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After 5 years of use my GT2256V was starting to show its age, bypassing some oil on the compressor side and occasionally making a *woo* sound when it spooled up from idle.
Having a GT2359V from an E320 CDI on my shelf, I decided to combine the best of both worlds into a hybrid turbo. And the GT2356V hybrid VNT was born.
Great exhaust flow of the GT23 turbine with the well matched flow characteristics (to an OM617) of the 56mm GT22 compressor.
I had to make a new adapter plate due to orientation differences between the Sprinter and E320 turbos. The Sprinter flange requires a slight upward tilt for the turbo's outlet flange to be level where the E320 is square with the T3 flange. The rearward stud on the adapter plate is longer to accommodate the intercooler's support bracket.
Spool up speed is nearly the same thanks to it's VNT design.
The exhaust backpressure : boost ratio is now always close to 1:1 across the RPM range, the GT22 turbine was 1.5:1 most of the time and rose to 2.5:1 on the top-end.
I got rid of the flex tubes that coupled the GT22 outlet to the exhaust, it was a constant leak issue trying to seal the thin metal with a clamp designed for pipe. The outlet pipe is now a 3" od-od coupler pipe welded directly to the turbine outlet and downpipe flange, with the flange being bell-mouthed to improve flow stability.
That also got rid of the support bracket that bolted to the manifold, reducing heat conduction loss from the manifold to downpipe. Here the exhaust manifold pressure (EMP) pipe can be seen.
The only down side so far is its louder at idle, both with vanes open and closed. Sound level measures 84db at full power at 70mph, thats with the shorty pipe outlet at the passenger door and windows up.
Its been raining pretty consistently the last few days, so my water injection system is not able to work (vaporize) as effectively as it can. Once the weather warms up and dries up I will get a dyno run to determine what kind of power gains I got from the improved EMP:boost ratio. Stay tuned!
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I have a new solution to the low-rpm surge problem that eventually wore out the 2256.
Bob Myers makes an electronic drop-in replacement for the stock tach amplifier. He will be programming one to trigger a vacuum solenoid from 0-2300rpm, that will control an air recirculation valve (ARV) to dump intake air from the manifold back to the turbo inlet via 3/4" hose. The valve to be used is a common air injection shutoff valve used on pretty much every g@sser W126 model.
This will increase the effective displacement of the engine by roughly 20% and bring airflow to the right of the surge line.
The graph below shows airflow at my altitude of 5200' from 1500-2300rpm at the 4, 10 and 13psi stages.
Red= no recirculation
Blue = recirculation w/water injection
If this works out there will no longer be any need to pursue an 1800rpm stall speed torque converter.
The valve is installed with a few alterations.
Bench testing found the valve can't hold more than 10psi without leaking. To counter this I made the vent side of the control solenoid open to manifold pressure with a check valve to prevent air constantly flowing in-out of the valve.
Water injection is disabled with the valve open to prevent water getting into the turbo's control system.
A light in the cluster was added to show when its open.
A manual switch was added to disable operation if desired.
The valve flows too much air when open, drive pressure is high and boost is very slow to build even at high throttle rates. I will modify the ARV with a stop screw to limit valve lift.
There is too much air flow noise, I will install a muffler from a Ford's Air injection system.
Garret's compressor wheels are designed for gasoline engines. Its a good, very fast spooling turbo, but it spools too fast for an OM617 and surges below 2000rpm. The ARV was a good compromise but ultimately not what I was really happy living with.
The Holset I have now is a much better turbo all-round; more efficient, better quality, more durable. All it needs is a VGT turbine, which Holset announced this year and should start producing any time. As soon as I can find a part number I'll buy one new.
I will be very interested to see you run one when they come out, sounds like it could potentially be the perfect turbo for these engines, but I guess there will be a controller involved. Your controller seems to be the best I've read about, but I was hoping an IC based one would come around for us to copy or buy. Thanks to you I have learned an immense amount about turbos overall and even more specifically pertaining to the 617, but I'm hesitant to replicate the analog controller due to complexity at least for now. But I appreciate yoru posts.
Its not complex at all. Its just 3 ball-spring regulators like used with normal turbos (manual boost controllers), two roller valves and a vacuum actuator. The valves could easily be substituted with electrical roller switches and vacuum solenoids but I wanted to make it electricity-free for simplicity and reliability.