If I upgrade to the EX head on my HX civic, will I need to change the ecu to the ex as well. As the HX stands right now the E-Vtec kicks in at about 3100 rpm's while the ex kicks in at 5700 I think. Does the ecu control this or will I need to pick one up?

yeah, go with the ex ecu. i think you will also need an adjustable cam gear to get it timed right.

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Yes, there's a "Replacement for Displacement". Its called Volumetric Efficiency.

My questions is do the HX's have VTEC or no cause i am told from some people that they do and from other people that they dont

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When you pull up to a Domestic you lean out the window a say "You wanna VTEC"

The HX is a VTEC but it's different from the ex. from 0-3100 rpms it only runs off of 12 valves, once it hits 3100 the vtec kicks in and it runs on all valves, this makes for a vehicle that has extremely good gas mileage in low rpm's (I've gotten 41 mpg before!!!) and a descent amount of power in the high rpm's. It's 15 less hp than the ex but still more than the dx, lx, or cx. Everyone likes to say that they are crap, however with mine I can take my girlfriend's 2003 ex in the higher rpms no problem. She has a cold air intake and mild exhaust. My hx has a cold air intake, Race headers, 2 1/4" full exhaust, NO catalytic converter and a straight through muffler (all smog illegal), and a msd ignition. In the higher rpms (on the freeway) I keep up if not beat integra's and si's (though I'm sure it's more driving capability than not, but still not bad for an hx) The worst part about the hx is the tranny, it's geared very high so my take-off's can't match the ex's.
Oh, and I just bought a ex head and intake manifold which I'm having a valve job on, milled and possibly ported. I'm also looking for a ex tranny

Oh ok, h9ow r the take-offs on your HX are they sluggish or descent?

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When you pull up to a Domestic you lean out the window a say "You wanna VTEC"

So the VTEC kicks in at 3100 and stays until the redline?

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When you pull up to a Domestic you lean out the window a say "You wanna VTEC"

One more thing are all HX's VTEC or just certain ones?

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When you pull up to a Domestic you lean out the window a say "You wanna VTEC"

Ok, all HX's are Vtec's, and once they hit 3100 ALL VALVES OPEN, and it runs like any other SOHC. The ex/si VTEC is different in that all valves all aready open, and the vtec gives that extra boost, but I'm not exactly sure what all the details are. Also the take-offs in my HX are sluggish especially compared to the ex. (That's why I'm looking for the ex/si tranny) They've gotten alot better with all the mods I've put on, but I just have to rev it real high to get a descent take-off

Uh, yeah. Never mind. Eyes play tricks on you when you read posts at 1 am or so.

hey c25, read the original REEEEAAALL slow.

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Yes, there's a "Replacement for Displacement". Its called Volumetric Efficiency.