After 50k miles I thought it was time to change my spark plugs before last weeks redline TA event. It is a stock Evo 8 except for a stock-boost mellon tune. I used OEM spark plugs, therfore did not gap (but checked and they were at the .021-.022 range).

The car feels noticably weaker, especially mid-range where the nice surge of torque seems significantly diminished. I checked the old plugs that came on the car and the gaps are .026 to .028. I think that is due to the erosion of the tips over 50k miles. Should I gap the new plugs to .026? I plan to experiment but if anyone has a similar experience I would appreciate the feedback.

Thanks!

 

Changed my plugs with OEM plugs, I didn't feel any different.

 

I've not seen any hp difference due to plug gap...Ive run them down to .018 and made 700+awhp

I would do a boost leak test first and go from there.

 

I agree boost leak down test ftw

 

Agreed, 1st thing I would check as well.

 

my father used to have a machine that tested plugs under cylinder pressures and you would be surprised at home many plugs out of the box did not fire under full cylinder pressure. He went through about 20 new plugs before he found 8 that were still firing at the cylinder pressure range on his vette.

put the original ones back in, if it fixes the problem you know you have a problem with the new plugs.

 

if u gap the plugs way off the recommendation range, your car or any car will run different my friend. I agree with u on doing a boost leak thou. Or something else wrong with his car.