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86 RX7 with Turbo LM7 and Megasquirt


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Unfortunately I have some bad news from this weekend. My turbo had not been spooling the last couple drives. Keep in mind I have only driven this car in the driveway about 10 times total. I pulled the air filter off to make sure the turbo spins freely, turns out the compressor shaft got bent somehow. When you spin the compressor by hand it wobbles around and touches the housing. The turbo was a rebuilt T6 (rebuilt by detroit diesel). I have never really read of anyone having this happen before. It had an air filter on it the hole time and the blades are perfect so nothing hit them. I guess it was heat that did it?? I had primed the oil line and it built boost the first couple drives. Pretty weird, I am going to talk to Dave at majestic turbo to try and understand what could cause this before I get another turbo or get this one rebuilt. I will probably have this one rebuilt with an 88mm wheel, that was my plan for further down the road. The turbine wheel does not seem to wobble, so the bend is only on the compressor wheel end. I checked the trubo repeatedly during the install whenever I would re-clock the housings to make sure the shaft spun freely and I never saw a problem with it. hmmmm.....

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  • 1 year later...
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OK, 18 months later I decided to put closure to the turbo failure. Mainly the car has been setting because I have been catching up other things. My son is now old enough to be interested in the car so I had him help me pull the turbo last night and inspect everything. This is what I believe and what I found:


-- Oil supply fittings, lines, all looks good and clear to the turbo(AN -4 no restriction). Feed is from recommended location on LSx oil pan above oil filter. This is filtered oil that it headed to the mains. Pressure measures good.


-- Drain is 3/4 inch to oil pan location specified by banks install manual. Angle is not great, room for improvement here. I can blow into the drain tube and air comes out crank vents, but pressure builds in crankcase and when I let off some air comes back out drain tube. That doesn't seem right, the engine is going to have more blow by than I can blow into the crankcase, I would think??. I do not have a crank vent to intake so vacuum under light throttle will help evacuate, maybe I better do this.


-- Took apart turbo and see that brass bushings and main shaft at location of bushings look OK. No scrapes, no heat marks, shaft still spins freely in bushings. Thrust surface is scuffed and has heat marks. Front seal is shot and scraped. Compressor wheel wobbles and hits housing. No signs of damage to fins from foreign object.


-- Some Facts: Car never had a blow off valve. Car was driven about 10 times down driveway, less than 5 miles. Few hits of boost, about 8psi. Compressor always chopped/surged when throttle plate closed since no BOV.


What I get from all of this:

I am no turbo expert, but I don't see signs of oil starvation. I believe the first thing that happened was the compressor hit the housing and the shock bent the shaft. Once this happened and the compressor wheel started wobbling, then the thrust bearing made contact and heated up, the front seal wore out and that is how the turbo sets now. I think only two things would have caused the wheel to hit the housing at boost rpms, short loss of oiling (not sure how this would happen, even with crankcase pressure I should only see the seals fail and burn some oil) or compressor surge on letting off the throttle after boost run caused the wheel to shake and hit the housing. I believe the second occurred, but have no way to prove it. Remember, this is a T6 frame turbo with a 76mm compressor wheel. It was pushing some serious volume when I would let off the throttle and cause surge, I know a lot of people don't believe surge can hurt a turbo but I am convinced that compressor hit the housing because of it. I could be wrong, but I have to go with something and I don't see lack of oiling by looking at the bushings.


What I apply to the next turbo setup from this experience:

Try to angle the drain line better. Try to evacuate crank pressure better. Install a BOV from the beginning. Maybe run with the 1 quart overfill for the well known LSx sump issues.

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Hey guys, just came across another thing that could have made the turbo fail. Saw this guy on another forum talking about a turbo failure he saw when teflon tape was used on the oil feed line fittings. Some of the tape ended up clogging the turbo oil passages. Guess what, I used teflon tape on the fittings. That probably makes the most sense.


Only other thing I saw was if the car sits for long periods to re-prime the turbo oil line before starting the car. I also see that it is recomended by several folks for this turbo size to use a AN -6 feed line and AN -12 drain. I'll look into that.


Anyway, I am going to replace the turbo with a Borg Warner s400. That is a T6 frame bolt in replacement and supports ~900hp. Should spool earlier with 1.10 AR Turbine housing.

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  • 10 months later...

Since I am still low on funds I am thinking of putting a stock converter on the powerglide and driving the car non-turbo this summer. Its a 5.3 with an LS6 cam so it gets around ok without boost. Guess I better put a muffler on it too :wink:

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  • 1 month later...

I got some inspiration and sold a bunch of parts out of the garage so I can get this car going.


So today I put an S475 turbo and JGS 50mm WG on order. :cheers:


This time I will be using AN-6 oil feed for the large T6 turbo.


The List of things to do to get this car running:

Install new wastegate

new turbo should be drop in replacement for the old, we shall see

Start tuning


That is it...I already had everything working on the car with the old turbo. I think I'm getting excited and if you know me that is rare :D

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  • 7 months later...

I worked on the car a bit over the weekend and I think I came up with a plan for this winter.


Right now the car only needs a muffler installed to be driven with MS1 running the engine and no turbo. I had already put a downpipe on the car so I could keep it running without the turbo, but no muffler. Sitting on the bench I have the S475 turbo, JGS wasteagate, new BOV, second fuel pump with dual fittings and MS3 computer, but none of these are installed.


So I think my plan will set up in three stages:


1. Put a muffler on it and drive it a couple days to work to see how everything works on the open road. The car has never been driven more than a couple miles at a time.


2. Then, put MS3 on the car and drive it some more to get tune working and colds start, IAC, etc.


3. Take the car down to install the new turbo and wastegate. At this time I need to re-build my hot piping with stainless and good flex joints that won't come apart. I also need to change my BOV and add the dual fuel pump setup. One other thing is that I need to put adjustable rear links on my 8.8 setup. I have no idea at this time what to do for exhaust with the turbo, that is one unknown. My current downpipe is 4".


Over the weekend I worked on two leaks. One was leaking from the bypass plate above the oil filter where I had tapped for turbo oil feed. The other leak is the speedo bullet on the powerglide. Looks like I have the old style bullet with only an o-ring seal and nothing on the speedo gear. So I ordered a new style with a seal on the gear as well.


Just another data point, this whole time I have kept my PC680 battery on a float charger and it still seems to work great.

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  • 2 years later...

I got back to work on the car in August and got it driving in the end of November this year without a turbo.  The car is running very good on MS3.  I re-did all of the power and gnds in the car and made my own relay center.  Tucked all the wiring.  I used a copper bus bar to allow everything to be grounded together and grounded to the engine block.  The LS truck coils have their high power ground connected to the heads.  No more electrical noise issues and MS3 is awesome.  Car starts immediately and idles fantastic with 80lb siemen deka injectors on pump gas.  BTW, the PC680 battery is still working great.  I did add a disconnect switch so I can be sure I'm not drawing power while on the float charger.  I did a host of other small things that are detailed in my build thread on norotors.com, connected trans brake, did a temporary v-band single exhaust that I can swap on to run non-turbo, etc, etc


All parts are ordered to get the S475 turbo and JGS 50mm wastegate installed over the Christmas break.  This time I am using C6 L3 exhaust manifolds pointing forward.  All stainless 304 v-bands, 2.5" piping, lined flex joints, and a single divided pipe to wastegate to maintain the divided housing.


Relay and Fuse center with MS3



PC680 battery, new fuel system, tucked wires



MS3 and Tuner Studio on JimStim



New Power Distribution Schematic



Main 80 amp fuse for entire car power


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  • 2 weeks later...

Surge can overload the thrust bearings and cause the thrust surface to "jump" the oil wedge. This flow reversal can deflect the shaft and if conditions are right precipitate a rub. Generally it occurs in the inducer radial region. An ultra-quick stop can bend a shaft also.... This could happen during surge if the thrust bearing oil wedge is jumped, and the bearing acts in conjunction with the airflow reversal to "brake" the wheel to a stop while the turbine is still getting inertial drive.


A bent shaft and imbalance will usually overload the journal bearings. Thrust bearings are in effect when on load and when surging. Balance should not effect them whatsoever.


Teflon tape is STRICTLY forbidden on most manufacturer's high speed rotating equipment these days. I have a long PowerPoint on sealants and assembly instructions basically stating Teflon Tape was miracle stuff in the 60's..but it's time has come and gone. Use nothing but Loctite 567 PST or other permutations for sealing threaded connections!


The Long King Equipment Warehouse Yard in Songjiang Shanghai is littered with rolls and rolls of Loctite 55 Teflon Cord thread sealant from me taking it out of our assembler's tool kits and throwing it over the fence! Those shards will get into the bearing and destroy the oil wedge, wrecking a machine....if they pass through unless you examine the return lines and sump VERY carefully you will chalk it up to something else. It's. Not so much "clogging" that is the issue, every manufacturer warns about the "teflon strings" that get cut off on sloppy installation and float freely into the high-speed rotating journal-bearing area. It screws up oil distribution, or in extreme cases actually wraps around the shaft! I go so far as to tell the piping contractors on site no Teflon on the water side, either...since big threads get into our oil coolers and plug up the works.


All arguments for proper application aside, the basic fact is anaerobic sealants are more reliable on threaded fasteners with absolutely no downside whatsoever... There is no reason to ever use Teflon tape to seal a threaded union any longer. The only place I concede it's usage these days is wrapping the un insulated junctions of Bently 3500 Vibration Probes!


Insofar as. Oil return goes, if the oil return is below the oil level, it will render the crankcase pressures you may experience moot. This is the case for crankcase breathers at least. On most high speed rotating machinery, the oil cream (whipped with entrained air) is returned over a surface plate to give the oil time to de-aerate before running into the sump. At worst it dumps atop the oil and "floats" while dissipating. This is where you make the return point as far away from the oil pickup point as possible so as not to suck up whipped oil into the pump for obvious reasons.


Hope this shed some light on what may have happened.

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  • 2 weeks later...

Thanks Tony.  I now use a proper thread sealant on all tapered fittings.  


Update pics.  Some of this is mock up. I installed the 34327 radiator up front and remounted my PG cooler.  I kept the taurus fan with this new radiator and the new location.  I replaced the plastic heater hose tee with a metal one.  Installed hood pins.   I threw together a quick junk bracket so I could get started on the hotside fab.  Everything is clearing good with the hood.
Whats left before the car starts:
Weld in drain fitting to timing cover
Here is the last pic I took before the turbo install started, shows old radiator placement
Here is new radiator placement
AN -12 pushloc disassembled to be welded into the timing cover for oil drain
Drivers side hot pipe allowing clearance for power steering connections
Symmetry went out the door in favor of placement for everything, exhaust, WG, intake piping, room for stainless heat shield
Subtle exhaust
Dual DSM BOVs 
Hood Pins
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  • 2 weeks later...

MS3 is working very good for me.  I have not had a chance to get the idle air controller working yet.  I would like to experiment with a boost controller at some point and set up at least the tableswitch input for E85 and pump gas via a toggle switch.  I don't know if I want to mess with the actual ethanol sensor for flex fuel vehicles.  I think two options would be good for me for fuel.  Hey, you are not too far away from me.  We need to meet up some time.  I'll let you know if I'm headed your way this summer.

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Made a tool to hold the balancer using a couple hardened 1/2 bolts through a large piece of angle.  It works great using a clamp to hold it up against the balancer.  The end catches the frame rail to allow loosening and final tightening of the balancer bolt.  This was my most dreaded job because I didn't have a good way to hold the engine and work the bolt being by myself.  I do have one of the pieces of all thread and a large thrust washer for installing the balancer that I made years ago when I swapped from LS1 to 5.3.









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OK, put everything back together.  Primed oil to the turbo and fired it up.  Just let it idle until thermostat opened.


Oil feed:





Engine View:



Start up vid, this was first try at startup after setting for one month.  PC680 battery and stock LS1 starter.  ASE needs a little more tuning, it almost died once.



Another vid of idling:



Looks like I will try a drive tomorrow and check the base WG setting.  

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