xbgs351

For those without a physics or engineering background, who may not have come across wave theory, I will give a brief explanation of how pressure waves are used to improve performance.


Picture a wave of pressure flowing down a pipe. This wave of pressure (called a compression wave) will have a slight pulling effect on the gas so that the gas moves in the same direction of the wave.
I will draw a compression wave like this: ^.


Next, picture a wave of low pressure flowing down a pipe. This wave of low pressure (called an expansion wave) will cause the gas to move in the opposite direction of the wave. I will draw an expansion wave like this: v.


Now picture the pipe being closed at the end.

-----------------------
I
-----------------------

When a wave traveling leftwards reaches the end of the pipe it is reflected and heads back to the right.

-----------------------
I ^ <---
-----------------------
becomes
-----------------------
I ^ --->
-----------------------



Now picture a pipe with the end open.

-----------------------

-----------------------

When a wave travelling leftwards reaches the end of the pipe it is reflected and heads back to the right. What it also does is change from an expansion wave to a compression wave or vice versa.

-----------------------
v <---
-----------------------
becomes
-----------------------
^ --->
-----------------------

or

-----------------------
^ <---
-----------------------
becomes
-----------------------
v --->
-----------------------
So what does this mean? Lets look at the exhaust for instance. Here we have positive pressure and hence compression waves. As the wave travels out of the heads it pulls the exhaust gas with it. When the wave reaches the collector which is seen as an opening, the wave is reflected and becomes an expansion wave which also pulls the exhaust gas out.

On the inlet side we may see low negative pressure. As an expansion wave travels down an inlet runner the air/fuel mixture is being pushed back towards the plenum, but when it reaches a closed valve, the wave is reflected and starts pulling the air/fuel mixture towards the cylinder. When the wave reaches the plenum which is seen as open end to the pipe the reflected wave becomes a compression wave and pulls the air/fuel mixture towards the cylinder.

But what if the valve is open?

That is the basics. Runner lengths and valve timing can then be selected so that at certain rpm's the inlet manifold pushes more air/fuel mixture in, and the exhaust system pulls out the exhaust gases and pulls some air/fuel into the chamber.



XBGS351

edit for spelling and to remove unintentioned bad feelings. 7/5/04

falcon coupe

What is the point of this post ?

davway

someone actually turned up to uni??
meh... i pay exhaust people to figure that stuff out!

__________________
HSV Herpes Simplex Virus
GAME OVER!

xbgs351

So you can make more horespower by understanding what goes on inside the motor.

By tuning inlet and exhaust runner lengths and diameters as well as choosing a camshaft with appropriate timing and lift, the engine can have a Volumetric Efficiency of well over 100%. How do you think the V8 supercars get so much horsepower out of a normally aspirated 5 litre motor?

horus14

Rev it to 7500rpm ?

xcgxl

Now I remember why I quit engineering. Blah blah blah blah blah blah. If I move my hand up and down fast enough thats called "stroking it"

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1978 XC Fairmont GXL, Emerald green, Jade Int. 351C, 750 VAC, C10, 9" LSD
Air, steer, power windows................

xcgxl

A V8 supercar is a technological dinosaur compared to the excellence that is a Boss 290 GT-P. Windsor engines and 9 inch diffs, compared with quad cams and irs. Crickey thats what you have to do to a Ford to make the commodore competitive. Put the old pushrod engine in it so they are equal, ha ha ha.

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1978 XC Fairmont GXL, Emerald green, Jade Int. 351C, 750 VAC, C10, 9" LSD
Air, steer, power windows................

xbgs351

Sorry vice versa. 302 puts out around 620 hp which = 2.05 hp/cubic inch.

The Boss 290 puts out 386 hp which from a 5.4 litre motor ( around 330 ci). Thats 1.17 hp / cubic inch.

In my opinion the Gen 3 motor is superior to the Ford Modular motor as:

It weighs a lot less
It takes up far less space
It has a superior bore/stroke ratio
Can be revved harder due to the shorter stroke.
Costs less to manufacture

Just because it's a ford motor doesn't make it a good motor.

xcgxl

Have they fixed the oil problems with Gen 111? What about the main bearing failure problem? Thats the one that happens because the engine is meant to be for automatics and cant handle the "thrust" from hard gear changes with a manual. Commodores are seriously overrated and so many people who know nothing about anything mechanical have been conned into buying them on image alone. The image I get is from the 4 clyinder shitters buzzing around europe (and N.Z) with Camira motors in them, ha ha. Peter Brock and the like will have you believe the Commodore is an Australian car. The Falcon is. There i nothing like it anywhere else in the world. Aussie designed and built 6cyl. engine, auto ..... OK they copied the diff but 2 out aint bad.

__________________
1978 XC Fairmont GXL, Emerald green, Jade Int. 351C, 750 VAC, C10, 9" LSD
Air, steer, power windows................

fairlanebyford

"Sorry vice versa. 302 puts out around 620 hp which = 2.05 hp/cubic inch.
The Boss 290 puts out 386 hp which from a 5.4 litre motor ( around 330 ci). Thats 1.17 hp / cubic inch."


Sorry? 302 ....... 620 HP? Ummmm, would that be a modified 302 perchance? Would the 386hp 330ci be unmodified?

A very good article on the web that phrases the above diatribe somewhat similarly is http://www.yawpower.com/jantech.html


PS; Isn't saying "For those without a physics or engineering backgraound (sic) I will give a brief explanation ...." a little condescending? Maybe we (I!) don't have a physics background but I'm not so stupid as to not understand such concepts.