hardtarget870

I finally decided to put a gauge in between my stocker/s400 and found out that the s400 is doing very little to no work at all. Like 40+ psi on my total boost gauge only yields about 5 psi out of the S400. Since installing the twins I have seen an increase in total pressure, which I guess is the output of the stocker, and lowered egts.

I thought that the first thing I would try is to reduce the spring tension on the wastegate of the stocker. I was already at the very end of the bolt that connects to the wastegate arm so right as I started to loosen the bolt I ran out of threads and it came apart. So I decided to take a run down the road and see what would happen with no wategate. Well, it made only about 6 psi of total pressure with increase egts.

So I connected the bolt with the spring back to the wastegate of the stock turbo and put a few more turns that I originally had. The result was plenty of quick boost and slightly higher egts than when I was on the last few threads of the bolt.

Sorry for the long post, but I am unsure where to go at this point. It feels like the spring that came in the twins kit for the wastegate on the stocker is too strong. So I would guess that the starting point might be to put a lighter spring and maybe use a fish scale to put a set amount of tension on the stock turbo's wastegate. But I am still unsure how to demand more effort from the S400. So I turn to all of the expertise from you guys and gals out there. Thank you for all your help.

JP-4.5

More fuel.....

Big Blue24

You are exactly right, you need to open the stock turbo's wastegate sooner. This will bypass hot exhaust gasses around the stock turbo's turbine wheel and give the S400 faster hotter exhaust so it performs a greater share of the air compressing.

If you plan on big 600+hp and you have a few hours on a Saturday, take the stock turbo off and port out the wastegate passage. It measures 19mm and can be ported to 26-27mm and still have an adequate seal with the puck/flapper. Increasing the port size will create more surface area for the exhaust pressure to work on. Increased surface area will let the puck open with less total drive pressure; this along with a larger port will bypass more exhaust flow all else being equal.

If you can find a lighter spring, that would definitely help drive the S400 harder and lighten up the load of the stock turbo.

KKB

I would call Nathan and see what he has to say. I am thinking of going the stocker/S400 route so it will be nice to see what you find out about this.

fahtb0y

hey, what's going on. didn't think i'd be able to pick you out that easily. I'm the hat in A Co with the red truck. So how's the new twin setup treating you?! and how much of a pain was it to install

hardtarget870

Thanks to everyone here, and Nathan at MPI has been giving me some great advice; I now know what I need to do to correct the problem and utilize both turbos. I will start by adj the pressure applied to the wastegate on the stocker and buy a Smarty sr. Will the options that say "added timing" assist in spooling my turbos?

Spooler

You will more than likely be using Timing 3 on the Revo tune to spool better while towing. If you are empty you will more than likely use the Timing 2 option. Are you adding any additional fuel over stock at the moment with a programmer or box at the moment? If not, The Smarty Sr will no doubt cure some of your fueling issues.

osci

What drive pressures are you seeing?

lmills

what are you running for fuel? I see nothing in your sig?!?

Green04HO

OSCI I see we are running similar twin setups. Have you checked drive pressures? I've always wanted to check mine but have never gotten to it yet.

osci

Yes, they are 1-1 @ 60 psi with this set. The stocker I ran prior to this was almost 2-1 @ 60psi.

Hintz

2-1 with the stocker/s400 or stocker by itself?

osci

This was with a stocker/ Gt4202.

hardtarget870

I dont have a drive pressure gauge installed right now. Should I get one of those since I am running twins, or more so because I am still running the stocker?

The only thing I have for fuel is the Smarty I just got.

So far I have cut a few coils off of the spring for the wastegate and put the Smarty on SW4. I now get about 20+psi out of the S400 and was approaching 48 psi when I took my foot out of it, dont have head studs yet. EGTs are slighty up from when I was running SW1. Also, it doesnt smoke on SW4 like it did with SW1, but when it was on SW1 I still hadnt fixed the wastegate spring.

Idaho CTD

Your still a little tight on the spring. You should see about 24psi at 48psi of total boost.