bz268

The theory behind VTEC is that as the engine spins faster and faster, the time for the fuel to be sucked into the engine reduces. Therefore, as the engine spins faster and faster, there is not enough fuel for the engine to burn.

I can see that VTEC helps the engine to produce constant output. In everyday driving, what does VTEC help? I mean... does it help the car go faster? does it help me if I want to past another car? or... If the TSX doesn't have VTEC, will it drive the same? How would it drives with or without VTEC?

Dan Martin

Here's your reading assignment for tonight: http://auto.howstuffworks.com/question229.htm

Once you get through that, I'll get you a thread on the differences between VTEC and i-VTEC.

bz268

This seems to be a better page:
http://auto.howstuffworks.com/framed...tec/index.html

As these pages have said, VTEC gives you constant power. but I already know that. However, I can see that the major benefit to have "constant power" is to save you gas and have better milage. I don't see other benefit.

Dan Martin

I'm not sure if I understand what you're asking, but I'll try to answer it this way:
There are two cam profiles in our car: one for high rpms and the other for low. The VTEC system automatically switches between the two to optimize performance and fuel economy. If we only had one cam profile, we would need to compromise on either low end performance or high end performance .
i-VTEC also adds variable timing control (VTC) to smooth the transition between the two cam profiles and give another increase to fuel economy. i-VTEC is the reason why you can't feel the kick between cam profiles like you could on older VTEC engines.

bz268

So VTEC is for fuel economy...

...Turbo is for power.

jlukja

Its not that simple. VTEC allows you to optimize power output along the entire rev range. So you can say that it IS for power too.

Dan Martin

Where did turbos come into this?

VTEC allows use of two cam profiles so you get optimum power and fuel economy. There's no reason a turbo can't be used on a VTEC equiped car.

bz268

Hmm.. sorry... let me try again...

VTEC for constant power... optimized power...
Turbo for added power...

"constant power" is the same as "optimized power", isn't it?

So... hmmm... by not lossing power = give you more power?

So... if two TSX. One with VTEC and the other one without VTEC, the one with VTEC will drive better because the one without VTEC is "lossing" power as it goes.

hmm I am not sure I am making any sense.

CarbonGray Earl

Not being a jerk, trust me....how old are you? Please be honest.

bz268

Can't tell you.

Dan Martin

The car with VTEC will have a wider power band. A car without VTEC could be tuned for high top end performance but it will likely lose power on the low end. The reverse is also possible. With VTEC you can optimize for both.

xizor

this thread hurts my head

CivicEx1998

thats not entirely true. Hoop in a RSX S, DC5 EP3, CL7 and u can fell Ivtec kick in.
but i agree with u, that TSX, accord, Base RSX doesnt really feel ivtec kick in.

mg7726

VTEC's main mission in life is for fuel consumption purposes. it's secondary objective is to give you whatever extra hp honda can squeeze out. get it?

jlukja

I think we have our answer.

aznt1217

haha he can't tell us his age...
Well good thread all the VTEC and i-VTEC answers are correct and awesome, but I still don't see why a turbo was brought up. turbo is totally different and so is supercharging... that is to the dude who can't tell us his age.

CGTSX2004

iTrader: (1)

I think our threadstarter needs to start here...

http://auto.howstuffworks.com/question562.htm

BusyShifter

By referring to turbo-like, bz268, I think you mean VTEC is something that gets turned on at higher RPM, which is not the case.

I did not know much about VTEC before reading this thread, and here is what I get out of it from reading the links posted here.

First, a given of how engine works is it does not provide the same horsepower through out the whole RPM range. The horsepower output of an engine changes as the RPM changes. So the "constant" in constant power output is only a relative term.

An engine with no VTEC cannot be optimized in both low and high RPM. It either suffers from poor fuel efficiency in lower RPM, or a signficant reduced horsepower output at higher RPM. However, VTEC allows the engine to have a dual-system that optmized for all RPMs.

youngTL

and
@ this thread!

The only way you could say power delivery is constant is that the DERIVATIVE of the power curve is constant (at least until it levels off at the very end).

Here's a dyno from the Temple of Vtec (at www.vtec.net)
http://sohc.vtec.net/news_files/102319/04tsx_ck.gif
It shows how the derivative of power is fairly constant (it does change a little bit) but on the TL dyno (which has strictly VTEC)

http://sohc.vtec.net/article_files/1...tldyno_tov.gif
you can see that the power is linear most of the way, but it levels off at the top end much sooner than the TSX.

Belzebutt

How's this different from the BMW variable valve timing, VANOS or whatever? Don't they have an infinitely variable system, unlike the VTEC's two profiles?

ldubuc

Here is my 2c. mecanicals engines are a compromise, vtec permit to extend this in the upper rev of the engine, ivtec however can be used on all rpms. so my guess is, on everyday driving you use the I in ivtec, pass 6,000 you use vtec. People buy Hp but use torque everyday.

ld

Motohip

In the simplist of words, VTEC is like having 2 cams. A street cam and a race cam. You can't idle smoothly with a racecam and you don't have much power up top with a street cam, so you have the best of both worlds.

stogie1020

If one train leaves New York headed West at 12:47 pm, and another leaves San Francisco headed East....

my brain hurts....

Press gass pedal, car goes vroooom..... (looks good doing it, too)

aaronng

You're confusing the 2 parts, Variable Valve timing and cam profile changing.

Variable Valve Timing: Changing the phasing of the inlet cam so that the valve timing changes in relation to the exhaust valve. Let's you improve fuel consumption as well as slightly improve low rpm torque. BMW uses this in VANOS (inlet) and Double VANOS (inlet and exhaust), Toyota with VVTi (inlet only), Double VVTi (inlet and exhaust, used only in JDM Toyota Altezza with 3S-GE), and Honda in iVTEC under the VTC part (inlet only)

Cam Profile changing: Cams can only be optimised for a certain RPM range. So if you have high rpm cams for 6000-8000rpm (for example), then your torque below that 6000rpm will be greatly reduced. The way to overcome it? Put in 2 cam profiles! One for idle to 6000rpm, and another for 6000-8000rpm. Of course, you don't need to put 2 camshafts for each inlet and 2 for each exhaust, you just add additional lobes to the existing 2 camshaft. Power optimised engines have cam profile changing on both inlet and exhaust, while economy ones have it on inlet only. What is changed is the valve lift and duration. This is Honda's VTEC, iVTEC (VTEC part), Toyota's VVTLi, Mitsubishi's Mivec, Nissan's VVL. BMW has a similar system called Valvetronic, but it doesn't work through the cams. Instead, the valves are controlled hydraulically, so they can adjust valve lift and duration directly.

Belzebutt

Thank you