jibberjive

So I just read up on these and am curious about correct implementation of them (possibly on an S4). So just some thoughts from stuff I've been reading:

In order to see the benefit (quick spool) of the twin scrolls, you have to have a very properly implemented header design because all of its benefits come from correctly utilizing the exhaust pulses. I've seen equal length header runners from aftermarket companies making twin scroll turbo kits, but I haven't looked at the subaru or evo factory headers to see if they're also equal length (for some reason I've got a feeling they're not, so I don't know what the proper runner length for twin scrolls is). So does one want equal length headers, or different runner lengths depending on the implementation?

You have to utilize the exhaust pulse just right, and I've read that you've got to "separate exhaust pulses as many crank degrees in the firing order as possible" and that that sometimes means combining the runners from different cylinder banks. Obviously runner length and diameter is going to affect the exhaust pulse (and velocity), as well as which cylinders you combine. So the question is, how does one account for all this (firing order, runner length, runner diameter)? If one were to just combining the runners from one bank to run one scroll and the other for the other scroll with the biggest runners reasonable of an arbitrary length, would the twin scroll even be beneficial (sorry that's a killer of a sentance ha)? I guess the worst that could happen is you have the spooling characteristics of a single scroll, eh?

I encourage any technical talk, knowledge, or experience to be shared here

strucnjak

I like it 20k is a bit too much

jibberjive

j/k I think I'm actually going to keep it.

TwoSnails

i have only seen it in single turbo cars. In the s4 it would mean you would be running 4 wastegates and have not seen a twin scroll single turbo that doesnt run two. And the twin scroll has been done many times. I am not sure about the cylinder pulses but i know thats how they design them. Alot of work and engineering come into play when designing a well made twin scroll kit.

btw i thought you were selling your car

jibberjive

and I just posted a feeler for my car. If I don't get a good enough offer in the next couple days I'm going to take down the ad and keep it. If I do sell it however, I'll be getting a super cheap S4 (high mileage, crappy) as a project car

jibberjive

even try finding someone who owns a low mileage one and offer them <$20k and watch them lol at you

jibberjive

And I'm surprised that no one has any input on the topic at hand

jibberjive

So I found this diagram of the firing order and was curious to what you guys think on this topic.
<a href="http://www.audidatabase.com-a.googlepages.com/firingorder_cyl_bank_location.gif" target="_blank"><img src="http://www.audidatabase.com-a.googlepages.com/firingorder_cyl_bank_location.gif" border="0" alt="Photobucket"></a>

I've heard that a decently effective way to utilize a twin scroll turbo setup without doing tons of developmental research and analysis, and much redesign is to combine the exhaust runners that are furthest from each other in crank degrees and try to make the runners as equal length as possible. So in the case of the S4 (from looking at this diagram) one would actually want to combine the 3 runners on a given bank, right? Each one of the cylinders is 60 degrees from the previous cylinder on the crank, so the furthest you can get from another is 120 degrees because you're combining 3 of the 6. So it appears that combining 1,2 and 3 from the left bank (degrees 0, 240, and 120 respectively) and 4,5 and 6 from the right bank (degrees 60, 180, 300 respectively) would be the way to go. Any thoughts on this?

RolledMySTi

A twin scroll set up requires a proper manifold to get the advantages of the twin scroll. So you would need a properly designed equal length manifold to run one. This is damn near impossible to do with the cramped engine bay we have. If you look at all the single turbo set ups on these cars they are far from equal length. It would be cheaper and easier just to run a 50 shot of nitrous to get the turbos spooled. The costs out weigh the benefits.

jibberjive

Cost and S4 feasibilty aside, is a decent way to do a twin scroll manifold without costly R&D to do equal length runners combining the cylinders furthest from each other in crank degrees? If the answer to that is yes, are the 3 runners from each bank the ones you would want to combine if one were to attempt it on the S4?