If I were to use a divided manifold with a true twin scroll turbo, is there any benefit to equal length runners since 1&4 and 2&3 don't meet until they're INSIDE the turbine? In addition to that, couldn't you use this to your advantage by having incredibly short runners on 2&3 feeding the "spool response" side of the twin scroll? Am I missing something here?

 

The benefits from using a divided turbo manifold, and a running a twin scroll (not divided I.e. Borg Warner EFR) turbine housing are extreme efficiency and usable power. The engine has to work less to make the same power, which transfers to effectively improving your driving experience. This is done by increasing exhaust gas velocity by pairing common cylinders 1/4 & 2/3 so there is no turbulence (restriction) inside the merge collector or turbine volutes. Increasing exhaust gas velocity also means for reduced spool times as the motor can breathe better allowing for better transient response.

When using an "equal length" manifold you have to be careful, as equal length doesn't mean equal flow. You would be better using a device like a quick spool valve on an open mmanifold to further increase velocity, but you already have the making for a spool monster setup by using "twin scroll"

 

Very true! I always see companies claim their manifold is equal length, and yeah that's fine and all but when one runner has a two 45* bends on it and another has two 90*s and a 45*, doesn't matter what the length is. One of the best things we have bought for the shop is those Lego kits for headers, lets you mock up a set of headers, and measure, add the total angle of bends used and move forward from there.

 

I absolutely agree that the "equal length" moniker ignores the importance that bends have on flow. I guess a better way to phrase my question would be, as long as the runners for 2&3 are similar and you're flowing into a twin scroll housing, having longer runners with more bends on 1&4 shouldn't have an impact right? Especially if the short, minimum bend runners for 2&3 feed the more responsive side of the twin scroll housing right?