What is really LV8?

[GN owner]

Dennis,

I can now see that ALL of the sensors and inputs to the ECM must be working in tip top shape in order for everything to come together and in the end determines the driveablity and performance of a vehicle. It appears that LV8 plays a bigger part in the final scheme of things than most people think me included!

 

[oneslobuick]

wow that thread was over my head

But my blm's are around 100 at idle. does the lv8 caluclation have anything to do with the car running rich.

I have adjusted the fp up and down with little change.
I did try another chip and the lv8 did go down to normal but there was very little change in blm's.



I think I need to get another chip.

thanks for the help.

 

[turbo2nr]

So, what about the people driving around with their speedo cable broken/disconnected? Will the LV8 be usless? No PE? Does ECM just guess?

What about wrong data from different rear end ratios?

It seems like it is very important to have the proper MPH info going to ECM, right?

I'm asking because I keep switching rear gears and tire heights, just trying different things.

Thanks.

 

[BJM]

Wow someone dug deep to revive this thread.

However you missed a couple of things. LV8 is basically a derived power level on the engine and its used to determine timing, fuel, when to go into PE, etc. It does not use speed (VSS) input so the engine will run fine without speed input but the TCC will not know when to lock up.

Your idle BLM at 100 is not likely an LV8 problem. If your chip is for an injector size smaller than what you are running this will happen. Fuel pressure way too high as well will do it.

 

[JDEstill]

Someone dug deep indeed! I've actually got something to contribute. Maybe others knew this, or maybe I'm wrong about it, but I've decided that LV8 is another way of saying manifold pressure. A table in the chip that is RPM vs. LV8 is equivalent to a table that is RPM vs. MAP. If you can figure out what LV8 equals what MAP, then you can lift that table and use it in a speed density type system.

Here is the stock ignition table for a speed density type setup (such as a DFI or FAST system):
http://pages.prodigy.net/buickv6/CarStuff/stock GN timing map.pdf

How did I come up with this you may ask? Let's do a little example and I'll show you.

Lets take a point off the ignition map, say 23.9 deg @ LV8 = 160 and RPM = 3200.

First I need to convert the LV8 to something usable, like the mass air flow. Using the equation further up in this thread I find the air flow required at LV8=160 and RPM=3200 is 96.2 gm/s.

Now I need to convert that MAF value to a MAP value. I could do this with my usual model (which takes rpm, MAP, and estimates for MAT and volumetric efficiency to give a MAF value), but luckily I have some data I got from gnjones a long time ago. He had built a datalogger for his mostly stock GN, and has MAP vs MAF and rpm data. Analyzing his data gave me an amazing simple formula for MAP vs. MAF as a function of rpm. (This formula is only good for a stock GN, between about 700 and 4500 rpm, and up to about 16 psi of boost, but in that range it seems to do pretty darn good.) So, using that formula, I determined that to get 96.2 gm/s of air flow at 3200 rpm requires a manifold pressure of 17.4 psia.

So now I can say that the example point of 23.9 deg at LV=160 and RPM=3200 is the same as 23.9 deg at MAP=17.4 and RPM=3200.

I then did that same analysis to every point on the ignition map (ain't spreadsheets grand?) and got a surprising result: going down a LV8 column at every rpm, figuring up the mass air flow required for that point, then determining the manifold pressure required, gave me just about the same pressure at every point! Well, close anyway, within +/- 0.5 to 0.75 psi between 1200 rpm and 4800 rpm. Below 1200 rpm it was a little further off, but still within 2 psi or so. But still, the assumption that constant LV8 = constant MAP looks surprisingly good.

So I just took the stock ignition map, changed the LV8 column headings to the equivalent MAPs, and voila – the stock GN ignition map ready for use in a speed density system.

Fun stuff, eh?

John