A long time ago the community was blessed with a lot of tuner interest and activity. Now as GM stopped with the 4 cyl SS additions the interest has died and people slowly started fading away and taking their knowledge and information with them. Credit is given where it belongs here and most of this information was put out by GMTech and the select few people who were around here when he was doing the most of his table testing. It took a while for people to get interested in the topic again, so digging up the information and doing a little testing to verify the thoughts took some time to get it all put back together. So the rambling ends and the info begins!
LNF Direct Injection Window Base Operation
The crankshaft for most people is viewed as a 360* object. TDC is at 0*, BDC is at 180* and again TDC is at 360*/0* again.
This is a misconception that has arisen from what i believe is the camshaft degree wheels doing. The Normal Camshaft Degree wheel is numbered in two ways.
First Design: TDC is labeled as 0*, and BDC is labeled as 0*. the midpoints between the two (after TDC to BDC midpoint and After BDC to TDC midpoint) are labeled both as 90*. This edition camshaft wheel takes a little bit of math as the user usually has to do a slightly longer conversion formula when trying to find the cylinders true TDC.
Second Design: This is the design that i blame for the 360* train of thought. TDC starts at 0*/360* and as you rotate clockwise it counts down from 360*, passing BDC at 180* and reaching TDC back at 0*/360*.
Now, the way it really works and everyone should be viewing it as:
Since the crankshaft is twice the speed of the camshaft (2:1 ratio), it is officially proven and known the the crankshaft does 360* twice when the camshaft does 360* once. The fuel injector is opened and closed on a degree based event just like the camshaft so thus we can plot its operation out just like a camshaft. So now the crank is a 720* rotation when the cam is only 360*
I'm going to plot a camshaft from a standard comp cams degree card which is used on a GM Ecotec LSJ Turbo application to help with the visualization process. This camshaft is XE246THR-13 and is an Xtreme Energy Camshaft for 2.0 Turbo applications. The .050" Values will be used for the example.
The Cam Plot on a 720* Base:
First the Overlap event on the camshaft takes place at the 360* mark. Compression sweeps through into 0*/720* where you get a spark event and start the power stroke which leads back into the overlap event at 360*.
So with the information the card gives us the intake cam center line is 112*. the 720* plot for center line puts this value at 248* IVCL . Divide 204* duration by two and you get 102* each direction for opening and closing * values which would be IVO at 350* and IVC at 146*. The exhaust is 113* separated so the center line is 361*. Halve the duration of 200* is 100* from the exhaust center line. This plots out as EVO is 461* and EVC is 261*.
when plotted on paper it looks something like this:
Now if you plot the opening values for the direct injection on the same chart you can see where the injector is starting to fire off during the cam event.
The minimum opening angle allowed is 240* and the maximum angle allowed is 431*. The DI Opening Angles got added to my previous plot and it looks like this:
Note this particular cam has 89* of overlap and is not a suitable choice for the Direct injection operation as the injector spends a lot of time spraying while the exhaust valve is open. Due to less overlap in the park position of the factory cams we can automatically see in our heads that the factory cams are better suited as the exhaust is more advanced thus letting the Injector spray more during the intake cycle than the overlap cycle where some energy is wasted. The camshaft events for direct injection face more deciding factors than that of a runner injection system like the lsj has. the lsj can have the exhaust retarded more as the fuel is sitting behind the intake valve where it waits for the valve to open before it enters the cylinder. this older setup can have more overlap to help flow out turbochargers as it helps draw that sitting fuel in where in the direct injection system its already in the cylinder so if overlap is occurring the fuel has a more direct exit. the piston shape helps divert the fuel upward into the cylinder head which should help keep it from flowing straight out the exhaust valve but there is a bigger loss in this system. cylinder temps also have a bigger play as after compression and ignition the piston dome is hot and fuel coming into contact with a hot piston can cause pre detonation. the oil passage in the piston head helps with that as well. overall the direct injection system has way more variables to think of when modifying both physical parts and calibration data.
With all this data presented in a form that is easy to understand by visual form you should now understand exactly what the Injection Angle Table Values mean and you can adjust them accordingly. The adjustment of these values drastically helps Knock Retard situations. If you increase the window angle by raising the value you will spray the injector before the cylinder gets really hot from dynamic compression and thus prevent the event of detonating bad fuel put out by today's gas stations.
I will be posting another Direct Injection post shortly to help everyone choose a side on the Direct Injection Event most commonly referred to as Injection/Spark Over-spray. My post requesting log information from turbo swap vehicles is to help plot data for this post. The more Turbo Swap logs i get with basic information will help me get the post up faster so if you know someone with some good logs that meet the qualifications please pass me some info so i can finish the information.
The Qualifications are listed in this thread: http://www.hptuners.com/forum/showth...-Data-LNF-Only
Alex Johnson
CobaltSSOverbooster
Photos Attached to Post so they can be viewed larger ad/or rotated for ease of viewing.
Enjoy!