400 heads.

I have a new set of Protoplines and they came without steam holes. I hear 50/50 as to drill them or not. Some say if street driven you need them. The car sees limited street or strip duty;about 1000 miles a year at best.
I do drive it to the local hang outs and to the track.Temp usually is between 160*-180*,but has seen 200* on really hot days.
Whats the worst that could happen if the holes aren't drilled ?

If you don't drill the holes, the coolant can boil between the cylinders, and the steam would be trapped there (pretty much forever). The holes would let the vapor vent into the heads.

I've heard both too, but if it was good enough for GM to spend money on... when I did a 406, I drilled. Not like it's hard to do or could hurt anything.

really, if it will make you feel better, go ahead and drill them.
but, with that said, no, you don't need them. that is unless you plan on spending 90% of your time at under 1500rpms, which is about the only time steam would build up at the siamesed area. yes, GM did it and they know what thier doing, but they were also building motors for delivery trucks, taxicabs and police cars, not a performance (or even semi performance) motor in somebodys weekend cruiser. just look at any of the aftermarket siamesed blocks, none are drilled for steam holes, at least that i know of. and they too know what they are doing.
and btw, this is info i acquired long before i did it myself, from several respected machinists. and i and every one of my friends that run 406's do so w/o steam holes, fwiw. all it really ends up being is a place to crack, something factory 400 heads are notorious for. but, you could absolutely do it, and probably be ok, so really, if it makes you feel better go ahead, but imo, its unnecessary.
enjoy your new 406! graemlins/beers.gif

I thought about the "then why did GM do it" , gotta be a reason, too.

I think I'll try it without the holes and if I have heating issues I'll have to tare them off and "do the drill".

Thanks, I guess I just needed a push.

honestly, you won't be sorry you didn't. if it comes back to bite you, by all means revive this thread and publicly humiliate me ;)

Just did some reading and they showed 400 "off road" gaskets w/o steam holes, operating RPM's 3000+.

i have seen that number as well, its probably a "safe" figure for the manufacturer, but i can assure you while mine sees above 3k, it spends lots of time below that, and runs 180 all day long. i actually use a head gasket w/ steam holes, because it fits my bore/thickness needs, they work great.
again, i'd just do what will give you piece of mind, one less thing to think about after all, but i still stand behind the "nay" side for steam holes. graemlins/beers.gif

Yep, I just used the Felpro gaskets with the holes and no drilled holes. So you better be right...lol. Really though, I think if I was towing and hauling it would be a different story.

uh oh, now i'm having second thoughts.... ;)
no, you'll be fine, i pretty much won't even speak up about something unless i'm sure or have done it myself, nothing worse than bad advice.
and i agree 100%, if it was a tow/hauling vehicle , or even grandma's impala, i would likely reconsider also.
good luck, you'll love it graemlins/thumbsup.gif
Sean

same here... and the only 400 I've done, I drilled and was fine, hench my ignorable caution