HP and TQ

[kinkyllama]

How does the engine create tq and hp.. i understand how it creates power. But what would make a engine have more or less torque? Or hp?

[Audacity Racing]

in reference to what?

[AcingTeam]

in reference to what?

I think he means components. I don't know... good question.

[PrecisionBoost]

Ok..... first off..... your engine produces torque.... not horsepower.

I'm going to explain a little about torque/power before I answer your questions.

Horsepower is a simple measurement to give people a sense of how much power the engine makes.

If you take a stick that's exactly 1 foot long.... hold it in your left hand and then press on the end of it with exactly 1 lb of force you will have created a torque of 1 ft-lb ( torque = force X distance )

You will feel it rotate your hand in the direction of the force.... that my friend is the basic premise of torque.

Engines make power by burning the Air/Fuel ratio in your cylinder which pushes down on the connecting rod which turns that power into torque.

That torque is then multiplied by a gear ratio in the transmission which creates a rotational torque (via the axle) to the tire.

The torque is then coverted back into force by dividing the torque by the radius of the wheel/tire.

So just as torque is created when a force is exerted at the end of a stick.... force is created at the end of the stick when you apply torque to the center of the stick.

So..... gear ratios and tire diameters will also affect the torque.

The smaller the tire.... the more power to the pavement you will create... and the faster the acceleration.

This acceleration comes at the cost of top speed.

If you decrease the diameter of your tire by 20% you will be decreasing the radius of the tire to axle distance by 20% which will increase your acceleration by 20% and decrease your speed in each gear by 20%

[PrecisionBoost]

Now.... for the internal stuff....

Since torque is generated by the force of the piston acting on the offset radius of the crankshaft...... increasing the stroke will increase that radius which will produce more torque. (as well this obviously increases the displacement of the engine)

As well.... increasing the bore will also increase the displacement which will result in more force put on the cranshaft.... which creates more torque.

The midband torque levels are typically dependant upon the efficency of your engine.

Small ports generate a higher velocity intake charge which burns better and creates more force on the pistons which results in more power to the crankshaft.

Large ports will have low velocity and less of the air/fuel will burn... so less energy is put on the pistons... which again... results in less torque.

But this is a double edged sword..... if the ports are small they will work awesome in making massive midrange torque but the torque near the top end will drop like a rock.

I have a feeling that our ports are small.... since the power and torque drops dramaticly after 5500 RPM.

Basicly.... it's like trying to suck air through a straw..... even with a turbo the effective volumetric efficency will drop as port size decreases.

So..... if you want to make more torque at high RPM (5500RPM).... open up the ports in the head a little.

If you want to make more power down in the mid range (3500 RPM) then you need to leave the ports alone.

Another thing that will effect how much of the intake air/fuel gets into the cylinder is the valve lift and valve size.

More lift means less restriction.... which translates into more power/torque at higher RPM and a drop in power in the lower and mid RPM areas.

Larger valves also mean less restriction..... which translates into more power/torque at higher RPM and a drop in power in the lower and mid RPM areas.

So..... if you want to make more high end power and torque out of a N/A engine have someone port your head, increase the valve sizes and go with a cam that has more lift and or duration.

[PrecisionBoost]

In your case Kinky..... the easiest way for you to gain some acceleration is to change the tire diameter on your car.

What you need to figure out is what the absolute maximum speed you will get to on the track.

If it's say 100 MPH then you might want to figure out how small of a tire you can put on and still maintain that speed.

Ok.... here are the gear ratios for your car...

First: 3.54
Second: 2.15
Third: 1.47
Fourth: 1.12
Fifth: 0.88
Final drive ratio: 3.50

So.... if you were to go on a dyno and find your car made 125 ft-lb torque at 5500 RPM this would be at a theoretical 1:1 ratio. (dyno computer calculates it based upon RPM vs Speed )

In reality the torque you put to the ground is increased through gearing.

So in first gear you have a total ratio of 3.54 X 3.50=12.39

So in reality.... at 5500RPM in 1st gear your putting down 1550 ft-lb of torque. (12.39 X 125ft-lb)

In second you would be putting down 940 ft-lb ( 2.15 X 3.50 X 125 ft-lb)
In third you would be putting down 643 ft-lb (1.47 X 3.50 X 125 ft-lb )
In fourth you would be putting down 490 ft-lb (1.12 X 3.50 X 125ft-lb )
In fifth you would be putting down 385 ft-lb (0.88 X 3.50 X 125 ft-lb)

With your stock 195/55/15 tires your tire diameter is 23.3"

So this equates to an axle center to outside of tire radius of 0.97083 feet

So.... you divide the torque by 0.97083 and that gives you the force that your car is exerting on the pavement to accelerate you.

1st --> 1597 lbs of force at a speed of 31 MPH
2nd --> 968 lbs of force at a speed of 51 MPH
3rd --> 662 lbs of force at a speed of 74 MPH
4th --> 505 lbs of force at a speed of 97 MPH
5th --> 397 lbs of force at a speed of 123 MPH

speed = ((3.14 X tire diameter)*0.000189 feet/mile ) ((RPM X 60 ) / total gear ratio )

Example.... 4th gear.... 5500 RPM.... total ratio = 3.92

In one revolution... tire will move by the distance of the circumference of the tire..... so 3.14 X Diameter = 3.14 X 23.3" =73.162 inches per tire revolution which is equal to 6.0968 feet per revolution

Next.... 5500 RPM =330,000 Revolutions per hour so the tire will move (330,000 rev per hour X 6.0968 feet =2,011,955 feet per hour)

Converting from feet to miles... multiply by 0.000189 = 380.25 miles per hour

Divide this by the total gear ratio and you get (380.25 / 3.92 )=97 MPH

So.... in theory if you had no transmission....you would have a 1:1 gear ratio.... so your car would only put 125 lb-ft of torque to the ground and 129 lbs of force to the pavement but the car would be travelling at 380.25 MPH !!!!

Of course this never happens due to the fact that the air resistance would equal the output of the engine way before it hit 380.25 MPH.

Odds are you might make something closer to 150MPH before hitting your terminal velocity.

Ok...... getting back to the main story.

Now if you changed those 195/55/15 tires for some 195/50/15 your tire diameter would drop from 23.3" to 22.7"

So.... this would result in the following numbers....

1st --> 1638 lbs of force at a speed of 30 MPH
2nd --> 993 lbs of force at a speed of 50 MPH
3rd --> 680 lbs of force at a speed of 72 MPH
4th --> 518 lbs of force at a speed of 95 MPH
5th --> 407 lbs of force at a speed of 120 MPH

The torque from the axle would converted of to force over 0.94583 feet instead of 0.97083 feet ( 2.575% increase in force & acceleration and 2.575% decrease in speed in each gear )

If your normal acceleration to 40MPH was 5 second you would drop that to something in the range of 4.87 sec with the smaller tires.

Of course since our tires are allready really small your limited to how much of a change you can make.

The next easiest way to make a change is to change the final drive ratio.

For example.... you could purchase another final drive ratio from Intimidator.

http://www.daewootech.com/forum/viewtopic.php?t=2383

They have 3.722 , 3.944, 4.176

With the 3.722 ratio... you would increase the force to the ground by about 6.34% and decrease the speed in each gear by 6.34%
(accelerate 6% faster but go slower by 6%)

4th --> 537 lbs of force at a speed of 91 MPH
5th --> 422 lbs of force at a speed of 116 MPH

With the 3.944 ratio... you would increase the force to the ground by about 12.7% and decrease the speed in each gear by 12.7%
(accelerate 13% faster but go slower by 13%)

4th --> 569 lbs of force at a speed of 86 MPH
5th --> 447 lbs of force at a speed of 109 MPH

With the 4.176 ratio... you would increase the force to the ground by about 19.3% and decrease the speed in each gear by 19.3%
(accelerate 19% faster but go slower by 19%)

4th --> 602 lbs of force at a speed of 81 MPH
5th --> 474 lbs of force at a speed of 103 MPH

So if you can live with decreasing your speed you will gain a pile in acceleration

The price is actually really cheap and it would make a 120hp engine feel like it had 144 hp ( if you went to the 4.176 drive ratio )

Of course the down side is highway driving.... your RPM levels at 80MPH would be 20% higher so you would use way more gasoline.

Sorry this was so long.... hopefully you get what I'm talking about.

[AcingTeam]

Oh my... it's about time we start paying Chris for his contributions to this site! wow so devoted to us... the daewoo family. Chris, we value your explanations very highly!!

[kinkyllama]

First off thanks alot for the in depth post.. i enjoyied reading it.

I under stand how the engine makes power/torque completly now. But when you go to the dyno and they give you your hp and tq #s... how do they do that? I understand how they would get overall power but not one or the other?




As for the tires.. w/ my current tires (if they were new, which they're far from) my top speed is 149.3mph.. i dont wanna mess with tire diameters and gear ratios untill i get the new suspension on, turbo, my new carbon wing, and front air dam/splitter cuz then ill know what speeds i can reach on the tracks. Currently i reach as much as 108mph.. which im hoping when im done with the previously listed things should be up to 130's... especialy when i get more track time. So i dont think ill wanna mess with that at all. Right new my power drops off (in 5th) at 138mph

[KnightWalace]

i think the dyno's are never 100% accurate because i have yet to see a car with a 1:1 gear ratio.

I think it measures the power in the entire powerband of the gear with the closest ratio to 1:1

i Just thought, maybe they measure how long it takes to scale the entire powerband. because if you go thru a 1:1 gear in 4 seconds.. you'll have some nice ponies... 8-10 seconds... not so nice ponies... more like old mares.

[PrecisionBoost]

The Dyno calculates the power with a 1:1 ratio because that is what you would see at the crank (since this is what the manufacturers use )

Basicly if you were on the dyno it would know both the RPM levels and the speed (RPM by hookup to the coil pack and speed by the dyno drum rotation)

So... if you dyno in 3rd gear (which is normally where it's done) the dyno would see a speed of 74 MPH at 5500 RPM

So it simply calculates the gear ratio and divides the measured torque on the drum by the gear ratio to give a "at the crank hp reading"

Now.... we allways call it wheel horsepower because it's a true measure of the power going to the pavement.

The difference between crank HP and wheel HP is the losses in the drivetrain in the transmission, bearings and tires. (since it takes power to rotate the wheel mass )

This is also why heavier wheel/tire setups hurt your performance..... the heavier the wheel/tire combo the more power it sucks from the engine during acceleration.

If you had two identical cars on the dyno and car A had a set of rims/tires that were 10 lbs heavier than car B you would find that Car A would not put as much power down on the Dyno.

Now this is "real world" power.... Car B would accelerate faster than Car A

So..... if your wondering about Dyno accuracy.... it's all dependant upon the manufacturer.

DynoJet makes a system that is expensive but extreemly accurate ( to within 1 or 2 hp )

Other dynos are very inaccurate due to a cheaper setup..... if I had my choice I would only ever go on a DynoJet Dyno.

[PrecisionBoost]

Oh.... by the way... I tested my calculated numbers last night and they were bang on.

At 5500 RPM my car was doing 50 km/h ( 31.25 MPH ) in first gear

In second gear my car was doing 82 Km/h (51.25 MPH) in second gear at 5500 RPM

So the calculated numbers of 31 MPH & 51 MPH are right on the money.

I would have been embarraced if they had not been correct.... although I could have blamed it on conversions (man I hate imperial for doing this kind of work..... I usually use meters, Newtons, Newton-meters and Km/h)

[kinkyllama]

Just kinda of woundering cuz when i dyno my car before the turbo it will have heavyier/bigger wheels on it and after the turbo it will probably have smaller/much lighter wheels (i cant help that).


How much of a difference do you think 10 pounds a wheel and an inch bigger in diameter (wheel only, not wheel and tire) will make? Also with an inch bigger then there is more weight on the outside

[PrecisionBoost]

Well.... yes.... it will make a difference....heavier wheels will decrease your dyno numbers a little..... but you should be less concerned with the physical numbers you made and more concerned about what the power band looks like.

It's not about "PEAK POWER" it's about how much you make all the way along the torque curve.

I honestly don't know how much power loss you will see with heavier wheels.... it could be as little as 1hp or as much as 10hp.... it depends on a number of factors.... even different designs of wheels with the same weight will give you slightly different dyno numbers.

Basicly more weight near the tire will require more power to spin it up.

If you have two wheels that weigh 22lbs..... one has the majority of it's weight near the tire and the other close to the hub....... the one with the weight on near the tire will require more power to spin it up.

I don't want to get too complex and start doing math on here.... (since I tend to do that a little too much ) but you can trust that I know what I'm talking about.

I will see if I can dig up some info on how much tire weight affects power.

[Efratech]

So, gearing also makes a difference then?

I dynoed my car with a long 3rd gear (around 180 kmh at 7000 rpm)... now i have a shorter 3rd gear (around 150 kmh at 7000 rpm)

last time i got 135 whp, and it was a bit scary reving the hell out of it on the dyno. but i did felt the engine kinda pushing too hard with that long 3rd gear.

[kinkyllama]

Oh i understand the whole wheel weight and size thing perfectly. I was just woundering how much power it might effect. Ive tried to dig stuff up and didnt have much luck. Actually most people disagree that if you have two wheels, one 15" and one 18" the same weight/design that the 15 will give you more power. But i know better! lol

Also more weight towards the outside means not as good braking.