What are the advantages/disadvantages of a divided or tangential divided housing/manifold versus a non divided housing? I require enlightenment. Thanks

 

Divided housings keep the exhaust flow from each rotor separate until they pass through the turbine. This helps spool up the turbo a few hundred RPM earlier in most cases. I do not know of any disadvantage.

 

Yea it creates less turbulance, so you get more flow. I think its useless unless you have a manifold that has a divider as well.

Correct me if im wrong, but doesnt this do the same thing as a collected header? takes the exhaust pulse from one rotor, and helps pull the one behind it from the second?

 

yet it seems people believe that the best NA (rotary) power will be had from an uncollected header/true dual all the way back. it's one of those great mysteries i guess. for piston guys though, you often see v8's with "dual" exhaust all the way back, but then they put in those crosspipe pieces for the effect you are referring too. i would imagine it makes alot more difference when it is as close to the engine as the exhaust manifold and turbo are though. maybe some more people will chime in about this.

 

A divided housing is designed to speed up spool AND have less back pressure at higher RPM’s. These work only on certain engine configurations were the exhaust pulses are even, like on the rotary (2 rotor) or on four cylinders. It keeps the exhaust pulses from mixing with the adjacent exhaust port. There is NO scavenging effect like with a collected N/A header, it works opposite. In a turbo system because there is backpressure, having a collected system doesn’t work as well unless you have the entire system tuned to work with one another. The result of a tuned collected turbo system generally is a LARGE turbine section and large A/R values for the turbine housing in order for the collector to work properly and results in extremely peaky power bands. Not good for a streetcar and this only works in small bands of RPM for a narrow torque peak. (keep in mind, the cast manifolds or even tubular collected systems available are not tunes at all). A fully divided system keeps the two exhaust pulses from interfering so there is less back pressure per port because one is not running into the other (because its not easy for exhaust gases or energy to back up once its past the turbine wheel). The result is a faster spool up and less exhaust backpressure. Generally because there’s a quicker spool you’d go up a A/R turbine housing size and still have better spool up AND better high RPM because less back pressure then a open valute turbine or non-divided.

On a collected N/A system, they work off of scavenging effect. Once the exhaust pulse leaves the port and travels down the runner it gets to the collector. The collector acts as a ventury and when this gas pulse reaches it, there’s a momentary low-pressure area as it shoots past the collector. The result is a pull on the other exhaust runner. So one exhaust pulse will create a pull or momentary low-pressure area to help scavenge the other exhaust port/runner. This only works at certain RPM’s and makes for a narrow torque peak if considering exhaust tuning only. At other RPM’s this system can hinder flow and one exhaust pulse can create backpressure for the other, thereby loosing power in these RPM bands. Also note, any significant backpressure in the exhaust system will not allow this all to function properly. Too much backpressure will make the exhaust pulse stall at the collect rather then allow it to shoot through it making a low-pressure area behind it. A turbo would be a good example of significant back-pressure in the exhaust stream.

On a true dual N/A exhaust it simply keeps the exhaust pulses separate (as does the divided turbine). There’s no interference from one pulse to another. These systems tend to have nice broad power bands (great for a street car) but wont make quite the peak torque a tuned collected system would (collected better for racing, were generally your always in high RPM and in a narrow power band)

Having said all this, now you know that a collected N/A system will have a higher peak out put number and a true dual will have a broader spread generally, there’s a whole lot more to it then this little thread.

A divided turbine housing works better for spool and top end because it keeps the pulses separate so one will not add pressure/resistance to the other pulse. Because this less back pressure and quicker spool you can go up in A/R there by gaining even more flow. A turbo system will hinder how a collector is suppose to work, so collecting is not optimal unless it’s a high rpm low restriction turbine. The divided system not only uses pressure to spin the turbine, but it also uses flow and sonic forces which in a collected system would be diluted by pulses from one another due to restriction that is the turbine.

The dual scroll or divided turbine works well on the rotary due to its 180-degree exhaust pulses. It works well also on four cylinder engines if cylinders 1 and 4 are collected and run on one scroll and cylinders 2 and 3 are collected and run in the other scroll. This imparts an equal 180 pulse on the turbine as well.

Now on strait 6, V6, or V8 configurations the dual scroll won’t work well due to exhaust pulses not being equally timed or in fazed unless you bring exhaust runners from adjacent cylinder banks crossed over. Even a twin turbo V8 unless it has a 180 degree crankshaft. This brings up another point. The reason for V8’s having a cross over or “H” pipe is just because the aforementioned reason. The cranks typically are NOT 180 degree so their headers (unless exhaust runners cross over from one side to another, which is impossible in most circumstances due to space) aren’t 100% optimal so a cross over pipe is used to equal out pressures from left to right banks.

Does this mean that a collected turbo manifold and open valute (non-divided) turbine is crap? NO, just not as optimal as a fully divided system. The HKS cast undivided manifolds work great and get the job done, but go tubular divided mani and turbine, you can expect quicker spool and better top end. How much? Depends on your system and designs of a number of things like porting, runner dia, runner length, exhaust system, compressor used, etc. etc. typically expect a low gain of 500 RPM quicker spool to as much as 1500.

Hope I cleared things up more then I confused….

~Mike…………

 

wow nice post, good info

 

Yeah, especially since another "guru" BDC claims that it doesn't do jack ****...

Entire thread:
http://www.teamfc3s.org/forum/showth...?threadid=8108


-Ted