When is 585 horsepower, really 585 h.p.?

well hp is just a measure of tq at certain rpm

so i higher reving engine will make more hp

i learned this after getting into diesels yeah there done at a 120 mph cause there at redline but until they get there they are monsters. if you could make a diesel rev to 6k it would make 800 hp . run a really high speed too. buicks are pretty much the same way.

tq is the sheer power of an engine. hp is just how well it put to use what tq it has.

 

Hi NHB,

It's great when you can make a massive amount of torque at 3000 r.p.m.. Doesn't a diesel, also, make good torque at low r.p.m.?

Talk later,

Nando.

 

Doesn't a diesel, also, make good torque at low r.p.m.?

there are few diesels that rev over 4000rpm, so yes, by definition, diesels make good low end torque.

 

600ft lbs and tach out around 3200 rpm in stock form

 

HuH? HP and TQ are completely different. And as far as "so i higher reving engine will make more hp", how do you explain the import crowd? Those hondas buzz at rediculous rpms, and lets not even talk about the wankel rotary engine. All of that spinning and they're not really going anywhere.
Also, there are some diesel trucks out there that go over 200 mph! Its alllllll about gearing.

 

HuH? HP and TQ are completely different.

no, your horsepower # is derived from your torque # depending on what rpm your engine is turning.

http://en.wikipedia.org/wiki/Horsepower#Relationship_with_torque

everyone normally shows the formula like this:
HP = ( TQ * rpm ) / 5252

but think of it this way:
HP = TQ * ( rpm / 5252 ) <<< if you look at it this way it becomes obvious that you're multipling your TQ rating by an "rpm factor". and the formulas are equivalent, the multiply and divide functions can be freely interchanged as long as they stay on the correct side of the equals sign.

at 5252rpm your TQ and HP will always be equal. 5252 / 5252 = 1

at 10504 your HP will be twice whatever your TQ is at that rpm. 10504 / 5252 = 2

at 2626rpm your HP will be half of your TQ rating. 2626 / 5252 = .5

so, you can increase HP by raising torque at a given rpm OR you can raise HP by increasing rpm while maintaining your torque curve.

this is why industrial diesel engines have such silly TQ ratings ( often north of 1000lbft ) while only being rated 300-400 HP. they don't turn any rpm and are normally wound out at 3000rpm or lower.

this is also how a 1000cc motorcycle can have 150HP while not having any torque. they're spinning up close to 10,000rpm. you only need ~80lbft when you're turning that fast.

now you understand why Nailheads aren't preferred on the drag strip. they make mountainous amounts of torque but it's extremely difficult to make them turn more than 5000rpm. when you're out there running against a BBC, Dodge or BBF that can turn 8000rpm without breaking a sweat, you're just giving up too much head room.

it's also easier to deal with a low torque, high rpm motor on the strip. less torque means easier to hook up while big rpm means you can run wider gearing and you'll be in each gear longer.

however, rpm is hell on durability. so, for street use, you want a Nail or diesel or something similiar with a lot of gears in your transmission. for street racing, torque will also normally destroy everybody else light to light. it's once the HP motors have a chance to stretch their legs out that you get into trouble.

NOTE:
you may object and say that you've just compared your TQ and HP rating on your engine and they don't calculate out in that formula. the answer is simple. your peak torque rating always occurs at a lower rpm than your peak horsepower rating. because of the multiplicative factor of rpm it's impossible for the HP peak to be at a lower rpm than your TQ peak and the only practical way to put both peaks on exactly the same rotations per minute would be to have a rev limiter on the motor at the TQ peak.

 

Actually a Cummins makes it's peak torque of well over 600 ft lbs at under 2,000 RPMS.

 

another reason that you see hondas making 200 hp and diesels making the same. the honda revs 8000 the diesel revs 3000

 

well depends on which cummins on that note man

 

Hi all,

Thanks for all the informative input. Applied Physics certainly at work in this thread! Besides the 500 c.i. Cadillac, how did Buick engineers derive so much torque from the 455, more than any other comparative big-block of that time? The engine is an oversquare design with a 4.3125" bore and 3.90" stroke. Was it the complete package : heads, intake, exhaust, that made this engine so much more efficient at low revs.? Or, what else stands out as the biggest contibutor to Buick 455's legendary stump-pulling torque?

Talk later,

Nando.

 

The engine is an oversquare design with a 4.3125" bore and 3.90" stroke.

it's unlikely that being oversquare has anything at all to do with the low rpm torque.

the Buick 340 and 350 small blocks were also notorious torque monsters ( for their size ) and they are badly undersquare. the 231ci and 3.8L v6's ( which were based on the SBB 300ci v8 ) are also well respected for torque vs displacement. those last three are quite a bit closer to the normally desired square / oversquare design though.

obviously runner cross section has a lot to do with it but i think the short con rods also help. it gets more angle on the crank closer to TDC where cylinder pressures are at their highest.



Besides the 500 c.i. Cadillac, how did Buick engineers derive so much torque from the 455

Hot Rod Mag or somebody made a comment within the last year that below 2500rpm the Buick actually makes more torque than the Caddy. now that's impressive.

 

Well I know my diesel with over 400,000 miles still has torque and a lot of it. Have the 96 dodge 3500 dually. Just spent over $2000 on tranny after I twisted mainshaft apart from spinning the tires in 2nd and slipping it in 3rd real fast and halfway thru 3rd there was a loud blam. And that was it. 2nd and 3rd gear was gone. And done some damage to one of the other gears. Oh did I mention it was stock. Not.

 

Quote from Bob: BBC, Dodge or BBF that can turn 8000rpm without breaking a sweat, you're just giving up too much head room.

Not quite....

 

The 1970 Buick GS Stage 1 455 made 510 ft lbs of torque at really low RPMs. I'm unsure of the RPM but I think it was around 2200 or something ridiculous like that. The 1970 LS6 454s were rated at 500 ft lbs. The Buick was rated around 390 hp while the 454 was rated at 450. The Buick GS Stage 1 would have stomped an LS6 Chevelle. Ok maybe not "stomped" but it would have been the victor.

 

Stage 1 was rated at 360 hp at 4600 and 510 ft/lbs at 2800

LS6 454 was 450 at 5600 and 490 ft/lbs at 3000

Cad 500 was 400 at 4400 and 550 ft/lbs at 3000

69 Hemi was 425 at 5000 and 490 ft/lbs at 4000

On the street with marginal ties of the day traction usually determined who won. So the excess torque usually hurt rather than helped so the hemi with the torque up higher had a bit of an advantage.

In the early 80s I used to race against stock LS6s and hemis (at the track of course) and WITH traction (with experimental MH drag radials) I usually won. But on the top end they were about to drive around me in my 70 Stage 1 GSX.

Bruce
BQUICK
JAGUICK

 

they say that manufactures under rated hp for insurance purposes, is this correct? and if so has anyone put bone stockers on the dyno? and got actual hp?

 

they say that manufactures under rated hp for insurance purposes, is this correct?

depends on which years you're talking about. some years, some makes or manufacturers were trying to play up how much power they had for marketing, some years or models they were trying to sneak things under the insurance adjusters noses so they were playing the numbers down.

i think i've seen it bandied about on here that a 455 Stage 1 rebuilt to "off the show room floor" conditions was showing something like 375hp gross. so Buick likely wasn't cheating the numbers much.

technically, any rating from before 1972 would be considered "exaggerated" today as they were using Gross HP numbers which gives you an extra 25% over the net ratings that you see now.

 

which even now once you figure in the rwhp vs flywheel there exaggerated

 

I think that under rated hp is a bunch of BS. I hate it when I hear that "Chevelle owners will tell you that the ls6 really put out close to 600 hp" Stupid **** like that. Like they can tell how much power it's making by driving it? Come on

Maybe they were under rated, why didn't anyone ever dyno them?

And above I was referring to the 2006 or 2007 5.9 Cummins motors. The peak torque is under 2 grand at 610 ft lbs.

 

Hi all,

I began this thread because, like all of you, it grinds me to think some laptop racers who are viewing, and comparing technical specs. between 2 cars, would say "an ol' Buick aint got a hope in hell of taking a new Shelby Mustang". I think nowadays, advertised h.p. figures sell cars, and some of these manufacturers' figures are bogus. You know, 425 h.p. SRTs, which might crack into the 13s. Any other examples, domesic or import, you can name?

Take care,

Nando.