Kicked around an idea to spool faster and was wondering if this method is a common way to do it. I saw a few methods when I searched but didn't see this. It uses exhaust cutouts adapted to work with a wastegate actuator ( this may also be commonly done ).

Under acceleration, exhaust pressure builds and Turbocharger TC-1 spins up. TC-2 cannot spin because it's outlet is blocked. When exhaust pressure builds enough, it opens CO-1 cutout which senses this pressure. This allows TC-2 to spin up. When turbo TC-2 builds enough pressure, it can now open CO-2 cutout and both turbos will be active.

Is this commonly done? Would it work?

I am contemplating my very first turbo build, so if this is rudimentary stuff, please forgive me.

Note: There is still a need for a wastegate and BOV though I don't show them.

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Check it out !!!

http://www.ebay.com/itm/2-5-63mm-Ex...ash=item36073e180c:g:v9EAAOSwMtxXsjLM&vxp=mtr

 

If you recall, Toyota did this on the Supra with two different sized turbos. They weren't compounded but valved similarly to come on in stages. The small turbo would build boost quick, then as the larger turbo came online the valves moved to blend the boost.

From wikipedia:

"The twin turbos 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 1800 rpm, where it already produced 300 lb·ft (410 N·m) of torque. At 3500 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 4000 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."​

 

Overcomplicating it for a first build IMO. If sized correctly with modern turbos and the correct parts... lag isn't an issue. Getting valves to live in those conditions is tough. Precise valve control is also difficult.

 

Before I posted this I searched for "parallel turbos" and for "quick spool turbo" and I thought I saw the layout that you describe. It showed 1st turbo feeding the second turbo and then switching modes and it seemed it would need a little R&D for it to work. The one I drew seemed a little easier for a home brew.

After I posted, I saw a few setups that were called "compound" turbos so I searched that and turned up lots more setups that more closely resembled what I had drawn. I thought I was being a bit clever though by putting the CO-1 valve after the turbo. I was thinking it would keep the housing at pressure already for a little quicker spool so maybe worth posting. Also, it seemed rather simple to implement if you are already doing twins.

 

"Overcomplicating it for a first build IMO. If sized correctly with modern turbos and the correct parts... lag isn't an issue. Getting valves to live in those conditions is tough. Precise valve control is also difficult."


Yeah, it is a little beyond my pay grade right now but my thought was to put the valves on with V-Bands in case it doesn't go anywhere. Pun intended. Seemed easy enough.

Now bear in mind that I had already decided to rear mount a pair of small twins and would not stake a lot of extra money on an untried idea ( my pay grade and all LOL) . So the addition of these valves seemed like it would be a fun project. Without the valves this system is commonplace, although proven inefficient for sure. Taking them off would not affect the build at all.

Another reason to try this is that the parts don't need to be fully engineered, as I will be using valves and actuators that are pretty much designed for what I am doing with them. The actuator for CO-2 would be a minor challenge. In fact, CO-2 function could be accomplished with a check valve, but I've not seen readily available check valves for these types of applications. ( you'd probably not want to hear it slam shut every time you let off the gas though )

Each turbo has it's own 2-1/4" double wrapped inlet, and I'm hoping I can use a manual boost control scheme to adjust where CO-1 opens. It should have the effect of holding exhaust pressure to a constant value until the main wastegates take over ( if they ever open at all LOL ).

My thought is that I will be cruising all day on just a single turbo that is just off boost, and maybe I'll have decent throttle response when I roll into it. Either that, or it will surge and buck and annoy me back to the drawing board.

 

They were the same size turbos. This is a widespread misconception of all sequential twin turbo factory cars, including the RX-7. If they were different sizes, the smaller one would restrict the larger one. So there is no advantage to having one larger, except in a compound setup, which is an entirely different subject.

Al

 

Looks like a complicated build. But, there is nothing wrong with trying to come up with new ideas.


I like to pay attention to hot side sizing, turbine A/R, ignition timing, and torque converter. When you get those things right, spooling is a non issue.

 

I am not sure if I indicated earlier that this is going to be a rear mount turbo setup which is known to be just a little bit laggy. I really would like a snappy throttle and figured why not try something like this to at least maximize the possible potential of 2 turbos. Maybe something will come of it; maybe not. Either way, fun.

To your point, picking ar may be tricky here as we are talking small turbos and large engine, but on the other hand there are 2 of them so........ I'll stick with turbos that can interchange housings; maybe even different ar between them.

There's gotta be a bunch of builders wanting to know what happens when you try this.

 

Randy Westmoreland has the rear mount thing working well. He has a red truck with a rear mount single on a LSX now. Its bad news too

https://youtu.be/uv3GpfHpwmk

 

I see hardly any lag at all lol.

Won't be hauling his friends furniture anymore either.

 

Have you considered a Vairable Geomerty Turbo or Variable Nozzle Turbo? Either would take a lot of effort to control, but I would guess much less effort than your drawing (I think :/)

 

Tell the truth, I've not looked at them at all. I've heard of them, but thought that they were a newer cutting edge technology and way beyond my reach at this point. The thing I drew seemed pretty simple and achievable bc all I am really doing is delaying turbo 2. Without the valves, this system is completely common and the way I am doing it is is also pretty cheap and easy to implement. I suspect that I will be buying some actuators to play with though.

I've already bought the valves bc they come from China and take so long in shipping.

 

I notice there are posters commenting on the complications of this scheme and I don't understand what makes it complicated. Then it hit me that if I were to add a second turbo and these valves to what was originally a "single" build, then yes, it is a rather complicated complication. I think I should have mentioned right at the start that it was going to be a twin turbo setup all along and that I am adding the two valves to try and improve the "lag" situation.

My thought is that if I shove both banks of the engine into one little turbo, it will react quicker and maybe improve transient response while normal city driving. When I stomp on it, the other turbo will come in gradually and maybe cause the power to level off as it warms up ( lag ); after which I should be sliding all over the road with a smile on my face.

So I don't picture this as a very good race setup. The lag will be there bc the other turbo, and it's piping, will mostly always be cold and that has to affect it when it ramps in. My hope is that spirited city driving will only involve turbo 1, and make the car a blast to drive.

Now if I could just do this with 87 octane ......

 

I've also wondered about another valved set-up for drag racing, but haven't felt like trying it. Make the hot side normal, but put a throttle body on the compressor outlet and a check valve in the pipe after this throttle body and before the intake manifold throttle body. The thought being that (while spooling) the compressor throttle body stops all air flow through the turbo so it can spin crazy fast, and the engine still breaths through the check valve. To launch, the compressor throttle body is opened and the check valve shuts so that all the turbo shaft speed crams a ton of air into the engine. Granted this would be really rough on the turbo, but I believe it'd work provided the turbo can hold up to the abuse.

 

So the valve opens when you dump the clutch at 4000 rpm. Oh please take me with you.....