Jr Stock piston rules

Lyn Smith · 01-17-2019, 04:36 PM

I was reading a 1968 NHRA rule book today.It said under the engine rules that you could use any replacement piston "as long as it doesn't increase the compression generally the same in appearance".So on the 1955 265 engine with the flat top piston could you use a piston that had valve reliefs like the 56 and 57 engines had?

Brian Fink · 01-17-2019, 07:25 PM

Unfortunately you have to make the 55 style work ; I believe CP is the only option as they made the first set for Carl Libucha after he sent NHRA a stock one.

Mark Yacavone · 01-17-2019, 08:06 PM

I would say yes. Probably wouldn't need them anyway, with the cams they had back then. Even if they did , they wouldn't work with the stock spring specs.

Dwight Southerland · 01-18-2019, 12:24 PM

Lyn -
I saw the Weir Bros. '55 Chev station wagon go through a tear down in 1968 and those pistons did have valve reliefs. They passed.

Lyn Smith · 01-18-2019, 02:54 PM

According to some vintage GM Parts Books I have, the flat top replacement GM pistons were discontinued in mid 1957,and replaced by the 56 57 piston with the reliefs.

01-17-2019, 04:36 PM	#1
Lyn Smith VIP Member Join Date: Dec 2001 Location: Pontiac,il. Posts: 1,183 Likes: 267 Liked 935 Times in 185 Posts	Jr Stock piston rules I was reading a 1968 NHRA rule book today.It said under the engine rules that you could use any replacement piston "as long as it doesn't increase the compression generally the same in appearance".So on the 1955 265 engine with the flat top piston could you use a piston that had valve reliefs like the 56 and 57 engines had?

01-17-2019, 07:25 PM	#2
Brian Fink Member Join Date: Jul 2007 Posts: 173 Likes: 39 Liked 28 Times in 9 Posts	Re: Jr Stock piston rules Unfortunately you have to make the 55 style work ; I believe CP is the only option as they made the first set for Carl Libucha after he sent NHRA a stock one.

01-17-2019, 08:06 PM	#3
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,742 Likes: 2,843 Liked 5,001 Times in 1,901 Posts	Re: Jr Stock piston rules I would say yes. Probably wouldn't need them anyway, with the cams they had back then. Even if they did , they wouldn't work with the stock spring specs. __________________ "We are lucky we don't get as much Government as we pay for." Will Rogers

01-18-2019, 12:24 PM	#4
Dwight Southerland VIP Member Join Date: Dec 2001 Location: Arkansas - In the middle of everything. Posts: 1,996 Likes: 63 Liked 756 Times in 189 Posts	Re: Jr Stock piston rules Lyn - I saw the Weir Bros. '55 Chev station wagon go through a tear down in 1968 and those pistons did have valve reliefs. They passed. __________________

01-18-2019, 02:54 PM	#5
Lyn Smith VIP Member Join Date: Dec 2001 Location: Pontiac,il. Posts: 1,183 Likes: 267 Liked 935 Times in 185 Posts	Re: Jr Stock piston rules According to some vintage GM Parts Books I have, the flat top replacement GM pistons were discontinued in mid 1957,and replaced by the 56 57 piston with the reliefs.