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Discussion Starter #1
Earlier this year I installed an HKS EVC IV boost controller.

It has performed very well and I'm satisified. At that time I did not change the plug gap on the standard NGK Platinum plugs from the stock gap. I'm running a 1.0 kg/cm2 (about 14.2 psi) max boost (measurements match between the HKS EVC IV digital display and my Greddy 60mm peak hold gauge).

I did the install at the start of the summer when the temperature tended to hover in the 80's (F) during the day and 70's at night. Everything worked well.

I've noticed that as the temperature has dropped I'm seeing a slight stumble/hesitation when I punch it hard and the air temps are low (less than 40 F). This lasts for a split second and passes. It only occurs under this condition. I could produce the same kind of result by setting the boost level to 1.1 kg/cm2 (about 15.6 psi) in the summer. This is too high a boost level for the car so I would not run this on 93 octane fuel with the stock pump, injectors and fuel control.

I'm suspicious that the colder temperature is making for a denser air charge and that I need to reduce the plug gap.

I'm looking for comments on this thinking, and to what gap I should go with the plugs. I plan to stick with the NGK platinums.

Beyond the boost controller the only other modifications that would be pertinent to the engine are a K & N FIPK, ATR downpipe and high flow cat, and a Borla exhaust.

The car is in excellant condition, about 20k miles. The plugs were new at about 6k along with a set of Magnecor wires. No reason to beleive that anything is wrong or worn.


1994 VR4

Got Boost?
4,242 Posts
Hopefully this will help you out. I am running the HKS EVC IV @ 1.05 kg/cm2 (14.9psi) with a .034 plug gap on the stock NGKs. I have NO problems what so ever with hesitation, not even in the colder weather.

Also, if you were getting it at 1.1 kg/cm2, then that would also seem to indicate that you were getting spark blowout because of the increased boost pressure.

I would try gapping them down to .034 (some people say .032) and see if that fixes your problems. It should. Keep us posted.
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