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Old 10-07-2002, 03:20 PM   #1
Scooby Specialist
Member#: 4980
Join Date: Mar 2001
Location: Albuquerque, NM USA
Default Utec dyno plots and target A/F ratios and some tuning advice.

First off, I want to thank so many of you for adopting the UTEC as your preferred form of engine management. We've been very busy over the last few months getting everything tested and ready for the mass public release of the UTEC.

So far our results have been great, but I am not happy with only our results being great. I want to give away as much advice and data as I can to help you guys tune your cars to the level that we are seeing here in our shop.

I've heard a lot of people spouting "misinformation" about Air: fuel ratios, timing numbers, and just about everything else that has to do with tuning.

I decided that I would post some of the data from a few dyno sessions we've had in the last week or so to help give you guys an idea of what we tune to here in the shop. This is not meant to be a "we know best" post, but simply a way to show you what works for us.

This first dyno plot is of a car that we did this weekend. The three curves on the plot, from lowest peak HP to highest peak HP, are; 1. Pump gas map, 2. C16 map and 3. C16 + NX express Nitrous N-ter Cooler.

The basic setup on this car;
Turboxs STG4 kit with the following; PE1820 turbo, headers, Turboxs Hyperflow TMI, and NX Express Nitrous n-ter cooler.

As you can see from the chart the car made 317hp on pump gas, 342 on race gas, and 362.9hp with both race gas and the NX intercooler spray kit. This car made a whole lot of power!

I was very pleased with the way the torque curve ended up with the exception of the extra lag that the headers likely caused.

This is what I would call a "good tune"

Letís look at another dyno plot

In this dyno plot you see the A/F ratios and the torque curves of this weekend's tune.

The first thing I want you to note is how rich we must run the air/fuel ratio to keep detonation away at this power level on pump gas. As a whole the Air fuel chart shows from about 10.7:1 to just over 11:1. This of course was a custom tune and we would run an off the shelf kit a bit richer in the upper RPM so that we could keep the whole chart down around 10.7:1.

On C16 (116 motor octane, 117.5 research octane) we can run the car a good deal leaner but still not as "lean" as some of you might think. The extra advance we run on race gas lets us run a little leaner mixture since we don't need so much extra gas to cool the cylinder temps. This plot shows that on C16 we usually run between 11.5 and 11.7:1. This level of tune is about where Phil was running when he was at the Subaru shoot-out. It's still pretty rich, there is good gas in the tank, and we can run very nice advance numbers to get great power.

The next line on this chart is kind of instructive as to what charge density does to your A/F ratio. We started spraying the N2o over the intercooler at about 3500rpms. With no other changes in the tune the car leaned out to be between 11.9 and 12.4:1 gaining 20hp in the process. I don't expect that we could have ran it quite that lean without the extra charge cooling that the n2o provided while it was spraying over the intercooler. The end result was pretty outstanding.

What you should take away from these charts is that charge temp AND octane level will allow you to get away with air fuel ratios that would cause severe detonation on pump gas. I've heard a lot of people throw around the 12.5:1 number as ideal for turbo charged cars. This may or may not be the place where peak power can be made, but most of the time you can not even get close to that on pump gas and for the most part there is no need.

The next chart that I want to put up is one that shows a STG4TMI plot vs. a stock plot.

This was a custom tuned UTEC STG4TMI on pump gas. Note how small the changes are in overall air fuel ratio. This is another case where we are able to run a stage 4 car to a 10.7:1 air fuel ratio and make very nice power numbers. We could lean it out a bit more before detonation would set in, but the additional cooling that the extra fuel provides is well worth it when you know that the car your tuning might just hit 140mph one day.

This last plot is the same UTEC stg4tmi car vs. stock, but we are showing HP instead of A/F.

My guess is that this post has created as many questions as it has answered, but for now I at least want you guys to have this data. Iíll try to answer as many questions as possible.

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