Triple Blowthrough Turbo

[Dat73z]

@AydinZ71 yep that was my understanding as well. To be honest I'm not even sure if localized boiling after shutdown is just a normal water cooled turbo thing but I'm under the impression it's not...

 

Curiosity got the better of me and since I'm still waiting for parts I decided to drive the car a bit more and see. 

 

Interestingly enough the temps on the car today were overall much lower and much more stable at the middle of the 240z gauge instead of fluctuating between the middle and the M in Temp. The fans only kicked on once in 30 mins instead of like 10 times. Both the upper and lower hoses got pressurized but not crazy pressure where I was blowing hoses. The rad was uniformly hot top to bottom including the hoses instead of the top hose cooking and the bottom cold. I was still getting boiling after shutdown at the heater core branch but everything felt cooler. 

 

I have no idea what's going on and now I'm questioning if the system got air locked or something. I'm going to see if I can pick up a vacuum bleeder tomorrow to pressure test/vacuum bleed the system but my work schedule has been crazy this week. 

[Dat73z]

It's been another crazy week but almost time to get back into the project. 

 

This morning I pressured the cooling system using an Autozone loaner tool. Unfortunately the tester cap didn't fit well enough to go beyond 15psi without leaking so I pressurized everything to 14psi and it's held steady for hours so I don't suspect a leak unless it's happening under very specific circumstances and allowing air in at the heater branch. I'll see if I can get it to 20psi and hold it there overnight. 

 

I also picked up a vacuum bleed/test tool from Harbor Freight. I think I'll try using this to test with vacuum then fill when I've reconfigured the system. I'm waiting for a new Borg Warner Tstat, fittings, and a Bossa Design water pump to come in beforeI drain and start reworking the system. 

 

I have been driving the car around a bit and I still get the gurgling/after boil at the heater branch on shutdown. After some further research this sounds like the convective cooling/thermal siphoning that's been discussed. Looking at other forums for subarus/miatas/etc. Both OE and aftermarket It seems like it's a mixed bag in terms of people who say it's not normal versus normal. It also varies by altitude e.g

 boiling point who experiences this. Some OEs apparently use a turbo coolant pump for circulation after shutdown to prevent this. 

 

Either way since I set up my system modularly with AN fittings I'm going to try a couple of different feed areas and can always go back if I like the original routing. 

 

Also I'm borrowing some jets later today from a friend to continue tuning. 

[Dat73z]

Did some more running and tuning today and I'm not sure what happened but on shutdown I can feel the coolant thermally siphoning/moving through the heater core branch from the lower rad hose. No more boiling, but faint gurgling as fluid is moving from the suction side through the turbo and to the tstat housing dumping at the upper hose. 

 

Maybe this entire time there was some airlock or something going on and the pressure testing multiple times dislodged it. I have no idea. Either way I feel better about it now and it's pretty cool to see thermodynamics in action. 

 

This weekend I'll continue tuning and shaking the car down. 

[Dat73z]

It's really faint to hear but at 2 and 6s you can hear the movement of the coolant as it cools the turbo post shutdown. 

[Dat73z]

Still waiting for parts so I continued tuning this AM. 

 

Things are finally looking up after all the new build drama. I was able to borrow a box of OER jets and the engine is running smooth at idle 11-12afrs and off idle but falls flat on it's face above 2-3k rpms pig rich 10afrs. 

 

A few years ago I put 36mm venturis into my 47 OERs thinking I was going to run it on my 2.5l turbo motor. When I moved, the 3.2 stroker was a last minute decision since I didn't want to put the spare engines and all of the stroker parts I had into storage. 

 

When I removed the main jet stack, the car cruised around at 12-13afrs. With the 36mm venturis on the pilots and my mains are coming online at 1.5krpms which is crazy but seems to make sense since the carbs are choked down to the lowest end of the range for 47s so the signal is much stronger. 

 

I'm going to borrow some mains jets from my other buddy today and if I can get the afrs at 11 across the board to start then I'll throw the surge tank on and start boosting/tuning from there. Really hoping I can get there this weekend 😁

[Dat73z]

After a couple hundred miles of street driving it was time to check the torque on everything again since everything was redone. 

 

So far so good, only my vbands were loose due to thermal cycling/relaxation. I torqued them back up and will check again in another few hundred miles. At that point I'll safety wire them in along with installing the inconel vband shields.

 

I should probably wipe the whole system down with acetone again too but I think that's just the ocd getting to me...it's an exhaust so it'll get banged up and stained. 

[Dat73z]

Since I'm still waiting on cooling system parts and jets, I decided to try my hand at soldering and drilling jets. 

 

I successfully got the car to 11-12 afrs across the board. More tuning to be done but it's decently drivable now and at a baseline where I'm comfortable with boosting. Tomorrow I'm going to tune a bit more after work and put the surge tank on. 

 

 

[Dat73z]

This morning I got up early and started taking some measurements for the AC system since it seems I may be waiting a while for parts...as is typical these days. 

 

I think I have most of the components for the AC so I can start cutting some shapes and welding up the compressor bracketry. I intentionally fabricated everything around where the AC components would go since I know my wife at least needs a heater and AC lol. The condensor I have fits perfectly between the intercoole/rad/oil cooler. I also already ran the integrated wiring for the AC when I reloomed the harness. 

 

I visited a friend this past week to borrow some OER jets and saw they had a really cool kick up/down solenoid on their triple Mikunis. I'm going to do some more research and see how I could implement this as my idle does drop a couple hundred rpms, esp with both efans going, probably more with an AC compressor running

[Dat73z]

Some good news, my 1/2 BSPT to -6an block fitting came in early today so tonight I'm going to install it and try out my new Harbor Freight vacuum bleeder. 

 

I think the strategy will be one change at a time. It will be another iterative and annoying development process, but hopefully one that gets me to a resolution. 

[Dat73z]

It's turning into another crazy week so I had to break jacking the car up into 2 days lol. 

 

This morning I got up early and got the car in the air to prepare coolant draining. 

 

I also did an undercarriage inspection since I've covered a few hundred street miles. Everything looks good except the typical rear cap seal seepage. Pretty annoying but it's minor enough that I can live with it for now. Usually I replace those seals myself even if someone else did them as they're tricky to get right. In this case I sent it but as is tradition with that strategy I'll need to rework it at some point 😂.

 

I snugged up the pan a bit more and will keep pressing forward. 

[Dat73z]

Over lunch I removed the block drain and installed the adapter fitting. I'm going to first attempt the block feed location before trying the water pump outlet. Mainly for convenience of routing. 

 

Hopefully I'll have some time later tonight to fabricate the hose. I'm curious how the coolant vacuum test/fill setup will work out. I'm pretty oldschool and have traditionally filled and burped cooling systems my entire life. 

[Zetsaz]

14 hours ago, Dat73z said:

It's turning into another crazy week so I had to break jacking the car up into 2 days lol. 

 

This morning I got up early and got the car in the air to prepare coolant draining. 

 

I also did an undercarriage inspection since I've covered a few hundred street miles. Everything looks good except the typical rear cap seal seepage. Pretty annoying but it's minor enough that I can live with it for now. Usually I replace those seals myself even if someone else did them as they're tricky to get right. In this case I sent it but as is tradition with that strategy I'll need to rework it at some point 😂.

 

I snugged up the pan a bit more and will keep pressing forward. 

 

Pretty sure mine is seeping from the same area, but much more, and it's driving me insane. 

[Dat73z]

@Zetsaz Yeah, probably the most annoying thing is there's no good way to fix it without pulling everything apart again. Oh well, a problem for another day 😂

[Dat73z]

As Loctite 567 has a cure time of 24 hours I've had some time to carefully look everything over and think things through a bit more. 

 

My CHRA has a slight clock to it upwards towards the DS maybe 5 degrees or so. I don't get boiling at all during running, but at shutdown, when there is no longer water pump pressure to force flow in the system the hot CHRA begins to boil the coolant which can result in localized steam pockets. 

 

Ideally, if the coolant has a gradual sloped return up with adequate delta T to promote thermal siphon this should not occur. At least that's what I think is going on based on a few hours of research. So I think ideally, the coolant lines in the turbo will need to be swapped around. 

 

Since I have everything set up modularly with AN fittings, I'm going to run down the following: 

 

1. System as-is full vacuum test/fill see of it was an air pocket/lock issue and ensure there are absolutely no other leaks in the system to set the baseline

2. Block feed

3. Lower rad hose feed

4. Swap lines around, block feed

5. Swap lines around, lower rad hose feed

 

I'm still not sure if this is really an issue, but I may as well take this as an opportunity to learn while optimizing the system. I think this should keep me busy this next few days. 

Edited August 3, 2022 by Dat73z

[Dat73z]

Early this morning I pulled vacuum on the system and held it at -25inHg for a couple hours. I have now both pressure tested and vacuum tested my system and am confident there are no leaks. 

 

I then filled the coolant via vacuum with the nose of the car elevated maybe 2 feet so the filler neck/coolant source was above the tstat housing. I reused the coolant + water wetter that I drained as it looks absolutely clean. I don't think I will ever traditionally fill a cooling system again if I can help it. Absolutely no mess and filled the system within 5 minutes. 

 

I will take the car out for a nice long drive over lunch to establish a baseline before making further changes to the cooling system. 

[Dat73z]

After a nice long drive, I'm still getting the coffee maker turbo boiling. 

 

I have some AN fittings coming in tomorrow so I'll need to wait on those to make the new lines. 

 

I'm really pleased though with how smooth the car is running now. Every time I take it out I've been refining the tune a bit more. I'm hoping it'll be ready for dyno tuning in a few weeks. 

[Dat73z]

I went for another long shakedown drive yesterday for an hour or so of mixed driving between traffic and high speed running. 

 

It is apparent one of the pitfalls of these setups is the extreme turbo heat. 

 

I noticed the plastic Lokar throttle cable I had recycled from my other build began melting from the radiant heat of the turbo. Also after long duration high speed running, if I don't open my hood at shutdown the fuel will boil in the carbs. 

 

I've ordered a stainless lokar cable and will relocate it away from the turbo along with additional heat sleeving and shielding plates under the carbs. 

[rossman]

Mine definitely suffers from heat soak if I restart it between ~20 min and 40 min after warming up. It is common for most Z's and especially turbo'd versions. It's the reason Nissan incorporated a blower that fed cool(er) air over injectors on later model ZXs.  

[rossman]

How long after shutdown do you get the boiling sounds? It could be that pulling water from the already heated block coolant is causing it overheat. I attached my coolant line to the water pump inlet to avoid that situation. After shutdown hot water flows up to the thermosphere and siphons water from the coolest point in the system to cool the turbo. At least that's what happens in theory.

[Dat73z]

@rossman a minute or two after shutdown the boiling from the CHRA starts. I think my issue is actually how I have my lines routed. You can see in the pic I drew on above, my turbo coolant line runs from the pass side, over the hot turbo and into the side closest to the DS shock tower. The return is lower on the opposite side. At shutdown the hot turbo heat rising into that line isn't helping either I'm sure and I think with the way that line is routed, instead of pulling cool water from the PS side it's boiling back over to the heater core branch...

 

I'm going to swap around the lines with one feeding from the block, and the other from the DS shock tower side back to the tstat housing first. Just waiting for parts as usual. 

 

For the heat soak I've decided to go all out on it. This AM I safety wired in the vband shield. I also ordered some of this to fabricate a large heatshield under the carbs: https://www.heatshieldproducts.com/inferno-shield

 

I will also do a brushless ducted fan or two to run after shutdown, similar to how I've seen some triple carb guys in Japan/tropical environments do to deal with the heat