Header design vs power

[TURBOZ]

I cant see how it would make that much of a difference on a turbo car, but I would like to see others points of view. Has there been much to gain on a turbo car with equal length headers compaired to something I have which are not?

 

[bruce]

Tuned header lenght, counts primarily for when NOT in boost, or your're running a Stage motor open exhaust and shifting at 7 grand, there maybe a little to be found, but for the none exotics of the crowd, the money for headers can be spent more effectively on other things.

Anything you do to fine tune one area of the curve will be at the detriment of someplace else.

 

[PCS74]

Theoretically, correctly designed equal length headers would be advantageous. In practice, on a street car, I doubt they would be designed correctly or be worth the investment.

The principals of engine operation do not change between a naturally aspirated and forced induction engine. It can be beneficial to think of the forced induction engine as a naturally aspirated engine operating in a high pressure environment.

Chris S

 

[Ormand]

As PCS74 mentioned, the "principles of engine operation" don't change. BUT... there are different effects from the same principles involved in a turbo engine and an engine without a turbine in the exhaust system, either supercharged or normally aspirated. In the turbo engine there is little or no "ram effect" which can actually pull the gasses out of the cylinder. The turbine, when it is working, will always require pressure in the exhaust system, so the scavenging effect will be minimal, if any. In addition, the requirement of combining the exhaust from all cylinders and running to a turbine inlet makes it almost impossible to get "equal length" tubes, for tuning. Of course, if you put the turbo in the trunk, like that Camaro set-up.. but that's not a Buick! For a race engine, running in a narrow power band, you can set up the turbo to operate with less back pressure, and then the "tuned headers" will be more useful, as Bruce mentioned. But a turbo set up that way will have a lot of lag, and be a pain to drive on the street. Bottom line.. what Bruce said. There are better things to spend your money on.

 

[bruce]

Originally posted by PCS74
It can be beneficial to think of the forced induction engine as a naturally aspirated engine operating in a high pressure environment.

I don't know if I fully agree with that.

In runner/plenum design, in a N/A application, they design things so that there are some higher then atmospheric waves within the plenum to help with cylinder filling withing specific and limited rpm bands. On a boosted engine, there is no need to design the intake to function like that. While you can configure it to do some better cylinder filling while in N/A mode, would that be of any help on a GN?. Almost without exception the GNs build boost below the stall/flash speed of the converter, so what gain would there be?.

And on the exhaust side, tuned lenght headers are for timing a low pressure area to be available as the exhaust gas slug is leaving as the exhaust is opening. With a turbo the high to low pulsations within the headers is going to be dramatically reduced.
The exception being when you go to twin turbos, and can get a true Bucci effect type exhaust system. Or a really well dual scroll turbo setup.

 

[n20junkie]

header design for a boosted engine is not the same as in a naturally aspirated engine, but it is important none the less, when the engine is operating in vacum it depends on header design to help the engine operate efficiently to aid in getting the turbo spooled up, then once it ir producing boost and high cylinder pressure it is good header design that will cause the gases to merge in an efficient way to prevent excess turbulance inthe header, and the smoother the air the cleaner the air the faster it can enter the turbine houseing and the faster it can turn the turbine and exit the housing, which makes for a efficient engine and the more efficint the the engine the more power it can develope, even though the exhaust is in a pressurized state its design will effect in every way in which the gas in it flows, but a bigger turbo is a little more bang for the buck i think too.
grant

 

[PCS74]

The turbocharger does not negate the need for efficient exhaust scavenging, it increases it.

Exhaust manifold diameter and length will change with every application, that is a given.

The over-scavenging of combustable air and fuel will primarily depend on the valve timing, the airflow dynamics of the intake runner/cylinder/exhaust runner and intake/exhaust pressure ratio. Over-scavenging is highly unlikely on the Buick, but turbocharged vehicles can achieve intake/exhaust pressure ratios >1.

Pressure pulses are still created in the intake and exhaust. Wave velocity will be reduced due to the increased air density and the amplitude will be diminished, but wave tuning can still be used to improve intake and exhaust flow. Once you approach the mach index, airs ability to transmit waves is reduced, but you are going to begin loosing power at that point anyway, wave tuning or not.

Comparing the turbo buick engine to a naturally aspirated engine in a high pressure environment is a stretch, you are all correct. With more modern designs it works very well.

Chris S

 

[Ormand]

Over-scavenging is highly unlikely on the Buick, but turbocharged vehicles can achieve intake/exhaust pressure ratios <1.

I think you meant the >, instead of the <, although it is close to correct as it is written. The intake pressure is almost always less than the exhaust under boost, giving a value of intake/exhaust of less than one. It is POSSIBLE, on highly tuned race engines like Formula 1, to get close to or, greater than 1, but in most street applications, the number will be close to 1/2. Since the exhaust pressure during boost periods will be significantly higher than the intake, the exhaust valve in a turbo engine should close pretty soon after TDC, and there is little/no possibility of using exhaust tuning to "pull" spent gasses from the combustion chamber. (Even on a normally aspirated engine, tuning headers for a 90 degree V6 is tricky) Some of the features used on NA headers should work well on our cars, though, like the "anti-reversion" design used by one of the big header vendors. And smooth transitions, gradual bends, etc, to get the flow to the turbine without losing energy or unnecessarily increasing backpressure are good, too. But it's hard to put a number on these, since there are few if any dyno tests. Just seems like there are better ways to spend a buck.

 

[bruce]

Originally posted by PCS74
The turbocharger does not negate the need for efficient exhaust scavenging, it increases it.

To really run headers with long enough primaries to be really effective on a street GN, the temps and velocities would be really down.

Spooling a turbo, is primarily about the pressure drop across it. Yes, there will be a sweet spot velocity wise.
But, if you really want to get the exhaust correct on a GN it's about doing it using Bucci's principles.
And I'm restricting my comments to street application GNs as I believe that is what the threader starter was talking about.

 

[PCS74]

Yes you are correct, I meant pressure ratios > 1 and it was in reference to correctly designed racing engines as you mentioned(2 porsche vehicles I know of personally, and a couple others I have heard of from reliable sources).

I don't mean to sound like I am advocating new headers, I am not. Definately better places to spend the money on a buick engine in the bang-for-the-buck department. TurboZ was looking for some different points of view and I was just injecting something different to think about.


Chris S