I'm running a 38mm tial wastegate. 2 thoughts.

1. I'm trying to figure out what springs to run. I'm thinking about using either a 14# spring OR a combo spring to run about 20#. Any thoughts?

2. What's the rule on wastegate sizing. Is 38mm too small? What's the rule of thumb on wastegate sizing?

 

Id say to get the 20#, I have the 14# spring and cant get over 25psi. FourDoor on here gave me some good info but apparently with the 14# spring Im pretty much maxed out at 25psi with the wastegate my limiting factor.
This is what fourdoor said:
"What is the base pressure of your wastegate? adjustability available from a boost controller is based on two main factors.

#1 factor is the size of your wastegate since the larger the surface area of the valve the less you can raise the boost above spring pressure using a boost controller.

#2 factor is the A/R of your exhaust housing. The more free flowing your exhaust housing the more adjustability you get with a boost controller.

In her case she has a 44 mm Tial WG and a .63 A/R exhaust housing resulting in a factor of aprox 1.38 adjustability. She can adjust boost to aprox 1.38 times the spring pressure in her Tial."


Dont know if any of that helps but Im putting in the 20# or 21# combo spring of large blue small red or large blue small green. Seems to me with the 38mm wastegate and a .63 a/r you would be able to adjust to 1.65 times the spring pressure in the tial. So 20# spring times 1.65 is 33psi.

 

Well the one thing to keep in mind, is can we run ~20# on 93 octane. Otherwise we're going to have to change the sprins if we change our fuel.

Good info Tom

 

Thats something I also was not sure about because I dont want to change the spring for the track and for driving around town. I know I dont like the 14# spring I have now.

 

I see no good reason to use a spring pressure of any less than the minimum amount of peak boost one expects to run on any occasion.

 

This is what I was thinking as well. But how about the other question. Is 38mm too small? How should we know what size to run?

 

It isn't easy to come by solid logic on wastegate sizing aside from the obvious:

- The greater the power potential, the greater the volume of airflow that must be controlled and therefore the larger the WG (generally speaking).

- The lower boost pressure one intends to run a large turbo, the larger the WG must be to effectively control the pressure.

- A WG that's too small will cause boost creep.

I can't help but feel a bit skeptical about the adjustability ratio quoted above. It would seem to me that is more so connected to the ability of the boost control solenoid. Nevertheless, assuming one runs a spring (or combination thereof) that matches the lowest expected peak boost (e.g. pump fuel map), the least amount of solenoid duty will be required to raise the boost for a race fuel map.

I chose a TiAl 44mm unit for my .63 A/R hotside, using a combination of springs that gives a pressure of 1.5 bar (~22 psi). According to what was said above, I shouldn't be able to get more than 30psi with that setting. I'm not sure I agree with that, as I'm spiking to 27psi and I'm fairly certain I can get to well over the 30psi figure that results from using the '1.38' factor. I chose the 44mm WG because I wanted adequate WG control given the expected power levels, and I much prefer v-bands (44mm WG) to bolts (38mm WG) when it comes to exhaust component fasteners.

Just my $.02.

 

With both the turbo kits I have had, I have been able to get ~1.7 times the wastegate spring. IMHO, you want the base pressure to be close to your pump gas boost. This will help control boost spikes too.

 

I agree that WG spring pressure should be as high as possible. I also ran a 20 psi spring on the stroker. Kind of strange not being able to go below 50 lbs/min, but it worked for me Low spring pressures always gave me boost control problems.

WG sizing has nothing to do with power levels, but more to do with how much of the turbo's potential airflow you intend to use. Running a 35R at 15 psi will require a larger WG, since so much exhaust flow will have to be bypassed. Running the same turbo at 30 psi will require very little wastegate flow. Another factor is WG placement. If you are venting all 4 runners, like most tubular manifolds, a 38 will do very well. With a 35R sized turbo I could hold 13 psi to redline on a 38. If the WG is on the O2 housing (not even sure any EVO kits do this) you will need a larger WG. The FP turbine housings are cast for a 40 or 44mm IIRC. I have had great luck with the 38s, but yes, vbands are the way to go with stuff like this that gets heat cycled a lot, and going bigger on the WG never hurts.

 

I wish I would have gone with the vband. Everything else I have is vband, but it'll require me to cut and reweld the manifold. (I know ATP has a flange, but it'd like a clean look.) Faaaack

On another note, here is some info from the Tial Website. http://www.tialsport.com/documents/w3_tial_38_sp.pdf
So based off this chart, I think I want to go with Lg Blue + Sm Red (20.3#) or Lg Blue + Sm Green (21.8#)

Anyone know off the top of their head what # people are using on the 93 octane street tunes?

 

I used the Lg Blue / Sm Green (1.5 bar) combination for my GT35R setup, and it gave me a steady ~22 psi for the 93 oct baseline.

 

Thanks for the info.

While we're at it, how much effect do spring rates have on boost creep?

 

I had a custom thick walled manifold setup for 38 tial. Not a lot of creep but I had to replace gaskets regularly. After going to a thick copper one it would last 3 four months but after 5 gaskets in a year, i ended up cutting it off and welding a flange and new 02 housing to run the 44 vband. No problems since. Just from a reliability pov, the 44 vband seems the way to go. It isn't the biggest deal to modify the manfold for it...

 

Gaskets? Isn't the metal ring the gasket?

 

i would use a Tial 44mm with 1.1 bar spring........ m2c....Ray