Have a look at this thread over on the engineering forum:
http://www.eng-tips.com/viewthread.cfm?qid=174690&page=1 ; you might consider joining and contacting member Warpspeed by PM and discussing your problem. He's pretty switched on about twin-charging :boggled:
Wow, I mean wow, what an incredible thread, one of the most interesting reads I had since researching everything I have researched so far, incredibly informative.
If anyone else hasn't already who is interested in the topic of TC&SC (twincharging) then go have a read of that thread, all of it and I mean all of it.
Wayne, have you had a read? It may well help you out greatly to get your setup working in the end and definitely see if you can have a chat with the Warpspeed chap, he may well be your savour!
Benji, what you're describing is the way the sequential twin turbo Supra is setup, and it's done with a combination of a one way reed valve and an intake control valve for the #2 turbo to put it in parallel with the #1. There's a schematic of this setup here:
http://www.lextreme.com/sqtt.html
Disregarding the exhaust side of the diagram, look how the two compressors of the turbos are piped together. The reed valve serves both as a one way valve, and also allows the #2 compressor to come online gradually without creating a pressure spike. It's not a full size valve, but it does allow the #2 to start flowing some air. Sometime after this, the intake control valve opens and that lets the full flow of the #2 compressor come in. This system works well because both turbos are sized identically, so they're both boosting to the same pressure and producing the same flow.
I've read up on the Supra TT system before, also very interesting but I have read that it also isn't perfect and the transition is noticable... even Toyota can't get it perfect so that is saying something. It seems that a lot of Supra tuners either ditch the system for a straight parallel system (even using the standard turbos) or ditching twins altogether and going single....
I'm a big fan of both the Supra and MR2 (Mk2). I love the Supra very very much, at one point I even considered buying one but after much research I really wanted a UK spec one since they seemed to be much better spec'd than the import ones for a change. The problem with official UK Supra's is that they are a little on the rare side and so can fetch quite a lot of money and the other issue is that they are a little on the lardy side for my liking....
The MR2 is a lot cheaper and lighter, again I've damn near brought one several times before. The thing with the MR2 that worries me is that it can be very difficult to tune in terms of physical space and there are way to many stories of melting pistons and cracking blocks for my liking, plus they've been done quite a lot before around here.... I'm really into my unique things.
If you were putting the SC in parallel with the turbo, you'd probably want to size the SC for sufficient boost down low, then have the turbo come in as the SC is running out of steam, say between 4000-4500 RPM. This wouldn't be two stage compression any more, but two single stage compressors working in two different RPM bands. You'd probably have to do this with twin TB's - one for each compressor system, and linked either with some sort of progressive linkage, or else a drive by wire system.
Thats
exactly what I was gunning for in my post above :tongue2: But from the discussions going on in that thread I am not sure that's entirely necessary since they seem pretty keen to just blow right through the SC and then the throttle body after that.
You'd also have to ensure the compressor of the turbo would be big enough to handle the total airflow at the maximum boost pressure you want, and then size the turbine side for it to come in only from the mid to high RPM range. You might even want to include a clutch for the SC to drop it out of the system once the turbo is on boost. All this would be way cool, but way $$$$ too....
Heh, well EVERYTHING I have talked about on this forum so far involves not just $$$$'s but $$$$$'s. :boggled:
But yeah, it seems from that thread that the idea is to have a small SC (smaller than you would perhaps imagine) and then big
big turbos, I was initially thinking GT42's but now after reading that thread maybe GT45's! :hypnotized:
Warpspeed said:
There is a fairly widespread and seemingly immortal urban myth, that once the turbo winds up, the supercharger will become restrictive. That can never be the case if the boost pressure at the outlet of the supercharger is higher than at the supercharger inlet pressure. It can never be restricting the flow if that is the case.
Now this is encouraging and TurboAndrew says it as well, I completely see the logic in it, but would I be right in saying that essentially the SC
still will be restrictive and
is technically a problem still.
Let me explain, an engine can only flow a certain amount of air, by their very nature TC's and SC's will flow more air than the engine can ingest hence why pressure ('boost') is created.
Now an SC can also only flow a certain amount of air as well just like the engine, now where I was getting hung up was that at some point surely the turbos are going to flow more air than the SC can ingest as well and thus be 'restrictive'.
However looking back at it, this is actually the whole point, again this creates pressure or 'boost' and whether the SC is there or not (in just a purely turbo setup) the engine is ALSO a restriction in the same sense as the SC would be in a twincharge system except that since the SC will
always flow more than the engine it cancels it out and it doesn't matter and means that the 'problem' isn't actually problem, its always been 'problem' whether I realised it or not, its the whole princple in which TC or SC is based on and why it exists!
In the case of twincharging the restriction is actually
less of problem (less restriction to the turbo) than in just straight TC however, would I be right in thinking then that in principle it would be a little harder essentially for the turbos to build pressure ('boost')?
In fact reading through this thread I see that TurbroAndrew has already said exactly what I have said but in a much better way! :tongue2:
turboandrew said:
Guys, it's simple physics, the supercharer is a positive displacement blower -it moves more CFM of air then the engine. It will injest air at a much higher rate than the engine alone, -reducing- the load on the turbo.
Amen to that! The answer was already there! So it seems that my worries aren't actually a problem at all and that twincharging is actually very complementry and works better than I realised! I just wonder why more people haven't done it?
