Hp max near the red line or before it,

[arakis]

I am interested what are the addvantges and disadvantiges in having you maximum hp near the red line, or haveing it 1000 or so rpm before the red line, how big is the torque drop off after the maximum hp is reached, and what is the most important engine spec for achiving highest top speed. off course all this info i am interested in race cars not roud cars, Thanks in addvance

[tristancliffe]

You don't want peak power at the redline, because you can't rev past that, and would therefore be missing out on a lot of potential. A normal shift point is a few hundred rpm after the peak power point.

The torque/power drop off after peak power can be caused and altered by many things - air restrictors (restrictors, valves, tracts, filters), valve bounce...

Highest top speed meaning engine speed or road speed? A high top road speed requires lots of power, little drag, and correct gearing. A high engine speed is usually determined by low reciprocating masses, often brought about by large bores and small strokes, and removing most of the piston skirt...

Such a vast topic really - you need to go to a library first and read up, because it would take every member of this forum several years of typing to be able to teach you from scratch.

[arakis]

no i know al the basics, realy, you might have not uderstood me, I was asking how should the geraing and engine torque curve be set up set up. or wich engine curve would achive greater road speed, the one with max hp at redline or the one that has it a 1000 rpm below.

the point being at witch point will the force pushing the car, Engine trough gearing equal with the force pulling the car ex wind and weight.

to achive gratest road speed, shoud you set up your gearing so that you reach max speed at max power or at red line.

my question is if the gearing setup is for max power = max speed (wind resistance), and your engne has 1000 or so rpm to go to red line, they would be useless in last gear

[Zico]

I think Tristan covered that..

It would depend on Drag vs bhp/torque and gearing, then you have variables of tail or headwind, road gradient etc
Also if you are talking about changing to a higher cam for max power near the redline not only are you losing lowdown torque.. which would result in lower corner exit speed and reduced drivability.. you also waste a slice of the descending power curve in the lower gears as you have shifted before you can use it all.. a big trade-off unless you were only attempting a straightline top speed test.

[tristancliffe]

You want to be AFTER the peak power but BEFORE the redline at the end of the fastest straight.
Arrange torque curves and gearing so that you shift AT the redline - no wasted revs or power!

If you have no worries about engine reliability and rebuilds, get maximum power 500rpm below redline, and set your gearing so that it is drivable out of slow corners. OR optimise your engine for mid-range torque so that you fly out of the corners, but don't have a very high top speed and hope that your corner exit advantage is enough for the longest straights.

The latter is generally better for less experienced drivers.

[arakis]

well never mind, I got all that, thank you for triing to teach me, even if we are not understanding each.

ok I'll refraze, we have two cars one has 997 RSR 1225kg, 430 NM at 7200 rpm, 465HP at 8000 and a red line at 9400, the other ferrari 430 495 NM at 5200, 445 hp at 6750 and red line at 7800, the porsche has 1400 rpm left from the time it reaches max hp to redline, while ferrari 1125kg has 1000, so I am wondering witch engine is better suited for le mans, take into account that porsche has 100kg more and thus the max hp diff should be anuled by how much power it wastes on the extra weight

oh tristancliffe we wrote the post at the sam time so mine refers to what was said before your last post

[Notso Swift]

OK, The maximum possible velocity will be reached at maximum power, with optimised gearing.
The red line is irrelevant to that part of the discussion (provided you are not over it!)

But the fastest lap may not come from this set up.
On a circuit you will rarely make Vmax, even the long straights of le Mans will see you a couple of kph away from what could be theoretically be achieved on a unlimited straight piece of road with perfect gearing. So average power under the curve is still more significant, after all you need to get to speed as fast as possible to string a lap together.
You also need to take into account that you will (inevitably) be in a situation where you have a tow from another vehicle, thereby changing the drag, and thereby changing the required power for a set speed. If you are not able to take advantage of that tow because you have run out of revs you will be at a further disadvantage

Having a greater head room for your power to redline is better, but that doesn’t mean that the Porsche will be faster

BTW the extra weight has nothing to do with the Vmax, that changes how fast it gets there, but Vmax is about drag and power

[arakis]

Originally Posted by Notso Swift

OK, The maximum possible velocity will be reached at maximum power, with optimised gearing.
The red line is irrelevant to that part of the discussion (provided you are not over it!)

But the fastest lap may not come from this set up.
On a circuit you will rarely make Vmax, even the long straights of le Mans will see you a couple of kph away from what could be theoretically be achieved on a unlimited straight piece of road with perfect gearing. So average power under the curve is still more significant, after all you need to get to speed as fast as possible to string a lap together.
You also need to take into account that you will (inevitably) be in a situation where you have a tow from another vehicle, thereby changing the drag, and thereby changing the required power for a set speed. If you are not able to take advantage of that tow because you have run out of revs you will be at a further disadvantage

Having a greater head room for your power to redline is better, but that doesn’t mean that the Porsche will be faster

BTW the extra weight has nothing to do with the Vmax, that changes how fast it gets there, but Vmax is about drag and power

thanks that covers exacly what I wanted to know, and thanks again to everyone for contributung their 2 cents

[AU N EGL]

Torque is measured, HP is caculated. with the SAE standards TQ=HP at 5252 RPMs.

Below 5252 rpms Torque is higher then HP. Above 5252 rpms HP is much higher then TQ.

Maybe helpful if you tell us what your engine is, rpm range and any other important items.

In general your shift point or red line is 1200 to 1500 rpms above peak HP. So when shift, there is a 1500 rpm drop, which puts you right into the sweet spot of peek HP.

[tristancliffe]

Only if you use hp and lb/ft with the same scale (on a graph) is it 5252. Other units have different crossover points.

Just to tweak what Au N Egl said, don't make your engine and gearing combination but you at peak hp after a shift. I know he didn't mean that, but that's how it came across. Shift AFTER peak power so that the revs drop to BEFORE peak power. How much on each side can quite easily be calculated if you know your torque curve.

But I agree about torque being measured and power being calculated. Funny how many people think that it's the other way around.