1970 lt1 hp
Burning Brakes
Joined: Jan 2009
Posts: 766
Likes: 97
From: Lake Norman, NC
Actually, I think 1972 was when the change from GROSS to NET HP was made. In any event, it was surely the beginning of the steep downward slope to very low performance across the industry.
Team Owner
Joined: May 2001
Posts: 87,330
Likes: 1,589
From: Western NY
Correct. 1971 was the year that the change in compression ratio (lowered, to work on low lead/unleaded fuel) was put in place, with net HP the following year. I could be wrong, but I think the LT-1 went from 370 HP, to 330 HP, then finally to 270HP, before it was dropped from the line up.
Racer
Joined: Sep 2019
Posts: 400
Likes: 207
From: Liberty Bay, WA
Correct. 1971 was the year that the change in compression ratio (lowered, to work on low lead/unleaded fuel) was put in place, with net HP the following year. I could be wrong, but I think the LT-1 went from 370 HP, to 330 HP, then finally to 270HP, before it was dropped from the line up.
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Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
Yep, you're right. Those were depressing times for us motorheads - not only was the actual power level going down (compression ratio decrease) but the way it was advertised (gross vs net) producing lower numbers also.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
HP for 72 was listed at 255 HP. The 71 and 72 LT-1 motors were almost identical. So on paper it looks like the 72 was much less but in reality they were side by side in performance.
Page from the 1972 Corvette brochure that introduced the now-standard security system. (Image courtesy of GM Media.) The base engine, designated ZQ-3, was rated at a conservative 200 brake horsepower. The LT-1 was rated at 255 horsepower and the LS-5 was rated only slightly higher at 270 horsepower.
Page from the 1972 Corvette brochure that introduced the now-standard security system. (Image courtesy of GM Media.) The base engine, designated ZQ-3, was rated at a conservative 200 brake horsepower. The LT-1 was rated at 255 horsepower and the LS-5 was rated only slightly higher at 270 horsepower.
Last edited by Gordonm; Nov 13, 2020 at 02:35 PM.
Le Mans Master
Joined: Dec 2004
Posts: 5,230
Likes: 418
1972 was the year that ONLY Net HP was first reported. In 1971, Chevrolet released BOTH Gross and Net HP. The following were the released power levels:
LS6 - 425HP Gross, 325HP Net
LS5 - 365HP Gross, 270HP Net
LT1 - 330HP Gross, 275HP Net
L48 - 270HP Gross, 210HP Net
Given that the small blocks exhibited a 55-60 HP loss from Gross to Net, that loss was likely in the range for the 70 LT1 as well. The 370 HP 1970 LT1 could have been as high as about 310 HP - HOWEVER - when the 1992 LT1 was released, Chevrolet Engineering called that year's 300HP LT1 the MOST POWERFUL LT1 produced by Chevrolet. This means that the 1970 LT1 likely was in the 290 to 295 range at the flywheel.
LS6 - 425HP Gross, 325HP Net
LS5 - 365HP Gross, 270HP Net
LT1 - 330HP Gross, 275HP Net
L48 - 270HP Gross, 210HP Net
Given that the small blocks exhibited a 55-60 HP loss from Gross to Net, that loss was likely in the range for the 70 LT1 as well. The 370 HP 1970 LT1 could have been as high as about 310 HP - HOWEVER - when the 1992 LT1 was released, Chevrolet Engineering called that year's 300HP LT1 the MOST POWERFUL LT1 produced by Chevrolet. This means that the 1970 LT1 likely was in the 290 to 295 range at the flywheel.
Last edited by bb62; Nov 13, 2020 at 11:12 PM.
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
about 10 years or so ago, Super Chevy did a real world dyno test of many of the famed high hp engines and it was interesting to say the least. I remember as an example, my 79 L-82 didn't fare too badly against the earlier famed engines. I'm pretty sure they did an LT-1, so you might google it and see what you can dig up, if nothing else, for conversation's sake.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,040
Likes: 4,395
From: Marlton NJ
I just found those dyno runs online here:
DZ302, L76. LT1 (70&71), L79, L46, L82
Spoiler alert! All 345-360HP except L82 at 313
http://www.superchevy.com/how-to/eng...k-dyno-testing
http://www.superchevy.com/how-to/pro...-block-testing
http://www.caribbean-joe.net/vette/sbtest-4.htm
DZ302, L76. LT1 (70&71), L79, L46, L82
Spoiler alert! All 345-360HP except L82 at 313
http://www.superchevy.com/how-to/eng...k-dyno-testing
http://www.superchevy.com/how-to/pro...-block-testing
http://www.caribbean-joe.net/vette/sbtest-4.htm
Last edited by leigh1322; Nov 17, 2020 at 01:04 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Yep...like I have said before, the LT-1 simply will not make its advertised number......it can't, the heads are done. Bolt a Dart 180 head to this engine with zero other changes and it will make 425 horsepower.
The low compression 9:1 LT-1 makes almost the same power as the high compression one because the open chamber unshrouds the intake valve.
It is interesting to note that the 65' 375 horse 327 actually did make 375 horses because of the tunnel ram runners in the plenum.
Jebby
The low compression 9:1 LT-1 makes almost the same power as the high compression one because the open chamber unshrouds the intake valve.
It is interesting to note that the 65' 375 horse 327 actually did make 375 horses because of the tunnel ram runners in the plenum.
Jebby
Melting Slicks
Joined: Feb 2017
Posts: 3,232
Likes: 1,232
From: PHX AZ
Team Owner
Joined: May 2001
Posts: 87,330
Likes: 1,589
From: Western NY
Very true, however, pretty much ALL of GM's engines were rated like that, so it's pretty much an "apples to apples" comparison....except where they were playing with the advertised horsepower of the really high output engines, and they wanted to placate the insurance companies.