why can't the vetc come on sooner?
Thread Starter
Joined: Nov 2002
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From: SF Bay Area
all of you good point and i feel enlightened. no complaint here, i love the dual personality of the engine performance....just curious if cake can be eaten too....i loved the face in the wind and 4 bbl examples, i am old enough to relate to both.
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Joined: Aug 2003
Posts: 3,660
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From: Midlothian
Yes they have to please a large population spanning tree-huggers and those that could care less about anything other than their personal gratification and have to dump the cats, but all the mfr's emissions bogeys go into the dumpster at WOT - they are tested for emissions compliance using a standard "test loop" which simulates driving conditions that are far from the ones we enjoy.
I think Honda has found a terrific balance; I first experienced VTEC magic on the first car to have it - the NSX, and when I bought mine and first warmed it up, found an open stretch of road on the return from North Carolina to Richmond, the sound and feel of the VTEC transition still echo mellifuously in the pleasant memory section of my cluttered mind.
I think Honda has found a terrific balance; I first experienced VTEC magic on the first car to have it - the NSX, and when I bought mine and first warmed it up, found an open stretch of road on the return from North Carolina to Richmond, the sound and feel of the VTEC transition still echo mellifuously in the pleasant memory section of my cluttered mind.
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Joined: Apr 2003
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From: Hawaii
Hey BenR...
I have to agree with both you and XViper... what XViper is saying is true, basically going to the basics where too much of anything isn't good, while your argument is like mine where if the timing of the engagement is set intellegently, there is some benefit.
I'm not as old as XViper (no offense intended) but I was into racing when using longer duration, big lift cams caused messed up idles, had poor low end power but was a blast at mid to upper rpms. On those cars, I had a race cam on my Rabbit GTI and if you went WOT at the wrong rpms, it would bog, maybe stall. In order to drive it on the street, you needed to keep the throttle closed just enough to maintain a high vacuum reading (I had a vacuum gauge installed back then).
On NA cars, you need air velocity (speed) to fill the cylinders with air at lower rpms... so a smaller port/opening is desirable whereas at higher rpms, you need to let the motor breathe so you need to remove any intake restriction that may impair power output.
With today's technology and equipment, it wouldn't be hard to squeeze out some power by lowering the VTEC point a little and like I said earlier, it'll remove that kick you'd feel at 6000 rpms but will provide a more linear power delivery. The problem is that along with the cams, the ECU switches to the high-cam map which doesn't change if you move the transition point lower, like say 5700 rpms. You're still going to be on the same ECU map for the low-cam when VTEC engages at 5700 rpms, and will change to the higher map at 6000 rpms (or wherever the precise MAP transition point is).
I have to agree with both you and XViper... what XViper is saying is true, basically going to the basics where too much of anything isn't good, while your argument is like mine where if the timing of the engagement is set intellegently, there is some benefit.
I'm not as old as XViper (no offense intended) but I was into racing when using longer duration, big lift cams caused messed up idles, had poor low end power but was a blast at mid to upper rpms. On those cars, I had a race cam on my Rabbit GTI and if you went WOT at the wrong rpms, it would bog, maybe stall. In order to drive it on the street, you needed to keep the throttle closed just enough to maintain a high vacuum reading (I had a vacuum gauge installed back then).
On NA cars, you need air velocity (speed) to fill the cylinders with air at lower rpms... so a smaller port/opening is desirable whereas at higher rpms, you need to let the motor breathe so you need to remove any intake restriction that may impair power output.
With today's technology and equipment, it wouldn't be hard to squeeze out some power by lowering the VTEC point a little and like I said earlier, it'll remove that kick you'd feel at 6000 rpms but will provide a more linear power delivery. The problem is that along with the cams, the ECU switches to the high-cam map which doesn't change if you move the transition point lower, like say 5700 rpms. You're still going to be on the same ECU map for the low-cam when VTEC engages at 5700 rpms, and will change to the higher map at 6000 rpms (or wherever the precise MAP transition point is).
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Joined: Mar 2004
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From: Cambridgeshire
Sorry, i've been away with a bad ass case of sunburn! haha
And again i apologise for not making myself clearer right from the get go, i make it a mistake of mine not to go over the basics everytime on forums for all the readers to fully understand where i'm comming from.
Anyhow.
What i was trying to get across was the fact that in the simple case of VE, too much is never 'enough'. Within sensible levels here, i'm not talking about several hundred percent. Its naturally VE %'ages that we are trying to increase in both NA and FI tuning and the effective RPM that we can sustain a usable VE %.
WHere does this tie in?
Well, again i go back to the kick that occurs with VTEC systems. For there to be a kick which is notable to the average driver, there MUST be a substantial and almost instant increase in power. This also means that the particular high cam profile (weather it be B16 or F20) will naturally be able to produce MORE power than the lower cam before it, at a lower rpm. All you have to do is lower the VTEC engagement point down the rpm scale until the high cam can no longer sustain a VE value higher than that of the low cam before it. Natural as a function of low operations speeds and overlap of the valves.
Hyper-X, your rabbit is basically the same as our Golf GTI in MK1 trim. So i am ssuming that you also ran the K-jetronic fuel injection system. This injection system run absolutely horribly with lumpy cams. The pulses that interact and cancel eachother out in teh plenham play havoc with the metering flap, leading to a very rough idle. And when you floor it, you get a momentary drop as the plenham equalises and the metering flap drops to near nothing. THis bogs the engine as it has to get air mass moving to lift teh flap, but it needs rpm to do this and it cant gain rpm without fuel. This is only worsened by running the stock injection system and stock head.
So, within reason, lowring the VTEC point will net you power, torque and smooth the delivery which is only a good thing at 100mph pulling nearly 1 lateral G. Last thing you want is to jerk the outputs. And fueling When running @ WOT, the ECU is at open loop to a degree, although i'm not too certain to what the degree this is, or if it even runs a true open loop system at WOT. But it will still be within the ECU's rpm/MAP/TPS/IAT/CT maps so interpolation will occur. Although i agree with tweeking it will be much much better. But again, its another asumption i would of made if you hadnt brought it up. I would of assumed that people would take the neccesary action to do it properly.
And again i apologise for not making myself clearer right from the get go, i make it a mistake of mine not to go over the basics everytime on forums for all the readers to fully understand where i'm comming from.
Anyhow.
What i was trying to get across was the fact that in the simple case of VE, too much is never 'enough'. Within sensible levels here, i'm not talking about several hundred percent. Its naturally VE %'ages that we are trying to increase in both NA and FI tuning and the effective RPM that we can sustain a usable VE %.
WHere does this tie in?
Well, again i go back to the kick that occurs with VTEC systems. For there to be a kick which is notable to the average driver, there MUST be a substantial and almost instant increase in power. This also means that the particular high cam profile (weather it be B16 or F20) will naturally be able to produce MORE power than the lower cam before it, at a lower rpm. All you have to do is lower the VTEC engagement point down the rpm scale until the high cam can no longer sustain a VE value higher than that of the low cam before it. Natural as a function of low operations speeds and overlap of the valves.
Hyper-X, your rabbit is basically the same as our Golf GTI in MK1 trim. So i am ssuming that you also ran the K-jetronic fuel injection system. This injection system run absolutely horribly with lumpy cams. The pulses that interact and cancel eachother out in teh plenham play havoc with the metering flap, leading to a very rough idle. And when you floor it, you get a momentary drop as the plenham equalises and the metering flap drops to near nothing. THis bogs the engine as it has to get air mass moving to lift teh flap, but it needs rpm to do this and it cant gain rpm without fuel. This is only worsened by running the stock injection system and stock head.
So, within reason, lowring the VTEC point will net you power, torque and smooth the delivery which is only a good thing at 100mph pulling nearly 1 lateral G. Last thing you want is to jerk the outputs. And fueling When running @ WOT, the ECU is at open loop to a degree, although i'm not too certain to what the degree this is, or if it even runs a true open loop system at WOT. But it will still be within the ECU's rpm/MAP/TPS/IAT/CT maps so interpolation will occur. Although i agree with tweeking it will be much much better. But again, its another asumption i would of made if you hadnt brought it up. I would of assumed that people would take the neccesary action to do it properly.
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Joined: May 2002
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From: Dublin, OH
hirev... please think about why a certain cam profile makes power or torque where it does. Everything depends on how well the cylinders fill with air. At high RPM it's beneficial to leave the intake valves open after BDC on the intake stroke because the cylinder is still filling with air. At low RPM that same valve timing causes air to actually get pushed back out the intake valves some. Of course intake runner length and port shape also have some effect on moving torque peak up and down but not really compared to cam profile.
Therefore, using the cam profile that allows lots of torque at high RPM (means good cylinder fill) would not be at all ideal for low RPM operation. Now that you know this, doesn't your question seem kind of silly?
Do you ever think about why small performance engines are usually designed to make peak torque at relatively high speed? Do you ever think about why large engines aren't? I'm kind of surprised no one else has posted a similar reply.
Therefore, using the cam profile that allows lots of torque at high RPM (means good cylinder fill) would not be at all ideal for low RPM operation. Now that you know this, doesn't your question seem kind of silly?
Do you ever think about why small performance engines are usually designed to make peak torque at relatively high speed? Do you ever think about why large engines aren't? I'm kind of surprised no one else has posted a similar reply.