72 Net Horsepower vs. Gross HP
04-26-2016, 02:47 PM
#1
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Thread Starter
72 Net Horsepower vs. Gross HP
My understanding is that before 1972 horsepower was measured on a blueprinted engine without accessories such as alternator, A/C, pb, etc... (Gross Horsepower). Then in 72 the engines were rated with all accessories and the exhaust system causing hp to be rated substantially lower (Net Horsepower). I have the C3 350-cid/200hp and was wondering if anyone knows what the blue-printed hp on this engine would be? Or am I totally misinformed???
Last edited by GlenJack; 04-26-2016 at 02:50 PM.
04-26-2016, 02:56 PM
#2
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Hi GJ,
I don't think the test engines were 'blueprinted', but WERE tested without 'accessories'.
I believe the 72 base engine is much the same as the 71 base engine that was rated at 270 horsepower.
The 71-72 engines were similar to the 350/300 base engine for 1970.
I believe the change that started the downward slide was the decrease in compression ratio from 1970 (10.25:1) to 1971 (8.5:1).
Regards,
Alan
I don't think the test engines were 'blueprinted', but WERE tested without 'accessories'.
I believe the 72 base engine is much the same as the 71 base engine that was rated at 270 horsepower.
The 71-72 engines were similar to the 350/300 base engine for 1970.
I believe the change that started the downward slide was the decrease in compression ratio from 1970 (10.25:1) to 1971 (8.5:1).
Regards,
Alan
Last edited by Alan 71; 04-26-2016 at 06:31 PM.
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GlenJack (04-26-2016)
04-26-2016, 05:54 PM
#3
Instructor
Thread Starter
Hi GJ,
I don't think the test engines were 'blueprinted' but were tested without accessories.
I believe the 72 base engine is much the same as the 71 base engine that was rated at 270 horsepower.
The 71-72 engines were similar to the 350/300 base engine for 1970.
I believe the change that started the downward slide was the decrease in compression ratio from 1970 (10.25:1) to 1971 (8.5:1).
Regards,
Alan
I don't think the test engines were 'blueprinted' but were tested without accessories.
I believe the 72 base engine is much the same as the 71 base engine that was rated at 270 horsepower.
The 71-72 engines were similar to the 350/300 base engine for 1970.
I believe the change that started the downward slide was the decrease in compression ratio from 1970 (10.25:1) to 1971 (8.5:1).
Regards,
Alan
04-26-2016, 07:27 PM
#4
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Alan 71 hit the nail on the head.
Here's a 71 brochure that shows both Gross & SAE Net.
http://www.lov2xlr8.no/brochures/che...t/bilder/2.jpg
Additionally GM revised (retarded) the advance curve timing in the distributor each year as well (70, 71, 72). That's why you also see a small loss in HP between the 71 vs 72 cars. Example 71 LT-1 275hp NET, 72 LT-1 255hp NET.
Here's a 71 brochure that shows both Gross & SAE Net.
http://www.lov2xlr8.no/brochures/che...t/bilder/2.jpg
Additionally GM revised (retarded) the advance curve timing in the distributor each year as well (70, 71, 72). That's why you also see a small loss in HP between the 71 vs 72 cars. Example 71 LT-1 275hp NET, 72 LT-1 255hp NET.
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GlenJack (04-26-2016)
04-26-2016, 07:35 PM
#5
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Thread Starter
Alan 71 hit the nail on the head.
Here's a 71 brochure that shows both Gross & SAE Net.
http://www.lov2xlr8.no/brochures/che...t/bilder/2.jpg
Additionally GM revised (retarded) the advance curve timing in the distributor each year as well (70, 71, 72). That's why you also see a small loss in HP between the 71 vs 72 cars. Example 71 LT-1 275hp NET, 72 LT-1 255hp NET.
Here's a 71 brochure that shows both Gross & SAE Net.
http://www.lov2xlr8.no/brochures/che...t/bilder/2.jpg
Additionally GM revised (retarded) the advance curve timing in the distributor each year as well (70, 71, 72). That's why you also see a small loss in HP between the 71 vs 72 cars. Example 71 LT-1 275hp NET, 72 LT-1 255hp NET.
But I appreciate the brochure!!
Last edited by GlenJack; 04-26-2016 at 07:41 PM.
04-27-2016, 07:56 AM
#6
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2020 C3 of the Year Finalist - Modified
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Emmissions and fuel economy. That was when both were getting alot of attention from the gov. First gas crisis was about then
Last edited by Rescue Rogers; 04-27-2016 at 07:56 AM.
04-27-2016, 08:28 AM
#7
Instructor
Revi, thank you for that link to the 71 brochure.
So, after seeing that the base engine for 1971 produced 270 Gross HP and 210 Net HP, it is not all that different from say a 1981 base engine that produced 190 Net HP.
Sure, that is 10% or so but not nearly as much difference as most posts on CF have lead me to believe that the earlier cars have so much more power making the earlier cars ridiculously faster.
Now with a BB, that’s a different story.
So, after seeing that the base engine for 1971 produced 270 Gross HP and 210 Net HP, it is not all that different from say a 1981 base engine that produced 190 Net HP.
Sure, that is 10% or so but not nearly as much difference as most posts on CF have lead me to believe that the earlier cars have so much more power making the earlier cars ridiculously faster.
Now with a BB, that’s a different story.