Question about VTEC.

[Savant]

OK, i'll try explain this the best i can.

[acronym:e42ded33a5="Valve Timing and lift Electronic Control"]VTEC[/acronym:e42ded33a5] is the use of a bigger cam lobe because it needs to let more air in and out at higher rpm. the smaller lobe is good for low rpm but at higher rpm it will start letting out air before it can combust, right? (basically)

So how is it possible to rev up to 8k with your foot only half pressed down on the accelerator (so [acronym:e42ded33a5="Valve Timing and lift Electronic Control"]VTEC[/acronym:e42ded33a5] doesn't engage)? This is with the car warmed up too.

[tinkerbell]

So how is it possible to rev up to 8k with your foot only half pressed down on the accelerator (so [acronym:5993608d6a="Valve Timing and lift Electronic Control"]VTEC[/acronym:5993608d6a] doesn't engage)? This is with the car warmed up too.

you can disconnect the vtec solenoid to do this if you really want to.

otherwise impossible.

[acronym:5993608d6a="Valve Timing and lift Electronic Control"]VTEC[/acronym:5993608d6a] will engage, you just might not hear/feel it.

[EG_2_TEG]

i think [acronym:9c98b87c2b="Valve Timing and lift Electronic Control"]VTEC[/acronym:9c98b87c2b] is also dependent on the amount of throttle
so if u rev it slowly to 8000rpm, [acronym:9c98b87c2b="Valve Timing and lift Electronic Control"]VTEC[/acronym:9c98b87c2b] shouldn't turn on

i reckon the only way to really know is to hook up a LED to the [acronym:9c98b87c2b="Valve Timing and lift Electronic Control"]VTEC[/acronym:9c98b87c2b] solenoid :|

[A'PEXi]

lol is that possible? rev slowly? :D

[ECU-MAN]

you can defenently rev it to 8k in lo cam..

[acronym:62ce748566="Valve Timing and lift Electronic Control"]VTEC[/acronym:62ce748566] wll NOT engage if your engine is cold
or not enogh engine load
or rpms to low

I have reved my Crx to 8 K before in low cam, the engine sounds crap above 6k and there is no power what so ever. its the valve trrain and the balance of the engine that lets it rev high. the cams just determine power band stage.

[Boost]

its actually not with a bigger lobe, but with an extra lobe which engages when high rpm is sensed and is actuated by the solenoid. Each cylinder will have 2 high rpm lobe. 1 for intake and 1 for exhaust.
I think even if you slowly accelerate the car up to the high rpm region, vtec should shill engage becasue it is dependant on rpm.

[wynode]

No.

There are two low RPM lobes and one high RPM lobe for each set of intake/exhuast valves..

The larger lobe is 'engaged' by locking the rocker arms together.

[tinkerbell]

you can defenently rev it to 8k in lo cam..


ok then, prove it.

[tinkerbell]

This is with the car warmed up too.

[ECU-MAN]

ok , I wont get to drive the car until the weekend , ill see if I can make a small video, I would rather disconnect the Vtec solenoid than rev my car to 8 k with a cold engine or do you want cold engine 8k proof. with a warm engine and Vtec solenoid not disconnected Vtec will engage.

[tinkerbell]

OK, lets re-cap:

Savant asked
So how is it possible to rev up to 8k with your foot only half pressed down on the accelerator (so [acronym:c066a369b2="Valve Timing and lift Electronic Control"]VTEC[/acronym:c066a369b2] doesn't engage)? This is with the car warmed up too.

tinkerbell answered:
you can disconnect the vtec solenoid to do this if you really want to.

otherwise impossible.

ecu-man said:
you can defenently rev it to 8k in lo cam..

tinkerbell said:
ok then, prove it.

now you are talking about cold engine revs to 8k? what has that got to do with anything? no-one here is questioning the behaviour of a cold engine.

if you think that a warm engine can rev to 8k without vtec engaging then i would like to know how you can prove this? i much prefer some technical proof, such as a writing about the ecu by a known resource that backs this claim up, and on what basis did Honda decide not to let [acronym:c066a369b2="Valve Timing and lift Electronic Control"]VTEC[/acronym:c066a369b2] engage once the [acronym:c066a369b2="Valve Timing and lift Electronic Control"]VTEC[/acronym:c066a369b2] crossover has been passed.

there is *one* way that i know how to do it, but it is so simple that i rekon you will miss it!!! this is without disconnecting anything as well!!!

[Ronin]

Yeah in Neutral

[tinkerbell]

Yeah in Neutral

yeah, OK, you got it.

for double points, what speed must the car be going to engage [acronym:9c0cc865d6="Valve Timing and lift Electronic Control"]VTEC[/acronym:9c0cc865d6]?

[poid]

its supposed to be around 20mph/ 30km/h isnt it?

[h22a accord]

im fairly sure my vtec engages above 5300 even if im on light throttle or not. Its just alot more noticable at WOT.


I know the vtec wont engage while engine is cold, infact, the engine wont rev above 6300rpm when cold.

My engine will not rev above 6300rpm in neutral at any time.


When engine is at operating temp, [acronym:c55adfcbe3="Valve Timing and lift Electronic Control"]VTEC[/acronym:c55adfcbe3] engages at 5300 and then the biatch screams like a whore all the way to 8000rpm cut out.

[bennjamin]

wtf is the point of this thread ? HOW to blow your engine in neutral ?

*why did you bother Dave....they obviously just wanted to find out if " my car is soo fast it hits VTECCCcc in neutral :)" *

[tinkerbell]

trick question - it is different for different models/ecu's...

but you are about right - it is between 20km/h to 30km/h...

[h22a accord]

me always thought vtec engagement was dependant on throttle position, engine revs, engine temp, oil pressure and engine load. never read anything about road speed before.

Does this mean if i disconnect my VSS (vehicle speed sensor) vtec wont work?

I know that if i disconnect my oil pressure sensor, vtec wont engage.

[tinkerbell]

wtf is the point of this thread ? HOW to blow your engine in neutral ?

*why did you bother Dave....they obviously just wanted to find out if " my car is soo fast it hits VTECCCcc in neutral :)" *

no that is this thread: http://www.ozhonda.com/viewtopic.php?t=8045

the reason i bother is because this is how i learnt, and i am still learning...

see - i just learnt that a H22A only revs to 6300 when cold...

[tinkerbell]

me always thought vtec engagement was dependant on throttle position, engine revs, engine temp, oil pressure and engine load. never read anything about road speed before.

Does this mean if i disconnect my VSS (vehicle speed sensor) vtec wont work?

I know that if i disconnect my oil pressure sensor, vtec wont engage.

i dont think it is dependant on TPS or engine load, where did you hear/read that?

the car needs to be going over 20km/h for [acronym:ba0ac86961="Valve Timing and lift Electronic Control"]VTEC[/acronym:ba0ac86961] to engage, that is why it doesnt engage when stationary. yes, it is the VSS signal.

if you are rolling, you can pop it in neutral and rev into [acronym:ba0ac86961="Valve Timing and lift Electronic Control"]VTEC[/acronym:ba0ac86961] if you want to...

[h22a accord]

i read it it my haynes manual for the sohc f22b1 accord motor.

Now i have h22a i would guess its the same.

hehe, also just read that oil pressure sensor is not dependant on vtec working. :oops:


This is what the manual says

the following are used to determine [acronym:1d9c2b23fc="Valve Timing and lift Electronic Control"]VTEC[/acronym:1d9c2b23fc] operation

a) Engine speed (rpm)
b) Vehicle speed (kph/mph)
c) Throttle position sensor (TPS)
d) Engine load measured by Manifold Absolute Pressure (MAP) sensor
e) Coolant temperature

[tinkerbell]

yes, the TPS and MAP need to be working, but i am not sure that they decide 'when' [acronym:a7f81d4e80="Valve Timing and lift Electronic Control"]VTEC[/acronym:a7f81d4e80] engages...

i have been told that [acronym:a7f81d4e80="Valve Timing and lift Electronic Control"]VTEC[/acronym:a7f81d4e80] engages later on partial loads, but this was never backed up. i have no way to test this as i am running OBD0 ecu and was told that the later OBDII ecus do this... can anyone confirm this?

yes, the "oil pressure sensor" is not looked for by the ecu, only the "[acronym:a7f81d4e80="Valve Timing and lift Electronic Control"]VTEC[/acronym:a7f81d4e80] oil pressure switch" is looked for and checked...

[poid]

yeh thats right, the oil pressure sender only sends a signal if the oil pressure is below about 5psi or so anyway so would be useless as an [acronym:8387c8869c="Engine Control Unit"]ECU[/acronym:8387c8869c] input for [acronym:8387c8869c="Valve Timing and lift Electronic Control"]VTEC[/acronym:8387c8869c]

[Boost]

win: if there are 2 low lobes and 1 high lobe for each set of intake and exhuast, then there will be a total of 6 lobes, 2 high and 4 low per cylinder. Isnt that correct?

[tinkerbell]

in a normal [acronym:81789e930d="Valve Timing and lift Electronic Control"]VTEC[/acronym:81789e930d] engine:

there are 3 'lobes' per clinder. 2 low and 1 high

ie 24 lobes in the head.

the three lobes are joined hydraulicly by a pin when vtec engages, creating one 'super lobe...'

ie 8 'super lobes' or 4 intake 'super lobes' and 4 exhaust 'super lobes'

[tinkerbell]

see here for a detailed explaination:

http://www.leecao.com/honda/vtec/

[pornstar]

my vtec engages whenver im in [acronym:0f2ab8af50="Wide Open Throttle"]WOT[/acronym:0f2ab8af50] :) hehe

[ECU-MAN]

hey tinkerbell

here is proof you can rev a B16a2 to 8000 rpm on the Lo speed camshaft.
engine is warm and [acronym:c7f7bc7295="Valve Timing and lift Electronic Control"]VTEC[/acronym:c7f7bc7295] solenoid is Disconnected, you will notice the Engine Check light on.

http://b16a2.kicks-ass.net/video/no-vtec.avi

the 2nd Video is with the Vtec solenoid reconnected

http://b16a2.kicks-ass.net/video/vtec.avi

listen to the note of the Engine.

Note Im running a [acronym:c7f7bc7295="Japanese Domestic Market"]JDM[/acronym:c7f7bc7295] P30 [acronym:c7f7bc7295="Engine Control Unit"]ECU[/acronym:c7f7bc7295]

[tinkerbell]

um, no one said anywhere that it was impossible to rev to 8000 with the vtec solenoid disconnected.

[ECU-MAN]

oh,,,, I thought wrong then

so you want proof that a cold engine will rev to 8k, well Iv done it before, and dont like doing it either.

[h22a accord]

a h22a will not rev higher than 6300 when cold


it has a rev limiter
will not rev higher than 6300 when clutch is engaged or in neutral, i think this would be to save the engine, gear box and drive line.

its not good to rev a motor really high when there is no load on it anyways

[ginganggooly]

*arsetalk disclaimer* i was reading about this a couple of weeks back, and i remember dave flood mentioning it to me... but apparently, one of the reasons a motec ecu is still better than a hondata (for example) is that you can make vtec engagement load based as well as -rather than exclusively- RPM based.
So you could rev it to 8k on the low cam provided you aren't using full throttle with a motec setup in that fashion, i guess.

[tinkerbell]

oh,,,, I thought wrong then

so you want proof that a cold engine will rev to 8k, well Iv done it before, and dont like doing it either.

maybe you need to check page 1 of this thread [acronym:f34d321a89="Engine Control Unit"]ECU[/acronym:f34d321a89]-MAN...

[SIKCVC]

Ok heres a sticky question for you guys...

How come some days [acronym:0fdf1e6f43="Valve Timing and lift Electronic Control"]VTEC[/acronym:0fdf1e6f43] is scary loud when it enguages and other days theres bairly a tone change? It often happens to me in one trip... sometimes its loud, other times its not. Ideas?

[tinkerbell]

Ok heres a sticky question for you guys...

How come some days [acronym:fb152b1b9a="Valve Timing and lift Electronic Control"]VTEC[/acronym:fb152b1b9a] is scary loud when it enguages and other days theres bairly a tone change? It often happens to me in one trip... sometimes its loud, other times its not. Ideas?

depends on throttle position and surrounding spatial attributes ;)