ESE's works engine tuner

[speedpro]

So the carb should flow enough for some reasonable horsepower. Just what are those 60/65cc motors rated to produce?

[TZ350]

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Well that didn’t go so good, I have been porting the transfers and changing the roof angles of my next cylinder. I changed the mains to 29deg and the secondarys to 15deg and boost to 65deg all opening at the same time.

Timing was to be:- a Wobbly design with trans opening at 115deg ATDC for a duration of 130deg. and EX opening 86deg ATDC for a duration of 172deg, and a Wobbly pipe.

After about 40 hours work re-angling and opening up the transfers I had a pretty good-looking cylinder with the matching transfer ports opening at the exact same time. The total area of the transfer windows is now pretty close to an RGV250 cylinder.

Thomas put my cylinder on a spare bottom end and degreed it up. The transfers came out at 140deg duration, opening at 110deg ATDC and the exhaust is 194 duration opening at 83deg ATDC. Whooops, not what I was looking for at all, so what to do now.

Well I now know I can do a pretty good port job and I am able to open up the transfers to whatever time area I may need. I have a spare and still want to try the Wobbly design so I will try again with that cylinder later.

According to Bell a transfer duration of 140deg is good for 12,500 to 13,000 rpm So I guess I will finish this cylinder as a hells death old school rip snorter for Taupo, razor sharp power band, lots of clutch, should be fun.

For 12,500 rpm Bell suggests 200deg or so Ex duration. I have a good software program that works out time-area requirements for a chosen rpm and bmep, then prints out a diagram of the port window shapes required and I also have pipe designs for RGV performance pipes so it all looks good.

I have made a pretty good Perspex cylinder head so I can fine-tune the scavenging flow patterns using water and fine air bubbles like SS90 suggested.

The problem is that restrictive 24mm carb. F5 Dave has suggested a possible solution.

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[sonic_v]

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Well that didn’t go so good, I have been porting the transfers and changing the roof angles of my next cylinder. I changed the mains to 29deg and the secondarys to 15deg and boost to 65deg all opening at the same time.

Timing was to be:- a Wobbly design with trans opening at 115deg ATDC for a duration of 130deg. and EX opening 86deg ATDC for a duration of 172deg, and a Wobbly pipe.

After about 40 hours work re-angling and opening up the transfers I had a pretty good-looking cylinder with the matching transfer ports opening at the exact same time. The total area of the transfer windows is now pretty close to an RGV250 cylinder.

Thomas put my cylinder on a spare bottom end and degreed it up. The transfers came out at 140deg duration, opening at 110deg ATDC and the exhaust is 194 duration opening at 83deg ATDC. Whooops, not what I was looking for at all, so what to do now.

Well I now know I can do a pretty good port job and I am able to open up the transfers to whatever time area I may need. I have a spare and still want to try the Wobbly design so I will try again with that cylinder later.

According to Bell a transfer duration of 140deg is good for 12,500 to 13,000 rpm So I guess I will finish this cylinder as a hells death old school rip snorter for Taupo, razor sharp power band, lots of clutch, should be fun.

For 12,500 rpm Bell suggests 200deg or so Ex duration. I have a good software program that works out time-area requirements for a chosen rpm and bmep, then prints out a diagram of the port window shapes required and I also have pipe designs for RGV performance pipes so it all looks good.

I have made a pretty good Perspex cylinder head so I can fine-tune the scavenging flow patterns using water and fine air bubbles like SS90 suggested.

The problem is that restrictive 24mm carb. F5 Dave has suggested a possible solution.

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tz, an exh opening of 86deg after tdc gives a duration of 188deg. Assuming that this is what you meant, it would appear that the final result is an exhaust duration with 6 extra degrees and a transfer duration with 10 extra degrees. It should be possible to get what you had intended by the use of thinner cylinder base gaskets or machining of base.

I have always found tall transfers to be very disappointing. Lowering the cylinder has always yielded an increase in performance.

There has been a lot of kart classes over the years that have used restrictive carbs. They all use the venturi principle plus the intake tract length tends to be longer than when a non restrictive carb is used.

Do you have an exhaust time area for the setup that you have been using.

[SS90]

I have a photo of an ignition map here Teezee, but I seem unable to post it for some strange reason.......

[TZ350]

tz, an exh opening of 86deg after tdc gives a duration of 188deg. Assuming that this is what you meant,

There has been a lot of kart classes over the years that have used restrictive carbs. They all use the venturi principle plus the intake tract length tends to be longer than when a non restrictive carb is used.

Do you have an exhaust time area for the setup that you have been using.

Yes your right duration 188, bad mental arithmetic on my part.

Venturi principle, can you tell me more.

No time area, built on the deg/rev durations for various ports suggested by Bell.

If the TV is really crap and I want to do something even less interesting than slitting my wrists I will work out the time areas as described by Jennings, and will also take a look at Blairs work to see how it compares.

For mechanical reasions its difficult for me to lower the barrel, I will make another using the Wobbly duration specs and work through the time area calcs to dial in the port areas.

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[TZ350]

I have a photo of an ignition map here Teezee, but I seem unable to post it for some strange reason.......

I would be very interested to see it if you can get it posted.

Thanks.

[F5 Dave]

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Venturi principle, can you tell me more. .

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Um, just the principle the carb works on. with a flow rate equal on both sides of the restriction the speed of flow has to increase in the smaller section (& pressure drops as a result which is handy in a carburetor). So theoretically if you can get the velocity as high as possible for the given restriction your ultimate flow will be more which is the whole point (assuming also that good atomisation is still occurring if it is a carb).

So look at the carb. perhaps you may be better off where flow is so critical & suction is so much more, than say a 65cc mx that velocity must be much more with a 125 pulling on it. I don't know that the flow potential of a carb can be directly related for power output with extreme examples.

You may find that a 22mm carb bored to 24mm may have a smoother flow than the std 24, in fact Bell suggests that too now I think about it.

[TZ350]

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Modifying the bell mouth of the GP125 carb. We think that the GP carb may have been made deliberately restrictive to meet the UK/Europe learner licence Hp laws.

Pic-1 the original carb with a concave bell mouth that looks like its designed to choke at high speeds.

Pic-2 Thomas acting up.

Pic-3 The carb is slowly rotated by the drill all day to smooth out the devcon. it takes 2-3 applications of devcon over a couple of days to get a good bellmouth shape. But when its finished we don't even have to sand it.

Pic-4 The finished modified bell mouth.

Pic-5 Shows how the carb is just pushed onto a wire brush wraped with some masking tape.

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[F5 Dave]

1.
not it wasn't (a restriction maneuver), the GP125 made 13hp & was merely around when the UK legislation came in. I think I've told this story before (from reading PB in the late 80s). Suzuki UK enlisted an engineer Leon Moss to measure & restrict the GP125 so they could sell it under the 12hp rules. He came up & supplied a washer that went on top of the carb to restrict movement. Later he made money from customers wanting to derestrict their GP125s, whereby he simply hooked the washer out ready to resell to UK Suzuki.
Maybe they made it that way as it worked best with the sidecover so close as they only use that shape on the rotary engines? Only a (bad) guess.

You can smooth Devcon (or JBweld) with a wet finger quite nicely.

[TZ350]

Thanks F5, I will have to dyno two carbs back to back and see.

With the drill rotating the carb the runny devcon stayed in place while it set.

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[TZ350]

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Water testing the scavinging flow patterns.

Pic-1 the motor setup for test

Pic-2 the acrilic head

Pic-3 setting it up

Pic-4 testing

Pic-5 no idea what we are looking at.

Pic-6 the flow formed a rolling pattern twisting around like a horizontal tornado with it tail in the exhaust port.

No idea what looks good or not.

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[bucketracer]

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I have just found "Thread Tools" at the top of the page. Thread Tools drops down to "View Thread Images" These are all the images posted on the thread. Clicking on any one will take you to the post where it was posted.

23 pages of great pictures, a great way to find a post.

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[SS90]

This is pretty much a generic curve that most guys use here with a squish head Teezee, most guys set it at 25 deg idle, 17 full retard, which seems to bring the most gains.

Obviously the top curve relates to the ignition timing (just to save confusion)

[TZ350]

Thanks SS90. it looks more like what I need.

We have got an acrylic head and air/water set. I expect with a bit of experimentation we will be able to start getting some worthwhile info from it.

I over cut the transfers on my new barrel, they are now opening 110deg ATDC I was trying for 116. But it may not be such a bad thing as I can now devcon them back to 116 or less and slowly open them up again looking for the blow-down sweet spot.

Last time I used Bells duration recommendations to plan my ports this time I will go to the extra effort and use time area's to plan them. I know I can re-angle them and increase their area so should be able to get any time/area required. The main port is quite wide and I could put a divider in the middle for extra control of the transfer stream.

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[TZ350]

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A quick look at my inlet port using Angle/Area from Jennings page 81-82
http://www.vintagesleds.com/library/...20Handbook.pdf

Angle/Area is not Port/Time/Area that's something else.

Finding the mean area for the Port/Time/Area calculation for exhaust and transfers is relativly straight forward but I used Angle/Area for the inlet because I am unsure of how to calculate the mean area of the rotary valve inlet port.

Angle/Area = Capacity X PortArea/Duration

For my GP125 with an inlet port area of 2.6cm3 and opens 145BTDC closes 85ATDC, Inlet Duration 230deg.

Angle/Area = 125 X 2.6/145 = 9.7

According to Jennings chart a rotary valve Angle/Area of 9.7 is ideal for 8,500 rpm

So using the quick and dirty Angle/Area I can see that the 24mm carb is a real problem.

To get the Angle/Area required for 10,500rpm I have to increase the Area of the Port (and carb) and/or the Duration which is pretty much at its limit.

I am taking a careful look at how to design a venture for maximum flow.

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