How does GM measure horsepower?

[deerefan]

When I bought my new silverado, i was told it had 315hp/335tq. The truck feels alot stronger than this. I drove a Titan that had similar hp numbers and it felt the same acceleration wise. Does GM measure these numbers at the rear wheels or flywheel? This trucks acceleration acts more like 350hp, which has me curious.

 

[sweettractors]

I am betting the GM 327 CID engines from the mid sixties with 300 hp will run circles around the 350-400 hp rated cars and trucks of today. Ken Sweet

 

[Diamondpilot]

When I bought my new silverado, i was told it had 315hp/335tq. The truck feels alot stronger than this. I drove a Titan that had similar hp numbers and it felt the same acceleration wise. Does GM measure these numbers at the rear wheels or flywheel? This trucks acceleration acts more like 350hp, which has me curious.

I have often wondered the same. By the way, the Titan has way more TQ (385 ft lb) but that is a mute point. As our buddy Builder has implied its more to do with the drive line and where the power is made. Keeping the truck in the power band is what is important then getting that to the ground.

Just like you I came out of another truck with similar numbers, 2007 F-150 with 300 HP and 365 ft lb TQ and the Titan feels much much stronger, especially on the bottom end where it counts.

Chris

 

[ace10]

Gearing.

 

[deerefan]

I am betting the GM 327 CID engines from the mid sixties with 300 hp will run circles around the 350-400 hp rated cars and trucks of today. Ken Sweet

It is funny you say that. I actually have a 300hp 327 in a 66 Nova and another in a 1970 Chevelle. My buddy had reg cab silverado 2wd with the 5.3, a tune and exhaust. The Nova can't touch him and the Chevelle gets him in the quarter, but barely. Both 327s were built to 300hp specs. Now, you want to see something funny? My dad's 70 350/350hp Vette hanles the new 400hp Camaro with ease, about 3-4 car lengths. Go figure. The main reason I feel the silverado gets me is not only hp. The throttle response and quick shifts are seamless as compared to both muscle cars. I think it is more technology making him quicker than raw power.

 

[JasG]

When I bought my new silverado, i was told it had 315hp/335tq. The truck feels alot stronger than this. I drove a Titan that had similar hp numbers and it felt the same acceleration wise. Does GM measure these numbers at the rear wheels or flywheel? This trucks acceleration acts more like 350hp, which has me curious.

There is a lot more to acceleration than just HP. Weight of the vehicle, gearing, both tranny and rear end, shift points etc. Unless you know the trucks are set up similar it is very hard to make an apples to apples test based just on acceleration or feel. I've driven 2 trucks that 1 had a 3.08 rear end, the other a 3.55, yet everthing other than that was the same, the 3.55 would smoke the 3.08, yet the 3.08 had better MPG. Now the MFG's are playing with the trans a lot more, of course they have more gears now to play with.

Every MFG likes to play with numbers to make sound like they have bigger engine.

At least thats my opinion.

 

[Heywood Jannockitov]

One of those TV programs such as "How do they do it" or Modern Marvels" or something showed a GM engine plant where they were testing the output on an engine with an SAE approved inspector present monitoring the test. It was just an engine on a test rig attached to a dynamometer, so I would guess the HP is measured with ancillary devices attached such as alternators, power steering pumps etc, but no driveline.

How a truck "feels" acceleration-wise is pretty subjective too, I would imagine. There are many sensory inputs to the brain that help enhance the impression of "delta V". Trans gearing, rear end, power to weight ratio, traction, exhaust tune (how pleasing it sounds!), suspension tune (how much the front end lifts when you put your foot into it, suppression of NVH.

All these things can make one truck "Feel" faster than another even if it really isn't.

 

[jonyyuma]

There is a lot more to acceleration than just HP. Weight of the vehicle, gearing, both tranny and rear end, shift points etc. Unless you know the trucks are set up similar it is very hard to make an apples to apples test based just on acceleration or feel. I've driven 2 trucks that 1 had a 3.08 rear end, the other a 3.55, yet everthing other than that was the same, the 3.55 would smoke the 3.08, yet the 3.08 had better MPG. Now the MFG's are playing with the trans a lot more, of course they have more gears now to play with.

Every MFG likes to play with numbers to make sound like they have bigger engine.

At least thats my opinion.

The old rule still stands. "It is how the Horsepower is applied to the ground". The ratings are set to confuse the consumer.

 

[sweettractors]

It is funny you say that. I actually have a 300hp 327 in a 66 Nova and another in a 1970 Chevelle. My buddy had reg cab silverado 2wd with the 5.3, a tune and exhaust. The Nova can't touch him and the Chevelle gets him in the quarter, but barely. Both 327s were built to 300hp specs. Now, you want to see something funny? My dad's 70 350/350hp Vette hanles the new 400hp Camaro with ease, about 3-4 car lengths. Go figure. The main reason I feel the silverado gets me is not only hp. The throttle response and quick shifts are seamless as compared to both muscle cars. I think it is more technology making him quicker than raw power.

How much HP did the tune add to the 5.3 Silverado pickup? Ken Sweet

 

[deerefan]

How much HP did the tune add to the 5.3 Silverado pickup? Ken Sweet

He picked up 22 hp with the addition of tuner and exhaust. I believe the tuner is from hypertech. The truck is an 05

 

[ChevyHDGert]

They advertise at less than they are capable of. This way, when another manufacturer ups them by 5 HP, then can advertise 10 more HP the following model year without having to tweak them.

After a few years, they tweak the computer or adjust the cam to gain more HP.

It's all a marketing gimmick to say who has the most HP.

 

[Diamondpilot]

Another issue is visual cues. Riding in my dads Corvette doing 80mph seems a lot faster than riding in my F-350 doing the same. I guess its being close to the ground. Same thing with a airplane. I fly at about 525mph at 38,000' and it seems like we are barley moving but when coming in to land at about 140mph it seems like we are screaming.

Chris

 

[Storm56]

When I bought my new silverado, i was told it had 315hp/335tq. The truck feels alot stronger than this. I drove a Titan that had similar hp numbers and it felt the same acceleration wise. Does GM measure these numbers at the rear wheels or flywheel? This trucks acceleration acts more like 350hp, which has me curious.

In direct response to your question, it is my understanding that all auto/truck manufacturers MUST use the same standards. Horsepower is measured at the flywheel with all accessories hooked up, not at the rear wheels.

By contrast all boat motors are measured at the propeller.

 

[deerefan]

In direct response to your question, it is my understanding that all auto/truck manufacturers MUST use the same standards. Horsepower is measured at the flywheel with all accessories hooked up, not at the rear wheels.

By contrast all boat motors are measured at the propeller.

That is what I was looking for. I figured that was where it was measured. I wonder if they test each and every engine??

 

[roamerr]

People talk about the muscle cars of the good ole days. The funny thing is both a new Honda Accord V6 and Toyota Camry V6 are faster 0 to 60 than most of the muscle cars. A 6 sec 0 to 60 was very rare years ago.

As for trucks the old carburated 350's, 454's, etc have nothing on the newer 5.7 to 6.2L V8's. The new vehicles really have great power. The old one's had plenty of grunt but were slow and ran out of breath quick...

 

[zzvyb6]

I worked in that area for quite a while at the GM Proving Grounds in Milford. The horsepower rating is the peak power at the max allowed rpm. When you draw a power or torque curve, the 'feel' you like is the rate of change of the horsepower (first derivative). Its the slope of the power curve that gets you the launch. In most cases in GM vehicles, power must be limited by computer management because of transmission or ring gear durability issues. When those issues are resolved, the fuel is often opened up if Marketting can swallow or buy into the CAFE loss. If they can't, then Engineering may investigate how to get into a lower Weight Class by use of aluminum structures or reduced content.

The EPA also has a hand in the power delivery because emissions is THE major player in power design. The motor's first 20 seconds of warmup during the EPA test cycle defines the performance allowed, because that's when the engine is dirtiest. Fuel economy goals have to be met too. In fact, extra raw fuel must be dumped into the motor to heat the converter ASAP to get the emissions requirements met. That extra fuel is expensed as a fuel economy penalty for the powertrain rating printed on the sticker.

I spent many hours in meetings and EPA test cells at the Emissions Lab watching this all go down.

 

[jonyyuma]

I worked in that area for quite a while at the GM Proving Grounds in Milford. The horsepower rating is the peak power at the max allowed rpm. When you draw a power or torque curve, the 'feel' you like is the rate of change of the horsepower (first derivative). Its the slope of the power curve that gets you the launch. In most cases in GM vehicles, power must be limited by computer management because of transmission or ring gear durability issues. When those issues are resolved, the fuel is often opened up if Marketting can swallow or buy into the CAFE loss. If they can't, then Engineering may investigate how to get into a lower Weight Class by use of aluminum structures or reduced content.

The EPA also has a hand in the power delivery because emissions is THE major player in power design. The motor's first 20 seconds of warmup during the EPA test cycle defines the performance allowed, because that's when the engine is dirtiest. Fuel economy goals have to be met too. In fact, extra raw fuel must be dumped into the motor to heat the converter ASAP to get the emissions requirements met. That extra fuel is expensed as a fuel economy penalty for the powertrain rating printed on the sticker.

I spent many hours in meetings and EPA test cells at the Emissions Lab watching this all go down.

Interesting facts from the Development dept.Personally I believe GM dropped the ball several years ago. I had been a totally loyal buyer for years. The product failed to perform. Now we are supposed to invest again at three times the past prices for a pick-up to drive to work.? Regardless of the HP ratings?? Jy.

 

[sld]

Nothing personal to Mr. Sweets, but 300 hp from the 60's can't hold a candle to todays 300 hp. The older ones were gross hp and todays are net hp. The rating method changed around 1972.

Now, some of those 60's engines rated at "300" were probably more as I think they were way conservative back then for insurance reasons.

Also, look how much vehicles weigh these days. They just keep getting heavier and heavier. A 300 hp truck from the 60's would probably need 450 hp in todays truck to feel the same.

 

[om21braz]

An another hp comparison. A couple of friends had a difference of opinion - one having a 1969 Chevelle SS 396 slightly built, the other with a 2006 Pontiac GTO with the 6.0L. Each thought he had the faster car - especially the guy with the 69 Chevelle as he initiated the challenge. From 20mph roll for approx. 1/8 mile. The GTO had him from the start and the lead grew the further they went. Pretty strong cars out there today.

 

[Diamondpilot]

An another hp comparison. A couple of friends had a difference of opinion - one having a 1969 Chevelle SS 396 slightly built, the other with a 2006 Pontiac GTO with the 6.0L. Each thought he had the faster car - especially the guy with the 69 Chevelle as he initiated the challenge. From 20mph roll for approx. 1/8 mile. The GTO had him from the start and the lead grew the further they went. Pretty strong cars out there today.

My neighbor had a 351W in a early 70's Mustang. He did quite a bit of stuff to it to do 13sec 1/4 miles. His wife's 2005 Lincoln Aviator will beat it stock.

Chris