View Full Version : What is a VTEC Controller (Apex VTEC , Fields VTEC)

Toda Party
05-27-2002, 03:26 PM
I keep writing these and they keep getting deleted. Anyway.

There are two main VTEC/Fuel Control Piggy-Back computers on the market...

the Field's unit for approx $250http://store5.yimg.com/I/twincamtech_1686_704429

and the Apex'i Unit for approx $300-350http://store5.yimg.com/I/twincamtech_1690_921403

The difference? Just that the apexi has a cool display and has some extra features like a more accurate tach, vaccum pressure dispay, throttle percentage, some some other crap.

The only difference between the Apexi VAFC and SAFC is the fact that the VAFC has the ability to fuck around w/ the VTEC engagement point, other than that, they still have the same Fuel tuning capabilites.

Same goes for the Field's Vtec controller and fields hyper-R.

What these do is that when you tap in the appropriate lines on the ECU harness to the controller, it reads, and modifies the signal coming to and from the ECU to and from the sensors. This is why its called a Piggy-Back computer. It can also allow you to take away percentages of fuel in i think 500 RPM increments. Now, this should be done in conjunction with a fuel pressure regulator. Why take away fuel? Most ECU's tend to run rich...meaning too much fuel, too little air, which doesnt produce the full amount of power that it can/should.

Now before you all go run out and buy a fuel controller and lean the fuck out of it, remember: too lean, and you can cause detonation...which u dont want. So I dont recommend you just tune it on some back road. Go to a dyno place with a wideband o2 sensor and let them or if you think you can do it, tune it there.

From what I gather, the afc tuning is just done to smooth out the powerband and eliminate dips and spikes on your power curve, so that you can have a nice flat linear torque and hp curve. It should not really be used when you are in dire need of bigger injectors becuase the duty cycle is 100% by 4,000 RPM and you turn fuel pressure to 500 psi then try to lean it out with the afc. that wont work.

Anyway, that's what the AFC (air, fuel control) part does.

Onto the VTEC controller part.

VTEC engagement on a stock car is OPTIMIZED. Do NOT fuck with it because all you are really doing is taking away power, depsite what it "feels" like

Now that we have that cleared up...YES, i know that bringing the VTEC crossover up or down around 500 or even 1000 rpm up or down may indeed improve your power curves. Again, this is something u can only really prove if you are on a dyno and u can see the immediate results.

So, why do you need a vtec controller? U dont, really. Unless you are using aftermarket cams, or have upped the compression, or some other internal modification that demands a shift in the VTEC x-over to again be optimized. AGAIN, something you should really be doing on the dyno, as every motor is different, not to mention weather conditions, grade of gasoiline, general condition of the motor, etc....

So when you hear people say "I got a vtec controller and i set vtec to 3,000 rpm so im maddddd fast now son" u know they're a fucking idiot.

Why? This leads into my explanation on how vtec works but basically....

on a vtec motor there is a vtec cam lobe and non vtec primary & secondary cam lobes. Those non vtec lobes are optimized for low end power delivery. However, @ upper RPM, the small lobes cannot deliver enough air nor keep the valves open long enough to continue to let the motor make power.

Hence, the VTEC crossover...where the VTEC cam lobe takes over duties in opening and closing the valves from the seconary and primary lobes. Since the vtec cam lobe is much taller, it can now provide more air and duration the motor needs to keep making power @ higher RPM.

Now think about it. What does setting VTEC at 3,000 rpm do? It makes a cam lobe designed to work well at HIGH rpm to work at LOW rpm. Conversely, setting VTEC too high will cause the motor to start dying out, then JUMP foward when the VTEC lobes take over.

Its like asking allen iverson to play center against shaq. it doesnt make sense, and therefore, people shouldnt do it cuz its pointless.

If u have or do get a vtec controller, try it one day.

Set vtec to 3,000 and see how much of a pig the car is down low. Then set vtec to say 7,500 rpm or something. See how the car accelerates, slows down, then springs foward again at vtec x-over.

you may think that is the car making more power, but if you were to look at dyno graphs, you would see the torque curve fall off, then rise back up @ your specified vtec cross over point.

the above is also a good way to determine a starting point for an optimal vtec x-over when you have done some internal mods and u would like to set vtec @ a certain point. Take a dyno pull with vtec set low, then another pull with vtec set really high.

Overlap the graphs and where the curves intersect where power falls off and where power comes up is where you should start to fuck around with a crossover point

anyway, my fingers hurt so im going to stop typing

05-27-2002, 04:27 PM
or there is always that bling bling effect...

Toda Party
05-27-2002, 04:37 PM
shut up riceboy. go get ur spoon paintjob :lol:

05-27-2002, 04:38 PM
So all in all a vtec controller doesn't add any power right?

A guy that lives in my city says that his 93 prelude SRV.....which only has vtec controler, C.A.I., and exhaust has 232hp......he also says that his car came factory with a special type R engine!.......from what i know i have never heard of a type r engine in one of those preludes......also a 93 prelude only has about 190hp...does it not?

Toda Party
05-27-2002, 05:15 PM
All in all, a vtec controller used to change the vtec crossover point will not add horespower, andif it does, it will be less than 10 whp at the most extreme case.

now if it was used to tune your fuel delivery, it might show some good increases. A friend of mine with an h22 swap in an accord gained some insane number like 25 hp and 25 ft-lbs in the midrange from fuel tuning w/ a vafc...peak numbers were only up by 5-7 hp tho

05-27-2002, 09:55 PM
shut up riceboy. go get ur spoon paintjob :lol:

dam strait spoon paintjob = functional rice!!!!! when i get backed into spoon front end with spoon paintjob....

05-28-2002, 12:00 PM
I dont gots no vtech waaaaaaa!!!!!!!!!

Hehehe. Thanks anyway Toda.

05-28-2002, 12:16 PM
lol ...this is wut? number 3 of toda's "informative posts"

05-28-2002, 02:25 PM
needed or helpful for stage1 camshafts?

Toda Party
05-28-2002, 10:35 PM
anytime u deviate from stock (internals) its helpful to retune your fuel, ignition, cam timing etc

10-14-2002, 02:58 PM
thanks toda,
so basiccaly, since my exaust is running black and its running ritch, i should reprogrm my ecu? i was going to but decided no too.

Toda Party
10-14-2002, 07:59 PM
it doesnt really reporgram it.

what it does is it modifies the signal going from the ecu to the injectors and allows you to lean out the fuel so u don't run as rich. u should do this on a dyno with a wideband o2 sensor to make sure u dont go too lean

10-18-2002, 01:39 AM
point in case about how vtec works and how u can feel it. went out this morning, its been cold as fuck down here in blacksburg and the car had just been started and the engine was freezing, no way vtec was engaging. anyway, just to fuck around i redlined it (8 grand :D ) and of course vtec didnt engage, man i could feel it, the car didnt pull nearly as hard, and it sounded like shit. with the winter months, people outta try this, it'll be hard to notice on a sohc motor but dohc you'll be able to tell pretty easily. start the car after a night of sitting in the cold, and immediately, before the car has a chance to warm up, redline that bitch in first. you'll see.

Toda Party
10-18-2002, 01:42 AM
:uhoh: i don't think i'd want to do it asap lol....at least let it warm up a LITTLE

10-18-2002, 02:24 AM
I would NEVER NEVER redline my car before the engine was warmed up. I barely rev to like 3,500 or 4k when its cold.

But I still have one question. As I was told earlier the primary lobes and secondary lobes on a dohc vtec engine run the intake and exhaust valves. That is 4 lobes, and 4 vavles per cylinder. But here is my question, when you cross over into vtec, you have two lobes controlling 4 valves, how does it do it?

Toda Party
10-18-2002, 09:12 AM
didn't i tell u to read my "how vtec works thread" ?

i'll TTT it for u