you are sort of correct in that it would cause a small back pressure to turn the blades, but the energy used is waste energy, also the motor does benefit from a small amount of back pressure anyway, (think: loosing power due to hole in exhaust)

but the reason the small turbo is not as good at high exhaust levels (usually high revs) is that each tubo is designed with an efficiency curve and the turbo is starting to loose efficiency at higher revs, in that the energy of the exhaust is not transferred aswell to the inlet (whether this is mainly due to fin design, flow capability or bearings im not actually sure so i could get slammed too yet!)

this made me think, that i was thinking the other day about the "power per litre" figures that were used to compare diffrent motors the other day, i think it is actually a bullshit way to compare them, its like half arsed getting half way through the calculations and using half baked figures, as revs have not been included to the equation yet, think an F1 at 15000rpm and a dag car at 8000rpm, even though the F1 car is 3ltr or whatever and the drag 7 litre, the F1 cycles nearly twice as much per minute to make its power, i think the true way to compare which is best designed is "energy in vs. power out (or desired energy out)" which as air is free and abundant its basically "fuel consumption vs. power", that will tell you which is the better motor

pic didnt work??

SORRY! Pic is supose to be on the forum page it should be in my profile

Steve & Feral
I was quite amused at the two of you saying "that was a nice save" in relation to Doc Spock. Thats the way it really went. How else do you think i came up with the name, & hey, isn't that what it really means anyway? Sure looked like it to me.

Turbo
OK blokes, heres the real deal. There is NO FREE LUNCH. However some lunches are cheaper than others.
The mechanicly driven blower uses some of the power from the engine to drive it. Thats a given. The power required is closely linked to the pressure it makes. In some of the top fuel engines, i read somewhere that it can be as much as 300hp at 10,000rpm, but i will try to stay in the real world.

The single turbo offers some restriction to exhaust gas flow, & as boost pressure increases, it takes more power from the exhaust driven turbine to produce it. This means that "some" power is lost by virtue of backpressure. As boost & RPM rise, this power loss also increases as a direct result of back pressure increases. How much? I don't know, but it's more than some think. i decline to accept that any back pressure is good as it simply reduces the pumping efficiencies of the engine.

As for a hole in the exhaust leading to a reduction in engine output, i think someone is going to do some fast talking to sell me that one.

The reason for very large exhaust pipes on turbo engines is to keep pressure in the exhaust to an absolute minimum. This in turn maximises the pressure diferential between the engine side of the turbine & the outlet side. Its the pressure diferential that does the work so this in turn maximises the turbines efficiency.

At the end of the day we need to decide which benefits that each system has to offer, that suits our needs best. Having settled on that, we need to refine what specific features we seek & how much we pay, both in term of cash money, & in terms of gains versus losses. IE

Small turbo = quick response, but reduced top end.
Big turbo = slower build up of boost, but killer top end.
Turbo's lose some of the power that would have been made at the same boost, if the engine was without back pressure.

Positive Displacement blower = bulk power whenever the throttle is opened, at almost any speed, but it probably uses more power to drive it than other designs, then again, maybee not.
Blowers make the power without the backpressure, but drain some of this power directly from the crankshaft.

You will pay the price of driving an air compressor one way or the other, but how much [in terms of power absorbed in gaining the boost] is for you to ponder.

It's something to mull over
Chris

Quote:

not from what i have been told, i dont know the theory behind it but for example people always say use a 2inch exhaust on an a-series not bigger, it will perform better as the engine needs some back pressure, i know 2 stroke engines need back pressure but again not sure why

somone who knows please tell him

link to my turbo setup:
here tis

there is a lot less plumbing with only one turbo , on the exhaust and inlet to turbs anyway

Turbo cars have very large exhaust to reduce back pressure AFTER the turbo. After the motor is a different story. 1200RC is right, that back pressure is essential and is the reason tuned length manifolds perform better.

Quote:

This will cause turbulence and have the same effect as a restriction in the exhaust. I have experienced this loss of power myself in a turbo rotary where exhaust flow is of utmost importance. It is very noticeable

I would never have thought of it that way? I guess it just shows I should start doing cryptic crosswords.

No offence was meant or nasty connotations implied.

"Pax Ultimus" If that is correct.
I havent seen a latin book for 40 years.

Chris plain and simple Phunk means funk, plus who would want to #### doctor spock?

Its all cool mate