octane levels and combustion temp
Thread Starter
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
octane levels and combustion temp
I was wondering if high test gas burns at a cooler temp than regular unleaded? My dialy driver just barely fail emissions today and im lookin for ways to cool the combustion chamber. ill probably advance the timing a couple of degrees and that should help too. and maybe replace the O2 sensor. the car failed NOx. State standard is 2.8GPMd the result was 3.0GPM. guy told me it was because combustion tems were to high. I bet if I had tested on a cooler day it would have passed. what a bugger. waste of my time..the car runs great. Any other cheap ideas to cool the cumbustion temp? what about spark plug heat range? Can that effect cumpustion temps? Thanks in advance for any suggestions.
Race Director
Joined: Mar 1999
Posts: 10,258
Likes: 1
From: Calif.
Re: octane levels and combustion temp (Jvette73)
Higher octane gas can sure lower your combustion temps. I had a similar situation the last time I had to get my D.D. smogged. It failed NOx. The tech said the same thing to me--along with the O2 sensor theory and the burnt out catalytic converter theory. Luckily I was almost on empty so I ran out the tank and re-filled with about 3 gallons of 100 octane unleaded race gas. Went back and passed with flying colors the same day on the same machine.
Your mileage may vary but it can't hurt to try.
Your mileage may vary but it can't hurt to try.
Thread Starter
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: octane levels and combustion temp (The Dude)
Thanks Dude thats good news. I just got done checking the timing and found that it did need to be advanced 2 degrees to be right on specs. So that should help the situation and cool the cylinder temps down a bit. I got a 1/2 tank of 87 in there now. ill burn it off and put some 94 in there and run it thru the test again. Thanks for the response. Its good news to hear that the switch to high octane got you passed the NOx. The car passed the other catagories just fine. it almost passed the NOx. Just barely missed it.
[Modified by Jvette73, 5:59 PM 7/8/2003]
[Modified by Jvette73, 5:59 PM 7/8/2003]
Drifting
Joined: Sep 2000
Posts: 1,355
Likes: 0
From: Germantown Maryland
Re: octane levels and combustion temp (Jvette73)
I am going thru the exact same situation. In Maryland also.. I failed twice so far. I failed 2.95 NOx witha required 2.8. :cuss The second time I I tried alcohol in the gas. Brought it down a little but still failed. The tech asked me If I had just driven on the highway, I said No, he told me drive 10 miles highway and bring it directly to the test. But the best tip I have gotten is the high test gas. Definetly will bring the temp down which causes less production of NOx. Another tip is don't go on either HoT or Humid days. Which means wait for now... You have 120 days to pass.
Thread Starter
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: octane levels and combustion temp (Clink69)
..im not so sure a cooler day would help the situation. Heres why. The cooler air is denser meaning that there is more of it per CFM. In theory...more air would lean the mixture. Leaner mixtures will tend to raise combustion temps. Now if yur O2 sensor and fuel injection sys was working optimal then it could probably adjust for the denser air. On a carburated engine which cant adjust for this, cooler intake air could cause a raise in cumbustion temps.
Thread Starter
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: octane levels and combustion temp (Jvette73)
Clink69, I think its pretty decent that here in MD we have that extra time to get it fixed before re-testing it again. One draw back of delaying though. When you finally pass or get a waiver, the results are good for 2 years from the "original" inspection due date. So the longer you drag it out, the less time that will pass before you have to get it tested again. I drug it out one time with an extension and then I took the max time to get it repaired and so on. I eventually passed. But less then 1 year later I got my notice for the next inspection. So im gonna try and get it thru asap so I have more time untill the next inspection.
