11-05-2020, 12:55 PM
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#91
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Quote:
Originally Posted by gamefreakgc
I thought about that too when I saw his last post but unlike a supercharger that needs a one-way valve, a turbo is pressurized all the way up to the MAF. I don't think it would have a way to leak? Just boost pressure making it's way in with the injector pulses.
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Yeah, it'll be dependent on how the intake system is run. But the air assist port is unrestricted on a stock 5vz, so boost can leak back out depending on the air source for that.
-Charlie
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11-05-2020, 08:43 PM
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#92
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Quote:
Originally Posted by phattyduck
Yeah, it'll be dependent on how the intake system is run. But the air assist port is unrestricted on a stock 5vz, so boost can leak back out depending on the air source for that.
-Charlie
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Can you help me understand what y’all are talking about?
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11-05-2020, 08:46 PM
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#93
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I noticed this weekend that my exhaust gasket was leaking. Finally bought a proper replacement. Just documenting the PN in case I need to replace it again.
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11-05-2020, 10:44 PM
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#94
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Quote:
Originally Posted by Myrunr2010
Can you help me understand what y’all are talking about?
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I'll try and explain as best I can. Under the throttle body you've got a vacuum hose that goes from the IAC valve to the intake manifold where it t's to both engine banks. This hose supplies air to the injectors which helps atomize the fuel at idle and low speeds. Under vacuum it's not an issue but on a supercharged engine it's a massive boost leak as you'll have pressurized air actually exiting the intake manifold, past the injectors and back into the throttle body/intake. Toyota addresses this by adding a one-way check valve to the hose to keep boost pressure from escaping.
My thought is with a turbo the entire intake is pressurized due to the turbo making boost before the throttle body and makes this a non-issue, but maybe not. You could add a one-way check valve to the IAC hose if you want to see if that solves it. Should only take $5 and 5 min of your time. You'll want the flow of air to go from throttle body -> intake manifold.
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11-06-2020, 05:16 AM
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#95
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Quote:
Originally Posted by gamefreakgc
I'll try and explain as best I can. Under the throttle body you've got a vacuum hose that goes from the IAC valve to the intake manifold where it t's to both engine banks. This hose supplies air to the injectors which helps atomize the fuel at idle and low speeds. Under vacuum it's not an issue but on a supercharged engine it's a massive boost leak as you'll have pressurized air actually exiting the intake manifold, past the injectors and back into the throttle body/intake. Toyota addresses this by adding a one-way check valve to the hose to keep boost pressure from escaping.
My thought is with a turbo the entire intake is pressurized due to the turbo making boost before the throttle body and makes this a non-issue, but maybe not. You could add a one-way check valve to the IAC hose if you want to see if that solves it. Should only take $5 and 5 min of your time. You'll want the flow of air to go from throttle body -> intake manifold.
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Interesting. Thanks for that!
I have been dealing with some boost leaks around the IAC, but I think it’s the gasket that secures it to the TB. It’s hard to tell exactly where it’s coming from when I do a leak test though.
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11-06-2020, 05:39 PM
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#96
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Quote:
Originally Posted by Myrunr2010
Interesting. Thanks for that!
I have been dealing with some boost leaks around the IAC, but I think it’s the gasket that secures it to the TB. It’s hard to tell exactly where it’s coming from when I do a leak test though.
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The gaskets Toyota use aren't made for boost, especially after they've had 10-20 years to degrade. The torque specs are too loose for boost as well. My repeat offender is the lower plenum to intake manifold connection. It leaks if I don't torque it almost 2x as tight as it says in the manual.
It might be worth the effort the next time you do some work on the engine to take off the throttle body and upper/lower plenum and just replace them all and torque them down tight. That way you can rule them all out and get a more reliable tune.
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11-06-2020, 09:11 PM
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#97
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Quote:
Originally Posted by gamefreakgc
The gaskets Toyota use aren't made for boost, especially after they've had 10-20 years to degrade. The torque specs are too loose for boost as well. My repeat offender is the lower plenum to intake manifold connection. It leaks if I don't torque it almost 2x as tight as it says in the manual.
It might be worth the effort the next time you do some work on the engine to take off the throttle body and upper/lower plenum and just replace them all and torque them down tight. That way you can rule them all out and get a more reliable tune.
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Yeah, I got the TB gasket and the IAC gasket replaced. Holding boost much better. Still not holding pressure perfect, but it takes like 20-25 seconds to leak down completely. The manifold gaskets seem to be holding ok.
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08-23-2021, 08:30 PM
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#98
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I’ve been thinking of reracking my exhaust some and dropping the muffler. I don’t make boost quite as early/quickly as I would like to. I’m hypothesizing that the bend I had to put in the exhaust between the cat and the muffler, coupled with the turbo flange being flush mounted to the pipe is causing a fair amount of turbulent flow and now allowing the turbo to spool up as quickly as it could with a faster flow.
If I lose the muffler I can push the turbo back and up some (the undercarriage gains a lot of height when you move back a little closer to axle) and use a straight pipe to 90 degree elbow like I had originally planned on doing.
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12-18-2022, 05:54 AM
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#99
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Updates??
Hoping this is still going strong. I am acquiring parts now looking to do something similar. I actually want to put the turbo where the cat mounts to maximize heat scavenging and minimize all other cons of a rear-mount. Kind of a best of best worlds underhood and rear-mount. What is your assessment of this? I like the idea of using a delay relay instead of a turbo timer. Great idea.
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12-18-2022, 07:07 AM
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#100
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Quote:
Originally Posted by KK99T4r
Hoping this is still going strong. I am acquiring parts now looking to do something similar. I actually want to put the turbo where the cat mounts to maximize heat scavenging and minimize all other cons of a rear-mount. Kind of a best of best worlds underhood and rear-mount. What is your assessment of this? I like the idea of using a delay relay instead of a turbo timer. Great idea.
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I don’t understand what you’re trying to do with the heat? Usually you want to limit your heat input, which is an advantage of the rear mount (ie no need for an intercooler). You would be running your oil lines significantly shorter, which could be an advantage just from a build logistics standpoint. I think a lot of cat piping only had a flange that is where the exhaust manifolds collect up next to the tranny. Would you cut your cat off and put a flange in? Height would be another concern, just getting it to fit and being able to run the intake to it and the boost piping back. It’s an awful lot going on right in that area.
I’m excited others are interested in the idea!! Keep us posted on the build! Turbos are fun!
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12-19-2022, 02:32 PM
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#101
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Quote:
Originally Posted by Myrunr2010
I don’t understand what you’re trying to do with the heat? Usually you want to limit your heat input, which is an advantage of the rear mount (ie no need for an intercooler).
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You want to maximize heat into the turbine (or, rather, wasted heat loss between the engine and turbine). This allows for the maximum energy extraction from the exhaust.
I've always seen the 'downpipe' area as a good possible spot for a turbo - especially coming from the Subaru world... Packaging is always an issue. I'd love to watch a build done that way.
-Charlie
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12-19-2022, 05:03 PM
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#102
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Quote:
Originally Posted by phattyduck
You want to maximize heat into the turbine (or, rather, wasted heat loss between the engine and turbine). This allows for the maximum energy extraction from the exhaust.
I've always seen the 'downpipe' area as a good possible spot for a turbo - especially coming from the Subaru world... Packaging is always an issue. I'd love to watch a build done that way.
-Charlie
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That doesn't really clear it up for me, unless my understanding on the physics of turbos is really off.
The turbo isn't anymore efficient with more heat, I'd wager it's less because that's a higher heat transfer to your incoming air, making it less dense and require cooling before putting it in the motor (ie an intercooler or meth injection).
Heat is just a byproduct of combustion, but a turbo would still work the same if the air coming out of the motor was cold.
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12-19-2022, 05:23 PM
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#103
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Quote:
Originally Posted by Myrunr2010
That doesn't really clear it up for me, unless my understanding on the physics of turbos is really off.
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Sounds like it is.
Higher heat for the same mass = more pressure (or volume). This is basic PV=nRT.
More pressure/volume from the same mass is more energy. The turbine acquires from the exhaust based on the pressure ratio between the inlet and outlet of the turbine (which is based on pressure and flow). More energy into the turbine = more energy available to be extracted.
Temperature on the compressor side of the turbo is (nearly) completely disconnected from temperature on the turbine side. The oil and water cooling, along with distance makes sure of that.
Look how literally EVERY OEM that is making turbo engines does everything they can to put the turbo as close to the engine as possible... Subaru low-mounts them now, many turbo v-engines are 'hot-vees" now, etc.
-Charlie
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12-19-2022, 05:54 PM
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#104
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Quote:
Originally Posted by phattyduck
Sounds like it is.
Higher heat for the same mass = more pressure (or volume). This is basic PV=nRT.
More pressure/volume from the same mass is more energy. The turbine acquires from the exhaust based on the pressure ratio between the inlet and outlet of the turbine (which is based on pressure and flow). More energy into the turbine = more energy available to be extracted.
Temperature on the compressor side of the turbo is (nearly) completely disconnected from temperature on the turbine side. The oil and water cooling, along with distance makes sure of that.
Look how literally EVERY OEM that is making turbo engines does everything they can to put the turbo as close to the engine as possible... Subaru low-mounts them now, many turbo v-engines are 'hot-vees" now, etc.
-Charlie
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I’d love to see some data on how much efficiency/energy is gained from that. In principle that makes sense though.
Curious how the temperature on the compressor side is disconnected from the turbine side? Just because the connection between the two sides isn’t that bulky and heat soak isn’t that bad?
How does Subaru handle oil return on the low-mounts?
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12-19-2022, 07:16 PM
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#105
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To put it another way, heat is energy. Hot gas expands in volume and when the gas cools (loses energy) it contracts and takes up less volume. In the terms of an exhaust pipe, the pipe cannot expand with heat but the gas does which translates to higher pressure and velocity which then in turn increases the RPM of the turbine. I agree on the concerns on heat dissipation from the intake charge though and that would be the part that would take the most time to figure out. In theory, the science of having a turbo as close to the exhaust as possible does increase power.
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