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Author Topic: Tuning the GX200  (Read 230 times)

Adrian

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Tuning the GX200
« on: 25 April 2022, 06:13:51 pm »
First post coming soon, (page just crashed).
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Adrian

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Re: Tuning the GX200
« Reply #1 on: 02 May 2022, 06:48:25 pm »
Setting a Standard?
In France, all Cyclekarts must use standard, out of the box engines.
Nice and simple, every car the same. 
In the USA, it’s clearly different since they seem to be more focused on speed.
In the UK most people have already tweaked their engine to some degree or other but nobody really knows how powerful they are but remember that there is only one reason for tuning an engine and that is to make your CycleKart go faster.
In the UK we have a generally accepted limit of 10h.p., but we cannot know what has been done to an engine and so we rely on the integrity of the owner. 
That’s a pretty loose ‘standard’ and as such is almost useless. What does it tell you?
Looking on the GX Tuning Store’s website it’s clear that a lot can be done to these engines to quite dramatically improve their performance.
I, no doubt like you, want to be competitive and not get left behind in the dust when we do speed events on go-kart tracks or demonstration runs.
In the UK, we do not run organised races with multiple cars on the track at the same time but we have fun on the track when two or three drivers might find they are having a bit of fun with each other. We often have little tussles on the track but just fun/practice stuff.
My cyclekart (the 1906 Renault) is heavy and using a stock engine is outpaced all the time.
What can I do to help it along a bit, so that it can keep up with the faster Cyclekarts?
Remember, these faster CycleKarts will have been tuned to some degree or other as well.  So, I have to tweak my engine in an effort to make up for it’s 100 kilo weight handicap.
I imagine this means more h.p. is required.
Well, if I am going to work on the engine, I need to investigate how the engine can be modified and what modifications give what increase in h.p.
Imagine there was such a list.
You could look down it and decide which items to pick in order to achieve your goal of 10h.p., delivered as you think best.
You could decide that quicker acceleration or high top speed was your goal.
Picking items off the list would enable you to tune your engine for the sort of performance you want but, just to complicate things a little, you will need to decide on the transmission you are going to use (clutch or CVT for example) and what if anything, can be done to it to improve its performance. Remember that there are no tweaking restrictions at all on the transmission. :>)
This suggest picking some items off list in order to get the full 10 h.p.
The question is how do you know your engine is not producing more than 10 h.p. and how would a scrutineer (which we don’t have) ever know you were playing fair? We don’t have a portable Dyno!
In my humble view, the only answer is to limit the performance parts you can use to those on a published list. Using some would give as much as 15 h.p. but that would be against the rules. When you have done, you must sign a document which (in good Faith) lists the choices you have made.
Of course, if everyone was using all the same parts it would have the same effect on the pastime as the French rules have on theirs. We would all be equal albeit that bit quicker. 
Honda produce this so that it delivers 6.5 h.p. no more, no less. It has the perfect crankshaft, piston, con-rod, cam-shaft, flywheel etc. etc. for its need with every bit of the engine fully satisfying the demands placed on it at the lowest cost possible.
Just keep that last bit in mind.
If we want to take the 6.5 h.p. up to 10 h.p. we need to do it as cheaply as possible.
Let’s look at what is needed to produce this increase of 3.5 h.p.
This example will result in an engine very close to the maximum power allowed, 10h.p. and at the lowest cost to you.
1.   Fit a tuned exhaust with muffler.
2.   Use the standard carb and change the main jet size to 75 and the emulsion tube to a size 140.
3.   Install 18 lb valve springs.
4.   Fit a 4° advanced timing key.
5.   Fit a 0.010" thin head gasket.
You’re up to 9 h.p. now so what about the tenth? 
We go back to our list and pick another item that gives just a 1 h.p. benefit and then do that.
For example you could open out the inlet and exhaust ports in the cylinder head to match their manifolds and polish them.
Now your up to 10h.p. so you have to stop there.
An alternative 1 h.p. gain could be to radius the back of the inlet valve, narrowing the valve/seat contact area.
Doing this effectively increases the valves diameter and lessens resistance to the incoming fuel/air mixture.
A new stage 1 cylinder head from GX Tuning cost about £250.
They do the following to it:
1.   Mill 0.080" off the flame face to increase the compression ratio and match and polished ports.
2.   They machine the valve seats to have 3 Angles on them, not just the one at 45°
3.   They fit larger valves which help the engines breathing and their lower mass reduces valve bounce.
4.   18 lb Valve Springs will help prevent valve bounce.
5.   Aluminium spring cups and split collets are to provide a more secure fixing at higher r.p.m.

All the above with the standard carb and exhaust being used.
There are other ways of tuning the engine of course.
In my opinion fitting a free-flow tuned exhaust is the first thing you should do.
It gives an immediate benefit by itself.
With the tuned pipe in place, a bigger carb can be used providing more power at a higher r.p.m.
A Billet flywheel and a billet con-rod are nice to look at but for our needs are pointless. They are not tuning bits as such but stronger components to cope with the stresses that further tuning (and higher rpm) will bring.
The heart of these engines is in the cylinder head. Concentrate your thoughts on the heart of the engine, the combustion bit, carb, inlet and exhaust.
Why am I saying all this when we are limited to 10hp. Well, lets take a look at what I am doing to the Renault (and for that matter, the Wee Beastie too though that has a dry clutch fitted).
With the Renault more power is need to keep up with everybody else but I don’t need that additional power for top speed. What I really need is not more ‘top end’ but more bottom end speed, more Torque.
Speed out of the corners and off the line is what’s needed so more h.p. is required to give me more useable engine rpm. With that I can lower the final drive/engine ratio for the improved acceleration I need but without a loss in top end speed.
So for me it’s a tuned exhaust, a Makuni 22mm card (re-jetted), a 4° offset woodruff key to advancing the timing, higher lift rocker arms (1.3:1) and 18lb valve springs.
That’s it as far as the engine is concerned. I think I will be within limit.
The Renault has a torque converter fitted and to help me utilise my new additional rpm I am modifying the clutch by cutting the weights in half and increasing the keeper spring rate so that the clutch engages at a much higher rpm which will help to prevent the engine from being ‘pulled down’ when trying to accelerate from slow corners or off the start line.
So, to achieve the 10hp from your standard engine, take your pick.
Be careful, this is where tuning balance steps in. Start with the easiest to do, the exhaust and see how you get on.
P.S.
Just for your information, the following might be of interest.
Petrol engines run on a mixture of petrol and air and the ideal ratio of petrol to air is around 14.7:1.
Wiki says:
The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all the fuel with no excess air.
For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every gram of fuel burned, 14.7 grams of air are required to burn it.
It's worth noting that our engines probably won’t start from cold on such a thin mixture. Putting the choke on, reduces this ratio a lot, maybe to 8:1 or less so that the charge in the cylinder will fire. Once the charge has fired the fuel/air ratio can be returned to 14.7:1. as the engine reaches it’s normal operating temperature.
Hope I haven’t bored the pants off you.
:>)

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Mark Under

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Re: Tuning the GX200
« Reply #2 on: 02 May 2022, 07:44:01 pm »
I have tried my kart in a very small car park with an untuned Honda and it is in need of tuning so I will be going with carb, exhaust, valve springs, etc etc until it reaches a more exciting speed.

Please don’t restrict engines too much as I for one would like to go as fast as possible, although my kart has a long way to go before it could be considered fast!

Ian F

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Re: Tuning the GX200
« Reply #3 on: 02 May 2022, 08:57:34 pm »
Engine modifications are very difficult to control without stripping them down and measuring parts.  There are also many ways of developing an engine and before you know it you end up in an expensive arms race spending ever increasing amounts of money for ever decreasing improvements.  I thought the aim of the Cyclekarts was to have some great fun at a reasonably low cost.  Probably one of the biggest performance limitations is the varying degrees of weight regarding the driver,  consequently for differing combinations of driver and karts some karts may require more power.  I just hope this can remain a fun pastime and not a wallet emptying exercise.  Suffice to say in just the few weeks I have been building the CK, I have been offered a 12 BHP engine and a 15 BHP engine! However, my plan was simply to use a Cadet kart engine that pushes out around 9 or 10 bhp which seem to be widely available.  For those that want to get into "competition" there is a vast array of championships to get involved in.  I would also suggest that beyond a certain sensible performance, CKs can become hazardous.

Graham Hill

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Re: Tuning the GX200
« Reply #4 on: 03 May 2022, 11:52:41 am »
I am personally keen to restrict CycleKarts to 10hp maximum. That's accepted as stage one tuning of the GX200. Anybody considering tuning their CK further for speed has not understood the ethos of CycleKarting.  The weight of the CycleKart or driver is irrelevant.
The tuning of the GX200 has been historically documented on many platforms, achieving 24hp in some instances. For CycleKarting my understanding and experience is ..... Stage One  ...  10hp max.
I have arranged events at Stretton Circuit since 2018 and will make it known early that all CycleKarts are welcome on 24th,  but any vehicle tuned over 10hp will be restricted to a static display only. All new-builds and existing-modified will be subject to peer-scrutiny before being allowed on track.
The guidelines have been available on the website for some time. However as a committee member I can advise that we have given much serious thought to this area of the build guidelines and they are to be confirmed and published imminently.
« Last Edit: 03 May 2022, 01:40:19 pm by Graham Hill »

Mark Under

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Re: Tuning the GX200
« Reply #5 on: 03 May 2022, 12:54:25 pm »
I am only putting the stage 1 mods on my kart, hopefully taking it nearer 10/than 6.5hp.
Hopefully the parts ordered, carb, exhaust, valve springs and timing key will take it up a bit.

I agree that to take it beyond this limit would get expensive and probably not add to the fun much.   

It would be a shame to be restricted to a bog standard engine as I think the French are, part of the fun is tuning the engine and getting the kart to go as fast as possible.


TheGiantTribble

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Re: Tuning the GX200
« Reply #6 on: 03 May 2022, 02:04:03 pm »
A couple of thoughts...

The fun isn't in the speed...I know counter intuitive but that's typical of CK's!
Mark, feel free to have a go in mine, I'm sorry to say all it has is a tuned exhaust (to up the torque slightly) and the oil sensor disconnected, and despite that's all it's got is still manages to be rather sprightly.
Ian...as soon as a CK is moving it indeed has become hazardous.
Graham, given how difficult some of these tuned engines are for people to start, could we introduce Le Mans style starts?  ;D  ;D  ;D Please  ;D

Graham Hill

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Re: Tuning the GX200
« Reply #7 on: 03 May 2022, 02:13:38 pm »
Are you suggesting any handicap for inside leg measurement?

Ian F

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Re: Tuning the GX200
« Reply #8 on: 03 May 2022, 02:50:33 pm »
Also think 10BHP is a sensible maximum guideline.  Thats enough to pull at least three rice pudding skins off  ;) and to stop them bogging down too much in tight corners.  Going as fast as possible will probably introduce additional hazaeds due to the limitations of the other aspects of Cyclekarts, surely the fun is to have a sensible working overall package.

TheGiantTribble

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Re: Tuning the GX200
« Reply #9 on: 03 May 2022, 03:51:18 pm »
Are you suggesting any handicap for inside leg measurement?
I think we could easily even it out for those of us who don't have the legs of a Gazelle...everyone just stand 12 paces away from their CK...I recons that's anywhere from 3 foot for you, to 20 meters for the likes of Adrian and Stephan!!! (sorry Adrian and Stephan)

Hay if you make rice pudding properly a Lambo shouldn't be able to pull a skin off let alone three!!!
Although that's now got me wondering if we couldn't add our own version of tractor pulling to our contest's???

Adrian

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Re: Tuning the GX200
« Reply #10 on: 03 May 2022, 05:47:00 pm »
Mr Tribble.
I know I'm a problem, but what is wrong with my legs?
:>)
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Adrian

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Re: Tuning the GX200
« Reply #11 on: 03 May 2022, 05:55:31 pm »
Your tractor pulling idea could be the solution we are looking for! If each Cyclekart is attached to scale, we could measure the pull and check the horsepower? We all have the same size wheels.
Before I get jumped on, its just a thought.
Stefan, would that work? Thanks for the ratios spreadsheet, I'm off to play with my spreadsheet now. Force times radius equals torque so force equals......... etc
?>'
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Applejack

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Re: Tuning the GX200
« Reply #12 on: 04 May 2022, 09:11:42 am »
I agree with everything you said Graham and remember guys the more you tune them the more they can be unreliable. The FUN is the building and the driving.

Ian F

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Re: Tuning the GX200
« Reply #13 on: 04 May 2022, 04:39:31 pm »
Just ordered my engine today, a Stage 1 Loncin copy from GX Tuning, about 9 to 10 BHP.

Tinworm

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Re: Tuning the GX200
« Reply #14 on: 04 May 2022, 04:48:27 pm »
The ethos of cyclekarting is important to me.