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As said on http://www.hondata.com/ecus.html

"The IAB or secondary intake runner is a set of butterflies in the intake manifold of B18C and H22A engines. The P72 ECU controls the IAB, but other ECUs do not. If IAB control is lost by swapping ECUs then the engine will always run on the shorter intake runners, typically losing 8 hp from 3,000 to 5,500 rpm."

If I have a gsr intake manifold, and a p28 computer, which is according to hondata not compatible with these IAB runners, will I lose the runners, or will they be functioning all the time?
A little further down on that same page on hondata.com, it says "Secondary intake runner operation will be lost if a P72 ECU is not used." Does that mean lost for good, or the fact that they open later is lost, and they are always "on" like the regular runners? I am quite concerned because I purchased a brand new p28 computer because i was recommended to, but do not want to lose the IAB system, or worse, the runners period. That seems like it would be a great power loss if those runners were just "shut down" and never opened. Thanks for your time.
-Matt
 

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What are you looking to do anyways to ask the question. Is it just out of curiousity?

P28 is a cheap ECU and it can control VTEC. Most people usually go with the Skunk2 route and ditch the GSR IM. So that is why the P28 is a good cheap choice for re-programming.
 

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If you want to go with Hondata and keep your dual-stage intake manifold, you need an OBD1 p72 ECU.

If you read our All About VTEC Article, you'll better understand the purpose of the dual-stage intake manifold.

Sak's right...most tuners ditch the 2-stage IMs in favor of a Skunk2 (ITR design) or JG Edlebrock.

But there's no two ways around it. IF you want to keep your 2 stage IM, you're going to have to have an OBD1 P72 ECU.
 

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Just connect the dots together to get the answer.

What do you know about the GSR IM and IAB?
Will you be using the GSR head?
Will you be using the GSR IM?
Will you need the P72 ECU?
 

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dohclsvtec on Mar/15/04 said:
Ok, so there is not major power loss, because the runners are always OPEN, not closed am i correct?
Matt,

long, small diameter runners or tubes have their peak torque occur (from the ram air effect or "resonance effect") at LOW to MID rpms.

short big diameter runners or tubes have their peak torque occur (from the "resonance effect") at HIGH rpms.

it's the old "know your specs" story and the "powerband location" thing all over again but this time it's dealing with the IM.


Normally the GSR IM works by having only the long narrow runners open at low to mid rpms for good low end torque and then after the air flow has built up enough with the revs, the short big diameter runners open along with the long runners for high end torque.: like the VTEC cams, the GSR IM has 2 powerbands instead of only 1. This gives it a wider overall powerband.


The problem with leaving the secondaries open all the time along with the long narrow runners is the fact you lose the benefit of the effects from the long runners: you lose low to mid rpm torque. You can gain some of it back with good fuel tuning but not all of it.

if you want to understand some of the basics about a 2 stage GSR "isolated runners" IM vs. a single stage "isolated runners" IM, then register here and read my IM Tech Article.
 

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There is a way to control the secondaries with a P28. I can't remember exactly how but the nitrious feature can be wired in to control the secondaries. You'd have to talk to your hodata installer/tuner as I don't believe this is a well known fact.
 
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