What does a greater - % change mean as you climb in RPM? Does this mean more fuel is being added?

 

Yep. It won't necessarily follow a smooth curve. Are you looking at a stock or modified file?

Rich Krause

 

Its a modified file and yes Rich it is not smooth like you said The last two values in the table for example are -2.0, -2.0

I was just wondering since the majority that have stock VE tables have negative values or values relatively close to 0 here and the ones that have altered VE tables have positve or values far from 0 here. Is this a coincidence or for a reason?

Also Rich, while I have you, whats your thought on increasing displacement(if any in the program) and its effect on the PE vs RPM tables?

 

AFAIK when you change the injector constant the only difference in output is that the injector pulse width changes in proportion. IOW if the original program was for 24lb injectors and you reprogram for 48lbs, the commanded pulse widths will be cut in half. Nothing else will change, or needs to be changed. The only exception is the injector offset, which is the method the PCM uses to compensate for the amount of time it takes the injector to open/close. Generally, larger injectors are operating at shorter pulsewidths so the offsets are more of an issue with big injectors. The offsets will affect mostly idle or other very light load situations but have no appreciable effect on WOT fueling. Changing displacement in the tables has exactly the same effect. Increases or decreases in the displacement will cause a proportionate change in pulse width. The computer isn't smart enough to "realize" that a motor with a different displacement will have a different VE.

I think that once you go into PE mode, VE is ignored. But that's a whole 'nother subject. The VE numbers have little to nothing to do with actual VE anyway. I generally leave the VE tables alone. The main way you tune WOT fuel is with the PE tables.

Am I at all addressing your question?

Rich Krause

 

Yes you did very much so...thanks a ton..so basically you either want to touch the injector constants or the displacement. I get the PE stuff too.

The offsets Ill have to play with when the car gets up and running. Ill be using 36lb SVO's which I have the correct offsets for...Ill see what happens.

BTW I told Bob to let me know when is good for him since it is a busy season for him. The motor will be in this weekend and fired up by the middle of next week.:crosses fingers:

 

I have 30# SVO's and I have ended up going back to stock offsets. I have changed my displacement constant for a 383 and I am using 31.58 as an injector constant. I had poor luck using the offsets listed at the carprogrammer.com website.

 

Interesting Rick, that might explain why the tune Im using kept the stock offsets for 30lb SVO's.

Do you think using 36 lbers will effect that much based on your experience? Also did you notice any improvement when you increased the displacement?

 

The change in pulse width based on displacement is going to be relatively small: (383-350)/350 = ~9%, so it's not gonna make a huge difference, but it makes sense to enter the "correct" number, that much more likely to run well without a lot of fiddling around. 30 to 36lb injectors is a 20% difference. IOW, if you installed them with no changes, it would tend to be way too rich. Probably still within the range of the PCM to "learn", but the best method is to program the "correct" values and tune for whatever specific condition is out of whack.

Rich Krause

 

Unfortunately, I made the displacement change the day I installed the 30's. I also made the injector constant change as well as setting the offsets higher. This resulted in a very rich condition. First I raised the injector constant to 33.33. This got my BLM's in line. Then I emailed Christian and he said he had not changed his offsets when using 30# SVO's. I changed back to stock offsets and reduced the constant back to 31.68. Finally I have reduced the constant to 31.58 and there I will stay.

I have seen similar comments from those using 42# SVO's and so would expect that the 36# would not need offset changes either.

 

Rich: I had this discussion with Bob once while Dave C. was getting his SS tuned at Kennedys...In your opinion is it better or (just as worth while) to insert a value of 30 or the corrective value of 31.5, 32 etc based on the fact that the SVO's are rated at a lower FP? Bob just set the value at 30....others like (rickb@lynk.com) have used a larger value to compensate for this.

Rick: Really appreciating your input so far....keep it coming.

 

It depends what you are trying to accomplish. As you mentioned, the ratings for various injectors are based on a specified pressure, and some manufacturers use slightly different pressure. And the actual FP is what will determine the flow rate. Differences in the injector constant of the magnitude you are mentioning, on the order 5-7%, will not make much of a difference in the actual AF ratio, they are just too small.

Sometimes the best way to make a gross adjustment in AF ratio though is to simply "lie" about the injector size. It's a sledge hammer instead of a scalpel, but can work well. My tune ended up with using a 42lb injector constant for 50lb injectors and the car ran beautifully. Of course, a lot of other tweaking went into the final result. But as a starting point, use something close to the rated flow.

Rich Krause

 

I see Rich. I guess it wont make all that much difference than. Thanks!