Whats the best fbo setup

[xQx]

Originally Posted by iminhell1

I've seen that said by more than a handful of people, more flow. Thing is it's not true.

[...]

FWIW, I have relocated inlets. I did it because it was the last mod I had left to do and I'd read that it really opened up the top end flow.
I can say that I have not experienced any of that and I'm very confident it was marketing and not proven science.
I don't regret doing inlets. I like them aesthetically. But that $500 could have been better spent on something else to make the car go faster.

Inlets, yes.
Outlets, not always.

If inlets are the last restriction in your intake air-flow, then they would provide faster spool-up; however, since they're on the uncompressed side of the turbo, they make absolutely no difference to the achievable pressure or peak power.

From what I know about fluid dynamics - I tend to agree with you that inlets are nothing but marketing. This has been studied extensively in commercial air-conditioner design, and the tl;dr version it is a slightly smaller straight pipe presents only a tiny restriction in flow; but a poorly designed bend in a pipe makes a huge difference. The stock inlets are very squashed compared with aftermarket inlets, but the bends are similar - so it's very possible they provide little to no benefit. They especially provide no benefit if the restriction is elsewhere in the chain (eg. stock airbox or intercooler). ... All that said, it's a lot harder for a compressor to suck than it is to blow (which is why pressure pumps are always at the bottom of a hill, not at the top); and there's a noticeable increase in noise with aftermarket inlets, so you assume that means less restriction. But if it's just marketing or a real gain is entirely dependent on if the restriction in the inlets is the greatest restriction in the whole inlet system... And your experience pretty conclusively proves it's not.

Outlets are a different story. Because your outlets connect the turbo to the intercooler - the air in them is the hottest and thus least dense of the entire compressed-side of the intake. (It's been heated by the turbo and is yet to be cooled by your intercooler). So, it makes sense to have the outlets larger in diameter than any of the plumbing on the cool side of the intercooler.

All things being equal - the hotter, less dense air in the outlets means the pressure in the outlets (and thus on the compressor wheel of the turbos) is higher than the pressure in the chargepipe - where the boost sensor sits. So, when the wastegate is fully closed, increased flow in your outlets means less work for the turbo -- ie. higher peak performance and faster spool up.

If you're limited by your boost limit - I though you're right. 17psi read at the boost sensor is 17psi going into the cylinders - so power won't change. But with a better intercooler and better outlets, 17psi at your boost gauge might mean 17psi at the turbo/outlets rather than (for example) 23psi in a more restricted system - meaning less work for the turbo.

I did both inlets and outlets at the same time, and below is a picture of what the stock RHD outlets look like - so the gains I experienced may have been 100% caused by the outlets.

[BimmerAg]

Originally Posted by hunginator

How do you guys cope w/ the smell after installing catless downpipes? Bearable or suffocating? lol

I haven't done it on this car, but I installed a catless y-pipe on my old 1998 chevy pickup and I didn't mind the smell at all...YMMV

Originally Posted by xQx

Why?
In addition to the cats in the downpipes (which you remove), there are also cats in the midpipes (which remain).

Not on his 2012 with the N55

[BimmerAg]

Originally Posted by xQx

If inlets are the last restriction in your intake air-flow, then they would provide faster spool-up; however, since they're on the uncompressed side of the turbo, they make absolutely no difference to the achievable pressure or peak power.

Have to disagree with this statement here. The compressor side of the turbo works based mainly on pressure ratio, which is the outlet pressure divided by the inlet pressure. At 15 psig of boost, the pressure ratio is about 2:1, since the atmospheric air at at 15 psia is being compressed to 30 psia (30 psia - 15 psia = 15 psig). Because of this pressure ratio, it means that any changes to the compressor inlet pressure are magnified 2x on the outlet side. If the inlet pressure with stock inlets is 14.5 psia, then to get to your 17 psi example (32 psia) the compressor has to provide a pressure ratio of 2.21. With upgraded inlets, the inlet restriction is reduced slightly, lets say to 14.75 psia inlet pressure. Now, to meet the same boost target, the pressure ratio only needs to be 2.17. Since the required pressure ratio is lower, the turbine can spin slightly slower and the wastegate can be opened a little more. This reduces the exhaust restriction and helps the engine breathe more efficiently to make more power.

On the other hand, lets assume you were previously limited to 17psi (32 psia) due to the turbo, and not fueling. Then you can increase your peak boost pressure while maintaining the same exhaust restriction. In this case, we use the same wastegate position as the stock case to get the 2.21 pressure ratio across the compressor. With the upgraded inlets, the peak boost pressure increases to 32.6 psia (17.6 psig). This allows you to inject slightly more fuel to get more power.

[hunginator]

Originally Posted by xQx

No difference unless you turn MHD Burble up and spew heaps of unburnt petrol into the exhaust.

Why?
In addition to the cats in the downpipes (which you remove), there are also cats in the midpipes (which remain).

If I do nothing other than installing catless down pipes, will my car throw a CEL? And if so, what is the required step to rectify?

[BimmerAg]

Originally Posted by hunginator

If I do nothing other than installing catless down pipes, will my car throw a CEL? And if so, what is the required step to rectify?

Yes. To clear it you can use MHD or buy a DP fix like this: http://www.vr-speed.com/vrsf-catless...-bmw-335i.html

[hunginator]

Originally Posted by BimmerAg

Yes. To clear it you can use MHD or buy a DP fix like this: http://www.vr-speed.com/vrsf-catless...-bmw-335i.html

Thanks!!!

[xQx]

Originally Posted by BimmerAg

Yes. To clear it you can use MHD or buy a DP fix like this: http://www.vr-speed.com/vrsf-catless...-bmw-335i.html

or get a second hand JB4.

the DP fix isn't fantastic for your engine.

[BimmerAg]

Originally Posted by xQx

the DP fix isn't fantastic for your engine.

Why is that? Doesn't it just plug into the downstream O2 sensor harness and simulate a working catalyst? Closed loop AFR control should be done using the upstream sensor so I wouldn't think that the DP fix would have any effect besides getting rid of the CEL...

[Mandinca]

Originally Posted by xQx

No difference unless you turn MHD Burble up and spew heaps of unburnt petrol into the exhaust.

Why?
In addition to the cats in the downpipes (which you remove), there are also cats in the midpipes (which remain).

I also just installed VRSF catless downpipes and the car stinks, especially when I run the heater or A/C. It's also noticeable when I first start the car and when I'm at a traffic light.

If I had an exhaust leak I didn't think it would show up as a DME code. No noticable leaking at the DP/Mid flanges so I'm kinda at a loss as to why it reeks so badly.....to the point where I considered putting my catted DP's back on.
If it was a badly fitted VBand at the manifold it would be blatantly obvious, wouldn't it ?

[iminhell1]

Originally Posted by Mandinca

I also just installed VRSF catless downpipes and the car stinks, especially when I run the heater or A/C. It's also noticeable when I first start the car and when I'm at a traffic light.

If I had an exhaust leak I didn't think it would show up as a DME code. No noticable leaking at the DP/Mid flanges so I'm kinda at a loss as to why it reeks so badly.....to the point where I considered putting my catted DP's back on.
If it was a badly fitted VBand at the manifold it would be blatantly obvious, wouldn't it ?

TBH, any time you do DP's you should replace the fire rings.


Also make sure you aren't melting the splash shield.

[Mandinca]

Originally Posted by iminhell1

TBH, any time you do DP's you should replace the fire rings.


Also make sure you aren't melting the splash shield.

Fire rings ? Do you mean the DP/Mid gaskets ? I replaced those along with new bolts.
I took the splash shield off and haven't put it back on yet....

[iminhell1]

Originally Posted by Mandinca

Fire rings ? Do you mean the DP/Mid gaskets ? I replaced those along with new bolts.
I took the splash shield off and haven't put it back on yet....

Nope. There's a gasket on the turbo's, to the DP flange.
PN (need 2): 18307553601

[Mandinca]

Originally Posted by iminhell1

Nope. There's a gasket on the turbo's, to the DP flange.
PN (need 2): 18307553601

Ah, I had to re-use the ones I had. Didn't know they were there before the install. My mazdaspeed didn't have one so I wasn't expecting it.

[iminhell1]

Originally Posted by Mandinca

Ah, I had to re-use the ones I had. Didn't know they were there before the install. My mazdaspeed didn't have one so I wasn't expecting it.

I think the only people who even notice it's there are the ones putting in new turbos. I know I didn't know there was anything there until I looked over the parts diagrams.

I have 2 new ones sitting here for when I have to get in there to do some updating.

[low135]

Didn't see it mentioned, is just a chargepipe okay for MHD stage 2+ or should I be going to a BOV with the chargepipe? Starting to gather parts and wanted to know if the extra cost is needed or if the stock DV will be okay for that level. TIA

[Dat Aus]

Originally Posted by low135

Didn't see it mentioned, is just a chargepipe okay for MHD stage 2+ or should I be going to a BOV with the chargepipe? Starting to gather parts and wanted to know if the extra cost is needed or if the stock DV will be okay for that level. TIA

You have to have downpipes and an upgraded intercooler for Stage 2+. You can't just throw in a new charge pipe and run that tune on stock downpipes and intercooler.

You should be changing your charge pipe for a metal one anyway before tuning the car because the stock ones are prone to cracking under increased boost. When you order the new charge pipe is when you'll need to decide if you want a vent-to-atmosphere BOV or OEM style diverter valves.

Using the OEM diverter valves will be absolutely fine for Stage 2+ but some people have reported that their OEM DVs leak a bit of boost. If you get a charge pipe with the fitting for DVs, the OEM units should be fine but if you have the money you may as well upgrade them to Forge diverter valves. The other option is obviously a BOV. Either will be fine for a Stage 2+ car.

I personally run an Evolution Racewerks charge pipe with the factory diverter valves. I have disconnected the valves though so I still get the sound of a vent-to-atmosphere BOV but I still have the option to reconnect them if I ever get bored of the sound. You should put some small filters on the ends if you do this though because the OEM DVs are open at idle.

[low135]

Originally Posted by Dat Aus

You have to have downpipes and an upgraded intercooler for Stage 2+. You can't just throw in a new charge pipe and run that tune on stock downpipes and intercooler.

You should be changing your charge pipe for a metal one anyway before tuning the car because the stock ones are prone to cracking under increased boost. When you order the new charge pipe is when you'll need to decide if you want a vent-to-atmosphere BOV or OEM style diverter valves.

Using the OEM diverter valves will be absolutely fine for Stage 2+ but some people have reported that their OEM DVs leak a bit of boost. If you get a charge pipe with the fitting for DVs, the OEM units should be fine but if you have the money you may as well upgrade them to Forge diverter valves. The other option is obviously a BOV. Either will be fine for a Stage 2+ car.

I personally run an Evolution Racewerks charge pipe with the factory diverter valves. I have disconnected the valves though so I still get the sound of a vent-to-atmosphere BOV but I still have the option to reconnect them if I ever get bored of the sound. You should put some small filters on the ends if you do this though because the OEM DVs are open at idle.

Thanks for the info. I know I have to do down pipes and intercooler for 2+. I was going to do charge pipe, intercooler, downpipes, and dci all in one shot. I had just wanted to know if running the stock DV was going to be okay for that.

[Dat Aus]

Originally Posted by low135

Thanks for the info. I know I have to do down pipes and intercooler for 2+. I was going to do charge pipe, intercooler, downpipes, and dci all in one shot. I had just wanted to know if running the stock DV was going to be okay for that.

Yes, stock DVs will be absolutely fine for you.

[Mandinca]

Originally Posted by Dat Aus

Yes, stock DVs will be absolutely fine for you.

I considered this when I was making my charge pipe decision because I don't want the "pscchhh" every time my AT changes gear. Concerned about leaking boost using the stock DV's I ended up getting a Chinese tial knock-off for <$200 so I'll see how that goes with the sound. If I don't like it I'll dump it and get a charge pipe for DV's and use my stock ones. If they leak boost I guess I'll have to spring for the forge DV's.

[iminhell1]

Originally Posted by Mandinca

I considered this when I was making my charge pipe decision because I don't want the "pscchhh" every time my AT changes gear. Concerned about leaking boost using the stock DV's I ended up getting a Chinese tial knock-off for <$200 so I'll see how that goes with the sound. If I don't like it I'll dump it and get a charge pipe for DV's and use my stock ones. If they leak boost I guess I'll have to spring for the forge DV's.

It won't make any BOV noise until you lift. Part of the auto advantage is the no loss of boost between shifts.
Most have no idea I'm boosted until I lift at the end of the track, then heads get scratched ... that thing is turbo'd? Yeppers.