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Discussion Starter · #1 · (Edited)
Yep, Im sure you guys remember my 3 threads about getting absolutely horrible gas mileage even when I would drive the car like granny (11-13mpg in town)

I tried many different things, brands of gas, etc with no luck.......that was on the canned 93 predator tune..........A few weeks ago I tried running both the 91 and 93 tunes in different variations up and down the hwy for about 2 hours, datalogging, and decided on going with the 91 CAI tune using 93 gas (even though I do not have a CAI right now), with 3% fuel added across the board at WOT........Im on my 3rd tank of gas right now with this tune and im now getting between 14.8-16.7mpg in town consistently, driving harder then I was when I getting 11-13mpg.........

So.........I guess its safe to say the 93 tune was too agressive for my car but what might have been some things I could have adjusted in the 93 tune to get the mileage im seeing now? With the 91CAI tune and fuel added, the car feels pretty good but doesnt seem to pull as hard as the 93 tune on WOT....should I look at adding more fuel then the 3% I have added now? Right now im basically getting 1 degree of ST knock at the shifts which goes away immediately, and 0 LT knock
 

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Yep, Im sure you guys remember my 3 threads about getting absolutely horrible gas mileage even when I would drive the car like granny (11-13mpg in town)

I tried many different things, brands of gas, etc with no luck.......that was on the canned 93 predator tune..........A few weeks ago I tried running both the 91 and 93 tunes in different variations up and down the hwy for about 2 hours, datalogging, and decided on going with the 91 CAI tune using 93 gas (even though I do not have a CAI right now), with 3% fuel added across the board at WOT........Im on my 3rd tank of gas right now with this tune and im now getting between 14.8-16.7mpg in town consistently, driving harder then I was when I getting 11-13mpg.........

So.........I guess its safe to say the 93 tune was too agressive for my car but what might have been some things I could have adjusted in the 93 tune to get the mileage im seeing now? With the 91CAI tune and fuel added, the car feels pretty good but doesnt seem to pull as hard as the 93 tune on WOT....should I look at adding more fuel then the 3% I have added now? Right now im basically getting 1 degree of ST knock at the shifts which goes away immediately, and 0 LT knock
It is my understanding that all the adjustments you can make to a canned tune are for wide open throttle only. So unless you're running WOT all the time, any adjustments will make no difference in mileage.

Were you getting knock before adding the 3% fuel? You're good with knock as is.
 

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Discussion Starter · #3 ·
It is my understanding that all the adjustments you can make to a canned tune are for wide open throttle only. So unless you're running WOT all the time, any adjustments will make no difference in mileage.

Were you getting knock before adding the 3% fuel? You're good with knock as is.
I dont know what the differences in the tunes are in how my car responds to them but thats the only change and mileage is back up.....a lot

I was getting 2 degrees knock before the 3% fuel........i want to add as much fuel as possible at WOT so it really pulls.........right now it still feels like it hits a spot or 2 where it wants more gas when I juice it
 

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thats pretty common, happened to me too bud.

plain and simple, the stock intakes are basicly a true CAI vs whats on the market now aftermarket wise. but enough on that, the focus is the pred canned tunes are a bit aggressive on timing. ussually about 8x% of the cars that are running canned tunes could use just a bump in fuel increase but most people do not datalog to find out if they need to or not.

when i got my cmr done, my tuner commented that even with my 91 canned tune on 93 gas that i could have actually got a little fatter in fuel on the upper range. and i already at 3, 3, and 4 fuel added. and this was on my modded srt airbox, so it either means i needed the added fuel from the airbox which i doubt or the tune was just very aggresive on timing.

i still say after t he exhaust is installed get a CMR, i chirp second gear with ease everytime after the cmr, the car feels so good. today i was out and its about 78 degrees here today and really cool. i hung with a older c5 vette till we both let off around 100. i was literally on his butt and was very steadily creep on him. right when i got door to door with him we had to slow. if we have another 100 feet i would past him no prob. i would never have been able to do that without the cmr

i went from 298 wheel to 319 wheel and 336 tq to 347tq. my tuner will also do a email cmr for ya if you send him a log or too, let me know if you wanna PM him
 

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First of all, good for you! I've been following your threads since I've ALWAYS had pretty lousy mileage regardless of my driving habits. Long term (Sept 05-present) I'm averaging 13.3mpg. That's over some 33000 miles. Yeah, it sucks. Unfortunately, it's not much different with or without the Predator in my case.

Back to you.

The techs at Diablo have said a number of times that the only differences between the 91 and 93 tunes (and 91 CAI and 93 CAI tunes) are the amount of timing. If you're seeing some ST knock on the 91 tune you're very likely to have been seeing more on the 93 tune, which would result in timing being pulled and you wasting fuel. However, this should only be at WOT. If you really were driving like a granny, this shouldn't have been an issue. Regarding what you could do with the 93 tune? You could pull timing which would end you back up where you are now: the 91 tune.

Adding fuel isn't always the right answer to getting more power; in fact, leaner typically makes power. The problem is that leaner is more dangerous to your engine. Unless you have a good way to measure your A/F ratio I wouldn't play too much with that. A couple % more fuel probably isn't going to hurt anything but if it doesn't help I'd take it back out.

Regarding changing the tunes back and forth, unless you're tuning exclusively in open-loop (WOT) mode, you're going to want to drive a while (not sure how much but 1-2 tanks is going to be plenty) on a tune to let the adaptives get learned. They're going to make a big difference overall since they're used at part throttle/cruising. If you load a tune and start running your tests, the adaptives haven't been learned yet so your results could be skewed - very likely skewed towards being too rich and wasting fuel. Since you've run a few tanks now and are seeing good results you're in good shape. I just wanted to mention it in case you want to run more tests. Over that period of time you're also going to have to deal with variables such as ambient temperature and humidity, traffic conditions, etc. You might want to revalidate your results by switching back to the 93 tune for a few tanks to see if the mileage goes back to where it was before. That would be good proof that your change is what made the difference.
 

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Discussion Starter · #6 ·
You might want to revalidate your results by switching back to the 93 tune for a few tanks to see if the mileage goes back to where it was before. That would be good proof that your change is what made the difference.
Going outside to load the 93 tune again right now.............Ill run it for a week and report re-up this thread with what I find..........I drive the exact same "city" pattern every single day, at the same times every single day so that'll be a good comparison
 

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Adding fuel isn't always the right answer to getting more power; in fact, leaner typically makes power. The problem is that leaner is more dangerous to your engine. Unless you have a good way to measure your A/F ratio I wouldn't play too much with that. A couple % more fuel probably isn't going to hurt anything but if it doesn't help I'd take it back out.
Yes! Exactly! Engines make maximum power right around 13.0 air/fuel ratio. Simply adding more fuel will NOT make more power if there's not enough oxygen to burn it (i.e. it's already running too rich). You have to error slightly on the rich side because it's safer, but it does cost power. Without looking at the air/fuel ratio, you're taking educated guesses.
 

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sublime, no need to load 93 back on. just take logs with the 91, if your not getting any st or lt knock your basiclly gonna be optimized for MPG wise.

i agree with above, always pull timing before fuel, however the trend around here on the forums is adding more fuel fixes the issues more then so if your having a small bit of ST kr, if your having LT kr, you need to pull timing before anything else, but 1 to 2 st kr can usually be fixed with adding a tad bit of fuel

cars do make more power being as lean as possible before detonation but 9 out of 10 times run better down low, uptop youll wanna be in the fatter range to pull harder and so forth (not to rich though, just more so then down low)

good luck.

edit, also are you gonna mod your srt box like the rest of us had been doing? i have some spare 4 inch memory tubing to seal the box to the grill area like the ae carbon design
 

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sort of covered above;

adding fuel does not make power.

you want as little fuel as possible to maintain roughly 12.8 a/f and get 0 knock

knock during a shift is no big deal, especially only 1 degree.

timing makes power. if youre feeling like youre leaving something on the table i would add 1* of spark to the powerband on your canned tune and log it and see if you increase in knock.

if not, i would add another degree

adding fuel will only make you feel slower if you dont need it.
 

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Discussion Starter · #10 · (Edited)
So I should drop the 3% fuel I added across the board back to 0 just like the canned tune has it, and try adding increments of spark in 1 degree segments?

I know with no fuel added the canned 91CAI tune does not feel anywhere near as it good as it does right now with 3% at WOT.....it just feels like the engine screams but the car doesnt really pull to match all that noise, but with the 3% it goes like it should........

If I add spark and start seeing more knock, do I keep the added spark AND add fuel to bring it back down, or does that just cancel out the benefit and I might as well just drop back down the spark?
 

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to add above, adding fuel is some cases does help, but youll never know until you log. i know for where i am at 100 feet above sea level that my tuner added more fuel then timing when doing my email cmr tunes and they kept on feeling better and better each run
 

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So I should drop the 3% fuel I added across the board back to 0 just like the canned tune has it, and try adding increments of spark in 1 degree segments?

I know with no fuel added the canned 91CAI tune does not feel anywhere near as it good as it does right now with 3% at WOT.....it just feels like the engine screams but the car doesnt really pull to match all that noise, but with the 3% it goes like it should........

If I add spark and start seeing more knock, do I keep the added spark AND add fuel to bring it back down, or does that just cancel out the benefit and I might as well just drop back down the spark?
im not saying you should lose the fuel,
its good to add some until youre not seeing knock.

timing is hard to play with,


generally, adding timing can lean out the motor out a bit,
but whose to say that you werent running lean from having an intake? or exhaust? or whatever.

so you can trim out the fuel for your mods, then you can add timing.
youre fuel should stay very close to where it was (a/f ratio that is) as long as youre not adding large ammounts of timing.

fyi- "adding timing" is adding a degree to when the spark plug fires.

cams are measured in degrees (out of 360, a full rotation on the motor)

so when you add 1* of timing, youre sparking 1* difference, which will allow for more compression of the cylinder.

to much and you get detonation, of course.


regardless, im just suggesting you try adding a bit, but its not as "safe" to play with as the fuel is... take many data logs each time you change it
 

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Discussion Starter · #13 ·
Do I need to log different times of the day to make sure what I added is safe consistently? Like if I log when I get out of work at night, and only show a degree of ST knock, could it change if I was to log in the middle of the hot day?

What PIDs should I log if im strictly only wanting to make sure im not causing problems with adding a little bit of fuel and timing? The last log I took was a quick one, all I had running was engine RPM, ST knock, and LT knock.......do I want to have cylender 1 spark logging too once I start with timing?

Thanks
 

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Do I need to log different times of the day to make sure what I added is safe consistently? Like if I log when I get out of work at night, and only show a degree of ST knock, could it change if I was to log in the middle of the hot day?

What PIDs should I log if im strictly only wanting to make sure im not causing problems with adding a little bit of fuel and timing? The last log I took was a quick one, all I had running was engine RPM, ST knock, and LT knock.......do I want to have cylender 1 spark logging too once I start with timing?

Thanks
hot days will typically show more.
that is normal.

when you do a datalog with the predator.... it is reading how much timing the computer is pulling for whatever reason.

the computer will pull timing due to many things like IATemps, Rattling from loose parts, Detonation etc.

the KR is there for all situations, and letting the motor do its job (assuming you were tuned on a cold day or whatever) is fine. i wouldnt concern myself with a few degrees of KR on on the hottest of days as long as it typically isnt there.

btw, STKR lasting for a period of time is what leads to LTKR
LTKR is something that actually hurts performance
STKR is like a signal.... its telling the car whats going on, and that it may have to get ready to pull some LTKR, but it does not actually cost you any power.

if youre only getting hints of STKR, youre not costing yourself anything, its normal


i cant remember which PID is which, i think there is one for overall timing.

typical timing for a cammed car (tuned with CMR) can be between 22-28 degrees advanced depending on specs, compression etc.

i cant speak much on a stock car, but i would imagine its in the same area
 

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I am not surprised.

I could not use the 93CAI tune day 1. As soon as I installed it, the car was a pig. Went to 91CAI, and all was good....or so I thought.

Just yesterday, after I filled up, I noticed a lot of knocking...the sound is so recognizable, to confirm, I even went to a road that has cement walls on both sides to verify. It was ugly. Pulled over, plugged in the Predator, did some logging of the KNK sensors. Off the charts, I could barely have any of the sensors stay at 0...even one sensor (don't remember) was as high as 13.0.

I put the car back to stock, and no sound, and no KNK shown...so, I am banking this on crappy gas. So I will leave it stock until I can fill up somewhere else...

So, when I though the 93CAI was aggressive...the 91CAI is not too far behind! These Diablo tunes really want clean fuel.

- Mark
 
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