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Discussion Starter #1
Seems like I get a boost of power/torque at about 4200 rpms fairly consistently. From what I've read, Vtec kicks in at about 2500-3200. So what's going on at 4200?

Also, maybe someone can elaborate on just what the Vtec system does? At low rpms, is the cam profile a low-lift, fuel economy one? And at 2500-3200, does the Vtec kick in, and is the cam profile a higher-lift, more power profile? Could my Vtec be kicking in at 4200? if so, why?
 

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When VTEC-E is in fuel efficiency mode, one of the two intake valves opens just a tiny bit. In power mode, both intake valves open fully. I believe that the cam profile is the same in both modes and that the exhaust valves operate identically in both modes.

I have noticed what feels like a drop in power under full acceleration somewhere in the 3,000 - 4,000 RPM range (I haven't paid close attention). But then the power increases at higher engine speeds. Maybe that's the power increase that you're feeling. I think the drop in power may be due to the timing being retarded, possibly due to ignition knock. I'll know better after I install my OBDIIC&C gauge.
 

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Discussion Starter #3
When VTEC-E is in fuel efficiency mode, one of the two intake valves opens just a tiny bit. In power mode, both intake valves open fully. I believe that the cam profile is the same in both modes .....
If one valve opens less than the other, pretty sure that'd be a function of a different cam profile, a lower, flatter one...

I have noticed what feels like a drop in power under full acceleration somewhere in the 3,000 - 4,000 RPM range (I haven't paid close attention). But then the power increases at higher engine speeds. Maybe that's the power increase that you're feeling. I think the drop in power may be due to the timing being retarded, possibly due to ignition knock. I'll know better after I install my OBDIIC&C gauge.
I haven't noticed a drop, but it's hard to say when one's got the electric assist and v-tec to worry about. Boost happens under acceleration without electric assist, not sure what throttle position - not full cuz then electric assist would probably be assisting... Probably usually in 2nd or 3rd gear. I'll be accelerating, probably without electric assist kicking in, 2nd gear above 2500 rpms, and when I hit about 4200 rpms - boom - something kicks in power (not electric though). The feeling is similar but maybe twice as strong as what I feel during an NOX purge when in lean burn mode...
 

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Id say you are getting full life on both sides, intake and exhaust. The i2 has a single profile cam and a joint between the lifter and valve. THe oil pressure regulated rather you get no lift, low lift or high lift and this is the same for the exhaust. So, the engine is a dual vvt type of engine where hte intake and exhaust can be adjusted by themselves.


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If one valve opens less than the other, pretty sure that'd be a function of a different cam profile, a lower, flatter one...
There is one almost round cam lobe for the secondary intake valve and a more normal cam lobe for the primary intake valve. At low engine speeds, both intake valves are operated by their own cam lobes (i.e., the secondary intake valve barely opens). Above ~2,500 RPM, the secondary intake valve's rocker arm is pinned to the primary intake valve's rocker arm so that both intake valves are operated by the primary intake valve cam lobe. This results in both intake valves opening fully. The exhaust valves use a single cam lobe regardless of engine speed. VTEC-E is designed for fuel efficiency at low engine speeds rather than for high power at high engine speeds. See this article for a better explanation.
 

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I suppose it's possible that your VTEC is kicking in at 4000+RPM. That definitely wouldn't be normal though. That would be a sign of low oil pressure?

When you get your OBDIIC&C Gauge, it has a VTEC Engaged flag, so you'll be able to see.

Back to the sweat sh.. err, basement. :D
 

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Discussion Starter #8
.... VTEC-E is designed for fuel efficiency at low engine speeds rather than for high power at high engine speeds. See this article for a better explanation.
Good description in that article - better than the one in the IC encyclopedia... There's 2 cam profiles at low rpms, one for each valve. One is normal, the other is more or less round, with little lift, so it doesn't open the valve much. At about 2500 rpms a mechanism actuates that locks the rocker arms together - so that now the normal cam profile is driving both valves, with normal lift... That's about what I was thinking was going on... I guess I'll just have to wait for my OBDIIC&C to understand what's going on with my ~4200 rpm boost. It does feel like a vtec kick, but if so I wonder why.

It's easiest to experience in 2nd gear - I just went for a drive to check that out. Electric assist kicks in pretty easily below about 2500 rpms, but not so easily above. I mean, it does if you mash the pedal, but not if I'm only about say 1/2 pedal maintaining decent acceleration in 2nd gear. If I hold the pedal about there, when rpms hit about 4200+ I get this boost that feels, like I mentioned above, just like the NOX purge, only double... Maybe i haven't experienced it in 3rd gear, as it's harder to accelerate without having electric assist kick in. Plus, by 4200 rpms in 3rd you're going fast... Not sure about first gear...
 

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My engine seems to growl when accelerating below 4000 rpm then like a switch it stops but I don't feel a boost or lack of power though the transition. Is this the VTEC kicking in (or out)?
 

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Discussion Starter #10 (Edited)
Anybody with an OBD2C&C (that name is too long) been noting the engine speed at which vtec's been kicking in?
 

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I've got the OBDCC3. I think it's a "load" thing vs. rpm, I'll check tomorrow.
(same as your permalink #8)

Willie
 

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Interesting comment about oil pressure and a delay in the vtec opening up. Its my experience most engines as they wear loose oil pressure at idle and near red line, so that leaves you with the mid range.

If the engine that is loose spins too fast it slings out the oil faster than it can be pumped in. A loose engine with a loose oil pump doesnt pump enough oil at idle so you also get low oil pressure there too if not knocking and rattles.


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All of my cars engage VTEC at 2800-3200RPM depending on conditions.

You shouldn't need the OBDIIC&C to determine this.. I've been aware that's the point that it kicks in since I first got the car. I guess some people aren't as in tune with their machines, lol.
 

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Late to this thread but I have a question, my manual iirc says vtec happens at 2500rpm. Note, at this moment I'm gas only, not sure if vtec changes in that mode. Anyhow, is the vtec engagement noticeable or not? On every other Honda I've had it's at least subtle, but there, or at the most quite obvious. On my car I don't notice any difference in either sound or performance.

Please advise, thanks!
 

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It is a silent assist. You should feel the increase in timing and VTEC around 3200 rpm. IMHO
 

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Discussion Starter #16
Ancient thread... Doesn't look like I ever verified what the '4200 RPM' boost was. I'll have to check that out. Off the top of my head, I'm thinking air/fuel ratio drops to around 12:1 around that engine speed, maybe not strictly as a function of engine speed, but maybe coincidentally. I know A/F does drop at some point 'up there', and as I recall there's a bit of a kick when that happens...
 

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Discussion Starter #17
...at this moment I'm gas only, not sure if vtec changes in that mode. Anyhow, is the vtec engagement noticeable or not?
I don't think it changes when you're gas only, at least not a wholesale change (there may be slight differences at the margins, due to different load, timing, etc. not having the IMA up and running)... In my car the transition is very noticeable, with or without the IMA active...
 

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I don't think it changes when you're gas only, at least not a wholesale change (there may be slight differences at the margins, due to different load, timing, etc. not having the IMA up and running)... In my car the transition is very noticeable, with or without the IMA active...
I usually shift around 3500 so I don't hit that dreaded "gas only battery/e brake lights come on at 4000rpm" moment and worry the car will leave me stranded. Maybe I never notice vtec for that reason. My battery arrives next Wednesday, if I'm not dead I hope to install it over the weekend (next) and then perhaps vtec will be more noticeable, and enjoyable.
 

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Discussion Starter #19
^ Funny: I'm usually shifting before VTEC kicks-in - and using the IMA for boost. But in any event, even if you shift at 3500 you should be able to notice VTEC.

The overall 'boost scheme' goes something like this: IMA (under ~2500), VTEC (~2500-3500), and then AFR drop (I'm thinking ~4200 onward, but I still gotta check that).
 

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Discussion Starter #20
^ I did one quick check of the AFR dropping to 12:1 at around 4200 RPM idea. Indeed, that's what happened.
 
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