sequenchial turbo setup

[dzlsrtbd]

has anyone attempted this what may i expect just finished the build up of the new motor and fabing up the manifold for the install on my 94 3500

 

[ak diesel driver]

it's doable but it takes alot of fuel. Probably more than we normally run. then there's always headgaskets and crankshafts and cracked blocks to worry about

 

[BigBlueChevy]

AK diesel driver is right. It is doable and would certainly make a unique rig, but there really is just no need for it on our trucks. The motor itself would just not be able to handle the amount of boost being generated. You could of course wastegate the system so that it makes no more than 15 or 20psi of boost, but you can do that with a single turbo.

You may want to consider using VGT. Set it up so that the vanes are almost completely closed at idle to make max boost, and rig a mechanical controller to keep the boost pinned at 15 psi during the entire RPM range. THAT will get you somewhere.

 

[dzlsrtbd]

thanks for the input i am building to pull all the time i oversized to .040 from stock and had some heads built to handle
more air flow just cosidering my options and trying to find out what works best for this setup

 

[buddy]

The sequential turbo is a good idea. It can achieve the most efficiency, were boost can be greater than backpressure. Which would make more power at less parasitic loss and load to the engine. Did you have certain turbos in mind or a setup drawn up?

 

[dzlsrtbd]

due to limited space i am useing two gm4 turbos slightly modified to utilize the wastgates for max spool and eficiency without
destroying my new motor. i am hopeing to lower my iat and egt for more reliable performance. i dont have any pics yet just finished the initial break in next step is the turbo mods

 

[buddy]

Typically with a sequential setup you would have a larger turbo feed the smaller turbo, because the second in line turbo is going to need to be able to draw air through the first one in order to compress the air. Even though the first turbo only compresses it slightly you still need to be able to draw more air through it than it is boosting, so the best modification for it would be a large compressor housing with larger exit size on the first turbo.

Do you have a diagram of how you connected the exhaust and intake, not necessarily a real picture but drawn concept?

 

[dzlsrtbd]

i have been brainstorming with the cat set up that has very similar sized turbos although slightly different, with the pair of 4s that i am useing is where my changes were made one has a basic stock compressor and the other has a modified copressor with a slight enlargement for more air i am fabing a mount for the second turbo to sit on as well as function to the stock location of the down pipe. my biggest road block right now is wich location is going to be the best to pull oil from

 

[buddy]

Well, seems like youre already on top of it then. Although the one other concern I would have is the way the wastegates are set up, since a turbo operates on a pressure differential, the turbo that sees exhaust first will not have a big pressure drop across it, if it directly feeds the second since both have small turbines. Thats why I was wondering if you had a concept drawn up. You probably need the second turbine to have a pretty loose wastegate so the first will spool.

 

[dzlsrtbd]

thanks for the feedback buddy i have this concept in my head that i have been working on for about a year trying different things i dont know how to put it on paper till after it works or maybee not i will post some pics as i finish these concepts to a working set up the wastgates have been a big concern so i am going to convert to a hx 35 style and drill and tap the compressor on the primary to control the secondary in hopes that as the air flow builds to max psi it will let it go to a nuetral boosting and let the primary take over not sure of the outcome but looking for any input that may help

 

[buddy]

So youre trying to do real sequential, that is somewhat difficult. I would recommend just going with compound turbos, thats what I was really talking about I guess. It can be more efficient with same benefit of sequential, so you never need a total neutral boost from either.

Here is something I had envisioned, wondering if you drew anyhting up. The internal wastegates make the install simpler. And I believe you would not even have to wastegate a large turbine turbo even in compound. I know for a fact that the GM4 will spool even with terrible exhaust restriction, so its possible that it will spool with a large turbo on its exhaust, but for real tweaking would have to have a wastegate for the larger turbo


With true sequential it wouldnt make sense to use two turbos of the same turbine size, that is why you do sequential, to use turbos of differing turbine sizes that have differences in efficiency range.

I think compound can still work with the GM4s though. Just need the GM4 that would be in my ATT position to have a larger compressor side and a loose wastegate. Then you wouldnt have to deal with any external wastegates.

 

[6.2 turbo]

I would do a compound setup for a low compression motor or one for each bank with high compression ,like Bill Heath.

 

[buddy]

I was wondering if you gave this any more thought? True sequential turbos is more complicated, but a simplified version could be done with a couple vacuum/boost actuated flaps in some exhaust pipes, like an exhaust brake for each turbo actuated oppositely. Like this picture, but again the whole point would be to have one small and one large turbine turbo, so two GM4s would not accomplish this.

 

[saturntech95]

I would think you need 2 air filters tho cause the GM turbo isnt gonna be able to flow the air that the ATT puts out it will just restrict it and shoot the IAT up.

 

[buddy]

The GM turbo will flow 20+ psi through it, whatever the density, I do it all the time, and it wont drive IATs up in the sequential mode because it wont be using the turbine to drive it after 10psi, but it will be a restriction in the intake, but so was the EGR system and it still worked. The problem with using two air filters is then you also need air intake block offs, because they cant hold the same boost on both turbos, so they will end up opposing eachother or just losing boost out one of them. Its way more complicated when using two turbos in sequential mode drawing separate air and feeding the intake separately. You would just be better off with twin turbos that are exactly the same.

In the compound setup the GM turbo also is not a restriction.