Sir Tripower

Hi over there!

I guess, wether anybody here has ever dyno-tested a stock 427/400 (L68) to find out, what real (net) horsepower it has, according to the nowadays test-specifications.

Are there any informations available?

Curious greets from good ol' Germany

Gerrit

Faster Rat

L36 and L68 were the same engine, except for carburetion. The factory just upped the rating from 390hp to 400hp to justify the added cost and subsequent price increase, but the 4 barrel Qjet on the L36 had more than enough cfm for the engine.

Are you asking for chassis dyno (net) results of an original, untouched engine? Or are you looking for engine dyno (gross) results for a rebuilt (no longer stock) engine? If the former, I can't help you. If the latter, here is a graph of the captured engine dyno data after my recent L36 rebuild using .030 over forged pistons and a Comp Cams #268H hydraulic flat tappet cam. These engines are low rpm torque monsters, not producers of high rpm horsepower. Your results may vary!

Sir Tripower

I'm asking for the (net) horsepower, measured at the rear wheel - as it is done on modern cars. So I'll have an comparison to actual cars horsepower.

Of course I know, that they stated 400 hp for the '69 L68 in those days. But I know as well, that it was measured "gros" with "engine only". On the other hand I could find out, that official horsepower rates were "downsized" because of insurance requirements.

I guess, wether anyone of you has had his (unmodified and stock) car on a dyno-tester and can report, what "really" horsepower the car has.

Yours
Gerrit

mashinter

The 1972 LS5 was rated 270 SAE net
The 1971 LS5 was rated 365 SAE gross
Best guess on L68: 400 X 270 / 365 = 296 SAE net

There's another formula for calculating SAE net from 1/4 mile trap speed. Car and Driver tested a '68 L68 and I calculate 294 SAE net from that test.

SAE net is at the clutch, not at the rear wheels. Reduce above by 15-20% for rear wheels. It depends on the transmission.

Faster Rat

Your car might have produced 400hp at the flywheel when new, without any accessories and open exhaust, maybe not. The chances of it producing the same power 42 years later, without having been rebuilt, are very slim. Assuming stock exhaust and engine-driven accessories, the drivetrain losses vary depending on whether your car is manual or automatic. I have heard chassis dyno RWHP could be 20 to 30% less than engine dyno flywheel HP. For discussion purposes, say 280 to 320 RWHP. Hopefully somebody can provide you with their actual chassis dyno results, for what it is worth. Good luck.......

Mike Ward

Modern cars still quote flywheel HP, not rear wheel.

MrJlr

MotorHead

I once had a chart that showed every C3 motor and what it produced in GROSS, NET and RWHP ( don't ask me how the RWHP figure were there but the ordinary engine dyno was invented in the 30's I believe so the big car companies might have had drive wheel dynos ) but someone, somehow had the GROSS and NET HP and RWHP figures for the pre SAE Net HP or GROSS HP cars ( 68- 71 ) and:

After the switchover to SAE NET HP the chart still showed both GROSS and NET HP and RWHP for the new cars up to '79 or '80. Methinks it was a dyno cell operator who put the chart / spreadsheet together. It was really quite amazing to look at. Of course I can't find it anymore I believe it was lost when one of my older PC's crashed.

Anyway I do remember the losses from to be huge from GROSS to RWHP especially in the 454 big blocks. One 454 Vette early 70's had over 30% loss and if I am not mistaken it was closer to 35%

Faster Rat

Gerrit
You do realize that all dynomometers only measure torque, don't you? The horsepower figures are only calculated as a function of the torque. That is why all torque versus horspower curves cross at something like 5252 rpm. Very interesting.

I realize many new high performance cars like to quote their RWHP at some astronomical rpm. Fine. Tell me what their torque is down low and I will tell you which car slams you back in the seat the hardest when you stomp on the pedal. That 600 RWHP is just fine if you want to drive the car at 200 mph. Oh, I forgot...you have the autobahn over there. Sorry.

elle88

Not sure but i think all modern cars have BHP ratings , without accesories, ence the big numbers.

from wikipedia:

Brake horsepower
Brake horsepower (bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc. Brake refers to a device which was used to load an engine and hold it at a desired RPM. During testing, the output torque and rotational speed were measured to determine the brake horsepower. Horsepower was originally measured and calculated by use of the indicator (a James Watt invention of the late 18th century), and later by means of a De Prony brake connected to the engine's output shaft. More recently, an engine dynamometer is used instead of a De Prony brake. The output delivered to the driving wheels is less than that obtainable at the engine's crankshaft.

SAE gross power
Prior to the 1972 model year, American automakers rated and advertised their engines in brake horsepower (bhp), frequently referred to as SAE gross horsepower, because it was measured in accord with the protocols defined in SAE standards J245 and J1995. As with other brake horsepower test protocols, SAE gross hp was measured using a stock test engine, generally running with few belt-driven accessories and sometimes fitted with long tube (test headers) in lieu of the OEM exhaust manifolds. The atmospheric correction standards for barometric pressure, humidity and temperature for testing were relatively idealistic.

[edit] SAE net power
In the United States, the term bhp fell into disuse in 1971-72, as automakers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349. Like SAE gross and other brake horsepower protocols, SAE Net hp is measured at the engine's crankshaft, and so does not account for transmission losses. However, the SAE net power testing protocol calls for standard production-type belt-driven accessories, air cleaner, emission controls, exhaust system, and other power-consuming accessories. This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold.

Shark Racer

elle88- incorrect. Modern cars use the SAE net power ratings as you quoted.

SAE net is a good measurement for comparing engines.

Dyno numbers are only particularly useful for the owner/operator/builder of the vehicle to track how a modification has affected power output. It can also be useful for determining shift points and other powerband related actions.

MotorHead

It also makes the same 600HP in first, second and third at that RPM

Sir Tripower

On the Autobahn I normally drive on cruising-speed with about 80-90 mph. Sometimes, when traffic allows, I speed up to 110 for a while or make a sprint up to 145 mph (while tach shows 4500 rpm). What a pitty for you over there, to be limited to 70 mph with such excellent highway-routes ....

Back to my question:
Indeed I don't know exactly, how modern cars hp is measured exactly. But I want to know, how much hp my '69 Vette has in comparsion to a modern car (for example a 300-hp rated BMW). So I'm interested in an actual hp-test of a stock 427/400, which give me the possibility to compare.

That's it!

Greets
Gerrit

Mike Ward

I doubt that anyone will be able to give you that answer you seek with anything other than an educated guess or a calculation. Net HP is measured on a dyno with all stock engine accessories and complete exhaust system installed. Don't know of anybody that does that.

The answer from mashinter above is probably pretty accurate.