Aussie66Fastback

most of us talk engine hp and tq. Dynos talk "rear wheel".

what's the rule of thumb to convert the dyno figs back to engine numbers? is it about 15% higher for manual trans?

Daze

15-20

Aussie66Fastback

so when they quote power figs for new cars, how do they measure the engine numbers?
and how does it compare to the 1960's hp numbers? what would a 306hp shelby read in todays numbers? i'm confused

67mustang302

Manufacturers measure at the crankshaft. And a 306hp Shelby if it were rated by SAE hp standards today, would prolly be like 260ish. The 426 Hemi from back in the day is a good example of power ratings, at one point Chrysler changed hp rating standards from gross to net to get more accurate, and the EXACT same engine that had been rated at 425hp became 375hp. It "lost" 50hp just by changing to a more realistic rating standard. The modern SAE Certified is a VERY precise standard, and requires a very particular set of testing done while beeing overseen by an official SAE representative.

BAY68_347

15-20 for manual?
Any guesstimates for a C4?
I know there are a lot of varying factors but just a rough estimate?

Starfury

Also realize that the Hemi motor was rated at 5000 rpm. It was never said that this was the maximum hp, just that it produced 425hp at 5000 rpm In reality, it was probably closer to 500 maximum gross hp. Similar underrating was performed on the Ford 428CJ

iirc, C4's chew up something like 25-35% but make up for some ofit in torque multiplication. C6's use something like 45% (ugh).

69thunder

There was a muscle car engine shootout done on I think on a show on the speed channel where they tested engines from back in the day (stock for the most part) on a dyno and they did all the legendary big blocks like chev 454, ford 427, chrysler 426 hemi and a few others and by far the hemi was the max HP king. I think it was somewhere around 600+ if I remember right. I wish I could remember the name of the show. The main thing was NONE of the engines reguardles of make was anywhere near what was advertised HP they were all much more.

BAY68_347

Thanks for the great info, fellas.

Art Brock

"There was a muscle car engine shootout done on I think on a show on the speed channel where they tested engines from back in the day "

I saw that too. That was a good show & I remember being shocked at the big block HP numbers & I think the motors were stock or very close to stock.
Seems a couple of motors (Hemi & 427 Ford) were about double the advertised HP. That show made me want a Big Block real bad!!

67mustang302

I've never seen a truely honest test of muscle era engines. Dynos can be very decieving, either unintentionally or intentionally. The fact of the matter is that 600hp isn't all that easy to coax out of a big block these days(it can be done, but requires decent parts and costs decent money), and it sure ain't gonna happen with a stock flat tappet cam and low voltage ignition, maybe not even with stock heads. The few times I've seen actual STOCK(I mean truely stock engine) muscle cars run, their trap speeds didn't show anything close to the kinda of horsepower they supposedly had.

The problem is that you're not likely to find an actual stock engine any more. The ones that claim to be stock are often rebuilt using much more modern parts, and because the intake and heads are the same someone says it's stock. The fact of the matter is from the outside there's no way you could tell the difference between a stock 427 with a flat tappet cam, and a wild *** solid rollered 427 stroker with worked stock heads and intake. Too many people like to play the "Oh, yeah, it's stock" game, when the fact is it's anything but stock.