4drcivic2k1

iTrader: (2)

I'm going to get a multimeter on it tonight and see.

bobsagator

iTrader: (13)

What would be the advantage of VTEC engaging at 2500? Minor fuel economy advantage at low rpms? If VTEC engages at 2500 and is almost always engaged, then what is the benefit of VTEC?

82801BA

Increase your horsepower at mid rpm, while providing excellent low end fuel economy. That's what the EX is for.

Sweet2K4EX

I don't know...my car feels a kick at about 4300 rpms...I have never felt a kick around 2500-3000 WOT of half...

82801BA

I hear a sound change and feel the kick at 2500 rpm full throttle. Got an Injen CAI but the lower part broke so using only the top part(but it sounds better than using both parts)

Jrfish007

iTrader: (3)

Nope not true, well mostly not true. The Kseries motors have far more ocmplicated cams than the d's or B's. What you ment to say is the D's work the same way as the B's, but with a single cam and VTEC only on the intake.


K series have VTEC-i, the i (which stand for intelligent I think) means the cams can change phase too. Let's not get into that since that adds a whole new dimension to VTEC. Long story short, while VTEC-i does change camm lobes on the VTEC valve, it does ALOT more thanj ust that.

But becasue of the phase change it can have a much wider range in which it can engage or disengage the VTEC, far more complicated, so the engeagment points will not be the same.

***Added: Also all Kseries motors have 5 speed mated to them which means at 70 MPH your RPM is around 2200, so if you have such a low idle, you can still get good MPH at normal speeds with a lowwer VTEC point. Honda will set the VTEC so that during normal highway cruising speeds the VTEC is on becasue more air=more gas, thats just a stupid idea. VTEC is for added power.

Jrfish007

iTrader: (3)

As for the point it engages, not sure, I do know the older d16's where suppose to enage at 4500-4900 RPMS.

Jrfish007

iTrader: (3)

Lets see, at 60-70 MPH, I'm guessing you are not in the low end of your RPM range, probably around 4-5,000 RPMS? Why would VTEC be engaged? You will be using more fuel if VTEC is on, more air=more fuel.

Sweet2K4EX

Well, I have a CAI and catback (2.25)...I feel the slight kick around 2500 but that only feels like some lag around 1000-2000...the big kick of horsepower is at 4500...

Sweet2K4EX

When I am crusing around 60 or 70 mph... I am only at about 3500-3800 rpms...so the motor is not using alot of fuel.

Jrfish007

iTrader: (3)

There is anouther effect you may be feeling around 2,500 RPM (I'm not sure if this is the right reason or not, but it is a possible answer). Anyway, every intake manifold has a specific runner length that at a certian point the can cause compression wave in the intake manifold. These compression waves come from the sound travelling out of the cylinder when the intake valve is open, going up the intake runner, bouncing off the intake pelum at whcich point it will create a sound wave which is strong enough to compress some air. If everything lines up just right, that wave of compressed air will travel down the runner right into the heads, and if the valve is open into the cylinder, hence causing more air to get in, thus a small amount of power. This only works for a range of about 500-1000 RPMS though. But this DOES make a difference, if you don't believe me, take a look at an 00-03 (ithink those are the years) M5 motor, and I think newwer M3 motors. If you know what to look for you will see BMW went so far as to creat a variable intake runner length manifold. That is expensive and only ever been seen on F1 cars. Believe me when I say this does happen, BMW spent million on harnessing this effect to be used over a broader range of RPMS.

Like I siad, this may not be what happens at 2500 RPMs, but it might be. Honda has a wierd intake manifold on the D17, not sure what that does to this effect.

hotrodcivic2004

wow when i'm 'cruising' at 60-70 i'm at 2800 rpm...in an auto yea, but what gear are u in? 4th?

Jrfish007

iTrader: (3)

LX/DX or EX. they have different gearing and hence different RPMS they cruise at. You probably are right, I haven't driven a 5 speed civic in a few months, so I forgot the RPMs everything goes at. But my point still stands that if VTEC engages at 2500 RPMS, at 3500, you will be consuming lots of gas, well maybe not lots, but more if VTEC is on.

4drcivic2k1

iTrader: (2)

The cams on a K series are no more complicated than those on a B series.

It does indeed stand for intelligent. The cams do not change phase. They use variable cam gears to adjust cam timing relative to the crank angle. This is called VTC. The VTEC mechanism is the same as the b series for all intensive purposes.

Somewhat true. The engagement point are not the same.


Not all K series. I know of automatic K series, as well as 6 speed.

gearbox

iTrader: (95)

My vtec light stays on constantly as soon as rpms hold at 3k. Usually this happens at 68mph on my auto.

Jrfish007

iTrader: (3)

So what K series auto has the 4 speed transmission? My Accord has a 5 speed auto, the CRV, Element, and the RSX all have 5 speed autos. Yeah some have 6 speeds, but that still means lowwer RPM at 60-70 which still falls under my point.

Jrfish007

iTrader: (3)

Okay, the cams them selves are the same, but the VTEC system is not. The lobe rocker assymebly yes, but B's don't have the variable cam phase (or what ever you call it). Comapnies like AEM sell adjustable (manually adjustible) cam gears for these engines. I've built 2 B16's in my basement, taken the heads and made sure everything was timed myself. I know the B's don't have variable cam shaft timing. If you change the cam timing you change the the timing the valves open and close, hence you have changed teh cams "apperent" profile to the engine, so this can very the time that the VTEC system should engage.




You say it changes the cam profile according to the crank. I say the crank is connected to the rods which are connected to the pistons. If you change the time the valves open and close accordinding to the piston, to me that sounds like you've changed the phase (or timing) of the cam. I guess I shouldn't say phase, how about cam timing? That sounds more appropiate.

4drcivic2k1

iTrader: (2)

The difference is that the K series can adjust the VTC on the fly. The B series cannot. Agreed adjusting cam timing can have an effect on where VTEC should be engaged, which is what the K series ecu is designed to do. Optimize cam timing, valve lift, and ignition and fuel timing to produce an effiecient engine.

4drcivic2k1

iTrader: (2)

You said 5 speed. I automatically assumed manual transmission. I do not believe any of the autos are 4 speed.

Jrfish007

iTrader: (3)

Yeah, that was my whole point, teh K series can change cam timeing on fly, hence VTEC should come on at different times, which adds a whole new dimension to this discions. That's all.

Jrfish007

iTrader: (3)

lol, I get a lot of people on that. But really the gearing from the auto to the manual is very simliar, 0.10 difference I think. I simply siad 5 speed becasue my point was that the extra gears and torque can allow for taller gearing that let for lowwer RPMs at higher speeds. Hence VTEC can kick in lowwer with out being on at highway speeds. So while my Accord is at 2,300 RPMs at 65 MPH, a civic is around 3,500 RPMS. So say my Accord has a stagnet VTEC engaegemnt point just for this conversation purpose of 3000, crousing down the highway it will not be on, that's a good thing, less air=less gas. The civic on the other hand that is going about 3,500 Rpms with a enagement point of 3000RPM will have it on the enitre time. To me this doesn't make sence because what is the point of VTEC if it is always on, why not just put a more aggressive cam in to start with and cut down the wieght of the engine by not having VTEC. So my though is that VTEC should not be on when in top gear at 65-75, other wise you are using lots of gas when just crusing down the road, which for a civic is around 3,500 to 4,000 RPMS. So it make sence to me that the VTEC would kick in just after 4,000 RPMS somewhere. It also makes sence that VTEC would be constantly engaged if you where "getting on the car" or racing, so when you shift at the red line, and drop your RPM, you should still be in the VTEC range, but nobody is arguing that, I hope. I could be very wrong,but that's what makes sence to me

DaddyFatSacks

I'm pretty sure the way VTEC-e work is....

We run 1 valve per cylinder till 2500 rpm's to give good low end and idle.
Then 2500 to VTEC we run 2 valves per cylinder.
And at VTEC to redline we run the bigger lobe and all valves.

I'm pretty sure thats the way it explained it in a brouchure.

4drcivic2k1

iTrader: (2)

Not quite.

We run 3 valve till VTEC. Then 4 valve till redline. There is no "big lobe."

Jrfish007

iTrader: (3)

D16's worked this way. Below is a picture of cam from a D16. You can see each cylinder has 5 lobes, 2 out, 2 normal in, one for VTEC. I haven't see the D17 cams, so I can't say.

4drcivic2k1

iTrader: (2)

The D17 has 2 Intake lobes. Low and High. One valve is always on each, then at VTEC both valves are on the high.

Jrfish007

iTrader: (3)

Yeah I know, I just saying that the other guy was thinking of the D16. By having only two intake valves you save lots of wieght on the camshaft, which is a really good thing. Adn I have not seen the D17 cam, so I can not use the cam to ilistrate how it works. That's all.

82801BA

Also save on the extra rocker, and can actually make the engine head/block even more compact than D16.

Jrfish007

iTrader: (3)

Very true.. good point

82801BA

This makes more sense because Honda manufactures the Civic only slightly smaller than the Accord, but it almost has the same strength of Accord. To keep weight lower, I think Honda made very good weight reduction on engine and transmission.

Jrfish007

iTrader: (3)

Bigger difference than you may think.

Accord is 14 inch longer, almost 5 inch wider and about the same height. Remeber this is this is the first Accord that is in the Mid size range. Previous Accord where actually close to the curretn civic, so 98-02 Accords are close to civic. (which is still a comact car.