VTEC discussion (from iVTEC sticker thread)

[THREE40SEVEN]

If vtec is so great, why do the higher HP hondas delete it? From my understanding (not from a great source) vtec is variable valve timing- it switches from one set of cam lobes to the another at a specific RPM(4000??). Is the intake runner length changed as well like on the yamaha SHO enigne?

[three.eighteen.]

Originally posted by THREE40SEVEN
If vtec is so great, why do the higher HP hondas delete it?

umm both the NSX and S2000 have vtec...

[buh_buh]

Originally posted by THREE40SEVEN
If vtec is so great, why do the higher HP hondas delete it?
that doesn't typically happen until your pushing a lot of hp. There's no magic number, but I'm guessing at around 400hp+
I believe the reason for this is because when your making so much power there is no need for the crossover (like it makes no difference), so that is why people "delete" it.

[THREE40SEVEN]

Originally posted by three.eighteen.


umm both the NSX and S2000 have vtec...
I meant serious power, not out of the box stuff.

Thanks buh_buh

[GTS Jeff]

Originally posted by THREE40SEVEN
If vtec is so great, why do the higher HP hondas delete it? From my understanding (not from a great source) vtec is variable valve timing- it switches from one set of cam lobes to the another at a specific RPM(4000??). Is the intake runner length changed as well like on the yamaha SHO enigne? refer to my vtec bible: http://forums.beyond.ca/showthread.php?s=&threadid=5372&

and vtec has nothing to do with intake runners, although the integra gsr did have secondary intake runners that opened up at some rpm via butterfly valves. none other hondas come to mind that have variable intake runners

[THREE40SEVEN]

Originally posted by Jeff TYPE R
refer to my vtec bible: http://forums.beyond.ca/showthread.php?s=&threadid=5372&

and vtec has nothing to do with intake runners, although the integra gsr did have secondary intake runners that opened up at some rpm via butterfly valves. none other hondas come to mind that have variable intake runners
With ivtec, how is the valve timing, lift, and or duration changed? Since cam profiles are fixed(machined) how are valve events changed? The only thing i can think of is no camshaft, and the valve are controlled through an electric solenoid. Saw that once as a prototype on a ford V8.
32 valve cobra engines(96-8) have a secondary rpm controlled runners(IMRC) like you had mentioned on the GSR.. The were dropped in 99 for a much improved tumble (single)port.
Sorry for the thread hijack....

[buh_buh]

Originally posted by THREE40SEVEN
Sorry for the thread hijack....
hijack fixed!:)

[CanadaCivicSIR]

Originally posted by THREE40SEVEN

With ivtec, how is the valve timing, lift, and or duration changed? Since cam profiles are fixed(machined) how are valve events changed? The only thing i can think of is no camshaft, and the valve are controlled through an electric solenoid. Saw that once as a prototype on a ford V8.
32 valve cobra engines(96-8) have a secondary rpm controlled runners(IMRC) like you had mentioned on the GSR.. The were dropped in 99 for a much improved tumble (single)port.
Sorry for the thread hijack....

ivtec, is some what similiar to normal vtec motors.
At a predetermined rpm a solenoids slams pins in to the rocker arms joing the arms together forceing them to ride on the high lobe of the camshaft.

However in ivtec the computer senses when you need this, by your driving style, load on motor and so on. Then it triggers the solenoid. Not always on a certain rpm, like the original vtec motors.

[GTS Jeff]

Originally posted by CanadaCivicSIR


ivtec, is some what similiar to normal vtec motors.
At a predetermined rpm a solenoids slams pins in to the rocker arms joing the arms together forceing them to ride on the high lobe of the camshaft.

However in ivtec the computer senses when you need this, by your driving style, load on motor and so on. Then it triggers the solenoid. Not always on a certain rpm, like the original vtec motors. mostly wrong.

ivtec is just hondas name for the same old vtec system PLUS camshaft phasing. so:

vtec: 2 distinct cam lobes
ivtec: 2 distinct cam lobes AND camshaft phasing (which honda calls VTC)

the camshaft phasing (VTC) is really good cuz it retards the cam timing by something stupid like 50 degrees at idle and advances it hardcore when it needs to. its continuously variable and is controlled based things like rpm, throttle, speed, load, etc..

[GTS Jeff]

Originally posted by THREE40SEVEN

With ivtec, how is the valve timing, lift, and or duration changed? Since cam profiles are fixed(machined) how are valve events changed? The only thing i can think of is no camshaft, and the valve are controlled through an electric solenoid. Saw that once as a prototype on a ford V8.
32 valve cobra engines(96-8) have a secondary rpm controlled runners(IMRC) like you had mentioned on the GSR.. The were dropped in 99 for a much improved tumble (single)port.
Sorry for the thread hijack.... the camshaft itself is basically wiggled around :)

[THREE40SEVEN]

Originally posted by Jeff TYPE R
the camshaft itself is basically wiggled around :)
Meaning point of which valves close and open is changed in relation to crankshaft degrees?- Meaning intake and exhaust centreline? Do you have any pics? I am having a hard time picturing this, as from what i gathered, the cam is still driven and indexed by the crankshaft(driven by a belt).

[GTS Jeff]

Originally posted by THREE40SEVEN

Meaning point of which valves close and open is changed in relation to crankshaft degrees?- Meaning intake and exhaust centreline? Do you have any pics? I am having a hard time picturing this, as from what i gathered, the cam is still driven and indexed by the crankshaft(driven by a belt). yea, im not actually sure how honda manages to adjust the camshaft phasing...but a lot of manufacturers are doing this nowadays...

hmmm ive found this, but it doesnt really explain too much:

http://www.honda.co.nz/h.nsf/ti_ivtec_pic5.jpg

edit: who cares, lets just say its magical and call it a day

[350hp_or_Bust]

On variable valve timing:
The camshaft phasing or variable valve timing or whatever manufacturer A and B call it is done by controlling the oil pressure in the 'phaser' (like a cam cog) ... basically the belt drives the cam cog or phaser, but the outside can rotate relative to the inside .. its like two concentric pipes. By increasing the oilpressure (based on RPM, throttle position etc) it will rotate the inside part (which is directly attached to the cam) relative to the outside part (which is directly attached to the timing belt/chain). I wish Jeff's picture showed up as more than a red X, then I might be able to explain it better.

to answer your first question 347, there are two distinct profiles cut on to VTEC cams ... the VTEC basically switches the valve following from one set of lobes to the other at a certain RPM (its like having a torquey camshaft at low RPMS that you can magically switch out to a high RPM camshaft at a given RPM)

[THREE40SEVEN]

Originally posted by 350hp_or_Bust
On variable valve timing:
The camshaft phasing or variable valve timing or whatever manufacturer A and B call it is done by controlling the oil pressure in the 'phaser' (like a cam cog) ... basically the belt drives the cam cog or phaser, but the outside can rotate relative to the inside .. its like two concentric pipes. By increasing the oilpressure (based on RPM, throttle position etc) it will rotate the inside part (which is directly attached to the cam) relative to the outside part (which is directly attached to the timing belt/chain). I wish Jeff's picture showed up as more than a red X, then I might be able to explain it better.

to answer your first question 347, there are two distinct profiles cut on to VTEC cams ... the VTEC basically switches the valve following from one set of lobes to the other at a certain RPM (its like having a torquey camshaft at low RPMS that you can magically switch out to a high RPM camshaft at a given RPM)
Makes sense- Thanks!

[GTS Jeff]

Originally posted by 350hp_or_Bust
On variable valve timing:
The camshaft phasing or variable valve timing or whatever manufacturer A and B call it is done by controlling the oil pressure in the 'phaser' (like a cam cog) ... basically the belt drives the cam cog or phaser, but the outside can rotate relative to the inside .. its like two concentric pipes. By increasing the oilpressure (based on RPM, throttle position etc) it will rotate the inside part (which is directly attached to the cam) relative to the outside part (which is directly attached to the timing belt/chain). I wish Jeff's picture showed up as more than a red X, then I might be able to explain it better.

to answer your first question 347, there are two distinct profiles cut on to VTEC cams ... the VTEC basically switches the valve following from one set of lobes to the other at a certain RPM (its like having a torquey camshaft at low RPMS that you can magically switch out to a high RPM camshaft at a given RPM) thats what my nonworking picture showed haha

[350hp_or_Bust]

ya, there ya go .. its working now.

off topic: hey Jeff Type R, were you pulled over on whitemud and 91st at about 11:15am Saturday? I thought I saw red/orange/whatever corolla and some oriental dude that looked like he was cursing at the car or something. was that you? ha ha

[MrX]

Originally posted by buh_buh

that doesn't typically happen until your pushing a lot of hp. There's no magic number, but I'm guessing at around 400hp+
I believe the reason for this is because when your making so much power there is no need for the crossover (like it makes no difference), so that is why people "delete" it.

If Vtec is designed for a NA application, theoretically wouldn't the system benefit from custom ground turbo cams for vtec application? From the limited number of examples i've seen, people usually "delete" vtec application when they run a bolt on turbo kit with stock valve train.

[GTS Jeff]

Originally posted by 350hp_or_Bust
ya, there ya go .. its working now.

off topic: hey Jeff Type R, were you pulled over on whitemud and 91st at about 11:15am Saturday? I thought I saw red/orange/whatever corolla and some oriental dude that looked like he was cursing at the car or something. was that you? ha ha hmm nope not me...i was still asleep at 11 in the morning on sat!

[350hp_or_Bust]

Originally posted by MrX


If Vtec is designed for a NA application, theoretically wouldn't the system benefit from custom ground turbo cams for vtec application? From the limited number of examples i've seen, people usually "delete" vtec application when they run a bolt on turbo kit with stock valve train.

my guess here (and its just a guess) is that the VTEC system isn't as durable under boost ... i.e. it'd be tough not only for that little pin that slams into the secondary rocker arm to get into place, but it'd also be tough for it not to shear while opening the valves under boost load. Particularly the exhaust would be susceptible to failure I think because it has to open against the force of the cylinder pressure (but most VTECs are only on the intake).

That's my guess is its just a durability issue (go ahead ppl ... flame on with how honda is second to none for durability and VTEC rules the world and blah blah blah if you don't want to believe me)

A turbo'd vehicle would undoubtably benifit from some kinda variable valve system though ... there's no reason it shouldn't. Subaru put VVT on the STi ... I'm sure there's some other high end cars with VVT or VVLift that are boosted.

I'm still waiting for solinoid actuated valves to come out ... it'd completely eliminate VTEC and any VVT systems out there .. .not to mention own them all. That's a whole other issue though.

[GTS Jeff]

actually, the reason ppl remove vtec under high boost applications is because the aggressive lobe is TOO aggresive...theres so much overlap that the boost basically forces the uncombusted mixture out the exhaust valves before the exhaust valves have a chance to close.

[MrX]

Originally posted by Jeff TYPE R
actually, the reason ppl remove vtec under high boost applications is because the aggressive lobe is TOO aggresive...theres so much overlap that the boost basically forces the uncombusted mixture out the exhaust valves before the exhaust valves have a chance to close.

So with a less aggressive cam profile or a custom grind where overlap is minimized, you may be able to take advantage of the vtec technology on boosted honda/acuras.

[350hp_or_Bust]

Originally posted by Jeff TYPE R
actually, the reason ppl remove vtec under high boost applications is because the aggressive lobe is TOO aggresive...theres so much overlap that the boost basically forces the uncombusted mixture out the exhaust valves before the exhaust valves have a chance to close.

Oh yeah... didn't think of that.


Originally posted by MrX


So with a less aggressive cam profile or a custom grind where overlap is minimized, you may be able to take advantage of the vtec technology on boosted honda/acuras.

Thats what I was just thinking too .... except a less aggressive profile would negate the purpose of having VTEC ... but a custom grind with high lift on the secondary lobes with either a shorter duration than the stock ones or advanced just enough to prevent much valve overlap would be where its at.

[THREE40SEVEN]

Valve overlap is mainly determined by lobe seperation angle. The higher the #, the less overlap-not duration.

[350hp_or_Bust]

not for DOHC

[THREE40SEVEN]

Originally posted by 350hp_or_Bust
not for DOHC
Explain to me why that would make a difference- 2 cams vs 1?

[350hp_or_Bust]

there is no such thing as lobe separation in DOHC ... not in the conventional sense anyhow.

for DOHC, there's typically one cam dedicated to the intake valvetrain, and one dedicated to the exhaust ... valve overlap is mostly a function of cam timing/synchronizing/degreeing ... i.e. you can decrease overlap if you degree the exhaust cam a few degrees retarded ... or the intake cam a few degrees advanced, or both (valve overlap will be reduced the same amout of degrees as the degrees you advance/retard the respective cams) ... the problem then lies in the duration cause if you advance the intake cam too much for example ... and your duration is too long, it will open the valve too early .. same story for the exhaust cam.

In the case of SOHC, or conventional push-rod valve trains (OHV) .. the exhaust AND intake profiles are cut on the same shaft, and (as I'm sure you know) the advance/retard of the intake and exhaust events relative to each other are determined by lobe separation.

hows that? sometimes I'm ass at explaining things