 = SV/CV
(R-1)/SV = 1/CV
SV/(R-1) = CV

CV = SV/(R-1)

So there you have it.

CV The ClearanceVolume is the bit you need in the cylinder head and it needs to be equal to the SweptVolume divided by the compression Ratio you want minus One.

So now you can chose a compression Ratio and work out the CC's for the ClearanceVolume required.

Speedpro knows all this.

F5 Dave you caught me, I think your comments are spot on, now ask me about the Science and Philosophy behind getting the compression ratio right, using a compression tester.

I dare you!!!

Please

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[TZ350]

.

Thomas wants to measure the compression ratio accurately and see how it compares to my compression tester method.

See page 16 of Graham Bells book for a discription of corrected and un-corrected compresion ratio.

http://www.kreidler.nl/artikelen/per...raham-bell.pdf

Basic dimensions are:- rod length 110mm between centers, -2mm piston pin offset, 56mm bore, 50mm stroke, 125cc.

Ex opens ATDC.....height.....Volume...8:1 CR...7.5:1 CR.....15:1 CR
......81...............23.8mm.....58.6cc....8.4cc. ...9.0cc.........8.9cc.........Race
......83...............24.7mm.....60.8cc....8.7cc. ...9.4cc.........8.9cc
......86...............26.0mm.....64.0cc....9.1cc. ...9.8cc.........8.9cc.........MotoX
......91...............28.2mm.....69.5cc....9.9cc. ..10.7cc.........8.9cc
......96...............30.5mm.....75.0cc...10.7cc. ..11.5cc........8.9cc.........Road...Enduro..and.. early.MotoX

At Ex opens 81 ATDC (road race) the clearance volume for the corrected and un-uncorrected compresion ratios are close but for Ex opens 96 ATDC (road or motoX) they are quite different.

It looks like Graham Bell at 15:1 uncorrected was talking more about the race end than road, even if your using AvGas.

Thomas says there is no right way, just better ways and CC'ing the combustion chamber is a better way.

He is real keen to see if my quick and dirty way is anywhere close to the more accepted CC'ing way for establishing a working compression ratio.

The design parameters are 125cc, Ex opens 81 degrees ATDC, and the ClearanceVolume should be 8.4cc for a corrected compression ratio of 8:1.

When we get a chance we will measure it to see how close to 8.4cc's it actually is and publish the results.

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[F5 Dave]

Corrected cr is probably relevant if you don't run an expansion chamber. If you do & the engine is running in the tuned frequency then all bets are off, but the real compression ratio & the full ratio are likely the same or close enough that you can use it to gauge where you're at vs fuel you use.

If it is 8.4cc then I'd say hmm 15.9:1 on an aircooled 125. Better retard that ignition quite somewhat if you want it to survive. I was nowhere near that high on my 125. I've run higher on my watercooled 40mm bore 50, but not these days, probably a tickle less.

When I measure with fluid I count 2 threads from bottom of spark plug to account for the sparkplug extra volume (about 0.2cc from foggy memory, but I measured it). A burrette makes it much easier to get consistent measurements.

[TZ350]

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Ex opens ATDC.....height.....Volume...8:1 CR...7.5:1 CR.....15:1 CR
......81...............23.8mm.....58.6cc....8.4cc. ...9.0cc.........8.9cc

From F5...."If it is 8.4cc then I'd say hmm 15.9:1 on an aircooled 125. Better retard that ignition quite somewhat."


Yes F5, I see what you mean.

.

[F5 Dave]

What would be nice is a fast burning fuel with a high octane & high calorific value. (kind of like the old red leaded super we used to get a decade ago). Then if you are keen running a high compression ratio then & esp with an engine perhaps a bit shy of too many revs for the crank assembly you could build a midrange monster suitable for kart tracks. With a reasonably large squish area hence small flame lead & thus a fairly high MSV figure + a matching supercross style pipe (with steep baffle to suppress over rev) then high comp is still a good idea.

My old H100 was built with this in mind. Not so flash on the longer ccts, but good fun everywhere else. Still was good enough to get a 3rd in old cct Taupo GP many moons ago even with a crash (almost a 2nd but that damn Diprose chap got me on his MB when I got run off the track ~ 2 laps from the end).

[TZ350]

Have CC'd the engine.

Thomas is really keen to CC the engine. The best way would be to take the engine out of the bike so it can be levelled up and CC’d through the sparkplug hole but we are to pressed for time to do this.

With the engine in the frame the spark plug hole is a bit inaccessible and the cylinder slopes forward. Taking the motor out is a bit more work than we wanted to do and because the engine is fitted with a flat piston with a small dish in it.

We figured we could get a fairly good result by CC’ing the bore with the piston at TDC, then the head and then adding the two results together. Working with what we could find.

We cut the top of a takeaway container to shape and put a small hole in it. Liquids because of their surface tension tend to bulge up.

So using the flat piece of plastic and pouring brake fluid through the small hole with a syringe would flatten the fluid bulge and allow us to measure more accurately how many CC’s it takes to fill the cylinder.

Piston at TDC, a light smear of grease to seal the rings. Another smear of grease to stick the plastic to the barrel. Inject the brake fluid and count the CC’s. Now the same for the head.

Results:-

Barrel/Piston = 5.3
Head&Plug = 5.7
Total ClearanceVolume = 11cc’s
Corrected Compresion Ratio = 6.3
Uncorrected Compression Ratio = 12.4

So we were safe.

Until Thomas reminded me that when we had 0.5mm static squish the piston was just touching the head at 10,000rpm and that we had added another 0.5mm giving a static squish of 1mm and a dynamic squish of 0.5mm.

0.5mm of squish in our engine is equal to 1cc.

So the total dynamic ClearanceVolume is now 10cc’s at 10,000rpm
Dynamic Corrected Compresion Ratio = 6.8
Dynamic Uncorrected Compression Ratio = 13.5

Our aim was for a bit more than this.

So a couple of skims and re-measures later we had:-

The total dynamic ClearanceVolume is now 9.4cc’s
Dynamic Corrected Compresion Ratio = 7.3
Dynamic Uncorrected Compression Ratio = 14.3

Close enough for us. We will be starting out with the ignition timing retarded and then incrementaly advance looking for the optimum. We will be doing many plug checks along the way looking for the change in colouration of the plugs earth strap. The colouration should end just before the bend of the earth strap for best results. See all those, reading plugs, posts earlier.

One symptom of over compression in a bike that ran well before, is that it now goes flat up top. This is the same for slightly over advanced ignition timing. This makes sense when you think about it.

As the piston is going up there is a negative pressure working on it. We want the maximum cylinder pressure to occur sometime (15 degrees approx) ATDC. If the maximum pressure has not quite reached detonation point but has moved closer to TDC then there is more negative pressure before TDC trying to push the piston back and we experience this as the engine going flat.

So as F5 Dave says, a faster burning fuel would allow maximum pressure after TDC with less negative pressure buildup (slowing us down) before TDC.

Its all about BMEP brake mean effective pressure, and how to achieve it.

So if we are careful we can test our handy work and dial it in without blowing it up.

The final compression test read lower than before we increased the compression ratio.

Yes I got away with it this time but using a compression tester to check the compression ratio, is not only quick and dirty but also lazy and very likely to bite one on the bum.

As I can find them I will put up details about other bikes compression ratios and ignition timing like the Honda RS125, Suzuki RM125 etc.

My next move is to build a programmable ignition, or at least one that can be setup advanced and then retards to the correct setting as the engine comes onto the pipe.

Water injection into the expansion chamber when the engine is running below peak torque.

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[Buckets4Me]

get Thomas onto my bike next please
you know the one the rs powed rs125 for the Slipway
and make sure he hase put puke gearing on it please
11 fround 54 rear thanks