My bus has a Holset hx55 turbo, which has a divider in the intake. I presume the exhaust manifold has a divider as well although I don't recall and I don't want to dismantle things to have a look at this point. But I added an extension about 12 in long of heavy wall pipe to move the turbo to the outside of the frame for packaging purposes. The pipe I used does not have a divider so I suppose the exhaust pulses mix in my extension pipe and then run into the divider at the turbo. I am wondering whether I should cut the divider out of the turbo. Is it doing any harm or any good at this point?
Divided inlet helps with spool if used with divided collectors that merge cyls of opposite firing order. You can use them just fine with regular manifolds but hurts spool a little. Cutting the divider out of the turbine housing increases volume (a/r) and will also cause slower spool but have better top end.
Paul_VR6 (Forum Supporter) said:
Divided inlet helps with spool if used with divided collectors that merge cyls of opposite firing order. You can use them just fine with regular manifolds but hurts spool a little. Cutting the divider out of the turbine housing increases volume (a/r) and will also cause slower spool but have better top end.
But a divider all by itself after 12 inches of no divider?
Which cylinders are being divided? If it's 1/4 and 2/3 paired, it's for spooling in the exhaust. If it's 1/2, and 3/4 (which is pretty easy) it's for distribution of flow. If it's the latter, adding a foot would kind of eliminate the need for distribution as it has a lot more space to mix. If it's the former, it's kind of up to you whether you want to accept the slight lag due to the lack of split flow.
It's not going to hurt anything, just slow the spool time.
alfadriver said:
Which cylinders are being divided? If it's 1/4 and 2/3 paired, it's for spooling in the exhaust. If it's 1/2, and 3/4 (which is pretty easy) it's for distribution of flow. If it's the latter, adding a foot would kind of eliminate the need for distribution as it has a lot more space to mix. If it's the former, it's kind of up to you whether you want to accept the slight lag due to the lack of split flow.
It's not going to hurt anything, just slow the spool time.
It is a Cummins ISM diesel so a straight six. I expect the divider was for quicker spool but since I have added the extension and eliminated that benefit I wonder if the slight obstruction left in the turbo is detrimental. And I am asking because I have the turbo off to replumb the drain line and now is a good time to cut it out if needed.
In reply to bearmtnmartin (Forum Supporter) :
Ah... Not really familiar with that set up. But in terms of the divider- how obstructive is it? And how far back does it go? Can you actually take some of it out? If it's truly dividing the exhaust, it will run all the way back into the collector, which means you may not be able to take much of it out without causing other problems. Flow wise, taking it out is fine, I would think. Others may have a better feel for it than I do. Paul and Pete may have some ideas.
And by "other problems" I mean structural, since it eventually ends up being the back side of the collector.
It would affect spoolup but not outright flow, I think.
A larger issue would be ensuring that the turbo is well supported, because that is a lot of weight to be hanging off of a 12" stick attached to a vibrating engine. Diesel EGTs are fairly low but they still get right up there to the dull-red region when under heavy load, too. So you not only have to support the turbo but do it in such a way that allows the pipe to grow with heat if you don't have an accordion section in the pipe. Back of the envelope calcs say it will probably expand by 1/8" or so, or die trying.
Pete. (l33t FS) said:
It would affect spoolup but not outright flow, I think.
A larger issue would be ensuring that the turbo is well supported, because that is a lot of weight to be hanging off of a 12" stick attached to a vibrating engine. Diesel EGTs are fairly low but they still get right up there to the dull-red region when under heavy load, too. So you not only have to support the turbo but do it in such a way that allows the pipe to grow with heat if you don't have an accordion section in the pipe. Back of the envelope calcs say it will probably expand by 1/8" or so, or die trying.
It is indeed a bigass weight hanging out there, but well supported.
