Thread: Coolant in cylinders; fresh 400 sbc build

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Just wondering if you read post #21. All this is mute not having pulled the heads yet

Originally Posted by cffisher

Just wondering if you read post #21. All this is mute not having pulled the heads yet

Yeah I read it. I will pull the heads after the tornados pass over. I should know something by Sunday and will post then

Originally Posted by Bigbzc

I said the block was stock. Never been machined.

You seem to be fixated on the block. We're not talking about the block. It has steam holes already in the decks from the factory. As Glenn told you, the heads and the gaskets must also have steam holes to match up with the holes in the block decks.

Guess I'll have to go out in the garage and take some pictures of my stock 400 heads so he'll know what we're talking about.

Originally Posted by techinspector1

You seem to be fixated on the block. We're not talking about the block. It has steam holes already in the decks from the factory. As Glenn told you, the heads and the gaskets must also have steam holes to match up with the holes in the block decks.

Yeah I got that plain and clear. I was responding to the post above that which said that I hadn't said whether the block had been bored over or anything and I believe somewhere in the begining of this thread that I mentioned that it was all stock and did not need work as it had very low mileage and no ring ridge. I think you are right about the heads being off a 350 because that is what was in it before I got it. How can I ID between the different heads? By the way, thanks for your help so far

Originally Posted by NTFDAY

Guess I'll have to go out in the garage and take some pictures of my stock 400 heads so he'll know what we're talking about.

I know exactly what you are talking about

I have to drill steam holes in heads between cylinders, a total of 6, got it.

I'll know after the storms blow over and I can remove heads to see if they are 400 heads or not.

Production Chevy heads have the casting number under the valve cover. It's 6, 7 or 8 digit number. Use an awl or something sharp like that to scratch around on the numbers. Many times, there is dried crud on them and a 3 might look like an 8.

Here's what 400 heads look like (steam holes circled)

Ok, I pulled th heads and there are no steam holes so I can only assume that they are 350 heads. the casting number is...
462624. Please tell me what kind of 350 heads they are.. (double hump) or what?

Oh yeah, one more thing that worries me. When I removed the head bolts from bank 1 (the lower head bolts) water just spewed from them. I noticed water in the lower bolt holes of bank 2 also

Bolts go into water jackets, so that is normal. thats why you always put sealer on all head bolts on a sbc

462624 1976-1979 350 with 75.5 cc chambers

Unfortunately, the 624 casting are probably the worst of the GM castings for cracking. They are prone to cracking across the exhaust seats and thru to the heat crossover. They’re not good candidates for any decking either.

Mortec says they are from a 75-86 350 or 400, 76cc chamber. They were manufactured with 1.72/1.5, 1.94/1.5 or 2.02/1.6 valves

If they have the 1.72/1.5 or the 2.02/1.6 valves and they are perfect – they may be worth drilling steam holes. If they are the small valves or (as is very likely) show any cracks, I’d start looking for new heads.

If you have any budget, the Vortecs are a good way to go. This means a new intake manifold as well, but will definitely bring the 400 alive. GM Part Number 25534421 ($1100 a set or less on ebay) is a great head, 185cc runners and 66cc chambers. They’ll need steam holes drilled.

Good Luck!
Glenn

We really need to know more information about the block and pistons before you jump and buy different heads. What is the piston crown configuration? Can you post a pic? Is there a part number stamped on the top of the piston? With the piston at TDC, how far is it down in the bore? You can measure this with a set of feeler gauges and a straightedge ruler. What I'm getting at is that you have a fairly short cam in the motor now and with the large chambers of the heads you have now, the static compression ratio works out ok on pump gas. But if you go with smaller chambers, you may exceed the match-up of static compression ratio with the cam timing you have now and you'll be tearing back into the motor to change the cam. Let's try to make this work the first time. Post the info I asked for.
You mentioned going with 305 heads. I can't think of a worse combination than 58cc heads on a 406 with a short cam and unknown squish. Detonation City.

With the short block on a stand, get a buddy to stand in front of the motor and turn the crank with a socket and long bar on the harmonic damper retaining bolt head. This bolt is torqued to 65 ft/lbs, so it will not unwind if you turn the crank backwards easily. Roll the crank around so that the #1 piston (driver's side front) is at approximately top dead center. You will be standing at the side of the block at #1. Stand your ruler up on edge and span across the cylinder bore about a half inch from the edge of the bore. You will place the ruler at either 3 oclock or 9 oclock position. Placing it at noon or 6 oclock will allow the piston to rock on the wrist pin and give you an erroneous reading. Start with 0.025" or so and slide the gauge blades under the ruler and all the way to the cylinder wall. Have your buddy rock the crank back and forth so that the piston is coming up to TDC and back down in the bore just ever so slightly. If the piston doesn't push the ruler off the deck, then use more feeler gauge blades and try again. Maybe go 0.005" at a time until you find how far the piston is down in the hole at TDC. This is called the piston deck height. We must know this dimension before going any further. And don't forget the pic of the piston crown.