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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 PointThe 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. TorqueIt'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)
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:
Engine BasicsWhen 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.
What Can Be Done
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).
SummaryThere 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:
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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Copyright © Rob Collingridge 2009 - Last updated 06 Oct 1999