03sierraslt

iTrader: (22)

Holly **** I just read that whole thread.... I have a headache from math and am going to go have a beer. Very good read, however considering my cam is spec'd for a blower my overlap is -6 so I dont think any of it will benefit me. I may however try playing with these tables a bit just to see if I can reduce some of the fuel smell at cold idle.

oakley6575

iTrader: (5)

So today I added 17% to the normal and make up tables. It didn't make the exhaust smell any better. Still smells like raw fuel. What I did notice though was a little better throttle response and 3% rich idle conditions. Also a lot less low idle rpm surging. In fact on my test drive, i didn't notice any surging. I will work on the VE table now to get that dialed in again and see where that gets me.

SlickSierra

iTrader: (4)

So thats why my truck smells rich. gonna have to ask the tuner about this

KLUG'S SS

iTrader: (6)

Yes it can help with that. Like I said especially with "large" cams in particular. See what is happening is with some of that raw fuel going right out the open exhaust valve the cylinders aren't getting a complete burn from each injection event and will actually show leaner on a wideband or in the fuel trims than it actually should be. That's why for anybody that has made an adjustment to the injection timing noticed their tune going towards the rich side. The airflow tables (VE/MAF) will have to be revisited.

As always though the rest of the tune needs to be done correctly like if someone is running larger injectors need to make sure that all of the injector data is correct in the tune. Very important!!!

SlickSierra

iTrader: (4)

Good info.

mcfarlnd

iTrader: (15)

Can you elaborate more on this? Give an example? Don't we need to account for the rapid closing rates as well. For example a "XER" lobe ramp rate is dramatically different than that of stock cam profiles.

mongooseboy000

Is this why the truck struggles to start? Sometimes i can smell fuel
Out
The exhaust but it takes a bunch of tries to start it.

KLUG'S SS

iTrader: (6)

No, it sounds like you've got some other issues going on there.

Big cam in your setup?

mcfarlnd

iTrader: (15)

As Klugg said, that's prolly another issue. If you can, start another thread and post up your tune so we can help. That way it's easier for us to help and so we don't jack the OP's thread.

Hemi2Slo

Sure. I don't think that the closing rates will effect it much, if at all. It seems that the conventional train of thought is to adjust the EIT by either a percentage or by the amount of overlap that the cam has. But after reading all the threads that I can find, I came up with this theory. The object is always to delay the injector spray enough to keep raw fuel from exiting the exhaust valve. But the question has always been how far to move it. It always seems to be somewhat of a mystery to everybody that talks about it because the computer reverse calculates the timing from end of injection. The question is always where the injection begins. From what I can put together, the beginning of injection is irrelevant. As I understand it, if you change the EIT it shifts the entire injection pulse forward or backward depending on which way you move it. So, that said, the beginning of the pulse becomes irrelevant. The stock settings have the injector spraying the back of the valve. We know where the pulse ends, but all we know about where it begins is that is begins sometime after the stock exhaust valve closes. That's all we need to know I believe. If our cam is bigger than stock, we just need to adjust the EIT by the number of degrees past stock the valve closes. Since the entire pulse is shifted by doing this, it will in turn change the beginning of the pulse by the same amount, thus moving the spray beyond the point of exhaust valve closing.

So what I do is use the spreadsheet from one of the threads on this discussion to calculate the valve events. It won't let me upload the file for some reason or I would. But I use the sheet to calculate:

1. Stock exhaust valve closing event
2. New cam exhaust valve closing event
3. Difference between two
4. Amount to move EIT

So for example, the stock valve closes at 16.5* BTDC on the exhaust stroke, or -16.5* ATDC on the intake stroke. From the worksheet, that's 343.5* in reference to the crank ATDC exhaust stroke.

So lets say our new cam is a 236 exhaust duration on a 112 LSA. The exhaust valve would close at 2*ATDC intake stroke. From the worksheet that's 362* in reference ATDC exhaust stroke.

To get the refernce degrees, you just take closing degrees and add 360 to it.

Now, I figure the difference between the two: 362-343.5= 18.5

Now divide that answer by 90: 18.5/90= .21

Now add the .21 to the normal and makeup tables. That will move the injection pulse forward, or delay it, by 18.5 degrees. Which should stop raw fuel from going through the exhaust.

Again, I have never tested this on a dyno, and I am by no means an expert. But the five or so cars I've done this to feel stronger on the low end and have pretty good increases in driveability. I honestly would have to reread all the threads on this to remember why all the math works like it does. I just memorized the relevant parts lol. I wish it would let me upload the spreadsheet. I may be totally off on all of this, but has worked for me so far.

Edit: I found it, Soundengineer came up with it on HPTuners forum. The spreadsheet I use is in post #36 of this thread: http://www.hptuners.com/forum/showthread.php?t=32510