Octane req. w/ tuned PCM's

[Dominance9]

Hey all, I did a search but didnt find anything. I was just wondering... I know dhp reccommends 91 octane or higher w/ their PCM. But has anyone not ran 91...maybe 89 only? Or does this put it too close to detonation?

Just wondering as I drive the car about 100 miles everyday and not looking foward to spending even more on gas. THe MPG seems to stay about the same???

I know its probably a dumb question, but let me know either way, thanks

[coupe]

El locko

[MMGT1]

Pretty sure that VCM has timing advanced for higher octaine. It really isn't that much of a difference tank to tank. To go from reg, say 90cnts/L to high test, say 105cnts/L works out to an extra 7.50/ tank. I get 500k to a tank so it cost an extra 1.5 cnts/km. Be nice to your car

[LoboMan7409]

Just spend the extra 3 bucks it costs to fill up on the good stuff

[coupe]

It wont even cost that much more to fill up

[Sprucegagt]

Honestly I don't think it makes a difference. But just for ****s and giggles I'll compare the DHP tune with the stock tune and find out how much timing has been added.

[alerored04]

its not worth worrying about the kr for what you save on 89. Like was said the difference per fillup is negligible so just dont buy that bottle of pop or pack of smokes when you fill up. Stick with the 91.

[LoboMan7409]

It wont even cost that much more to fill up

Yeah I didnt think so, from empty it should only cost like 1.10 mor to fill up on the good stuff

[Dominance9]

Yes I know it was a dumb question and I know its not much more to just go w/ the good stuff . But I had to ask it.

Now I know, thanks

[AaronGTR]

If you were really THAT worried about octane and spending money, you could always get a powertuner and tune it yourself on 89 octane gas. Upside is you'll always get better results with a custom tune rather than a generic program since they are tuned safely to apply to a wide range of cars. Downside is it's more complicated and time consuming so you'll have a lot more learning to do.

The other downside is of course, tuning it for 89 octane instead of 91+ will result in less HP. Which is fine if you don't mind that. You can actually tune it for 87 octane if you want and try and get more gas milage out of it. Thats what I'm doing. I use my powertuner to tune my grand am for power, but my '97 grand prix thats my daily driver I'm going to tune for milage.

[Gizm0815]

i know dhp recomends premium, if u get a tune from MP Racing you can run regular safely. i ran the last tank on regular just fine im trying this tank on premium to see if there a difference in performance or mpg on the tank so far i notice no difference.

[AaronGTR]

i know dhp recomends premium, if u get a tune from MP Racing you can run regular safely. i ran the last tank on regular just fine im trying this tank on premium to see if there a difference in performance or mpg on the tank so far i notice no difference.


It's only safe to run on regular if he tunes it for regular, and again it won't have as much ignition timing so you won't get much hp gain from the tune. And if he tunes it for regular you will see no difference in performance or mpg from running premium. All you will be doing is burning money.

[coupe]

It's only safe to run on regular if he tunes it for regular, and again it won't have as much ignition timing so you won't get much hp gain from the tune. And if he tunes it for regular you will see no difference in performance or mpg from running premium.

Which makes buying a tuned PCM/tuner a complete waiste of money.

[MMGT1]

Question about timing........


I am using the HP tuners program in my car. The timing has been set for 94 octaine.(I hit about 30* at 5600 and goes to 6400) Through the HP community they have suggested that going above 27* is useless. So, on my last tank I put 91 in and "Gave her ****". Well, while scaning, I had 0.4* of KR show, just for an instant on the shift from 1st to 2nd....that's it!! So, am I wasting my money putting in the 94? I guess I'm asking if anyone is running higher advancement in their VCM than I am. Like I said, I am toppping out at about 30* right now.

[Sprucegagt]

Which makes buying a tuned PCM/tuner a complete waiste of money.

But do you really need premium gas to safely increase ignition timing? :nope:

[lvemy3100]

I'm not giving away any tuning secrets of my own since I do this for a living but you can tune an NA car to run on 87oct gas and use the same tune for a little extra performance when running 87 or higher octane... boosted and high CR are a bit more tempermental so this is not able to be done for them..

however it is true that if you completely dial in your car to use only a certain octane fuel that you will see your best mpg and perfomance using strictly that octane or higher.. anything lower may result in poor perforrmance or damage to the motor...

in the future Gizm0815 will be running a tune that requires a set octane or higher but that is a story for another thread...

I will say this though anyone who has a DHP tuner has access to the same info that I had when I started tuning PCM's via the DHP tuner so they can figure this out just as quick as I did if not quicker since there seems to be alot more breakthoughs lately..

[Sprucegagt]

Question about timing........


I am using the HP tuners program in my car. The timing has been set for 94 octaine.(I hit about 30* at 5600 and goes to 6400) Through the HP community they have suggested that going above 27* is useless. So, on my last tank I put 91 in and "Gave her ****". Well, while scaning, I had 0.4* of KR show, just for an instant on the shift from 1st to 2nd....that's it!! So, am I wasting my money putting in the 94? I guess I'm asking if anyone is running higher advancement in their VCM than I am. Like I said, I am toppping out at about 30* right now.

Thing is I doubt 30* is the max you hit throughout the rpm scale. It's more like 40 + unless you have changed things. It's under part throttle that you can have a problem with KR and then may need premium. Usually at WOT you can richen it up and get rid of most if not all of the KR with regular gas. Granted that's for engines with a stock short block and no boost.

[lvemy3100]

Question about timing........


I am using the HP tuners program in my car. The timing has been set for 94 octaine.(I hit about 30* at 5600 and goes to 6400) Through the HP community they have suggested that going above 27* is useless. So, on my last tank I put 91 in and "Gave her ****". Well, while scaning, I had 0.4* of KR show, just for an instant on the shift from 1st to 2nd....that's it!! So, am I wasting my money putting in the 94? I guess I'm asking if anyone is running higher advancement in their VCM than I am. Like I said, I am toppping out at about 30* right now.


that would be normal if you still have any TQ management.. it reduces torque during upshift and down shift.. this shows as KR

[coupe]

But do you really need premium gas to safely increase ignition timing? :nope:

As far as i know yes.
If you increase ignition timing and run 87 wouldnt you have KR up the ass?

[Sprucegagt]

So you've scanned your car and found that out? I ask because on the DHP forums some guys have found out that they can increase timing a little and still use 87 octane without getting KR. The trick is getting the rest of your tune in order first before playing with the timing. That way the computer doesn't have to make large adjustments, which can lead to a larger error of correction.

I'm not trying to rag on you Rand just adding to the debate.

[coupe]

So you've scanned your car and found that out? I ask because on the DHP forums some guys have found out that they can increase timing a little and still use 87 octane without getting KR. The trick is getting the rest of your tune in order first before playing with the timing. That way the computer doesn't have to make large adjustments, which can lead to a larger error of correction.

I'm not trying to rag on you Rand just adding to the debate.

I was asking, if i scanned it myself would i have asked that question?

Looks like im right though, to get any better HP out of a tune you need to increase timing which means you need to run higher octane so you dont get KR.
Am i wrong by thinking that?
If so tell me how to increase timing to be worth while AND still run 87 octane.

Why would you want to increase timing just a little?
If your tuning little like that why even bother tuning at all?

The whole complaint about running 91 compared to 87 is so retarded its not even funny. If a whopping $2 more a full tank (if that much) is gonna break you then you shouldnt be modding your car period becuase its obvious you cant afford to mod.
I see it all the time, newbs want performance and HP but *oh no* not if they have to run higher octane.

[Sprucegagt]

I was asking, if i scanned it myself would i have asked that question?

Looks like im right though, to get any better HP out of a tune you need to increase timing which means you need to run higher octane so you dont get KR.
Am i wrong by thinking that?
If so tell me how to increase timing to be worth while AND still run 87 octane.

Why would you want to increase timing just a little?
If your tuning little like that why even bother tuning at all?

The whole complaint about running 91 compared to 87 is so retarded its not even funny. If a whopping $2 more a full tank (if that much) is gonna break you then you shouldnt be modding your car period becuase its obvious you cant afford to mod.
I see it all the time, newbs want performance and HP but *oh no* not if they have to run higher octane.

Depends on how much timing you can add before it becomes counter productive. There is a point where you can add to much timing, not get KR, yet still lose HP because the flame front has started so early that it now wants to prevent the piston from coming up to TDC.

For the GA your not going to see a large advancement in timing. Stock timing is already way high to begin with. Instead small is all your going to see. Like around < 6*. Even if it was 2* you would still feel it and you can add that on 87 octane, if like I said the rest of the tune is in order. You need tuning software to do that. A "canned" PCM will not do it.

As for the complaint about 87 vs. 91 octane, price wise it really is no big deal. I agree that if you can't afford the extra few bucks for 91 then you shouldn't be modding. But my reason for wanting to run 87 is it burns hotter and will leave less deposits than 91. More deposits mean more chances for hot spots on the piston and causing KR, defeating the purpose of 91 to begin with.

[harvester45]

First, I do believe you can run regular gas with a tuned PCM, unless whoever edited it changed the "bad fuel spark" table. If I remember correctly, if you have enough KR (which would be caused by running 87 with the higher timing), doesn't your PCM just revert to the bad fuel spark table? Now this doesn't make any sense from a performance standpoint, and it may not even make sense if you're looking for MPG, since I believe the spark advance is pretty conservative in the bad fuel table. So to answer the question "can you run 87 with a tuned PCM" yes you can, and no, you probably shouldn't.

Second, there could be a lot of reasons for tuning a PCM when you're just running 87. You can get significantly better performance (raised timing, tranny settings, TQ management, etc) while still on 87 octane. I would just buy a powrtuner, though, so you can balance MPG and HP to your own preferences. If this is someone's DD, I can see wanting to run lower octane while still taking advantage of other elements of a good tune. I wouldn't do it, but it isn't idiotic like some here may think.

[Sprucegagt]

First, I do believe you can run regular gas with a tuned PCM, unless whoever edited it changed the "bad fuel spark" table. If I remember correctly, if you have enough KR (which would be caused by running 87 with the higher timing), doesn't your PCM just revert to the bad fuel spark table? Now this doesn't make any sense from a performance standpoint, and it may not even make sense if you're looking for MPG, since I believe the spark advance is pretty conservative in the bad fuel table. So to answer the question "can you run 87 with a tuned PCM" yes you can, and no, you probably shouldn't.

You haven't actually compared the Good Fuel Spark Table with the Bad Fuel Spark Table have you? In the low mg/cyl ranges (about <300) both tables are almost identical. The Bad Fuel Spark Table only has a little lower timing at idle. Why GM made it like this I have no idea. Believe me I was surprised when I noticed it. But considering that most N/A cars are running at that 300 mg/cyl range and below, the bad fuel table doesn't help you much.

[harvester45]

You haven't actually compared the Good Fuel Spark Table with the Bad Fuel Spark Table have you? In the low mg/cyl ranges (about <300) both tables are almost identical. The Bad Fuel Spark Table only has a little lower timing at idle. Why GM made it like this I have no idea. Believe me I was surprised when I noticed it. But considering that most N/A cars are running at that 300 mg/cyl range and below, the bad fuel table doesn't help you much.

I guess my point was that the car would run fine on 87 if you were to use it with a tuned PCM, since only the good fuel spark table should be adjusted on a tuned PCM (I don't have any idea, though, if the MBT table interacts with the bad spark table, so I guess there still is the potential for problems). But if the GFS and BFS tables are so similar, then this bodes well for someone only looking for the other benefits of a canned PCM. They could have little to no loss in HP from stock form, while gaining improved Transmission, Traction Control, etc. settings.