yeah and the exhaust pipes would be connected so that extra back pressure would shoot over to the lower resistance outlet (bigger turbo)

 

this is bascialy i twin turbo setup then! if you wanted to do something like that then i would install a "block off" valve in the exhaust track of the smaller turbo! then at a set rpm (when you know the big one is up and running) you can swtich the vavle so you get 100% of the exhaust gasses going through the big turbo!

thanks Chris

 

If the exhaust was split right, the exhaust flow would move over to the bigger one on its own.

I just thought of a potential problem with this. Since both sides are connected, at lower exhaust pressures there is nothing that would force the air to the little one to spool it up...the exhaust would want to take the path of least resistance and that would probably be through the larger turbine.

 

SOURCE: http://en.wikipedia.org/wiki/Turbo

"Some car makers combat lag by using two small turbos (like Toyota, Subaru, Maserati, Mazda, and Audi). A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher RPM. Early designs would have one turbocharger active up to a certain RPM, after which both turbochargers are active. Below this RPM, both exhaust and air inlet of the secondary turbo are closed . Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher RPM range allows it to get to full rotational speed before it is required. Such combinations are referred to as "sequential turbos". Sequential turbochargers are usually much more complicated than single or twin-turbocharger systems because they require what amounts to three sets of pipes-intake and wastegate pipes for the two turbochargers as well as valves to control the direction of the exhaust gases. An example of this is the current BMW E60 5-Series 535d. Many new diesel engines use this technology to not only eliminate lag but also to reduce fuel consumption and produce cleaner emissions. An example of this would be the Ford Power Stroke engine."

 

A Multistage turbo would give you the same benefits of a sequential setup but with a common shaft single turbo. All it adds is a 2-stage scroll housing with a valve that diverts the exh. into a tighter AR scroll to get to speed..then switches to both to combat back pressure at high rpms. It all integral, so it looks like there isn't mush to it but some additional vac/boost signal lines
Heres the pic at the bottom of the page:http://www.atsdiesel.com/atswebsite/...dge/DTurbo.gif

 

yeah these turbos look very interesting. a bit like a simpler version of VGT idea.

be ncie to see them in practice on a pertrol engine! any idea what sizes these come in???

thans Chris.

 

I think this would work just fine, but I think I would use the same exhaust housings for both turbos, just diferent compressor housings to differ the amount of pressure at different engine speeds.

What do you think of this?

 

Anyone?

 

At the plant my mom/uncle works at, they have a huge gas-turbine generator. The STARTER is a detroit diesel with 2 huge turbos dumping directly into a roots blower.

750hp STARTER.

The gas turbine makes so much electricity, they actually sell it to the power plant which is about 1 mile away.

 

ok....are you drag racing? if so I have your answer..its cheap too...try a 50-75 shot of nitrous to sppol it..or a two step....

 

You took the words right out of my fingers! I've been studying this for a little while now, and after sorting through all the acronyms, I think I finnaly get it. http://www.max-boost.co.uk/max-boost/supra/turbo.htm
To me, this system is perfect for a car like a Supra, small displacement, stick-shift, and street-oriented. As far as camaroextra's question, turbo-lag shouldn't be much of an issue with our big V8s to begin with (unless you're talking about a huge hairdryer!), it's the tiny 4bangers that take 30 min to spool up If you're looking for a drag only car, your best bet is get a huge single and a high-stalled slushbox so you can build boost on the line (this is what turbo Buick guys do almost exclusively) and if you really feel it necesary, give it a shot of nitros to spool up. But if you're talking about a street car, a well set up single or twin setup is probly going to suit you just fine in addition to being simpler. Just my .02

 

by the way, VW has just releast a tiny 1.4ltr golf that has a supercharger AND a trubo on there! just to show that it can be done!

thanks Chris.

 

Even with turbos that are too big for the application but still reasonable size you will not experience enough lag to need anything like this. My Twin T70s would spool from VACC to 9+PSI in approx 0.5 sec with a 3k converter.

 

ive been thinkin about this... what about a smaller turbos compressor outlet feeding into the compressor inlet of a bigger turbo to spool it up and then when it gets up to full spool route the air coming from the smaller turbo just straight into the intake and let the big turbo just suck its air from outside like normal... it might work

 

ya cutout valves would work to divert the exhaust
either servo or diaphram actuated based off boost/rpm
kinda like a giant wastegate

 

thax guys this giving me an idea i gotta try it out

 

i just thought of something after looking on the corvetforum site.

there are a few corvettes running MASSIVE (like 101mm!!) rear mounts. so could you run a front mont that conects into a rear mount????

this would give you compound boost like the big dieseld guys run. so you could run a little say t76 upfront and then hang a big 100mm turbo off the back! the smaller turbo would take care of things at low rpm and the big mother ****** would set the top end alight!

you would have to have the engine of course!

so what you guys think? could/would it work? there are NO vavles to complicate things (apart from the wastegate that would dump to atmospher located before the first turbo).

thanks Chris.

 

I would also like to add that 3rd Generation RX-7's also used the sequential twin turbo setup, but most people did end up switching to big singles.

One reason for the switch was due to the complexity with all the intake pipes. Another reason was that the stock twins were poor units that did have common failures. People also reported that the twins were way more fun, and lag was an issue on the big single.

Then again, they are only 1.3liters, and you guys should have no problem's spinning some BIG twins.

 

I was actually thinking the same thing. Use a small turbo's boost to spin a larger turbo's turbine, after a certain RPM the smaller turbo may become a restriction, so you could bypass the smaller turbo and have only the excess gas vented directly into the inlet of the larger turbo. You could think of this as a supercharger that is exhaust driven instead of belt.

Here is a crude "how it would work" in my mind:

1) Exhaust -> Small Turbo Inlet
2) Small Turbo Boost -> Large Turbo Inlet
3a) Small Turbo Exhaust -> Bypass to Exhaust Exit
3b) Small Turbo Exhaust -> After x,xxx RPM Bypass Directly to Large Turbo Inlet
4) Large Turbo Boost -> Intake Manifold
5) Large Turbo Exhaust -> Exhaust Exit

#3 could be 1 in 2 out bypass valve, and the RPM could be adjusted to get the best powerband for the application of the car. You could also have multiple profiles.

This could allow larger turbos to produce boost from very low RPMs, relative to how they would work if they were spooled directly by exhaust. Lag would be reduced, but not eliminated.

That's pretty much it.

 

My advice would be to form a X-pipe off the headers. On the big turbo side, run a boost actuated cut out that is normally closed before the turbo. These can be controlled with a manual boost controller to set opening point. Set the opening point 200rpm after you would see full spool of the large turbo (given the small turbo will not be in stall). The small turbo gives you the low end grunt and the big turbo gives you the top end. I have thought about doing something similar to my car. Well see.

Might look like this





This example is more of what I might try and do if I have the room in my engine bay.



In this example there are 3 boost actuated cut outs. I would open one to the large turbo say 5psi, second one to the large turbo at say 10 psi and close off the small turbo once the large turbo was spooled (based on a PSI setting). Since the exhaust is a 3" X-pipe, I would use a flow master Y-collector to go from dual 3" to single 4" or even 5" in to the big turbo. Just another thought.