ESE's works engine tuner

[TZ350]

I was wondering Teezee, what are the exhaust port specs of an original GP125?

I really think you can make the tractor you want from a GP125, but still making 20PS!, but at lower revs.

Std GP 125 exhaust port width 36mm, 64% of bore diameter, opens 86 deg ATDC.

Working Jennings Port/Time/Area’s at 9,000rpm
(Exhaust 0.00014 to 0.00015, Transfers 0.00008 to 0.00010, Disk Valve Inlet 0.00018 to 0.00019)

I get:-

Ex opens 86 deg ATDC for 188 duration and port/time/area of 0.00015

Blowdown 28 deg

Transfers open 116 deg ATDC for 128 duration and port/time/area of 0.00010

Inlet, 26mm dia port (24mm carb) opens 145 deg BTDC and closes 55 ATDC
230 degree duration and port/time/area of 0.00012

And if the rotary disk is cut for 145/85 port/time/area becomes 0.00014

So even at 9,000rpm the limiting factor still looks like the carb size.

But, like you, I think the GP still can be improved.

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[SS90]

Wow, the GP125 really are pretty good standard!

The numbers you posted pretty much fall in what I would be aiming for on a Polini cylinder.

As a matter of interest, what is the time area of the exhaust if you widen it to 72%?

If it is too extreme, you always have the option of removing material from the cases, (or the bottom of the cylinder) and bring the duration down to compensate, It will require a little work with the transfers, but I think it would be an "easy" option.

The Kawasaki pistons you posted would quite likely fall into the category I would deem "racing". Personal experience with Japanese pistons in the last few years has shown that 75% is ok.

The most powerful (unbridged) cylinders I see/make are always wider than 72%

I occasionally hear of people exceeding that (no problems) but I suspect regular ring replacement is needed!

The 2 pictures I have included show what I use with a Polini small frame cylinder.

As you know a Trapezoid is the best shape, the second picture is a completed work (after honing)

[TZ350]

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Hi SS90 thanks for your reply and pictures nice work. It is interesting to hear that you have been able to run exhaust ports at 75%.

I make the Ex port/time/area of a standard GP125 widened to 72% at 0.00018. The std GP125 exhaust port is very square and the ones I have modified became elongated ovals. I will take some port tracings and pictures.

At the moment I am most interested in making sense of the blow-down period. There is plenty of info about port/time/area requirements for the ports but in spite of its importance I have found very little on blow-down time/area.

Pic's of a standard GP125 exhaust port. In pic-1 you can see on the very straight top edge where the ring has snagged and worn the edge away. When I widen the exhaust port I curve the top a little more and increase the radius's at the sides.

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[Buckets4Me]

found out how TZ350 is getting his bike to go so fast cheaply

http://farm3.static.flickr.com/2472/...e2e73840_o.jpg

he has child labour (just like fishy but this time it's his youngest grandchild)

[SS90]

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Hi SS90 thanks for your reply and pictures nice work. It is interesting to hear that you have been able to run exhaust ports at 75%.

I make the Ex port/time/area of a standard GP125 widened to 72% at 0.00018. The std GP125 exhaust port is very square and the ones I have modified became elongated ovals. I will take some port tracings and pictures.

At the moment I am most interested in making sense of the blow-down period. There is plenty of info about port/time/area requirements for the ports but in spite of its importance I have found very little on blow-down time/area.

Pic's of a standard GP125 exhaust port. In pic-1 you can see on the very straight top edge where the ring has snagged and worn the edge away. When I widen the exhaust port I curve the top a little more and increase the radius's at the sides.

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The picture of the port map I posted is at 72%, (57mm bore, 51mm stroke) and I know you can run this with the standard 1.5mm Polini rings and piston.

I recently found a supplier who sells 1.5mm rings to fit this piston, but the word is they can run upwards of 75% no worries, (and cost less than original.)

Anything "high revving" (race style) I would expect to see a quality piston with 1mm rings, and these are what I use to get 75% safely.

I do occasionally hear of over this figure tho........

Interestingly, the design of this particular aftermarket piston was born from a TZR250! (just a little different)


I will see what is available on blow down times over here, but most stuff I know came from personal experience, and I suspect others have found the same, and I have never read anything helpful yet!

[TZ350]

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Modified transfer ducts on number two cylinder and 72% exhaust Port.

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[bucketracer]

TZ you really have opened those transfers up, they look like open cast gold mines. Having bigger holes to blow through won't do much good if you cant suck enough of the good stuff through the carburetor. What are you going to do there.

[F5 Dave]

Pass the Devcon. More direct may be an improvement but I'd be slowly contouring those which will reduce the volume throughout. May help to build up the inside it that is the direction you are after.

[bucketracer]

TeeZee if your going to try and air cool an RGV cylinder, for what its worth, I scraped this from an RGV site:-

My take on what may work with the RGV ports in general is.

Action - Clean up the intake side of the transfer tunnels, even enlarge them if possible.
Result - to increase mixture velocity at port outlet

Action - Port divider (case side) needs to be rounded rather than knife edged
Result - knife edge seems to cause mixture to cling to tunnel wall, well rounded divider edge allows mixture to flow "along" tunnel wall.

Action - Exhaust port can be enlarged by elongating port "ears" further around bore.
Result - Improves exhaust port flow.

Action - Deburr exhaust port walls and divider, remove casting lump at the corner of the main ex port at the bottom of the "ears".
Result - Increase exhaust port flow.

Action - Raise and level exhaust port height by upto 1.0mm, must blend PV's to suit as well.
Result - Increase exhaust port time/area and angle. Flow.

Action - Raise main transfer ports roof angle upto 1.0mm, blending to outer tunnel wall (to angle the roof upward).
Result - Directs more mixture towards the combustion chamber and helps evacuate exhausts gases. Raises port time/area.

Action - Angle Main transfer ports toward boost port away from the Exhaust port.
Result - To allow cylinder to be evenly filled with mixture and helps evacuate exhaust gas.

Action - Raise Aux transfer port to match Main port height but with a level port roof.
Result - Increase's port time/area, mixture passes across piston crown to reduce crown temp.

Action - Widen aux ports on both sides. 1.0mm each side of each port.
Result - Increases bulk flow of mixture across piston crown at lower pressure with a wider spread to stop flow from being shot directly out exhaust ports.

Action - Reduce area directly below cylinder by partially filling with epoxy putty and shape as desired. Requires volumetric efficiency study/simulation!
Result - Increases primary compression by lowering case volume and increasing pumping efficiency.

Action - Build a pipe to suit the characteristics for the cylinder.
Result - Maximizes engine pumping efficiency.

Pic-1 std RGV cylinder, Pic-2 modified, Pic-3 here you go Stefano Genuine A-Kit HRC ex-Pedrosa RSW250 cylinder, a very special race cylinder and Pic-4 on the left official RSW125 2002 crude, in the bottom Honda RS125 2003 for inshore boat use and on the right my rare official Cagiva Mito 125SP 1995
cylinder.

http://www.rgv250.co.uk/forums/index...ic=32195&st=80

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[speedpro]

RGV ports are already too big for bucket racing. I suspect the time/area values are excessive. I've already built a bucket using one - watercooled, sleeved down 100cc, full crankcase reed TS125 bottom end.

[bucketracer]

.

But how would it go as an air cooled 125?

Anyway it makes interesting reading and they are pretty pics. Here is a couple more.

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[SS90]

Pass the Devcon. More direct may be an improvement but I'd be slowly contouring those which will reduce the volume throughout. May help to build up the inside it that is the direction you are after.

I have to agree there Dave, unfortunatley there are no hard and fast rules for Teezee to go on, and he just needs to have a "suck it and see approach"

It fly's in the face of current tuning practices, but the carb size is the problem!

[TZ350]

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But how would it go as an air cooled 125?

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Interesting pictures but the same old problem, the carb. Max power is really not an option.

SS90 has pointed the way, "less rev's and think tractor".

Number two cylinder pictured is a bit OTT but number three will be more refined and planned.

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[SS90]

I'm still looking for some data on blowdown times so you can put some science to it Teezee, a friend is emailing me a scanned article from a magazine (not on blowdown times, but more general stuff, and he is a "genius") it's "Auf Deutsch", do you have a program that can translate from a series of images?

I could translate it if needed, but it will possibly take 3 or 4 days.

[speedpro]

Finally I know what it's like to work at ESE, 1:26pm on a Fri, browsing Kiwibiker. Excellent