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Yes and maybe.
Posts by lo bux racer
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He didn't ask about twincharging a tC, the question appeared to be general, can you do it. Sure you can. I wouldn't do it to a tC without doing a LOT of other things first, like closing the deck the way Jotech did with theirs. Of course that brings cooling system issues, then there's fuel, and engine management, fasteners, rod and crank strength...it just goes on. But you sure can twincharge anything you want...
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This Mazda block has an open deck.
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This is a V-6 with an open deck here. Notice the open ring all the way around the top of the cylinder.
Here's a closed deck (conventional) block
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Now look at Jotech's solution to the problem.
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They need all this support to run boost. Thin cylinders with open decks do not survive boost. Even the venerable 2JZ should be ultrasonically tested for wall thickness at the top of the cylinder if boost over 25 psi is planned. An open deck makes it cheaper to cast the block, and it makes the block much lighter. It also severely limits the power potential unless you "close" the deck the way Jotech did. It is very common to close the deck on Honda engines for running boost.
This is a V-6 with an open deck here. Notice the open ring all the way around the top of the cylinder.
Here's a closed deck (conventional) block
Now look at Jotech's solution to the problem.
They need all this support to run boost. Thin cylinders with open decks do not survive boost. Even the venerable 2JZ should be ultrasonically tested for wall thickness at the top of the cylinder if boost over 25 psi is planned. An open deck makes it cheaper to cast the block, and it makes the block much lighter. It also severely limits the power potential unless you "close" the deck the way Jotech did. It is very common to close the deck on Honda engines for running boost.
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It's not only 8 psi. Compressors work with pressure ratios. If I feed a turbocharger air at 8 psi and it has a 3:1 compression ratio, I'll get 24 psi out. It's pretty obvious if you look at the compressor maps.
Did you ever see a tractor pull with triple charged diesel? They push 200+ psi because each of the three sections multiplies the output of the last. Even with a moderate 2:1 ratio, you end up with 8 times atmospheric (117 psi at STP) without accounting for pressure rise from compression heating.
The trick with twin-charging is to set it up for the supercharger to work at low rpm and the turbocharger to work at high rpm with a switchover strategy. That's how HKS does it to provide the best of both worlds.
Did you ever see a tractor pull with triple charged diesel? They push 200+ psi because each of the three sections multiplies the output of the last. Even with a moderate 2:1 ratio, you end up with 8 times atmospheric (117 psi at STP) without accounting for pressure rise from compression heating.
The trick with twin-charging is to set it up for the supercharger to work at low rpm and the turbocharger to work at high rpm with a switchover strategy. That's how HKS does it to provide the best of both worlds.
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I must be stupid. I had a AW11 with the 4A-GZE, and I'd swear it was a 1.6 liter. Wait, that's what everyone else on the web says too. Hmmm. Great info.
You just have no idea who I am or what I know, but you keep trying...
You just have no idea who I am or what I know, but you keep trying...
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12,590 Posts
I am actually a well respected member of the Supra community at www.mkiv.com. I am also familiar with the ST185, and have a few friends in that community as well.
Calling a Roots blower "not a compressor" is semantics. It is a compressor or it could not build pressure. It just happens to be the least efficient of all compressors at about 60% (with new rotor seals). If you feed it pressurized air, it will put out more air than it would at atmospheric, just like any other good compressor. I completely agree it is the least desireable of all the supercharger types available. I'd take a Lysholm or Whipple over a Roots in a second.
Insane boost is a relative term. It's hard to find insane on a 2JZ, however, the 2AZ is not cut of the same cloth. It won't matter much how you pressurize the air with a 2AZ, the block just isn't up to much boost without major modification. Here is where I take strong exception to your statement "it all comes down to tuning". The block will not support high boost without major mods. Why are there no 1000 hp NSX's? Their blocks don't support boost without cracking very shortly after they are boosted. The tC will suffer the same fate. I'd be surprised if the stock unmodified block will tolerate even 8 psi for any significant length of time before it cracks.
AFA compound boost, twincharging isn't compound boost (semantics again). Compound boost is putting multiple compressors in series. Twincharging is using one method at low rpm, and another at high rpm to make a small engine perform like a big one (for the most part: BSFC says little engines with forced induction still need more fuel to make the same power). I understand the concept just fine, and I followed Toysport's MR2 Twincharging project many years ago. I have also seen one in the flesh at a shop near my house. They go really well with good fuel in them.
In any case, they make power down low with the supercharger and switch over to the turbocharger once the combination of rpm and load supports the turbo moving more air than the supercharger can move efficiently. The turbocharger is also inherently more efficient than any supercharger (except a Vortech, because a Vortech is just a gear driver turbo compressor section). I understand all this just fine.
Calling a Roots blower "not a compressor" is semantics. It is a compressor or it could not build pressure. It just happens to be the least efficient of all compressors at about 60% (with new rotor seals). If you feed it pressurized air, it will put out more air than it would at atmospheric, just like any other good compressor. I completely agree it is the least desireable of all the supercharger types available. I'd take a Lysholm or Whipple over a Roots in a second.
Insane boost is a relative term. It's hard to find insane on a 2JZ, however, the 2AZ is not cut of the same cloth. It won't matter much how you pressurize the air with a 2AZ, the block just isn't up to much boost without major modification. Here is where I take strong exception to your statement "it all comes down to tuning". The block will not support high boost without major mods. Why are there no 1000 hp NSX's? Their blocks don't support boost without cracking very shortly after they are boosted. The tC will suffer the same fate. I'd be surprised if the stock unmodified block will tolerate even 8 psi for any significant length of time before it cracks.
AFA compound boost, twincharging isn't compound boost (semantics again). Compound boost is putting multiple compressors in series. Twincharging is using one method at low rpm, and another at high rpm to make a small engine perform like a big one (for the most part: BSFC says little engines with forced induction still need more fuel to make the same power). I understand the concept just fine, and I followed Toysport's MR2 Twincharging project many years ago. I have also seen one in the flesh at a shop near my house. They go really well with good fuel in them.
In any case, they make power down low with the supercharger and switch over to the turbocharger once the combination of rpm and load supports the turbo moving more air than the supercharger can move efficiently. The turbocharger is also inherently more efficient than any supercharger (except a Vortech, because a Vortech is just a gear driver turbo compressor section). I understand all this just fine.
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