piston CC ?

rod · 04-27-2022, 12:33 PM

stock gen 1 SBC, any idea how many cc's are in the 1 or 4 eyebrows on a stock flat top?
OR, if I put clay in one, and drop it in a cc cup, will the displacement be accurate?

thanks Rod in AZ

richie 2 · 04-27-2022, 02:41 PM

best is clay i believe. you cant go by manufactures number...

Tim H · 04-27-2022, 02:51 PM

TRW L2256 4 eyebrow are 6 cc's, but absolutely best idea to measure if possible.

Larry Hill · 04-28-2022, 07:32 AM

I understand how to fix it if cc’s are small, but how do you fix if cc’s are big without changing compression hight or top ring lane dimension ?

richie 2 · 04-28-2022, 09:56 AM

i dont believe u can...

Greg Reimer 7376 · 04-28-2022, 10:24 AM

Sometimes with a 4 eyebrow flat top piston,327 or a flat top 350,if the valve clearance eyebrows are near or at minimum, and your deck height is near minimum, piston to valve clearance becomes an issue. It then becomes an issue as which method to employ to arrive at the correct piston to valve clearance. Machining the valve clearance notches seem to be the best way to gain piston to valve clearance with the removal of the least amount of metal anyplace else. Excessive deck height gives up a lot, and since the bore diameter is always less than the inner diameter of head gasket bore openings, that would give back even more. Keeping things as close to optimum as far as the total CC's removed is the goal here.

Greg Reimer 7376 · 04-28-2022, 11:29 AM

In a re evaluation of the 327 275 horse combo for 1968, it calls for a deck height of.002", and a head gasket thickness of .018. I couldn't find a spec for the CC's of the valve notches on the pistons. Experience has taught me that an absolute minimum of about .035" is needed between the top of the piston and the bottom of the cylinder head. I had a 327 years ago with 6 cylinders at .030", one at .028" and another at .026. After a few years of running this thing,I had it apart and noticed that those two pistons had a faint imprint that corresponded with the outline of the combustion chamber. There's no way you could have built this engine with .020" total deck height and run it over about 3000 RPM. Sometimes the engine specs are not always attainable and this is one example. The 350/295 horse has the same spec. One must always remember that despite the engine specs, the laws of physics will ultimately prevail and always win.

mtkawboy · 04-28-2022, 12:49 PM

I know people years back that have tried the .020 total, results were not good

04-27-2022, 12:33 PM	#1
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	piston CC ? stock gen 1 SBC, any idea how many cc's are in the 1 or 4 eyebrows on a stock flat top? OR, if I put clay in one, and drop it in a cc cup, will the displacement be accurate? thanks Rod in AZ

04-27-2022, 02:41 PM	#2
richie 2 Senior Member Join Date: Feb 2009 Posts: 971 Likes: 425 Liked 205 Times in 93 Posts	Re: piston CC ? best is clay i believe. you cant go by manufactures number...

04-27-2022, 02:51 PM	#3
Tim H VIP Member Join Date: Jan 2007 Posts: 1,041 Likes: 1,068 Liked 481 Times in 158 Posts	Re: piston CC ? TRW L2256 4 eyebrow are 6 cc's, but absolutely best idea to measure if possible.

04-28-2022, 07:32 AM	#4
Larry Hill Live Reporter Join Date: Oct 2004 Location: Hickory, Ky Posts: 10,633 Likes: 1,927 Liked 10,687 Times in 2,225 Posts	Re: piston CC ? I understand how to fix it if cc’s are small, but how do you fix if cc’s are big without changing compression hight or top ring lane dimension ? __________________ IHM Used Parts https://ihmusedparts.com 888-821-1817

04-28-2022, 09:56 AM	#5
richie 2 Senior Member Join Date: Feb 2009 Posts: 971 Likes: 425 Liked 205 Times in 93 Posts	Re: piston CC ? i dont believe u can...

04-28-2022, 10:24 AM	#6
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,135 Likes: 172 Liked 704 Times in 218 Posts	Re: piston CC ? Sometimes with a 4 eyebrow flat top piston,327 or a flat top 350,if the valve clearance eyebrows are near or at minimum, and your deck height is near minimum, piston to valve clearance becomes an issue. It then becomes an issue as which method to employ to arrive at the correct piston to valve clearance. Machining the valve clearance notches seem to be the best way to gain piston to valve clearance with the removal of the least amount of metal anyplace else. Excessive deck height gives up a lot, and since the bore diameter is always less than the inner diameter of head gasket bore openings, that would give back even more. Keeping things as close to optimum as far as the total CC's removed is the goal here.

04-28-2022, 11:29 AM	#7
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,135 Likes: 172 Liked 704 Times in 218 Posts	Re: piston CC ? In a re evaluation of the 327 275 horse combo for 1968, it calls for a deck height of.002", and a head gasket thickness of .018. I couldn't find a spec for the CC's of the valve notches on the pistons. Experience has taught me that an absolute minimum of about .035" is needed between the top of the piston and the bottom of the cylinder head. I had a 327 years ago with 6 cylinders at .030", one at .028" and another at .026. After a few years of running this thing,I had it apart and noticed that those two pistons had a faint imprint that corresponded with the outline of the combustion chamber. There's no way you could have built this engine with .020" total deck height and run it over about 3000 RPM. Sometimes the engine specs are not always attainable and this is one example. The 350/295 horse has the same spec. One must always remember that despite the engine specs, the laws of physics will ultimately prevail and always win. Last edited by Greg Reimer 7376; 04-30-2022 at 09:14 AM.

04-28-2022, 12:49 PM	#8
mtkawboy Member Join Date: May 2003 Location: Billings Mt Posts: 281 Likes: 183 Liked 54 Times in 18 Posts	Re: piston CC ? I know people years back that have tried the .020 total, results were not good