I saw this on another forum (http://www.dieseltechtalk.com/forums/showthread.php?70-Stock-turbo-Mod) and figured I would give it a shot since I am sooo close to having EGT's completely controlled. I think this will set me over the edge and I will be able to do whatever I want with the truck.

The thread states that a stock HX35 has only the back 3 cylinders wastegated because of the divider between them. They carry on to say that this design raises EGT's under full boost (wastegate open) conditions. By drilling the wastegate port through to the other side of the exhaust (through the divider), all 6 cylinders are wastegated and provide more flow through the turbo, lowering EGT's. Of course I like to test everything myself so that I can say it worked on my specific truck as well

They said a 3/4" works good but since I have a mill here, I set it all up dead center and drilled it to 15/16". I might go back with a 1" end mill later, still deciding if I should or not. It has to be dead center for it to be that tight as the wastegate valve thing that covers the hole is 1 1/8" diameter, so you don't want it to be off any if you use a big drill bit.

I still need to test it and put the turbo back together, and finish wiring the truck and, yeah it will never run again lol. Maybe friday.

Here's a video I made showing the planning process.

http-~~-//www.youtube.com/watch?v=kyhHRPUF7NA

Here is a pic of my turbo when I got done.

That's interesting. I'm curious to see the (if any) changes are recorded.

I wonder if the hole in the divider will cause turbulance? Like the idea of exhaust turning a 90* angle and then flow across another path of exhaust to the wastegate just doesn't sound too good. I know some people go as far as milling out the entire divider...

Not that I've yet put shop air to my wastegate to test it, but I wonder if this may be the cause of my overboost issue with the potentially increased flow from the 24v head??

I was thinking along the same lines, Mike. That has to create a butt-load of turbulence right at a choke-point.

I can see where milling the entire divider out would make more benefit to this mod, rather than just a passage. But with milling out the entire divider, you now possibly induce a resonant pulse of exhaust pressures within the exh. manifold. That's partly the reasoning for the divider, in the first place; the concept is to DIVIDE or separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy.

For example, on a four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending its expansion stroke and opening its exhaust valve while cylinder #2 still has its exhaust valve open (cylinder #2 is in its overlap period). In an undivided exhaust manifold, this pressure pulse from cylinder #1's exhaust blow-down event is much more likely to contaminate cylinder #2 with high pressure exhaust gas. Not only does this hurt cylinder #2's ability to breathe properly, but this pulse energy would have been better utilized in the turbine.

The proper grouping for this engine is to keep complementary cylinders grouped together-- #1 and #4 are complementary; as are cylinders #2 and #3. In this example, the you would need the divider to coincide with this design.

For the CTD (firing order: 1-5-3-6-2-4 ), the exhaust manifold's "dual scroll" division should isolate 1-3-2 and 5-6-4, which it does. Opening that gap between with now reduce exhaust pulse scavenging. I'd be curious to see an unmodded manifold/turbo setup, with dual EGT probes, calibrated together, and install one in each side of the divider (manifold-side) that is accurate enough to read EGT variances. Take these readings pre/post drill mod, to determine if there is, indeed a change and where it truly occurs.

ISX, where is your EGT probe located? IOW, which side of the divider on the exh. manifold (1-3-2 side, or 5-6-4 side) if that is where your probe is mounted?

Related to your comments Rogan, I'm now cursing my rear-bank EGT probe as I'd expect the front 3 to be hotter without wastegate release

I wonder if the hole in the divider will cause turbulance? Like the idea of exhaust turning a 90* angle and then flow across another path of exhaust to the wastegate just doesn't sound too good. I know some people go as far as milling out the entire divider...

I agree.. I think it will raise EGTs across the board due to greater turbulence. The turbo I just bought is wastegated only on once half of the divider as well, and it's not a cheap turbo. I figure if it didn't work they wouldn't do it that way. I just don't see how it really matters if it pulls from one side or the other. The point in a WG is to control boost and limit turbo speed. All it does is simply pull air away from the blades. Only taking pressure from one half doesn't change that. Less exhaust gets to the turbine wheel, thus no increased boost. You should also get lower pressure on the 1-3 bank, but i'll verify that later this month when I get my turbo installed.

I'd expect a measurable difference in drive pressures with one side being wastegated and the other not.... but that's strictly off the cuff.

I would expect 'this' to be a better use of machining.. At least more 'bang' for the buck (time)..that, along with knife-edging the "taint".. or divider ;), depending on how well it matches the manifold..

Very interesting points. All seem to contradict the thread I got it from Should be interesting to see the result.

My probe is in the back divider so it sees 4/5/6.

One thing to note is that the HY35 has no divider. That might be different from a divider with a hole in it but is still something to think about.

Here's a pic I stole from a DTR thread of the HY and HX.

I would expect 'this' to be a better use of machining.. At least more 'bang' for the buck (time).. [ATTACH=CONFIG]2680[/ATTACH] that, along with knife-edging the "taint".. or divider ;), depending on how well it matches the manifold..

That would be the best bang for the buck flow wise... Little port matching...

Some turbo's are divided and some aren't. It really depends on the application. A divided housing is supposed to help spool a little better as the pulses are maintained. Also of note the HY 9cm is supposed to flow about as much as the HX12cm due to being div/undiv. I have also been searching for pics of the S300's that use two WG pucks on a divided housing, so they pull from both halves but don't disrupt flow, but can't find any.

Bump to the top. What was the verdict on this mod ISX????

I'm kind of itchy to hear too...

I have read a few other threads about this in the recent weeks... Still amazes me that it works, or is supposed to... looks like it will be horrible exhaust flow with the WG open.

I was thinking along the same lines, Mike. That has to create a butt-load of turbulence right at a choke-point.

I can see where milling the entire divider out would make more benefit to this mod, rather than just a passage. But with milling out the entire divider, you now possibly induce a resonant pulse of exhaust pressures within the exh. manifold. That's partly the reasoning for the divider, in the first place; the concept is to DIVIDE or separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy.

For example, on a four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending its expansion stroke and opening its exhaust valve while cylinder #2 still has its exhaust valve open (cylinder #2 is in its overlap period). In an undivided exhaust manifold, this pressure pulse from cylinder #1's exhaust blow-down event is much more likely to contaminate cylinder #2 with high pressure exhaust gas. Not only does this hurt cylinder #2's ability to breathe properly, but this pulse energy would have been better utilized in the turbine.

The proper grouping for this engine is to keep complementary cylinders grouped together-- #1 and #4 are complementary; as are cylinders #2 and #3. In this example, the you would need the divider to coincide with this design.

For the CTD (firing order: 1-5-3-6-2-4 ), the exhaust manifold's "dual scroll" division should isolate 1-3-2 and 5-6-4, which it does. Opening that gap between with now reduce exhaust pulse scavenging. I'd be curious to see an unmodded manifold/turbo setup, with dual EGT probes, calibrated together, and install one in each side of the divider (manifold-side) that is accurate enough to read EGT variances. Take these readings pre/post drill mod, to determine if there is, indeed a change and where it truly occurs.

ISX, where is your EGT probe located? IOW, which side of the divider on the exh. manifold (1-3-2 side, or 5-6-4 side) if that is where your probe is mounted?

I have to disagree with this, with the exception of being in low boost situations. The boost pressure should always be higher than exhaust gas pressure as long as the turbo isn't a variable vane turbo where the ecm pretty much makes the backpressure whatever it wants to. So the scavenging effect is greatly reduced if not eliminated in a forced induction scenario since the clean air coming in would force the exhaust gases out and thus eliminate the need to utilize the scavenging effect.

I do agree that there would be a lot of turbulence created unless the whole divider is removed but don't think removing it would have a negative effect on performance. It certainly would on a naturally aspirated engine, but then we wouldn't be talking about turbos in that case. Of course I have been wrong before. This is just my

I have to disagree with this, with the exception of being in low boost situations. The boost pressure should always be higher than exhaust gas pressure as long as the turbo isn't a variable vane turbo where the ecm pretty much makes the backpressure whatever it wants to.

I would have agreed with you until I installed my Garrett. At the bottom of a grade DP will be +2 of boost, but -02 at the top, has happened on most decent hills for me. It really allows for a lot of clean air to be entering the cylinder! A VNT or VGT doesn't necessarily fall into this category as if you drop the drive pressure you may drop the boost, it all depends on the efficiency and drag of the turbo.

I would have agreed with you until I installed my Garrett. At the bottom of a grade DP will be +2 of boost, but -02 at the top, has happened on most decent hills for me. It really allows for a lot of clean air to be entering the cylinder! A VNT or VGT doesn't necessarily fall into this category as if you drop the drive pressure you may drop the boost, it all depends on the efficiency and drag of the turbo.

I'm not exactly sure what you are referring to with the DP. Do you have a pressure gauge in the exhaust system or am I way off. :banghead: I know that with the VGT on the 6.0 powerchoke would actually spool at idle with something as small as the a/c compressor clutch kicking on. When they would spool they would close the vanes and raise exhaust back pressure but increase the velocity. Atleast thats how the engineer explained it to me. So until you actually reached around the peak torque range of that particular engine with the VGT the back pressure was higher than the boost.

I forgot all about this thread. Truck is still down but I got all the stuff to get it back on the road just a few hours ago so sometime this week it will be back up. I got some issues but I'm just gonna turn a blind eye for now, I need more time. But definitely will have a verdict on the turbo by the end of the week.

I forgot all about this thread. Truck is still down but I got all the stuff to get it back on the road just a few hours ago so sometime this week it will be back up. I got some issues but I'm just gonna turn a blind eye for now, I need more time. But definitely will have a verdict on the turbo by the end of the week.

Slacker!!!!:lmao2:

I'm not exactly sure what you are referring to with the DP. Do you have a pressure gauge in the exhaust system or am I way off. :banghead: I know that with the VGT on the 6.0 powerchoke would actually spool at idle with something as small as the a/c compressor clutch kicking on. When they would spool they would close the vanes and raise exhaust back pressure but increase the velocity. Atleast thats how the engineer explained it to me. So until you actually reached around the peak torque range of that particular engine with the VGT the back pressure was higher than the boost.

Yes I run a pressure gauge in my exhaust manifold. In very general terms that is a correct statement. But there are several variable. Under normal acceleration DP is generally at or higher than boost, but not much unless the turbo is really too small for the application or was designed to have higher backpressure for spool/emissions reasons. Once the rpms stabilize and power stabilizes the drive pressure will normally drop while boost stays constant. But drive pressure does not have to exceed boost for the turbo to accelerate.