The Ultimate FA20 ITB thread.

[Dr. BRZ]

Originally Posted by new2subaru

Ever thought about a build thread?

I don't have patience for it lol. I only check the forum every few times. I can list my mods.
All tomei el headers and exhaust system. 2lb battery, inlet tube, throttle body spacer, kn air filter, pullies, lw flywheel, snorkel, aluminum driveshaft, irp shifter, and gutted interior.

[sato]

I don't know much about ITB IRL, but from what I can guess, you are essentially shortening the path of air to the engine substantially and thereby being able to feed the engine more air at high RPM (at the expense of maybe losing torque down low). Longer intake tracts usually benefit torque (search for the Crawford Power Blocks for a better idea) at the expense of higher RPM power.

Originally Posted by Captain Snooze

@CSG Mike and all.

Noob question time. Ready?
If the inlet diameter and length are the same how do itb generate more power? I get responsiveness, not the power increase.

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[Roadcone]

Originally Posted by Captain Snooze

@CSG Mike and all.

Noob question time. Ready?
If the inlet diameter and length are the same how do itb generate more power? I get responsiveness, not the power increase.

Resonance frequencies can cause funky thinks to happen.

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[Lowe1978]

Checking in from over the pond. This has seriously piqued my interest, the Greddy kit in particular. I already have an Ecutek licence and there's a Ecutek tuner about 45 mins from me... ITBs is about the only thing I've never done to a car, I'm not chasing numbers, just looking for a nice noise and to tick a box on the bucket list. Any performance increase is a bonus as far as I'm concerned.

That said, I'm a realist. I don't really know much about ITBs or how this might effect the general usage of the car. More air means more fuel so mileage is going to take a hit yes. But what about sticky throttle in cold weather? Heard that can be an issue if there isn't coolant running around the TBs and you live somewhere that gets near freezing temps. My car is a daily and in the UK we do get some interesting weather/seasons but nothing to the extremes that you might see in say, Canada. So something to be wary of or am I overthinking it?

Anyhoo I'll be keeping a close eye on this thread, hope to see some numbers and some more info soon.

[mrha]

Originally Posted by Lantanafrs2

Itbs are nice but cosworth has a few sc kits left for 5 grand that will give you actual gains. Maybe get a t-shirt and coffee cup too lol

Which site sells them for 5k?

[86TOYO2k17]

Curious myself as to how ITBs would increase any torque/hp. I can see if runner lengths where shorter shifting power higher for higher peak number but,
From my understanding stock manifold and throttle body are both more then high enough flowing that increasing diameter on either has no benefit, as well as the runner length seems to already be optimized for top end power so much so that some people opt to use manifold spacers effectively increasing runner length to slightly shift peak power down.

So unless you are building the head with cams, valves, and springs to rev to 8k+ and maybe getting an ace 150header for a high revving NA beast. Not sure decreasing intake runner length would have any positive effect.

Seems like you are essentially paying 2,000$ + tuning costs for slightly quicker throttle response and the sound associated from ITBs.

But I would love to be proven wrong. If this shows a solid 10whp increase from at least 4500-7500rpm then I am sold. Just don’t see how it’s possible.

[Lantanafrs2]

Originally Posted by mrha

Which site sells them for 5k?

Directly through cosworth

[RayRay88]

Originally Posted by 86TOYO2k17

Curious myself as to how ITBs would increase any torque/hp. I can see if runner lengths where shorter shifting power higher for higher peak number but,
From my understanding stock manifold and throttle body are both more then high enough flowing that increasing diameter on either has no benefit, as well as the runner length seems to already be optimized for top end power so much so that some people opt to use manifold spacers effectively increasing runner length to slightly shift peak power down.

So unless you are building the head with cams, valves, and springs to rev to 8k+ and maybe getting an ace 150header for a high revving NA beast. Not sure decreasing intake runner length would have any positive effect.

Seems like you are essentially paying 2,000$ + tuning costs for slightly quicker throttle response and the sound associated from ITBs.

But I would love to be proven wrong. If this shows a solid 10whp increase from at least 4500-7500rpm then I am sold. Just don’t see how it’s possible.

Benefits would probably include throttle response and more mid range torque.


Most of these systems will be used with some sort of manifold so any runner length tuning effects would probably be minimized.


If this gives a flatter torque curve with peaks of 180ftlbs or close it would definitely, IMO, be worth it.


I would love to see if there are any HP gains to be had with Cams and these ITB's.

[86TOYO2k17]

Originally Posted by RayRay88

Benefits would probably include throttle response and more mid range torque.


Most of these systems will be used with some sort of manifold so any runner length tuning effects would probably be minimized.


If this gives a flatter torque curve with peaks of 180ftlbs or close it would definitely, IMO, be worth it.


I would love to see if there are any HP gains to be had with Cams and these ITB's.

How would this give more mid range? Unless the runner lengths where much longer and then sacrificed top end power essentially similar to intake manifold spacers.

I just don’t see or maybe I don’t understand the theory behind why it would make anymore power anywhere, unless like I mentioned the runner lengths where longer for lower rpm power or shorter for top end power.

The stock manifold and throttle body have already been proven to flow more then enough air.

Seems rather expensive for slightly better throttle response and the ITB sound.

But again please prove me wrong so I have something to throw my money away on!

[Roadcone]

Originally Posted by 86TOYO2k17

How would this give more mid range? Unless the runner lengths where much longer and then sacrificed top end power essentially similar to intake manifold spacers.

I just don’t see or maybe I don’t understand the theory behind why it would make anymore power anywhere, unless like I mentioned the runner lengths where longer for lower rpm power or shorter for top end power.

The stock manifold and throttle body have already been proven to flow more then enough air.

Seems rather expensive for slightly better throttle response and the ITB sound.

But again please prove me wrong so I have something to throw my money away on!

Look at what itbs do on most other engines. On LS engines it gets rid of a weird 3500ishrpm torque dip on big cam engines. I think the little common plenum will negate the benefits but once they out trumpets on it you'll see gains.

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[86TOYO2k17]

Originally Posted by Roadcone

Look at what itbs do on most other engines. On LS engines it gets rid of a weird 3500ishrpm torque dip on big cam engines. I think the little common plenum will negate the benefits but once they out trumpets on it you'll see gains.

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Other platforms are not this platform. What works for one might not work for another.

Seems like on the other applications of ITBs on other platforms they saw gains because the stock manifold and or throttle body did not flow sufficient enough (ours already does)

or they are running with trumpets or very short runners, which again seems like it is just changing to shorter runners for shifting the power band up.

I’m just trying to see and understand the theory or physics behind why going from one throttle body (already bigger then needed) to four individual TBs would inherently in and of itself even when “tuned properly” would give any benefit other then sound and maybe initial throttle response.

[Roadcone]

Originally Posted by 86TOYO2k17

Other platforms are not this platform. What works for one might not work for another.

Seems like on the other applications of ITBs on other platforms they saw gains because the stock manifold and or throttle body did not flow sufficient enough (ours already does)

or they are running with trumpets or very short runners, which again seems like it is just changing to shorter runners for shifting the power band up.

I’m just trying to see and understand the theory or physics behind why going from one throttle body (already bigger then needed) to four individual TBs would inherently in and of itself even when “tuned properly” would give any benefit other then sound and maybe initial throttle response.

And with that said the oem intake manifold usually shows the best mid-range. Itbs usually make more midrange than oem. It's all speculation right now until they release Dyno sheets. It might lose 40hp and gain 150tq it also might do nothing lol

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[RayRay88]

Originally Posted by 86TOYO2k17

How would this give more mid range? Unless the runner lengths where much longer and then sacrificed top end power essentially similar to intake manifold spacers.

I just don’t see or maybe I don’t understand the theory behind why it would make anymore power anywhere, unless like I mentioned the runner lengths where longer for lower rpm power or shorter for top end power.

The stock manifold and throttle body have already been proven to flow more then enough air.

Seems rather expensive for slightly better throttle response and the ITB sound.

But again please prove me wrong so I have something to throw my money away on!

Intake velocity and more efficient air flow distribution between cylinders comes to mind.



Stock manifolds/Single Throttle body is still prone to mal-distribution and reversion.

[CSG Mike]

Originally Posted by Captain Snooze

@CSG Mike and all.

Noob question time. Ready?
If the inlet diameter and length are the same how do itb generate more power? I get responsiveness, not the power increase.

It functions as a velocity stack, and offers less restriction done properly.

The OEM TB and accessories are not choke points for this car, at all.

For example, compare our OEM TB to a S2000 TB; the S2000 is way, WAY smaller.