hey all

i just recently dropped a 97 j-spec ITR motor into my car. as you all probably know - the accompanying S80 transmission has a speed-sensing gear that sends an electric signal to the dash for the speedo. however, my 90 si civic is equipped with a mechanical speedo cable.

so - this is my question. I have heard that VTEC doesnt engage in neutral, nor does it engage before the car reaches 12 mph. it sounds like VTEC is engaging, but im not really sure if it is. I hear DOHC VTEC engines all the time, and mine sounds identical. -- it just seems like there isn't much of a power increase when the audible switchover occurs. i just dont know HOW it could be engaging since the ECU has no way of knowing how fast the car is going.

but on the other hand - the guy from Locash racing (who supplied us with the wiring harness stuff) - said that some JDM engines dont rely on speed sensor data for VTEC.

so - cliffs notes - is VTEC really engaging?? aaand: if not, what do i need to do to successfully interface the tranny speedo gear and the speedometer gauge in the dash.
any help would be appreciated. thanks
-SM

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by streetmodified &raquo;</TD></TR><TR><TD CLASS="quote">I have heard that VTEC doesnt engage in neutral, nor does it engage before the car reaches 12 mph. it sounds like VTEC is engaging, but im not really sure if it is.</TD></TR></TABLE>
It isn't.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">I hear DOHC VTEC engines all the time, and mine sounds identical. -- it just seems like there isn't much of a power increase when the audible switchover occurs.</TD></TR></TABLE>
That's because there isn't supposed to be a noticeable power increase. If there is, then something is wrong. The torque curve should feel like one continuous, constant pull from idle to redline.

If you're hearing an audible changeover, then VTEC is engaging.

 

wait - you say it isnt, then you say it is.

final answer?

i am definitely hearing a switchover. i just dont know how it could be without the ECU knowing the engine speed.

or is it true that jdm engines dont use the speed sensor for vtec engagement?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by streetmodified &raquo;</TD></TR><TR><TD CLASS="quote">wait - you say it isnt, then you say it is.

final answer?
</TD></TR></TABLE>

I believe he meant it isn't activating (at idle) and it is (when moving). I wouldn't use sound as a means of telling when VTEC is activating or not. But I've read that one way to tell if VTEC is engaging is if you have a oil pressure gauge hooked up. If you have one, then at VTEC x-over your oil pressure will drop when you hit the X-over.

But AFAIK, VTEC only engages if the correct coolant temp, oil pressure, RPM, peed, and throttle position.

 

Does it rev all the way to redline? If so vtec is xing over.

Ryan

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by droppedcrxsi &raquo;</TD></TR><TR><TD CLASS="quote">Does it rev all the way to redline? If so vtec is xing over.

Ryan</TD></TR></TABLE>

not true. even if vtec wasn't kicking in it would still go to redline.

if you hear a change in the exhaust note/engine intake what ever then its kicking in.

you'll have to wait for some other users to plug in about your actual question.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by droppedcrxsi &raquo;</TD></TR><TR><TD CLASS="quote">Does it rev all the way to redline? If so vtec is xing over.

Ryan</TD></TR></TABLE>


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by manson &raquo;</TD></TR><TR><TD CLASS="quote">

not true. even if vtec wasn't kicking in it would still go to redline.

if you hear a change in the exhaust note/engine intake what ever then its kicking in.

you'll have to wait for some other users to plug in about your actual question.</TD></TR></TABLE>

Actually, if VTEC doesn't enguage, it will have a lower revlimit. You can see this when you actually see the way honda sets up its fuel and timing maps. In the "low" cam tables the rev-limit is lower than the "high" cam profile.

As far as needing a speed signal for the JDM ecus... I have a OBD-1 P72 on my can and it will not go into vtec with out a speed signal.

Your stock guage cluster can send a electric signal to your ecu while using a mechanical speed sending unit.

 

what ecu are you using??

 

interesting... im sure its not very far off from the vtec lobe...

in any case i'll look into that... interesting stuff.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TrueNorthStar &raquo;</TD></TR><TR><TD CLASS="quote">Actually, if VTEC doesn't engauge, it will have a lower revlimit. You can see this when you actually see the way honda sets up its fuel and timing maps. In the "low" cam tables the rev-limit is lower than the "high" cam profile.</TD></TR></TABLE>

this is correct. i believe it to be the same rev-limit the ecu sees when the motor is cold.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by phan &raquo;</TD></TR><TR><TD CLASS="quote">this is correct. i believe it to be the same rev-limit the ecu sees when the motor is cold.</TD></TR></TABLE>

Also true, on b series engines its 7something (no vtec) and 8something (with vtec). B series engines have different redlines, so thats why I said "something"

Basically, rev your b18c (r) to 8,400 at normal opperating temp, and see if it goes all the way.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TrueNorthStar &raquo;</TD></TR><TR><TD CLASS="quote">
Your stock guage cluster can send a electric signal to your ecu while using a mechanical speed sending unit.</TD></TR></TABLE>

oh cool - i didnt know that! so it sounds like all i need to do is get a DA speedo gear to complete the swap.

i DO believe that VTEC is kicking in, though. just yesterday i was autocrossing on a higher speed course - i was hitting 8000-8100 rpm (in 2nd gear) on some parts. and the engine definitely SOUNDS like its in vtec. so i assume its working. i just dont know why or how!


thanks to everyone that responded to this post. you all are very helpful!-SM

 

You can try unplugging your VTEC solinoid and see if it feels different.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TrueNorthStar &raquo;</TD></TR><TR><TD CLASS="quote">You can try unplugging your VTEC solinoid and see if it feels different.</TD></TR></TABLE>

And if you want to see if the VTEC solenoid is kicking in its signal, wire up a simple 12v light/led tapped into the wire and run it into the driver compartment. When VTEC engages so will the light/led. Kinda ghetto but it works.

 

man - my dad and i were thinking about doing both of those things.

if (or when) he reads this, he's going to give me a huge round of "i-told-you-so's"

i think im going to try the solenoid trick tomorrow.
thanks guys! keep it coming!

 

bill, your motor was absolutely working correctly and the vtec x over was fine. no doubt about that what so ever. if it wasnt, you would feel the power really die off after 6k and be absolutely dead by 7k

im not sure on how you did the wiring for your swap, but i know mine works fine without a speedo gear hooked up. as long as the vtec solenoid is given power at the right rpm it will work.

and if you would wire up a piggy back such as a vafc like im running, the ecu doesent even wait for the motor to warm up or check for oil pressure or anything before allowing the cam to switch profiles. it just gives it power at the rpm you set and it switches.

anyways, like i said its fine and dont worry about it.

 

yeah, im convinced its working. still, im going to go to THE junkyard tomorrow morning to get a speedo gear for the tranny. (jer - you know which yard im talking about)

hopefully i'll stop throwing a code 17

i'll keep you guys posted.
-SM

 

yeah, i know the place well. you should stop out andy's(green b16 hatch) shop sometime if you are heading out since its a whole 7 minutes away from there.