Diamond

Just got curious this morning and once I get started on something I wont stop so was trying to compare a 530 with 255hp/225tq to a 550 with 360/360.




530 w/ final drive 3.73

1st 4.32-----225ft/lb engine torque * 4.32*3.73 =3625 ft/lbs at wheels
2nd 2.46 ------same calc----2064fl/lbs at wheels





550 final 3.38----Will calculate torque and horsepower at the WHEELS-using its peak torque which is at 3400

1.4.17- 360*4.17*3.38=5074ft/lbs wheel. Now HP-5074*3400/5252-----3284hp at the wheels at 3400rpms (its peak torque rpm)

2.34 --------------2847ft/lbs wheels

Now compare this new info

Engine torque diff is 360/225----1.6 so the 550 has 1.6 times the engine torque at its peak tq of 3750
Wheel torque-------5074/3625---1.37 so at the wheels the 550 has only 1.37 times the torque at 3750


Then you can take weight into account with the 400 pound difference using a 10-1 power to hp ratio-in effective the that 400 pounds less is equive to 40hp when ONLY comparing to this specific car we are compariing which is the 550.

IN Summary-a closer comparisons is
530-295hp with 258 ft/pounds

550 360hp with 360ft pounds

Still clearly the 550 is a weigh faster car but not AS MUCH faster as they make it appear. That helps sales and marketing and just the fact the average consumer cant care or understand the impacts of weight and gearing on all this.

One thing, tire radius is in the equation but since they have equal tire radiuss I left that out completely.

Now again this is a relative comparison to these two cars for comparison if you put one car against the other. I am not saying the 530 has 295hp but am saying in this case its 400 les pounds gives it the same advantage as 40hp would. So the 550 weighs 400 pounds more but has 40 extra hp. Or you can lose 400 pounds from a car and you will nee 40 less hp to move the car as quickly.

These numbers are at each cars peak torque-that is the only number I had available from the bmw website-if you had a dyno graph you could calculate it at each rpm and figure wayyyyyy more info out. There is much more to this-just a thought when you are looking at cars-atleast consider two thinsg

1.Final drive and gear ratios and overall tire diamater
2. weight differences

Huge differences to the wheels with these factors-and its at the wheels it counts

Richard in NC

I think your basic assumptions are correct. At peak torque, given the ratios, weights, etc there doesn't seem to be much difference of rear wheel torque. However, during acceleration, an engine doesn't stay at the one RPM. During a max acceleration run, an engine varies across the higher RPMs. Comparing the HP peak is more relavent. But you do have to map out the rear wheel torque available across the RPM range the cars stay at in each gear.

Another factor is this. A car with a lower rear end (higher numeric) ratio will not be able to stay in gear as long. Therefore it will shift into the next gear and loose its advantage sooner. Lastly, the time spent in 1st or even 2nd is minimal. If you'd ever run the cars side by side, you'd see that the 530i is close to the 550i at the end of 1st but by the end of 2nd, the 550i is pulling away, and really shows its HP advantage by 3rd. Same story with the 550i vs M5. The 550i has similar torque and less weight, but has a ratio disadvantage and a huge HP disadvantage. The 550i can almost hang with the M5 thru 1st and 2nd but looses out big time beyond that.

Diamond

Oh I was not saying the 530 was even close in torque-it would get blown away off the line-not my point at all and agreed this is a snapshot of an entire gear cycle.

Just some food for thought when you read magazines comparing cars-some will say 400 hp yet will get beat by 340 hp car or whatever.

The one that comes to mind is the new caddy cts with its 300hp posted slower number than any other cars it was up against with equal or less hp.


I am just saying there is more to comparisons than one thinks.

My biggest point is lighter cars with higher gear ratios need less hp-and the numbers sometimes are decieving slow. People knocked the 330i e90 for being way behind in hp/tq-and quite frankly it is but nonetheless it is not as far behind as people would think taking gearing, weight etc.

I dunno I am a nerd-I like this kind of stuf!

v_therussian

I like how you think

sdg1871

Correct. The 550 only has 24 lbs-ft less of torque than the M5. And the 550 has more of the torque available down low. I have gone up against a stock M5 from a light on a number of occasions. My 550 gets out in front of the M5 for about the first 100-200 feet. Then the M5 passes it (as horsepower become the key measure once you are rolling) and walks away from my 550 like it were standing still.

Brit_in_NJ

Everyone know you drive like a grandma Scott!

sdg1871

I do. I do.

v_therussian

I wish all grandmas drove like Scott... on the second thought

sdg1871

Oh come on Vlad. I am sure that your friends who I drove on Gate Hill Road last Saturday in the wet would tell you that I drove like a grandma there...