Extractors and turbos
Posted: Sun Mar 15, 2009 4:40 pm
I know the reason for extractors on NA engines but what about on turboed engines? Are they needed since the turbo itself acts as a restriction and increases back pressure etc?
is this what your talking about? coz i would still call it a exhaust manifold and not extractorstweak'e wrote:you can have them. its just a custom manifold thats tuned more than a stock one. not worth bothering with unless your doing an extreme engine build.
That looks like what I would call a "split-pulse" manifold, intended to make better use at low revs of the pulsatile nature of exhaust flow, helping the turbo to spool up faster.KYSI wrote:
The length itself doesn't matter other than shorter is better. You can't pulse tune when the exhaust gas changes temperature soo much.-Scott- wrote: The length of the individual runners is important; get it wrong and you may not be much better off than a simple log manifold.
True; absolute length is probably not important, but to take advantage of the "split pulse" concept all runners should be as close to the same length as possible. Otherwise, what's the point of a split housing, such as that manifold is designed for?KiwiBacon wrote:The length itself doesn't matter other than shorter is better. You can't pulse tune when the exhaust gas changes temperature soo much.-Scott- wrote: The length of the individual runners is important; get it wrong and you may not be much better off than a simple log manifold.
Yep.-Scott- wrote:True; absolute length is probably not important, but to take advantage of the "split pulse" concept all runners should be as close to the same length as possible. Otherwise, what's the point of a split housing, such as that manifold is designed for?
yeah thas one example. i've seen other deigns where they pair up certain ports, kinda like a short 6-3-1 or 6-2-1 extractors. bit more common with petrol motors as you have some RPM to play with.KYSI wrote:is this what your talking about? coz i would still call it a exhaust manifold and not extractorstweak'e wrote:you can have them. its just a custom manifold thats tuned more than a stock one. not worth bothering with unless your doing an extreme engine build.
It is supposed to work best on 6 cyl engines and the result if done right is earlier spool.tweak'e wrote:yeah thas one example. i've seen other deigns where they pair up certain ports, kinda like a short 6-3-1 or 6-2-1 extractors. bit more common with petrol motors as you have some RPM to play with.KYSI wrote:is this what your talking about? coz i would still call it a exhaust manifold and not extractorstweak'e wrote:you can have them. its just a custom manifold thats tuned more than a stock one. not worth bothering with unless your doing an extreme engine build.
complicated, exspencive and gives small gains. but if your chasing every last drop of power and have unlimited budget........
With my petrol fun toys, i was under the impression, longer runners = torque curve change, shorter = power curve.KiwiBacon wrote:The length itself doesn't matter other than shorter is better. You can't pulse tune when the exhaust gas changes temperature soo much.-Scott- wrote: The length of the individual runners is important; get it wrong and you may not be much better off than a simple log manifold.
Equal length headers like that will be better at high end, but for transient response the smallest dead volume wins. Notice all the modern diesels have the most compact headers they can, helps to keep the turbo spooled to meet emissions.
Are you talking intake or exhaust, na or forced? Tuned length runners work best at a given rev range - the shorter the runner, the higher the rev range. And, as others have mentioned, I believe forced induction systems really prefer shorter, more for reduced "dead space" to reduce lag.berad wrote:With my petrol fun toys, i was under the impression, longer runners = torque curve change, shorter = power curve.
considering power is calculated from torque and rpm, if the torque changes the power changes at the same point.berad wrote:With my petrol fun toys, i was under the impression, longer runners = torque curve change, shorter = power curve.KiwiBacon wrote:The length itself doesn't matter other than shorter is better. You can't pulse tune when the exhaust gas changes temperature soo much.-Scott- wrote: The length of the individual runners is important; get it wrong and you may not be much better off than a simple log manifold.
Equal length headers like that will be better at high end, but for transient response the smallest dead volume wins. Notice all the modern diesels have the most compact headers they can, helps to keep the turbo spooled to meet emissions.
That only works on non-turbo engines. With a turbo your gas temp changes constantly, which changes the speed that pulses travel through the gas. The result means pulse tuning is limited to keeping them evenly spaced (which is where the equal length comes into play).berad wrote: With my petrol fun toys, i was under the impression, longer runners = torque curve change, shorter = power curve.
Thats right. Thats why the variable intake length mechanisms seen in the N/A falcon 4.0L's are locked in the turbo variants.KiwiBacon wrote:That only works on non-turbo engines. With a turbo your gas temp changes constantly, which changes the speed that pulses travel through the gas. The result means pulse tuning is limited to keeping them evenly spaced (which is where the equal length comes into play).berad wrote: With my petrol fun toys, i was under the impression, longer runners = torque curve change, shorter = power curve.
IIRC a four stroke cylinder fires ever second revolution ? making it two firings / rev ?coxy321 wrote: (from only four cylinders firing per revolution).
My bad - you are spot on the money there. Always half the firing per revolution as there is cylinders.MightyMouse wrote:IIRC a four stroke cylinder fires ever second revolution ? making it two firings / rev ?coxy321 wrote: (from only four cylinders firing per revolution).
Of course the underlying issue is as you described - less firings, greater need to harness pulse energy.
Yes, that's why all the factory diesels have the smallest volume exhaust manifold they can use. Keeps lag to a minimum so they can meet euro 5 emissions and still wind 280hp from a 3 litre diesel.DAMKIA wrote:I would have thought that with turbos (petrol and diesel) that keeping all the turbo to engine volumes at a minimum would have been more important than any equal length issues.
The minimal volume b/t the turbo and engine will reduce the amount of gas exhaust that is required to spin up the turbo (if you like, "primary lag") as well as reduce the time it takes to pressurise the inlet manifold ("secondary lag").
In the exhaust to turbo example it should also reduce the heat loss if the manifold pipes are shorter and thicker (volume to surface area ratio greater). The turbo will have a natural damping effect ("elastic" effective volume effect) on any exhaust pulses that may scavenge gas from the cylinder.
The other point to mention, most turbo engines run around no valve overlap, where the typical NA setup with extracters can run heaps.DAMKIA wrote: From what little I know, tuned pipes of any description are only of value in high or contant RPM engines where you are trying to scavenge as much exhaust gas as you can out of the cylinder.
IMO, an exhaust manifold is exactly that. An aftermarket manifold designed to improve the path/flow of exhaust gasses is call a set of extractors. Also, turbo manifolds are just turbo manifolds - however i think its fair that people call the custom units extractors.zagan wrote:isn't extractor just the nick for exhaust manifold?
I never really heard of anyone making out an extractor is sonething different.
Bit like Torque converter is the same as stall converter or stally.
That pic would be a single bank, as the exhast all ends up at the 1 point, I that it the other piping is a bypass for excess exhuast gas, unless it's for a twin turbo setup.
LOL potato cakecoxy321 wrote:IMO, an exhaust manifold is exactly that. An aftermarket manifold designed to improve the path/flow of exhaust gasses is call a set of extractors. Also, turbo manifolds are just turbo manifolds - however i think its fair that people call the custom units extractors.zagan wrote:isn't extractor just the nick for exhaust manifold?
I never really heard of anyone making out an extractor is sonething different.
Bit like Torque converter is the same as stall converter or stally.
That pic would be a single bank, as the exhast all ends up at the 1 point, I that it the other piping is a bypass for excess exhuast gas, unless it's for a twin turbo setup.
Any of you northerners want a potato cake??