Supporting Mods For F/I Applications

[diss7]

Originally Posted by SnapOv3st3r

From the other thread:



No, that's when you would do something like this instead.

Lets not take what I side out of context. I'm sure the above picture would be great for top end, that was never what was being discussed.

[Tansey86]

Originally Posted by diss7

Lets not take what I side out of context. I'm sure the above picture would be great for top end, that was never what was being discussed.

I don't think its out of context, its an example of how the less backpressure the better for a turbo setup.

[diss7]

Define better. If you mean top end, then I agree. You also stated in the previous thread that a larger exhaust is better for spool, a comment I disagreed with. I went further and said that according to your stand, that no/minimal exhaust would spool the turbo the quickest. A point I still believe to be incorrect, and which was not mentioned when quoting me above.

[Coheed]

Originally Posted by diss7

Define better. If you mean top end, then I agree. You also stated in the previous thread that a larger exhaust is better for spool, a comment I disagreed with. I went further and said that according to your stand, that no/minimal exhaust would spool the turbo the quickest. A point I still believe to be incorrect, and which was not mentioned when quoting me above.

A larger/no exhaust will spool the turbo faster. Here is a dyno I did with full exhaust vs open downpipe...

[IMG][/IMG]

Look at red graph vs the blue graph. Both were pulls in 3rd, green was open downpipe in 4th.

A larger exhaust is always better for turbo if you can fit it in there.

[diss7]

Originally Posted by Coheed

A larger/no exhaust will spool the turbo faster. Here is a dyno I did with full exhaust vs open downpipe...

[IMG][/IMG]

Look at red graph vs the blue graph. Both were pulls in 3rd, green was open downpipe in 4th.

A larger exhaust is always better for turbo if you can fit it in there.

Interesting! Backwards to my understanding, but seems to be more proof against me than for.

[sw20kosh]

Originally Posted by diss7

Interesting! Backwards to my understanding, but seems to be more proof against me than for.

Years ago everyone (especially in the honda world) was talking about back pressure. It was the big thing. It caught on.

It makes no sense on a turbo application. You free up the exhaust by replacing the small stock piping with larger piping so that more hot air can flow faster over the turbine blades. This spins the turbine wheel faster. Back pressure would slow the exhaust air down and would inhibit the turbine wheel from spinning faster.

I wish I had my old dyno chart to show you what an immense impact 3" does vs. 2.5 on FI motor pushing decent power. And no, no other parameters where changed.

Here is one from a honda motor (turbo'd).
Blue is 2.5" 20 psi
Red is 3.0" 19 psi

He was able to spool the turbo faster and he achieved the same HP with one less psi of boost.



Here is 15 psi 2.5 vs. 3" piping. The car has a 2.5" Downpipe in both configurations. It would gain even more spool and power with a 3" Downpipe.

Blue is 2.5"
Red is 3.0" exhaust


http://www.clubsi.com/ubbthreads.php.../Number/182608

People have gone 4" but for much higher HP applications as it is a pain getting it to fit under a car, is really loud, and is heavier.

[diss7]

Unreal. Those differences are massive

[Huehuecoyotl]

good thread we need this here
Dyno charts are way over rated if you ask me, I drive it daily, rain etc

Potentially an early adopter with Vortech's kit with upgraded pulley @8.5psi today maybe some more tomorrow(10?12?),

Exhaust:
I suspect any 2.5" good flowing pipe will do + optional Headers(?) ideally livable noise and low end grunt. too big pipes= loss of low end

Intakes:
Vortech, no options here, good thing right?

Fuel system:
OE to 7400, I dont need to run this thing past redline really, I feel better beating snot out of it this way, no real 'need' for e85 if I am happy @ 8.5psi-10, or 12psi per Perrins last post at 12psi sounds nutty enough, who needs more really?

Instrumentation:
want it stock inside all but a scanguage for oil temp(Sti and wrx are fine on factory oil too) Thicker oil actually can mean less power so I am not of the 10W40 camp.

Cooling:
OE fine for my goals

Brakes:
Upgraded fluid and new pads seem great so far, but this is with stock power

Traction:
R-compounds, with SC you dont have the same power surge as TC, so wheel spin shouldn't be as much of an issue with a different power curve/delivery model

no sense trying to break the bank, the car or the back wheels loose with any more power than 'needed'

[sw20kosh]

Originally Posted by Huehuecoyotl

too big pipes= loss of low end

No. See above.

What you know about exhaust size for NA do not apply to FI.

[Huehuecoyotl]

Originally Posted by sw20kosh

No. See above.

What you know about exhaust size for NA do not apply to FI.

for sure you're right, however, would like to see data that show real world gains going from 2.5" to 3" on a 10-12psi setup before putting money where it may not pay, there arent many 3" systems on market either...(yet?)

[TyperRspec789]

Mods made due to turbo:
- Vacuum Block
- Manual Boost Controller
- Boost Gauge
- Brand new set wheels/tires- RPF1 17x9 w/ 255 wide BFGoodrich G-Force KDW2
- ACT 6 puck clutch (a must)
- 4 Bar Map sensor
- Larger injectors (I'm not saying what size- I'll reveal within a week)
- Perrin plate relocator (details in "soon" section)
- Whiteline rear subframe bushings and transmission bushing

Soon:
- turbo blanket
- Grill removal mod with custom cutouts for intake
- GT86 fog light vents

Future:
- FBM large radiator
- Oil Cooler kit
- Seibon Carbon Fiber vented hood
- Undisclosed front brake upgrade
- "Open" valve mod on frontpipe or downpipe

My plans are very vague right now.. But with my eyes set on breaking the 11sec mark.. Who knows.

[mad_sb]

I think people always equate larger pipes with lower back pressure. I'm fairly sure it has been proven time and again that less back pressure is always better, FI or NA.

The issue is, going to a larger or shorter exhaust does not always reduce back pressure... What happens when gas expands... it slows down... what happens when it slows down.. pressure increases. Poor designs, rapid diameter changes that induce turbulence or stagnation, etc etc.

The best way to know your moving in the right direction is to measure back pressure at the exhaust valve before and after changes... In an ideal world the vendors would do that... sadly, not many do.

[Supermassive]

I think the real hang up as far as exhaust diameter lies in the damn override, I want to go with a 3" system but finding a kit that will mate up with my down pipe, just isn't happening at the moment. I will require a custom fabbed downtime for starters since the one on my kit is 3" v band at the turbo outlet to a 2.5" flange. Then I would need a custom over pipe, and then the last real hurdle is where the exhaust passes under the rear subframe...with the 2.5" I'm already paranoid about banging it on something...

[SnapOv3st3r]

Originally Posted by diss7

Define better. If you mean top end, then I agree. You also stated in the previous thread that a larger exhaust is better for spool, a comment I disagreed with. I went further and said that according to your stand, that no/minimal exhaust would spool the turbo the quickest. A point I still believe to be incorrect, and which was not mentioned when quoting me above.

Lets face it. If you are at the point that you are needing something bigger than 3" then you don't really care about daily driving out of boost and having less hp than stock at those rpms. You aren't even racing at that DD activity so does it even matter. Sidebar, the amount of whp that you might have lost isn't even noticeable. You aren't accelerating hard enough to even care.

Larger exhaust is better for spooling sorry. Backpressure and turbo does not belong in the same sentence. Backpressure and N/A does.