ZeroBanger

Just curious...

my car is runs pretty lean. I know its tuned from 11:5 to 12:1. That by itself would not matter much. Today coming home from the city on the highway im boosting to only 11 psi and stayed the entire time on my first turbo....

My water injection runs full time and my knock as literally no more than 10. During the summer my knock without the WI never went above 35.

Anyway, I can tell when my water runs out cause its stops slurping (yes, no joke it slurps when its injection water). Anyway I floored it a few times (on my first turbo only) noticed I was out of water. I looked at the knock when I got home and it was exactly 100. I dont know if its related to my water injection not running, or the cold air or what.

is this strange?

911GT2

Well the point of the WI is to cool the intake charge, so without it, it would make sense that the knock would increase.

But cold air shouldn't increase knock unless you're having boost control issues. But you said it stayed at a solid 11 psi the whole time, so it should be good.

Probably just WI related.

Roar 629

hey ZB.. merry xmas!!

ZeroBanger

Merry X-mas to you too william!

Hey 911GT2...Do you think it may have just been random noises the knock sensor picked up? And why would knock be related solely to boost? I thought it was just from running too lean?

911GT2

What are you using for knock readings, the PFC? From what I remember about a knock readings debate, the Power FC just plain sucks at it. Everyone seems to have different number values, but the general consensus was that as long as it was stable, you were ok.

The knock sensor is known to pick up noises, especially when shifting. If I look at my knock readings while shifting, it skyrockets for like a tenth of a second, then settles back down. That happens at full throttle at redline, and it happens when cruising. So it could just be that it was picking up noises. But when you said your reading was 100, was that a peak, or a constant reading?

I didn't mean that knock was solely boost related, what I meant was that since the air was colder, your knock readings should, in theory, go down. As previously mentioned, the point of WI is to lower intake temps to reduce the chance of knocking, and increase power. High intake temps=detonation, so it stands to reason that low intake temps=decreased chance of detonation.

So knock can be caused from running too lean, but there are other factors as well. One is intake temps, another is boost.

ZeroBanger

Power fc of course. I understand the theory behind water injection and the intake charge, etc. The fact that it was so cold outside and I didn't over boost made me curious why I got a 100 reading on my power fc. The stock knock sensor is not great, I realize its fault. Where my problem lay is that most of us with a power fc have some consistency with the knock reading. a reading of 35 with the water injection off was typical for my car almost never went above that. Thats why its out of the blue a 100 reading. It makes me believe maybe the cold air was affecting it. Maybe i hit a bad bump, I dunno.

rynberg

Zero, was that reading under WOT or did you just look down and see that peak number? I have seen readings over 100 from going off throttle, shifting, bad bumps, etc.

FWIW, I went for a little wind-down drive at about 3am last night. It was about 34-35F (fricking cold for the Bay Area). My peak knock never went above 70 and was usually quite a bit less, even though I was hitting 14 psi instead of 13 due to the cold weather (not bad considering the Profec was tuned on a 70-80F degree day).

Unless you saw that number under continuous WOT, I wouldn't worry about it at all.

ZeroBanger

Tyler..

I never hit the 2nd turbo, but I definately hit 11 psi on my 2nd turbo. I cant guarantee that it was when I was boosting because I looked at the peak after I parked when I arrived home. I can say that the 100 number happened after my WI ran out, thats all I know.

Im making some adjustments to my WI, doctor demente is at it again.

David Beale

Well, colder air has more O2 in it per cc so it -could- lean out the mixture a bit. Not sure how well the Power FC compensates for that. I notice that my car is more powerful/responsive when it's cold. Haven't watched the knock readings though (also running a Power FC and it's perhaps a bit lean). I will have to wait till April to take any readings.