I have a 1990 Firebird Formula with a pretty much stock 305 tbi. I want to know if it's possible to twincharge this engine, and what i'd need to do to make it work. I study automotive engineering and this seems like a fun project to tackle and could have future potential in my field. Any thoughts?

 

what is a "twincharge"

 

Twincharging is where a supercharger and a turbocharger are used in conjunction. Typically in series where to supercharger feeds into the turbo, which then is fed into the intake manifold. As far as i've seen, you need a massive intercooler after the turbo or it will destroy the engine.

 

u have that backwards the turbo feeds the supercharger.
the supercharger is used for low end boost and the turbo makes up for the fficiancy loss at higher rpms. it basically etends the powerband of a supercharged engine that has a supercharger that is to small and just heats up the air/loses efficiancy


a poperly sized turbo will produce better results and cost less

 

Honestly how "well" it works is depending on your HP goals. For modest goals the 305 should work well, but the fueling system and engine management are going to be flaws in the setup before the engine its self will be. A good intake and cam should allow even a stockish engine to make decent power.

Twincharging is horribly expensive, and the only reason I'd even think about it is if I was trying to use a turbo that was grossly over sized/over turbined for the N/A engine's HP. As an example, I have a TMF5502 from a Detroit Diesel engine sitting here, it's a 1.34 A/R turbine but a 71mm T6 compressor. Flat out huge. Chances are that the spool will be pretty bad with a typical 305 and nothing like a 2-step, nitrous etc. If I stuck the blower on there and got it to spool up say 1500 RPM earlier it would likely be a lot more usable. Honestly, even so I'm mismatching a bit as it'd be better to do something like a huge compressor and the supercharger. Even something like a 142 blower would work great in my case as it would be in the efficiency range of the engine.

 

Can you? Sure.

Should you? Probably not.

Typically for that kind of application you're talking about a very low compression gas engine or a diesel. The L03 is fairly high compression, and without a lot of effort controlling detonation you would not be able to run much boost. This is somewhat counter what you end up with with a compound setup, where the at full bogie the second compressor is building on the first one's boost. To do low boost like that you'd end up having to find compressors that have very good adiabatic efficinecies at very low pressure ratios, which aren't common (the typical pressure ratio that you see on most 'charged gas engine is below the sweet spot for most turbos and many superchargers, half that is a much bigger problem).

And you are correct, even on an appropriate engine you need good intercooling between compressors and after the second one, since every step raises temp and without it you would not only have a very high IAT but you'd loose efficiency because of it.

 

I spent most of work today researching how exactly this would be possible though. And Drac0nic's right. Theoretically, having a massively over sized turbo would be the best way, with a roots blower feeding directly into the intake, and the turbo feeding through a huge intercooler, and then into the super charger.

I drew a diagram where each header feeds a separate turbo and then both of those feed through intercoolers and then into the blower, which in theory would work.

And as far as PR goes, they work compoundly, and roots blower actually are incredibly efficient at low PR.


I'm not entirely sure about the pressure ratios on turbos, but I do know with compound boost, that the efficiencies are multiplied, meaning the end result is fairly inefficient,
Like I said before, this is purely a "Can it be done, and how would I do it" type of thing. And maybe I can do it better where it becomes both a useful and cost effective way of getting more performance out of an engine.