I'm getting picky here but fuelers in the states are now being estimated between 9000-10,000 HPV8Patrol wrote:Manifolds do create a reasonable amount of back pressure, this is why so many people fit headers/extractors when searching for extra horsepower, that combined with larger diameter exhaust tube and more "open" mufflers, twin systems, etc all decrease back pressure.
The only true zero back pressure setup would be a straight out exhaust port for a minimul distance.
I know I said above that drag cars run a zero backpressure and that wasnt exactly right, they do have a very small amount. The pipes we see comming off of the "Funny Cars" and Rail Cars" is gives a very low pressure reading, its the 90degree bend that gives a regulated control of backpressure that these engines need. You must ofcourse take into account that they are 6500 HP engines and run totally differant fuels to the stock familly sedan...... they also only last a few minutes of running before requiring a full rebuild, many topfuelers will actually replace pistons,crank,& heads between runs !
On another track the turbo diesel engine really doesnt need that much of an exhaust, the turbo does a fair amount of the noise reduction that the EPA require and it also gives back pressure at the same time, the problem here is that we have to by law have the exhaust fumes exiting from the behind the rear most opening door for safety reasons, realistically the exhaust pipe is just plumbing that takes the fumes out where they have to exit.
This is why many members on OL with turbo diesel engines go for that 3" exhaust on their 4bys..... the muffler thay fit just needs to quieten down that "crack" from the zorst.
A well designed zorst system will see gains in power, ecconomy, engine life, a poor system sees the opposite. I have seen the local "boys" and their 2litre screamers actually drop top speed because of an over opened up zorst system...... you have to remember that the manafactures designed their engines to have some degree of back pressure.
There are many differant variants involved in a good system and one has to consider all of them to get a 'good flow" thats not detrimental to the motor.
Things like ........... is it a ....
inline motor ( 4 cyl & 6 cyl typicaly ) where the exhaust ports are all on the same side.
A "V' engine ( V6 , V8, V10, V12 ) where the ports exit from bothe sides of the engine.
a rotary engine ..... whole new kettle of fish !
Then we have to look at the fuel we run .....
The petrol we get here in Australia is crap compared to what Americans use ..... you would not belive the differance between it !
Even the diesel we have is of a low std compared to other countries.
Methanol fuels are cheap to produce but the volume a motor consumes to do the same miles is huge in comparison to running on petrol. Sure you get a 30% horsepower increase but you use 4 times as much, not to mention the mods a petrol motor needs to run methanol correctly !
LPG is one of the better fuels we have the chioces of and again it has differant requirements both on the intake side aswell as the exhaust side.
Nitro......... very few can afford this mothers milk let alone the engine !
So with all that to consider you can begin to imagine the exhaust differance requirements between a non turboed V10 diesel motor and a rotary motor running on nitromethane......
Engine mods also come into consideration......
add a supercharger and a differant back pressure is required,
Up the compression ratio from 6-8 to 1 ( familly sedan) to 10 - 11 to 1 and start lookin at straight LPG or Methanol + a new back pressure requirement.
grab a 500 cubic inch alloy block, stuff some $20,000 heads on it, add a blower, plus an injection setup and fuel it with nitro and all ya need is 3' long extractor pipe with a bend half way along it per port !
Its the age old question ........
How Fast Can You Afford ?
Kingy
and aussie fuelers approx 7500 HPNice to see you listed half of the 100,000 variables for everyone to scratch thier heads over
I'd love to see a nitro burnin rotary, untill then our $25/L petrol SBC will have to do 
Low 8's and 930HP here we come 