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Calculate Crank power and tq

3K views 30 replies 7 participants last post by  straybullitt 
#1 ·
I recently bought a 2012 gt. Got it tuned and datalogged. I was playing with livelink software, extracted some data and made this. Only mod i have is 93 oct race tune . Dont know how accurate it is but thats all crank numbers.

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#2 ·
#5 · (Edited)
Although what you are trying to do is a "guesstimate", an engine dyno is far more accurate with HP/TQ numbers than a chassis dyno.
Not sure why crankshaft HP/TQ numbers are worthless...it's where most race engines get their HP/TQ figures. My 408 made 650HP/544lbft on the engine dyno and ran 9.80's in the 1/4...on paper it shouldn't have turned in the 9's at all.
Paper/computer programs are a good guide...real world is the "proof of the pudding"...IMHO
 
#7 ·
I made 439 horse on my 2012 manual GT, on the Procal FRPP tune. It was an outlier, definitely; I don't think you're making 450 tune only. My power level was dragstrip dyno tested.

My current ride, through its slightly more power sucking auto, made 431 on a VMP 91 tune, similarly calculated.
 
#8 ·
I'm not trying to be argumentative...just trying to point out that any dyno is only as good as it's software and operator and many other variables. Plus it's about torque...that's what pushes you down the road and the little 5.0l just doesn't have much unless you help it with more than a tune.

Although I haven't taken my Caddy to a drag strip I did see a stock one like mine turn a 12 flat at 120 in the quarter on street tires...so I would assume it's making around 425 to the rear wheels and that one had the carbon fiber package like mine...the weight with him and 1/4 tank was 3615...so I would think your 12 was a little less than 425 to the wheels and if you had slicks maybe down to around 410...all just guesses and assuming you have had a fair amount of seat time in the car at the lights.

What was the race weight of the 12 and the 14 with you in it???
What was the torque reading on the dyno for your 12 and 14???

Chassis dyno's are good starting points for tuning although I think an engine dyno is better. I only had the Maverick on a chassis dyno one time and the numbers were 678HP/590TQ to the rear wheels...the engine dyno said 650HP/555TQ and I know those numbers were correct. If I would have had that kind of HP I could have turned a 9.5 instead of 9.8.
The formula for calculating HP is pretty simple although it takes into account no variables.
Chassis dyno's are over rated in my humble opinion, but that's just me.
 
#10 ·
So here's something i would like to discuss with you, and this is more for my own understanding than me disagreeing with what you are saying.

Lets take a 2011 M3 and a 2011 5.0 for example. I picked those cars because i remember the head to head motortrend did and it was very close in the 1/4.

So the comment i would like to address is torque which, like you mentioned, is the most important part of going fast. What i would like to discuss however, is the transmission's impact on torque, and therefore the 1/4 numbers.

As i'm sure you know, but for the sake of others following this discussion, a vehicle's total output torque is the engine torque multiplied by the transmission factor (gear * final drive). Comparing the 2011 m6 M3 to the 2011 m6 5.0, the M3 has 30% more gear torque in 1st gear, 13% more in 2nd, 9% more in 3rd, and 5% more in 4th when compared to a 5.0 with a 3.31 final drive.

So, that would mean if both cars made the exact same torque at the exact same RPM(s), that effectively the M3 would be 30% faster in 1st gear, 13% faster in 2nd gear etc... weight, traction and other factors notwithstanding. However, when we add engine torque to the calculation, the 5.0 makes 390 whereas the M3 makes 295, or essentially 25% less.

So if we take that 25% deficit and apply it to the initial gearing advantage, the M3 essentially goes from:
1: +30%
2: +13%
3. +9%
4. +5%

To

1: +5%
2: -12%
3: -16%
4: -20%

However, both cars trap right around 109-111... i suppose the question at the end of this ramble is how do you quantify engine output at the 1/4 when variables such as that exist? Or do the calculators used take that into account and i'm just rambling for no reason?
 
#9 ·
Well, it's never been on a dyno. As I said, it was dragstrip dyno, which means weight and MPH calculations. This ain't rocket surgery. People have been doing weight and speed calculations to determine crank hp for decades.

The bias slick I was using can sap a mph or so at the big end because the tire is more motile and less stable than a radial but, I don't think it took much, if anything out here. The same slick was used for both cars.

Race weight varied on different times at the strip, depending on fuel load. These cars are not as heavy as some think, even fully loaded as both of mine are/were. The '12 was 3680 the day i did this. The auto weighs 3740 on fumes but was filled to 3825 last time I ran it n/a and confirmed its power level. I was 30 pounds heavier too when I did this in the 2014, so, that should help me a touch this season, especially on my drag bike.

I did confirm the '12's weight on a separate calibrated scale as well.
 
#11 ·
The old torque-wins-races statement is not really true. HP is a measure of torque applied over time. You need HP to win races or we'd all be strapping Cummins diesel V8s into our hot rods and not just the Welderup crew.... For instantaneous acceleration, torque rules due to F=MA. For sustained acceleration, you need alot of HP or acceleration drops with each gear change. As for the calculators, they are basing HP calcs primarily off final trap speed and weight, which are less affected by gearing at the big end, as you've spent most of the 1/4 mile generating as much power as the engine is going to, due to WOT operation for 95% of the run. Torque and HP are proportional to one another so, it's not really possible to separate them.

In the comparison chosen, the M3 has a much smaller engine (4.0) but can also weigh less than the 5.0 so, it's a fairly even power-to-weight situation. Plus, the M3 has an optional dual clutch trans that transfers power to the road better.
 
#14 ·
Torque is force times distance and HP is a unit of power.
Talking about HP vs TQ is like asking which is faster, speed or weight???

To quote Enzo Ferrari, "Horsepower sells cars, torque wins races", was true then and is still true, given good amounts of HP/TQ. In road racing you have a lot of turns, acceleration and braking...torque wins hands down as long as you have the HP along with it. Without HP, diesel trucks would win auto races and without torque jet powered vehicles would win all races.
A short story here...I had my 97 Cobra in three Silver States Classic events. The first event I had done no internal mod's and it was N/A, stock 3:23 gears, Tremec 5 spd and 26" diameter tires...although I can't remember what the underdrive in 5th was...the car chassis dyno'd at 323hp and 318lbft of torque in 4th gear. My Tech speed was about 140 and on the 14 mile straight I tried to shift into 5th...the Mustang actually slowed down...was that due to lack of HP or TQ?
 
#17 ·
2 hp....
 
#20 ·
Yep, that's what usually happens in OD. You'd need to be at such a high theoretical speed to bring the car into a useful engine rpm range and then you run into an aerodynamic wall the car doesn't have enough horsepower to push through.
 
#21 ·
I have an old big block powered F250 that has a lot more torque than horsepower in it's current configuration. It actually does reasonably well in the local "stoplight gran-prix" that take place in the area. For a daily driver, I'll take torque over horsepower any day of the week. ;)
Without torque there is no horsepower... So technically, both Enzo and Olerodder are correct.
 
#22 ·
That was the whole ethic of the 70s....relatively huge gutless V8s with tip-in torque and that was it. They'd beat anything across the crosswalk but, after that, not so much. Combining that with rear axle ratios like the 2.47 peg-leg like my 1979 Mustang 302 Ghia coupe had to lever its awesome 130 horse 2 bbl 302 and it was a dark period indeed. How far we've come....

That 79 302 still claimed 250 lb/ft of torque but was completely done by 4000 rpm.
 
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