VTEC removal: can it be done?

Ok, here is my setup: '02, 27000 kms (>10,000 kms this year , K&N, Micon, PCIII, O2 Elims, absolutely aweful transition. I'll post some video of the transition, it's completely rediculous. I have a host of other things to tweak prior to going down this road but I was hoping someone (Lgn001) would say that its potentially as easy as swapping lifters. Also, I assume that the bike has roller lifters (which may not be the case) so lifter wear patterns shouldnt be an issue.

In my opinion the 6th gen guys put too much faith in the fact that vtec actually works significantly at low rpm. Serioulsy, how often do you get on the throttle stop at 4500 rpm and expect hard acceleration. You dump a gear and get the engine spinning.

I believe at least a portion of the reason it was implimented in this bike was to improve VE and emissions. Whenever I'm riding the VFR I pretty much run above 4000 rpm to smooth it out as it feels a lot like a v-twin below that. I believe if you followed the torque curve on its trend back below the vtec transition you would only be a few ft-lbs low and you'd just have a much smoother riding bike.



Wesley J

 

Aw, not again! Yet another thread about VTEC that went south and became annoying. This one had potential because it asked a very specific technical question - albeit one that has been discussed before.

 

Nope, the lifters (or "followers") are flat. They almost have to be in a DOHC engine, particularly a small displacement high RPM engine, for two reasons;

1. A roller lifter has to be keyed, or retained in some fashion, so it cannot rotate in the lifter bore.

2. Rollers and their associated considerations add weight, take up space and cost more, weight being the key issue. More weight equals bigger valve springs, more parasitic power loss, etc.

And just to feel myself type, and also at the risk of offending my fellow gearheads, all normally aspirated engines (i.e. non-supercharged) need a high velocity airstream for efficient cylinder filling, regardless of the RPM. At a low engine RPM, a single valve of a given diameter with a complimentary intake port will maintain a much higher velocity than two valves of the same diameter, all other factors being equal. If you design a cylinder head to efficiently fill a cylinder in a given RPM range, the RPM ranges above and below the design range will become less efficient. There is no way around this. The basic design can be optimized and fooled with to make it less of an issue, but it will be an issue.

So I guess my point is that even if the VTEC operation was eliminated and the fuel/ignition remapped successfully to keep all of the operating parameters where they should be, the engine will be less efficient in its lower RPM range than it is now, simply because the cylinders will not be getting filled as much as they currently are with two valve operation. Where exactly I haven't a clue, but I would guess below 5000 RPM might be pretty flat.

And again, you never know until you try. Other than the oil passages and mounting locations for the various VTEC bits and pieces, are the ports, combustion chambers and piston crowns the same as the 5th Gens? Who knows?

From my perspective, the VTEC idea is a decent engineering solution to the physical reality of engine design limitations and trade offs. Perhaps not the best or well-executed, but it is what it is. Personally, I don't care for the intake noise between 6400 and 8500 RPM, so I downshift twice instead of once if I am feeling intolerant at the time. :smile::smile:

 

albeit one that has been discussed before

Not to be an ass but if you're gonna bother posting this please link to it as my searches came up with FKL.


Nope, the lifters (or "followers") are flat. They almost have to be in a DOHC engine, particularly a small displacement high RPM engine, for two reasons;

I would have thought that the benefits of the drastically better lobe profiles gained from a roller would have relagated all little motors to rollers decades ago.

1. A roller lifter has to be keyed, or retained in some fashion, so it cannot rotate in the lifter bore.

2. Rollers and their associated considerations add weight, take up space and cost more, weight being the key issue. More weight equals bigger valve springs, more parasitic power loss, etc.

Good points

And just to feel myself type, and also at the risk of offending my fellow gearheads, all normally aspirated engines (i.e. non-supercharged) need a high velocity airstream for efficient cylinder filling, regardless of the RPM. At a low engine RPM, a single valve of a given diameter with a complimentary intake port will maintain a much higher velocity than two valves of the same diameter, all other factors being equal. If you design a cylinder head to efficiently fill a cylinder in a given RPM range, the RPM ranges above and below the design range will become less efficient. There is no way around this. The basic design can be optimized and fooled with to make it less of an issue, but it will be an issue.

Yup, no argueing there, all pretty basic stuff. The thing is, these little motors still dont make any torque even with vtec so why bother? Emmisions must be the answer
So I guess my point is that even if the VTEC operation was eliminated and the fuel/ignition remapped successfully to keep all of the operating parameters where they should be, the engine will be less efficient in its lower RPM range than it is now, simply because the cylinders will not be getting filled as much as they currently are with two valve operation. Where exactly I haven't a clue, but I would guess below 5000 RPM might be pretty flat.

You betcha, kinda like I was getting at with the torque curve extrapolation above. Even a 10% reduction in torque is what, 4 ft-lbs in that RPM range? Remap would be maditory to keep from smoking a piston.
And again, you never know until you try. Other than the oil passages and mounting locations for the various VTEC bits and pieces, are the ports, combustion chambers and piston crowns the same as the 5th Gens? Who knows?

From my perspective, the VTEC idea is a decent engineering solution to the physical reality of engine design limitations and trade offs. Perhaps not the best or well-executed, but it is what it is. Personally, I don't care for the intake noise between 6400 and 8500 RPM, so I downshift twice instead of once if I am feeling intolerant at the time. [/QUOTE]

Ah ha, so you dont use the "extra" torque either. ;-)

 

idunno.. the grunt and wicked V4 sound that's produced when ya open her up at 4grand is amazing. The power is there, it needs to be taken advantage of.

 

I make use of the low RPM torque from this motor. Lately I've been doing an experiment in which I commute in 8 valve mode only (shifting at about 5000-6000 in most situations). The bike moves along effortlessly and my fuel economy results have been pretty promising thus far... I'll have to wait until this tank is used up before I can accurately calculate it though.

 

hey Wesley, what PC map are you running with this set-up? That might attribute a lot to that harsh transition.

 

Not to be an even bigger ass, but I don't want to.

 

$h!t... I'd like to do #2

...and I don't care how big an ass anybody thinks I am. :bootyshake2:

 

Alasskan, unfortuntely you failed.

For the rest of you, here's how I spent my morning:

 

I don't think I failed.

 

Your welcome. I've spent about 3 weeks on the road this spring (in Cali, BC and Alberta) and have to as that that morning was just as, if not more magical than any others. There's something to be said about riding alone.

I came to a clearing/meadow and there was a black bear running along side the road. He was a bit startled by the sound of my bike so I pulled in the clutch and hit the kill. He ran along for a while then crossed the road casually about 10 feet in front of me. Fantastic.

Wesley J