Compound boost.

[Jaden]

The reason you compound boost in a gas car is to increase low end torque, so the size of the engine is paramount to proper turbo selection.

You need to know at what p/r you need to run to generate what power level you want to select the right setup.

In a different setup than an FA20, you might not want to run the same combo.

Like for instance, if you're putting a T04Z as a compound boost setup in a car that is say 3.5L and makes 300hp n/a, unless it only makes 150lb/ft of torque, it would be silly to go to the expense of doing it.

You would only need a p/r of about 1.8 to get the max airflow that a t04z can provide at the p/r you would need to run it at in a compound boost setup.

IOW, you could run a T04Z by itself at 12 psi and still get 450 hp out of it because the car running at 12 psi is capable of ingesting enough air to make 450 hp and running it at a higher total p/r will just starve the engine of air because the T04Z can only provide 45-50 lbs a minute at it's individual p/r but the engine would be capable of ingesting 75-80lbs a minute at a p/r of say 3.2 which is closer to what you'd be providing it in a compound boost arrangement.

Compound boost is designed to provide higher p/r at lower rpms than a turbo is capable of alone which in turn gives you better low end torque.

Jaden

This is why it is important to know what amount of power the engine you're compound boosting is capable of providing at a given p/r.

The FA20 has shown that it is capable of providing 650-700 hp at about 35 psi. That's a p/r at a tad above sea level of about 3.5. So you need to choose the correct F/I solutions where the primary can provide 65-75 lbs a minute of air at a p/r of about 2.1 and then run a secondary at about 1.7ish to get max power and max low end torque.

a GTX 4202r is a good candidate for that with a tvs 1320 as a secondary.

[DustinS]

Do we have anywhere to fit a 4202?? lol

I am starting to see the Cosworth Supercharger as too small of a supercharger then. I may still go cosworth and just step up to a GTX4294R and see where it lands me. I have a few months to get everything squared away anyway

[cdrazic93]

...fudge it, sprintex 335 feeding a gtx4508R with a 1.44 a/r

[Jaden]

Originally Posted by DustinS

Do we have anywhere to fit a 4202?? lol

I am starting to see the Cosworth Supercharger as too small of a supercharger then. I may still go cosworth and just step up to a GTX4294R and see where it lands me. I have a few months to get everything squared away anyway

The 4294r will get you at 600-650 at about 74-75% efficiency and with good enough cooling you might be able to push it up to 700hp...

The 4294 will spool up quicker than the 4202 so you'd get max torque about 2-300 rpm sooner with it.

Jaden

p.s. while that's still a huge turbo, remember, it only has to spool to 12 psi for you to hit max boost of 30 psi...

[DustinS]

Originally Posted by Jaden

The 4294r will get you at 600-650 at about 74-75% efficiency and with good enough cooling you might be able to push it up to 700hp...

The 4294 will spool up quicker than the 4202 so you'd get max torque about 2-300 rpm sooner with it.

Jaden

p.s. while that's still a huge turbo, remember, it only has to spool to 12 psi for you to hit max boost of 30 psi...

That is actually right where I want to be. So that works out great.

It's been almost a month now with no word from my parts guy, even after asking if there was an update last week. So I will be shopping around. Hope to start ordering parts soon so I can get any modifications out of the way.



hmm... Wastegate ports aren't ideal, but boy does it look good, and decently cheap.

[DustinS]

@Jaden What is your thought on Twin Scroll vs Non-Twin Scroll for a twin-charge set-up. As I gets closer to buying the parts (Should get my price list back from my parts guy today) I am starting to wonder how twin scroll will affect the hp/tq curve.

[Jaden]

Originally Posted by DustinS

@Jaden What is your thought on Twin Scroll vs Non-Twin Scroll for a twin-charge set-up. As I gets closer to buying the parts (Should get my price list back from my parts guy today) I am starting to wonder how twin scroll will affect the hp/tq curve.

So I would say go for it, if the additional cost isn't an issue. The quicker you can spool, the better your torque curve will be. It might change the sizing requirements a bit to get the most out of it.

It becomes an issue of diminishing returns for cost. A twin scroll on a turbo you're only boosting to 12 psi might not give you as much benefit per the additional cost.

You might get max torque a couple hundred rpm sooner.

Now I could see a twin scroll being specifically designed for compound boost giving you more benefit though.

The demand for compound boost is just too low though for anyone to bother and a twin scroll by itself gets you pretty close to where you're at with a well planned compound boost setup.

You can expect with a well planned and executed compound boost setup to get torque about 500-600 rpm sooner than a good twin scroll. If they were to design a twin scroll specifically for compound boosting, you might be able to double that.

If you use an existing twin scroll, expect max torque to come on about 700-900 sooner than a twin scroll alone.

It's up to you to determine if the additional cost is worth it. This is all just guestimates on my part based on what I've seen from both and I know of no one who has used a twin scroll in a compound boost setup.

Jaden

p.s. let me give it some thought, it might be possible to hybrid a twin scroll in a way that could be beneficial, but really probably not, because what would really need to change is the difference between the two chambers in the turbine housing. If you use a larger compressor with a smaller turbine housing, it might help some, since you're only building 12 psi of boost with the turbo. but you would need large wastegates to avoid boost creep and avoiding boost creep is more important in a compound boost setup because just a little boost creep from the primary could result in a LOT more total boost, especially when you're using a relatively fixed secondary like a pos disp. s/c.

[DustinS]

Originally Posted by Jaden

It's up to you to determine if the additional cost is worth it. This is all just guestimates on my part based on what I've seen from both and I know of no one who has used a twin scroll in a compound boost setup.

That Twincharged Evo I posted about early was using a Twin scroll T04Z. He then switched to a twin scroll GTX42

Blue line, 2.4 4G64, s205, pump fuel (stock TB, manifold)
Green line, 2.2 4G63, 850R, E85 (big spec, fully built)
Red line Madmac's twincharged motor, pump fuel



T04Z Dyno*

[mrk1]

Originally Posted by DustinS

That is actually right where I want to be. So that works out great.

It's been almost a month now with no word from my parts guy, even after asking if there was an update last week. So I will be shopping around. Hope to start ordering parts soon so I can get any modifications out of the way.



hmm... Wastegate ports aren't ideal, but boy does it look good, and decently cheap.

I have one of these sitting on my shelf if your interested