[HoustonSC300]

Hey all.
I heard from a BMW tech that you do not have to run as low as gap in the plug as you might have too in lower elevation. While I was in California I was running a .028 gap it ran and idled fine. Here in Colorado (5280 Ft) it seems to have a rough idle, kind of lumpy. If the tech is right then I should be ok with running a little wider gap with the same boost levels. I was just curious if any one else has heard of this.
Sh

 

[houstonT]

Scot, all you have to do is UP the gap a bit and see if the car misses under boost. If not, then keep it that way. The only reason to gap down is to keep the spark from being blown out. Ideally, you should run the highest possible gap that keep the burn...
Peter

 

[Lagtime]

Hey all.
I heard from a BMW tech that you do not have to run as low as gap in the plug as you might have too in lower elevation. While I was in California I was running a .028 gap it ran and idled fine. Here in Colorado (5280 Ft) it seems to have a rough idle, kind of lumpy. If the tech is right then I should be ok with running a little wider gap with the same boost levels. I was just curious if any one else has heard of this.
Sh

It makes sense when you consider that cylinder pressures are likely to be lower for any given amount of boost at high altitude vs. sea level.

As Peter said, the best way to find out is to open up the gap a bit and see what happens.

I shoot for the biggest gap I can without hurting trap speed. On my BPU car I found I could go as high as .036 at 3000 feet without missing, but when I dyno'd the car at 500 feet I had 2 misses (heard the exhaust pop, saw the drop on the graph) on 2 out of 3 dyno runs, so the .036 was really pushing things at lower elevation. I backed the gap down to .032, no more missing but the idle is *slightly* rougher than at .036.