Temporarily, I installed some from ACE H/W - lock washers too.
That doesn't sound very sexy, does it?
And, just to be safe, I slathered some RED (high temp) RTV on both sides of the gaakets.
I've since pulled the motor twice, and meant to get some sexy header bolts, and I will...really...no REALLY!
Well, that was 4 mountain runs, 2 years of Wanna Go Fast runs (including the one where I "got air"...some 20k miles now and I promise I'll get around to installing some sexy header bolts...ONE of these days...soon as I get a leak OR someone points and laughs: "Oh, look! He's got ACE H/W bolts on his headers! Hahaha!"
Yeah, I should get me some sexy locking header bolts and pitch these ACE bolts in the trash. But, sometimes simple and elegant is better than complex and wonderful! Besides, they serve as a distraction: keeps people from noticing my stainless headers are not ceramic coated either! OMG...the horror!
