More knock in cold weather?

[mikeandjen]

Hey guys,

I have noticed considerably more knock retard in cold weather, especially in initial tip in throttle. I am assuming this is from the cold dense air, and increased oxygen flow. Can this issue be solved by just increasing fuel pressure a couple of pounds? Also noticed a slight boost increase of about a pound or two total so up from 16 to about 17-18. I guess I can dial this down a bit. The only other thing I could attribute to the knock I am seeing, since I can't hear any considerable "pinging" is maybe the louder valvetrain in the cold weather?

Any thoughts?

Also I have noticed a slight miss, at idle. It doesn't affect driveability whatsoever, and acts similiar to a larger lobed cam, cold weather and not having an egr play into effect? I am going to check all plug wires and ohm them, but since no miss whatsoever under load don't see that being a factor,

Thanks
Mike

 

[87GNSteve]

Where are you located?

Some states change to winter oxygenated fuels there are a few possibe effects as it has a different formulation and might require a tuning tweak.
For more info:
http://www.epa.gov/otaq/regs/fuels/ostp-3.pdf

 

[bison]

Id think the oxygenates would raise the knock limit since they have a higher latent heat of vaporization and lower boiling point than gasoline. Id try adding fuel if your pinging. I had my car out last night and had to add a bunch of alky to turn my boost back up to 24.5 psi from the 22 psi ive had it at. It was 38*. I actually added another .035 jet to my DIY kit. So now im running of two feeds at WOT. In the 80* air i actually pulled about 7% out for the times in my sig on the single nozzle setup. Ive since added all i pulled out back in and went 12% beyond that and had to add another nozzle . With the 4" MAFS pipe i added and the cold air i am estimating i have 80-100hp more than i did on the 126mph run. Ill keep my fingers crossed on the stock bottom end:biggrin: . If you have a tip in problem i suspect a malfunctioning EGR or an EGR chip and a blocked or malfunctioning EGR.

 

[87GNSteve]

Id think the oxygenates would raise the knock limit since they have a higher latent heat of vaporization and lower boiling point than gasoline. Id try adding fuel if your pinging.QUOTE]

I cut an paste from the link since links are hardly utilzed anymore.

"Oxygenates boost research octane to a greater extent than motor octane, however, and as a result, it is possible for an oxygenated fuel, with the same posted octane rating as a nonoxygenated fuel, to have a slightly lower motor octane level.
Some engines respond more strongly to motor octane than research octane. At high speeds or under heavy load conditions, for instance when pulling a trailer up a hill, motor octane is the best indicator of antiknock performance. For these engines, a small reduction in motor octane could result in a slightly higher incidence of engine performance problems, such as engine knock, . dieseling, or increased temperature.

 

[mikeandjen]

I don't think it is change in fuel mixture for winter, granted I am in the midwest, I strictly use bp 93 and I have never ran into this issue before. I am going to try and add 1-2# of fuel pressure and see what happens.