Which Is Faster - 600hp@6200 or 600hp@7100

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Daniel Jones
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Re: Which Is Faster

Post by Daniel Jones » Tue Sep 19, 2017 2:37 pm

> That somewhat makes sense to me, but by that logic, the more you rpm a car the faster it should go.

Only if the area under the HP curve also increases with increased RPM. While power is a direct function of RPM, it's also a function of torque:

HP = (TQ*2.0*PI*RPM)/33000.0

where:

TQ = torque in ft-lbs
HP = power in horsepower
RPM = engine speed in revolutions per minute
PI = the mathematical constant PI (approximately 3.141592654)
Note: 33000 = conversion factor (550 ft-lbs/sec * 60 sec/min)

At some point, the torque curve will drop off faster than the RPM increases so the resultant power will drop off. At that point, acceleration will also begin dropping off. As far as the amount of RPM that can be traded for rear wheel torque, it's the HP that is important, not the RPM itself. Rear wheel torque accelerates the vehicle and is the product of the engine torque and the gearing provided by the transmission, rear end, and tires. Horsepower is the measure of how much rear wheel torque you can potentially gain from gearing.

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Re: Which Is Faster

Post by cgarb » Tue Sep 19, 2017 2:46 pm

77cruiser wrote:
cgarb wrote:That somewhat makes sense to me, but by that logic, the more you rpm a car the faster it should go. My car I shift at 6800, I had also tried shifting at 7500 and it ran almost the exact same slip. One hundreth faster, but that could have been a weather change. Why would more RPM not net me a gain in that instance then?
Where does it make peak HP at?
Not being a smart ass, but my car has yet to print me a Dyno sheet...lol. I have never had the engine across a Dyno I just know what makes it faster or not. I think my intake is holding my car back a little. I took off a ported 300-2 Holley and put on a Weiand team G with the cast on 2" spacer. It lost MPH. I think that's where I lost it anyway. I made too many changes last winter to be sure, so I have to go back and sort them out 1 by 1 till I find it. It didn't respond to a carb change from a 750 to a 950 so that's what's pushing me towards an intake problem.

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Re: Which Is Faster

Post by turbo2256b » Tue Sep 19, 2017 4:23 pm

A 351 C i BUILT FOR MY 69 Shelby Mustang GT350 back in the early 70s would turn max RPM around 10500 RPM (might have gone more but was scared to). HP at the rear wheels with factory Hemi muffs on dyno run gave up around 8000 rpm as we couldnt hold it on the rollers pulled 650 RWHP. Only took it to 10500 about 3 times just to go over 200 MPH. It was my daily driver

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Re: Which Is Faster

Post by digger » Tue Sep 19, 2017 6:30 pm

Abbottracingheads wrote:RPM wins evertime. Perfect example--- This weekend in Dallas in Top Sportsman our Pro Stock truck with a 565 NA engine outran several 665,632, and even a 704 ci engines with probably comparable power, but we were turning 8800 and they were turning 7000-7500 rpms. RPM increases power pulses to the tires and is always faster.
The strength of the "power pulses" you refer to are actually proportional to torque as it's driven by cylinder pressures. So the comparison is stronger less frequent pulses vs slightly weaker more frequent pulses which comes out in the wash as we are told same hp. So it's just a matter of gearing and efficiency as to how much of the hp gets translated to the road .

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Re: Which Is Faster

Post by tt 383 » Tue Sep 19, 2017 7:11 pm

Abbottracingheads wrote:RPM wins evertime. Perfect example--- This weekend in Dallas in Top Sportsman our Pro Stock truck with a 565 NA engine outran several 665,632, and even a 704 ci engines with probably comparable power, but we were turning 8800 and they were turning 7000-7500 rpms. RPM increases power pulses to the tires and is always faster.
Not trying to be a smart ass here so please don't take it that way, but I fail to understand how Index racing and comparing differing engine combinations proves anything in this instance. I took the OP to mean same engine, same power at differing rpm... obvious that's me inferring a lot (taking into account what OP typically known for) but in this "hobby" that's the normal supposition when comparing a blanket statement/question ... If I am missing something obvious here please correct me.

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Re: Which Is Faster

Post by Abbottracingheads » Tue Sep 19, 2017 7:18 pm

Just as I said. The point you are missing is the 565 makes about the same power as the bigger engines, but at higher rpm--and runs faster. RPM for the sake of rpm without power is not fast.
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Re: Which Is Faster

Post by jacksoni » Tue Sep 19, 2017 7:25 pm

Geeez, what a bunch of pikers; only 5 pages. Same argument (AGAIN AND AGAIN) took up 93 pages over 5 years here: viewtopic.php?f=15&t=29115&hilit=accele ... start=1365 and more recently another 7 here: viewtopic.php?f=1&t=46939&hilit=acceleration+torque :lol:

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Re: Which Is Faster

Post by digger » Tue Sep 19, 2017 7:44 pm

Abbottracingheads wrote:Just as I said. The point you are missing is the 565 makes about the same power as the bigger engines, but at higher rpm--and runs faster. RPM for the sake of rpm without power is not fast.
Doesn't the 600hp @7100 fall Into the "rpm for the sake of rpm" given you can meet the hp at 6200rpm with the same size engine ?

The reality is the power curves are not going to be the same shape both before and after the peak hp rpm so unless this is known it's pretty hard to be decisive

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Re: Which Is Faster

Post by roc » Tue Sep 19, 2017 8:54 pm

Daniel Jones wrote:> Does rpm have that much to do with it?

The physics is straightforward and easy to derive. Torque is the rotary equivalent of force and is what accelerates a vehicle but it's the torque at the rear wheels that accelerates the vehicle, not the torque at the crankshaft. Horsepower (at the crankshaft) is the measure of how much RPM can be traded for rear wheel torque via gearing. Assuming you have sufficient traction, it's the average of power between shift points (including the down time for the shift) that is important, not a single peak power point. Also, it's the overall gearing provided by the transmission, rear end, and tire diameter that is important. Furthermore, it's the total inertia of the vehicle that has to be accelerated. That includes not just the weight (mass) of the vehicle but also the inertia of all the rotational bits (flywheel, crankshaft, driveshaft, axles, wheels, tires, etc.).

> RPM is the WILDCARD above 5252 RPM.

The 5252 RPM cross-over (of the torque and HP curves) has no significance whatsoever. It's just an artifact of the units chosen. Change the units to newton-meters and the cross-over point changes to a different RPM.

> Big difference in pulling a heavy load & accelerating a light car.

The physics are the same. A truck with 1100 ft-lbs of torque but only 200 HP average between shifts will be beaten by one with 300 HP average and 300 ft-lbs of torque (regardless of load) if both are geared optimally for their respective power curves.

> RPM wins every time.

There's an optimum RPM range for a given power curve. Operate above (or below) that range and you'll slow down (assumes no traction issues and optimal gearing).

> IIRC,most guys shift near peak torque as a general rule.

For maximum acceleration, you generally shift beyond the peak HP RPM. The idea is to maximize the area under the HP curve, including the down time for the shift.

Dan Jones
Best collection of answers so far, thanks for typing this up Dan.
RPM increases power pulses to the tires and is always faster.
Power pulses... #-o

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Re: Which Is Faster

Post by gvx » Tue Sep 19, 2017 9:14 pm

jacksoni wrote:Geeez, what a bunch of pikers; only 5 pages. Same argument (AGAIN AND AGAIN) took up 93 pages over 5 years here: viewtopic.php?f=15&t=29115&hilit=accele ... start=1365 and more recently another 7 here: viewtopic.php?f=1&t=46939&hilit=acceleration+torque :lol:
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Re: Hp vs tq
PostSun Jul 17, 2016 7:57 am

Why is this heavily debated at least twice a year!?! LOL
Torque always wins if it makes 600 hp at 6200 it will make much more hp at 7100 than 600. You must reduce torque to limit the 7100 engine to 600 hp so reguardless the average torque must be the same in either engine so if you optimize the car in a lab mathmaticly correct for each engine the outcome should be equal.
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Re: Which Is Faster

Post by pastry_chef » Tue Sep 19, 2017 11:04 pm

gvx wrote: Torque always wins if it makes 600 hp at 6200 it will make much more hp at 7100 than 600. You must reduce torque to limit the 7100 engine to 600 hp so reguardless the average torque must be the same in either engine so if you optimize the car in a lab mathmaticly correct for each engine the outcome should be equal.
So many would be better off if "torque" was erased from the dictionary!
If it was, ALL the race winners and record holders would remain the same.
Mike R

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Re: Which Is Faster

Post by gvx » Tue Sep 19, 2017 11:43 pm

pastry_chef wrote:
gvx wrote: Torque always wins if it makes 600 hp at 6200 it will make much more hp at 7100 than 600. You must reduce torque to limit the 7100 engine to 600 hp so reguardless the average torque must be the same in either engine so if you optimize the car in a lab mathmaticly correct for each engine the outcome should be equal.
So many would be better off if "torque" was erased from the dictionary!
If it was, ALL the race winners and record holders would remain the same.
You dont get it. Without torque you dont have horsepower. What i am saying is with these 2 hypothetical engines the 7100 rpm 600 hp engine makes less torque than the same at 6200 rpm. But if you add the average sum of the lower torque engine's added rpm the over-all average should be the same for both with an insignificant margin of error. As the rpm increases torque doesnt disappear it is just multiplied by the Rpm. So horsepower is not an individual measurement it is married to the torque numbers. I will get flamed for this but her goes. In a way horsepower is just a feel-good calculation based on torque multiplied be rpm
3 DAY SEMINAR. Instructor DAVID VIZARD.
Announcing GOODSON is sponsoring 2 performance TECH SCHOOL students
Jan 12-14 location Mt HolleyNC
Please refer candidates >
http://www.davidvizardperformanceseminars.com
davidvizardseminar@gmail.com

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Re: Which Is Faster

Post by pastry_chef » Wed Sep 20, 2017 12:44 am

gvx wrote:You dont get it. Without torque you dont have horsepower.
NOPE.
Torque is NOT the source of HP.
Cylinder pressure is!

Not factoring for aero, parasitic driveline or rolling resistance. Irrelevant to the argument.
Acceleration can be obtained from cylinder pressure, bore area, piston speed, drive wheel speed and vehicle weight.
Increasing the first three will improve acceleration. The higher the last two are the acceleration goes down.
No torque, no gears, no BS in the mix.
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Re: Which Is Faster

Post by cgarb » Wed Sep 20, 2017 12:49 am

What accelerates an electric car?

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Re: Which Is Faster

Post by The Radius Kid » Wed Sep 20, 2017 12:52 am

pastry_chef wrote:
gvx wrote:You dont get it. Without torque you dont have horsepower.
NOPE.
Torque is NOT the source of HP.
Cylinder pressure is!

Not factoring for aero, parasitic driveline or rolling resistance. Irrelevant to the argument.
Acceleration can be obtained from cylinder pressure, bore area, piston speed, drive wheel speed and vehicle weight.
Increasing the first three will improve acceleration. The higher the last two are the acceleration goes down.
No torque, no gears, no BS in the mix.
Cylinder pressure creates the torque.
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