Classic Audi - "Injecting" more power?

Classic Audi (http://www.classic-audi.co.uk/forum/index.php)

- Engine (http://www.classic-audi.co.uk/forum/forumdisplay.php?f=31)

- - "Injecting" more power? (http://www.classic-audi.co.uk/forum/showthread.php?t=13693)

Quote:

Originally Posted by 20vcqdriver (Post 162761)

Really, sure it was after 1995, I stand corrected. Removed the CAT on my TDi 1996, still passed the MOT:rock:

Diesels it doesn't matter!

I removed the cat from my 2003'T4 and it passed first rev of the engine.

"Injecting" more power?

@ MSH

Again, it's your opinion that lowered cars are ugly, but it's basic tuning knowledge that lowering the cars centre of gravity will enhance the cars handling. This combined with the fact that lowering springs are normally stiffer than stock springs.

Also I have mentioned that I have modified the standard air box and will not be fitting a cone filter as the major flaw with cone filters is heat soak.

No one should be fitting a straight through exhaust to a NA engine, as anyone who knows anything about engines will tell you, an NA engine needs a certain amount of back pressure in order to function correctly and efficiently.

As mentioned in my previous post a proper performance exhaust system is normally only marginally louder.

At the end of the day, what I find acceptable and what you find acceptable is obviously vastly different.

Do not under estimate us Northern Irish, we know a thing or two about cars!!

@ others

Petrol cars post 93 must be fitted with a CAT, diesel cars post 95 must be fitted with a CAT

Quote:

Originally Posted by Blackie (Post 162706)

For a 1.6?

Shit sorry no, it was for a 1.8/2.0

Quote:

Originally Posted by msh (Post 162750)

Well, how about valve overlap? Stock cam is designed not only with power and torque in mind, but also with stock intake and exhaust resistance in mind - but u want to change these resistances. After all, what happens when NA engine is equipped with straight pipe exhaust? Right, fuel and air mixture is flowing out, because exhaust has too less resistance.

Quote:

Originally Posted by Blackie (Post 162763)

No one should be fitting a straight through exhaust to a NA engine, as anyone who knows anything about engines will tell you, an NA engine needs a certain amount of back pressure in order to function correctly and efficiently.

Point of order Mr Speaker! :D

The old backpressure myth continues to crop up.

Theres only one instance when backpressure in an exhaust is a "good thing", in fact only one instance where its absolutely a necessary thing.
That instance is only when dealing with turbo charged engines.
The reason is this.
For a turbocharger to function it has to be driven by the pressure differential across the turbine.
Thats why when the wastegate opens and diverts exhaust gas away from the turbine it slows down and boost lowers.
Its the difference between a high pressure at the exhaust valve and a low pressure area downstream of the turbine.
No pressure differential= no turbine movement.
So, you want an exhaust system downstream of the turbo that is as free flowing as possible because???? because if the pressure in the pipe is higher than atmospheric it means you need to apply more pressure before the turbine to drive it.

Now, applying what we know about pressure differentials to an N/A engines exhaust system, we immediately notice it has no turbo,
However, supposing we just for a moment accept the myths assertions, that we need "some" backpressure.
How much and Why? Are the two questions i ask.

What result will occur if backpressure at the tailpipe is higher than atmospheric?
The result will be that it takes energy to pump that gas out rather than utilising the pressure differential ( high always flows to low! which is why cold water runs from a tap), of a high pressure gas exploding out the port into a low pressure area.
That energy gets robbed from the engine itself in the form of pumping losses when a high pressure exists inside an exhaust pipe.
An easy example i always use is to suggest placing a hand over ones mouth and then go run a mile or two in that condition....makes breathing hard both on intake and exhaust eh?

Same situation for an engine, low losses, low backpressure= a more powerful engine.

Backpressures a universally bad thing for power production. :tup:

Quote:

Originally Posted by 4v6 (Post 162771)

What about overlap?

When you improve the rest of the induction and exhaust tract youre simply making it more efficient in terms of inducing and exhausting gases.

The actual timing of how much is trapped in the cylinders isnt altered, only the amount of gases trapped for burning or exhausting changes, which is why removal of restrictions that have a measurable pressure drop across them, such as air filters and induction tracts, heads and exhaust systems alters the power output.

Point of order Mr Speaker! :D

The old backpressure myth continues to crop up.

Theres only one instance when backpressure in an exhaust is a "good thing", in fact only one instance where its absolutely a necessary thing.
That instance is only when dealing with turbo charged engines.
The reason is this.
For a turbocharger to function it has to be driven by the pressure differential across the turbine.
Thats why when the wastegate opens and diverts exhaust gas away from the turbine it slows down and boost lowers.
Its the difference between a high pressure at the exhaust valve and a low pressure area downstream of the turbine.
No pressure differential= no turbine movement.
So, you want an exhaust system downstream of the turbo that is as free flowing as possible because???? because if the pressure in the pipe is higher than atmospheric it means you need to apply more pressure before the turbine to drive it.

Now, applying what we know about pressure differentials to an N/A engines exhaust system, we immediately notice it has no turbo,
However, supposing we just for a moment accept the myths assertions, that we need "some" backpressure.
How much and Why? Are the two questions i ask.

What result will occur if backpressure at the tailpipe is higher than atmospheric?
The result will be that it takes energy to pump that gas out rather than utilising the pressure differential ( high always flows to low! which is why cold water runs from a tap), of a high pressure gas exploding out the port into a low pressure area.
That energy gets robbed from the engine itself in the form of pumping losses when a high pressure exists inside an exhaust pipe.
An easy example i always use is to suggest placing a hand over ones mouth and then go run a mile or two in that condition....makes breathing hard both on intake and exhaust eh?

Same situation for an engine, low losses, low backpressure= a more powerful engine.

Backpressures a universally bad thing for power production. :tup:

I think people get confused between backpressure and having a tuned exhaust. It has been shown that the likes of a 1.2 engine running a 3" exhaust will be slower than the same car on a 2" due to the speed of the exiting gasses being a lot slower. In a properly tuned /sized system on N/A engines (not applicable really to turbos where bigger is better) the speed of the gasses helps to initially 'pull' the gases out the engine as the exhaust opens following the sudden closure of the previous exhaust stroke. Have an article on this somewhere;)

Quote:

Originally Posted by 20vcqdriver (Post 162776)

I tend to work on the assumption that the correct tuned lengths are already being used and that its simply a back to back comparison, one with high backpressure (crimped pipes anyone? :D) vs one with low static pressure being tested.

Have a read of a book by the renowned automotive scientists, Philip H. Smith and John C. Morrison ( Scientific design of intake and exhaust systems) for more in depth ( very) info on this kind of thing.:tup:

Quote:

Originally Posted by Blackie (Post 162763)

@ others

Petrol cars post 93 must be fitted with a CAT, diesel cars post 95 must be fitted with a CAT

not true.

92J has a more lax emissions target.
92K has a more stringent emissions target which it is highly unlikely it will meet without a cat. Hence a cat isn't a legal requirement, what it does to the emissions is. If you in theory had a mega clean 92K reg car, it could pass without a cat.

Diesel cars do not need a cat by law. The cat is to remove soot particles, as long as your engine is in reasonable condition it should pass without a cat.

My 2003 VW T4 Caravelle (2.5 TDI 102bhp) was decatted in May 2010 and passed the MoT in September 2010, the smoke test only took 1 "rev" to pass (the tester said they normally take 4 or 5 "revs" to pass), but as there was no cat to block up with sooty crap (when taking a diesel with a cat for an MoT, get it warmed up and sit it at about 4500rpm to clear out the crap on the way to the test centre, something you don't normally do in everyday driving). No cat, no sooty crap, hence passed 1st "rev"

"Injecting" more power?

Quote:

Originally Posted by 20vcqdriver (Post 162776)

That's exactly what I'm getting confused with, sorry peeps.

Quote:

Originally Posted by pimpdriver (Post 162780)

diesel diesel diesel

Lucky brittons with their high quality fuel.