Divided turbo on undivided manifold

Hello all,
I'm getting my build going finally as I had some bummer hold-ups from the shop it was at, back when I bought the S&H Performance single turbo stealth kit in May of 2015. Everything sat in a box, and Comp Turbo drop-shipped the turbo.
Now that I have opened everything up and checking it out closely, I found the turbo had a divided housing with an A/R of .84 when it was supposed to be an undivided .81, as the manifold for the kit is also undivided and only a single waste gate.

Thankfully Comp is willing to swap it out for the correct one, but before I do, I wanted to make sure I am making a good decision.

If I were to stay with the .84 divided, would it work better?
From what I have read on other forums and articles, it is not a straight forward answer, since some say there is no issue, and others say it will cause surging, spiking, uneven amounts of air in the housing, and possibly even crack it.

Not sure what to do here, and it's a big decision since if I proceed forward only to hit an issue later, it's an expensive mistake.

Thanks all.

It shouldn't be that much of an issue. With 8 cylinders feeding into it, both sides will get plenty of exhaust to move the turbine.
The divided inlet-or twin scroll is mostly so you can match up cylinders to make an even exhaust pulse. An example would be on a 2.0 L Zetec 4 cylinder that has a 1-3-4-2 firing order, feeding cylinders 1 and 4 to one side, 2 and 3 to the other, that way each side gets a pulse from every second time a cylinder fires. If you don't watch this with a smaller engine or do not have them paired correctly, that is when you will get surging, spiking, etc...
So I would say that it should not be an issue.

RED09GT said:

It shouldn't be that much of an issue. With 8 cylinders feeding into it, both sides will get plenty of exhaust to move the turbine.
The divided inlet-or twin scroll is mostly so you can match up cylinders to make an even exhaust pulse. An example would be on a 2.0 L Zetec 4 cylinder that has a 1-3-4-2 firing order, feeding cylinders 1 and 4 to one side, 2 and 3 to the other, that way each side gets a pulse from every second time a cylinder fires. If you don't watch this with a smaller engine or do not have them paired correctly, that is when you will get surging, spiking, etc...
So I would say that it should not be an issue.

Click to expand...

Thank you. More specifically, is it "preferable" to keep it, or to go with the undivided .81, since I have the option?

Thanks.

No issues running my Garret with divided housing. Didn't affect power production at all.

Hot exhaust gases are going to go to the hole, whether is one big hole or a divided hole.

I am interested in this concept.

The difference will likely be negligible, the amount of area lost by the divider will probably be about the same as the difference between the 0.81 and 0.84 housing.

You could split hairs and say that the extra wall from the divider is another potential area for friction but it is best not to go down that rabbit hole looking for that microscopic amount of horsepower that you may have left on the table. It will work just fine, these things make HP plenty easy with a turbo.

Thank you all. I just confirmed with Comp as well that it won't cause issue and is actually quite common to run divided on an undivided manifold since some of their larger turbos are not even available as an open design.

RED09GT said:

It shouldn't be that much of an issue. With 8 cylinders feeding into it, both sides will get plenty of exhaust to move the turbine.
The divided inlet-or twin scroll is mostly so you can match up cylinders to make an even exhaust pulse. An example would be on a 2.0 L Zetec 4 cylinder that has a 1-3-4-2 firing order, feeding cylinders 1 and 4 to one side, 2 and 3 to the other, that way each side gets a pulse from every second time a cylinder fires. If you don't watch this with a smaller engine or do not have them paired correctly, that is when you will get surging, spiking, etc...
So I would say that it should not be an issue.

Click to expand...

RED09GT said:

The difference will likely be negligible, the amount of area lost by the divider will probably be about the same as the difference between the 0.81 and 0.84 housing.

You could split hairs and say that the extra wall from the divider is another potential area for friction but it is best not to go down that rabbit hole looking for that microscopic amount of horsepower that you may have left on the table. It will work just fine, these things make HP plenty easy with a turbo.

Click to expand...

Exactly this.

tjm73 said:

Hot exhaust gases are going to go to the hole, whether is one big hole or a divided hole.

I am interested in this concept.

Click to expand...

I like this idea a lot. On a v8 at 6-7k rpm not much to be had in this realm it seems, somewhere in the 100-300rpm gain in transient response and full spool. But would still feel more responsive on the street I bet, seat of the pants anyways. It would allow you to balance in a slightly larger turbine to promote top end with out sacrificing as much lowend feel depending on your setup and power level.

I did a similar concept on my car but with a butterfly throttle blade on one side with an arm and internal style waste gate actuator to open it at 12psi. I haven't done a comparison with any hard data yet though.

I do know on smaller motors that rev higher and run much higher pressure ratios, they see more gains from these kinds of things as they tend to be laggy as they run a lot bigger turbos to make the power to compensate for lack of na power. 500-1000rpm gain in spool on those kinds of setups. But we are talking a car that would normally not make 30-35psi till like 6k rpms so there is a larger window for improvement. It seems on a v8 where 10-20psi can be had by 3-4k rpms there is less of an improvement from something like this.