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Discussion Starter #1
Read the latest issue of Turbo or Street Perf.(forgot). And there was this RX-7 with two turbos. Now you say,So what, all RX-7(3'rd gen.) come with two turbos,and you would be right, but this one had them piped in parallel, and one was smaller and had a diff. compressor so it would spool up in the lower RPMs and the other kicks in later. My point, can similar set up be mounted on an L28 with wastegates tuned to diff. pressure to allow this split. That way there would be no lag, and you could run higher PSI's. Or the weight of the piping will render the set up useless?
 

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The RX-7s came with the different size turbo's. The mod to make them run parallel takes about 1 hour from what I have heard. The only problem I can see is when high RPMs are reached there is a possibility of over spooling the smaller turbo. From everything I have read the single turbo is the solution or running twin turbo with the same size turbos.
 

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3rd Gen RX-7 turboz are the same

I have extensive experience tuning the 3rd gen RX-7 and I can tell you that the two turbos used on that car are the same. However, they are tuned to come in at different times. Like stated, one comes on at lower rpm (below about 3100) and the other joins in the fun above that. They share a common wastegate, and are controlled by valves in both the intake and exhaust systems.

What happens as the engine accelerates is that the primary turbo starts making boost at about 1500 rpm. At about 2700 a valve (called the precontrol) is opened in the exhaust manifold. This allows exhaust gasses to start spinning the secondary turbo. At about 3100 rpm, a valve in the intake system (called turbo control) opens and the secondary turbo then supplies the engine w/additional air. The turbos on those cars are both the same size, and yes, they are both small. The only advantage to having the sequential setup is to eliminate turbo lag. If any of you have ever driven a 3rd gen RX-7 that worked corectly, you will know that they have instant boost response regardless of engine speed.

The reason the really fast RX-7's use one turbo is for shear air flow rate. However, ask Peter Farrell about his road race RX-7 that ran a 10 second quarter mile with the stock turbos.

As far as installing sequential turbos on an L28, the RX-7 and Supra systems are very elaborate, computer controlled devices. It is not a matter of having two turbos with two wastegate settings. You would have to have a way to turn the secondary turbo on and off as needed. That is what these cars do. You may be better off using a twin turbo setup like the 300ZX and Mits 3000GT VR4. These are not sequential. Each turbo feeds one bank of the engine (3 cylinders). By doing this, the required turbo is smaller and has less rotational inertia. This will reduce lag slightly.

I don't know of anybody with twin turbos on an L28. If no one has done it, then there is probably a reason. That reason is that it is not worth the effort and expense. A single turbo works wonderfully on the L28 and a properly setup L28ET will have tons of power with respectable response.

Ian
 

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Discussion Starter #4
Accualy, i ment, having one turbo smaller then the other, with straight fins on the compressor, for low RPM response, as well as having some kind of valve to close the exchaust flow to it, once it reaches it's limit, and let the other one take over. anyway, just a thought ;-)
Stan.
 

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It would be way to difficult to put a sequential twin turbo system in a Z car motor. What they dont tell you is theres a whole pole of solenoids, and 76 vacuum lines controling the turbos. Its way to complex and to difficult. If you wanted to add a twin turbo system the easiest way would be to have each of the turbos run 3 cylinders, therefore 2 custom manifolds would have to be constructed. In the end, it is much easier to run one turbo. If boost lag is a major concern, use a modified header (6 into 1 is easiest to work with) bend the collector to be able totake a turbo, weld a flange on it, and from there run a 3.5 inch exhaust. The only problem with this is that an electric oil pump will be needed between the oil return and the oilpan. If this pump is not there oil will back up in the turbo and burn the bearings. If you want more info, email me.
 
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