DjElucid

I haven't really been able to push my car yet.... still at 540 miles. When does the i-vtec kick in (RPM)? Does it have that kick like the preludes do? I've driven a 94 vtec prelude, and when it hits about 5400 RPM, you really feel a kick to it.

fdl

Vtec comes in very high on the TSX...6200 rpms. ...and there is little or no kick felt at all. With i-vtec you have most of you power thruogh-out the rev range..so there is no sudden surge of power.

There have been some discussions on this ...a search for vtec might yield some more info for you.

Santacruz

What iVTEC does differently than VTEC is advance or retard the phase of the cams lobes. It creates a much smoother transition...here's a good link that explains it pretty well.


http://www.carkeys.co.uk/features/FE000235.htm

moda_way

Actually, there are three lobes and the rough RPMs at which they engage is 0-4500, 4500-6200ish, and 6200ish-redline.

fdl

Are you sure about this? Can you reference a link?

DjElucid

I felt a little change in power when I hit about 4500 this morning, that's why I had asked the question about it.

fdl

From everything I have read, vtec engagement on the TSX is 6200.

Kwijybo19

For regular (as if VTEC is anything but regular) old VTEC, there are two cam lobes. One is for anywhere from 0-5 or 6k depending on the car. Then there is a second set of cams that engage high up, from the transition to the redline. In my Civic it's 5000 to the 7000 rpm redline. This gives it a kick, that most are accustomed to, especially in DOHC VTEC engines (B-series, and especially the H-series. Not to mention the C30 and C32).

Anyway, for i-VTEC, it adds variable timing control (VTC) to both the intake and exhaust, resulting in three different sets of cam lobes. The first one engages from 0-usually 3 or 4000 rpms and is designed for fuel economy. The second is the mid-range, usually from 3 or 4000 to 5 or 6000. The third is the high-performance cams that engage from 5 or 6000 to the redline. This allows the engine to be smoother across the entire rev range, instead of being smooth and then getting that kick in the arse that so many of us love and cherish (I'm one!!).

Originally, VTEC was designed to be a seamless transition across the entire rev range, where power was abundant throughout. With i-VTEC, Honda's engineers were able to smooth this out, considerably, so that the "kick" is virtually non-existent, but the surge in horsepower is still apparent. This is done through three cams, in comparison to two, which are found on plain VTEC systems.

Side note: That's why when people in their new Civic Si's install VTEC indicator lights and see them going off at like 3000 rpms, they think what the hell, it should be much higher.

-eric

fdl

Again I need to point out that every thing I have read, every publication has stated that VTEC engagement on the TSX, is at 6200 RPM. So 2 CAM lobes...on for 0-6200, and one for 6200-7100+. If you have read otherwise...can you post a link? I may be completely wrong here, I am just going by what I have read so give me something else to read

DEVO

Yes, there are only 2 sets of cam lobes. The difference is how the upper rpm lobe engages. In the old vtec system it used a single pin so the engagement could be felt... it wasn't as refined as the new system which I believe uses 3 pins (i think this is where the confusion lies) for a smoother transition to the upper RPM lobe.

Again, VTEC is always on whether you are at low rpms or high rpms. The "i" in i-vtec means that the timing is advanced or retarded depending on the RPM of the engine.

TWong1200

I personally can't "feel" the changeover. I personally like the original VTEC over my TSX's i-VTEC. Although the i-VTEC assists in gaining more torque, the feel of my B16A in my CRX is just awesome. Especially when the tires start to spin when VTEC crosses over and you fight for grip (and to keep it straight).

But they're both great though.

finalheaven

I know a couple of my friends who feel that sudden gain to feel that the car is powerful. They say they do not want a smooth acceleration but want a sudden burst when they want. I myself perfer a smooth acceleration. I guess they think it feels less powerful without it.

Ozzman

Not sure if this answers the question of 2 versus three cam lobes, but there are apparantly three sets of rockers (I don't know enough about cars to understand any of this much)

Here is the link . . .

http://hondanews.com/Forms/acura/TSX...h+currentacura

Click on Powertrain 1 and scroll towards the bottom

AdamC

Your friends need turbo cars....

MrChad

The older F22B and F23A Vtec SOHC Accord/CL engines also used 3 sets of lobes and rockers for the intake valve half of the cam too. The large rush felt for VTEC kick in the B and H series DOHC engines only happened on the Exhaust side anyway.

The later 3 lobe SOHC VTEC was a 2nd generation design primarly with Fuel economy in mind. the newer K24 engines tend to mend both the power and fuel vtec curve designs. At least on the power pistion motors (TSX and Type-S RSX)

VTEC kick in the early engines was kinda a pain to have if you ever tried to road coarse the cars. The wild kicks could be problamatic, though not to the degree of a turbo boost.

Just be very glad Honda smoothed the transition. If you really want a wicked kick just install a bottle of juice.

finalheaven

yea... most of them grew up idolizing supras.

Colin

This is incorrect. There are three lobes over each cylinder. The outer two actuate the valves directly through their rocker arms. These contact the low lift cam lobes. The high lift cam is free wheeling below 6000ish RPM. Once the VTEC controller sends oil pressure to the pin, it moves and locks the outer two rocker arms to the middle arm. This arm is riding the high lift cam lobe and forces the valves to follow this profile.

VTC (Variable Timing Control) is the "i" in "i-VTEC" This system rotates THE WHOLE intake camshaft meaning both the low and high lift lobes. The range of adjustment is around 50 degrees relative to top dead center. By continueously varying the intake cam phasing, Honda is able to lower emissions, and smooth out the torque curve. This operates in conjunction with the pin switching VTEC system.

PS. the TSX uses the 3 lobe VTEC system on both the intake and exhaust cams.

PPS. There is no VTC on the exhaust since the phasing shift is a relative shift, there is no need to rotate both intake and exhaust...

PPPS. Devo is partially correct (on the i-VTEC part) but his description of the pins is off, and there are three lobes over each cylinder (two profiles, but three lobes)

PPPPS. Mr. Chad is incorrect. The SOHC versions (accord/CL) were a two lobe system. He is correct that they are only on the intake side though. I'm not sure about the VTEC-e which is the fuel economy version, but I do know the the design staggered the intake valves opening to introduce more swirl in the combustion chamber improving fuel economy.

fdl

Thanks for this post. Let me see if I get this right. I will dumb it down but tell me if I am on the right track.

- Regular vtec engines (integra gsr etc) will have one point in the rpm range where the lower rpm profile lobes get switched to the higher rpm profile lobes.

- TSX i-vtec engine have the same thing , (which happens around 6200), but in addition on the lower rpm lobes the camshaft itself can be slightly moved or rotated to make minor adjustments before these higher rpm lobes come into play.

I am in the ball park here? If I am..my question is..why the need for the high rpm lobes at all. Can we use one set of lobes and rotate the entire camshaft throughout the entire rpm range?

Or even do something like ferrari has been doing ...

"The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft -- but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized. "

Colin

I'm assuming that in your statement above, you meant to say "lower rpm lobes the camshaft itself can be slightly moved or rotated" not "cant". If so, you are on the right track. However, the amount of cam phasing shift is HUGE! People talk about advancing timing by 1-2 degrees to tune a engine for more performance. We're taking a range of up to 50 degrees!

The most important thing that people always forget about when talking about VTEC is that it stands for Variable valve Timing and lift Electronic Control. By totally switching the cam to a different lobe, we are not only advancing timing but also increasing lift and duration. This is the magic of VTEC. We can open the valves wider and hold them open longer when we ride the "hot" profile.

Our way of doing this is patented. When Toyota needed a variable timing head, they asked Yamaha to come up with something (Yamaha DESIGNS ALL of Toyota's performance heads). The invented VVT-i. They originally had no lift and duration control. This came much later. Porsche's Variocam and BMW's Vanos system were all their verions of variable timing. It took all of them years to come up with a way to change lift and duration. Ferrari's method sounds like its a lot of work, but it is intreging isn't it? To be fair to Honda, shouldn't you expect that kind of technical wizardry in a car that costs that much? VTEC is avaialble in our least expensive cars!

fdl

Woops, ya..I meant can. Sometimes i type too fast for my own good


Well thanks for all this clarification....this is a great stuff.

Judging by some of the posts in this thread I think people have been misunderstanding how it all works.

MrChad

I'm fairly sure the F23A runs three lobes as it requires service limit inspection of a Primary, mid, and secondary lobes--all on intake all having different lifts.

1.4872" lift / 1.5640" lift / 1.3575" lift respectively.

Exhaust is 1.5105" lift only.

The above don't apply for F23A non-vtec DX 98-02Accords.

If I'm incorrect I'm sorry, but I'd find it odd that intake has 3 lob spec difined.

AdamC

Colin did you go to school for this?
I haven't came across an Acura salesperson as knowledgeable.
Great and detailed explaination there man.

Colin

Actually you're close. The cam (remember its one cam in this design) DOES have three lobes over each cylinder. One lobe is a low lift intake, the middle one is an exhaust lobe (which operates both exhaust valves via a rocker arm), and the other end is a high lift high duration intake. They are arranged like I E I. This is why you see three different specs for the lobes.

AdamC. I've been to several Acura product introductions on the mainland, but mostly I just like to know how things work in our cars.

TWong1200

First of all, Collin is completely correct in his explanations. Thanks Collin. Saved me some time not having to type it out.

fdl.....The reason why the high rpm lobes are needed is this. If, for example, we omit the low lift lobes and kept the valves opening on teh higher lift lobes at all times and just vary the cam timing, we get a motor that will lope at idle. Have you ever been in a car with a huge high lift cam at idle? It just lopes along struggling to stay alive. Sure this may be ok in race apps but on production cars, the average consumer would not like it. This is the great thing about VTEC, you get the benefits of a smooth idle and the performance advantage of a high lift/long duration cam profile. In essence, the best of both worlds.

Toyota's VVTL-i is the same technology as the TSX's i-VTEC system. Variable intake cam timing and lift control as well. Albeit not the same design as Honda. Oh yah...and 11.5:1 compression ratio!!!

DEVO

Ideally you want an infinite amount of lobes, each tuned for a certain rpm range.... since that isn't going to happen for a million reason you comprimise. By having 2 cam profiles (forget about the actual number of lobes which isn't important for this point) you get the best of both worlds... tooling around town and putting a grin on your face.

Thanks colins for setting us straight.

MrChad

Um--yes but if you look at the actual Cam it has 5 lobes per cylinder.

Exhaust,Primary(intake),Mid(intake),Secondary(inta ke),Exhaust.
On the SOHC when the VTEC is activated the two inner Intake rocker arms Primary and Secondary both then follow the path of the Mid lobe. If you count you will see 20 cam lobes on the SOHC vtec F-series engine.

The engine has only 4 rockers arms. You were correct though -- the exhaust rocker arms do sit outside splaid around the intake rocker arms.

The DOHC engines like the H22A do have the configuration of small lob, big lob, small lob. And again both outer lobes lock to follow the center one as well.

Colin

Chad, you're correct of course, there have to be exhaust lobes in addition to the intake lobes, and this totals 5 over each cylinder. I was thinking only about the intake track when I said three. Sorry for the confusion on this matter. Man, that sure is a "hard working" cam huh?

dbjb

i completely agree. i like my TSX, but I love the VTEC "kick" at 6k RPM in my S2k.

1killercls

Cool feature...Cut & Paste.

MrChad

Yea, I couldn't believe it the first time I realised it had 20 lobes, on 1-cam.

For an engine as old in technology (Dates back to early 90's and earlier then that if you count non-VTEC versions) I'm still amazed by the old SOHC VTEC F-series. It took how many years for other mfg. to make a 150hp/152torq engine? I have to laugh when I see Torg and HP numbers from many mfg. Super Charged and Turbo'd large displacement 4's.

And the new K-series cylinder head design (TSX,RSX,etc.)
THE Mighty K!
the iVTEC part is chump compared to the amount of casting perfection Honda put into that head. I mean think of this, the Type-R and Euro-R version of the K-series don't have any special port or polishing like all previous gen Type-R's did, wow!

I can't wait to replace the wife's car with a TSX in a year or so

Colin

Whatever FWIW, if I cut and paste, I credit my source. If I write it myself for my webpage, AND THEN cut and paste it here, I don't credit myself :shakehd:

Bass Mechanic

Colin is exactly on target, i was reading this thread hoping someone would spell it out, good post Colin.
i would also like to add that there has been some research into the idea of using electronic valve control. i belive ford as bad as i hate to admidt it was working on such a design. the concept is that if you can use an electronic actuator or solinoid to open and close the valves by computer control you would have no need for a cam. the computer can determin the timing to open the intake and or exhaust valves and determin how far they open and and the overlap between exhaust and intake timing. not only that unlike a cam lobe the valves would be able to open and close more rapidly because they dont have to follow the ramp of a cam lobe.
last i heard the engine does work however the electrical system had to be increased to i think 48 volts to handel the power requirement to actuate these valves. i also heard that thgere was a LOT of valve noise due to them being opened and shut so fast. im sure they would close and hit the cylender head with a pretty loud snap.
i really wish / hope honda is working on a design, if they can work the bugs out they would definitly have the lead on cylender head proformance technology. im sure someone had a patent on it by now so who knows if it will ever become commonplace.

RogerPodacter

A while back i read somewhere that, soon all cars would run from 48 V systems to account for increased demand in complex electrical systems...

fdl

If I may add to this already great thread ...

Check out this link for some good info on the differnet vtec systems Honda uses. Unfortunately i-vtec isnt included.

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