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Old 07-22-2005, 10:30 AM
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longassname longassname is offline
Just some dude.
Join Date: Sep 2002
Location: Miami, FL
Posts: 3,987
Significant Technical Input
I've taken a little time to get some software work done. I recently got back the test reports on the injectors we will be using. The software I made during the testing phase was based on the test reports for the factory injectors, the advertised flow rate of the new injectors, and latency values that have worked for other people on other cars. Of course the test reports are dead on accurate--they are advanced tests based on my criteria to get all the exact information I need to know for doing the software perfectly.

Having made the precise mass air flow meter measurements and now having the fuel injector test reports I was ready to start putting together the final version of the software. I won't get into the numbers again as you already know the basics on the flow rate of the injectors and explaining the the more complex stuff that controls the timing of when fuel is injected is complex and unneccessary--though an important ingredient of performance. What I have for you today is the timing and fuel maps.

Some reworking of the maps is an inherent part of changing the fuel injectors. The fuel injector change doesn't call for changing the shape of the map but since the values for calculated load which make up one of the axis of the maps are changed when the fuel injectors are changed it is necessary to rescale the values of the load axis on all maps. The problem you run into is when you rescale the values you don't necessarily get whole #'s so it takes some work to calculate from the original table values what the values should be with the new scale so that the shape of the map stays the same. We do this but we also take it a bit further. The load range of the factory maps does not include the increased load range we are running with the forced induction. When choosing our new scaling we expand the load range covered. We then use the data from the factory table to fill in the part of the load range corresponding to the original range and extrapolate new data to fill in the extended range based upon the characteristics of the engine, general tuning principles, and experience with other fuel and ignition timing maps.

I'll show the timing maps first as it is easier to understand and a cleaner looking map in the factory form. The SVX uses both a lot and very little timing due to the engines design. The ignition timing map goes all the way from 50 degrees at high rpms and low load to 0 degrees at low rpms and high load. Here's the factory timing map:

Here is the stage 3 timing map. Allthough it is actually the same number of datapoints you can see it as a larger map containing the factory map. It now covers a larger load range on out to where values for both low and high rpms are 0. The original values are not decreased to retard the ignition timing. With the load range properly expanded there is no need to decrease the ignition timing at the factory load levels. We simply need to have the correct values at the higher load levels which correspond to boost conditions.

As I have said before the factory fuel map is a fuel revision map. It does not say how much fuel to inject. It says how much more fuel to inject above the amount the ecu calculates is needed to get an afr of 14.7 based on rpms and load. So you have you picture the plane on which these maps is built as being an afr of 14.7 and the values of the tables are the additional fuel added to reach a lower afr. The factory fuel map is a bit ugly looking but can be understood with a little knowledge and though. Normally fuel maps climb as rpm and load increases. At frist glance the SVX fuel map looks to be backwards. It isn't though. You have to keep scale in mind and remember this is a revision map--the difference between the highest and lowest points in this map is only about 1.5 in the afr. That said to the trained eye what you have here is the traditional map you would expect with a hump of extra fuel added at low load accross the entire rpm scale. This map won't look so ugly as part of our larger fuel map.

I expanded the load range of the fuel map just as I did with the ignition timing map. The values on the left side of the map are mostly taken from the factory fuel map. Values on the right side of the map correspond to boost conditions. Some of the values for higher rpm ranges on the left side of the map were changed as well. The original factory maping can be seen in the blue area. The rest is my doing. I don't want to get into explaining map creation any more than I have but you can get the general idea of increasing fuel as rpms and load increase. This map should work extremely well for us.

The questions on the stage 2 sofware have settled down and I have the final version of the stage 3 software ready to go in the car when i get a chance to switch back to the nismo injectors. I'm going to go get lunch and get back into metal work. Today I'm going to work on cutting the metal to enclose the left and right sections of the manifolds.
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