Actual power of 60's and 70's GROSS engines?

[Mikej89]

Hey guys,

Have you noticed a lot of widespread ignorance about the difference between GROSS and NET ratings? If you aren't aware, the big power GROSS engines from the 60s and early 70s were rated in ideal climate controlled conditions, with no air filter, no accessories, and just test headers. The NET engines were rated just like they go into the car.

That's why a 1969 station wagon with the standard non-performance 350 2bbl and single exhaust is rated at 250hp. Rated with the '72-on net system I'd estimate it at 180hp or 15hp better than the same engine in '72 due to slightly better flow. The performance engines were closer to the GROSS rating cause they actually had dual exhaust, free flowing filters, etc. I'd be willing to guess a '67 Corvette 327-300hp would be around 245hp and the 327-350hp probably around 315hp. So basically the way I see it, the higher you get in performance the closer the gross ratings are. It really gets confusing too because some engines actually were underrated in the GROSS system for insurance. For example, the 396 L78 was rated at 375hp but actually did make about 400 net hp. Those are purely the top performance engines of the day though.

What do you guys think? Those are just my estimates...

 

[rustyroger]

You are right. in the early'70s America came into line with the rest of the world and started quoting net (or "real life") figures.

Roger.

 

[Blake442]

Bottom line is you can't trust any of the advertised hp numbers from back then.
Manufacturers were lying thru their teeth to dupe other brands and most importantly, the insurance companies.

Ever notice how most cars followed the 10 hp/100 lbs rule?
The best example is the Boss 429 Mustang.
Rated at 330 hp in a 3300 lb car.
In reality that was a 520+ hp motor...

 

[Mike P]

The factory HP ratings were (are) really primarily an advertising tool and in real life the engines on the assembly going into the car were a far cry from the engine that had actually been set on the DYNO to verify/certify the HP ratings.

The dyno/certified engines were hand built blueprinted engines. REAL blueprinting ( a term often abused by many people especially when they are selling an engine) is very labor intensive and costly and involves bringing every critical engine spec to the dimensions specified in the original design blueprint. Blocks are line honed, square decked, debured etc. Crankshafts are also debured, checked for straightness, indexed and polished. Rods and pistons are hand selected and matched. Heads are reworked to the blueprint spec, usually with special attention given to cleaning up ports, the cam is indexed and degreed. Bearing clearances are matched and on and on. Things like carburetors and distributors got the same attention. Basically these engines got/get the same attention as a Top Fuel or NASCAR engine. Once they were on the DYNO if the targeted numbers were not met the engine was fine tuned until it did.

The engines coming down the assembly line were a far cry from the DYNO mules. The little 283 I’m currently building is typical of the engines that actually went in the cars was. On the block I started with, one deck was .012 taller than the other and ranged from .003 to .005 difference end to end. The heads advertised as 60cc chambers actually measure between 62cc and 64cc after they were milled .015 and they also had a pretty fair amount of casting flash left in the ports. While the engine was advertised as 8:1 compression in real life it was probably closer to 7.5:1. With the lower compression, one size fits all tune-up/jetting and the uneven cylinder pressures it was a FAR cry from the advertised HP. That was actually pretty typical and it doesn’t mean it was a bad engine, it was still within factory specs to get thru QC and it did run over 100,000 miles.

By the late 60s insurance companies were really starting to look at HP ratings due to the amount of accidents and payouts they had to make on high HP cars. Downgrading the advertised HP ratings on the high performance engines was really simple. As Horse Power is a number based on RPM and Torque, all the factory had to do was take their targeted HP number from the RPM it occurred at. In other words if factory wanted to claim the engine made 400HP and that occurred at 4500 RPM that’s what they claimed, regardless of the fact that the engine was capable of making 450HP at 6000 RPM. It wasn’t really a lie, just stretching the way the number were reported.

 

[pontiacgp]

you can measure torque, you have to "calculate" hp

 

[vanrah]

I was 23 the summer of 69

Good Morning Guys; Can we turn back the clock? When I returned from the first 1/2 of my military (4 yrs) days I had ordered a 1968 L-78 (375 HP) Camaro. The L-78 was rated @ 425 HP in the 65 Vette and the only difference was the transistorized distributor. That car ran 13.99 @ 101 MPH bone stock. With headers & distributor work it ran in the mid 12's, and a best of 12.39 with slicks & open headers. I had been putting down 12.7 & 12.8's on the street so very few other cars could get by me in the day. Because the Camaro was lighter than a Chevelle & most everything else it was one of the fastest street cars of the day from the factory. I street raced everything that would race me and wasn't beat very often. If you had a hydraulic cammed car (GTO's, most Ford's & Mopar's) you would not have been worth wasting my gas. As most hydraulic cammed cars were out breath at somewhere under 6000 RPM & the L-78 would easily rev to 7000. I was in Spokane the last 2 years of service & one of the fastest cars before I arrived was a 67 Mustang with a FE 427 side oiler & by the time I met the guy (LS D Nunn was his name) he had traded for a 400 HP 427 vette and he beat me on the street, not at the track. One of the first guys I challenged had a 67 Fairlane 427 FE (one of 60?) but he would NOT race me. The following year (1969) with a new owner I put him down at the drag strip, but not because I made more power. More experienced driver, similar to me getting put down be the 400 HP vette. But the quickest car in Spokane on the street that summer was a 67 Chevelle with a L-72 He ran 12.11 best & easily could run a 12.5-6 on the street. The guy with the 400 HP vette traded for a Boss 429 (69 solid lifters) and he was very disappointed with stock (factory) performance and I easily beat him, but! And one of my favorite memories is with a friend driving my Camaro and a (67?) Plymouth hemi. He pulled up beside us, I told my buddy to bring the engine up to 3000 & drop the clutch and go for 7000, we pulled the Plymouth by a car just in first gear, race over. I remember 2 guys with Z-28's, both had pulled their new engines and sent them to the engine shop to be balanced & clearanced properly, bigger cams (solid of course) and neither one of them could get by my headered L-78. They ran high 12's & that wasn't enough! If you wanted to go fast with OE stuff back then you had better have purchased a SOLID lifter car & most if not all of them were very under rated (L-88's). And the factories did not advertise them (other than Z-28's & Shelby's) so the total number of cars made with those engines were small (big value these days). Anyway thanks guys for triggering my memory button. Bob Jr.

 

[Mikej89]

Bottom line is you can't trust any of the advertised hp numbers from back then.
Manufacturers were lying thru their teeth to dupe other brands and most importantly, the insurance companies.

Ever notice how most cars followed the 10 hp/100 lbs rule?
The best example is the Boss 429 Mustang.
Rated at 330 hp in a 3300 lb car.
In reality that was a 520+ hp motor...

The Boss 429 was rated at 375hp, but probably really had about 450hp stock like the 426 Hemi and similar engines. Hi-revving race engine but I'd take a 428 Cobra-Jet any day on the street.

 

[Mikej89]

Re: I was 23 the summer of 69

Good Morning Guys; Can we turn back the clock? When I returned from the first 1/2 of my military (4 yrs) days I had ordered a 1968 L-78 (375 HP) Camaro. The L-78 was rated @ 425 HP in the 65 Vette and the only difference was the transistorized distributor. That car ran 13.99 @ 101 MPH bone stock. With headers & distributor work it ran in the mid 12's, and a best of 12.39 with slicks & open headers. I had been putting down 12.7 & 12.8's on the street so very few other cars could get by me in the day. Because the Camaro was lighter than a Chevelle & most everything else it was one of the fastest street cars of the day from the factory. I street raced everything that would race me and wasn't beat very often. If you had a hydraulic cammed car (GTO's, most Ford's & Mopar's) you would not have been worth wasting my gas. As most hydraulic cammed cars were out breath at somewhere under 6000 RPM & the L-78 would easily rev to 7000. I was in Spokane the last 2 years of service & one of the fastest cars before I arrived was a 67 Mustang with a FE 427 side oiler & by the time I met the guy (LS D Nunn was his name) he had traded for a 400 HP 427 vette and he beat me on the street, not at the track. One of the first guys I challenged had a 67 Fairlane 427 FE (one of 60?) but he would NOT race me. The following year (1969) with a new owner I put him down at the drag strip, but not because I made more power. More experienced driver, similar to me getting put down be the 400 HP vette. But the quickest car in Spokane on the street that summer was a 67 Chevelle with a L-72 He ran 12.11 best & easily could run a 12.5-6 on the street. The guy with the 400 HP vette traded for a Boss 429 (69 solid lifters) and he was very disappointed with stock (factory) performance and I easily beat him, but! And one of my favorite memories is with a friend driving my Camaro and a (67?) Plymouth hemi. He pulled up beside us, I told my buddy to bring the engine up to 3000 & drop the clutch and go for 7000, we pulled the Plymouth by a car just in first gear, race over. I remember 2 guys with Z-28's, both had pulled their new engines and sent them to the engine shop to be balanced & clearanced properly, bigger cams (solid of course) and neither one of them could get by my headered L-78. They ran high 12's & that wasn't enough! If you wanted to go fast with OE stuff back then you had better have purchased a SOLID lifter car & most if not all of them were very under rated (L-88's). And the factories did not advertise them (other than Z-28's & Shelby's) so the total number of cars made with those engines were small (big value these days). Anyway thanks guys for triggering my memory button. Bob Jr.

Great story, thanks for sharing! The only hydraulic cam cars I'd imagine that would give you a run for your $$$ would be the bigger cube stuff like GS 455, 440-6 Mopars, etc. Beating a '67 Hemi car is awesome though.

 

[Mikej89]

We're sorta getting into the "big fish stories" talking about all the underrated cars from the day LOL... The bottom line is, a lot of the muscle cars made significantly less power than they were rated at. I was just reading an article where they put a '69 Chevelle 396-325hp auto on a chassis dyno and it put down 205rwhp/284rwtq after carb tuning (stock except for Edelbrock intake and Flowmaster mufflers). So roughly 263hp and 364tq at the crank if you use a 22% loss with the old automatic. Really those aren't bad numbers at all and make more sense with the level of performance. It's just that people have trouble letting go off the big factory numbers and want to tell all their buddies it's got 325hp LOL.

 

[Clone TIE Pilot]

It is still sort of like that today. For example with HP and MPG ratings the manufacturers use the results of different tests. No engine will get it's best MPG while pumping out it's max HP. Also there is far less government oversight over testing and ratings now than back then, these days they just take the manufacturer's word that the ratings are accurate which allows the manufacturers to lie within reason. The EU uses a very different test system that gives less real world results than the US standards of testing. Which is why European cars have a better MPG rating than US cars, it is just diffent testing standards. At any rate, car ratings are always a rough estimate.