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Registered:
March 2004
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 Tunning an engine
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Thu, 11 March 2004 22:49
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 Yesterday, a owner of a 94gt4 was complaining about is tune, so i tried my best to fix it. First i make sure the car is warm, offcould start and running in a conventional mode (no fault lights et cetera).
I then select the tallest gear possible that will keep the dyno speed under 200km h at the end of the run. This gives the least torque multiplication and, in my opinion, the most accurate figures.
The trick is to run the engine up more than once. A single dyno pull will tell you very little about the management setup of any vehicle. My recommendation is for three dyno pulls back to back. This will get everything warm and stabilised enough inside the engine for representative results and, most importantly, enable you to see the engines self protection strategies at work.
Most common with 2000onwards vehicles would be the cat protection. Its a relatively new phenomenon, but one that is plain to see on the dyno.When the engine has been making calculated power(worked out via internal management algorithms based on continues load speed numbers) for a preset period of time, this protection is invoked.
A big stepoff in the air fuel ratio occurs, like flicking a switch, enriching the mixture via an overalll 20 30 percent trim. Weird.
The odd part about this cat protection strategy is that my experience had always pointed to suddently enriching airfuel ratios as being the worst way of protecting the catalytic converter from excessive heat.
Basically, more fuel equals more component for the reaction in the converter, and thus more energy(hence heat)that would be released via the process. There is a little more to it than this, though.
A lot more to it, in fact, as cat protection isnt the only enriching strategy commonly being used by manufacturers. Almost everywhere you look in modern factory software(and in some instances via programs like ls1 edit we can actually do this) there are non emission control related engine protection strategies based on adding excess fuel at high load conditions.
You can only figure that these strategies are carried out in the interest of durability, as adding fuel is an approach that is totally at odds with both good fuel consumption numbers and maximum power.
If you make one assumption about the automotive industry, make the safe one, that the engineering teams who write and apply this code are far from stupid.
This is why i often get a shudder when i see airfuel ratios and tuning strategies being applied to aftermarket equipped engines. Dont get me wrong there are some clever guys out there doing the stuff, but there are also plenty that have no concept of the basic premises surrounding durability and thermal management.
How many tuners ever look at anything other than peak power numbers on the dyno when punching the numbers into a computer? Why would they? to some its simply a game of lotto that works on figures.
Get the same vehicle tuned for peak power off the dyno and onto the test track. Hold it flat in fourth gear. Hold it flat in fifth gear and wacth the airfuel ratios. It is then, and only then, that you will find massive tuning problems. What worked on the dyno my result in severe and unexpected detonation under these much more difficult real world conditions.
The big humps and dips in the manufactures airfuel curves all of a sudden make sense out there here, bleeding seamlessly into the mix, and keeping strong repeatable figures on the airfuel ratio meter.
My point? Its simple one, and a message that alot of people performing there own tuning should plant firmly in the backs of their minds. Dont make the mistake of solely chasing dyno numbers or listening to advice of others that encourage you to run your engine lean on the dyno. Its an approach that may work well in dyno comp events, or events, or even for the 10 14 seconds it takes to belt from one end of the dragstrip to the other.
Its hardly a sensible and durable approach to working on your own car, and one that i suggest you avoid at all costs. Temper enthusiasm with the sensibilities of the design engineers. Please Consider.
[Updated on: Fri, 12 March 2004 05:39]
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| | Subject | Poster | Date |
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Tunning an engine
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HYP04A | Thu, 11 March 2004 22:49 |
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Re: Tunning an engine
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gold28 | Fri, 12 March 2004 00:13 |
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Re: Tunning an engine
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boris | Fri, 12 March 2004 00:26 |
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Re: Tunning an engine
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oldcorollas | Fri, 12 March 2004 01:47 |
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Re: Tunning an engine
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HYP04A | Fri, 12 March 2004 05:48 |
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Re: Tunning an engine
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oldcorollas | Fri, 12 March 2004 06:14 |
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Re: Tunning an engine
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Fattony | Fri, 12 March 2004 06:23 |
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Re: Tunning an engine
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Esteban | Sat, 13 March 2004 06:06 |
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