Parallel Twinz vs. Compound Twinz - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
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post #1 of 4 (permalink) Old 10-08-2008, 09:30 PM Thread Starter
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Parallel Twinz vs. Compound Twinz

Parallel Twin GT4094s versus Compound 62mm & 82 mm. (turbochargers may be changed, this is just for comparison)

Which system will make full boost earlier?

At the same boost level of 60 psi, which system makes more power?

Which system will have the least backpressure? Compound system can/may increase backpressure due to the smaller turbocharger`s housing?
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post #2 of 4 (permalink) Old 10-08-2008, 09:46 PM
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Re: Parallel Twinz vs. Compound Twinz

Full boost earlier goes to compounds because the second stage can be sized very small, and get things rolling well, and when gated properly will not inhibit exhaust drive flow.

Most power at 60psi I would also lean toward the compounds because each charger would only be responsible for the square root of the full PR of 5 if you chose to balance the ratios. That would be comparing the efficiency of a compressor running 60lbs to that of one running 18lbs. It should be easier to locate a compressor that have greater efficiency at 18psig than one at 60psig. If you didn't balance the stages I still wouldn't expect you to run more than about 35-40psi max on any one stage. Which should still be easier to rank high efficiency with compared to producing 60psi in a single stage.

On drive pressure I can't say.
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post #3 of 4 (permalink) Old 10-08-2008, 10:02 PM Thread Starter
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Re: Parallel Twinz vs. Compound Twinz

Charles thank you very much.

Is it a good idea to have a small A/R on the small turbocharger so that the boost response and initial boost build will be better?

Lets say total boost pressure is 60 psi and air flow into the engine is 160 lbs. We use a Gt35 (60 lbs max) & we use a GT4718 (140 lbs max).
Of this 60 psi, how much power/airflow does the Gt47 supply and how much power/airflow does the Gt35 supply?
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post #4 of 4 (permalink) Old 10-08-2008, 10:16 PM
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Re: Parallel Twinz vs. Compound Twinz

Well since you've listed mass flow, it's simple. If the first stage is moving 140lbs/min then at every point in the system you are still moving 140lbs/min, unless you're going nuclear and gaining/losing mass. In which case the power is going to go out of sight. Course you'd better be wearing 400,000,000 spf otherwise you're going to have a really bad day. lol.

But in all seriousness. How are you moving 160lbs/min of air into the engine when the first stage is only moving 140lbs/min? The first stage compressor is responsible for bringing in all of the air for the system. You will not move any more air than it can physically flow.

And the A/R for the second stage should be chosen based on the goal for the vehicle. If absolute response is paramount (see my thread in the smack talk section for further explanation of my view on this) then you can justify potentially sacrificing some losses to exhaust drive increases and ultimate power. I personally run the largest housing made for the second stage. I think it spools well. Others may think it's laggy as can be. But that is mostly subjective anyway.
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