This post is an answer to help anybody else that may run into this problem

I have had this engine combo together for about 5k miles and decided to ditch the TMIC and get an FMIC.

Before I added the FMIC I was boosting at 5 psi no creep, no drop. 5 psi to redline

After adding the FMIC my boost would still go to 5 psi but would start to drop off at 5k rpms and dropped to 2 psi by 7k.(S5 turbo, ported WG)

To diagnose the problem I hooked up a second boost gauge to the turbo and found out I had 10 psi at the turbo, still only 2 psi in the intake.

I figured there was a restriction in the system somewhere, just had to find it.

Through much trial and error i finally found it, my secondary throttle blades were not opening all the way, the primary was opening all the way but not the secondaries. It looked like they were opening all the way while the TB was installed, but when I removed the TB I could see they were not.

The linkage on the TB needed to be tweaked a little to correct it. Done. From what I can tell this TB never opened the Sec. all the way, it was like this from the factory.

Anyhow on the test drive after the fix I now have 8 psi @ intake and it creeps to 10 psi @ redline. Throttle response is much improved as well.

HTH someone else with a similar problem.

 

remove the blades!

 

There is going to be a pressure drop in the system from having more piping in the system and the intercooler itself will also have a pressure drop across it. 80% pressure drop sounds wrong...like there is a boost leak somewhere, possibly cheap couplers.

 

yes if your No. 2 secondary throttle plates are not opening fully, you can remove them as long as you plug the holes appropriately. This is the worthwhile part of the TB mod.

You should also pressure test for boost leaks. Do a search, there have been recent threads on this topic.

 

Don't remove the TB blades, waste of time and effort, and for no realistic benefit. Just get a new/good second hand TB and be done with it.

 

you do the TB mod?
http://www.fc3spro.com/TECH/HOWTO/TBM/tbm.html

do you have an exhaust?

 

Do "new/good second hand TB" grow on trees in your neighborhood?
If the secondaries aren't functioning- most likely due to a failed dashpot- removing them and plugging the holes takes about an hour and has no real side effects (bad or good) that I can tell.

 

yeah i just remove a dashpot, then they work, done.

 

The dashpots fail in the open position anyway, so if the outer set of secondary plates refuse to fully open, there is something else going on.

 

I see it took a while for anyone to reply to this post.

the TB mod was done before I got it.

Exhaust is full RB-2.5" DP to 3" mid\Y, dual 2.375" mufflers

As it turns out the sec blades did not completely solve the problem. I tested the car with a straight pipe in place of the FMIC on and posted this. After I re-installed the FMIC the boost still dropped off, just not as bad(gained 2psi).

The other change that made a big difference was getting rid of the stock 2" elbow from the TMIC.

Now that I have 2.5" pipe from the turbo to the TB, peak boost is 9 psi and drops to 6 at 7k rpm.

My combo is
86 NA-Turbo swap
S4 6 port irons with street port
S4 NA rotors
S4 turbo housings
T2 UIM, LIM and TB ported to match irons
S5 hybrid turbo
3" TID
Bosch style BPV(
RB turbo back exhaust(2.5" DP)
550cc primary injectors
680cc secondary injectors
S4 T2 ECU(332 stock)
HKS FCD set to 11
NA engine harness
Walbro 255HP pump(no resistor)
Aeromotive AFPR @ 40 psi
JDM\Emotor\ebay FMIC 18x7x2.5 core
2.5" piping turbo to TB

Anyhow I did test the FMIC for leaks by capping one end and filling with water, let it sit for several hours, It did not leak a single drop.

I feel that the couplers were tested when I took the FMIC off and replaced it with a section of 2.5"straight pipe(3rd gear pull resulted in 10 psi at compressor and 10 psi at intake all the way to 7k rpm). So I am pretty sure there are no leaks in any of the piping or couplers.

When I put the FMIC back on I get 10 psi at the turbo and 9 psi at the intake dropping to 6 psi at 7k rpm

Any thoughts?

 

Read this for a second.


Why do people go through such elaborate procedures to avoid pressure testing for boost leaks? you're not the first. "well if the FMIC doesn't drip water with absolutely no pressure applied, it MUST not be leaking when pressurized air is applied." huh? I also love when people say "oh I have no boost leaks" when they do the old carb cleaner trick in the engine bay. Just because it doesn't leak at atmospheric pressure or under a vacuum does not mean it's free of boost leaks.

are you too cheap to buy a low-end air compressor? too lazy to drill and tap a pvc cap from home depot, or buy one from Fighter's Garage or Boostpro.net? I guess I'm coming across as a dick now, but seriously, read your own post. You can't check for leaks of pressurized air without applying pressure to the system!

 

Just what arghx said. why so stupid? It's easy man. Air compressor, rattle can (spray paint can cap) cap, the fitting that plugs into the air compressor. Thats all you need, it's like free to make one. Use a plastic cup from your cabinet when moms not home. ****'s simple. If you have a air compressor it's a couple min job. ive done it with a bike pump also.

 

Dude. you say you run the stock turbo what size is your intercooler does it match tha original or is it king size you might need a larger turbo to hold more pressure when air gets colder it shrinks so your pressure would drop slightly , you could try a boost controller to pump up the wastgate so it will take more boost , but if your turbo is small , t3/t4, but if you have good engine vacume,a sign of good compression ,try installing a rising rate (TURBO) fuel regulater to increase your fuel pressurefrom 28psi stock to about 43lbs remember you need 1000cc of fuel for every 100hp,and your current set up lacks fuel. on our race car NA 88 6 port we currently use 2 450 primarys with 2 1000cc secondarys at 40psi and it drinks fuel like a dry camel sucks water. as far as your secondary flaps on your TB they are there for the CHOKE . IF YOU REMOVE THEM, you can expect a long gas pedal holding start up Pain in the asstry instead to remove the hot wax pellet on the turbo clean of the crud stuck in the waterline under the gasket so the water flows properly and when the pellet expands and knocks of the high speed idle Cold startcam (which pushes on your secondary butterflys creating the initial High speed Idle, your car will run perfect ,as long as you adjust the idle properly as well as the TPS and idle fuel mix. As far as the low 'boost' look for vacume loss or bad intake manifold gaskets or burnt injecter o rings or blown egr ,open solinoids, burnt wiring,I use water to locate the leaks por it on when it starts to sputter your in the neghbourhood , also listen hard for air leaks they hisssssssssssssssstry using a rubber hose stuck in your ear and probe around the intake and turbo and IC till you either find it or eliminate that possibility ----------------good luck , I can't tell you how many times I 've been there on rx7s ps also look at your computer and check it for any burnt resisters (lite blue) bottom board