Just for the sake of discussion, can hot air causes knock? Ie before spark ignit, air inside combustion chamber get's too hot and burnt itself?? I might datalog air temp in my next run.

I also assume air is cooled after intercooler and knock won't happen because of hot air!

 

I don't know if hot air can cause pre-ignition alone but certainly will not help with cylinder residual temperatures as the heat climbs. One thing is for sure is the hotter that air becomes then the less dense it will be even at pressure until diminishing returns are met. Colder air will typically mean more power.

 

Thanks, I agree. Still looking for answer if they would cause knock

 

I am pretty sure hot air causes knock. I have had my car on the dyno and the intake temps were like 130* and ambient temp was like 100*. Car would not make any power at all. Had to run it really rich and pull out a lot of timing. Temps dropped down 10-15* and the car makes way more power running leaner and more timing.

 

Short Answer, yes it will cause knock.

 

+1 yes, you will be more prone to knock then with cooler temp air.

 

Thanks! I'll keep that in mind

 

heat can cause knock. Higher ambient temps make it harder for the engine to get rid of excess heat. the block and heads get hot. The intake air is hotter and all contribute to increasing the amount of heat in the combustion chamber increasing the possiblity of pre-igniting the mixture.

 

I hate to bring this up again ... but I can run more aggressively in the summer than the winter. I know it goes against most of what we know, but I've seen it 2 years straight on my own car.

I just re-tuned about a week ago and I'm running about 2º advanced across the map from my winter tune with 0 knock. Boost is ECU controlled and PSI based and I didn't change those maps. I was at 2º at peak boost and 10º at redline ... I'm now at 3º-4º at peak and 13º at redline.

Last summer I ran 26 psi and had no issues. As the temps dropped knock started to occur. 7-9 counts on a drag run. I pulled timing, knock went away and my traps and ETs got better by about .4".

A few of us actually had a pretty big discussion on this a while back ... the possible differences between denser air at the intake and denser air after the intake (better FMIC). Even stranger still, my upgraded FMIC (which should have a similar effect as cooler temps) also allows me to run more timing. So the data is contradictory. We tossed around the idea of winter blended fuel being a partial cause.

I will say that DLL shows basically identical power curves when comparing the less advanced winter tune and the advanced summer tune ... so you do make more power in the winter with less timing. No issue there.

 

I'd what your experienced is actually to totally different things effecting your setup. First for the heat making the air less dense that is absolutely true but given the state you live in its almost more likely that humidity is giving you the ability to run more timing rather than heat.

For the intercooler which is producing less back pressure in the intake system is making the turbo more efficient. With the turbo not working as hard to get pressure into the engine back pressure in the exhaust should be reduced which is helpful in running more timing.

Just my thoughts

 

You know, I have noticed that also. I returned my car for the summer, and I was able to add a bit more timing then my winter tune.

Winter blend/Summer blend would make complete since though.

I will tell you this though, Having a gt30r with a stock intercooler I was barely able to run 3-4 degrees timing. I since upgrade to ETS 4" intercooler, I am now running 7-8 degrees.

 

what about air/fuel ratios differences from winter to summer. I bet you can run more timing because the ECU has richen up the ratio a bit.

 

I'm purposely running 11.2:1 right now ... I ran 11.5:1 in the winter. Last summer I ran 11.8:1 for a while to see how it was and only had to pull 1º in a few places.

I did consider humidity in the equation ... I even got in touch with a meteorologist friend to see if she could tell me any differences between summer and winter air that might affect tuning. She said there was no notable difference in the air other than the temperature. Mrfred suggested that winter air couldn't hold as much moisture as summer air, and that too might be part of it.

It humid here all year round ... but obviously more so in the summer. Winter can still have 70%+ humidity. Also, our winters only get down to about 25º during the day on the coldest days.

 

yeah humidity is suppose to help reduce knock. I live in louisiana, so its always pretty hott. I keep my a/fs between 11.5-11.8

 

just because you're able to advance the timing that doesn't mean you're making more power in the summer....it probably just means the intake air is less dense due to the heat.

Timing & airflow hinge on each other. If airflow increases, timing needs to decrease...if airflow decreases, timing can be increased.