s15 vtc question

[jskateborders]

I picked up an s13 with an s15 sr swap in it, and the vtc is wired up so its always getting power, and its a constant 12v. Does anyone know if the signal to the vct is supposed to vary, or if it is a switch type (off/on only).

Im thinking about wiring it to draw power based off of the nuetral switch, and in the fsm it seems like its just an on off operation, however that would mean that the intake cam would only be at 1 degree or 20 degrees, which seems like an odd way to setup variable cam timing.

[sean350z]

If your neutral position switch isn't wired up to the ECU it'll be on all the time. Check that and report back.

[jskateborders]

Theres no continuity between the ecu pin and the plug for the vct, so it doesnt really matter how its supposed to work,\ because the po hardwired it from some other power supply.
I dont really have the time to tear apart the harness and re-do everything right, I just need to know how the solenoid itself works for now.
Thanks for the info though!

[jr_ss]

VTC is a switched source controlled by the ecu. It's on at 1500ish and off at 5200ish. It was designed to increase lowend trq. If you've driven an S13 and an S14/15 sr20dets you'll know that the later has a lot more trq down low than the S13 motors.

[jskateborders]

So is it only on and off, or does it vary at all. In other words, can the intake cam only be at 1 degree or 20 degrees, or is that an instance where the vtc will put it at 10 degrees? Will the solenoid in proper operation only get or 12 volts, or will the ecu give it say 6 v at some point?

[sean350z]

It's either off or on. When on, it sends oil to the sprocket and advances the intake cam. It's 1 degree of overlap when on between 1k-5.7k. The reason the overlap increases to 20 degrees is for higher rpm power. To get better power band at higher rpm you want to decrease the overlap which happens when the vtc is turned off. This all changes when you have higher duration cams though...

There's a lot of stuff that goes into tuning cams...of which I'm not an expert.

[sean350z]

Oh sorry...it sees either battery voltage or 0v

0V when off
Battery voltage when on

[jskateborders]

thats what i was looking for, thx

[fufanu180]

If the timing isn't at 15 btdc does this wack out the vtc and make The car run like shit?

CenTex240

[sean350z]

If the engine's timing isn't correct, it will make the car run like shit VTC or not.

[fufanu180]

But is it crucial on the 14's and 15's since they have vtc? The 13 Can be adjusted a little here and there but I would think that since the newer sr's have a mechanism that works with the timing that The timing itself needs to be at 15 no more no less....

?

CenTex240

[jr_ss]

If your mechanical timing is spot on but you're off a few degrees high or low, say 17bdtc, I don't see it causing too many problems. But if you're a good 5degrees from base, then I'd fix it.

[jskateborders]

imo personally, with boost and that much overlap it is better to get as close to 15 for base timing as you can, especially without a wide-band. Too easy to lean out and damage the motor.

[fufanu180]

I apologize in advance for the stupid question but I need to clear this up. By advancing the timing the car runs leaner....and if the timing is pulled back then it runs richer?

CenTex240

[xpertsnowcarver]

^That is mostly incorrect. Timing is more focused on whether you are detonating/knocking or not, though it can influence the AFR because combustion is or isn't occurring properly. Running rich or lean is strictly based on fuel injection which is monitored by AFRs.

Sean pretty much covered everything regarding VTC though.

[fufanu180]

Thanks for clearing it all up. Oh, and sorry for jacking your thread bud.

CenTex240