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Old 09-12-2019, 03:44 PM
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Default HP vs TRQ at the track

Im assuming HP will always trump trq when the gears,converter,etc are optimized for each setup? Say a motor makes 500 hp and 570 trq in a 4000lb car and then put in a 550 hp ,530 trq motor,,the 550 hp would run a better time? I know we like trq to get these heavy cars up and going but I would assume with the higher hp,lower trq motor you would gear it lower or higher stall converter to take advantage?

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72 lemans,455 e-head, UD 255/263 solid flat,3.73 gears,,,10" 4400 converter,, 6.68 at 101.8 mph,,1.44 60 ft.2007
(cam 271/278 roller)9"CC.4.11gear 6.41 at 106.32 mph 1.42 60 ft.(2009) SOLD,SOLD
1970 GTO 455 4 speed #matching,, 3.31 posi.Stock manifolds. # 64 heads.A factory mint tuquoise ,69' judge stripe car. 8.64 @ 87.3 mph on slippery street tires.Bad 2.25 60ft.Owned since 86'
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Old 09-12-2019, 05:12 PM
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Yes on all accounts. If the 550hp engine is geared to be over max horsepower rpm at the stripe, and has a converter that flashes at or slightly over peak torque. But the “tractor motored” cars can run very respectfully with less cam,gear,converter, and rpm.

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Old 09-12-2019, 07:09 PM
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Optimize HP where the engine spends time.
https://performancetrends.com/blog/?p=7

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Old 09-13-2019, 07:05 AM
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So if using a 4000 lb car with high gears and a stock converter,,,the ets might be a wash between the 2 engines where the higher trq might 60 ft better but not quite run the mph?

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72 lemans,455 e-head, UD 255/263 solid flat,3.73 gears,,,10" 4400 converter,, 6.68 at 101.8 mph,,1.44 60 ft.2007
(cam 271/278 roller)9"CC.4.11gear 6.41 at 106.32 mph 1.42 60 ft.(2009) SOLD,SOLD
1970 GTO 455 4 speed #matching,, 3.31 posi.Stock manifolds. # 64 heads.A factory mint tuquoise ,69' judge stripe car. 8.64 @ 87.3 mph on slippery street tires.Bad 2.25 60ft.Owned since 86'
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Old 09-13-2019, 08:07 AM
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Power is..power. So the full ET time (8-14 seconds) ought to be in the Power peak (on paper).

In practice, the dynamics of best traction for 60-foot & crossing the line at peak HP cause Tire-Gear-Transission ration-Converter decisions.

When said & done, the load on the engine just might affect the engine's ability to accelerate (rate of RPM increase).

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Old 09-13-2019, 08:29 AM
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Quote:
So if using a 4000 lb car with high gears and a stock converter,,,the ets might be a wash between the 2 engines where the higher trq might 60 ft better but not quite run the mph?
It could very well be quicker since you wouldn't be using the power band of the engine.
You'd be using the torque band for street driving. (would also probably feel better on street).

But if racing against a vehicle with same engine that was optimized for the power band, it would blow your doors off.


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Old 09-13-2019, 09:15 AM
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The thing that accelerates the car is tangential force at the contact patch of the tire. That is governed by tire radius and axle torque.

Horsepower at the engine is the winner IF the gearing and tire size are optimized to produce the highest force at the tire contact patch.

On the other hand, if gearing and tire size are held constant, then increased engine torque will give you increased axle torque and more tangential force at the contact patch.

Eric

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Old 09-13-2019, 09:50 AM
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contact patch force pounds now = (horsepower now x 375) / MPH now.

Not factoring for aero or rolling resistance.

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Old 09-13-2019, 10:02 AM
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Quote:
Originally Posted by Elarson View Post
The thing that accelerates the car is tangential force at the contact patch of the tire. That is governed by tire radius and axle torque.

Horsepower at the engine is the winner IF the gearing and tire size are optimized to produce the highest force at the tire contact patch.

On the other hand, if gearing and tire size are held constant, then increased engine torque will give you increased axle torque and more tangential force at the contact patch.

Eric
Basically what I was saying, but in much more eloquent terms.

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68 GTO,3860#
Stock Original 400/M-20 Muncie,3.55’s
13.86 @ 100
Old combo:
462 10.75 CR,,SD 330CFM Round Port E's,Old Faithful cam,Jim Hand Continental,3.42's.
1968 Pontiac GTO : 11.114 @ 120.130 MPH

New combo:
517 MR-1,10.8 CR,SD 350CFM E's,QFT 950/Northwind,246/252 HR,9.5” 4000 stall,3.42's
636HP/654TQ
1.452 10.603 @ 125.09
http://www.dragtimes.com/Pontiac-GTO...lip-31594.html
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Old 09-13-2019, 10:11 AM
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The Solution is rather amazing when we consider the RPM ratio of the Tires: ZERO RPM to 1440 RPM tire RPM @120 MPH.

28" dia tire is 2.33 foot dia. Is 7.33' circumference roll-out.
1320' distance shows 180 turns.

How well can your Driveline increase roll-out velocity (accelerate) across 180 tire rotations, for a constant 4000 Lb?


Last edited by Half-Inch Stud; 09-13-2019 at 10:19 AM.
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Old 09-13-2019, 10:13 AM
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Quote:
Originally Posted by pastry_chef View Post
contact patch force pounds now = (horsepower now x 375) / MPH now.

Not factoring for aero or rolling resistance.
Just to clarify Mike's equation. HorsePower Now is Rear Wheel HP.

Stan

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Old 09-16-2019, 04:37 PM
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Let's look at 2 extreme hypothetical examples: Car A has 1000 hp and 100 ft lb. Car B has 1000 ft-lb and 100 hp. Both engines make peak hp right at their repective rpm limit (so A turns 52k rpm, B turns 525 rpm). Lets assume we want these cars to go side by side down the track, exactly matching speed at every point, with each engine operating at peak hp. The 2 cars are identical otherwise. In order for them to match speed at every point, gearing (overall) will need to be much different between the two (by a factor of 1000).

Car B with its slower turning engine will need to be geared up much lower numerically compared to A to keep up with speed. Physics says that this results in torque reduction compared to A which is much higher gearing numerically, in comparison. Even with 1000 ft lb on tap, dividing it by a factor of 1000 results in very low torque available to accelerate the car (F=ma), resuliting in a very low acceleration comparatively, so our assumption falls apart completely. Car B loses to the higher hp Car A

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Old 09-16-2019, 05:00 PM
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Quote:
Originally Posted by 70GS455 View Post
Let's look at 2 extreme hypothetical examples: Car A has 1000 hp and 100 ft lb. Car B has 1000 ft-lb and 100 hp. Both engines make peak hp right at their repective rpm limit (so A turns 52k rpm, B turns 525 rpm). Lets assume we want these cars to go side by side down the track, exactly matching speed at every point, with each engine operating at peak hp. The 2 cars are identical otherwise. In order for them to match speed at every point, gearing (overall) will need to be much different between the two (by a factor of 1000).

Car B with its slower turning engine will need to be geared up much lower numerically compared to A to keep up with speed. Physics says that this results in torque reduction compared to A which is much higher gearing numerically, in comparison. Even with 1000 ft lb on tap, dividing it by a factor of 1000 results in very low torque available to accelerate the car (F=ma), resuliting in a very low acceleration comparatively, so our assumption falls apart completely. Car B loses to the higher hp Car A

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Are you talking CVT?

Could you please explain where 1000 comes from?

Stan

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Old 09-16-2019, 07:35 PM
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stop smoking this
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Old 09-16-2019, 08:15 PM
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A few years back, pair of virtual 3500 lbs cars (aero drag same and not applicable). Traction not an issue. ---Using Quarter PRO sim
Both cars used GM standard TH400 trans and 29 inch rear tire.

Torque combo 1)

600 cubes
400 HP at 3000 RPM, 750 lbs of torque

2.0 rear axle ratio 29 inch tire. (lack of engine RPM ability seriously limits rear axle ratio)

ET
11.9 at 115 MPH
1.6 at 60 feet

---------------
Horsepower combo 2)
300 cubes
600 HP at 8000, 393 lbs torque

4.88 gear 29 inch tire

ET
10.62 at 130.5 MPH
1.55 at 60 feet


Install an engine with more horsepower into a tractor - https://youtu.be/9yHl24QynOM A tractor doing burnouts on asphalt.


Last edited by pastry_chef; 09-16-2019 at 08:23 PM.
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Old 09-16-2019, 11:46 PM
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Quote:
Originally Posted by pastry_chef View Post
A few years back, pair of virtual 3500 lbs cars (aero drag same and not applicable). Traction not an issue. ---Using Quarter PRO sim
Both cars used GM standard TH400 trans and 29 inch rear tire.

Torque combo 1)

600 cubes
400 HP at 3000 RPM, 750 lbs of torque

2.0 rear axle ratio 29 inch tire. (lack of engine RPM ability seriously limits rear axle ratio)

ET
11.9 at 115 MPH
1.6 at 60 feet

---------------
Horsepower combo 2)
300 cubes
600 HP at 8000, 393 lbs torque

4.88 gear 29 inch tire

ET
10.62 at 130.5 MPH
1.55 at 60 feet


Install an engine with more horsepower into a tractor - https://youtu.be/9yHl24QynOM A tractor doing burnouts on asphalt.
Mike,
What was this test trying to prove?

In high gear car 1 ► 2 * 750 = 1500 torque at axle

In high gear car 2 ► 4.88 * 393 = 1917.84 torque at axle

But 400 HP @ 3000 is 700 torque

In high gear car 1 ► 2 * 700 = 1400 torque at axle

Stan

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Old 09-17-2019, 07:41 AM
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Quote:
Originally Posted by Stan Weiss View Post
Mike,
What was this test trying to prove?
Funny enough, years ago on Speed-talk some who should know better thought the 600 cube (less HP) engine would win a 1/4 mile race.

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Old 09-17-2019, 03:16 PM
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Quote:
Originally Posted by Stan Weiss View Post
Are you talking CVT?

Could you please explain where 1000 comes from?

Stan
"Let's look at 2 extreme hypothetical..." kind of says it all

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Old 09-17-2019, 04:07 PM
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Got you. 1000 HP and 100 Torque would be 52,520 RPM.

Stan

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