Twin Turbo Superchargers '62-63 Conversion

[California Racer]

Looking at the exhaust mounting sort of made me think of this.

How would the engine run if you added second Turbo Supercharger?

Using '62-63 engine as an example to attempt to keep things simple.

That is you run both output ducts into a chamber and then a duct from that out to each head.Two ducts total out from chamber.

How would that engine run fixed up like that?

[bbodie52]

If both turbochargers were the same size and same capacity, I doubt there would be a performance improvement. I believe the single turbocharger had enough capacity to provide the street-tuned 145 CI engine with adequate boost. A slightly larger turbocharger was fitted in 1965 to make use of the increased displacement 164 Ci engine that was introduced in 1964. A very large-displacement engine might benefit from dual matched turbochargers.

I believe that the Toyota Supra Mk IV had a 3.0-liter twin-turbo I-6 with 320 hp.

The twin turbochargers operated in sequential mode, not parallel. Initially, all of the exhaust is routed to the first turbine for reduced lag. This resulted in boost and enhanced torque as early as 1,800 rpm, where it already produced 300 lb⋅ft of torque. At 3,500 rpm, some of the exhaust is routed to the second turbine for a "pre-boost" mode, although none of the compressor output is used by the engine at this point. At 4,000 rpm, the second turbo's output is used to augment the first turbo's output. Compared to the parallel mode, sequential mode turbos provide quicker low RPM response and increased high RPM boost. This high RPM boost was also aided with technology originally present in the 7M-GE in the form of the Acoustic Control Induction System (ACIS) which is a way of managing the air compression pulses within the intake piping as to increase power.

The air-cooled Corvair engine would likely have heat dissipation and detonation problems if it were asked to produce more horsepower. Adding modern turbo technologies might make it possible to increase low RPM acceleration response with a small turbo, and then bring on more high RPM boost to produce more horsepower with a second turbo if the engine bottom-end was strengthened and if the resulting engine heat could be managed. It would be a complex engineering problem and not something that could easily be integrated (hot-rodded) into the existing 1960's engine design.

A normally aspirated engine modification with Weber 3-barrel carburetors or some form of Electronic Fuel Injection would probably produce continuous increased horsepower that could be used more-effectively in long-duration road racing competition events without over-taxing the air cooled engines limited capacity to manage and dissipate operating heat from the high performance state of tune. Supercharging or turbocharging could probably produce more peak horsepower — but it would likely exceed the engine's structural strength or abilit to deal with the operating heat.

[63Turbo]

Twin turbo in parallel has been done a few times... a guy I know built one in the 70's and he did it exactly the way Hughe MacInnes did his as shown in his fine book "Turbochargers". He used 140 heads and had no problem hitting 25psi of boost.
What a lot of people don't realize is that it is super simple to get that kind of boost with a single turbo and these days modern efficient turbo's and good timing control have reduced lag to the point where it is really difficult to tell the difference between an NA engine at the same hp level as the turbo. I've found as others have that most of what is called turbo lag on Corvairs is actually caused by a rotten timing curve coupled with a hopelessly small carb, and a way too small cross over manifold. A efi system like I have coupled with some tricks to the turbo does wonders for lag. I routinely get 10-12 psi in 1st gear and 20 psi in 2nd using a F-flow compressor and a B-flow exhaust. Yes it does scream and I suggest trying something simple like addressing the real faults with the stock set-up before trying a serial type twin.

[63Turbo]

[California Racer]

Thanks Brad and 63Turbo

Let me ask the question a different way.

If you ran one '62-63 factory turbosupercharger feeding one bank and another '62-63 factory with turbosupercharger

feeding the other bank.Both with Carter YH's.Small YH's.

Stock exhaust manifolds and stock ducting.Just fabricated generally the same.So you don't butcher and make unusable

original parts.

How would it run?

You start it up and what happens?

How would boost read out on I suppose a boost meter on each side.

Thanks!

[bbodie52]

As mentioned before, a single turbo can provide plenty of boost to support the small displacement Corvair engine. The added complexity of a separate turbo for each bank of cylinders would offer little gain. Two turbos in series (one small and one larger), might be done to reduce boost delay and provide a rapid spin-up at low RPM. The 1962-1964 turbo has a smaller impeller that spins up more quickly, but lacks capacity to provide a peak horsepower increase with the added displacement (145 CI to 164 CI) found in 1964 and later engines. The 1965-66 turbo was redesigned for greater capacity to boost horsepower to 180 hp instead of the 150 hp rating on earlier engines, but the larger impeller is a little slower to spin up.

The potential for greater boost with a larger turbo, a Weber carburetor, etc. can provide more horsepower, but detonation control using water injection, a more sophisticated ignition system to prevent detonation, etc. is needed for any upgrade to be successful. Short-duration turbo engines running in drag racing and similar events may work well, but long duration road racing events using normally aspirated engines may be more successful because of fewer heat management problems and more-manageable tuning with less detonation and associated engine self-destruction.

[California Racer]

Thanks Brad!

Duly noted the points you are making.

We will let it lie for now.

[63Turbo]

Here's how my car runs: https://www.youtube.com/watch?v=Hf0WBG2afrI
With a twin turbo (parallel like you are thinking about), with 2 stock F-flow turbo's, it will have 800 cfm worth of airflow.
A single E-flow compressor is rated at around 650 cfm and is in it's sweet spot between 15 and 25 psi of boost. 25psi of boost is a ridiculous amount on a street car, and is enough to break stuff like transmissions and differentials if not careful.
If you want to try a parallel twin using a Corvair turbo, use 2 of the smaller B-flow turbos, which will give you roughly 650 cfm, just like having a single with an E-flow compressor. It will start, and run and drive around just like every other turbo car does, but because of the older design will still not spool as fast as a modern single that is properly sized for your boost and power goals- if reliability is a consideration, keeping the engine hp to 300 or less is a really good idea, and for that, 20psi or less. You don't need a twin for that!

[California Racer]

Thanks 63Turbo

Was told there is not enough exhaust from one bank of a Corvair engine to drive a '62-64 Turbo Supercharger.

Will look into that.

Meantime.Will find out this week how soon we will be getting a '62-64 Turbo Supercharger.

[63Turbo]

The reason "there isn't enough exhaust" is because there isn't enough intake from that puny little yh. There's a lot more to it than simply displacement of the engine. It matters a heck of a lot more as to the relative size of the intake compressor vs the exhaust turbine than displacement by itself does. If you have your heart set on doing a twin turbo, yes, 2 b-flow turbo's will work way better than 2 f-flow turbos will, and even better would be 2 b-flow exhaust turbines with f-flow compressors.
better yet would be that combo but only a single turbo with enough throttle area to flow what the turbo is actually capable of flowing.
One good thing about a twin like you are cogitating, the extra exhaust capacity does act like a natural boost limiter and would help the engine run cooler, but would be fairly laggy compared to a single.

[California Racer]

Thanks 63Turbo

Plan is to get one and then figure out what is what.