I have a bone stock 400 sbc with less than 1k miles on it since its rebuild. Before I bought this motor a friend of mine ran alcohol through it on his competition pulling tractor. Blew the head gaskets during a run, pulled the motor and rebuilt it with the intentions of putting it back in his tractor. But instead I bought it with intentions of making a mild build and putting it in my Camaro. Since buying the 400 I've decided I wanted to do a Vortec carb build on this motor, so I've picked up some '99 "062" 350 Vortec heads. I'll end up probably going with an Edelbrock RPM Air Gap Vortec Manifold and a Demon 750cc 4-bbl carb. Still not sure what cam I want to run, but I'm sure it will be a Lunati brand of cam. The idea behind this car is for a fun weekend street car with intentions of hitting the track a few times.

Now that you have a bit of background on the motor, here are the issues and things I know I need to do before I can get the Vortec heads to properly work with the 400 block. I know I will need to have a machine shop drill the steam ports on the heads, and cut the guides back to allow for a bigger cam. Also I need to upgrade to a bit stiffer of springs and retainers, and while I'm at it I'm gonna install new valve stem seals as well. After that the heads should be good as far as I know to bolt to the 400 with the appropriate intake manifold of course. One other problem I face from what I've been reading online that I will see very high compression ratios on this motor with the stock bottom end. Some sources say even as high as 11:1 CR, that is just way to high for me to want to run on the road. I would really like to keep the CR around 9.5:1-9.8:1 I think that will be manageable without have to worry about detonation on pump gas, I plan on running 94oct in this car anyways just to be on the safe side of things. Hell the 305 in the car now is a 9.3:1CR and runs fine on 87oct...

Anyways, what I understand is that I can replace my stock pistons for a deeper dished piston. Around 18cc-22cc dished pistons on the 350 Vortec heads will land me pretty close to 9.5:1 which is where I would like to be. What I would like to know, does anybody know what the stock 400 sbc piston dish is? I cannot find this info online for the life of me, some say around 15cc-16cc dish on the stock pistons. But I cannot find anything to back this info up. Also is there a way to measure the dish on the pistons I have now in the 400? The PO said they are stock, but I kind of doubt they are for the simple reason that he ran stock 305 heads on this motor while it was in his pulling tractor. The 305 heads would create around 11.7:1CR on this 400 if my math is correct...

305 sbc heads = 52cc chamber
350 Vortec heads = 64cc chamber

So this is why I'm confused because if we take the information we know about what I have so far it will look like this:

400 Bore: 4.125 in.
400 Stroke: 3.75in.
350 Vortec Head Volume: 64cc
400 Stock Piston Dome Volume: 16cc????? (That's the closest I've heard so far, so I'm not sure)
Cometic head gasket: 0.040in.

And lets just say there is no reason to do any deck clearance on the motor because I'm not sure if it needs to be done yet or not...

But if the stock pistons are a 16cc dished piston that would land me around 10.2:1CR, WAY TO HIGH!! But if I go with a 22cc dished piston that will land me around 9.6:1CR which is right about where I would like to be.

So can you guys help me find out what the dish size on stock 400 pistons are? And if you have any other suggestions at all for me on this build that would be great as well. Thanks for listening to me ramble on and on haha.

 

I'm not sure what you mean by bone stock, but I can't imagine anyone competing in anything with a stock 400.

There were three different stock dish sizes depending on what year it was.i can't remember the specifics, but I wouldn't count on your motor having any of them.

 

Well my pistons are dished, I'm not exactly sure the year of the motor. But the ID on it is 330817...

 

That block was used 1970-1980, so you could have any of the three. Maybe if you can post a pic someone could ID them.

 

I'll get some pictures up tonight.

 

Also I noticed that in the same spot on every piston is a small hole drilled in the top. Not sure what these are, any clue?

 

That looks like the smallest dish. Around 12cc if I remember right. I got a list of them somewhere in storage and I'm sorry to say I won't be finding it anytime soon. I hope someone can be more definite for you. The next size doesn't have deep valve reliefs and the big dish has none.

 

Oh so the holes that I'm referring to is for the valve reliefs?

 

The crescent shapes are the valve reliefs.

I'm not sure what that hole is there for. The notch is to indicate which side of the piston goes to the front of the engine.

 

If that hole only goes to the top ring land, it may be there to help seal the rings by combustion pressure.

 

Those are usually several holes around the perimeter, and a lot closer to the edge of the piston (and a lot smaller than that).

 

Well, I'm not sure what the holes are for either. The holes are in the same spot on every piston facing the front of the engine...

 

Talked to the guy at work that I bought the motor from, turns out the holes are indicators to show what way to put the pistons in. And I asked him if remembered what the dish size on the pistons were. He said he could not remember, so on my lunch break I bought a package of 20cc syringes and tested it myself. After testing about 5 times, I have not come to an exact measurement. But I can the pistons have a dish of between 20-22cc. So they are not the stock replacement pistons, which explains how he was able to run 305 heads without issues. And this answers all my questions, and lets me know that I can run my Vortec heads without issue with compression and detonation.