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1970-71 LT1 engines

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Old 07-25-2012, 09:59 PM   #1
riverracer au
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Default 1970-71 LT1 engines

a mate has just bought a '71 LT1 and we got talking about the engine.
what makes the '70 with 370 hp so special over the '71 with 330hp?
was it the 186 heads, cam, higher compression pistons etc, or what?
or was it the new rating system, but i thought that came in '72?

where can we find a break down/listing of parts that go in a LT1 engine?
ie: cam specs, pistons used etc.

any good engine books on this?

this mite solve/start a bar fight for us...

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Old 07-25-2012, 10:49 PM   #2
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In 1971 GM mandated a compression drop on all engines to a max of 9.5 to 1. That is most of the difference from 1970 to 1971. Gm did change rating in 1972 so the HP changed again.
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Old 07-26-2012, 12:25 AM   #3
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The 70 LT-1 has 11-1 pistons, while the 71 has 9.5-1 pistons. GM was preparing for regular un-leaded fuel.
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Old 07-26-2012, 12:51 AM   #4
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The 70 LT-1 had 11 to 1 comp. ratio, as stated. The 71 LT-1 actually dropped to a 9 to 1 comp. ratio.
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Old 07-26-2012, 12:55 AM   #5
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Maybe a little more info on the leaded fuel thing. Adding lead to fuel was a cheap way to bump octane rating. This turned out to be a bad thing coming out of the tail pipe, so was phased out. At first, there was low lead gas, that still allowed a little octane boost, but after a couple years, that was gone too. Todays higher octane fuel, is done through further refinement, yielding less actual fuel, per given crude oil input. It's now considered a more politically correct thing to limit premium octace to 91, in CA and other states, to save maybe 1% crude over doing 93 octane, allowed in other states. No lead's actually a good thing though, as the engines combustion chambers burn much cleaner now.
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Old 07-26-2012, 08:42 AM   #6
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Quote:
Originally Posted by riverracer au View Post
...where can we find a break down/listing of parts that go in a LT1 engine?...ie: cam specs, pistons used etc....
Try Google. Tons of information has been published on the LT-1s.

Last edited by Easy Mike; 07-26-2012 at 12:40 PM.
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Old 07-26-2012, 11:22 AM   #7
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Quote:
Originally Posted by riverracer au View Post
a mate has just bought a '71 LT1 and we got talking about the engine.
what makes the '70 with 370 hp so special over the '71 with 330hp?
was it the 186 heads, cam, higher compression pistons etc, or what?
or was it the new rating system, but i thought that came in '72?

where can we find a break down/listing of parts that go in a LT1 engine?
ie: cam specs, pistons used etc.

any good engine books on this?

this mite solve/start a bar fight for us...

To lower the compression ratio...
Pistons - flat top versus .100" dome
Heads - 76 cc chambers versus 64 cc chambers
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Old 07-26-2012, 11:32 AM   #8
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1972 was the first year of Net HP ratings, which is the current standard today. Prior to 1972, all the engines were rated at Gross HP which is very misleading since the engine power is measured at the flywheel with no accessories on the engine including water pump, power steering pump, Alternator (not sure about this one), and most importantly an open exhaust (or lack thereof-no OEM exhaust manifolds, exhaust pipes, mufflers etc). The best example of the difference between Gross and net HP ratings on the C3 corvette is the 1971 LT-1 rated at 330 Gross HP an and the 1972 LT-1 which is essentially the same motor as the 71 LT-1 which was rated at 255 Net HP-which is a 75 HP difference between the 2 rating systems on the same engine. For the uninitiated the difference between Gross and Net HP is very confusing and misleading! Hope that helps!
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Old 07-26-2012, 11:41 AM   #9
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Quote:
Originally Posted by jb78L-82 View Post
1972 was the first year of Net HP ratings, which is the current standard today. Prior to 1972, all the engines were rated at Gross HP which is very misleading since the engine power is measured at the flywheel with no accessories on the engine including water pump, power steering pump, Alternator (not sure about this one), and most importantly an open exhaust (or lack thereof-no OEM exhaust manifolds, exhaust pipes, mufflers etc). The best example of the difference between Gross and net HP ratings on the C3 corvette is the 1971 LT-1 rated at 330 Gross HP an and the 1972 LT-1 which is essentially the same motor as the 71 LT-1 which was rated at 255 Net HP-which is a 75 HP difference between the 2 rating systems on the same engine. For the uninitiated the difference between Gross and Net HP is very confusing and misleading! Hope that helps!
No alternator, no air cleaner, no engine driven smog stuff, no nothing.
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Old 07-26-2012, 11:54 AM   #10
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thanks for the in-depth info
makes me want to rebuild my piddly underpowered '72 L48 to match earlier specs
maybe a set of '70 186 heads, new manifold and cam to match to keep the stock look
just thinking/rambling....
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Old 07-26-2012, 03:41 PM   #11
Alan 71
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Hi,
I believe that Chevrolet did publish the SAE net hp ratings for 71 engines, but the info wasn't widely disseminated.
This chart is from the Corvette News edition that had the 71 introduction info in it.
There are a couple of interesting numbers if you look closely.
Regards,
Alan



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Old 07-26-2012, 08:12 PM   #12
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186 heads should add 20HP to a later LT-1 motor, combustion chamber shape much better fro making HP. We used to swap 292 "Turbo" heads back in the 70's, these heads really woke up those low compression smog headed motors. My buddies 70 Z28 360HP Camaro went from 14.40's at the drags to 13.90s with this swap (done by 18 year old kids who didn't know much back then.)
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Old 07-26-2012, 09:02 PM   #13
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Quote:
Originally Posted by Vette5.5 View Post
Maybe a little more info on the leaded fuel thing. Adding lead to fuel was a cheap way to bump octane rating. This turned out to be a bad thing coming out of the tail pipe, so was phased out. At first, there was low lead gas, that still allowed a little octane boost, but after a couple years, that was gone too. Todays higher octane fuel, is done through further refinement, yielding less actual fuel, per given crude oil input. It's now considered a more politically correct thing to limit premium octace to 91, in CA and other states, to save maybe 1% crude over doing 93 octane, allowed in other states. No lead's actually a good thing though, as the engines combustion chambers burn much cleaner now.
Not to hijack the thread, but the lead also lubricated the valves, the reason older engines need hardened valve seats installed.
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Old 07-26-2012, 09:32 PM   #14
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A little more LT-1 trivia....

- Crankshaft = Forged Steel, Tuff Trided Journals (Base engine = Cast)
- Rods = Shot Peened/Magnafluxed (pink) (Base engine = not)
- Pistons = Forged TRW (Base engine = cast)
- Heads = 2.02 I / 1.6 E with Push rod Guides (Base engine = 1.94 I)
- Intake = High rise Aluminum (Winters Foundry) (Base engine = cast Q-Jet)
- Carb = Holley (Base engine = Q-jet)
- Cam = Solid lifter Hi-Perf (Base engine = Hydraulic Lo-Perf)
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