Alloytec octane requirements

[Boost]

What octane gasoline are you guys running in your Alloytec engines? I have an '07 CTS stock that I have been using premium fuel in, and after careful research I think I will start filling it with 87 octane, since that's what the manual says. It is the 3.6 liter. I thought there may be a reliability and performance benefit due to extreme IATs here, but it's getting rather poor economy so if it doesn't knock on regular, I will stick with that. Very little chance that the specified lower octane will actually burn better, right? One hears rumors that on "some cars", regular gas runs better. That is certainly not been my experience with various other models though... thanks for the input, I hope I can start using a good brand of 87 in this sucker!

[joecar]

Use compression ratio as a guide.

[Boost]

Ok, it's 10.2:1. (?)

[GMPX]

I will say that on my car (3.0L LFW) it struggles on our local 91 Octane (which is rated different to the US, I think it's about the same as your 87). We have 91, 95 & 98 Octane at the pump.
On 91 there is audible knock!! Mind you, Holden have about 6 degrees more timing in their tables vs the same engine in the US :shock:
No difference in fuel economy between them all.

[joecar]

Compressio ratio 10:1 or greater is considered high compression, and rule of thumb is to use Super (92-93 in US 49 states).

98 Aust. equates to about 92-93 US.

[Boost]

So could it be like the the new 1.4t Ecotec where they say it runs on 87 but it runs like crap unless you use 93? 87 is recommended, should I even try it? The tiny bit of saving would be welcome but not it it pings and drives piss poor. Maybe I'll try it a little and let you guys know. How about 89? :( Initially from reading up on it I thought this thing might actually run "better" on regular, lol

[joecar]

Try it, and monitor for knock.

[Boost]

I will! Can I scan and log it even though there is should I no support? It's an '07 CTS 3.6. Or should I use the Tech2? Thanks!

[joecar]

No pid...?

Then listen very carefully for knock, maybe even using knock phones.

[Boost]

I was under the impression that my '07 Caddy CTS 3.6 was not supported / tuneable with EFILive, but hoping it could be scanned?? Can you set me straight on this?
What controller?

[joecar]

Any GM ECM should be able to be scanned for OBD2 data...

to see if you can log pids you have to try logging, you might have to change the scan mode (e.g. Stream-Fast might not work on the Caddy).

[ I guess scan mode should really be called log mode ]

[kangsta]

you can scan generic and even some of the enhanced PIDs if its the E55/E77 ecm even thought tuning isnt supported. Not sure if the KR pid is valid though.

[Boost]

Ok, I suspected so, thanks a lot guys I will try that!

[Boost]

no scanning / logging yet but, so far runs GREAT on 87 octane regular!!! :)

[Boost]

:( I was unable to log or monitor any data. I did not see E55 on the list so I selected "generic CAN ECM". It seemed to connect fine and even validated basic PIDs and read DTCs, but when I tried to record or monitor it said function not available. Can someone please tell me how I could connect to it to monitor knock?

Also, seems to be running and shifting smooth with the 87 octane. While I feel the performance and economy is about the same, my wife seems to think it has improved. However, since my ears / senses are better trained for this, I think I detect an occasional mild ping at part throttle, not enough to cause a concern. More so, at full throttle blasting down the highway there is a severe and audible "what I think is detonation / knock" only at very high rpm (6500+ to redline). Of couse for this reason I would really really like to log data. If all else fails, I can go back to high octane and verify the redline knocking is gone. The thing is, we are saving over $6 / fillup with the regular the car is supposed to require, AND wifey really seems to think the car is driving much much better. :confused:

[slows10]

I dont think you will be able to do any spirited performance type driving running 87 octane fuel. The ecm is probably pulling a bunch of timing. Not that it is a bad thing running 87 but maybe leaving some response and performance on the table.

[slows10]

You also said it was getting poor fuel economy. What is it getting?

[ScarabEpic22]

Try scanning it as an E39 too, E38 and E67 might also work.

[Boost]

I will do that Erik! I "think" it was averaging around 17 mpg, now it seems to be around 19-20 mostly highway driving. I do not feel a noticeable loss of power. But I wonder, the knock strategy is supposed to be good on these cars, why would it consistently knock at redline pull after pull? I could understand the first times as it adjusts the octane scalar, but is the max timing it's allowed to pull not enough to lower audible knock because of a few octane points and hot IAT? I guess we shall see if I am able to log data somehow. Thanks

[Boost]

:( I was unsuccessful. I tried as an E39, 38, 67. Nothing. Then I started connecting as a Generic CAN since this is a different type of ecm. I have tried all the logging modes, general, dynamic, fast, slow. Mode not supported when I hit monitor or record. I get as far as connecting, validating, and reading dtcs. What should I try? Again this is an '07 Caddy CTS 3.6 automatic. All I want to do is log a few simple PIDs, especially knock.

I can feel what I would describe as a single hit of "burst knock" when suddenly transitioning into a little load at low RPMs. Also severe knock-type pinging at WOT above 6000 RPM. I believe it's due to the 87 octane and high IATs. But since the car requires 87 minimum and it has knock control strategy, I am giving it a chance to "learn" a few tanks. Just want to diagnose and verify that 87 is out of the question. It drives very well otherwise, with some city driving the mpg has settled back down to 18 mpg, as before on the 93. Thanks!

[joecar]

Knock learn strategy is very short term... ECM detects knock and starts using weighted average of HO and LO spark tables with the weight sliding toward the LO table... then if it sees no more knock it slides back up to the HO table... probably within 10's of seconds or less.

[Boost]

Ok, thanks Joe. I am going to have to try 89 octane (midgrade) and listen for any knock.

[Boost]

Stayed on the 87, it finally got used to it and runs perfect without any knock now. May be missing a few horses though.