Official ITB Reference Thread

[Professor X]

The issue to me with the roof scoop is that in order to draw filtered air, you need a snorkel stack/filterbox that mates to the snorkel. That will block up most of your rear view window. Not a huge issue in racing (Fangio: "what is behind me on the circuit is of no concern"), but it would be annoying on the street.

Youre right, having a black snorkel could be an inconvenience for street use. Im thinking about molding an exact replica in Polycarbonate Lexan material of the snorkel/scoop posted above where it's all clear so the driver can have much better visibility opposed to the black snorkel,. Now I need to find that exact snorkel from the picture above.

 

[MrenvyEG9]

Loving the look of those carbon boxes gentlemen they are the business. After getting locked our of my old account I'm back to update where I left off with my itb setup. My civic with the nsx heart consists of
c23b block, rods and crank
Toda 3.2 pistons
balanced and checked.
ATI damper
3.0l heads, standard valves with nsx-r valve springs,seats and retainers and a regrind on the cam shafts
my itbs are Toyota 48mm and I haven't managed to make trumpets yet so good gains still to be had.
We finished run in on the dyno after doing all of the low cam tuning before we pushed it and lost 8kw at 5000rpm with the oil change at that point and have yet to change oils again but will wait until I have made some trumpets to test at the same time. Just over 251kw at the wheels and 325nm. 336hp with plenty left to improve was a nice result

 

[scammy]

wicked set up

 

[JLCoolman]

No worries lol. My thought is that BMW used factory ITBs on the M5 that were integrated into a nice box that attached to a factory filter box. I want to do the same thing for the NSX- open up the hatch and it should look like Honda put it there. If there was a way to mold the ITB airbox from black ABS plastic, I'd do that, since that is how the OEMs do it. The issue to me with the roof scoop is that in order to draw filtered air, you need a snorkel stack/filterbox that mates to the snorkel. That will block up most of your rear view window. Not a huge issue in racing (Fangio: "what is behind me on the circuit is of no concern"), but it would be annoying on the street.

I know what you were intending Paul. And this goes for BBVNSX below as well, what about a nice RB26DETT OEM look with a turbocharged and ITB airbox setup instead then? Anybody heard of the old TonyTheTiger turbocharged/ITB'd GSR integra?
And I totally agree, I wish it was easier to make black ABS plastic OEM-like parts. (i.e. the original OEM front lip, lol)

^^ +1 FI is not for me, as i want to stay NA, but nice reliable and "OEM look" ITB setup would be great! especially if we could keep it all bellow the NSX-R OEM engine cover :wink:

Keeping it all below the NSX-R OEM engine cover is a big, big ask. And if possible, would not be very efficient and/or performance-oriented, I think.

Youre right, having a black snorkel could be an inconvenience for street use. Im thinking about molding an exact replica in Polycarbonate Lexan material of the snorkel/scoop posted above where it's all clear so the driver can have much better visibility opposed to the black snorkel,. Now I need to find that exact snorkel from the picture above.

Which brings us to this. My thoughts exactly, Professor X took the words out of my mouth. A clear/see-through low-profile functional hatch scoop.
Get it done and then let me know Professor X!

Loving the look of those carbon boxes gentlemen they are the business. After getting locked our of my old account I'm back to update where I left off with my itb setup. My civic with the nsx heart consists of
c23b block, rods and crank
Toda 3.2 pistons
balanced and checked.
ATI damper
3.0l heads, standard valves with nsx-r valve springs,seats and retainers and a regrind on the cam shafts
my itbs are Toyota 48mm and I haven't managed to make trumpets yet so good gains still to be had.
We finished run in on the dyno after doing all of the low cam tuning before we pushed it and lost 8kw at 5000rpm with the oil change at that point and have yet to change oils again but will wait until I have made some trumpets to test at the same time. Just over 251kw at the wheels and 325nm. 336hp with plenty left to improve was a nice result
View attachment 155455
View attachment 155456
View attachment 155457

You are my hero.
What is your drivetrain setup?
Are you going to post up some drifting videos? (I'm being dead serious.)

 

[MrenvyEG9]

Haha not just yet until I have it all road legal over here as that’s been the main goal. A s2000 6 speed gearbox mated to a nissan r200 skyline/Silvia rear end. Bigger itr hubs up front and s14 rears. Makes things fun

 

[BBVNSX]

Keeping it all below the NSX-R OEM engine cover is a big, big ask. And if possible, would not be very efficient and/or performance-oriented, I think.

You are probably right... but from some pictures of ITB’s setup it kind of looks possible...

 

[Honcho]

You are probably right... but from some pictures of ITB’s setup it kind of looks possible...

Definitely possible. Just comes down to smart box design. I like KSP's take the most.

 

[Professor X]

I have some pics of itbs under the stock engine cover.... will try to post them when i look through my nsx folder pics

 

[BBVNSX]

Definitely possible. Just comes down to smart box design. I like KSP's take the most.

Wasn't aware that KSP also had ITB setup / Box... do you have pics/link of it? Thanks!

I have some pics of itbs under the stock engine cover.... will try to post them when i look through my nsx folder pics

That would be nice! Thanks!

 

[Honcho]

Wasn't aware that KSP also had ITB setup / Box... do you have pics/link of it? Thanks!

See post # 128. Last pic.

 

[BBVNSX]

See post # 128. Last pic.

Thanks! Looks clean and simple, something like that with a cover with shape inspired by the OEM Intake cover and allowing the use of OEM Intake Manifold Cover Plate would be perfect in my book! all this connected to the factory airbox and filter and fitted below the NSX-R engine cover :biggrin:

 

[SR-71]

Loving the look of those carbon boxes gentlemen they are the business. After getting locked our of my old account I'm back to update where I left off with my itb setup. My civic with the nsx heart consists of
c23b block, rods and crank
Toda 3.2 pistons
balanced and checked.
ATI damper
3.0l heads, standard valves with nsx-r valve springs,seats and retainers and a regrind on the cam shafts
my itbs are Toyota 48mm and I haven't managed to make trumpets yet so good gains still to be had.
We finished run in on the dyno after doing all of the low cam tuning before we pushed it and lost 8kw at 5000rpm with the oil change at that point and have yet to change oils again but will wait until I have made some trumpets to test at the same time. Just over 251kw at the wheels and 325nm. 336hp with plenty left to improve was a nice result
View attachment 155455
View attachment 155456
View attachment 155457

Amazing
What compression ratio did you go with and what's the lift and duration of the reground cams?

 

[MrenvyEG9]

About 10.9/1 compression so not a large jump, and cams were based off toda spec 2 b series cams from the information I have but the paperwork I have for them makes no sense to non camshaft informed people like myself. About 1mm more life on vtec and a little less off. All lobes were modified

 

[Mac Attack]

That's really cool MrEnvy!

 

[SR-71]

About 10.9/1 compression so not a large jump, and cams were based off toda spec 2 b series cams from the information I have but the paperwork I have for them makes no sense to non camshaft informed people like myself. About 1mm more life on vtec and a little less off. All lobes were modified

Nice. Do you know how they treated the cams after regrind them? Oil or electronic? Who did you use?

 

[RYU]

Prime is filled with a bunch of smart folks.. does anyone here know how to calculate the optimal volume for an intake plenum for an ITB setup? I feel like the KSP one looks good but it feels a bit small.

Any thoughts from our resident rocket scientist? ahem [MENTION=12356]Mac Attack[/MENTION]

 

[Mac Attack]

Prime is filled with a bunch of smart folks.. does anyone here know how to calculate the optimal volume for an intake plenum for an ITB setup? I feel like the KSP one looks good but it feels a bit small.

Any thoughts from our resident rocket scientist? ahem [MENTION=12356]Mac Attack[/MENTION]

Let's put it this way... I was jealous of my rocket scientist college roommate that could party almost every night while I was suffering through nuclear magnetic inertial confinement fusion problems!

I haven't done any research on it since it never applied to me, but my understanding is that the ITB runners/trumpet length and diameter take care of the primary induction resonant and inertial tuning. A box around them should therefore have little effect, other than to possibly screw up the pressure distribution with a poor design (see below).

The only two reasons I would use an intake plenum on a vehicle equipped with ITB's is to duct cool air to the intakes, or to use an air filter. Perhaps another benefit would be some kind of MAP-based tuning instead of solely relying on TPS-based tuning, but it seems like people with TPS-based tuning only are OK with it.

Cool Air:
Unless you have a sealed underbody, the engine bay air turnover rate is pretty high in the NSX at any speed over 30 MPH (according to my temperature measurements), so really the primary reason to run an airbox on most ITB'd NSX's is to use an air filter.

Air Filtration:
Unless you live in an environment with a lot of airborne silica, I would just run a mesh screen on top of each trumpet and change the oil more often. Seems like a lot of people using ITBs on the street do just that (not just NSX owners). If you only put a couple thousand miles on the engine in a year it will probably last a long time.

The internet myth is that the airbox volume should be between ~1 to 2 times the engine displacement. Actually, an infinite volume is best until you run into size and weight issues. The NSX rear strut bar creates a problem if you want a semi-balanced box that doesn't put a box wall right up next to a trumpet, or spill over to one side of the engine and look ugly.

Certainly, the largest airbox size would come courtesy of Honda. From internet pictures, it looks like Honda could have certainly gone with a bigger airbox on the longitudinal GT500 C32-based N/A engine, but chose not to. You can roughly scale GT500 internet pictures to get an idea of the max. volume.

Back to air pressure distributions inside the box, consider what Mugen did for their GT300 restricted engine... It would be interesting to see if there are any flow dividers underneath the airbox cover here. Personally, I like to see out the back of my NSX when driving and would not be able to stand a snorkel blocking that view, but, this is purely a racecar:
View attachment 157076View attachment 157078

My $0.02.

 

[RYU]

Always good info @Mac Attack. Thanks for being so generous with your knowledge!

My primary purpose for the airbox would be for metering the airflow properly for the ECU tune. I feel like the most accurate way would be thru a MAF sensor first, or a MAP. I also want an airbox for *some* sound suppression (I know i'm crazy right?). I've listened to a few and they're just simply too loud for me in the open trumpet format.

I believe for a stock motor the MAF looses accuracy if placed in an intake tube larger than about 3" - 3.5" but I don't know this for sure. I can only observe from other MFGs who've implemented ITBs. My tuner and I are up for the challenge of tuning an ITB setup because, you know me... if it doesn't drive perfectly on the street, i'm just not interested. I feel like the vacuum tree solution that SOS/Hayward uses with the MAP sensor just isn't robust enough. I don't blame SOS for not selling it anymore. I could never do only Alpha N/TPS tuning for the kind of driving I do. At a min I need a MAF or a MAP solution. We are considering implementing multiple maps that rely on a Alpha N *with* MAF/MAP correction. I believe my HKS computer can take a few different inputs simultaneously. I suppose correction via O2 wideband is also possible. Lastly, air filter is optional but desired. I don't mind the slight loss of power here as long as the loss is not egregious.

BTW... a big ass box blocking my rear view would drive me insane too. Also, thanks for mentioning that very important point about resonance but particularly how it's not a concern when designing an air box. That's definitely above the classes I took in college

So now.. if I was to go ITBs these would be my open questions.
1. How to best design an intake plenum pre-ITBs? i.e. optimal volume and what type of air entry orifice.
2. Use a MAF or MAP
3. Where to mount an air filter? Cone element or flat element? Use the OEM air filter box perhaps?

 

[docjohn]

any issues with airflow can be fixed with strategic location of Mugen stickers....

 

[RYU]

any issues with airflow can be fixed with strategic location of Mugen stickers....

That's plan B.

 

[Mac Attack]

Always good info @Mac Attack. Thanks for being so generous with your knowledge!

My primary purpose for the airbox would be for metering the airflow properly for the ECU tune. I feel like the most accurate way would be thru a MAF sensor first, or a MAP. I also want an airbox for *some* sound suppression (I know i'm crazy right?). I've listened to a few and they're just simply too loud for me in the open trumpet format.

I believe for a stock motor the MAF looses accuracy if placed in an intake tube larger than about 3" - 3.5" but I don't know this for sure. I can only observe from other MFGs who've implemented ITBs. My tuner and I are up for the challenge of tuning an ITB setup because, you know me... if it doesn't drive perfectly on the street, i'm just not interested. I feel like the vacuum tree solution that SOS/Hayward uses with the MAP sensor just isn't robust enough. I don't blame SOS for not selling it anymore. I could never do only Alpha N/TPS tuning for the kind of driving I do. At a min I need a MAF or a MAP solution. We are considering implementing multiple maps that rely on a Alpha N *with* MAF/MAP correction. I believe my HKS computer can take a few different inputs simultaneously. I suppose correction via O2 wideband is also possible. Lastly, air filter is optional but desired. I don't mind the slight loss of power here as long as the loss is not egregious.

BTW... a big ass box blocking my rear view would drive me insane too. Also, thanks for mentioning that very important point about resonance but particularly how it's not a concern when designing an air box. That's definitely above the classes I took in college

So now.. if I was to go ITBs these would be my open questions.
1. How to best design an intake plenum pre-ITBs? i.e. optimal volume and what type of air entry orifice.
2. Use a MAF or MAP
3. Where to mount an air filter? Cone element or flat element? Use the OEM air filter box perhaps?

Thanks, but I don't know how good of info it is as I don't have any direct experience with this.

In regards to your questions:

1) The best design will be a balance of what kind of filters (and where) you're going to place them, and also what kind of air inlet and where you're going to place that. That's the whole inlet pressure distribution concern. We also have to work with that rear strut bar, which is most likely too close to the rear cylinder trumpets to make a nice box around and not impact those negatively.

2) I don't know why you'd want to do a MAF instead of a MAP. The alpha-N tune is fine for anything other than idle, just off idle, or cruise. I think the big sport bikes use MAP up to around 20% throttle opening and then swap to alpha-N. I wouldn't want to deal with the hassle of a MAF or multiple MAFs. A MAP is smaller, lighter, and cheaper, as long as you keep the OEM low-speed cams that pull decent vacuum.

3) ? That will have to be designed around your first question.

 

[RYU]

Thanks, but I don't know how good of info it is as I don't have any direct experience with this.

In regards to your questions:

1) The best design will be a balance of what kind of filters (and where) you're going to place them, and also what kind of air inlet and where you're going to place that. That's the whole inlet pressure distribution concern. We also have to work with that rear strut bar, which is most likely too close to the rear cylinder trumpets to make a nice box around and not impact those negatively.

2) I don't know why you'd want to do a MAF instead of a MAP. The alpha-N tune is fine for anything other than idle, just off idle, or cruise. I think the big sport bikes use MAP up to around 20% throttle opening and then swap to alpha-N. I wouldn't want to deal with the hassle of a MAF or multiple MAFs. A MAP is smaller, lighter, and cheaper, as long as you keep the OEM low-speed cams that pull decent vacuum.

3) ? That will have to be designed around your first question.

re: #2 - I experience a decent amount of barometric pressure changes. TPS simply wouldn't be able to compensate especially with finicky ITBs. Again, I have no experience here. It's just what my small brain is leading me to believe. Also, regarding MAP vs. MAF, to install a MAP i'd have to do it either before the butterflies (inside the airbox plenum) or after the butterflies which will require a bunch of hoses and a vacuum tree of some kind. I might have a solution for the after-butterfly scenario which I can share with you privately. People will just think i'm crazy here haha. In terms of the MAP inside a big open plenum like i'm imagining, it seems the vacuum signal will be diluted by the volume of the plenum to be of any accuracy. Actually, I think that's also the problem with the MAP sensor on the SOS vacuum tree.. it might not have enough volume for accuracy - this part obviously is just me pondering. I wish I had a setup here to test this kind of stuff...

btw.. my preference for a MAF is influenced by the current BMW M ITB setups. They primarly use a MAF before the butterflies but after the air filter. I don't believe they use a MAP anywhere.

 

[Old Guy]

Also, regarding MAP vs. MAF, to install a MAP i'd have to do it either before the butterflies (inside the airbox plenum) or after the butterflies which will require a bunch of hoses and a vacuum tree of some kind. I might have a solution for the after-butterfly scenario which I can share with you privately. People will just think i'm crazy here haha. In terms of the MAP inside a big open plenum like i'm imagining, it seems the vacuum signal will be diluted by the volume of the plenum to be of any accuracy.

So, you are still talking about ITBs? If so, I think the presumption is, as Mac Attack alludes to, that in an ideal world the ITB intake bell would be in 'free undisturbed air'. Aside from the air filtration and ducting of non heated air into the engine, the only other purpose of the air box might be to 'still' the air to help insure uniform pressure across all the inlets. Ideally, the pressure inside the airbox would be as close to atmospheric as possible because any reduction in pressure in the air box reduces your potential maximum horsepower. Its then axiomatic that if the airbox is ideal there should be no pressure change in the airbox and no signal for a speed x density control algorithm. You could use a MAF on the inlet to the air box to meter air mass flow; however, a MAF does introduce a pressure drop. At some point, in terms of peak flow I would start to miss the difference between a 2.5" diameter MAF on the inlet to an air box versus a 2.5" diameter throttle body with a suitably thin throttle plate at 90 deg wide open throttle on a similar intake plenum.

I have seen arrangements similar to the SOS adapter for use with a pressure sensor on ITBs for a speed x density algorithm. I think the pressure signal is accurate in that the signal accurately represents the current pressure at the time the ECU grabs the signal. I think the greater issue is the fluctuation in the signal as the piston goes through its stroke. A MAP sensor attached to a common intake manifold gets a time averaged signal because of the inherent storage in the intake plenum. It might not be 'instantaneously accurate'; but, it is usable signal representing the average operating condition of the engine at a particular operating point. By mixing individual cylinder signals, SOS style adapters attempt to provide a proxy for the averaging generated by an intake plenum. I have no direct experience so I can't comment on how successful or unsuccessful this might be. A different approach that I have seen discussed is to time the acquisition of the pressure signal to crank position (rather than letting the signal be grabbed by whatever loop the fuel algorithm is running in). This gives you a consistent pressure signal that can be used to represent the engines current operating condition. I think the signal was pulled from a single port on one cylinder and that the presumption is made that the rest of the cylinders have matching Ve values. Of course, with O2 sensors or EGT probes on each cylinder and firmware that allows you to set individual fuel trims for each cylinder you can correct differences between each cylinder. Of course, doing a tune starts to look like doing a tune X 6!

Your comment about the dilution of a MAP signal is relevant for MAP sensors attached to an intake manifold (plenum). The issue is not dilution; but, rather transient response. Because of the 'stored air' in the plenum, the larger the volume of the intake manifold, the longer it takes for the pressure in the manifold to arrive at a new steady state value following a change in the throttle body opening. I think that is the basis for the internet rule of thumb about the volume of the intake manifold being 1.5 - 2 times the engine volume for good transient response.

Finally, in post #168 you wrote " I suppose correction via O2 wideband is also possible." If you were serious about the idea of relying on some kind of closed loop fuel control system I advise against this. My personal take is that you should get the fuel tables set such that you are hitting your target AFRs with the smallest possible EGO correction possible. The engine should be able to run just fine without O2 sensors. I like to try and get my fuel table settings to the point that I have less than 2% correction and I run open loop above a MAP of 75 kPa. In my limited experience, wide band O2 sensors do not have the durability where I would want to count on them for closed loop control at wide open throttle. I might try that on a race engine where I treated the sensors like spark plugs and chucked them after every race; but, not on a car that is closer to a daily driver.

 

[austrian type-R]

I ask for a membership in the ITB club, please!

My setup incl airbox!

 

[RYU]

You can't just drop the bomb and not share details!!!

Engine mgmt? Who makes this? Who built the box? C'mon man... don't do this to me hahaha

I ask for a membership in the ITB club, please!

My setup incl airbox!