Thread: Coolant in cylinders; fresh 400 sbc build

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Originally Posted by Bigbzc

No sorry haven't had time. Here are my compression numbers...

#1 = 175 psi, 3 = 150, 5 = 140, 7 = 170

#2 = 142 psi, 4 = 168, 6 = 166, 8 = 157

#4 is the one that water flows out of. 1, 6, and 7 only have a little when I turn it over.

The heads were done by a machine shop before I got this mess. I can only assume that they are fine.

Not if they don't have steam holes drilled in them.

Originally Posted by NTFDAY

Not if they don't have steam holes drilled in them.

so with no steam holes I can have coolant going directly into the cylinders?

Well – here’s my two cents worth on what may be your problem. The 400 block starts life with a 4.125 bore (verses a 4.00 for a 350). You didn’t say if the block was bored but if it was, the bore would now be between 4.155 and 4.185. In any case, the head gaskets for a 400 typically are sized for a larger initial bore size and they have steam holes. The 400 block requires specific head gaskets with matching steam holes (Fel-Pro PN 17031).

The 350 heads are intended to be used on a smaller bore and they do not (in their stock form) have steam holes. 350 head gaskets do not have steam holes. Many well intended hot rodders have put 350 heads on their 400 blocks in anticipation of upping the compression ratio with the smaller chambers only to have a real disappointment in a very short time if steam holes were not drilled and proper gaskets not used.

When using heads without steam holes, the pressure immediately builds and more often than not, compromises the gasket. When that happens, water in the cylinders is common. I think you’ll find the gaskets have been compromised – as evidenced by compression being significantly lower in #2 cylinder.

I’d recommend pulling the heads, making sure you have steam holes and correct gaskets and reassembling.

Good Luck,
Glenn

I said the block was stock. Never been machined.

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.

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

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)

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.