OK... So I have some down time for the Christmas season (intentionally scheduled). My plans are to go ahead with a twin turbo setup. The setup that I'm currently running is 100hp BD injectors (I'm not 100% sold on keeping these...I may go with 125's or 150's), Smarty S-03, FASS DDRP (no fuel pressure problems currently, but I plan on upgrading to a larger FASS), and I plan on, most likely, stacking an Edge with the new CTS2 with what I already have. So my question for those who have gone before me is this:

Which bottom turbo should I go with? I plan on using the HX35 that I currently have as the top turbo. I want a fairly quick spooling setup, and I use my truck most often for just driving around, but I do tow with it once in a while...usually fairly heavy. It's not necessarily my daily driver, either, as I do have other cars. It has been recommended to me to go with an S472 with 83mm turbine and 1.10 housing. This seems a little on the small side if I go with larger injectors but, then again, so does the HX35 up top. I see a lot of guys going with an S475 with 96mm turbine and 1.32 housing. These seem to be fairly cheap, too.

How should I mod the wastegate to work best with the compound setup. The turbo I have right now is currently unmodified... 

I really don't want to change the top turbo. In my opinion, that would price this project right out of the realm of feasibility. I can afford it, but at the end of the day, it's just a 2nd Gen 24V, and spending that much on a turbo setup just doesn't make sense.

Opinions...?

The HX35 will be okay but the waste gate configuration only vents one of the volutes in the turbine housing which may cause higher than normal drive pressure for 3 of the 6 cylinders compared to a S300G. 

16 minutes ago, Vais01 said:

The HX35 will be okay but the waste gate configuration only vents one of the volutes in the turbine housing which may cause higher than normal drive pressure for 3 of the 6 cylinders compared to a S300G. 

That's why Cowboy said this  

On 12/9/2015 at 9:38 AM, Cowboy said:

Drilling the divider across from the wastegate hole works well, drilling in that location helps retain some of the advantages of the twin scroll, while still gating both volutes.

 

12 hours ago, Vais01 said:

The HX35 will be okay but the waste gate configuration only vents one of the volutes in the turbine housing which may cause higher than normal drive pressure for 3 of the 6 cylinders compared to a S300G. 

That's a myth that I plan on busting....  Once I get my truck back together.  

5 hours ago, Cowboy said:

That's a myth that I plan on busting....  Once I get my truck back together.  

I will be waiting on that.  

I wouldn't want the skinny shafted and a turbine with a single vented volute on a twin turbo truck.

1 hour ago, Vais01 said:

I will be waiting on that.  

I wouldn't want the skinny shafted and a turbine with a single vented volute on a twin turbo truck.

Oh absolutely!  For compounds that poor HX35 wastegate needs all the help it can get.

On single setups, I've heard convincing arguments from both sides, one of which being Weston.  This is just one of those things I have to see for myself.  Might as well, I have everything needed. 

3 hours ago, Cowboy said:

Oh absolutely!  For compounds that poor HX35 wastegate needs all the help it can get.

On single setups, I've heard convincing arguments from both sides, one of which being Weston.  This is just one of those things I have to see for myself.  Might as well, I have everything needed. 

I wish you all the best. It would be ashame to ingest metal over trying to prove a point.

Well, I intend to use my HX35 with modded wastegate for a top turbo as well. While it would be nice to have any number of different turbos as the top turbo, I just can't justify buying two new turbos for a $12K truck that, technically, doesn't even need ANY new turbos. It runs just fine the way it is. I guess I'm just bored this Holiday Season, and all my other projects are at a standstill for one reason or another.

4 minutes ago, Dynamic said:

Well, I intend to use my HX35 with modded wastegate for a top turbo as well. While it would be nice to have any number of different turbos as the top turbo, I just can't justify buying two new turbos for a $12K truck that, technically, doesn't even need ANY new turbos. It runs just fine the way it is. I guess I'm just bored this Holiday Season, and all my other projects are at a standstill for one reason or another.

Do you have head studs?

27 minutes ago, Vais01 said:

Do you have head studs?

I will...

13 hours ago, Vais01 said:

I wish you all the best. It would be ashame to ingest metal over trying to prove a point.

That's one way of putting it, but I preffer "In the name of science"!

Besides, I highly doubt there will be any carnige.

14 hours ago, Vais01 said:

I wish you all the best. It would be ashame to ingest metal over trying to prove a point.

What point are you trying to make with this? Do you really think the hx won't hold up or what? It's a tried and true setup....

Yep definitely not the first person to run this setup. 

I believe that was directed to me and my experimenting.

8 hours ago, Cowboy said:

I believe that was directed to me and my experimenting.

Yes it was to your experimenting. 

 

The turbo can hold up bit the drive pressure is of concern. If you can I say install a drive pressure gauge to see where you stand at various boost levels. If I understand what a turbo specialist told me the choke point on a .70 A/R turbine housing (12cm) is around 38 PSI. Also the HX35 only flows 58 Lb/min or .47 Kg/sec. I understand thats running solo and not being force fed. That forward volute for cylinders 1-3 will show higher drive pressure even with a drilled divider. 

I'm curious on the numbers though so please post it when you get it figured out.

8 hours ago, Buzzinhalfdozen said:

Yep definitely not the first person to run this setup. 

Your correct he is not the first but there is weak points in the HX35 that's why most companies opt for the stronger Borg Warner turbos.

So this isn't a apples to apples comparison, but I do have some readings.  I've had a drive pressure gauge for a couple months now, and have been recording runs before/after various modifications.  The last mod having been the head porting.  Normally I have the drive pressure gauge in the front ports and the EGT's in the rear.  However I swapped them for this run.  So these are basically identical conditions other then the head porting, and the fact that it's 50* out instead of the 70* it was before.

Yes, you are looking at that right, cylinders 4-6, which are the ones gated, have higher drive pressure then 1-3.  I would assume that it is due to the head porting, but I think that that shows that there isn't any major difference between the two volutes.  Hopefully I can swap the probes again and get some more readings.  That way it's more apples to apples due to both readings having been taken after the head porting.

Here's some more graphs, only difference being the the probes swapped.

Yep, pressure in the gated volute is higher.