testarossa_td

Alright so I thought hey I will fill up with some gas...so I pulled into Texaco® who has the worst labeled pumps ever and their names....but I want techron® and they and Chevron® are the only ones(aside from buying the bottle). So long story short I put in 89. as long as I don't get boost crazy I really don't have to worry as our Turbos have less compression than an NA ANy way
But I was curios if anyone had any two cents or science to fill in the blanks....on another note I did run it up to 4psi boost to no ill effect...but I am not a fan of pushing it much further.

Thanks for any additional information.

Zero10

Well, I _did_ run 23psi on 87 octane

Seriously though, if you're running stock boost levels, you can run 87 octane. So 89 is already affording you a margin of safety.
If you are running higher than stock boost levels, my opinion is to keep it under 15psi.

testarossa_td

Sounds like I might be saving myself some money at the tank

EdC

When running lower octane you will notice when under boost you are making less power. Off boost no difference. When the weather is hot I prefer the higher octane, but now that it is cooling off, I too may go down to 89.

Rip It

has anyone ever heard a 951 engine ping or knock ? what does it sound like ?

toddk911

I have heard ping, but not on a 951. Just like a can full of BB's.

There is a foruma to see octane vs. psi, but not sure of exact formual off hand. I know it takes 3 octane for each 2 psi increase in boost.

So from stock 12 psi at 87, could go to about 13.5-14psi on 89. That's assuming yo ucan run 87 octane on stock boost.

toddk911

if you CAN run 87 octane on stock 12 psi(11.9), then you could run 16 psi on 93, WITHOUT chips needed; i.e. 3 octane per 2 psi increase.

Also, for every 15 degree intake temp drop, you can run 1 more psi.

Yes, your a/f would be off, but should be not alarm about ping issues.

All of this is from Corkey Bell.

m42racer

I know NZ runs one. For around $ 300.00 you should look into buying a "Knock Block". Plug in Head phones and listen for detenation.

NZ, jump in here, and give your 2 cents worth on its merits. Cheap insurance and costs way less than engine repairs.

Black Arrow

When I bought my car about 3 years ago I took it to a dyno shop. At 98 octane Euro (93 US) and some unknown chips, my car got high EGT and knock at 1.3 bar boost(18.8psi) I did heard the knock, but its a bit hard to explain.. It was a thin, load(but couldnt hear when I drove the car, just at dyno) ticking sound. If you imagine a old type of clock, but loader and faster ticking sound. Not easy to explain, sorry! :P

fast951

You want to detect knock WAY before you can hear it.. The KLR has some nice software and filtering mechanism for knock detection.. The beauty of the KLR is that the code is for our engine!! The bad think about the KLR is the lack of "notification".. We are developing a "Knock Display" which will read the data from the KLR and will make it available as a 0-5V signal and a bar graph.. Will be released soon after the Wasted Spark..

Evan70

Just out of curiosity, what is the voltage on the existing knock sensor and what does it indicate? I've got a spare port on my SBC that will accept any sensor input (just have to input the voltage and scale for it do display) that I could possibly use to display knock right now.

fast951

The knock is a bit more complicated, you have the signal as well as the time to factor in...

Evan70

I kind of figured that. Couldn't I use pin 15 on the KLR (Knocking yes/no) to at least tell me if I was getting knock? Since it's a yes/no it should be pretty simple for that as 0 volts should be an indicator of no knock, and whatever it's output voltage is should be knock, correct?

Zero10

You can run more than 12psi on 87 octane, especially with our low compression ratios, and with the stock chips, they're tuned pretty conservatively.

You will not make more power with 89 octane or 91 or anything, at the same boost levels, it simply won't happen. I don't really want to get into that argument. Any 'better' running effects you get from running a higher grade gas come from the additive packages, not from the octane rating of the fuel.

The only way this can be true is if you turn down your boost levels when you change the octane rating of the gas you use.

Zero10

On a side note, I was hoping to get some more details on logging the knock sensor, and about what to expect regarding output from it. I guess it's simply a microphone?... If that's the case, then it might be easy to log. I would be interested in logging my knock sensor to prove that it won't knock on 87 octane with stock chips once I get my new rings installed, and my motor back together.

Evan70, the output of the knock sensor looks rather like static to the untrained eye from what I have read, it's not a simple yes/no type of thing.