Page **7** of **33**

### Re: Which Is Faster

Posted: **Fri Sep 22, 2017 6:59 pm**

by **MadBill**

With a normally aspirated V-8 it's not that difficult to get 1.3-1.4 lb-ft. per c.i. but mighty hard to pick it up to much more than 1.6, so for a given displacement, that just leaves RPM as the path to bigger power.

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 7:57 pm**

by **rewguy**

This is mathematically so simple.

If 427 #1 makes 600 hp at 6200, and we will even give it a torque advantage of 15 ft lbs...... for arguments sake we will say 580.

If 427 # 2 makes 600 hp at 7100 and say 565 ft lbs of torque.

IF BOTH are geared and convertered and shifted for MAX EFFORT elapsed time...... (as Larry Meaux stated once...... ALL record holding, data logged, three speed automatic superstocks shift 300-500 over peak horsepower, and cross 800-1000 rpm over peak horsepower)..... It will play out like this......PERIOD

Car one, (to cross at say 7100......out of breath....maximum low e.t. attained), may have a 4.30 gear w 29" tire.........take the torque multiplied by first gear in trans(will say 2.48 for arguments sake), then multiplied by rear gear ratio. so.... 580 x 2.48 x 4.30 = 6185 ft lbs at the tire.

Car two, (to cross at say 8200.....out of breath.....maximum low e.t. attained), may have a 4.88 gear with a 29" tire........same math applies.....

565 x 2.48 x 4.88 = 6,837 ft. lbs at the tire.

THAT is why....... NO OTHER REASON. SIMPLE MATH. Two cars geared and convertered to perfection.......crossing the finish line AS THEY SHOULD.... in max low e.t. form....... MOST RPM ALWAYS ALWAYS ALWAYS has the advantage for this reason. More torque at the ground through a given gear.

Frictional losses may be involved for added rpm, but obviously the added torque at the ground far outweighs the losses.

So....in result......a 400 cube engine that makes 600 horsepower at 7600 and say 525 ft lbs, that needs a 5.38 gear to cross at 8600.....

525 x 2.48 x 5.38 = 7004 ft lbs. Again....advantage.

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 8:53 pm**

by **John Wallace**

If 427 #1 makes 600 hp at 6200, and we will even give it a torque advantage of 15 ft lbs...... for arguments sake we will say 580.

If 427 # 2 makes 600 hp at 7100 and say 565 ft lbs of torque.

600HP at 6200 RPM = 508.25 lb/ft

600HP at 7100 RPM = 443.83 lb/ft

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 8:57 pm**

by **MadBill**

<EDIT> Penned before seeing above post.

rewguy wrote:This is mathematically so simple.

If 427 #1 makes 600 hp at 6200, and we will even give it a torque advantage of 15 ft lbs...... for arguments sake we will say 580.

If 427 # 2 makes 600 hp at 7100 and say 565 ft lbs of torque....

But for this to be a meaningful comparison, the

shape of the power/torque curves must be proportional to each other through the entire range*, i.e. the lower RPM engine will have 7100/6200 or 14.5% more torque/power at any equivalent RPM percentage of their peaks. Maximum torque of 565 for the high RPM engine would equate to 647 for the low RPM one. At peak power, it would be 444 for the high revver and 508 for the low.

(*One way to visualize this would be to have two RPM scales along the bottom of the power/torque chart, one with 14.5% more space between each RPM interval. Plotted on this chart, the two sets of curves should perfectly overlie one another.)

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 9:01 pm**

by **vortecpro**

rewguy wrote:This is mathematically so simple.

If 427 #1 makes 600 hp at 6200, and we will even give it a torque advantage of 15 ft lbs...... for arguments sake we will say 580.

If 427 # 2 makes 600 hp at 7100 and say 565 ft lbs of torque.

IF BOTH are geared and convertered and shifted for MAX EFFORT elapsed time...... (as Larry Meaux stated once...... ALL record holding, data logged, three speed automatic superstocks shift 300-500 over peak horsepower, and cross 800-1000 rpm over peak horsepower)..... It will play out like this......PERIOD

Car one, (to cross at say 7100......out of breath....maximum low e.t. attained), may have a 4.30 gear w 29" tire.........take the torque multiplied by first gear in trans(will say 2.48 for arguments sake), then multiplied by rear gear ratio. so.... 580 x 2.48 x 4.30 = 6185 ft lbs at the tire.

Car two, (to cross at say 8200.....out of breath.....maximum low e.t. attained), may have a 4.88 gear with a 29" tire........same math applies.....

565 x 2.48 x 4.88 = 6,837 ft. lbs at the tire.

THAT is why....... NO OTHER REASON. SIMPLE MATH. Two cars geared and convertered to perfection.......crossing the finish line AS THEY SHOULD.... in max low e.t. form....... MOST RPM ALWAYS ALWAYS ALWAYS has the advantage for this reason. More torque at the ground through a given gear.

Frictional losses may be involved for added rpm, but obviously the added torque at the ground far outweighs the losses.

So....in result......a 400 cube engine that makes 600 horsepower at 7600 and say 525 ft lbs, that needs a 5.38 gear to cross at 8600.....

525 x 2.48 x 5.38 = 7004 ft lbs. Again....advantage.

Pretty simple isn't it.........Its always about moving the power UP

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 9:07 pm**

by **MadBill**

if you said "moving the torque up" I wouldn't argue..

Here's another visual: Imagine each engine is enclosed in a black box with an external PTO shaft connected to the driveline. Engine 'A' makes 600 HP @ 10,000 RPM and engine 'B' makes 600 HP @ 5,000 RPM,

but engine 'A' is connected to a 2:1 reduction box, so it's PTO output RPM at peak power is also 5,000 RPM. Ignoring the reduction box friction of 'B' and the higher rotational inertia loads of 'A', how can the car know the difference?

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 9:24 pm**

by **vortecpro**

Power/TQ same thing.

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 10:57 pm**

by **swampbuggy**

Correct (or) incorrect ? For a race car engine the objective while dyno testing is to make the biggest torque number possible, and make that torque number as HIGH as possible in the RPM range ??? Thanks Mark.

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 10:59 pm**

by **hoffman900**

swampbuggy wrote:Correct (or) incorrect ? For a race car engine the objective while dyno testing is to make the biggest torque number possible, and make that torque number as HIGH as possible in the RPM range ??? Thanks Mark.

Since VE peaks when torque peaks, I always think of it as doing everything possible to hold on to and minimize the the torque fall off as RPMs rise from torque peak.

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 11:26 pm**

by **GARY C**

THAT is why....... NO OTHER REASON. SIMPLE MATH. Two cars geared and convertered to perfection.......crossing the finish line AS THEY SHOULD.... in max low e.t. form....... MOST RPM ALWAYS ALWAYS ALWAYS has the advantage for this reason. More torque at the ground through a given gear.

Frictional losses may be involved for added rpm, but obviously the added torque at the ground far outweighs the losses.

Simple math does not factor in the average tq curve for the usable rpm, wheel speed, gear efficiency just to name a few..If it were that simple then all cars would be faster with a TH vs a Power glide and thats usually not the case.

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 11:42 pm**

by **pdq67**

I always liked cams that allowed both Hp and T to go up after 5252 rpm.

It just seems that power just follows right along up top is all.

pdq67

### Re: Which Is Faster

Posted: **Sat Sep 23, 2017 11:54 pm**

by **cab0154**

vortecpro wrote:Power/TQ same thing.

So many people do not understand that concept....

### Re: Which Is Faster

Posted: **Sun Sep 24, 2017 5:26 am**

by **rewguy**

John Wallace wrote:If 427 #1 makes 600 hp at 6200, and we will even give it a torque advantage of 15 ft lbs...... for arguments sake we will say 580.

If 427 # 2 makes 600 hp at 7100 and say 565 ft lbs of torque.

600HP at 6200 RPM = 508.25 lb/ft

600HP at 7100 RPM = 443.83 lb/ft

This is an exerpt from a hotrod magazine dyno test of a 427 cube ls7 engine.

"Combined with a pair of 13/4-to-17/8-inch step headers, the Stage 3 cammade exactly 600 hp at 6,800 rpm and 526 lb-ft of torque at 4,800 rpm,or 1.40 hp/ci with the SAE correction factor at Katech EngineDevelopment. That’s a 90hp gain over the stock cam with the sameheaders, and it’s a damn good answer to our question."

Doesnt seem anywhere close to your math? so.................

?

And if that line of thinking is correct, how is this possible......?

2 different engines. both small chevys. engine A 408 cube. engine B 409 cube. Same exact dyno. Engine A made 711hp@7400, 535 ft lbs@6200. Engine B made 713hp@7900, 532 ft lbs@6400.

BOTH engines were installed in similar weight cars.

Engine A went in all steel 67 camaro, factory interior, (was iron headed) Mild steel 6 pt bar, 255 lb driver, weighed 3430 race weight...... ran 9.66@137. th400, 29" tire, 4.56 gear

Engine B went in an '80 Chevy Malibu, all steel except for glass hood, (alum headed), factory split bench interior, Ford 9 inch w heavy nod. center, 360 lb driver "big Jeff". It weighed 3455 race weight. ran 9.61@136 th350, 28" tire, 4.56 gear

Neither car was 100% figured out....BUT both were close. Were both raced in similar air. So yes....the dyno hp correlated well with the et.

### Re: Which Is Faster

Posted: **Sun Sep 24, 2017 5:31 am**

by **paulzig**

vortecpro wrote:[

Pretty simple isn't it.........Its always about moving the power UP

Yeah but, 427cu.in making 600HP@ 7100RPM the VE is down a fair bit...

### Re: Which Is Faster

Posted: **Sun Sep 24, 2017 5:50 am**

by **digger**

rewguy wrote:John Wallace wrote:If 427 #1 makes 600 hp at 6200, and we will even give it a torque advantage of 15 ft lbs...... for arguments sake we will say 580.

If 427 # 2 makes 600 hp at 7100 and say 565 ft lbs of torque.

600HP at 6200 RPM = 508.25 lb/ft

600HP at 7100 RPM = 443.83 lb/ft

This is an exerpt from a hotrod magazine dyno test of a 427 cube ls7 engine.

"Combined with a pair of 13/4-to-17/8-inch step headers, the Stage 3 cammade exactly 600 hp at 6,800 rpm and 526 lb-ft of torque at 4,800 rpm,or 1.40 hp/ci with the SAE correction factor at Katech EngineDevelopment. That’s a 90hp gain over the stock cam with the sameheaders, and it’s a damn good answer to our question."

Doesnt seem anywhere close to your math? so.................

?

It's simple

Hp=tq x rpm / 5252 rearrange the equation

Tq = hp x 5252 / rpm