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Simon Scuffham's Tuning Overview (28/6/99)

Simon Scuffham has been racing the Elise for a few years and has amassed considerable knowledge on the car and it's tuning options. The following is an overview posted to the alt.cars.lotus newsgroup by simon and I've included it here for reference:

This is not meant to be a definitive guide to engine tuning, but more of a basic reference of what's possible and what isn't.

The Start Point

The Elise uses the Rover 1.8 'K' engine, it is not modified in any way from the MGF installation, even down to the exhaust (only the tail pipes are different). In standard trim this produces some 118Bhp @ 5,500rpm but as with all production engines, this varies from car to car.

For all anybody says about the 'K' series, it was never designed to be 1.8, it was a 1.4, thus to get to 1.8 it has a longer stoke than is ideal, the downside to that it limit's the ultimate tuning potential, the upside is that it gives good torque at relatively low revs.

Power vs. Torque

It's all very well saying you want more power from an engine, but you need to understand what you are asking for. An engine produces torque, this is measurable, power is calculated from torque and Rpm that the torque is produced. In simplistic form this works like this:

Power = Torque * Rotational speed (radians/second)
or Power (Bhp) = (Torque (Ft/Lbs.) x Rpm) / 5250
or in metric form Power (Watts) = Torque (Nm) * RPM * 2 * PI / 60

So to get 118Bhp @ 5,500Rpm you need to produce 113Ft/Lbs. @ 5,500Rpm. Having grasped that concept, what you need to understand is what you 'feel' when you are accelerating in your car, it's the torque, and not power you feel. If you want to improve the acceleration you have two ways of doing this:

  1. increase the torque the engine can produce
  2. reduce the gearing, thus increasing the torque to the wheels
Now the first is the obvious one, but you need to consider at what cost (in terms of engine performance). The second is the more intelligent approach, as even if you get more torque out of the engine, you will need to think about gearing to get the best out of it.

Engine Basics

When all said and done, the torque an engine produces has more to do with it's capacity than just about anything else, to use the American expression, 'there ain't no substitute for cubic inches'. The most highly tuned engines, irrespective of what kind, will make about 1Ft/Lb torque for every 11-12cc, thus realistically the best peek torque from a 1.8 is about 50-160Ft/Lbs. The trick is to get the engine to produce this figure over the widest range of Rpm possible.

The basic production engine was designed to meet all sorts of criteria, from cost and ease of manufacture to emissions and service life, thus there are all sorts of compromises made with it, this gives the following basic limitations.

  1. The engine is basically safe to rev only to 7,000Rpm before rods/pistons/followers/springs will need changing.
  2. The plastic inlet manifold is at it's best at low to mid Rpm, it's not got the airflow to meet high rev air requirements.
  3. The standard Exhaust manifold is a compromise and limits top end performance significantly.
  4. The valve and port sizes are not big, thus top end breathing is seriously limited.
  5. The Mems ECU is not re-programmable (to all intense purposes).

What Can Be Done

  1. Improve the cylinder head
  2. Change the induction system
  3. Replace the ECU (I don't mean chips/ICON's/Interceptors)
  4. Change the cams/followers
  5. Change the exhaust system (not just the box)
  6. Replace the crank, rods & pistons
  7. Forced induction - supercharging/turbocharging
The thing to remember is that individually, each of these will not give you the 'Holy Grail' of performance and most will have a downside. The best place to start is not to bolt something on, but to refine what you have, the Lotus 135 kit is a fine (if vastly over-priced) example of this. Basically, it's a well-ported head with the better proportioned plenum based manifold from the VVC engine, this gives about 143Bhp and is about the practical limit of the plenum based manifolds.

This gives about the best you can get without sacrificing the lower rev range significantly (although it will reduce it), the only area this could be improved without compromise would be to replace the ECU with a custom mapped one for this set-up.

Changing the ECU on it's own will give you the ability to map the engine to the limits, I am told with Super-Unleaded it possible to get to 130Bhp, but this is not without problems.

Changing the cams/followers can dramatically alter the engine characteristics, but most are aimed at improving the mid to top end at the cost of low to mid range torque.

Replacing the exhaust system with a tuned system will have little positive effect without re-timing the cams and mapping to take advantage of it, however, that done it will allow you to gain the most from any conversion, particularly at the top end. By replacing the crank/rods/pistons with racing lightweight items, it becomes possible to spin the engine to 8,000Rpm, before you hit the limits of the standard liner's. This will have other benefits, they will have less inertia thus need less energy to spin, thus freeing up more power.

The last option is technically the cheat's option, this overcomes the capacity limitations of an engine by forcing more fuel/air into the same chamber size and thus increasing torque (and power).

Summary

There is no perfect solution, you need to decide what you want from you engine, if you don't mind having to use the upper half of the rev range all the time, then go for re-gearing and tune the engine for all out power. If you want more low-down pull without having to stir the 'box, go for the forced induction solution.

The things to remember are that:

  1. Using throttle bodies WILL kill off good torque below 3,500-4,000Rpm
  2. The plenum based manifold will never work well over 4,000-5,000Rpm (I don't believe that with all the work in the world, greater than 160-170Bhp can be achieved)
  3. Porting a head is not an exact science, some people are better at it than others, and there are varying levels that can be gone to, the limit for a port only job is about 140Bhp.
  4. Re-gearing is by far the simplest and most effective way of making the car go faster, the Lotus C/R box will give a 6.5% advantage in 3 & 4th over the standard box.
So next time you are told that you can get 160Bhp from , a ported head, a cam kit, a Chip kit, a Sports exhaust, or a free-flow air filter, you can say that that's complete bollocks and where's the evidence to prove it! It is possible to get well over 200Bhp from this engine, but it's NOT a cheap simple job.

One final point - Dyno prints are very subjective - especially from rolling roads, you should always go for getting a print before and after, this will give the real picture. For more detailed info on what can be done, it's well worth reading Dave Andrew's write-up on the 'K' at: http://members.aol.com/_ht_a/DVAndrews/kengine.htm

These are my own opinions, you may not agree with it, but this is the way I see it. I am not about to recommend that you should get anybody's kit, but this should help you understand what your getting for you money, and above all, TRY it first!
 

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