Hey guys-
What is the range of boost pressures that the FP 25psi WGA can control using EBC and a 3-port BCS on the stock ECU? Low to high end

I'm running an FP Green 74HTA with 84mm surge cover on my Evo 8, with a stock TB, inlet mani, head and exhaust mani, 3in Megan O2, 3in DP, 3in TBE, and hi-flow cat. I want to run 23 psi tapering to 20 for 91 pump, and 27 psi holding for E85.

The reason for my question is that I've got a problem controlling boost above 25psi with my existing WGA, which is a FP 18psi unit. I'm already driving my GM 3-port EBC at 98% wastegate duty duty cycle and I've maxed out the pre-load at 6 turns. I find if I go over 98% WGDC I get uncontrollable spikes on spool and surges up to 30-32 psi. I think I need to upgrade to the 25 psi WGA to bring the WGDC back down to a useful range.

What do you advise?

 

What exactly do you mean by, "...maxed out the preload at six turns...."? Are you saying that the end of the actuator rod is bottomed out inside the turnbuckle? Do you mean that it is physically impossible for you to pull the turnbuckle back up onto the flapper valve's pivot arm? Or do you mean someting else altogether?

 

Yes the end of the actuator rod is bottomed out inside the turnbuckle. I trimmed the end of the rod slightly to get it to six full turns. I am able to pull the turnbuckle back up and connect to the arm no problem. In this config, 17-18 psi from a bicycle pump moves the arm and cracks the wastegate open. When running wastegate only (0% WGDC) with this amount of preload I log 17-18 psi of boost.

 

Sparky is king of WGA troubleshooting Wherever there is a WGA thread there he is!

 

Are you getting knock on your 91 octane map at 23 PSI?

 

There is an inherent problem optimizing WG preload on these dual map pump/Ethanol setups. Do you know what I am getting at OP?

To be more precise, it is going to be a compromise any time that you try to set optimal WG preload on the same turbo for two different peak boost levels. You should be able to get pretty close to optimal preload for the lower peak boost level which is your pump gas tune, but you are going to have to let spring pressure be way soft for your higher peakboost level. Do you know what I mean?

 

Hi Sparky - thanks for chipping in.
No knock on 91 at 23 psi. How does that relate to a decision to upgrade to the FP 25 psi WGA? Do you think the lower limit of controllable boost pressure with the 25 psi WGA will be @ 23 psi?

 

I like to run the preload up as close to the peak boost level as humanly possible. So for your 27# peak I'd like to see you running about 23-25 PSI of spring pressure. If there is no creep whatsoever then I would shoot for 24-25 PSI of spring pressure.

Obviously, 25 PSI of spring pressure is not gonna be doable in your case, right? It is not possible because then you would overshoot your 20 PSI pump gas peak. You would be running 25# on 91 octane. The need to have the flapper full open at the relatively low 20# makes running 25# of spring pressure an impossibility, doesn't it?

 

You should be able to run as low as 18ish with the 25# WGA. A couple guys on here saw 18# when installed with the turnbuckle at its longest setting. That is 18# base pressure with the thing.

 

I was just kinda thinking out loud. I run about 22-23# on 90 octane with my Red. I have a fairly low timing/high boost tune though. As opposed to high timing/ low boost. In general, there is an inversely proportional tradeoff between timing and boost.

With a low octane pump gas tune I prefer running the highest boost possible and pulling some timing. Your E85 tune on the other hand will take gobs of timing.

So, to try and get as much preload as possible considering your 27# E85 tune, I would advise running a low timing/high boost pump gas tune. This will allow you to run the 23# peak without the roll off down to 20#.

So, you could thus, run a flat 23# peak boost level and do with with straight wastegate. That is control your 23# pump gas peak boost level with straight wastegate spring pressure. This allows you to raise your preload up 6 PSI, from your current 17# to 23#. This will be close to optimal preload for your 27# E85 tune.

This is the approach that I would personally take in dealing with your issue. I think that you really don't need the 25# WGA for 27# of peak boost pressure. Just cut another 3/8" off the tip of the actuator rod on your 18# unit. Just my O2.

 

Cheers Sparky. That's what I needed to hear. I understand the inherent compromise required for WG spring pressure when alternating between 91 and E85. It also means I will be able to use the 25 psi WGA to get the WGDC settings back into a controllable range for both fuels. If I set the turnbuckle to give 20# base pressure, I can then use EBC to modulate boost levels for both fuels without hitting 100% WGDC on E85. I expect this will stop me from running into the surging problem I'm seeing with the 18# WGA on E85 as WGDC approaches 100%.

 

Hmmm. I was in San Francisco just a couple weeks ago. Caught a couple Giants-Dodgers games. I would have loved to swing by and tinker with the preload on your Evo. Maybe next trip.....

 

I like this line of reasoning. It sounds like a good plan to me. Incidentally, is your Green fitted with the anti-surge comp cover? Also, what DV/BOV setup are you running? I don't remember you mentioning surge in your earlier posts. I do recall you mentioned a boost spike problem. Or, are you not talking about compressor surge per se? Did you mean boost spike/creep.?

 

Thanks sparky - sounds like I'm on the right track then. Yes i've got the 84mm anti surge cover. I'm running the IX BOV crushed which holds 30 psi before it cracks. With this set up on E85, I get uncontrollable creep from 27 to 32 psi, between 5500 and 6500, if WGCD is raised above 98%. I believe changing to the higher spring rate of the 25 psi WGA but keeping the preload to 23# will allow me to reduce WGDC to a range where I can prevent creep. See my sig for a full mods list.

 

Boost creep is not necessarily caused by WGA issues. You may want to think about porting the merge port in your Megan O2 housing if it was not already ported. Also, porting the entrance to the WG bypass port(s) inside the turbine inlet area of your turbo is almost always beneficial in getting boost creep under control. Just some more food for thought.