Technical Nailhead info required

Hi,
I need to find an approximate compression ratio for my 401 Nailhead. Its bored 60 over, so I can calculate the increase in swept volume making the cylinder volume 15.4609 cubic inches.

If I knew the volume of the cylinder head combustion chamber and the thickness of a standard gasket I could approximate a compression ratio.

Can anyone tell me what the combustion chamber volume is on a 401 Nailhead?

Many thanks
Gus

 

Cylinder head casting number 1196914 (typically used) is 125cc +/-. Other castings used on the 401 are quoted to be 123-125cc. The steel shim gasket used by Buick for US cars compressed to about .020, composite gasket .040.
Other considerations are replacement piston compression height (factory is 1.925), dome cc, and deck height. Mocking up the motor will give you a true ratio.

 

Thanks, but I don't want to strip my motor just to find out. I just want to approximate the difference between stock and a 60 over bore. Do you know what the dome cc and deck clearance are on a standard 401?

 

Not sure what year your engine is, but some of the cars in the higher lines were listed as 10.25 (pretty sure). Then there was the engines in the lower lines, like Special or Super, and they had 8.75. These are tech specs listed in the Hollander interchange books. But your cylinder volume number looks like its transposed, and should be a bit over 50 CI. 401÷8...

 

you could shoot Matt or his dad Russ an email or call they are both nail head experts (nailheadbuick.com)

 

Already on it. I have dealt with Russ a lot over the years.

 

Standard deck clearance is .050 in the hole, and dome cc will depend on the replacement piston brand, but most around 45cc.

Russ or Matt can help, as well as Tim @ TAPerformance.

I currently have a 1964 401 in the machine shop. Mocking it up for 10.5 CR

 

Look up Matt Martin on face book. He spe******es in building nailhead.

 

Gus, Dont you have some heads off your spare 401 , a piece of clear perspex and a big syringe with some light oil to cc your chamber ?

 

Good info so far, but as discussed on another post on this site, you are looking at static compression, with a.060 "over bore it get a boost, but the camshaft design will determine dynamic or "effective" compression. Your Buick experts should ask what the cam specs are in order to guide you on what parts to use for your application, get that info together before you call them.