I debated this myself, (dropped a 406 in my 79 last summer). I've had lots of people I trust tell me the steam holes don't really matter.

I have also heard a ton of stories about steam holes being more critical under something like 3000 RPM, and I suspect application plays a role.

I eventually opted to drill them myself - My application is A DD with good power, not a drag racer or high-RPM car. So it was simply peace of mind for me - My thought was that as long as I'm careful, it can't hurt, and it's far easier to do it now than to have to pull the heads after the motor has been installed. Maybe it wasn't needed - but it sure didn't hurt. Ultimately, I decided GM had them for some reason, and I didn't feel like second-guessing their engineers.

 

I don't know, can't see myself taking a drill to my new heads. I just feels like a disaster waiting to happen

 

You can have a machine shop drill them cheaply if your uncomfortable doing it.

 

I'll admit it was nerve-wracking until the first one was drilled. Go slow and cautious.
Or as BlueDawg said - most shops will do it, and its not expensive. ON the other hand, I'm not convinced it's required. Like I said, it was just peace of mind relative to cooling.

 

I agree completely, but thinner cylinder walls will transmit more heat and it won't hurt anything either, I've not know anyone who had issues, but I've read posts on forums wear guys w ere over heating and solved the problem by steam holes, how true that is, I don't know, but it won't hurt and it's easier than tearing down the top end to drill steam holes.

 

There is a reason GM did it. My understanding is the 400 will generate excessive heat due to the siamesed cylinders design when idling or low RPM for extended periods. The steam holes allow this steam/heat buildup to escape allowing better cooling under certain specific conditions. If you get bottled up in a traffic jam or stop and go traffic in the summer you might want the steam holes. They would not be required or needed under most circumstances but they will not hurt anything. Your overbore increases the odds of cooling issues and bore stability at high temperatures. I would do it because you don't lose anything by doing it and it is a real pain to do it later.

 

Think I'd outsource it anyways. No ill effect for use on a non 400" motor, say a. 350 block, gasket. Would cover hole, so no effect at all?

 

What spark plug should I be buying for this setup?

 

Pro-filer reccomends ngk 4091 or colder.

 

Compression ratio and cam don't have an effect on selection then?
Never really gave it a thought until today

 

Several things can influence your plug choice. Mostly the heat range. Looking at the specs on that recommended plug it is heat range 7.
http://www.ngk.com/product.aspx?zpid=10043

It is a racing plug which means it runs a bit cooler than a street plug and will be less prone to detonation under race conditions, but it will also be more prone to fouling under street conditions.
Also notice that the ground strap is ground 1/2 way back over the electrode. Most plugs are covering the electrode.
These come gapped at .032". This smaller gap is good for high compression and rpms.

I run heat range 5 NGK's on my aluminum heads.
I also grind the ground strap back for more spark exposure to the fuel. I Gap them at .045" or .050". It will misfire if gap is too big for your compression/RPM/ignition system.
My Effective CR due to altitude is 9:1
On hot days or during the peak summer temps this is further reduced by density altitude. This allows me a larger gap without misfire.
With hot intake temps and a hot plug you may get closer to detonation or experience dieseling if the plugs retain too much heat.
What you need is the proper reach for an aluminum head which is 3/4" or 19mm. Then choose a heat range based on your application, street, street/strip, racing. Also consider the temps the engine will be running in hotter outside may need a cooler running plug.
The gap can be choosen based on your compression and the strength of your ignition system.
You may need to experiment to get the best combo.

 

Heat Range

The term Heat Range refers to the speed with which a plug can transfer heat from the combustion chamber to the engine head. Whether the plug is to be installed in a boat, lawnmower or race car, it has been found the optimum combustion chamber temperature for gasoline engines is between 500°C–850°C. Within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits that cause fouling.







The spark plug design determines its ability to remove heat from the combustion chamber. The primary method used to do this is by altering the internal length of the core nose. In addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges.



- When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, keeping the firing tip cooler.



- A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter.





An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as adding a turbo or supercharger, increasing compression, timing changes, use of alternate fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature, necessitating a colder plug.



A good rule of thumb: use one heat range colder for every 75–100hp added.



In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber.





The heat range numbering system used by spark plug manufacturers is not universal.



For example, a 10 heat range in Champion is not the same as a 10 heat range in NGK nor the same in Autolite.









Some manufacturers numbering systems are opposite the other - for Champion, Autolite and Bosch, the higher the number, the hotter the plug. For NGK, Denso and Pulstar, the higher the number, the colder the plug.



It is not recommended that you make spark plug changes at the same time as another engine modification, such as injection, carburetion or timing changes. Performing too many modifications or tune-ups at once will lead to misleading and inaccurate conclusions if any issues occur (an exception would be when the alternate plugs came as part of a single pre-calibrated upgrade kit).



When making spark plug heat range changes, it is better to err on the side of too cold a plug. Running too cold a plug can only cause it to foul out, whereas running too hot a plug can cause severe engine damage.







From NGK site. There I already learned something for today, can shut Down the brain until tomorrow
1 heat range colder for every 75-100 hp added. Any idea where that puts me?

 

Given that the siamesed cylinders may run hotter I'd start with a 7 heat range in the NGK. If that fouls then move to a 6.

 

Playing around. Found best results with cam 4* retarded, any thoughts?

 

Don't believe it. Straight up is best. If it needs to be retarded or advanced you need a different cam. Most cams have 4 degrees advance ground in. Did you take that into account? If not that might be what your seeing.

 

Didn't factor that in... Just playing with the DD. I used what specs I had for the parts I ordered. Then I switched back and forth with carbs I have, then played with advance/retard. This is what I got.

That's when I decided I'd better ask the forum.

 

 

Ok,... I read this today and I was ok with it, but somehow I've got myself mixed up here. If the cam advance wasn't entered, so how should I interpret this, here goes, straight up is +4* and then i retard it 4* and then were @ 0*?

See what I mean... Sometimes I have more ? Than answers

When I -4* on the DD all I did was really put it dot to dot right??

 

Just line em up. Those retard/advance marks are off half the time anyway. Keep it simple

 

This is something that I have wondered about for awhile now, and can't seem to get a straight answer on: If you have a camshaft with 4 degrees of advance ground in, and you install it "straight up", is it advanced 4 degrees or not?

Scott