Reputable tuner singing a different tune to the forum...

[gaz097]

Hi everyone,

A reputable tuner (not wanting to name names but comes highly recommended on the forum) has told me that with a high flow cat, 3.5inch x-force catback and antz intercooler that a tune will not stop over-boost from occuring, especially during cold nights. I'm told that the only option is to get a waste gate and turbo actuator to stop a mechanical problem from eventuating.

Can anyone shed some light here?

This is correct.

On a baby FG turbo it doesn't really matter (watch jet flip) that the wastegate hole is too small when you fit a free flowing cat and exhaust, cause it can't really generate enough boost to hurt a FG motor (well almost).

This doesn't mean the boost control is perfect (or actually in control) as with a 5psi gate spring you will be making 16psi IN THE MID (when hot, and closer to 20 when cold) then 12psi up top of the rev range. Tuna should know this and will tune accordingly.

Alternative is to make the wastegate hole bigger to run a lower boost in the mid (and actually hit the target 12 psi with the 12psi spring) then the tuner can dial in the tune 100% as when the weather cools and the boost wants to increase the wastegate can actually waste the air through the gate to keep boost at the correct level.

Once you go to a GTX, or the larger ba/f, FG F6 turbo the larger port is a must to keep boost levels lower and in control.

[Puffwagon]

Or just use all the springs and run all the boost all the time. Works everytime half the time all the time 

[FGeorge]

So to summarise my understanding, flapper and wastegate critical for bigger turbos.

 

Stock fg turbo may not need it and largely appears to come down to the tune. However, it is advisable to get the flapper mod done so as to limit danger to the motor and turbo, and provide more reliable psi across cold nights and hot days.

 

Am I understanding correctly?

 

Then, would it make sense that by tuning the psi to a moderate level it will allow spikes on cold nights without damage? Or is the issue that these psi spikes are 'unexpected' so the motor runs lean? Would running my injectors under capacity allow them to compensate for this or am I just dreaming?

[El Andrew]

Sort of. The boost spike happens because the turbo controls boost by opening the wastegate but its size limits the extent to which it can do this. Exhaust gases make the turbine spin, which makes the compressor spin, which compresses the intake air.

When you have more exhaust gas than you need to make all that happen for the target boost, the wastegate opens to relieve the excess. If the wastegate isn't big enough then not enough exhaust gas is released and you make more boost than your target.

Is worse when cold as cold air is denser and makes more 'boost' than warm air.

As Gaz said, stock FG turbo is going to struggle to make more than 15 psi.

Tuning for a lower boost target won't make a difference, as this issue is due to exceeding mechanical capability. Managing wastegate control as the limit is approached will help. Surplus injector capacity won't help much as you won't have a fuel table that knows what to do at unplanned boost levels - so the computer won't know to use that extra capacity. But if you are targeting rich AFRs at peak boost you are probably pretty well covered.

Each exhaust combo is different though. If your tuner says he can't do it without a bigger wastegate port and flapper then must have a reason. But yes, plenty of 300ish FGs with stock turbos out there without the wastegate modded.

Edit: Have a read of some info on how turbos work. Some of the above posts are correct and some aren't. Flapper and port mod doesn't help you make more power, it helps you maintain control over peak boost. Boost don't leak out the exhaust. There are plenty of good books and articles if you want to get into the nitty gritty.

[FGeorge]

Thank you El Andrew

 

I reckon I'll do the mod to be safe but I'll still do research because I'm finding this to be very interesting. Plus, I bet understanding the way the turbo works will make the turbo noises all the more arousing

[El Andrew]

How much is the mod? If it's affordable and helps you sleep at night then probably worth it

If you are good on the tools you will save a heap by removing the turbo yourself.

[bjc]

Devil's advocate here...

If the car has the stock 3576 then don't bother, it'll hit 18psi in the mid and die off up top without being forced to try and hold more boosts for a timely death depending. If it's a 3582 (gt3540) and you want to wind it to "Max Headroom" then you'll need the mod to make use of it or pull timing and be down on power but still have a decent amount of boost going to waste.
It's like saying you need headstuds, I understand the tuner pov and path but it's not required until you step way WAY past your power point but not all tuners tune the same, some like boost while others prefer timing. I live in a tropical climate so what I see done down south on 98oct I'd laugh at with that same car up here...
300-330kw on the stock 3576 on 98oct with all supporting mods imo will be fine, otherwise step up in turbo size (gtx3576 for a great street turbo and still good top end power) and get the iwg ported (if going just the supercore) or go external gate as tuners prefer it due to easier boost control.
You'll want more power regardless in the end mate (this is the way) but it depends on what your end goals are. The stock 3576 with a decent set of tyres on the back is a brilliant combo for street, highway overtaking and towing.
I understand your questions and need for wanting reassurance as it's hard earned money (otherwise you wouldn't be asking) and it's similar to Impulse buying where you can feel guilty.
If the tuner was a stroker and didn't want to explain properly to a potential customer then that's my queue to bounce. People come in all sorts though, it doesn't mean they aren't great at what they do!

For future reference, you should give as much information as possible when starting a thread (turbo size for instance and fuel type) as replies keep stabbing in the dark until you hand it out.
Everyone likes to learn as we all start somewhere.

I'm not a tuner btw so take my reply with a grain of salt yada yada...
I just rambled like a champion there!

[Panda Eyes]

4 hours ago, bjc said:

I understand your questions and need for wanting reassurance as it's hard earned money

 

OP: you play- you pay. Accept this right from the outset or don't start down the modifying path. Its gonna cost more than you think in the end anyway....

[gaz097]

If the car has the stock 3576 then don't bother, it'll hit 18psi in the mid

Will it? Your gate is pegged open. It will hit whatever it wants depending on conditions.

Boost limited is not boost control.

[FGeorge]

I'm so glad I opened this thread.

 

Does anyone know a good mechanic who can rip out my turbo in the sydney region? 

 

It appears to be a full on job and I want to make sure it's done correctly.

 

Since we're on the topic, flapper mod... What kind of power levels does it unlock on 98 with the stock fg baby turbo?