70 LT1 vs 71 LT1 all else equal
Thread Starter
Drifting
Joined: Apr 2004
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From: Allen Park Mi
70 LT1 vs 71 LT1 all else equal
I'm curious to know how much of a performance difference one might expect between the 70 vs 71 LT1 -
basically, how much the 2 point drop in compression changes the performance?
the reason I ask.... i built a 421 stroker with the 1970 LT1 camshaft -
my compression is 9.5:1 the car seems to run quite well - but i'm curious if the drop in compression vs the added cubes makes up...
i'm also wondering if the tiny lift on the intake side is gonna make that 421 "hunt" for air....
basically, how much the 2 point drop in compression changes the performance?
the reason I ask.... i built a 421 stroker with the 1970 LT1 camshaft -
my compression is 9.5:1 the car seems to run quite well - but i'm curious if the drop in compression vs the added cubes makes up...
i'm also wondering if the tiny lift on the intake side is gonna make that 421 "hunt" for air....
Le Mans Master
Joined: Oct 2010
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
The more cubic inches the milder the cam will act. Shooting from the hip with an engine that size you could do much better.as far as the performance difference between the 2 years,some say there wasn't much.I thought it killed it dropping compression.
Race Director
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From: Grapevine Tx
2018 C3 of Year Finalist
2016 C3 of the Year Finalist
Super Chevy mag did an engine build-up series to compare Chevy and Ford high perf. engines of that time. They did a 70 LT-1 and a 71/72 LT-1. The later engines had lower compression, but higher flowing heads. They basically made the same gross horsepower as the 70. About 367 horsepower.
Back then, manufacturer horsepower wasn't always actual hp for insurance reasons.
Back then, manufacturer horsepower wasn't always actual hp for insurance reasons.
Last edited by F4Gary; Mar 25, 2016 at 08:10 PM.
Le Mans Master
Joined: Dec 2003
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From: Fremont CA
The 70 will always be slightly faster than a 71/72. One trick many dealers did on 71/72 LT-1 Vettes (and Z28s) was....order a 4:11 Axel instead of the usual 3.70....it made up for the reduced torque of the lower compression motors. My 72 LT-1 was a factory 4:11 car against a 70 with 4:11s there will probably be a 2 tenths/2-3 MPH loss of 1/4 mile performance.
You said you built a 421 cu/in motor and put a LT-1 cam in it? You left about 50-70 HP that could be easily gained if you did....the specs for a big cu/in motor are way different requirements than a 350 motor.
You said you built a 421 cu/in motor and put a LT-1 cam in it? You left about 50-70 HP that could be easily gained if you did....the specs for a big cu/in motor are way different requirements than a 350 motor.
Thread Starter
Drifting
Joined: Apr 2004
Posts: 1,303
Likes: 36
From: Allen Park Mi
The 70 will always be slightly faster than a 71/72. One trick many dealers did on 71/72 LT-1 Vettes (and Z28s) was....order a 4:11 Axel instead of the usual 3.70....it made up for the reduced torque of the lower compression motors. My 72 LT-1 was a factory 4:11 car against a 70 with 4:11s there will probably be a 2 tenths/2-3 MPH loss of 1/4 mile performance.
You said you built a 421 cu/in motor and put a LT-1 cam in it? You left about 50-70 HP that could be easily gained if you did....the specs for a big cu/in motor are way different requirements than a 350 motor.
You said you built a 421 cu/in motor and put a LT-1 cam in it? You left about 50-70 HP that could be easily gained if you did....the specs for a big cu/in motor are way different requirements than a 350 motor.
thats pretty much what i was thinking - the LT1 as most know, borrows the intake lobe from the L72 cam but its got about .100 more lift on the BBC grind - i'm def gonna pull it out and go with something more suitable for 420cubes and 9.5:1 compression. Cheers
Last edited by aaronz28; Mar 26, 2016 at 09:40 AM.
Race Director
Joined: Dec 1999
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From: Forked River NJ
Honestly you built a 421 and used the crappy LT1 cam in it. That design is 45 years old. Many will not like that comment but it was designed with high compression and better fuel. You spent the dollars with a 421 put a roller cam in it and I hope you used a set of big heads and you will make a ton more power than your current setup with that cam. I have driven a 421 with a roller cam and good heads and it made well into the upper 500 HP. Your not doing it with that cam.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
My real question would why any body would even use a 45+ year old cam that wasn't very efficient back then on a big stroker build today?
Drifting
Joined: Oct 2005
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From: Forth Worth TX
While the 70 had more compression, the 71/72's had better flowing heads.
Additionally the timing advance curve was altered between each year, progressively getting slower.
So in your comparison, if each years timing advance curve was adjusted to be the same (36*@ 3000rpm) the difference in hp would be minimal.
With all things being equal (timing advance curve, build tolerance, etc.) you will see very little difference between a 70 LT-1 vs a 71/72 LT-1 on a dyno.
Additionally the timing advance curve was altered between each year, progressively getting slower.
So in your comparison, if each years timing advance curve was adjusted to be the same (36*@ 3000rpm) the difference in hp would be minimal.
With all things being equal (timing advance curve, build tolerance, etc.) you will see very little difference between a 70 LT-1 vs a 71/72 LT-1 on a dyno.
Last edited by Revi; Mar 26, 2016 at 10:35 AM.
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