Torque or HP..Which is the problem????

[karlblues2]

Hi guys
On the Oz Audi forum, one of the local tuners is asserting a maximum safe HP for an Audi B6 1.8 engine is around 300HP. I understood from threads on this forum that torque is the major killer of engines and bending of conrods vide purely a HP rating. Have I missed the point
Attached is his response. Is the last paragraph technically correct
Cheers guys
Karl

HP and Torque are directly related.

Torque = (HP x 5252) / RPM

In essence with the Current B6 engine actually are much weaker
and can not stand as much torque, and therefore HP.

In a stock engine the weakest point generally is Con Rod and Rods Bolts.
If you look into the design and dynamics of rotating assemblies, you will find there is more stress on a Conrod and Crank on the Return Stroke and less on the compression.
Otherwise why would you need to upgrade rods bolts? They do almost nothing on compression, but old bigend together on return stroke.
As the RPM increase, stress on return stroke on Conrod, rod bolt and crank increase dramatically and hence you will see from relationship that HP is the main factor.

[JSHADZI]

Hi guys
On the Oz Audi forum, one of the local tuners is asserting a maximum safe HP for an Audi B6 1.8 engine is around 300HP. I understood from threads on this forum that torque is the major killer of engines and bending of conrods vide purely a HP rating. Have I missed the point
Attached is his response. Is the last paragraph technically correct
Cheers guys
Karl

There are guys in the states here getting 400whp (480 crank HP) on B6 1.8's, if properly tuned.

[karlblues2]

There are guys in the states here getting 400whp (480 crank HP) on B6 1.8's, if properly tuned.

That's awesome. I guess the key part of your statement though is the last bit....'if properly tuned'. By that, do you mean substantial internal upgrades
Cheers for the response
Karl

[olsonjus]

Here is a stock internal 1.8t that makes 443whp

http://www.vwsport.com/viewtopic.php?t=8073

[S2central.net]

We need some proper, independent advice from the mechanical engineers on the forum - like Lee, Marco, Javad & Co.

There are some critical equations which define this behaviour. It is my understanding that torque is the enemy of conrods, but power and heat are the enemies of bearings and pistons. I won't even try to explain why at this time of the morning. Its all a bit grey as power and torque are intrinsically linked by engine speed which comes into play.

We need some objective description of the related mathematics on this so that a decent understanding can be quantified and shared with the non-mechies amongst us.

Paul

[S2-racer]

a friend of mine is running an S3 1.8T engine in a mk2 golf. because it wasnt mapped correctly its was pinking at high rpm and boost. i have heard of plenty of these engines going 'pop' recently, i would have thought that people could tune them by now??

it did achieve 349hp at the wheels, ONCE, but it did ruin the pistions and compression rings. all now replaced. and the engine is running sweet (but still only front wheel drive, lol!! and he tried to race me off the line in the wet, lmao!!)

[JSHADZI]

That's awesome. I guess the key part of your statement though is the last bit....'if properly tuned'. By that, do you mean substantial internal upgrades
Cheers for the response
Karl

Hello Karl, by "tuned" I mean engine management alone, proper timing and fuel calculations, on an otherwise stock internal motor. If properly tuned, most VAG motors are capable of insane power figures. Many of the arbitrary HP limits placed on motors are due to improper tuning, for example, excessive ignition advance that causes detonation and destroys a rod is often blamed on the rod's weakness, when in fact it was just a fuse for an improper tuning condition.

(quick, jammed our response below)
TQ will break things like driveshafts and transmissions, but ultimately, HP will blow up motors and bend rods as well. IMO, the relationship to TQ is that it is typically applied and relatively "low speeds", meaning the accelerative force is amplified in having to overcome the inertia of the mass of the car and drivetrain. TQ is often blamed for breaking things due to this, and often its true. Applying TQ when the mass is moving is much safer on components than applying it when the mass is still or having to overcome great inertia. You'll never break a drivetrain trying to acclerate on ice because of TQ or HP.

Regardless, 300HP seems awfully low for a properly tuned motor.

[karlblues2]

Hello Karl, by "tuned" I mean engine management alone, proper timing and fuel calculations, on an otherwise stock internal motor. If properly tuned, most VAG motors are capable of insane power figures. Many of the arbitrary HP limits placed on motors are due to improper tuning, for example, excessive ignition advance that causes detonation and destroys a rod is often blamed on the rod's weakness, when in fact it was just a fuse for an improper tuning condition.

(quick, jammed our response below)
TQ will break things like driveshafts and transmissions, but ultimately, HP will blow up motors and bend rods as well. IMO, the relationship to TQ is that it is typically applied and relatively "low speeds", meaning the accelerative force is amplified in having to overcome the inertia of the mass of the car and drivetrain. TQ is often blamed for breaking things due to this, and often its true. Applying TQ when the mass is moving is much safer on components than applying it when the mass is still or having to overcome great inertia. You'll never break a drivetrain trying to acclerate on ice because of TQ or HP.

Regardless, 300HP seems awfully low for a properly tuned motor.

Thanks for that I have an awful lot to learn Regarding your last statement though, if 300HP seems low, what torque would you expect with that HP on a stock internal B6 1.8 T motor I'm guessing that you could feasibly tune a car with 300HP, but with different amounts of torque. Is this true or is there a linear relationship between HP and torque achieved in any given state of tune

[Pisobiker]

This is a problem I've tryed to analyze a while back, and already discussed in a thread I sand back at:

http://www.s2forum.com/forum/showthread.php?t=322&highlight=conrods+stress

Anyway, without digging too deep in the problem, like the above thread was meant to do, as I already sayed many times, this is how I see the facts:

From a mechanical point of view:

A) The real force an engine delivers to turn the cranckshaft at each revolution is TORQUE (to be more precyse it represents the work the engine can produce at each cycle), directly related to pressure inside the cylinder on each combustion cycle, therefore force applied on top of pistons -> conrods -> cranckshaft etc.

B) Power is a measure of how much total work the engine can produce in a given period of time, as a multiplication of torque and speed (in this case rotational speed).
To make an example (maybe silly, but that's all I can think of right now) try to think of torque as a jerk you give, through a rope, pulling a hand-cart. Each time you give a jerk the cart will increase its speed, so if you increase the frequency of the jerks (keeping same pulling force) the cart will accelerate faster.

In this respect if a mechanical device is supposed to withstand a given load (torque), it doesn't matter if this is done while running at 2000 or 8000 rpm.
What makes difference might be "fatigue" stress (tipical of metals), which represents how many times the device (in this case the "conrod") can withstand a cyclical compressing + estending force. This is related to load applyed, so that while putting an X force at a given rpm, conrod might last Y millions of cycles, while at 2X force it might last less than 1/2*Y millions of cycles.

Going back to the hand-cart and rope example, lets say the rope can withstand a max of 10 kg stretching force, so if you apply one 10kg jerk per second or 100 jerks (10kg each) per second it doesn't make difference for the rope. But it does in the respect of acceleration, being power 100 times greater.


Problem with braking conrods due to too high rotational speed doesn't have anything to do with torque and power, but only about inertial loads of the reciprocating masses (pistons + part of the conrods) accelerating and decelerating 2 times each revolution. Those loads increase with the square of the rotational speed therefore, expecially in NA engine often greatly exceeding (in absolute value) combustion forces (see the thread I mentioned above).

As JSHADZI sayed, Hp also produce heat loads which may cause piston and valves damage, and, if this heat cannot be efficiently exchanged with the cooling system, lead to detonation with all the consequencyes for pistons and conrods.


Marco

[JSHADZI]

Thanks for that I have an awful lot to learn Regarding your last statement though, if 300HP seems low, what torque would you expect with that HP on a stock internal B6 1.8 T motor I'm guessing that you could feasibly tune a car with 300HP, but with different amounts of torque. Is this true or is there a linear relationship between HP and torque achieved in any given state of tune

Piso, thanks for the informative post, totally agreed.

Yes, since HP is a function of TQ and engine speed, where that TQ is produced relative to RPM results, mathematically, in different HP levels. Thus, making 100TQ at 2k rpm will result in a lower HP # than if you make that 100TQ at 4krpm. This is why you always see high strung, high rpm motors make much more HP than TQ, because as the RPM factor increases, so does the HP value in relation to TQ.

Typically, in a motor built by an OEM (ie VAG), with OEM cams and induction/exhuast, TQ will peak in the 3krpm range, thus producing a very simlar HP value to TQ.

Assuming you're using stock Audi cams, HP and TQ values will be very close to each other (but of course, turbo size, exhaust, etc can all contribute to this factor). These are broad generalizations to be used as "rules of thumb"

[S2central.net]

Applying TQ when the mass is moving is much safer on components than applying it when the mass is still or having to overcome great inertia. You'll never break a drivetrain trying to acclerate on ice because of TQ or HP.

This is ABSOLUTELY true, as Audi's works spec rally quattros rarely finished Irish tarmac rallies - such is the brutal nature of all that destructive torque when the wheels have such good traction onto tarmac. Sad but true...


Paul

[S2central.net]

Anyway, without digging too deep in the problem, like the above thread was meant to do, as I already sayed many times, this is how I see the facts:
Marco

Nicely put Marco - I had forgotten the failure scenario due to cycles per second and the squared nature of loads increasing with engine speed.

Over time I'm going to try and compile a paper (in the stylee of the 'Turbology' paper) on this stuff - blagging/compiling/extrapolating the info from the best books and posts on this subject. I *WILL* be asking for your assistance ! Lord knows when I'll get started on it so don't hold your breath...


CHeers,

Paul