I'm not sure I follow?
Wouldn't work. To keep the smaller tubs working in their efficiency range, you need to control their waste gates by calculating the ratio of absolute pressures across the compressors, not as relative boost above atmospheric.Originally Posted by SEAN-NZ
When the bigger single is producing no boost, then you'd want the little tubs' wastegates to open at a manifold boost of, say, 1 bar. But when the big single presents the little tubs with one bar then you want the little turbos' wastegates to open at a manifold boost of 3 bar.
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Seems to me the best idea would be to have waste gates that will open at the lowest pressure needed, and electronically control them so you can have them opening at higher pressures.
Doubt it's centrifugal, unless it was fitted aftermarket to the toyota. AFAIK centrifugals aren't generally fitted to production vehicles for a number a reasons, the main one being that if you were starting from scratch, it's not a good design. Turbos and PD are better methods of forced induction.
They're popular with V-Techs, because their linear boost increase with rpm matches nicely with the power delivery of the honda lump. V-Tech engines are gutless below about 5000RPM and so would be ruined with, say, a roots blower. However, they come on song later in the rev range, just as the centri starts to sap power.
That said, I understand that centris are generally more efficient than PD in terms of parasitic loss.
Centris are also easy to install which makes them popular for aftermarket fitment, but because none are fitted by manufacturers, it means there isn't a glut of them lying around scrap yards.
Last edited by Jesus-Ninja; 13-04-2012 at 08:31 AM.
I'll have to ask him what it is when he gets back on Monday.
They'd be as adequate as the turbo that's feeding themThey flow volume so, in principle, if they can comfortably compress atmospheric (1 bar) air to 2 bar (ie 1 bar boost), then if you fed them 3 bar instead of 1 bar, they'd compress that 3 bar to 6 bar (ie 5 bar boost) - however heat management appears to become the issue, so either a massive intercooler after everything, or possibly even an intercooler between the single and the twins and then another after the twins. Packaging becomes complicated. Air>Water>Air charge coolers?
Something like this maybe, if you don't want to go down the route of water cooling:
Car021Large.jpg
Definitely something like that
I'm thinking that for a mild setup using stock twins, that you want a single to feed them that flows really well but doesn't make mental boost.
Here's what would, in theory, happen if you ran the twins to produce about a bar of boost on their own (peaking at just over a bar and then trailing off, so not pushing them hard), and then added a bigger single that only made 10psi
curve2.JPG
I tell a lie - seems they used one on the Scion. http://www.motortrend.com/features/p..._05.html#photoDoubt it's centrifugal
What if we were to use a differential pressure sensor between the inlet and outlet of the smaller turbo's compressor. This would give us the pressure ratio currently being generated and could be used to control the smaller turbo's waste gate.
It would give you the difference, but you want the factor. Eg with no boost from the big one, the difference for a bar of boost on the little one(s) would be 1 bar, but at the same ratio with the big one producing one bar, the difference would be 2 bar. You'd need something clever to electronically work out when the ratio is 1:2, unless there is some other mechanical way of doing it that my brain can't compute
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Ok, so three pressure sensors. One before the turbos (there's actually already one in the MAF we could use), one between the turbos, and one after the turbos.
The difference between the first and second gives us the pressure ratio of the larger turbo, the difference between the second and third the pressure ratio of the smaller turbos, and the difference between the first and third, the overall pressure ratio.
I'm thinking... an Arduino could be used to monitor the 3 MAP sensors via AnalogIn, control the duty cycle on multiple wastegates via PWMOut through a Transistor / Darlington Array, and then perform some calculations and either output a MAF emulation signal (PWMOut again) or a MAP sensor signal (AnalogOut) to connect to an ECU
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Kinda what I was thinking.I'm thinking... an Arduino could be used to monitor the 3 MAP sensors via AnalogIn, control the duty cycle on multiple wastegates via PWMOut through a Transistor / Darlington Array, and then perform some calculations and either output a MAF emulation signal (PWMOut again) or a MAP sensor signal (AnalogOut) to connect to an ECU
Stop stealing my thoughts!
Okay, assuming you get it all working with separate boost controllers, or use wastegate spring pressure... will the internals of our engines hold up to 30 psi?
I know you are going for forged bits Scott, but there is still that factor of potentially scattering engine parts all over the place once the big turbo kicks in.
The big turbo doesn't kick in.. it gradually spools up as it normally would. You just have the advantage of already having boost from the smaller one. If you size the turbos right you get a nice smooth transition.
I was always told above 1.5 bar (22 PSI) was Kenny Loggins (Danger Zone).
Why would we want that high boost anyway to start with? Surely just being able to hold 1.2 bar boost with relatively colder air through the rev range would be a far better for power top end?
Initially yes. But where's the fun in stopping there?
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