Where's the HP???
Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,297
Likes: 0
From: Spring TX
Where's the HP???
In what year did GM detune the C3 and take the guts (HP) out? I know the late 70's & early 80's were detuned but when did it start, 75?
Also, is there any way (cheap way) to get the HP back? What did GM do to these lovely cars that made them so "eco-friendly"?
Thanks
Shane
Also, is there any way (cheap way) to get the HP back? What did GM do to these lovely cars that made them so "eco-friendly"?
Thanks
Shane
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
It was the 70's version of global warming, a combination of a supposed oil shortage and environmentalists doing their thing turned them into smog mobiles with lots of HP eating modifications starting in 72 I believe 
You can reverse the gross indecency, look at my sig and pull out your wallet
You can reverse the gross indecency, look at my sig and pull out your wallet
Last edited by MotorHead; Aug 11, 2009 at 11:20 AM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Compression ratios were dropped in '71 to pave the way for low and no-lead fuel with their lower octane ratings and to address NOX emissions. The rating standard changed in '72 from gross to net measurements. When you put these two factors together you have a 1970 350/300 that, in 1972, is now a 350/200 (loss of 30hp from the compression drop in '71 and the change in how the engines were rated in '72. The power didn't actually change in '72, just the way it was measured) There really wasn't much detuning following '71 and the power differences were relatively minor. The addition of EGR in '73, cat converters in '75, and some minor ignition and camshaft updates is the bulk of the detuning.
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
Other than the Blue Flame 6 cylinder engines........., the 1975 Corvette (base engine) was the lowest HP rated Corvette ever (190HP ??). Ask me how I know this wonderful little fact................
Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,297
Likes: 0
From: Spring TX
Thanks for the quick responses!
So if I'm planning on a driver for my wife there isn't much diff between a 71 & a 82 based on HP, or power in general? She doesn't need a 454, probably a 350. It'll be a weekend warrior/sunny day driver. I think she likes the early 80's models, lots of curves and a few more creature comforts but with all the Eco HP reducing crap of the late 70's early 80's I was worried about buying her a car with no get up and go. She likes the power of my C6 but wants the look of the C3, and I have no desire to drop a crate engine in for her.
Are there things you can remove or add to increase the power some?
So if I'm planning on a driver for my wife there isn't much diff between a 71 & a 82 based on HP, or power in general? She doesn't need a 454, probably a 350. It'll be a weekend warrior/sunny day driver. I think she likes the early 80's models, lots of curves and a few more creature comforts but with all the Eco HP reducing crap of the late 70's early 80's I was worried about buying her a car with no get up and go. She likes the power of my C6 but wants the look of the C3, and I have no desire to drop a crate engine in for her.
Are there things you can remove or add to increase the power some?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,297
Likes: 0
From: Spring TX
With these changes can you add a cam, change the ignition, exhaust, etc. and add power, decent power, to say an 82?
When I say cheap I'm talking a few thousand or less.
When I say cheap I'm talking a few thousand or less.
Compression ratios were dropped in '71 to pave the way for low and no-lead fuel with their lower octane ratings and to address NOX emissions. The rating standard changed in '72 from gross to net measurements. When you put these two factors together you have a 1970 350/300 that, in 1972, is now a 350/200 (loss of 30hp from the compression drop in '71 and the change in how the engines were rated in '72. The power didn't actually change in '72, just the way it was measured) There really wasn't much detuning following '71 and the power differences were relatively minor. The addition of EGR in '73, cat converters in '75, and some minor ignition and camshaft updates is the bulk of the detuning.
Burning Brakes
Joined: Jul 2006
Posts: 830
Likes: 1
In what year did GM detune the C3 and take the guts (HP) out? I know the late 70's & early 80's were detuned but when did it start, 75?
Also, is there any way (cheap way) to get the HP back? What did GM do to these lovely cars that made them so "eco-friendly"?
Thanks
Shane
Also, is there any way (cheap way) to get the HP back? What did GM do to these lovely cars that made them so "eco-friendly"?
Thanks
Shane
The detuning actually happened EOY 1970. By 1975 the Vette was by many accounts only around 150-160HP. But good news, by 1979 the HP ratings actually started increasing again to peak out the C3 era with the 1980 L82 (HP ratings are 230 or 235, depending on the publication).
Engine code: ZBC denotes the L82 350-cid 235-hp V-8 9.0:1 compression engine. In 1980 only the automatic transmission was available. They all (even the CA car) had a standard four-barrel carburetor.
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
You're right......... 165HP. It was awhile ago and my mind must have inflated the number to make me feel better. I stand corrected. Wow, 165HP............. I think the L82 was 210HP...... but I'm not sure.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
a step is to undo the things GM did.
IE, up the C/R and advance the timing.
I see you are in Tex. Lucky you. They are less strict on mods.
Here in Ca, if it cam with fac specs, you better conform.
I am limited by a base timing of 6deg and can't get any facts
on how much C/R I can run and still pass NOX.
IE, up the C/R and advance the timing.
I see you are in Tex. Lucky you. They are less strict on mods.
Here in Ca, if it cam with fac specs, you better conform.
I am limited by a base timing of 6deg and can't get any facts
on how much C/R I can run and still pass NOX.
Thread Starter
Drifting
Joined: Dec 2007
Posts: 1,297
Likes: 0
From: Spring TX
If you drop a crate engine in one of these (est. $3k) how much does it cost to have it all installed? If it costs $5k to do the whole thing and get it up and running I may be better off looking for an early model C3 with a good strong engine, driver... not a show car by any means.
