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.
:>)