HP vs Torque Discussion (No Jokes, No bantering. Just facts and reality)
02-16-2009, 04:55 AM
#346
Rennlist Member
Thread Starter
Thanks for posting that. It makes the point that this entire discussion depends on the shape of the HP curve.
I always wondered why those Pesky BMWs were so strong. amazing little creatures. all out of a stock 3.2 euro motor with only some ECU mods. (maybe cams i think too)
By the way this V8 still pays to redline altough the HP does fall off up top but its pretty characteristic of many V8 dyno runs in shape. the M3 is very unique and Ill admit its usually the exception to the rule that VR was leaning on.
MK
I always wondered why those Pesky BMWs were so strong. amazing little creatures. all out of a stock 3.2 euro motor with only some ECU mods. (maybe cams i think too)
By the way this V8 still pays to redline altough the HP does fall off up top but its pretty characteristic of many V8 dyno runs in shape. the M3 is very unique and Ill admit its usually the exception to the rule that VR was leaning on.
MK
Well, since the V8 does not have a HP curve that rises all the way to redline, it calls for a different approach.*
As before, assume that both cars are geared such that gearing is irrelevant. Rather than each car redlining in each gear at the same speed, we have to find the optimum shift point, because it's not necessarily redline. Maybe it is, but let's check. I'm arbitrarily going to pick a 6K shift point and see where that lands us. Doing the math, we would drop to 4,380 RPM when shifting -- far down the curve from peak. OK, based on that I think we can go to redline -- 6,200 RPM -- and shifting will drop us to 4,526.
The L6 redlines at 7,600 RPM, shifting to a gear that is the assumed .73 away gives us 5,548 RPM in the next gear.
Based on the above, I would derive the ideal RPM ranges for each as follows:
L6: 5,548 - 7,600 RPM
V8: 4,526 - 6,200 RPM
Using the upper HP curve for the L6, I then find the point on the HP curve where we will be after shifting to the next higher gear:
L6: 5,548 RPM, ~245 HP
V8: 4,526 RPM, ~255 HP
It seems the L6 is dropping off a touch further than the V8. Let's see what happens if we shift 500 or 1,000 RPM early(for whatever reason).
500 RPM Early:
L6: 5,048 RPM, ~230 HP
V8: 4,026 RPM, ~220 HP
1,000 RPM Early:
L6: 4,548 RPM, ~200 HP
V8: 3,526 RPM, ~180 HP
So in this case there is a slight edge to the L6 engine in that it seems to have a somewhat broader powerband.
* When a horsepower curve falls off like this the ideal RPM range may not include redline; the goal is to fit the usable RPM range to the highest possible points on either side of the peak of the horsepower curve.
As before, assume that both cars are geared such that gearing is irrelevant. Rather than each car redlining in each gear at the same speed, we have to find the optimum shift point, because it's not necessarily redline. Maybe it is, but let's check. I'm arbitrarily going to pick a 6K shift point and see where that lands us. Doing the math, we would drop to 4,380 RPM when shifting -- far down the curve from peak. OK, based on that I think we can go to redline -- 6,200 RPM -- and shifting will drop us to 4,526.
The L6 redlines at 7,600 RPM, shifting to a gear that is the assumed .73 away gives us 5,548 RPM in the next gear.
Based on the above, I would derive the ideal RPM ranges for each as follows:
L6: 5,548 - 7,600 RPM
V8: 4,526 - 6,200 RPM
Using the upper HP curve for the L6, I then find the point on the HP curve where we will be after shifting to the next higher gear:
L6: 5,548 RPM, ~245 HP
V8: 4,526 RPM, ~255 HP
It seems the L6 is dropping off a touch further than the V8. Let's see what happens if we shift 500 or 1,000 RPM early(for whatever reason).
500 RPM Early:
L6: 5,048 RPM, ~230 HP
V8: 4,026 RPM, ~220 HP
1,000 RPM Early:
L6: 4,548 RPM, ~200 HP
V8: 3,526 RPM, ~180 HP
So in this case there is a slight edge to the L6 engine in that it seems to have a somewhat broader powerband.
* When a horsepower curve falls off like this the ideal RPM range may not include redline; the goal is to fit the usable RPM range to the highest possible points on either side of the peak of the horsepower curve.
02-16-2009, 02:27 PM
#347
Rennlist Member
It was easy to take that out of context, as a blanket statement. I see what you meant now.
02-16-2009, 02:32 PM
#348
Rennlist Member
Thread Starter
Its interesting that the desired torque curve is actually a downward slope, not flat not rising if you are comparing two equal hp engines. Lot's of this stuff is counter intuitive.
Mk
Mk
