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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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Location:
Madrid - Spain
Registered:
August 2002
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Re: Tunning an engine
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Fri, 12 March 2004 00:13
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I tend to agree with you. I think that it is rediculous that someone can achieve a better state of tune with an aftermarket ecu than a team of design engineers with significant resources behind them could.
I do think however that as soon as you take a particular engine outside of the manufacturers design scope, ie different reliability requirements, operating environment engine components etc, you have compromised the OEM's "optimal" state of tune. The more changes made, the worse it gets.
The biggest problem that the aftermarket faces is to acknowledge that given the OEM's design scope, their state of tune must be very close to optimal.
Now if the user of this vehicle has decided that they would prefer to compromise the vehicle reliability to achieve performance gains, then they should be made aware of that. Likewise if they want significant increases in power, that will come at the expense of reliability and driveability.
Unfortunatly it is very difficult to achieve OEM standards when it comes to all these requirements. Therefore the customer has to accept these compromises or pay the huge developmental costs involved in achieving these standards.
If the customer wants a dyno champion, give him/her that, but be very clear that it comes with some drawbacks.
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I supported Toymods
On probation
Location:
Brisbane, Queensland
Registered:
January 2003
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Re: Tunning an engine
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Fri, 12 March 2004 00:26
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wow, maybe you could put some paragraphs next time i was going cross eyed trying to read that!
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Tunning an engine
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Fri, 12 March 2004 01:47
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wow, cut and paste? 
more fuel = more heat in the cat IF there is enough air to combust it... a RICH mixture has LESS residual oxygen, and will COOL the exhaust gas AND the cat.
of course, almost anyone using aftermarket ECU will realise that they are compromising durability.
driving with more than 5000rpm compromises durability!!!!
driving with more than half throttle compromises durability!!!!
people who do their own tuning should know what they are doing beforehand. some engines like to run lean, some like to run rich, and decent tuning requires more than just the dyno readout. EGT and engine temps for a start.
least gear multiplication? you mean 4th gear 1:1 ratio?
i believe a 'dyno pull' is not the best or even a good way to tune an engine!!!!!! locking the dyno at a given rpm, and then applying different loads is the way to seat the base fuel table. when accelerating and other transient conditions is where "enrichments" and "fuel trim" come into play, and often these can only really be set on the street..
you must also remember that a dyno pull in 4th gear is nothing like the fast transient pull of 1st gear on the street.
Cya, Stewart
ps, wow, look, spaces and paragraphs  
[Updated on: Fri, 12 March 2004 01:49]
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Registered:
March 2004
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Re: Tunning an engine
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Fri, 12 March 2004 05:48
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 better?
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Tunning an engine
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Fri, 12 March 2004 06:14
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LOL  surprisingly yes!!
it aint easy to read large blocks of text.. but it's funny to watch ppls eyes start wigglign when they try
thanks for the spaces!
Cya,S tewart
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Location:
Melbourne
Registered:
May 2002
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Re: Tunning an engine
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Fri, 12 March 2004 06:23
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Reading this gives me the thought that when most ppl out there are chasing performance, they forget 2 things. Loss of reliability and drivability. Consider that manufactures spend millions of dollars developing a engine and a car. I cannot see how one person on a dyno can apparantly make the car run better than wat comes out of the factory. Remember that cars now come with warrenties, hence they have to last. The best warranty you get out of a workshop is a concrete one. Im glad that there are other ppl out there who happen to share the same opinion as me, but knowing all this still doenst stop me from modifying my car. Its just that i wont be supprised when something breaks. Thats why i have spares. lol
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Location:
Brisbane - Chapel Hill
Registered:
June 2002
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Re: Tunning an engine
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Sat, 13 March 2004 06:06
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I think another thing that needs to be remembered is that factory engines and their tuning, are designed to operate effectively over a wide range of operating conditions. This means there are going to be compromises affecting performance.
After all, an engine that breaks down in cold weather, or refuses to start when hot, is going to cost a company a lot more than an engine that has 10kw less and is reliable over a broader range of conditions. Factory engines are built for joe average anyway.
In that respect, im sure professional tuners can tune an engine to run a lot better than stock, but under a much _narrower_ range of operating conditions. Hence the "real world tuning" comments.
Regards,
Esteban
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