YakATK

Not sure if I should be posting this in this section or the 2nd gen section...but here it goes.

I may be getting a TII soon. I am gonna have FCD, 3inch straight exhaust, Walbro Fuel Pump, BOV done on it pretty much right away (hopefully).

Would having the straight 3inch exhaust make boost go up alot? Or does it only affect boost levels a little bit? How much boost would adding on a cone filter add? Would it rise up a couple PSI?

And, how much boost can the stock injectors with the Walbro pump handle? I have heard 10psi tops to be safe.

btw, if it matters it would be on an 87 TII.

Thanks for info in advance.

chris-reedtn

boost will go up alot, i recomend getting an s5 turbo, and then porting its wastegate. If you dont port its wastegate boost will still go up but not as much as the s4 will.

-Chris

BDC

I wouldn't use an FCD in that combination. It's the root of a time bomb waiting to happen.

B

YakATK

Doesn't the FCD make it safer for your engine by not allowing it to cut fuel when in boost though?

And, if boost would go up quite a bit, then would my stock injectors not be good enough? I will have the Walbro fuel pump installed for sure. Would I need to do any other upgrades?

Josepi

A FCD is a mere bandaid to keep you from experiencing fuel cut. THAT'S IT.

The problem with FCDs is, boost level keeps rising past the point of fuel cut. What is the ECU doing? It's putting out the amount of fuel for the value right below fuel cut (3.xx V?!).

So, imagine 2 lines on the same slope. Both are going up at the same rate. Now one of the line decides to just stop climbing and go parallel to the bottom. The other line keeps rising.

The line that keeps rising is your boost. The line that plateaus (sp?!) is the amount of fuel sent via the ECU to the motor. All of that extra boost now is not being met with extra fuel from the ECU. You are beginning to run lean. Raise it enough, your going to run lean enough to detonate under boost, and wa-la. Motor is gone.

My suggestion? Get a S5 turbo, port the living hell out of the wastegate, and run without a FCD and keep your boost set below the fuel cut off point on the factory ECU. Don't by a S-AFC, that's just going to be another band-aid. Save for an EMS.

BDC

Well said. Also, let's not forget the issue of spark retard at higher boost levels ....

B

YakATK

Yeah I was thinking about the FCD thing and sorta started to figure out why not to get one, was exact reason you said.

But now the other question:

If I did 3inch straight pipe, and maybe a cone filter intake. What kind of boost levels would I be hitting? And would I need to upgrade any fuel system parts or would the stock system be fine? Would a Walbro pump be good enough? Why can I not just port the S4 turbo wastegate?

I guess a better question is:

If I get the TII and put on 3inch DP and straight pipe it back to a muffler, and do a cone filter intake. What other mods will I HAVE to do to not damage my engine? What other mods are SUGGESTED I do to not wreck my engine?

Thanks for all the help with this, I am still a Turbo n00b, but am learning.

YakATK

bump.

Josepi

Someone had a writeup of everything they did and the boost levels netted from it...I'm going to hunt it down if I get time (at work! )...

I'd suggest you keep the stock airbox for now. That'll keep your boost down somewhat (after you put in a DP/MP). Not only that, but your intake air temps WILL be lower with the stock box instead of an unshielded cone.

NZConvertible

I've seen an S4 Turbo reach 17psi with that combo and no other mods, but not for long...

If you intend to do those mods, the first thing you should do is port the wastegate. The S4 turbo has a very small wastegate port, and as soon as you free up intake and exhaust it can no longer bypass enough exhaust gas to control boost. Although swapping to the superior S5 turbo is a good idea, they're not always easy to find. There's enough room in the S4 turbo to port it well past the edges of the stock flap and replace that with a bigger flap. If you can't do this yourself, a turbo workshop will have no trouble.

Next is an upgraded fuel pump. This is the weakest link in the fuel system, not the injectors as you may have heard. The stock turbo should not be taken past 11-12psi (especially with the stock top-mount intercooler), and at that boost the injectors are well within their capacity as long as you can maintain pressure behind them, hence the pump. Just keep that boost down.

I assume you already have a boost gauge. If not get one before doing anything else. Watch it like a hawk after doing any mods, especially in higher gears. That's when boost creep becomes a problem. If you see it start to rise get off the gas immediately. A trip to the dyno is even better, because you can load the engine up in 4th gear while watching both boost and air/fuel mixtures to see if boost is under control and that mixtures are adequately rich.

Hope that helps.

YakATK

Thanks for info. Yeah it definatly helped. I don't have a TII yet but may be getting one within the next couple weeks (hopefully). I wanted to get some mods done right away but of course want to still have a car to drive, now I know what precations to take Thanks again.