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I think the killer of the vj11 for the Mx6/Probe is no real oil cooler, and the crappy stock blow off valve
The F2T oil cooler is not an issue, or it would be a bigger problem on bigger turbos making more power = more heat, but it isn't.
The crappy factory bypass valve could very well kill VJ-11 turbos trying to run 15psi, because it leaks above 12psi causing to turbo to have to generate more compressor boost to deliver 15psi.

I have always done the chip, bov and boost control together. So I can't contribute any of the many dozens of IHI turbos my shop partner and I has disintegrated over the year. I can tell you my ported and polished heads are VJ-11 killers.
 

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Discussion Starter #22
Quick update. My tuner got back to me yesterday saying we picked up 33 horse, so looking at 231 vs 198 prior on a mustang dyno (add 15% to dyno jet). he did say the curve looked about the same as last time, meaning it starts falling off in the upper rpm. I was kinda surprised, as it was pulling hard all the way up before i brought it over, but obviously running on the lean side. Don't have the graph yet, but will post as soon as he sends it over. I say getting almost 17% pickup for $250 is not bad at all.

Tuner did mention that he thought it could be exhaust restricted. Told him it's 2.5" from down-pipe out back with no cat/resonator and only a muffler. Somebody did mention an upgrade to the stock O2 housing/elbow. Any thoughts on that?
 

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Discussion Starter #23
As promised, updated dyno graph. Old run is on here as well. New boost graph isn't on here, but he said she held steady. I'm running just the wg pressure and this is exactly where I wanted her to be. Not pushing my luck for a few extra hp on stock bottom end.
13553
 

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Quick update. My tuner got back to me yesterday saying we picked up 33 horse, so looking at 231 vs 198 prior on a mustang dyno (add 15% to dyno jet). he did say the curve looked about the same as last time, meaning it starts falling off in the upper rpm. I was kinda surprised, as it was pulling hard all the way up before i brought it over, but obviously running on the lean side. Don't have the graph yet, but will post as soon as he sends it over. I say getting almost 17% pickup for $250 is not bad at all.

Tuner did mention that he thought it could be exhaust restricted. Told him it's 2.5" from down-pipe out back with no cat/resonator and only a muffler. Somebody did mention an upgrade to the stock O2 housing/elbow. Any thoughts on that?
Is that at the same boost for both turbo's?

That is a good gain for the money.
However if that gain could have been made on extra boost on the VJ-11 ...
 

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Discussion Starter #25
Is that at the same boost for both turbo's?

That is a good gain for the money.
However if that gain could have been made on extra boost on the VJ-11 ...
i did up the boost on vj11 to about 15 pounds and it got better but nothing compared to this. do you think trying to make a custom elbow or finding one on here is worth it?
 

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As promised, updated dyno graph. Old run is on here as well. New boost graph isn't on here, but he said she held steady. I'm running just the wg pressure and this is exactly where I wanted her to be. Not pushing my luck for a few extra hp on stock bottom end.
View attachment 13553
Where you just running wastegate boost on both runs? It looks to me like the T-bird ran higher boost, if it wasn't for the t-bird lag up to 4080 rpm I would swear that was the same turbo at higher boost.

On the original run you can see boost falling off at 4800rpm and the powerband reflects it perfectly. The Tbird power band follows the VJ-11 power band almost exactly. The part that doesn't make sense is that if the T-bird boost graph is steady as the VJ-11 clearly is not than with a steady boost graph the VJ-11 would make as much or more power as the T-bird from 5000 rpm to redline.

Remember I wasn't criticizing your choice of RHB5 turbo on your build but the RHB5 in general and the T-bird as an upgrade for the VJ-11. Also normally when upgrading turbo's the turbo that gets replaced has been maxed out.

I don't think your falling powerband is exhaust flow because you managed to make more redline gains on the Tbird.
If it was exhaust flow restrictions the T-birds higher power band would tapper more to redline than the VJ-11.

Since the beginning I have been preaching boost control. Hear me out again. Look at your VJ-11 powerband and boost curve. Imagine the boost was perfectly steady to redline and correct the powerband to match, your overall power gains (area under the curve) to redline would be as great or greater than the gains from the turbo upgrade.
Could you manage to hold steady boost to redline for under 250$, I say yes.




Your powerband has some similarities to the F2T's powerbands higher mid range power:
13559

This is factory set-up and factory boost bone stock with and without Thermo spacers.
What causes such a power curve is the factory turbo solenoid valve, it only opens in mid range RPM from about 3000 to 4000 rpm allowing 1.5 to 2 PSI more boost than just the wastegate, you can definitely see by the powerband the effect lowering the boost mid rpm has, At 4000rpm when the solenoid valve shuts and pulls 1.5-2 psi boost from the wastegates operation while that extra boost (air) is still in the engine, the wastegate flap gets overwhelmed and boost (power) drops like a brick.

This I believe is Gavin's dyno without the factory turbo solenoid valve on stock boost:
13560


As you can see the powerband is broader but still falls to 90ft-lbs and 110hp near redline.
All three dyno's (yours included) reflect the flow characteristics of the VJ-11 turbo but I think the wastegate and falling boost play as big of a role in the power curve as the VJ-11. I say the drop in the torque curve on all three dynos is the wastegate flap getting overwhelmed by exhaust after the engine reaches peak torque.
If you where to add 20 ft-lbs torque to the entire curve on the above dyno chart (to be reflected on the HP band) VS having the same peak torque (190) but holding more power to redline and having the HP curve rising from 5000 rpm on the performance gains would be the same.

For me the first and easiest step in my F2T builds is to make it hold steady boost to redline, then move the powerband up on the chart.

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You mention not pushing your luck on a stock bottom end for a few extra HP.
I would like to mention that on your dyno sheet your torque line is a direct map of how much air you are getting in the engine burning and converting to energy at the wheels, weather you make that torque band at 3psi boost or 15psi boost the load on the engine (amount of air and pressure) is exactly the same.
Now you seem happy with the IHI and committed to it.
By running a divorce pipe better flowing O2 housing on the same wastegate will result in about the same curve on the dyno but at more power, you mention you don't want to push the bottom end so to match your peak torque you would have to turn the boost down a tiny bit, how different would the torque curve be?.

My recommendation for your build is to build a custom O2 housing but upgrade the wastegate, either to an adjustable internal actuator (user the end of the VJ-11 wastegate, cut it off and drill the new wastegate hole to fit over the factory wastegate end, and use the factory end and clip to attach the new wastegate to the swing arm) or an external wastegate running off the divorce wastegate pipe (you would need to cut the factory wastegate flap off the housing and plug the swing arms hole, enlarge the wastegate hole in the housing and have your divorced wastegate pipe recessed into the flange so it sits against turbine housing when the flange is bolted down.).

Flanges are available:
TRITDT Turbine Outlet Flange For Mazda MX6 / 626 RHB5 VJ11 Connect Dumppipe | eBay

Some of my experiences:

With a T3 45trim on my 89mx6 running a factory VJ-11 wastegate I had all kinds of problems holding any tipe of steady boost above 16psi, in order to run 21psi I added springs to stiffen the wastegate which would spike to 27psi and taper down. When I built a custom 2.5" O2 housing with divorced external wastegate the set-up held perfect boost 21psi all the time and was faster, the downpipe has a 2.5" electric exhaust cut right after the divorced wastegate .
13562

But the External wastegate and boost controller set up maintains boost so well that the car is no faster with the exhaust cut out opened, exactly the same 1/4 mile time and trap speed, 0 performance gain at 5" of flow over 2.5".

Now I attributed the cars performance gains to the better flowing housing I built and then the better boost control.

Step forward a few years, this is where things get interesting.


My 88 626 running a T3 60trim (60% larger than the 45 trim) and a random internal adjustable wastegate actuator on a modified bracket with the hand me down factory Saab 2 1/8" O2 pipe and wastegate swing arm housing that used to be on the 89mx6 before it's "upgrade". I figured the Saab housing would be restrictive and the internal flap would give me trouble maintaining steady boost, I though this was going to be a problem and I would be following the path of the MX6 with an external wastegate and even though the 626 is a budget build if I hit a wall I will have to change build plans...
But to my amazement and surprise the saab housing and customized internal wastegate make and hold boost just as well as the 2.5" external divorced wastegate on the MX6 and on a larger turbo running 30psi holds perfect boost all the time and is rocket fast.

And I was wrong, none of the 89mx6 GT's power gains came from the ported, smoothed seem, stainless steel, custom, divorced wastegate O2 housing/downpipe with exhaust cut out I built. All performance gains on the MX6 came from the external wastegate, not because it's external but because it holds steady boost.
So on an F2T with .48A/R exhaust housing and a T3 (up to 36lb/min flow) this:
13563


Flows as well and holds steady boost as well as this:
13564


Now perhaps when I find a 5bolt T3 stage 3 (T31) turbine housing for the T3/T4 F1-62 Turbonetic I have for the MX6 will it's custom O2 housing will possibly be necessary but only if I flow more air than the T3 60trim at 30psi on the 626 and I am not sure I need the MX6 to be any faster than the 626.

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So here we are full circle back at the beginning.
The problem is the spring in the VJ-11 wastegate, either they are all too old and heat cycled or they are just too weak.
Most internal wastegates have larger (not higher rated) springs, although a garrett 7psi and Vj-11 actuator will both move at the same 7 psi boost pressure at the diaphragm. But it will take a lot more pressure on the swing arm to move the garrett rod beyond it's opened point with 7psi signal. Old building pneumatic control actuators are the same as as wastegates on cars, buildings run at a max 15 PSI air line pressure, applying 15psi to the actuators will move the actuator rod but two grown men could not pull the rod out by hand the spring in the actuator is that strong. Can be moved with 15psi from one side but withstand 300psi+ from the other. This is because the 15psi is spread over 1 square foot of area and pulling 300 psi on the 1 inch shaft results in less overall overall pressure.
Most wastegates are like this because the spring diameter is larger than the flap diameter but the VJ-11 doesn't seem to be like that if you move it with 7psi pressure at the diaphragm and put a wrench on the swing arm it will only take a couple pounds torque on the wrench to move the swing arm farther opened.

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do you think trying to make a custom elbow or finding one on here is worth it?
Above is the long answer to your question, the Why. This is the shorter answer:

Until the turbo is operating at it's optimum across the power band and holding the steadiest boost it can there is no way of saying or knowing if running a custom elbow will be of benefit/worth it or necessary.
I guessed I needed one without knowing if I did and guessed wrong.
You may very well need one you are putting down good power.

The one thing that is for sure is that with either housing custom or saab had I continued running the VJ-11 actuator boost would have been all over the place and unmanageable and either set-up would have a lousy powerband.

The boost controller set-up I mentioned on page one works very well at maintaining boost to redline and improving the wastegates function but with larger turbos at higher boost the VJ-11 wastegate is junk.
Your running a larger turbo and every turbo flows different amounts of air per psi on different engines.

So the best and first thing is an adjustable Wastegate set to the boost you are running now.
Then you will know if an upgraded O2 housing is needed.
If you plan to use manual boost control the set-up I posted works better on every wastegate set-up than any other manual device or layout.

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You might think the MX6 custom pipe is way cooler but if you look at it this way If I was driving the mx6 and someone else owned and was driving my 626 (modded like it is) and we raced they would win. Afterwards if we both stood there with the hoods opened discussing mods and builds and we compared the MX6 downpipe/wastegate cost (650+$) to the 626 downpipe/wastegate cost (0$) which one of us would look like an idiot?
In my defense the O2 housing is part of the build I plan that's still in progress and because of the VJ-11 wastegate I had no faith in internal wastegates holding steady boost.

But looking at your dyno chart and taking into account the fact that torque is air consumed by the engine and if you look at the F2T base dynos you can see why the F2T snaps the shaft in the VJ-11 so easily above 15psi even though they don't make much more than 205peak HP the amount of early torque would be about 270ft-lb at the wheels. So the factory VJ-11 O2 housing may not be flowing it's limit on your car.
 

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Discussion Starter #27
i will definitely need to come back and re-read your post several times, but i will answer some questions. the first dyno i've posted with vj-11 had boost leaks (running wg pressure). i didn't have a compressor at the time and was using a raggity electric pump, so that's all on me for bringing a half-assed car to the tuner. however, even when i did fix the leaks and turned the boost up, vj-11 never pulled as hard as t-bird at wg pressure. honestly, i'm very happy with where she sits right now. if i can find this elbow at a decent price, i'll get it and test, but will otherwise just enjoy it until the time comes to upgrade the internals. not committed to the ihi setup at all. in hind sight, i should've searched around for a better kit back in the day, but i knew nothing about fi at the time. thanks a lot for your comments, MC, lots of good stuff in there to digest.
 
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