1970 vs 1971 Corvette Base Engine
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Instructor
Joined: Feb 2011
Posts: 100
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From: Molalla Oregon
1970 vs 1971 Corvette Base Engine
Can anyone give me the specs for the differences in the base engines for a 1970 and 1971 Corvette 350.
I know the following:
Compression went from 10.25:1 to 8.9:1 or 8.5: 1 lower depending on transmission.
The head design changed. Both had 1.94 int. valves and 1.72 exhaust, but I think the combustion chambers varied between the two? I think the 1970 350 had 64cc combustion chambers and they were larger on the 1971 350 heads.(70 + cc)
The Camshaft specs. changed. I need these( lift and duration for both engines)
I am looking for the cam and head specs for both engines and any other major differences in heads, carb, etc.... Both 70 and 71 ran Rochester Quadrajet 4MV's.
If you took a factory 1971 RPO L48(300 hp) and wanted to rebuild it to 1970 RP0 Zx3(300 hp), what would that involve?
Obviously - flattop 10:25:1 pistons, cam change, but would the heads on the 1971 cooperate due to the differences in combustion chamber volume in the 1971 heads.?
I realize that heads, cam specs, compression, and fuel delivery are all one package and need to be matched. The factory did a nice job of this.
Any info. would be helpful.
Thanks
I know the following:
Compression went from 10.25:1 to 8.9:1 or 8.5: 1 lower depending on transmission.
The head design changed. Both had 1.94 int. valves and 1.72 exhaust, but I think the combustion chambers varied between the two? I think the 1970 350 had 64cc combustion chambers and they were larger on the 1971 350 heads.(70 + cc)
The Camshaft specs. changed. I need these( lift and duration for both engines)
I am looking for the cam and head specs for both engines and any other major differences in heads, carb, etc.... Both 70 and 71 ran Rochester Quadrajet 4MV's.
If you took a factory 1971 RPO L48(300 hp) and wanted to rebuild it to 1970 RP0 Zx3(300 hp), what would that involve?
Obviously - flattop 10:25:1 pistons, cam change, but would the heads on the 1971 cooperate due to the differences in combustion chamber volume in the 1971 heads.?
I realize that heads, cam specs, compression, and fuel delivery are all one package and need to be matched. The factory did a nice job of this.
Any info. would be helpful.
Thanks
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
Go to corvettec3.ca and click on the specs manual link. You can then click on the appropriate year and wait for it to download to view.
The 1970 (base) 300 hp engine used the flat top piston that GM continued to use in the L-82 engine through it's production run. The L-82, btw has the same cam from the L46 engine The piston head type is described as " flat-notched". The piston head type used in the 71 base engine is described as "sump" which GM continued to use throughout it's production run. As far as the transmission(s) are concerned, they had/have no effect on the static compression ratio. The camshafts of the base engines were the same. The cylinder head combustion chamber was increased to 70cc and over the years grew to 76cc and in addition, the heads were of a lighter casting over the years. This is the short version.
The 1970 (base) 300 hp engine used the flat top piston that GM continued to use in the L-82 engine through it's production run. The L-82, btw has the same cam from the L46 engine The piston head type is described as " flat-notched". The piston head type used in the 71 base engine is described as "sump" which GM continued to use throughout it's production run. As far as the transmission(s) are concerned, they had/have no effect on the static compression ratio. The camshafts of the base engines were the same. The cylinder head combustion chamber was increased to 70cc and over the years grew to 76cc and in addition, the heads were of a lighter casting over the years. This is the short version.
Last edited by Oldguard 7; Mar 27, 2011 at 12:13 AM.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
Go to corvettec3.ca and click on the specs manual link. You can then click on the appropriate year and wait for it to download to view.
The 1970 (base) 300 hp engine used the flat top piston that GM continued to use in the L-82 engine through it's production run. The L-82, btw has the same cam from the L46 engine The piston head type is described as " flat-notched". The piston head type used in the 71 base engine is described as "sump" which GM continued to use throughout it's production run. As far as the transmission(s) are concerned, they had/have no effect on the static compression ratio. The camshafts of the base engines were the same. The cylinder head combustion chamber was increased to 70cc and over the years grew to 76cc and in addition, the heads were of a lighter casting over the years. This is the short version.
The 1970 (base) 300 hp engine used the flat top piston that GM continued to use in the L-82 engine through it's production run. The L-82, btw has the same cam from the L46 engine The piston head type is described as " flat-notched". The piston head type used in the 71 base engine is described as "sump" which GM continued to use throughout it's production run. As far as the transmission(s) are concerned, they had/have no effect on the static compression ratio. The camshafts of the base engines were the same. The cylinder head combustion chamber was increased to 70cc and over the years grew to 76cc and in addition, the heads were of a lighter casting over the years. This is the short version.
The 70 base 350 had a 4 valve relief cast aluminum piston. The L-46 (350HP) LT-1/L-82 piston is forged! The biggest difference in power output is the open chamber "smog heads" used on 71 and later motors. The combustion chambers had a poor shape for making HP but because the HP was down the NOX emissions were less so they did the trick for early emissions reductions. Putting a set of Vortec or aluminum heads on your motor and a change to mild cam would make it perform on par with a 70 L-46 350 while still living on today's pump gas. Search there are hundreds of threads on this subject.
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
WRONG
The 70 base 350 had a 4 valve relief cast aluminum piston. The L-46 (350HP) LT-1/L-82 piston is forged! The biggest difference in power output is the open chamber "smog heads" used on 71 and later motors. The combustion chambers had a poor shape for making HP but because the HP was down the NOX emissions were less so they did the trick for early emissions reductions. Putting a set of Vortec or aluminum heads on your motor and a change to mild cam would make it perform on par with a 70 L-46 350 while still living on today's pump gas. Search there are hundreds of threads on this subject.
The 70 base 350 had a 4 valve relief cast aluminum piston. The L-46 (350HP) LT-1/L-82 piston is forged! The biggest difference in power output is the open chamber "smog heads" used on 71 and later motors. The combustion chambers had a poor shape for making HP but because the HP was down the NOX emissions were less so they did the trick for early emissions reductions. Putting a set of Vortec or aluminum heads on your motor and a change to mild cam would make it perform on par with a 70 L-46 350 while still living on today's pump gas. Search there are hundreds of threads on this subject.
Last edited by Oldguard 7; Mar 28, 2011 at 11:13 AM.
