Modified Turbo Manifold for Twin-scroll.

[DevilZX]

So here I sit with a Holset I purchased on a whim a couple years ago. I was looking for an HX35W and found one but didn't really research things until this last year or so. After I found out it is a twin-scroll turbo and after reading many threads on various forums I came to the conclusion that I either needed a different turbo or somehow I needed a twin scroll manifold. 

At some point during my research about how twin scrolls work, I decided to look at the Cummins setup. I already knew that the Holset equipped Cummins engines were an inline 6 variety so I decided to look at how the exhaust manifold was designed. I soon came across this image:


and I thought that looked oddly familiar... 

I didn't have direct access to my car so I continued to look for images of the L28ET manifold. After noticing cylinders 3 & 4 share a wall directly in the center, I decided what must be done but before I set off on my mighty ambitious adventure (never having welded before and basic cutting tools), I looked into what possible firing order the Cummins engine uses to fully take advantage of the twin-scroll design. Much to my surprise, the firing order is identical to the L-series! 1-5-3-6-2-4.

Now, I thought, all I need to do is get my hands on a spare manifold to really look at and see if I can actually pull this off. It didn't take long before I sourced one from a member. I bought the manifold, got it in the mail and brought it to work with me.

I remember reading a lot about the exhaust porting on JeffP's website and after seeing the runner inlets for myself I went out and bought a set of carbide burrs.
This here is what I started with:

 

Runners 1, 2, 5 & 6 were all like this. I was careful not to take too much material off as the exterior of the runners squishes inward to make room for the bolts. After a couple hours and a few slivers later, I ended up with what will work for me. 

 

 

I did not enlarge the ports at all I only removed the large bumps inside. Before I felt like I needed to be super ambitious now, I turned a little attention to the turbo itself. I found out that the diesel guys deal with boost creep on these turbos when using the internal gate and followed their advice. I marked the area around the wastegate flapper and enlarged the hole to as big as I felt needed before I lose a sealing surface. The picture is an in-progress photo which shows the not-quite-round porting... I also took a page from the diesel guys about what they do to take care of the boost creep without running a second wastegate. I drilled a hole directly through the internal divider to let off the pressure which would keep the turbine spinning even though the wastegate is fully open. This does sacrifice a little bit of the twin-scroll functionality but not enough to make this project pointless. It seems as though the ~1/2" hole between the divider lets off enough pressure to get rid of the boost creep issue (I'll find out more after I install it).

 

 

Now that I had (hopefully) taken care of the turbo side of things, I decided to go ahead and open up the manifold! I just used the turbo inlet flange gasket as a template and marked off where I wanted to put the new hole. Using my Harbor Freight cut-off grinder, I chopped up a nice big hole in the manifold. 

 

 

Now I had a good idea of what I had in store for me. My employer had recently purchased a new spring compressor for our shop and I took the liberty of scavenging the materials from the old unit. I had a lot of ~1/4" thick steel from the various pieces of the compressor which I thought would work nicely with the ~1/4" divider already inside the manifold. After eyeballing the inside I made a template out of some card paper and laid it out on the steel I found. Lots of work with a sawzall, bench grinder and hand file I came up with a piece to maneuver into the hole. 

 

 

It looks crude and it is two separate pieces but it fit decently. I took it out, cleaned all the paint off and Used the same process to make a block-off plate for the factory hole. I grabbed some bolts from my parts department and fastened the block-off down.

 

I then decided it was time to try to use the shop welder for the first time.... Oh what a learning process! For almost the entire time I tried to weld in this divider, I had the welder on the highest heat setting... What I neglected to figure out (why it looks like a bird pooped inside the mani) was that my wire feed was set to the absolute lowest it could be. Essentially, I tack welded the whole piece in. A buddy came by when he heard how the welds sounded and twisted that feed knob. Voila! This went so much better after that! I still had a lot of spatter and cleaning up to do but that was OK with me. Just to test it out, I heated the manifold with a torch to glowing and hit the center divider with a hammer a few times. No movement, no cracking and the welds held up. I felt this would be worse than what the engine exhaust can do to it so I proceeded ahead.

I don't have any pictures of the current progress as I wasn't too proud of my welds.. 

Now I needed to find a new flange to finish off this work... I found the cheapest, mild steel, 1" thick, divided T3 spacer I could and ordered it up. Came in two days and I got to work as soon as I could. Because there is a curve in the manifold and the new flange is flat, I took the flange to the bench grinder and carved up a nice contour in the bottom to wrap around the manifold. Again, I used the carbide burrs to clean up the grinding and test fit the piece. Good enough! 

Because the spacer is made to attach to an existing flange with longer studs, the holes for mounting the studs were too big. I simply slid them inside the holes and welded them into the bottom of the flange. I could have tapped the flange for larger diameter studs and then drilled out the turbo flange holes but I felt that the nuts would have been too large and caused a problem when I went to mount the turbo. 

I proceeded to tack the new flange in place for final visual inspection. It looked good to me so I went for it. Welded all the way around the exterior of the flange to the manifold and the inside divider to the flange divider. I welded everywhere I could reach effectively inside the manifold to double seal these seems as best I could. Then I brought the finished product to my bench, broke out the carbide burrs and cleaned up everything I could reach. Any little spots of spatter I couldn't reach with the burrs I used a hammer and chisel on to knock them out. 

I now have myself a seemingly decent twin-scroll manifold for use on the L-series engine. I am dealing with the fitment, exhaust, intake, and oiling at a later date but for now I feel confident it will work.

 

 

Let me know what you think. I welcome criticism. 

Edited February 15, 2013 by DevilZX

[DevilZX]

Also, while I was waiting on parts to come, I made a throttle body spacer to run my KA24 tb for my future MS3X install. I had found a big aluminum "coin" (about 12" in diameter) a while back and shaped a crude spacer out of it. I don't care that this isn't the most glamorous piece but it sure is functional!

[NewZed]

I've no clue if your new design will work as intended, but I wonder if all of the welding has caused any warping.  Probably worthwhile to check the manifold-to-head sealing surfaces.

[DevilZX]

I do plan on checking that before installation. Initial inspection with a small straight edge doesn't show any warping but I will have to use something longer to see if anything got out of line from end-to-end.

[Xnke]

It'll work just fine as far as the divided flange portion goes. I'd have taken the grinder to the old T-3 flange and smoothed it off, and welded in a block off panel, myself. That would probably have warped it up some, though.

[skirkland1980]

One good thing is, since your turbo will be a few inches forward, you will have a lot better angle on your downpipe.

[brianZortiz]

DevilZX, looks good I'm glad you used Cummings engine as inspiration. I have been around those 16 litre inline 6 big rig engines since I was a kid. Im glad to see the manifold put to good work. Keep it up and hope you can update us with progress and results. Also, should have cleaned the manifold from the surface rust before shipped it out. Sorry.

[DevilZX]

I made some progress on the install. The manifold turned out to have no warpage so I am good in that department but when I went to mock up the turbo, it ran into the engine mount without the compressor housing on! I cut, drilled and welded some pieces together and moved the engine mount forward ~6 inches and used the factory A/C compressor mounting holes. I was able to then get the turbo mounted on the flange with the comp. housing but have 1-2mm of clearance between the air inlet pipe and the engine mount. Fine in my book since everything moves as a unit anyway. 

I was able to modify the factory wastegate actuator to work on the Holset and also was able to use the entire factory oiling. I cut the drain flange and ran a new hose for that. Next step I need to run a new hose for the PCV but that wont be difficult as there is plenty of room. 

There is still ample space to run the factory AFM but I have run out of rubber hose for the inlet side of things and it just happens that my new Megasquirt unit showed up today. I will be installing that on Monday with my LC-1 and the new exhaust section to run to my already custom 3" downpipe. 

Not an easy install, this. I really am starting to hope that it will be worth it...

[DevilZX]

Good news! Everything has been installed, wired up and is running! I have MS3 running Cygnus's latest msq. and it needs some custom tailoring to my specific application but I got to drive it for a short distance. One thing to note is that the exhaust note has changed slightly. I think this is due to the exhaust manifold setup. I liken the sound to have a slight RB quality to it. . 

I got it to spool up to ~8psi at about 3000 RPM. I wasn't trying for anything special on the first run and my MBC was set to 12psi on the factory T3. 

 

Edited March 1, 2013 by DevilZX

[BluDestiny]

Pics?

[billyssp]

Good news! Everything has been installed, wired up and is running! I have MS3 running Cygnus's latest msq. and it needs some custom tailoring to my specific application but I got to drive it for a short distance. One thing to note is that the exhaust note has changed slightly. I think this is due to the exhaust manifold setup. I liken the sound to have a slight RB quality to it. . 

 

I got it to spool up to ~8psi at about 3000 RPM. I wasn't trying for anything special on the first run and my MBC was set to 12psi on the factory T3. 

 

 

I would love to hear the new exhaust sound. Any videos?

[DevilZX]

Installed pictures. No video yet.

[DevilZX]

I was cleaning up the old factory turbo today and I decided to remove the exhaust outlet/wastegate flap housing. In the process I managed to snap off two of the bolts. I was a little upset but what I found underneath there made the bolts less of an issue. I now have a nice chunk of Datsun history for decoration!

[DevilZX]

Well here we have a first video! Sound quality is atrocious... Video obviously taken in-car but this was with drivers window down, indoors and on my phone. 

3" turbo-back, open exhaust. This had been idling for 1 minute prior so it is still cold (rich). 

Edited March 9, 2013 by DevilZX

[DevilZX]

Got some tuning time in and was able to push it pretty hard. Short story here, wastegate is not sufficient. With factory 280zx wastegate and NO MBC used I am still seeing 15+ psi. Comes on quick at 3200-3500 from what I could tell before the T5 let go and locked itself into first gear... 

Lesson learned twice: Don't push the T5 hard in 5th gear... They like to fall apart and lock into first gear with gear selector in neutral. Once this transmission issue is sorted, I feel the head gasket is the next thing to go unless I can better control this boost. I would really like to avoid trying to fit two externals in there (space is very limited now) so I will open up the divider hole and make the flapper hole larger and modify it to open further. I think it only opens ~1/2" at the most. 

Time will tell.

[lowrider]

I had the same issue with my HX35. I ported the wastegate hole and it helped a bit but still didn't control boost to my liking. Then I removed the divider all the way to the wastegate hole (I'm using the factory non-divided T3). I then replaced the flapper with a larger 35mm piece along with porting the hole more, it helped but didn't solve the problem. Finally I had enough and finally went external, boost control is no longer a problem. I would suggest going external if possible, it provides a substantial amount of control over the internal flapper.

[DevilZX]

Figured it out. I will post a picture or two of my solution. I didn't have a lot of room for two external gates and really didn't want to spend $500+ for them either. I ended up cutting a hole in the exhaust downpipe flange for the wastegate flapper to open all the way instead of the 1/4" or so it was opening. I opened up the gate hole larger and welded a washer on. After I routed the wastegate exhaust to come out then back into the main exhaust stream I tested it out. 

I was able to reduce overboost to ~10psi while running the stock wastegate actuator. I feel like 10 psi is just good enough for the $ involved. 

I did, however, run into an issue. The gate was able to fully open and allow most of the excess pressure out but when the throttle was let off after a boost condition, the flapper stayed stuck open. This was because the flapper moves in an arc and the actuator couldn't pull it back around a curve. ( when I was able to build boost at 5k RPM again it would sometimes return to its home position but this was not very good)

To correct this issue I built a bell crank device to operate the flapper with the actuator in the only spot I could fit it all. This worked out wonderfully but there still remained a small problem. Since there are now 4 pivot points for the actuator, the tension to keep the flapper seated was so low that at idle the exhaust pressure would push the gate open and boost would spool SLOWLY!

A trip to the auto parts store yielded a 5 pack of various springs. Found one that was just right to keep the gate seated but not hold too much to cause another overboost condition. 

I was able to re-install my MBC and now spool hard and fast to ~15psi at ~ 3300-3400 RPM.