At what point does the vtec kick in ? Is it determined by the rpm or oil pressure ?

Typically VTEC would increase the time duration for which the intake valves remain open at higher rpm. Does anyone know what is the time duration (in degrees) that the intake valves are open when it is in vtec and non-vtec mode ?

Thanks!

 

what motor are you talking about?

 

Ooops... I think I should create a signature..


Its for a 99 LX 4-cyl Auto sedan.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AnAccordIsForever &raquo;</TD></TR><TR><TD CLASS="quote">Ooops... I think I should create a signature..


Its for a 99 LX 4-cyl Auto sedan.</TD></TR></TABLE>

~4000rpm

 

it has a variable engagement point... as low as ~2300rpm.

 

hmm..could be possible. found in the haynes manual that engagement of the vtec depends on -

engine rpm
vehicle speed
engine load
throttle position
coolant temperature

dont know why I thought oil pressure was also a factor. Anyway, still searching for the intake timing question...

 

correct. unless u put ur foot down after the rpm has passes 2300. then its 4200.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drivinaway367 &raquo;</TD></TR><TR><TD CLASS="quote">correct. unless u put ur foot down after the rpm has passes 2300. then its 4200.</TD></TR></TABLE>

I'm not quite sure exactly what you're trying to say, so I'll explain a little further. Let's say you have a rolling, second gear start, with about 40% throttle. VTEC will engage at 2300rpm. If, once it engages, you floor it to 100% throttle, it still stay in VTEC. The problem with this is however, VTEC is hurting performace at this low of an rpm at 100% throttle. Let's say you start from a stop, with 100% throttle. VTEC will engage at it's latest setting (3800, 4200, whatever it actually is).

It's variable b/c under certain part-throttle, low-rpm conditions, VTEC is beneficial. Under full-throttle, it is more beneficial to have VTEC engage at a higher rpm.

 

that is the first time i ahve heard someone say that vtec engages later under full throttle, specailly since i have never seen that happen in real life. In general under part throttle vtec will engage later, while heavy throttle causes an earlier engagement. but hey maybe it really is backward on the accord compared to all other models of honda.

 

So when does v-tec kick in for an 01 v6? and lets say you don't use v-tec much or hardly at all. Would it still work later on? And would v-tec work in neutral?

 

To sum it up, its the F23A engine, 150hp, 152ft/lbs. VTEC at 2500 at full throttle, 2900 at partial. It's a SOHC motor, so its not all performance. If it were a DOHC, then that would be ****.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by v4lu3s &raquo;</TD></TR><TR><TD CLASS="quote">that is the first time i ahve heard someone say that vtec engages later under full throttle, specailly since i have never seen that happen in real life. In general under part throttle vtec will engage later, while heavy throttle causes an earlier engagement. but hey maybe it really is backward on the accord compared to all other models of honda.</TD></TR></TABLE>

The F23 is the only engine I've known to work that way. Keep in mind, when I said partial throttle, it was just an example of ~50% throttle, second gear starts. On the other hand, if you were to accelerate from a stop with say, 15% throttle, VTEC would not engage until later.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by XzIpK &raquo;</TD></TR><TR><TD CLASS="quote">To sum it up, its the F23A engine, 150hp, 152ft/lbs. VTEC at 2500 at full throttle, 2900 at partial. It's a SOHC motor, so its not all performance. If it were a DOHC, then that would be ****.</TD></TR></TABLE>

Sorry, this is NOT correct when it comes to the F23. It's completely variable. I would say it's mostly based on load, throttle position, and engine speed. It is too complicated to simply say partial throttle = xx rpm, full throttle = xx rpm. Full throttle, from a stop, it will engage at ~3800. Partial throttle, it will depend on load, throttle position, and engine speed, and it will vary anywhere from 2300-3800 rpm.

I gave an example of a <U>high-load</U>, <U>mid-throttle</U>, <U>low-engine speed</U> situation. The ECU uses this data, performs some calculation, and determines the engagement point.

Now what if we said, from a stop, 1st gear, 20% throttle? It probably won't engage until 3800. But then again, I would have no need to rev that high while accelerating so slowly...

Do you see why I'm trying to say, that with the F23 (same motor as the original poster), VTEC engagement is complicated, and the answer is best left at:

Variable, 2300-3800 rpm, depending on conditions.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by philadd &raquo;</TD></TR><TR><TD CLASS="quote">
Variable, 2300-3800 rpm, depending on conditions.</TD></TR></TABLE>

yes. hence the actual name: Variable valve Timing and lift Electronic Control.

 

vtec does not work in neutral, only under load

 

Ok, here's something to ponder... When watching the 12 signal to the VTEC solenoid, (with a test light) From 2200rpms and on up, the light will illuminate at anything over ~50% throttle. Does this represent VTEC's engagement? Or is there a second step after the solenoid before it fully engages? What confuses me is on the dyno chart, full throttle starting at 2Krpms, it's obvious that VTEC engages at 4100rpms. What gives?

 

Read through my previous posts, as I gave an example of exactly what you are talking about.

 

if anyone has an f23 can you FEEL vtec engage? i thought it was at 5000rpm? ---&gt; 2300? really?.......SWEET never really noticed, damit! well...... kinda if i think about it.

 

If infact it IS engaging at these low rpms, then yes. I can feel a significant torque kick usually between 2K and 3K, coincidently just when the light illuminates. Perhaps that's how my torque curve is so smooth from 2K on up...

 

OK, Let me see if I understand what everyone here is saying.

With it's variable vtec cross over point, and the fact that it can cross over at low rpms in certain situations, would it be safe to say that the F23's vtec was meant for economy rather than performance?

I always thought vtec was for added performance only. When the vtec in my '94 EX actually works, it is always at a particular point (~5000rpm) and you can definately feel it. The two grinds on normal vtec are economy then performance, but with the F23 it seems it's economy / economy. Why even have two different grinds in the first place then?

 

f22b1- when i hooked up the test light.. vtec hit around 2300rpm with 50-100% throttle.. and stayed on untill i shifted.. i dont remember if it stayed on after.. but with the same accleeration im sure it kickied in again...

you say that its not benificial to engage at low rpms... i dont see how.. becuase if it engages lower.. then i make the rpms go up faster.. thats what you want.. now if your trying to save gas.. then yes.. its not good.. when im trying to save gas.i give it about 20-35% throttle and keep it under 3000prm

 

With DOHC engines, VTEC was designed with performance in mind. With SOHC engines, it's more for low-end performance and economy, but it still optimizes top-end performance. The difference is that DOHC VTEC affects both the intake and exhaust sides, while SOHC VTEC only affects the intake side.

AFAccord,
During some partial throttle conditions, yes, it will engage that low. I definitely can feel it, as well as hear it (via AEM intake), when it engages at ~2300 rpm. It's also possible that in your case, JET may have also slightly altered the VTEC engagement points when they reprogrammed your ECU, but you'd have to ask them to be sure.

pooMan,
Did you read the whole thread? It engages anywhere between ~2300-3800 rpm, depending on conditions. And the engagement point will generally not be as noticeable as with DOHC VTEC engines.

Thag,
Generally, at higher rpm, it is more efficient to open the intake and exhaust valves for a longer time, thus the longer duration and different grinds. If I'm not mistaken, there's a pretty good explanation on the How Stuff Works website. It has to do with how quickly the piston can "suck" and "push" the air in and out of the cylinder.

 

Dj14aZnS,
It is not always beneficial to have the valves open longer (VTEC engaged) for a longer duration. It has to do with how much air needs to be moved in and out of the cylinder. That's why the ECU uses load, throttle position, engine rpm, and whatnot to determine the engagement points.

 

so basically to sume it up, under full throttle it engages at 2300, under anything less it varies between 2300 and 3800.... correct, this seemed not as complicated

 

/\ interesting............. hope its right cause that makes sense. obviously it is the same for auto trannys..... yup? ya? of course &lt;---- im right, right?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xcessivespeedz &raquo;</TD></TR><TR><TD CLASS="quote">so basically to sume it up, under full throttle it engages at 2300, under anything less it varies between 2300 and 3800.... correct, this seemed not as complicated</TD></TR></TABLE>

No.
Under full throttle, ~3800.
Partial throttle, ~2300-3800.

I feel like I'm repeating myself... I guess I didn't make it as clear as I thought. Oh well.

EDIT
People, you have to stop thinking about just rpm. How much load is on the engine affects it greatly. When do you think there is more load on an engine: 2nd gear, 3/4 throttle, 2000 rpm; or 1st gear, full throttle, 4000 rpm?

- 1st gear, 1/2 throttle, from a stop: probably won't engage until ~3800, or maybe not at all. If the load is not great enough (like maybe at 10% throttle, assuming you rev higher and higher), VTEC won't engage.
- 2nd gear, 1/2 throttle, from a stop: the load is much greater b/c of the gearing. VTEC will engage at ~2300.

Do you see what I'm trying to say?