VTEC Crossover
Thread Starter
Joined: Nov 2002
Posts: 326
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From: Oakville, ON, Canada
VTEC Crossover
Hey All,
I have done a couple searches but was unable to find any posts on understanding the benefits of changes the vtec crossover point. I dont understand why you would want to....
is that keeping the 4400 rpm on my set up will negatively effect my power because it is opening its opening too soon and causing a power loss?
any help greatly appreciated or links...
YV
I have done a couple searches but was unable to find any posts on understanding the benefits of changes the vtec crossover point. I dont understand why you would want to....
is that keeping the 4400 rpm on my set up will negatively effect my power because it is opening its opening too soon and causing a power loss?
any help greatly appreciated or links...
YV
Honda-Tech Member
Joined: Oct 2001
Posts: 7,536
Likes: 1
From: Edgewater, MD / La Jolla, CA
Re: VTEC Crossover (youngvedder)
you basically want the vtec to hit so it's a smooth transition on the torque curve. ideally vtec should activate where the torque curve starts to drop
Thread Starter
Joined: Nov 2002
Posts: 326
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From: Oakville, ON, Canada
Re: VTEC Crossover (Tweakmeister)
ahh, so as the power starts to drop off the VTEC there is to pick up where it left off......but, wouldn't engaging VTEC early prolong the Torque curve?
just trying to understand....
YV
just trying to understand....
YV
Joined: Apr 2003
Posts: 1,296
Likes: 1
From: EJ2 type DX number 511,096
Re: VTEC Crossover (youngvedder)
in order to vtec to be effective, you have to set it high enough to where it will make power, but not so low as it will bog the engine. i think you will get a better understanding of this if you know how vtec works.
http://www.geocities.com/gkurka2001/VTEC/VTEC.htm
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by some website »</TD></TR><TR><TD CLASS="quote">Honda's VTEC (Variable-valve timing and electronic-lift control) technology to maximize efficiency. In general, VTEC works by switching between different sets of lobes on the camshaft. It's the shape (or grind) of the lobes that determine the timing and lift of the intake and exhaust valves. Initially VTEC technology was used to increase engine performance, switching to an aggressive cam profile at high rpm to increase torque and horsepower and then returning to a more traditional profile at lower rpm</TD></TR></TABLE>
http://www.geocities.com/gkurka2001/VTEC/VTEC.htm
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by some website »</TD></TR><TR><TD CLASS="quote">Honda's VTEC (Variable-valve timing and electronic-lift control) technology to maximize efficiency. In general, VTEC works by switching between different sets of lobes on the camshaft. It's the shape (or grind) of the lobes that determine the timing and lift of the intake and exhaust valves. Initially VTEC technology was used to increase engine performance, switching to an aggressive cam profile at high rpm to increase torque and horsepower and then returning to a more traditional profile at lower rpm</TD></TR></TABLE>
Member
Joined: Apr 2003
Posts: 2,289
Likes: 0
From: Windsor, PA
Re: VTEC Crossover (skribblah)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LONE LUDER »</TD></TR><TR><TD CLASS="quote">CAMS:
Many people think that you can gain massive amounst of power by making VTEC engage at, oh, 3500rpm. Well, you won't. The way VTEC works is by giving the best of both worlds, higherlift cams for up top, with low lift cams for down low. Honda conbined the two and you have both on ONE camshaft.
HOW VTEC WORKSYou have two smaller lobes that the valves ride on most of the time, called primaries. The VTEC lobe is larger and lifts higher but sits in the middle of these two and has a seperate rocker that isn't connected to anything. When not in VTEC, it just rides by itself. The two primary lifters stay on the valves at all times, BUT when VTEC kicks in pins lock the primary rockers and connect them to the VTEC rocker. Then the VTEC lobe forces the two rockers to lift higher and open the valves more.
Remember when I talked about airflow? How you can't have too much or you disturb the balance of things? The same applies in cams. If you have too much air/fuel moving in at a low RPM, then you aren't gaining anything, you're losing it. So when you make VTEC engage (using a VAFC or standalone) too early, you are trying to outflow the flow. There basically isn't enough air movement to handle what you're trying to do. This is a problem the old V8 guys have to deal with. If you've ever heard a V8 that idled like hell, with a nasty lope to it, that's because he had a higher lift, longer duration cam in there. It was flowing too much for low end and that causes it to idle poorly. But it sounds phat as hell. They have poor low end, but gain much more up top, where they race. Anyway, I digress....
</TD></TR></TABLE>
this thread is stickied at the top of the prelude forum. " a few things to think about when going NA"
https://honda-tech.com/zerothread?id=180883
Many people think that you can gain massive amounst of power by making VTEC engage at, oh, 3500rpm. Well, you won't. The way VTEC works is by giving the best of both worlds, higherlift cams for up top, with low lift cams for down low. Honda conbined the two and you have both on ONE camshaft.
HOW VTEC WORKSYou have two smaller lobes that the valves ride on most of the time, called primaries. The VTEC lobe is larger and lifts higher but sits in the middle of these two and has a seperate rocker that isn't connected to anything. When not in VTEC, it just rides by itself. The two primary lifters stay on the valves at all times, BUT when VTEC kicks in pins lock the primary rockers and connect them to the VTEC rocker. Then the VTEC lobe forces the two rockers to lift higher and open the valves more.
Remember when I talked about airflow? How you can't have too much or you disturb the balance of things? The same applies in cams. If you have too much air/fuel moving in at a low RPM, then you aren't gaining anything, you're losing it. So when you make VTEC engage (using a VAFC or standalone) too early, you are trying to outflow the flow. There basically isn't enough air movement to handle what you're trying to do. This is a problem the old V8 guys have to deal with. If you've ever heard a V8 that idled like hell, with a nasty lope to it, that's because he had a higher lift, longer duration cam in there. It was flowing too much for low end and that causes it to idle poorly. But it sounds phat as hell. They have poor low end, but gain much more up top, where they race. Anyway, I digress....
</TD></TR></TABLE>
this thread is stickied at the top of the prelude forum. " a few things to think about when going NA"
https://honda-tech.com/zerothread?id=180883
Honda-Tech Member
Joined: Jan 2003
Posts: 8,132
Likes: 5
Re: VTEC Crossover (youngvedder)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by youngvedder »</TD></TR><TR><TD CLASS="quote">....but, wouldn't engaging VTEC early prolong the Torque curve?</TD></TR></TABLE>
Think of it this way...
Imagine you could manually turn VTEC on & off. Do 2 dyno runs, first with it turned off, then with it turned on. Superimpose the curves on the same plot. At low rpm you'll have more torque & power with it turned off. At high rpm you'll have more torque & power with it turned on.
SOMEWHERE, the curves will cross each other. That's your crossover point. At any particular rpm you're using the cam profile that gives you the most power at that rpm.
Think of it this way...
Imagine you could manually turn VTEC on & off. Do 2 dyno runs, first with it turned off, then with it turned on. Superimpose the curves on the same plot. At low rpm you'll have more torque & power with it turned off. At high rpm you'll have more torque & power with it turned on.
SOMEWHERE, the curves will cross each other. That's your crossover point. At any particular rpm you're using the cam profile that gives you the most power at that rpm.
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