Chamber volume for 3748770 heads

[Thomas H.]

I hesitate to ask this as the information should be easily found, but.......

I'm in the process of rebuilding the engine for my 58 and spent yesterday measuring the cyl head chamber volumes. Six of the eight chambers measure in at 63cc while the other two are 63.2 and 62.8. I know these heads had been milled by the previous owner and wanted to compare the volumes I was measuring to the stock volume. Mind you, all of my past engine building experience is with big blocks so I have very little reference material here for small blocks. I figured that this information would easily be found with a quick google search but I have been unable to find a definitive statement that says the chamber volume of these heads is "X". I get a general feeling it is 64 cc but would like to know for sure.

Thanks,

Tom

[Edward B.]

Re: Chamber volume for 3748770 heads

Hmmmm. CBTN shows these heads (which are 1958 only) as having 59.669cc's.

Ed

[Thomas H.]

Re: Chamber volume for 3748770 heads

Hmmmm. CBTN shows these heads (which are 1958 only) as having 59.669cc's.

Ed

Ed,

What is CBTN?

These heads are "X58" if that makes any difference. I find it hard to believe they are 59 cc heads, There is no evidence of chamber work to enlarge them to the 63-ish I was measuring.

Tom

[Joe L.]

Re: Chamber volume for 3748770 heads

Ed,

What is CBTN?

These heads are "X58" if that makes any difference. I find it hard to believe they are 59 cc heads, There is no evidence of chamber work to enlarge them to the 63-ish I was measuring.

Tom

Tom------

The 3748770 heads have a nominal chamber volume of 60 cc. That's when they are new. Each time the valves are ground, the chamber volume increases slightly. After a few valve grinds, you could get to the volume you're finding. In 56 years, it would be reasonable to expect that at least a few valve grinds have occurred.

[Edward B.]

Re: Chamber volume for 3748770 heads

And CBTN is "Chevrolet by the Numbers", by Alan Colvin. GREAT reference books when you're looking for block, head, crank, alternator, intake, exhaust, carburetor, camshaft, axle and transmission casting, date code and part number information.Ed

[Thomas H.]

Re: Chamber volume for 3748770 heads

Thanks for the input guys.

I suppose I need to revisit my measurements. I ran the compression calculations last night and I'm coming up with right around 8.0:1. I was hoping fr closer to 9. Varying gasket thickness only gains about 0.2.

Quick numbers:

Chamber 63cc
Bore 3.935 (0.060 over 283)
Stroke 3.0
Gasket opening 4.125 (Felpro Perma torque)
Compressed thickness 0.039
Piston Volume -5.6cc (flat top, four valve reliefs)
Piston to Deck clearance 0.041

Fun stuff...........

Tom

[Duke W.]

Re: Chamber volume for 3748770 heads

Use the '61 FI domed pistons. Your deck clearance is very large (.025" is nominal), and, of course, the head chambers are oversize, which combine to kill the compression ratio. I think you can buy the '61 FI pistons from Danchuck. Another alternative is custom pistons with higher compression height, and if there is no pin offset as with the OE pistons, only two valve clearance notches are required.

Also, consider a thin shim gasket. If the head and deck surfaces are level, it will seal. I think the Felpro 1094 is .015".

You didn't say what cam, but if it's the base cam I recommend 10:1 max and 10.25 with the Duntov. Your current low compression will run on regular unleaded, but you are leaving a lot of torque, power, and fuel economy on the table.

Duke

[Thomas H.]

Re: Chamber volume for 3748770 heads

Hi Duke,

This "professionally rebuilt" engine that came with the project 58 I bought has been nothing but a hodge podge of thrown together parts and poor workmanship. The engine was never run after the rebuild and the previous owners son (owner passed away) knew nothing about what was done to the engine other then his dad had it "professionally rebuilt". I tore it down so I knew what I was working with and found a lot of issues such as scored rod bearings from piston assys being installed without protective coverings over the rod bolts to keep the crank from damage. Five of the eight journals were nicked and scored the bearings down to the copper. Mix matched rocker arms and push rods. Incorrectly shimmed valves and the cam was installed 4 deg retarded. I could not identify the cam they used, but it measured close to a base cam although the lobe separation was not the same as a base cam. I believe I measured 110 and it should be 108 or vice versa, I did that last fall and I'm going by memory as I don't have my notes here at work.

I sourced a better block (date code aligns with the car) and crank. I had the block decked and bored and the crank needed to be cut 0.010. I reused the pistons from the old block as they are new. I too was surprised to see the deck clearance at 0.041 as I was expecting nominal 0.025 minus the decking.

I think I'm going to regroup tonight and double check all of my volume and clearance measurements just to make sure I didn't miss anything. But the way it looks right now is I'm going to be heading down the path of domed pistons to get the CR up in the 9.5 range. Looks like Keith Black makes a set that will work, a bit pricey though. I have yet to check Danchuck as you suggested, but I will.

The cam I will be using is a Comp Cams (12-105-3) replacement for the base 283 cam. It is a 245hp set up so it has dual 4bbls.

Tom