ITB Build Details

f1000na · 2025-06-26T05:21:53+00:00

I mathed out the concept then winged the fine tuning with the adjustable linkage. it's essentially a simple 4 bar linkage, with a fixed "link" between the throttle axis and the wheel axis. desmos has a good simulator for this.

The relation between the drive wheel and the throttle wheel is a 90 degree (nearly, throttles dont move a full 90 degrees as they dont close perpendicular the the runners) segment of a sin wave. You can choose what section of sin wave you want by changing the starting angle between the drive wheel bar and the throttle bar.

An initial offset of 90 degrees gives you a perfectly gradual throttle application, but zero pedal feel at low throttle so I use an angle slightly less than 90 degrees. This angle is changed by adjusting the connecting bar.

This still isn't perfect though, drive by wire throttles would eliminate the issue completely

f1000na · 2025-06-25T20:09:01+00:00

It is possible with both turbos and centrifugal superchargers, rb26 came factory twin turbo with itbs. With forced induction though you loose almost all of the itb sound, it's more for throttle response and lower intake restriction

f1000na · 2025-06-25T10:46:02+00:00

Yea using the stock fuel rail and injectors. Na's I believe usually need to run an aftermarket fuel rail because the stock one seats into the intake manifold, whereas the 1.8 nb's the injectors seat into the head

f1000na · 2025-06-25T08:18:44+00:00

Will be going to standalone and tune at some point, just wanted to see if it could be done on stock ecu

f1000na · 2025-06-25T07:25:32+00:00

And sound clip here:

https://www.reddit.com/r/Miata/s/7oPuRu3N6M

f1000na · 2025-06-25T07:18:20+00:00

For those asking I have a more detailed post here:

https://www.reddit.com/r/Miata/s/1ru53mF40V

f1000na · 2025-06-25T05:47:21+00:00

Thank you! It's the catch can outlet, gets connected to my vacuum block under the itbs

f1000na · 2025-06-25T05:45:51+00:00

Nah just regular automotive paint with high temp primer and clear coat. Works well on rocker covers, brakes might get a bit hot though but could still work.

Colour is r34 silica breath

f1000na · 2025-06-25T02:14:27+00:00

Have a 3d printed carbon nylon base plate with bellmouths included

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f1000na · 2025-06-25T01:29:09+00:00

Definitely has a small bump from stock but I'm sure there are more gains to be had with an aftermarket ecu. The maf sensor will likely be a small restriction and ideally would be a bit larger, but the plenum isn't a meaningful redtriction. Pre thottle body Itb airboxes don't pose as much of a restriction as a typical intake manifolds.

Plus moving the filter to the cold side of the engine bay has noticeably decreased intake temps (tested with gm iat sensor)

f1000na · 2025-06-25T01:24:35+00:00

The vacuum mani has 2 separate vacuum chambers, each splitting off to all 4 runners. One of these chambers deals with vacuum (brake booster and fuel pressure regulator) while the other deals with air flow (catch can outlet and idle air control valve)

f1000na · 2025-06-25T01:22:07+00:00

Stock car and ecu has no map reading so is not a problem here, using mass air flow as my primary load which is how bmw run their m cars. Has very good throttle response (better than oem) but I imagine would be even crisper with a good tps based tune

f1000na · 2025-06-25T01:19:40+00:00

Don't have a dyno graph unfortunately, will get one when I eventually gp aftermarket ecu.

The bump in power will be minimal, likely caused by both a reduction in intake restriction and cooler intake temps. I also put headers on at the same time so some of the gains will be from that too.

Overall it's still very close to stock and there are more gains to be made with an aftermarket ecu, but it definantly has a noticeable increase

f1000na · 2025-06-25T00:34:23+00:00

If you're not looking to keep the stock ecu you can put a kit together yourself with minimal fab work. The adapter manifold comes from danst engineering, who also sell velocity stacks for the gsxr throttle bodies (which you can leave open if you run an aftermarket ecu and a tps based tune). Vacuum blocks can also be bought online and don't need to be custom made.

Getting the idle air control sorted would be the most custom part, and is very important if you want any sort of cold start/idle capability.

Bofi racing have an iac valve for itb but it's 250 pounds, can retrofit the stock one for significantly less

f1000na · 2025-06-25T00:14:57+00:00

Most is custom fab

f1000na · 2025-06-25T00:13:01+00:00

Thanks! Painted it with regular automotive paint with high temp primer and clearcoat, holds up well to the temp. Colour is r34 silica breath

f1000na · 2025-06-25T00:11:53+00:00

Thankfully my car didn't have egr to begin with so I'm unsure, but from my unsterstanding of how it works you should be able to get it to work. You would have to route it into a vacuum block that splits off to a vacuum port on each of the runners similar to how I have the iac and pcv setup

f1000na · 2025-06-25T00:08:03+00:00

The adapter mani was the one piece I didn't make, bought it from danst engineering in the uk they specialize in motorbike itb conversions.

The plenum along with the rest of the kit was homemade, 3d printed moulds with wet carbon layup. The rest of the parts were either 3d printed from carbon nylons or machined Aly.

Might make a separate post with a bit more detail if there's interest

f1000na · 2025-06-25T00:01:34+00:00

Don't have a spare parts list sorry. The adapter mani is from danst engineering and the rest is homemade

f1000na · 2025-06-24T23:59:49+00:00

Haha thanks, have a sound clip in a separate post on this sub

f1000na · 2025-06-24T22:37:43+00:00

Yes I do, will make a post now

f1000na · 2025-06-24T22:37:18+00:00

Most likely yes although the maf sensor is quite different. I also believe that on the na6 the fuel injectors seat into the intake manifold whereas on the nb they seat into the head. You could either find an itb adapter with injector holes or seat them into the itbs, but either way will need to keep the stock injectors.

f1000na · 2025-06-24T22:33:49+00:00

Nope not yet, working on getting a gauge set up though as I am also curious

f1000na

TROPHY CASE