Why are people obsessed with HP numbers on a TDI?

[savannah996]

Since this type of engine was never designed for peak, or any other type of horsepower, why is the first thing someone posts in this forum HP numbers?
A broad TQ curve is where its at!

PS; If its all about numbers, I hate to break it to y'all but the 2.0 direct injection gas turbo's are in the 400+'s. Dont get me wrong I think my TDI is great and I like all VW's

 

[shizzler]

Why? Because HP dominates acceleration. But you are right that a broad torque curve is where its at. In fact, if you can hold a flat 400 lbf-ft of torque through red-line, then your doing great, because it means your HP will be awesome at high rpms. But 400 lbf-ft of torque at 1500rpm does not accelerate your vehicle at the same rate that 400 lbf-ft at 4500rpm accelerates it.

Obviously we all know that gasoline turbo motors can push 2x or even 3x our horsepower with ease, and as a result, are much faster. But they cant achieve that simultaneously with 40+ mpg. The modern, robustly designed diesel engine holds a distinct advantage in the amount of power headroom (up to 200% !!) with zero penalty in fuel economy. My car is optimistically 75% over stock power with better mileage than ever. woot.

 

[dvst8r]

Since this type of engine was never designed for peak, or any other type of horsepower, why is the first thing someone posts in this forum HP numbers?
A broad TQ curve is where its at!

PS; If its all about numbers, I hate to break it to y'all but the 2.0 direct injection gas turbo's are in the 400+'s. Dont get me wrong I think my TDI is great and I like all VW's

Same reason we spend 100's of thousands of dollars trying to go a few extra feet with a tractor. Because we can.

 

[ndamico]

or a pull truck

our dmax truck engines were meant for 240whp but we have them around a 1000 now because its fun and as dvst8r so eloquently put it "Because we can. "

Same reason we spend 100's of thousands of dollars trying to go a few extra feet with a tractor. Because we can.

 

[devonutopia]

A broad TQ curve is where its at!

But I think a broad HP curve is equally as important. Always been told "maximise the area under the curves" and I'm sure we all appreciate a nice pair of curves don't we? (talking about dyno plots of course.....)

 

[05_new_jetta]

In lighter vehicles hp rules I would think because their isn't any weight, I would think torque only helps down low but hp steps in where tq stops. Anyone want to clarify what I am trying to say?

 

[streeker02]

In lighter vehicles hp rules I would think because their isn't any weight, I would think torque only helps down low but hp steps in where tq stops. Anyone want to clarify what I am trying to say?

I have no idea what you're trying to say.

Torque only helps down low? What does that mean???

HP is the number assigned to correlate the torque value of an engine at a given RPM. HP=TQxRPM/5252.

HP steps in where tq stops? What does that mean??? An engine that maintains high torque at high RPM with have higher horsepower than an engine that makes high torque at lower RPM.

 

[bluesmoker]

Since this type of engine was never designed for peak, or any other type of horsepower, why is the first thing someone posts in this forum HP numbers?
A broad TQ curve is where its at!

PS; If its all about numbers, I hate to break it to y'all but the 2.0 direct injection gas turbo's are in the 400+'s. Dont get me wrong I think my TDI is great and I like all VW's

simple , because making more hp is fun

 

[Variant TDI]

HP steps in where tq stops?

That's exactly right. Torqxs are only good at low RPMS, and going up hills. Then they get tired, and the Horsepowers take over.

That's why a VW will beat any honda... but only if it's from a standing start, and the race is up a hill.

 

[Dakta]

Don't go there. Love it when someone brings their diesel to me, say the raced a six cylinder gasser then proudly explain it's down to having more torque 'than him'.

In my life I've tried to explain this away but the question will not die.

It's a shame because it's easy enough. RPM multiplies torque, so if you don't have much torque, get a few more revs behind ya for the same BHP, and vice versa. As far as the wheel tread is concerned after all the egaring etc etc the end result is more or less the same.

 

[shizzler]

Do you know the relationship between torque and hp?

Of course I do. I'm a mechanical engineer and work in an engine dyno lab.

Not sure what my quoted statement has anything to do with that, though. All I said was that comparable displacement turbo gasoline motors can easily reach 2x or 3x our best effort HP #s. Do you disagree?

 

[ccvdubs]

torque is the big guy moving a ton of rocks in one trip, hp is a small guy moving a ton of rocks in many quick trips both in the same amount of time

 

[UFO]

torque is the big guy moving a ton of rocks in one trip, hp is a small guy moving a ton of rocks in many quick trips both in the same amount of time

No, hp is moving the same load of rocks faster.

 

[turbobooster]

If the two guys are moving the rock piles in the same amount of time, they have the same horsepower. The little guy needs to take more trips, or revs, because he doesn't have the torque of the bigger guy. But their hp numbers are the same.

 

[ccvdubs]

No, hp is moving the same load of rocks faster.

but many trips , instead of one

 

[Dakta]

but many trips , instead of one

yep, if you've a lot of revs and not a lot of torque

Ideas right, I just think the translation got a bit fuzzy

 

[ccvdubs]

Ideas right, I just think the translation got a bit fuzzy [/quote]
very possible

 

[heuiinj]

Torque vs Horsepower

I think it's best explained with a picture of a crankshaft and a horse. The horse being the piston pulling on the crank instead of pushing but the force applied is the same.

When the horse is pulling on the crankshaft at a constant speed the closer the horse gets to center the faster the crankshaft turns. The horse doesn't travel as far per revolution so we have a Shorter Stroke which creates faster acceleration. Horsepower

The further the horse gets from the center at a constant speed the longer he has to travel per revolution but he has more leverage. Longer Stroke. The crankshaft turns slower but the horse has more leverage which creates more twisting force. Torque

The distance of the connecting rod journal from the center of the crankshaft determines the horsepower and torque characteristics of the motor. Of course piston speed and travel increases as you increase stroke distance and limits come into play.

 

[Gearhead51]

Power = work/time

Torque is the force applied. RPM is how fast that torque is spinning an object, or a way to measure how "fast" the work is occurring.

10,000lb ft of torque trying to twist an immovable bar = 0HP. The force was there, but nothing happened.

A dumptruck moving a ton of rocks in an hour did the same work as a thousand lollipop kids from the wizard of oz moving a ton of rocks in an hour. The work/time was the same.

 

[Stealth TDI]

Horsepower AND Torque:

Sure, there's a mileage penalty. But I sometimes think I'd rather have a 28-mpg GTI that can do THAT ^ than a 40-mpg CRD that can't... especially now that delicate emissions are in question.

 

[ChippedNotBroken]

Since this type of engine was never designed for peak, or any other type of horsepower, why is the first thing someone posts in this forum HP numbers?
A broad TQ curve is where its at!

PS; If its all about numbers, I hate to break it to y'all but the 2.0 direct injection gas turbo's are in the 400+'s. Dont get me wrong I think my TDI is great and I like all VW's

This is one of those questions where the answer is:

'Cause it's there.

 

[SBAtdijetta]

Horsepower AND Torque:

Sure, there's a mileage penalty. But I sometimes think I'd rather have a 28-mpg GTI that can do THAT ^ than a 40-mpg CRD that can't... especially now that delicate emissions are in question.

I beg of you stop posting that Dyno graph!

My 2.0T is very jealous, and wants a bigger turbine.

 

[SBAtdijetta]

Since this type of engine was never designed for peak, or any other type of horsepower, why is the first thing someone posts in this forum HP numbers?
A broad TQ curve is where its at!

PS; If its all about numbers, I hate to break it to y'all but the 2.0 direct injection gas turbo's are in the 400+'s. Dont get me wrong I think my TDI is great and I like all VW's

Why what should we use to talk about power... KW or PS.

This is the "Power" enhancement section after all. HP = Power (work done).

Torque is only the potential to do work, with out revolutions applied (RPM) it is nothing.

 

[perrone]

I think it's best explained with a picture of a crankshaft and a horse. The horse being the piston pulling on the crank instead of pushing but the force applied is the same.

When the horse is pulling on the crankshaft at a constant speed the closer the horse gets to center the faster the crankshaft turns. The horse doesn't travel as far per revolution so we have a Shorter Stroke which creates faster acceleration. Horsepower

The further the horse gets from the center at a constant speed the longer he has to travel per revolution but he has more leverage. Longer Stroke. The crankshaft turns slower but the horse has more leverage which creates more twisting force. Torque

The distance of the connecting rod journal from the center of the crankshaft determines the horsepower and torque characteristics of the motor. Of course piston speed and travel increases as you increase stroke distance and limits come into play.

I think this explains it pretty well.

 

[Stealth TDI]

HAHA!

I beg of you stop posting that Dyno graph!
My 2.0T is very jealous, and wants a bigger turbine.

I hear ya! That kit is $$$! But APR's Stage II (chip/intake/exhaust) is not bad at all and still yields 276-hp and 314-lb/ft! I'll send further non-TDI remarks via PM.

Scott

 

[jhota]

"Horsepower sells cars, torque wins races." - Carroll Shelby

 

[LowlyOilBurner]

I don't know. I daily drive my 181.4whp tdi, and it's fun to drive. I'm building my 1994 Audi UrS4 with a 42R, revving to 10k, all the bells and go fast whistles, it'll prolly suck. The power band is gonna be from about 5500 to 10k. Sure, it will make damn near 800awhp, for 4500revs. My tdi makes power through out the whole rpm range, it's fun. At the same time, I've learned my lesson, if you want really big numbers and turbos, you gotta do it with a gasser.

 

[gborgh]

Unless you can fit a really big diesel in a small car. Check out the red mustang in diesel power mag this month.

 

[ducesrwld]

if you want really big numbers and turbos, you gotta do it with a gasser.

I beg to differ with a lot of the opinions mentioned here. Sure a tdi will never hang with the modified gassers but that doesn't mean diesels can't hang in general. the fact that a tdi can perform with mods like they do are impressive considering what they were originally built to do....get top of the line gas mileage. Now consider a duramax with just efi live and exhaust that can pump out 500 whp and 1000 ft-lbs of torque....seeing these trucks smoke some pretty quick sports cars is just awesome. i'll take a diesel over a gasser anyday.

 

[Diesel_Benz]

At the same time, I've learned my lesson, if you want really big numbers and turbos, you gotta do it with a gasser.

The big issue is you VW guys have only 1.9/2.0L to work with.