Blipping The Throttle

[hengti 2]

WOT TF??!

[PumaRacing 1]

Doesn't that depend on what part actually broke?

 

I mean, if the engine is trying to exert it's power on some components and you're restricting the movement of those components, (or components further down the chain e.g. the wheels) by applying a load/braking force then they are more likely to break aren't they ? To a lay-person (sp?) that may be interpreted as "you've blown my engine up".

 

Not saying the bloke is right, just trying to see why he might have said that.

 

You can't load any engine component more heavily on a dyno than you can by applying full throttle on the road or even full throttle with the engine stationary as per the question. That's the bit that people struggle with hence the point of this thread. Any time an engine is producing power that power is being dissipated against something whether that be a hill, the mass of the car or just the inertia of its own internal components. It might seem that there is no 'load' if the engine is revving with the car stationary but the load is in fact just the same as if the car were being driven or held back with a dyno brake. It's turning into kinetic energy of the engine itself rather than kinetic energy of the car or the dyno.

 

As an aside, many years ago when I was building engines for the XR2 Challenge series the scrutineer introduced a little computer device to check engine output and spot modified ones. This plugged into the ignition system and then controlled rpm by cutting sparks at random. You start the engine, apply full throttle and the computer then takes over and controls the engine speed. By bringing it up to a given rpm and then letting it accelerate flat out briefly between two known rpm points the computer measured the acceleration rate and compared it to datums for a standard engine.

 

This is actually a superb method of detecting power increases and is in fact potentially one of the most accurate engine dynos it's possible to create. Provided the component masses don't alter then acceleration rate is purely dependent on power at a particular rpm. There's no need to take the engine out of the car or use any other external machinery, the box of tricks only costs pennies to make, the gearbox and tyres are excluded from the equation so its pure flywheel power that's being measured.

 

The only problem in practice is that to get actual bhp you need a datum acceleration curve for each engine because the computer doesn't know how much the engine components weigh. However, even if these are unknown it can detect power increases from head porting, cams etc in percentage terms very accurately if a baseline curve is taken before the modifications are made.

 

An entire power curve takes only as long to measure as it takes the engine to accelerate once from idle to the redline. In other words about 2 seconds. Hardly any fuel is used, no need to take the car off the driveway and you can check dozens of combinations of jetting, cam timing, fuel settings in minutes. The measurement is so quick the engine can't overheat and a few seconds back at idle will dissipate any heat that has started to build up.

[DrSeuss 0]

Its alot harder to hold an engine at a high load situation for several minutes on the road when compared to the dyno. Also with the lack of efficient cooling (low air speed from the dyno room fans) you suffer alot of heat soak issues?

 

Thus your customer could be right, the dyno room produces abnormally high stress on an engine mostly thanks to the extended high load periods (assuming its during mapping).

[maturin23 10]

Is that the answer?, a bit blunt

 

I'm sorry but its sounds your on another ego trip again Dave, do you have a personailty?

 

That response has really let you down - I was enjoying the thread (as I've enjoyed your's) and your post was like a fart in a lift.

 

It was clear what the thread about from the start.

 

Do the decent thing and say 'sorry'.

[RichF 1 2 Cars]

Hypothectically, what if (and I really haven't bothered to think this through) the hill's so steep (or the dyno brake is so strong) that the engine can't turn the wheels ? Surely that increases the chance of something snapping ?

 

I agree that you can't load up the engine any more on a dyno than on the road, can only assume that either:

 

1. The bloke normally drove around using very little power thus not exposing the weakness in the engine.

2. The dyno operator was unlucky that the engine gave up whilst on the rollers, it could just have easily have happened when the owner floored it on the way to the session ! (but the average owner is obviously going to blame the RR session)

 

I await the flames

Edited March 11, 2006 by RichF

[Rippthrough 98]

Hypothectically, what if (and I really haven't bothered to think this through) the hill's so steep (or the dyno brake is so strong) that the engine can't turn the wheels ? Surely that increases the chance of something snapping ?

 

I agree that you can't load up the engine any more on a dyno than on the road, can only assume that either:

 

1. The bloke normally drove around using very little power thus not exposing the weakness in the engine.

2. The dyno operator was unlucky that the engine gave up whilst on the rollers, it could just have easily have happened when the owner floored it on the way to the session ! (but the average owner is obviously going to blame the RR session)

 

I await the flames

 

 

Your clutch makes a funny burning smell, and so do your tyres.

Edited March 11, 2006 by Rippthrough

[jonD6B 0]

You can't load any engine component more heavily on a dyno than you can by applying full throttle on the road or even full throttle with the engine stationary as per the question. That's the bit that people struggle with hence the point of this thread. Any time an engine is producing power that power is being dissipated against something whether that be a hill, the mass of the car or just the inertia of its own internal components. It might seem that there is no 'load' if the engine is revving with the car stationary but the load is in fact just the same as if the car were being driven or held back with a dyno brake. It's turning into kinetic energy of the engine itself rather than kinetic energy of the car or the dyno.

 

As an aside, many years ago when I was building engines for the XR2 Challenge series the scrutineer introduced a little computer device to check engine output and spot modified ones. This plugged into the ignition system and then controlled rpm by cutting sparks at random. You start the engine, apply full throttle and the computer then takes over and controls the engine speed. By bringing it up to a given rpm and then letting it accelerate flat out briefly between two known rpm points the computer measured the acceleration rate and compared it to datums for a standard engine.

 

This is actually a superb method of detecting power increases and is in fact potentially one of the most accurate engine dynos it's possible to create. Provided the component masses don't alter then acceleration rate is purely dependent on power at a particular rpm. There's no need to take the engine out of the car or use any other external machinery, the box of tricks only costs pennies to make, the gearbox and tyres are excluded from the equation so its pure flywheel power that's being measured.

 

The only problem in practice is that to get actual bhp you need a datum acceleration curve for each engine because the computer doesn't know how much the engine components weigh. However, even if these are unknown it can detect power increases from head porting, cams etc in percentage terms very accurately if a baseline curve is taken before the modifications are made.

 

An entire power curve takes only as long to measure as it takes the engine to accelerate once from idle to the redline. In other words about 2 seconds. Hardly any fuel is used, no need to take the car off the driveway and you can check dozens of combinations of jetting, cam timing, fuel settings in minutes. The measurement is so quick the engine can't overheat and a few seconds back at idle will dissipate any heat that has started to build up.

 

 

So when are you going to produce one of these devices for various 205's and hire it out on the forum?

[RichF 1 2 Cars]

Your clutch makes a funny burning smell, and so do your tyres.

 

sorry, I should have stated, assume perfect grip and the clutch doesn't slip (in this hypothetical situation).

[Rippthrough 98]

sorry, I should have stated, assume perfect grip and the clutch doesn't slip (in this hypothetical situation).

 

 

You put the brakes on sharpish otherwise your engine starts going the wrong way

[cybernck 400 1 Cars]

Martin> Puma is trying to get people to think about how the engine works

and his replies that are slowly revealing the answer are there for a reason,

therefore your attitude was very wrong and you nearly got a warn for it.

 

if he asked the question and fully answered it all in a single post, would there

be any point in posting it at all?

 

also... he's a bit older than you .

 

thanks.

[Ahl 4]

Boo, I was very wrong

 

Still, gave me something to think about

Yes, as above.

I was looking at it wrongly and thinking of sitting on my driveway, holding the thing at a steady 6000rpm as opposed to going up a hill holding it at 6000rpm.

 

Um, so in that case, it wouldn't be making full power I presume? Only enough torque to overcome the frictional losses at a steady 6000rpm?

[efy2bjg 0]

To bed in rings you ideally need short bursts of full throttle to generate high cylinder pressures and force the rings hard against the bore walls. The external load won't affect the cylinder pressures but it will affect how long and how quickly the car accelerates for.

 

This makes sense now, thanks.

 

But why does the engine note change under load?

[RichF 1 2 Cars]

You put the brakes on sharpish otherwise your engine starts going the wrong way

 

 

*sighs*

[Owain1602 0]

i presume then note doesnt change, say if you were going up a steep hill in a gear, then you actually keep the car at a set rev range for a period of time at WOT so you can actually hear the note produced by the engine properly, but if you were accelerating on a flat road or downhill with WOT then you cant keep the engine at a certain rev long enought to actually hear the notes produced. if this sint what you were referring to then im sorry.

 

also, if you thought that the fact that there was no load on the engine reving in the drive way meant it produced less power, then do you mean to say that on a rolling road it would produce less power than on the road becuase the loads put on the engine to turn the rollers will be less than to turn the wheels on the road?

 

you are trying to complicate things too much i think, someone said the car will be using less petrol at 6000revs on the driveway than 6000revs on the hill. what if you want to do an emission test on a car in the workshop, you're saying these readings will be wrong as it uses less petrol than it would on the road so an emission test in the workshop is useless??

[XLR8 0]

The way I see it is that, as soon a WOT is applied, the engine is producing the same power & using the same ammount of fuel at any given rpm as it is going up or down a hill or on a rolling road.

I remember reading it in your article Dave in 'PREPARING FOR A ROLLING ROAD TUNING SESSION - PART 1'.

So why is it bad to drive a car when the engine is struggling, eg driving at wot at 20mph in 5th, or towing a heavy load (damage to brakes & clutches aside)?

[Rippthrough 98]

The way I see it is that, as soon a WOT is applied, the engine is producing the same power & using the same ammount of fuel at any given rpm as it is going up or down a hill or on a rolling road.

I remember reading it in your article Dave in 'PREPARING FOR A ROLLING ROAD TUNING SESSION - PART 1'.

So why is it bad to drive a car when the engine is struggling, eg driving at wot at 20mph in 5th, or towing a heavy load (damage to brakes & clutches aside)?

 

 

The crank hammers the bearings into the block.

[C_W 3 1 Cars]

Yea, what is actually happening when you hear that really bad rattle when old biddy's are accelerating at 15mph in 5th?