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IAT's put to the test

2007GPGTSC

2007GPGTSC

New member
So over the last 2 days I have put some common IAT questions to test. Some state that when the weather is colder thus allowing the change of air density that KR is reduced vs hot weather (or high IAT's) I decided to do a simple test because I began thinking. correct me if I am wrong but doesn't colder air = more power ? or virtually more boost due to the fact of more air being crammed in because of density change? wouldn't this in fact increase KR ?

I am not saying I am the brightest crayon in the box so correct me if I am wrong please - but do not troll.... because even to me my results were somewhat shocking

Tests :

2007 GP GT S/C
HAI
TR55's
10.5mm wires
180 tstat

Test 1
__________

52° day (drove 1 hour prior city)
IAT temp (per aeroforce) - 96°
20mph - 75mph pull (merging on freeway uphill)
KR readings peaked @ 6.0° (ranged 2.0° - 6.0°)

Test 2
__________

16° night (drove 1 hour prior highway)
IAT temp (per aeroforce) - 33°
20mph - 70mph pull (merging on freeway uphill)
KR readings peaked @ 7.6° (ranged .8 - 7.6)

not that is matters but here are the coolant temps and trans temps for the trolls who may claim the car was not fully warmed up

Test 1

Trans : 167°
Coolant : 191°

Test 2

Trans : 144°
Coolant : 171°

I wasn't smart enough to record the first run but here is the second run :

http://www.youtube.com/watch?v=O3MLCn3UO_w

These results were shocking to me for a nearly stock vehicle so I want so discussion to begin about this because I am quite confused and I think 7.6° of KR is high ... too high

I have a plog, and 3inch dp I have yet to install which should knock off a few °

But what the h3ll !!!!!!!!!! I thought on colder nights the car runs better clearly not ... unless the knock is false ...
 


some people will run a winter tune when modded, or pulley up to help fight KR in the winter.

so your findings are right, cold air can cause more KR.
 
Stock cars knock 5-7* which isn't uncommon.


And well let's face it your pretty much stock

So it's fine...one you get some other mods and a decent tune you should see a decrease
 


I would assume it would happen the way your results turned out. I think you will get more power on a cold day vs a hot day due to the air being more dense, but I would also think that would mean more KR since the air is denser you are compressing more air and it is going to heat up more than if you compressed the less dense hotter air.

I'm not a scientist but that's just my thoughts. I do agree with your assumption that you get more power with colder air (In a perfect scenario anyways, obviously if your getting KR your loosing a little power but if you could do it without getting KR you would definitely have more power)

Very cool to see someone actually go out and test a theory out.
 
if all factors being equal and the car running knock free, it will run better in colder weather because it'll make more boost.

in the dead of summer i'd make ~10-11 pounds of boost on a 3.4 whereas in the cold winter months i'd push ~13-14 pounds of boost.
 
What you found is the result of the inefficient m90. Delta temps are directly related to boost levels. So even thought it was 40* colder outside, the temps coming out of the blower were higher in 'test 2'.

The car is still making more power, but it'll also knock more because your boost levels are higher, causing higher delta temps and higher parasitic drag.
 
From what I have gathered just because there is KR doesnt mean its "knocking"... if it were the motor would be dead already in most cases.

Im running a a2a cooler with 2.55" pulley on my Commodore L67... In winter I had around 100°F intake temps lol... My IAT sensor is directly in the LIM... not the airbox btw because I'm running MAF-less with MAP sensor instead.
We were able to get alot more timing into the tune especially at the bottom end with those colder IA temps. My tune is 14 - 15 degrees bottom and mid and 17 degrees near redline at WOT. Im seeing just under 14PSI at the LIM. Torque is 420 ft/lbs at 2500 rpm

A word on timing: Ive noticed that over in the united states people seem to run insane amounts of spark timing compared to here in Australia... numbers which are unheard of here. People running 22+ degrees at WOT uncooled etc.... these timing numbers are barely achieved with E85 and a2a intercoolers over here in Aus... so something must be going on.
My tuner reckons there could be some sort of difference in how your ECUs measure spark timing compared to our ECUs used in our Holden Commodores.
 
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It could be possible that the individuals running high timing are still running a larger pulley. I don't like to see anymore than 19/20* on pump gas.
 


One thing not accounted for in the test is that on a stock PCM file the spark and commanded fuel offset changes depending on iat and coolant temp.
 
Your findings aren't surprising and smart people who don't have the capability to tune will typically pulley up in the winter time.
 
I am also tracking IAT temps and spark advance in my manifold thread. There will be more pulls done at a later date. I have IAT fairly close to ambient. Close enough for me anyway. I am running a modified air box. I'll post pics or put some links up later today in that thread.
 
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