What RPM range is our i-VTEC supposed to kick in?

[idrive]

I'm still in my break-in period so i havent gotten a chance to really test it out... but on the few times that i felt kinda frisky and went up to about 5.5k i didnt feel a thing? I'm used to driving a bmws with a nice linear power curve... and thats pretty much what it felt like.. smooth power? Is i-VTEC disabled during the break-in period or does it kick in after 5.5k? When exactly does the i-VTEC kick in on our cars? and what does it feel like? i've driven an RSX-S before, is it something similar to that? nothing strong... but still an obvious sign that the vtec just kicked in?

http://idrive.aeropixel.net/ep_sig.jpg

[SiRman]

iVTEC engages at either 2200 or 2400 RPM (I can never remember)

No it is nothing like the RSX-S, totally different system.

It doesn't feel like anything, you just feel the engine pull smoothly.(I can't feel it on my car anyways)

[Will2K2]

Variable Cam Timing = 2000 and up
Variable Valve Timing (Vtec) = 4700 and up

[myeverlovinsir]

Whoops, sorry to burst that bubble again. I was of the same opinion that the Vtec (high profile lobes) solenoid engaged at ~4800rpms. My reasoning was due to the large torque hump occuring there on the dyno sheet. I have since retracted that theory. Vtec engagement occurs at 2200rpms and below this you have one valve which is slighly closed to promote a swirl effect inside the cylinder for improved torque and fuel economy in the lower rpms.

The power hump most of us notice at ~4800rpms is due to a resonating air flow, that promotes the intake air to be aided along by sound waves. (Harmonics)

Most CAI's are tuned using sound as feedback vs. air flow and seem to promote this resonating torque hump quite well.

With respect to the VTC (variable timing control) is is always in effect throughout the full range of rmps. Unfortunately we only have advancement and retardation of the intake valves (+/-25 degrees) This is an oil pressure controled device.

Both of these components make up the current i-Vtec system in the K20A3. hth ;)

[BlairSpeed]

I notice my SRI gets alot more audible when I hit 4800rpms and I notice it pull harder too. but your saying that its not vtec but its harmonic sound waves? hmmm. :rolleyes: Im sure your more educated than I on the subject but never heard of any sort of harmonics being part of performance. It also doesnt make sense that the v-tec would engage at 2300rpms? whats the point of that? so we are always cruising in v-tec mode unless we shift before 2300rpms? why would honda do that? odd.

[SiRman]

why would honda do that? odd


to promote a swirl effect inside the cylinder for improved torque and fuel economy in the lower rpms.

[NamingException]

I thought VTEC engaged around 2300 and the power boost around 4500 was from the switch to short intake runners from long ones.

See Hondata's K-series tech page:

http://hondata.com/techk20general.html

[myeverlovinsir]

Originally posted by BlairSpeed
I notice my SRI gets alot more audible when I hit 4800rpms and I notice it pull harder too. but your saying that its not vtec but its harmonic sound waves? hmmm. :rolleyes: Im sure your more educated than I on the subject but never heard of any sort of harmonics being part of performance. It also doesnt make sense that the v-tec would engage at 2300rpms? whats the point of that? so we are always cruising in v-tec mode unless we shift before 2300rpms? why would honda do that? odd.

The harmonics, or resonating frequency of the engine, along with the type of intake you have, has commonly shown moderate gains on most engines. I think that the torque hump on the Si

[myeverlovinsir]

Originally posted by NamingException
I thought VTEC engaged around 2300 and the power boost around 4500 was from the switch to short intake runners from long ones.

See Hondata's K-series tech page:

http://hondata.com/techk20general.html

They are refering to the dual runners on the base RSX intake manifold. Our manifold is the same as the type-R and type-S. hth:D

[BlairSpeed]

:cool: you know, its nice to have intelligent people around to explain questions that you otherwise would never have an answer to. :cool:

[chet]

About 1/3rd of the way down a long reply begins

http://www.superhonda.com/forum/showthread.php?s=&threadid=108177

[Will2K2]

Originally posted by chet
About 1/3rd of the way down a long reply begins

http://www.superhonda.com/forum/showthread.php?s=&threadid=108177

Can't access that site

[Will2K2]

Originally posted by myeverlovinsir
Vtec engagement @2200 rpms is beneficial for fuel economy and the LEV rating Honda was aiming for. In fact the lower the Vtec engagement, usually the better.(more air/fuel allowed to get in) Much of Hondata's improvements to stock ECU's, such as the ITR tune they released for the type-S also involved the lowering of the Vtec engagement and showed the significant gains as a result. If you look at say an older prelude Vtec engagement dyno graph, it is quite obvious at 5k rpms where it engages to the larger lobes. It peaks quickly (straight up) and drops off quickly (in a curve), and below that mark it is quite docile. There are advantages to having a lower Vtec engagement, but every case is unique to the engine it's being used on and size of the cam lobes.;)

I gotta call you out on this.

Are you going to tell me that I am constantly in Vtec? Cause I spent about 1% of total driving below 2000rpm.

What would be the point of having the less agressive profile if it really does engage at lower than 2000rpm?, that range isn't used for just about ANY regular driving.

Furthermore, emissions testing and mileage (Lev, Ulev etccccc) have nothing to do with this, and they tests that are used to evaluate efficiency towards these ratings, have little are no use for data below 2,000rpm.

Hell the S-2000 has Vtec on Exhaust and Intake and Its still Ulev!!!!!

Sure some (aftermarket tuning) companies lower the Vtec engagement point a 1,000rpm or so but to think that its working from 2,000 all the way to 6,800(4,800rpm spread) is kinda ridiculous. No Honda Vtec car could possibly account for all the tuning required to run the Big Cam , both that low, and that high.

Thats why when guys do Toda B's, Jun Cams, whatever cams in B's and H's and they try to lower their crossover point, they actually lose!!!! power. ALL of the hardcore NA guys actually RAISE!!! their Crossover points (as is beneficial with any big cam)

Another point: the only reason the old Prelude (H22) and Civic/Teg(B-series) graphs are so much more agressive than ours(at the Vtec Crossover) is because of several factors.

-First they don't have variable CAM TIMING down low to help fill in their bottom end, thus making a much weaker bottom end than we do, and making the difference between their soggy bottom end and their crazy top-end even more apparent.

-Second, (and this is the important part) EVERY SINGLE one of them (b-16, b-18, H22) feature MUCH MORE AGRESSIVE cams,
AND!!!!!!!!!!!!! VTEC on both INTAKE and EXHAUST!!!!!, that is the only reason for their crossover being so abrubt. Their small cam is truly that; a cam just for idle and around town smoothness, and their Big cams are obviously pretty agressive.

As for sound, the reason that their(H series, B-Series) AEM's are louder is that because of their MUCH MORE agressive cams, their intake AND Exhaust valves are open at the same time!!!!!!! (obviously for a very very short duration), where as in our car, the two events(Intake and exhaust) happen without overlapping each other.

W

[BlasTech]

Originally posted by myeverlovinsir

The power hump most of us notice at ~4800rpms is due to a resonating air flow, that promotes the intake air to be aided along by sound waves. (Harmonics)


The sound part is a side-effect, that can be used to help measure out the optimal airflow for a certain sized tube, since the pitch of the sound is made by the frequency of air waves, and the volume of the sound is made by the amplitude of the air waves.

Don't get the impression that sound waves are causing anything, as sound is the result of a harmonic air frequency in the tube.

The idea frequency would be when the pulsations of air are proportional to the size of a tube in a way that will allow the maximum velocity to be sucked in, and my educated guess is that it would probably be the highest possible clean note before the sound suddenly jumps up an octave, or before the engine reaches its redline. A clean note represents a group of waves fitting evenly whithin the length of the tube.

[Jpax]

Oh for facks scakes.........:rolleyes:

[BlasTech]

Well, so long as nobody tries to put speakers in thier intake to create soundwaves... :angel:

[Jpax]

Originally posted by BlasTech
Well, so long as nobody tries to put speakers in thier intake to create soundwaves... :angel:

Allready been done......

[BlasTech]

:D LOL
How many hors will you get wit dat deh shit yo?

[chakra71]

i am also not sure exactly why honda made the vtec portion in our cars so crappy. a dyno chart doesn't usually show any reliable numbers under 2200 rpm, and i sure as hell can't feel it as i power thru the gears. I usually don't get under 2200 as i launch and i have some damn nice times for a completely stock car.

as far as driving goes... it's almost impossible to get the rpms under 2200 in a real world scenario (at least around here with all the hills and stuff). 5th gear at 40 mph gets close... but then i can't go up a hill and the engine lugs hardcore.

but we definatly don't have the 'real' vtec system like the K20A2. just look at the cams in this picture of the heads that was posted up a few days ago...

http://www.violentdreams.net/john/images/ep3/k20head.jpg

[myeverlovinsir]

Most of the harmful emissions are when you're idling. Honda is simply making this as economical and emission friendly by allowing a lower profile. (< 2200rpm)

What should be compared for power sake, is the size, lift and duration of the high lobes on the A3 vs. the A2.;)

[Will2K2]

Originally posted by BlasTech
Well, so long as nobody tries to put speakers in thier intake to create soundwaves... :angel:

NO SHIT!!!!!

THE 350Z has a piece that comes off the Intake manifold(I believe)

THE SOLE PURPOSE OF THIS PIECE IS TO FUNNEL ENGINE SOUND THROUGH A HOLE IN THE FIREWALL INTO THE CABIN

I SHIT YOU NOT!!!!!!!!!!!!!!!!!

[Mulder]

Originally posted by myeverlovinsir
Most of the harmful emissions are when you're idling. Honda is simply making this as economical and emission friendly by allowing a lower profile. (< 2200rpm)

What should be compared for power sake, is the size, lift and duration of the high lobes on the A3 vs. the A2.;)

By reading your other posts in the engine forum you seem to think the Si (k20a3) has different sized cam lobes. It does not have a higher profile cam lobe, as indicated in the photo above.

A quote from Honda's own site:

(k20a3)During low rpm operation,intake air is drawn almost exclusively through the primary intakevalve, thereby creating a very strong swirl effect to maximizecombustion. At 2,200 rpm, the secondary rocker arm engages theprimary rocker causing both intake valves to open for the same liftand duration, substantially increasing airflow into the cylinder andboosting performance.

(k20a2)The 200 horsepower RSX Type-S uses the same high-performance VTECdesign as the NSX,a three rocker arm system that varies the lift andduration of both the intake and exhaust valves for maximum poweroutput. At lower rpm, the valves follow low lift, short durationcamshaft profiles to help boost low-end torque. Above 5,800 rpm, theintake and exhaust valves are operated by high-lift, long-durationcam profiles, for maximum high rpm horsepower.

http://www.hondanews.com/Forms/acura/RSX/*ws4d-db-query-Show.ws4d?*ws4d-db-query-Show***003299***-wieck_media***-***acura(directory)RSX(directory)***.ws4d?acura/RSX/results(r)_text.html

[cbecker333]

Originally posted by BlairSpeed
I notice my SRI gets alot more audible when I hit 4800rpms and I notice it pull harder too. but your saying that its not vtec but its harmonic sound waves? hmmm. :rolleyes: Im sure your more educated than I on the subject but never heard of any sort of harmonics being part of performance.

The dimensions of the cai harbor one specific family of wavelengths (known as a harmonic), more than others. When your engine produces a frequencey in that harmonic, the resulting sound waves are able to play nicely with each other, instead of bumping into each other and creating disorder in the cai. heheh...I do remember physics!



It also doesnt make sense that the v-tec would engage at 2300rpms? whats the point of that? so we are always cruising in v-tec mode unless we shift before 2300rpms? why would honda do that? odd.
Dude, our car has different vtec than the other hondas, and it serves a sorta different purpose at times. Everybody get hp, torque from their vtec, but when ours engages @ about 2200 it is working to do that, and to be efficient, and to be clean (LEV-clean). Running in vtec through the low rpms doesn't eat more gas or anything...not on the k20A3. In fact, honda's recommended shift points (in the manual) imply that you really shouldn't try to use the engine under about 2000 rpms.

[myeverlovinsir]

Originally posted by Mulder


By reading your other posts in the engine forum you seem to think the Si (k20a3) has different sized cam lobes. It does not have a higher profile cam lobe, as indicated in the photo above.



The info posted by Honda is stating operation. I am concerned with geometry differences between the A2 and A3 high lobes. You think the photo shows a higher lobe in the A3? I would prefer to see the actual dims. There is a lot which looks common to both heads.

Don't think anyone has ever posted, what the profile differences are (larger or smaller). Probably because no one has this info handy yet, but a comparison would be nice.:D

[Glix]

Vtec at 2200 RPM is the base RSX we have no proof at this point that our engines are tuned the same way.

If they are then we most likely operate at 12 valves below 2200 rpm just like they do. I seriously doubt this, judging by our dyno's on hondata we do not operate the way they do, even if the engine is the same.

[cbecker333]

Originally posted by Glix
Vtec at 2200 RPM is the base RSX we have no proof at this point that our engines are tuned the same way.

If they are then we most likely operate at 12 valves below 2200 rpm just like they do. I seriously doubt this, judging by our dyno's on hondata we do not operate the way they do, even if the engine is the same.

Well, I don't know about you, but I trust the research of Hondata on this one...The length and depth of their experience speaks for itself. Hondata says 2200, I say 2200.

Hondata has also proven (to me) that the difference in dyno's is because of the dual-length intake runners on the RSX, which is replaced by a single intake path in the Si.

[chunky]

intake resonance is a real phenomenon, and it DOES help fill the cylinder with more air, which gives a corresponding increase in torque while the resonance is favorable.

When intake resonance is occuring, the pressure wave in the intake manifold runner arrives at the back of the valve at the same time that the resonating sound wave arrives at the back of the valve - this is engineered to occur when the valve is open for the intake stroke- creating a denser spot of air just behind the valve.

When the intake valve snaps shut, it creates a sound wave that travels backwards up the intake manifold runner, and then reflects back down. Simultaneously, there is a resonance of the actual air column inside the manifold runner due to the length of the tube. The trick is to get those two waves to coincide - it only happens once or twice in the entire RPM range, and you observe bumps in the torque curve as a result.

This resonance is due to the intake manifold geometry, not the air intake itself.


And i'm with the guys that say that the vtec system engages at 2200rpm.

[cbecker333]

Thanks chunky for explaining the resonance....I was a bit off...too much verbal with the herbal, again

[Mulder]

Originally posted by myeverlovinsir


The info posted by Honda is stating operation. I am concerned with geometry differences between the A2 and A3 high lobes. You think the photo shows a higher lobe in the A3?

[FROM the engine forum]... 1st stage (in the pic) representing the valve lift from the intake cam. Each valve rides independantly one their separate lobes, one valve is only slightly open to increase torque by creating a swirl effect inside the cylinder. This occurs below 2200 rpm for improved emmissions.

2nd stage shows both valves engaged through the vtec solenoid to ride on the lower profile cam lobe. (A2 has independant cam lobes for each lower profile lift) This occurs after 2200 rpm

3rd stage is high lift profile where both intake valves are made to ride off of the large cam lobe. This occurs after 4800 rpm and disengages at 4600 rpm. (or there abouts)

Hope that helps.



I was just trying to point out the fact the k20a3 does not have the high performance version of the vtec, and the k20a2 does. The k20a3 does not have a "high" lobe, nor does it have a 3 stage vtec. The k20a2 incorperates a "three rocker arm system" utilizing "low" profile camshaft lobes for the low and mid range, and a "high" profile lobe for high RPMs, on both intake and exhaust. The k20a3 version of vtec is the emissions friendly version which works only on intake. And all it does is lock the secondary rocker arm to the primary rocker (two rocker arms only) at 2200 rpm causing both intake valves to ride "one" camshaft lobe all the way to redline.

The photo above depicts 3 lobes for both intake and exhaust for the k20a2. For the k20a3 it shows 1 lobe for exhaust and 2 lobes for intake. The intake side consisting of 1 normal lobe and a mini lobe. To answer your question, the k20a2 has a bigger cam because it is the only one with the "high" profile lobe.

peace

[myeverlovinsir]

My explanation quoted above is for a 3 stage intake system that was probably only used in Japan. But utilizes a similar mechanical setup in the A2.

http://asia.vtec.net/spfeature/vtecimpl/img9.jpg

[Dunrick]

I thought it only kicked in at 2200 rpm if you stomped on the pedal...thats the whole point of I-vtec, it takes into consideration of the throttle response...Just my 2 cents, and I dont really know what I'm talking about, but this topic does need to be tackled...Peace

[myeverlovinsir]

Originally posted by Dunrick
I thought it only kicked in at 2200 rpm if you stomped on the pedal...thats the whole point of I-vtec, it takes into consideration of the throttle response...Just my 2 cents, and I dont really know what I'm talking about, but this topic does need to be tackled...Peace


Yes, I think it matters if you stomp on it or not, but don't know how the maps look in the ECU, it may extend the crossover into the 3k rpm range if little power is required, also adding to fuel efficiency during low loads. Good point. :D

VTC uses hydraulics to control the intake cam. While ECU driven, it considers more than just the throttle or TPS position; such as Air/Fuel ratio, timing pulses, injector durations, etc. are also considered. The second part of I-Vtec is a solenoid pulse, also electronically controlled.

Throttle position in the TPS is part of an ECU map and is just one part of the total equation involved in increasing/decreasing throttle response. Of course an i/h/e help in throttle response by allowing more air to flow, however anyone with hondata tune will soon tell you that