High coolant temperatures = more spark knock?
 

I have noticed on my ZX2 that as my coolant temperatures increase steadily that the amount of spark knock increases as well. The car is fine up too 200*, then it goes down hill from there. For example, I hit too many red lights in town today and my ECTs started climbing. I was having spark knock at any load over just 60%! Has anyone else experienced this problem? What could possibly alleviate it?

I know some options are:

- Less grill block; don't want the worsening aero though.

- Avoid driving at all

- Higher octane fuel

I should mention that I have the ignition timing advanced and run with the knock sensor removed. Before anybody freaks out, this is standard protocol with the ZX2. It was recommended by Ford themselves. Another interesting point is Gassaver's member COZX2 reported that the most efficient temperatures for our engines was in the range of 210-225*, which coincides with my worsening knock.

The knock has gotten worse on this tank due to a switch to see how 87 octane would work with the new computer. I usually run 89 octane, and it is not this bad.

It is bad enough that I want to pump my gas out, sell it at a discounted price to someone and buy 89/93 octance lol!

have you been watching your intake air temps? If running a little less grill block lets you run cheaper gas, I think you would be ahead vs high octane

sounds like too much grill block! the old kia did the same! you use the engine too much to ignore it tho. it wasn't a big deal for the kia because I only ran the engine for 30 seconds at a time and turned it off before it could realize it was overheating and knocking / misfiring.

the kia is gone now don't be a fool like I was...

( mpg is high at 237*F)

The IATs sit between 100 - 110* from what I have seen. Using higher octane fuel is recommended with the mods I have, and I don't mind spending a couple extra dollars per tank. I realized last night that the place I get gas from, his 89 is the same price as other's 93. So I will be switching locations.

Ugh! I was hoping that I could get around taking grill block out. It is only a problem in city driving, and I avoid that kind of driving as much as possible. Timing lights is crucial to me! The high fan switch I'm working on should help me in the city.

I'd just pull your timing back a couple degrees for this tank.

The timing is set by the PCM, unfortunately. It is advanced by having resistors in the IAT wires, showing the PCM a cooler air temperature than what it really is. I'd rather not take them out and have to resolder the wiring.

I will soon go with 93 octane to avoid this problem from now on. I noticed that I had a little spark knock at 190*. 87 just does not work for the engine now I am pushing the efficiency barrier.

You could throw in a qt of toluene for this tank.;)

Now that is an idea! :D

If I were serious, a 2.5% mix (1 qt in 10 gals) of 114 octane toluene would up the overall octane by... only 0.675 points :( might need more than a quart Russell!

37 ml of acetone and 37 ml of water per gallon of gasoline... the acetone gives a small bump in octane rating, but it's really there to act as the go-between to bind the water to the gasoline. Acetone is completely miscible in water, and completely miscible in gasoline, so it acts to make the water miscible in gasoline.

The water has a high latent heat of vaporization, will damp combustion temperature peaks, will slow the flame front (only slightly at these low concentrations), and will add to cylinder pressure. That should knock down any spark knock you've got. And it'll clean out your fuel system, and steam clean your piston of any carbon deposits.

The only thing you have to watch for is if your gasoline has ethanol in it, it may already have some water in it, as well, so you'd have to adjust the proportions of acetone and water. Easiest way is to get a 5 gallon HDPE carboy (Utah Biodiesel Supply has them for $16 each), put your acetone / water mix in, put your gasoline in, then look on the bottom for any water settling out. If there is, add small amounts of acetone until the water is miscible with the gasoline.

E85 has the high latent heat as well, high octane and under $2 a gallon(varies by location).

2 gallons E85 with 10 of 87 E0 would make E14 at 90 octane,

3 and 9 would be E21 at 91.5 octane.