IAB switch point

s300 and SManager software questions & answers
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90TegGSR
Posts: 24
Joined: Fri Jan 10, 2020 10:19 am

IAB switch point

Post by 90TegGSR »

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I'm looking for data regarding where the IAB switch point should be set.

In the default setup for the 92-95 B18C, it's set at 5750. Is that high or should they switch lower then that. This is a mostly stock jdm '96 b18c, with all converted to obd1, and a usdm p72.

I understand it changes the length of the intake runners by using a butterfly valve, directing the intake from one set of runners to anther set of runners. One set shorter, one set longer. I'm not clear on what does what. Weather longer runners work better at high rpms or the opposite.

Is 5750 about right?
I do have K&N cold air intake tube and DC Sport 4-2-1 header. I don't think it's much different the then oem, maybe a little better air flow.
Thx
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Spunkster
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Re: IAB switch point

Post by Spunkster »

The only way you can adjust this is if you have it on the dyno and can see what different settings do for power and adjust for the best gains.

90TegGSR
Posts: 24
Joined: Fri Jan 10, 2020 10:19 am

Re: IAB switch point

Post by 90TegGSR »

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My understanding was.... the secondary runners are the for better mid-range. ....or if they change at 5750 rpms, then the lower to mid-range runners are open first, then at 5750 it switches to the higher rpm runners.

You could say that the secondary runners are for higher rpms....it's the primary runners that are open by default.

So 5750 is opening the secondary runners near the end of the mid-range.

A nomenclature issue.

90TegGSR
Posts: 24
Joined: Fri Jan 10, 2020 10:19 am

Re: IAB switch point

Post by 90TegGSR »

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... better explained:

When you start the engine, the primary runners are open. These runners are shorter and suited for low and mid-range rpms. The secondary runners which on my engine are set to open at 5750 are longer runners that are suited for higher rpms.

Yes? Is that correct?
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crluver123
Posts: 147
Joined: Tue Oct 10, 2006 10:13 pm

Re: IAB switch point

Post by crluver123 »

90TegGSR wrote:
Fri Feb 07, 2020 1:15 pm
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... better explained:

When you start the engine, the primary runners are open. These runners are shorter and suited for low and mid-range rpms. The secondary runners which on my engine are set to open at 5750 are longer runners that are suited for higher rpms.

Yes? Is that correct?
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No that is backwards. Long skinny runners are better for lower rpm, shorter fatter runners are better for higher rpm. But this is a very generalized explanation. Intake runner length is very specific with pulse tuning. specific lengths work well at specific rpms and terrible at other rpms, and also work according to first pulse, second pulse, third pulse, etc. You can research intake pulse tuning and learn a lot about it and how and why it works. Honda manifolds are manufactured to specific lengths that work at specific rpms for specific engines.

How they operate is always the same though: at lower rpm the primary runners; long thin runners, are open and the secondary runners; short fat runners, are closed. When the IAB switch point rpm is reached and exceeded, the secondary runners open and the primary runners also remain open.

90TegGSR
Posts: 24
Joined: Fri Jan 10, 2020 10:19 am

Re: IAB switch point

Post by 90TegGSR »

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Thanks for very specific data. Pulses? I'll see if I can search that .
My jdm b18c is running very well with the default map, but I want understand how this engine works. The installation took me most of the winter, but went well....no heat in my garage.
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