Drilling Heads for 400 - Team Camaro Tech
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post #1 of 9 (permalink) Old Jan 27th, 08, 04:10 PM Thread Starter
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Drilling Heads for 400

Hello everyone, I am getting ready to start working on the 400 motor to go into my Z-28 and I have done the search on the subject of drilling the steam holes for a 400 and well, after doing some reading I am not sure what to do. I have a set Dart Pro 1 Aluminum heads that will be going on this engine. The cam will be a retro hydraulic roller unit with .563"/.574" with 1.6 Comp Cams Pro Magnum rockers. I have ROL head gaskets for the 400 that have the steam holes and Dart sent me instructions on drilling them but I unsure if I need them. I'm not sure I can do it myself and finding a machine shop here can be a challenge as well.Also, I have read here that you should do a retorque of the head bolts after running the motor through a heat cycle but that also poses a problem in that I can't get to all the head bolts with my engine in the car since these third gen don't offer much room. What's your take on this subject as well? Thanks for any info and help with this.
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post #2 of 9 (permalink) Old Jan 27th, 08, 05:33 PM
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Re: Drilling Heads for 400

Its probably not a bad idea if its a street driven car. The straight holes are fairly easy to do but the angles ones are a pain. They are pretty deep and you have to be very careful not to break the small drill bit. Lots of cutting lube and very slow going. I do them on my seat and guide mnachine, makes it easy to set the head up at the corect angle to drill them.

As far as the head bolts go, here is what I do. First make sure to use sealer on the bolts, and make sure to use some oil on the bolt head where it hits the washer. Then go ahead and torque the bolts like normal. Wait about an hour, then go back and starting with the first bolt in the sequence, loosen it up about a turn then torque it right back down to the final torque in one smooth pull. Go to the next bolt and do the same .... and all the rest in sequence.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md
1971 Chevelle "Heavy Chevy" original owner

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post #3 of 9 (permalink) Old Jan 28th, 08, 10:42 PM
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Re: Drilling Heads for 400

This is a long debated subject. That said, from my experience, the research I did prior to building my first 400, and everyone I know running them (quite a few guys), they are not needed unless you plan on idling for hours in the heat, and I mean hours.
The only reason GM did it was because they need to design a motor that can sit at idle and below 1700 rpm the majority of it's life in Arizona type heat. Not one manufacturer I know of of aftermarket siamesed blocks drill holes in them if thats any indication.
As I always have said in previous discussions, by all means drill them if it makes you feel better, but as Bill points out, it's not a slam dunk piece of cake to do yourself, so you will end up paying to have it done likely. I will tell you this, I have seen way more guys sorry they tried to drill the holes and make a mistake (several) than guys that wish they had drilled them (none).


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post #4 of 9 (permalink) Old Jan 29th, 08, 11:30 AM
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Chet, I drilled the steam holes in my aftermarket cast iron heads without much issue. I was scared as h#*% to do it, but I took my time and it went fine. I used a cheap drill press and as said, the straight holes were easier, but, for the angled holes, I bought a magnetic angle guide, stuck it on the face of the head, angled the head, then set up a jig to hold it in place and went on ahead and drilled the hole. Maybe I was just lucky, but it went real smoothly and worked great.


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post #5 of 9 (permalink) Old Jan 29th, 08, 12:55 PM
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Re: Drilling Heads for 400

I don't have the steam holes drilled on my heads. Even in the brutal Phoenix summer heat I have not seen any abnormal cooling problems. This is with two 406's one with Dart iron heads and one with aluminum heads.

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post #6 of 9 (permalink) Old Jan 29th, 08, 03:09 PM
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Re: Drilling Heads for 400

If the motor will see life in traffic and lots of low RPM's/idleing... you could do it.

If little traffic,2000+ RPM's cruising,not very much idleing... not really needed.

I didn't drill mine but I have a th350 tranny (no OD), 3.73's, and a 3000 stall, does see street time but little traffic....NO PROBLEMS

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post #7 of 9 (permalink) Old Jan 30th, 08, 05:03 PM
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I drilled my virgin, big valve, -461's w/ I THINK(??) 1/8th and a 3/16th inch bits. One hole straight down and the other angled at 30 to 45 degree's, but I forget how I did it b/c I did it in the summer of '83.

Check W/P's site b/c I think they tell/show pic's of how to do this??

I did use my 400's stock headgaskets to drill my Mr. Gasket 350 engine .020" thick steel shims and then I hand fit them to my 406 block by mocking them up and reaching up inside w/ a sharp scribe and marked them.

I just took them out and hand removed the excess metal and used good old Dauber CopperCote and re-torqued them over three heat cycles b/c I'm almost anal on this!!

I used two drill bits the size of the head dowels as locators and it went nice using a 1/4" drill.


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post #8 of 9 (permalink) Old Jan 30th, 08, 07:27 PM
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Re: Drilling Heads for 400

The 400's i have done have not been drilled , i used the good Edelbrock victor water pumps with no problems at all , and as sean said all the dart , motown blocks don't need it done . Our car with the 427 will sit in 100 degree weather and sit at 185 to 190 all day long .

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post #9 of 9 (permalink) Old Feb 11th, 08, 05:14 PM Thread Starter
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Re: Drilling Heads for 400

Thanks to all who chimed in on this, I haven't been on the forum awhile, so I just started getting caught up. I do run a high flow water pump and as for sitting and idling for long periods of time, well, I drive this car to shows and love to drive it when I get the chance and sitting in traffic is part of it for me, but not for any real length of time. I may just go ahead and try it without and see what happens. Again thanks, and I am sure I will have more questions as I get started on this project.
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