geokr1

Can someone explain (in real simple terms) why horsepower and torque aren't exactly related. For example, I was on the E60 engine info page and see that the 550 has 360 hp and 360 ft-lbs torque. The M5 has 500 hp and 383 ft-lbs torque. It seem odd that with 140 more hp that only 23 more ft-lbs of torque are produced in this huge V10 engine. The specs for other engines are all over the map. You would think torque and hp would vary more or less directly. And Part 2 of the question - isn't torque really the final measure of how much power you get to the wheels anyway? Appreciate any answer or references to other posts. Thanks.

swajames

They're directly related. HP, torque and RPM are inextricably linked: Horsepower = (Torque x Engine speed)/5,252

The difference between the M5 and 550 is in RPM. The M5 revs much higher than the 550 and it produces its peak HP at very high RPM.

geokr1

OK - then is that extra hp lost to producing the higher rpm and not available as torque to the wheels? The light still hasn't come on.....

swajames

Nope, torque is a product of HP and RPM.

Take 2 engines producing 300hp. If one of them produces its peak 300hp at relatively low RPM such as 4000rpm, it will always produce more torque than a gas engine producing the same peak 300hp at say 6500 rpm. A diesel engine may produce prodigious torque because it's able to produce its peak power at a relatively low RPM, and an F1 car revving to 19,000 RPM only produces around 275 lb/ft of torque - but both are calculated according to the same formulas, and higher RPM cars will always tend to output lower torque relative to their peak HP.

Here's a link to one of many decent explanations you'll find on the web:

http://www.procivic.com/pages-horsep...que/index.html

At the end, the author provides a good explanation of why the extra RPM means that the M5 will blow away the 550 despite both having pretty close peak torque numbers. Hope this answers your question!

geokr1

Excelent answer! I'll check it out and when driving my 550 tomorrow I'll not try to outrun any M5s I meet thinking that my superior driving skills will make up for a little less torque. Well, maybe I will just for the hell of it.

swajames

Those superior driving skills count for a lot - they're easily as good as a few extra horses!

geokr1

Why did you switch to the Porsche?

swajames

My 550 was a lemon

It ended up being bought back, and other than the Audi S6 there really weren't any other sedans that I liked or wanted so I just thought I'd try something completely different. No regrets, the 997 is incredible, but I do sometimes miss my E60. The blend of comfort/sport/luxury in the E60 is hard to beat in its class.

doug_999

swajames has given you some great technical answers, here are some guidelines (meaning there are exceptions but in general.......)

The size of the motor has a lot to do with the torque. The M5's engine and 550s engine are almost the same size and therefore produce similar numbers. As pointed out, the M5s engine is tuned for a lot of HP and that comes at a higher RPM (remember that is going to affect where the max torque occurs)- and guess what, as pointed out, the 550 makes more torque down low (and yes, feels faster 0-30 for the most part).

Diesels have decent torque, especially when coupled with turbos. The new 335d has something like 425+ lb-ft of torque - that car will push you back in your seat something fierce.

Now before you go off racing M5s with your superior torque curve, go figure out a formula one engine's torque (they are something like 2.4L) and produce about 750hp at 19,000 RPM. The number will surprise you

Dr Dave

my 530d now its been remapped only has 303 bhp, but it has 502 lb/ft of torque...more than an M5