Did GM publish the real "Net HP" in 1972?

[Tom L.]

While doing some work on the vette in this inclemant weather, I was looking through the AIM and came across a page that must have been added for 1972. It listed the engine codes (and HP ratings) that were going to be included in the VIN# for the 1st time. What I found interesting was the ratings of the engines offered in that year. I was under the impression that my '72 LS-5 was 270 HP Net. The AIM lists this rating at 365 HP Gross, 285 Net. It can be found on page M297, sheet F1.

Was this a mistake or was GM altering HP ratings to make insurance companies happy?

[Warren F.]

Re: Did GM publish the real "Net HP" in 1972?

Lynn,

Nope. There were additional timing and carburetor/distributor adjustments from '71 to '72, further lowering the horsepower rating. 270 hp is correct for 1972 versus 285 hp for 1971.
The gross horsepower rating for your '72 LS5 is 350 hp.

[Duke W.]

Re: Did GM publish the real "Net HP" in 1972?

It comes down to what document your're looking at. GM only "advertised" SAE net ratings in 1972 in materials that were easily available to the general public, like sales brochures, but the AIM is not in that category.

In 1971 they advertised gross ratings, but net ratings were included in parentheses - 365 (285) for LS-5, but '72 net ratings were reduced from '71. I don't know why because there were few major configuration changes from '71 to '72 - just fuel and spark map calibrations.

It could be that the SAE net rating procedure was still in work in mid-'70 when '71 ratings had to be finalized, and the final procedure released for the '72 model year caused a slight reduction in ratings. Or it could just be a matter of less aggressive spark advance maps for either emissions or to ward off detonation. The ratings reduction was a few percent.

SAE net air density is about 4.5 percent lower than "gross", which uses standard sea level conditions. The rest of the difference is the effect of exhaust backpressure from the production vehicle exhaust system, front end accessories, and having to run the production fuel and spark calibrations rather than whatever it took in the lab to get big gross numbers.

Duke

[Tom L.]

Re: Did GM publish the real "Net HP" in 1972?

I understand all of the facory and government regulated data. My question is purely troublemaking. What I posted is from the GM AIM. If you have a copy look, it seems weird.

[Mark K.]

Re: Did GM publish the real "Net HP" in 1972?

I understand all of the facory and government regulated data. My question is purely troublemaking. What I posted is from the GM AIM. If you have a copy look, it seems weird.

It doesn't seem wierd to me at all. Considering that the AIM was for a vehicle that was little changed year over year, it's not surprising that GM didn't allocate resources to proofread a document that really didn't need to change - even if certain specs might have changed over time.