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Old 09-05-08, 11:26 PM   #1
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compund/sequential turbo turbo system

ive been going overboard with my turbo ideas, but ive been putting this one at the top of the list.

i want to make an aftermarket sequential twin system with somethring really small like a garrett 25r and something big like a 45r. my manifold idea has some similarities to how a compound turbo system works, much like this one http://forums.dieselstation.com/inde...howtopic=17291 the major difference being that both compressor outlets are routed to the I/C and the manifold will have wastegates plumbed to the larger turbo.


heres a basic idea of what im thinking

long runner tubular manifold goes straight to smaller turbo
downpipe and wastegate(s) (something like dual 50 or 60mm ones.) will flow to hotside to spool the larger turbo.

my last problem is coming up with the plumbing for the larger turbos wastegate... and obviously this system will take up some space...

so what do you think? am i on the right track or doomed for failure from the start?

any input is helpful and if anybody knows of any systems like this one that i could steal ideas from please speak up.
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88 TII - 90TII engine rebuilt\ported by Banzai, Hybrid turbo, LTx8, walboro 255. 720\1680 inj. 3" exhaust, 9lb flywheel.
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Old 09-05-08, 11:48 PM   #2
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I can appreciate that you are thinking of something other than a standard single stage system.

There are two flaws with the system you are describing below.

1. With a turbine stage that you are describing, once you use the WG to transition to the larger turbine, you are starting that turbo from a condition where that turbo is not spinning. Not only will you have massive oil leakage, but you will have a large boost drop off once you transition. I'll let you think of the solution

2. With both compressors routed to the intercooler like you described (pure parallel), and with one compressor creating all of the boost (either the GT25 or GT45 and the other turbo not spinning) you will leak all of your boost through the other compressor inlet.

The system that you are describing will not fundamentally work.


Quote:
Originally Posted by dean23 View Post
ive been going overboard with my turbo ideas, but ive been putting this one at the top of the list.

i want to make an aftermarket sequential twin system with somethring really small like a garrett 25r and something big like a 45r. my manifold idea has some similarities to how a compound turbo system works, much like this one http://forums.dieselstation.com/inde...howtopic=17291 the major difference being that both compressor outlets are routed to the I/C and the manifold will have wastegates plumbed to the larger turbo.


heres a basic idea of what im thinking

long runner tubular manifold goes straight to smaller turbo
downpipe and wastegate(s) (something like dual 50 or 60mm ones.) will flow to hotside to spool the larger turbo.

my last problem is coming up with the plumbing for the larger turbos wastegate... and obviously this system will take up some space...

so what do you think? am i on the right track or doomed for failure from the start?

any input is helpful and if anybody knows of any systems like this one that i could steal ideas from please speak up.
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Old 09-06-08, 02:58 AM   #3
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How about this-

A large turbo with wastegate as normal, but the exhaust of the large one feeds a smaller turbo (compunded).

Likewise the small turbo compressor is the ambient air inlet and its outlet feeds the inlet of the large turbo (compunded).

However, unlike a normal high boost compounded turbo you have a large wastegate after the large turbo and before the small turbo as well.

This allows the small turbo to provide initial spool, while the large turbo is also spooling.

Then as desired full boost is almost reached the wastegate between the two turbos opens so that the small turbo slows down to freewheeling and post turbine exhaust pressure for the large turbo decreases suddenly increasing its acceleration.

Now you could have an alternate intake tract to the large turbo compressor inlet that is normally closed off with a reedvalve to reduce pressure drop from the large turbo "sucking" through the freewheeling small one.

The normal wastegate before the large turbo would now control the desired peak boost.

I am not certain this would work.
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Old 09-06-08, 03:59 AM   #4
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What I want to build for myself is a MUCH simpler system.

Like the S4 TII turbo it would be a switched dual scroll unit, but much better performance.

Use a turbo with whatever compressor you want and a very large divided exhaust housing.

Have a tubular exhaust manifold that is equal length and merges into just one of the two exhaust inlet scrolls for high exhaust energy at lower turbo speeds.

Then as desired full boost is almost reached a large 60mm swing valve "wastegate" opens off of the front rotor's runner so that its exhaust now runs through the "wastegate" into the other previously unused second scroll. It is easy to also set this up as equal length to the (now) rear rotor's runner.

Once full boost is reached a moment later another normal wastegate opens to control peak boost. This wastegate is located where the front and rear runners had merged into the primary turbo scroll (now equal length WG runners).

I have this set up sketched out and it ends up being a very tidy and smooth flowing exhaust manifold that is basically only one 60mm swing valve wastegate more complicated than a standard turbo system.

I have the front rotor exhaust run through the swing valve wastegate to the secondary turbo scroll for two reasons.

It fits into the equal length and equal bend design well.

It will also have slightly more pressure drop (and so exhaust backpressure) than the regular tube bend of the rear rotors path and this will even out the slightly higher thermal load the rear rotor is usually under from its secondary position in the coolant path rather than exacerbate this problem.
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Old 09-06-08, 04:16 AM   #5
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damn. not only did yo beat me, but you did it twice.

i like the second idea a lot.. i never even thought about a twin scroll system. just shows me i still have a lot to learn, hahaha.

your first idea, if you are unaware, is extremely similar to how *most turbo diesel trucks operate. fro my understanding the majority of those are wastegate operated though.
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Old 09-06-08, 05:15 AM   #6
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using the twin scroll idea seems like it would have a laggy lower end to me... wouldnt it b compareable to a turbo with a small exhaust side and a much larger compressor side?
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Old 09-06-08, 03:58 PM   #7
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Yep, I know the first idea is regular compound turbo system except I am talking about pulling the primary turbo out of the circuit once desired (low for compund turbo) boost is achieved.



The second idea, dual scroll, does work.

The larger compressor and small high velocity exhaust section does work well for quick spool on a rotary, if you are mindful of a few things. You want to maintain high exhaust velocity without causing excessive backpressure to choke out our high overlap engines.

What I have found is critical is to have a VERY free flowing post turbo exhaust, then a large diameter exhaust wheel for the forceful rotary exhaust pulse to have great leverage on while maintaing a large flow area and last a decent size A/R with small volume to MAINTAIN velocity out of the engine instead of trying to RAISE velocity with a small tight A/R in a larger volume manifold/housing.

For instace, my current set up is just a 60-1 compressor w/ clipped "P" trim exhaust in a bored out, ported out stock S5 turbo housing/manifold and a 3.5" exhaust.

Data logs show positive manifold pressure literally off 1,000rpm idle, ~2psi by 2,000rpm and full 15psi boost before 3,500rpm.

Eliminating boost creep was the real challenge. After putting on a 60mm external WG did not fix boost creep I had to port out the stock velocity stacks in the manifold to slow the exhaust and port the runners to favor wastegate flow.

The problems w/ decent compressor, small exhaust, giant wastegate system like I have is that although the spool is great and top end is great the relaibility suffers when you have it under full load for long periods of time like back to back freeway pulls or endurance racing as the engine to turbo exhaust backpressure is so high the exhaust heat transfers more quickly to engine internals and turbo components.

Melted EGT probes, melted gaskets, failed manifolds and even warped apex seals result.

So, diverting the exhaust first through a second flow path once spooled and then finally through the wastegate once the limits of the now larger turbo are exceeded allows for lower engine to exhaust backpressure and greater reliability as well as slightly better top end power due to less charge dilution with overlap.



Look at it this way, even on a very high power rotary we are demanding full boost at ~3,000rpm to help low rpm power on our "oversquare" engines.

The problem is the engine is at best making 100RWHP of exhaust flow at 3,000rpm.

Now you want to at least quadruple it to 400RWHP of exhaust flow while maintaing the same boost over the next 5,000+rpm.

You need more volume in the system for the increased exhaust flow. I tried to do this by adding a huge wastegate, but this raises engine to turbo exhaust backpressure
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Old 09-06-08, 04:27 PM   #8
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Instead of having the smaller turbine see flow after the larger turbine, you should have the smaller turbine see flow first.

This will allow your quick spool up, because significant exhaust energy is lost after it goes through one turbine. If you had the smaller turbine routed after the larger turbine, you would be hurting your low end performance.

Quote:
Originally Posted by BLUE TII View Post
How about this-

A large turbo with wastegate as normal, but the exhaust of the large one feeds a smaller turbo (compunded).

Likewise the small turbo compressor is the ambient air inlet and its outlet feeds the inlet of the large turbo (compunded).

However, unlike a normal high boost compounded turbo you have a large wastegate after the large turbo and before the small turbo as well.

This allows the small turbo to provide initial spool, while the large turbo is also spooling.

Then as desired full boost is almost reached the wastegate between the two turbos opens so that the small turbo slows down to freewheeling and post turbine exhaust pressure for the large turbo decreases suddenly increasing its acceleration.

Now you could have an alternate intake tract to the large turbo compressor inlet that is normally closed off with a reedvalve to reduce pressure drop from the large turbo "sucking" through the freewheeling small one.

The normal wastegate before the large turbo would now control the desired peak boost.

I am not certain this would work.
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Old 09-07-08, 03:44 PM   #9
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blue tii- i like the sound of your setup, but im a bit confused as to why its getting so hot? and did you say you were using the stock manifold?

carbon - thats wat i initially thought.
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88 TII - 90TII engine rebuilt\ported by Banzai, Hybrid turbo, LTx8, walboro 255. 720\1680 inj. 3" exhaust, 9lb flywheel.
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Old 09-13-08, 01:49 PM   #10
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im starting to grow on the idea of a supercharger (centrifigal), but i would have to find some type of clutched pulley system to make it work the way i want. basically an on off switch. any ideas?
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Old 09-13-08, 01:49 PM
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