Injector timing for camshafts
#11
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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.
#12
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.
#13
So thats why my truck smells rich. gonna have to ask the tuner about this
#14
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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!!!
#16
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When I tune cars/trucks with larger cams I have been delaying the injector by the number of degrees that the exhaust valve closing event deviates from stock. That has worked well for me so far. But I have not put anything on the dyno. But the engines usually feel better and it seems to cure a lot of low rpm surge.
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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
Last edited by Hemi2Slo; 04-16-2012 at 07:34 PM.