Turbo Efficiency Range for RX-8
01-04-2012, 01:29 PM
#302
Divided housing and external wastegate are the keys.
Total turbine flow doesn't matter much anymore when you can have up to 100% total flow in a wastegate-preferred manifold design.
You can almost double total throughput of the turbos discussed above just by shifting the exhaust path to the wastegate.
Total turbine flow doesn't matter much anymore when you can have up to 100% total flow in a wastegate-preferred manifold design.
You can almost double total throughput of the turbos discussed above just by shifting the exhaust path to the wastegate.
For the fast response we are talking about here the wastegate will be completely closed for spool-up so how can it make any difference where it is ?
All the exhaust flow is through the turbine.
And for total throughput I can't see it making much difference either . The turbo needs almost all the available flow through it to drive the compressor when you are maxing out the capacity of the turbo .
For control I can see it making a huge difference - which is , I believe , why you want to have an external wastegate.
Flame suit ................................................on .
Last edited by Brettus; 01-04-2012 at 01:56 PM.
01-04-2012, 05:06 PM
#303
Exhaust throughput are everything on a motor with the tremendous amount of exhaust output of a rotary. Going to a large turbine and housing to handle that energy just means you have to wait for it to spin the compressor.
Go with a small turbine and housing and simply divert what you don't need through a properly sized wastegate and you gain a significant amount of throughput at no penalty to the net shaft speeds.
Look up Lingenfelter and see what he has been doing for years on the Corvette builds.
Last edited by MazdaManiac; 01-04-2012 at 05:08 PM.
01-04-2012, 07:53 PM
#304
In other words, you are not stalling flow and building excessive exhaust pressure relative to intake flow and pressure. Think big wastegate area(s), in some cases an entirely separate wastegate exhaust system parallel to the main exhaust system, though when the main system is large enough for the output level in can be merged if done properly.
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Last edited by TeamRX8; 01-04-2012 at 08:02 PM.
01-05-2012, 01:24 PM
#306
Ok - I can see the benefit of dumping exhaust to atmosphere which effectively increases the size of your exhaust system thereby reducing backpressure .
But surely if you ran a large bore exhaust system with an internal wastegate the effect would be similar .
But surely if you ran a large bore exhaust system with an internal wastegate the effect would be similar .
01-05-2012, 01:46 PM
#307
If it could have a large enough area, but it can't.
Have you ever heard an open header rotary engine? That is what a large wastgate atmospheric dump will sound like because it is essentially the same thing.
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Have you ever heard an open header rotary engine? That is what a large wastgate atmospheric dump will sound like because it is essentially the same thing.
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Last edited by TeamRX8; 01-05-2012 at 01:51 PM.
01-05-2012, 05:28 PM
#310
That is a really crappy example.
Not only is it a "turbine-preferred" design, but the cylinders are not equally accessible to the WG, causing a significant disruption to the balance of exhaust flow across the engine.
The WG flange should be directly off of the turbine inlet and at an angle that the exhaust would favor over the turbo.
For a rotary, the WG should be a 50mm gate if possible. I'm using a 40mm gate right now and it really isn't big enough.
Not only is it a "turbine-preferred" design, but the cylinders are not equally accessible to the WG, causing a significant disruption to the balance of exhaust flow across the engine.
The WG flange should be directly off of the turbine inlet and at an angle that the exhaust would favor over the turbo.
For a rotary, the WG should be a 50mm gate if possible. I'm using a 40mm gate right now and it really isn't big enough.
Last edited by MazdaManiac; 01-05-2012 at 05:42 PM.
01-05-2012, 05:41 PM
#312
The other hidden problem is the heat an external wastegate must endure on a high output rotary.
I've destroyed 5 diaphragms on two separate Turbosmart wastegates over the last year. A wategate-preferred path puts most of the heat from the exhaust directly into the WG piston. I am trying a TiAL water-cooled gate now, but the next design will probably have two such gates.
When I was using an internal gate, I would destroy a turbine housing - cracking the wall between the main discharge and the WG flap - every couple of months.
Large gates or even two large gates would ameliorate that problem to some extent.
01-05-2012, 06:08 PM
#316
That is a really crappy example.
Not only is it a "turbine-preferred" design, but the cylinders are not equally accessible to the WG, causing a significant disruption to the balance of exhaust flow across the engine.
The WG flange should be directly off of the turbine inlet and at an angle that the exhaust would favor over the turbo.
For a rotary, the WG should be a 50mm gate if possible. I'm using a 40mm gate right now and it really isn't big enough.
Not only is it a "turbine-preferred" design, but the cylinders are not equally accessible to the WG, causing a significant disruption to the balance of exhaust flow across the engine.
The WG flange should be directly off of the turbine inlet and at an angle that the exhaust would favor over the turbo.
For a rotary, the WG should be a 50mm gate if possible. I'm using a 40mm gate right now and it really isn't big enough.
01-05-2012, 06:58 PM
#317
The boost control comes from the flow favoring the wastegate once it opens, which was the point of posting it. If the flow does not favor diverting to the wastegate you won't accomplish the objective of avoiding boost creep or having enough venting capacity to accomplish what we're discussing even if it is theoretically sized large enough. Flow does not just magically turn sharp corners regardless of whether it is a vacuum or pressure condition.
01-05-2012, 07:00 PM
#318
Hoping I can get educated on something I am wondering.
On a high/front mounted turbo, would you want the wastegate in front of or behind the 02 sensor?
I seem to recall a thread that stated the sensor needs to be 18" from the last exhaust port.
On a high/front mounted turbo, would you want the wastegate in front of or behind the 02 sensor?
I seem to recall a thread that stated the sensor needs to be 18" from the last exhaust port.
01-05-2012, 08:30 PM
#319
The turbo changed a few times along the way, too.
However, once again, I will refer you to Lingenfelter. There is a reason he uses such tiny turbines on his 1000+ HP Corvettes.
It doesn't really matter, unless the WG is VTA, in which case it would need to be before it.
01-06-2012, 02:41 PM
#320
01-06-2012, 03:45 PM
#321
wtf dude, very 1st hit on Google .... http://www.lingenfelter.com/
and I'm not sure if they are precisely relevant, they also do a lot of unique out of the box camshaft timing and other such tools that assists them on their reciprocating piston engine stuff that we obviously can't employ in a rotary application. A lot of that info is only available in very specific contexts and locations, you may or may not be able to get your hands on it.
and I'm not sure if they are precisely relevant, they also do a lot of unique out of the box camshaft timing and other such tools that assists them on their reciprocating piston engine stuff that we obviously can't employ in a rotary application. A lot of that info is only available in very specific contexts and locations, you may or may not be able to get your hands on it.
01-06-2012, 06:24 PM
#322
Not trying to make excuses for JoeMin, but it took about 20 minutes to find that VWVortex manifold shot. The Lingenfelter site is 1st among Google hits, but it shows damn all of the piping for their installations. Turblown's site is "Gray's Anatomy" in comparison.
Thanks for the PW46 PDF, quite informative.
Thanks for the PW46 PDF, quite informative.
