Originally Posted by MorrisonFab

The boost vs drive pressure gradient was especially interesting how it flipped around on each! It would be great to see more than just the drive pressure as its only a lumped average- and instead some pressure traces that show what is really going on in the background. Each test seems to only leave a wanting for more





A "small" runner 1-1/4NPS manifold will almost certainly spool a turbo quicker (and augment the midrange) than a more common "large" runner 1-1/2NPS manifold. Our response was written entirely with runner size being equal between the two, and specifically about small runners, as it would certainly change the conversation and results.

We offer many of our manifolds as either large and small runner so it can be tailored to the rest of the setup. For example, we only offer our divided T3 DSM offering in small runner, as each of the inlets on a divided T3 flange is smaller than a single "large" runner and the flow potential of the divided T3 footprint is less than a small runner manifold to begin with. So offering it in large runner would only make it lazier than it needs to be without much, if any, benefit up top. This has been the trend with every large runner 1-1/2NPS divided T3 manifold we've seen. There is always a give and take, of course, as the increased velocity eventually comes at the cost of higher blowdown pressure and frictional losses, but the right combinations can really shine and we like to see that taken advantage of- especially when the primary size isn't the limiting factor to begin with. The power level where small runner shows an overall gain over large runner is much higher than people tend to expect, but what's "right" for each still comes down to many variables and ultimately what kind of powerband gets you the most excited.

Matching primary size to the rest of the setup isn't new, but has always seemed a bit uncomfortable going to something smaller than the exhaust port and making that transition requires some attention to get right in our opinion. Using the smaller 1-1/4NPS isn't as common but we aren't the first by any means to offer it, for a divided T4 or otherwise, but feel that our approach to stepping down from the exhaust port size to the runner itself is done very well. If you look at our small runner offerings, it's hard to tell any indication as it forms from the oval exhaust port size to the round smaller runner size seamlessly. Getting that wrong could risk negating the benefits all together and not give it a fair fight.

Originally Posted by RWD4G63

Lol, it’s a T4 divided flange dumbass. You still don’t understand that Area/Radius is what matters and that T4 divided will and does spool just as fast as T3 divided if the right A/R is chosen. It’s not the flange, it’s the A/R. T4 divided is usually available in better sizes and is easier to work on and has more durable gaskets.

Originally Posted by 2winscroll

Thanks for the detailed response! This is what I have been saying all along.
I have never seen an off the shelf T4 1.25” pipe manifold for an Evo until seeing yours, but that doesn’t mean they aren’t out there.

My point was that a small runner (T3) manifold will spool faster than a large runner (T4) on an S200 turbo with T4 flange and T3 ports.
But hey, I have a very rough grasp of how turbochargers work.

Cheers, 2winscroll

Originally Posted by morrisman1

They are still there!

The advantages of the twin scroll I believe go beyond boost threshold and spool time, the response at part throttle, when feathering throttle in turns etc is brilliant, its very much like driving an N/A except with a bit more grunt. I don't run a blow off valve, that doesn't appear to have any negative effects at all (and I'm happy with the 360 degree thrust and large centre shaft the Borg will not be damaged)

Obviously given the type of racing that I am doing, there is a significant amount more importance on having a huge and usable mid range power,and this turbo seems to fit that requirement well. Looking forwards to getting the new gearbox together so I can throw a bit more boost at it.

Originally Posted by rism

Question, will porting the t3 volutes to t4 sized volutes affect the spool up of the turbo? If using a t4 small runner manifold. I'm asking this as I'm concerned about the 'bottleneck' in flow between the t4 divided manifold flange and t4/t3 volute turbine housing inlet.

Originally Posted by 240Z TwinTurbo

However, a T3 TS is physically smaller than a T4 TS so even with an equivalent a/r, the T3 TS will flow less.

Originally Posted by MorrisonFab

We've never quite been able to nail down the correct way of thinking about this.

Because of the smaller inlets at the flange inlet interface or because of a different way the A/R is calculated? For example, if the turbine wheel is the same will they flow the same in the volute itself? Or does a T4 turbine housing tend to set the R to the centroid out further in the housing and that also increases the centroid's CSA (the A in A/R)?

Originally Posted by 2winscroll

This is what I’m dealing with^^^^

Sure you can put a choked down hotside on it to get the boost threshold lower, but I would much rather run a larger a/r and correct size pipe header, It will make a much better power curve.