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Does hot outside air temp contribute to engine knock?


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#1 Tosh

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Posted 06 June 2016 - 11:34 PM

I have a 2009 GTR, full bolt ons (see signature). I'm running COBBs 91 Octane with Big SF tune.(Have GotBoost 3" intakes)
Normally, it runs great. However whenever the weather is +30C/ 86F or hotter it runs like crap and starts to knock.
I know our 91 octane fuel in BC is crap, and Chevrons 94 is worse, but I just peaked at -1509 on my Accessport with the outside air temp at 84F.

The knocking starts at 3000 RPM or so but right as soon as I change gear. I can feel the loss in power immediately with the boost gauge flashing etc. If I stay in the same gear and redline it, it will not knock. It's as if the shift is too harsh and the air/fuel doesn't know what to do, and timing gets pulled.

When the weather is cooler, it runs great. Also drove down to Colorado last August on 91 Octane, in 85+ weather and didn't knock once. American fuel is much better than whatever I'm putting in.

Does this happen to anyone else? I'll attach a datalog if anyone can decipher it..

Thanks in advance

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#2 240Z TwinTurbo

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Posted 07 June 2016 - 05:48 AM

Yes, increased IATs have the potential to induce knock. I looked through the software and didn't see a compensation table for this so you will need to have the timing adjusted accordingly. Most software will allow for adjustments in fuel/ignition based on IAT changes, but that may be a table I didn't see or has not been uncovered. Also, MAF is preturbo so that could complicated somewhat. If not already upgraded, a nice aftermarket IC setup always helps.

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#3 Adrian B

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Posted 07 June 2016 - 07:30 AM

Put a couple of gallons of e85 in the car each fill up. Its little enough that the concentration wont go above the ~10% E content that some stations have anyways so you aren't damaging anything. I know its a bit of a drive for you to go to Van, but if you are ever in the area take a bunch of empty gas cans and fill them have.

E85 is far more resistant to knock, and having just a gallon or 2 will give you gains in all weather conditions.

If not try octane booster, the thing with that is that it makes your lines yellow and in my opinion isnt as good as an alternative to the e85 method.

Im sure Amir, the owner of the e85 station and all the other guys in Van will chime in as well when they see your post.

Edited by Adrian B, 07 June 2016 - 07:31 AM.

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#4 Tosh

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Posted 12 June 2016 - 01:48 PM

Thanks guys! I didn't know about the e85 method. I figured I'd need upgraded fuel pumps to even run a little bit of it. I've tried octane booster and have not noticed any difference.

I think the reason American fuel made it run better was most, if not all 91 Octane fuel has up to 10% Ethanol, and our 91 doesn't have any. Just 87 & 89 has the ~10% label.


On a better note, the weather recently dropped to 52F/11C the other day. Drove about 250km and only registered a maximum -307 on the knock count at one time. This was on the same tank of fuel. Perhaps it's as simple as a cooling issue.

Edited by Tosh, 12 June 2016 - 01:50 PM.

2009 GT-R, Satin Black wrap, JacksTrans RR700 build, Cobb AP, Password JDM Mid, Meisterschaft Exhaust, Gotboost 3" intakes, GFB bov's, front & rear cameras, quad projector headlights

2009 Yamaha FZ6R, Bi-Xenon headlight retrofit

#5 Goonthree

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Posted 12 June 2016 - 03:17 PM

Ecutek has table for timing reduction based on intake temp.

Yes, increased IATs have the potential to induce knock. I looked through the software and didn't see a compensation table for this so you will need to have the timing adjusted accordingly. Most software will allow for adjustments in fuel/ignition based on IAT changes, but that may be a table I didn't see or has not been uncovered. Also, MAF is preturbo so that could complicated somewhat. If not already upgraded, a nice aftermarket IC setup always helps.



#6 gyoja

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Posted 12 June 2016 - 03:49 PM

We talked about this in pm. You need to add 10% ethanol to chevron 94 or shell 91. Don't rely on any other 91 to have the correct octane value or ethanol percentage.
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#7 Boostd4

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Posted 13 June 2016 - 03:44 PM

Definitely get off of that OTS map and get a custom tune...even with the minimal mods. Given that 91 is really the lowest tier of fuel you can run in this car, you have to at least get a solid tune specific to your car/fuel. I have a custom tune for 91 and I still see some knock, and this is really just due to the fact that 91 is really crappy fuel to begin with. I buffer my tune with a few gallons of 100 which is luckily readily available to me.

I really just need to get on a Flexfuel setup...
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#8 [email protected]

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Posted 13 June 2016 - 05:03 PM

@Boostd I have flex kits in stock ;)

@Tosh I'd be glad to get you sorted with a custom tune for your local conditions!


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#9 Wicked

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Posted 14 June 2016 - 08:44 AM

Buy a barrel of e85 from Amir.
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