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: 1,146 Likes: 247 Liked 913 Times in 172 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: 172 Likes: 35 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: 7,660 Likes: 2,765 Liked 4,849 Times in 1,843 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. __________________ Real life never quite adds up.... Jay Farrar

01-18-2019, 12:24 PM	#4
Dwight Southerland VIP Member Join Date: Dec 2001 Location: Arkansas - In the middle of everything. Posts: 1,986 Likes: 56 Liked 731 Times in 180 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: 1,146 Likes: 247 Liked 913 Times in 172 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.