Acceleration in vtec ?

[aaronek4]

Hi I've had my teg for a couple of months now and have always thought that it doesn't pull as much as it should in vtec . I put it into a Honda garage and they told me the timing chain was slightly stretched, common problem apparently. After getting new chain and pulley fitted and and all round check (solenoid etc.)I still feel it should be pulling more. It seems to pull stronger in the lower revs then less in the vtec ?

 

[C&S Evo7]

i certainly wouldnt say timing chain stretching is a common problem at all, for a start honda say its a lifespan item with only checking it until worn. theres no official guide mileage for replacement.

BUT there are a few things that can affect vtec operation, you should certainly feel it on changeover,
the vtec system relies on oil pressure to operate, if the oil level is low it can affect its operation and if the oil flow isnt correct . the vtec solenoid has a gauze filter inside which can get blocked and restrict the oil flow. if the engine oil level is low it also makes a difference, i would always recomend it is kept full, it should be checked when warm and ideally wants to be on the top mark. anywhere round the min level and it probably wont work properly.

 

[Johngreen537]

As above really.
All the K20's I've owned, and have ever known owned by others, the timing chains stretch very rarely.

Honda themselves even changed thee service interval from 75k to 150k (precautionary), which tells you about the confidence in them.

I'd agree with the solenoid gauze, if there's an issue.

It's not just misconception is it? I mean, the DC5 is nowhere near as pronounced (audibly) in vtec, which can give you the impression it's not kicking in as hard as it should.

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[aaronek4]

Yeah I thought that myself about the chains and it had only done 68k . The garage assured me the solenoid and oil levels were fine but il maybe check them myself if it's not too complicated . It was a Honda dealership garage and they seemed genuine so I'd hope it's not that . If you can post videos on here il try upload one of the speedo

 

[C&S Evo7]

take off the lid of the airbox, and go and give it a try, you will definately hear if its changing over, you shoulkd definately feel the extra urge,

 

[Crazylegs]

From my understanding VTEC shouldn't 'kick' in anyway, it's a smooth process.

Not sure where people get this idea that it kicks in when it doesn't. The K20 pulls well up until redline without any kind of extra grunt.

 

[aaronek4]

Thanks for the advice I've got the aemv2 air intake and an aftermarket exhaust that was fitted before I bought it, want to go back to original exhaust trying to source one just now

 

[aaronek4]

Thanks for the advice I've got the aemv2 air intake and an aftermarket exhaust that was fitted before I bought it, want to go back to original exhaust trying to source one just now

 

[jrscho]

Maybe get valve clearances done if it's not been done before?

 

[Fahadl786]

get a video of the pull posted up?

 

[ferret]

From my understanding VTEC shouldn't 'kick' in anyway, it's a smooth process.

Not sure where people get this idea that it kicks in when it doesn't. The K20 pulls well up until redline without any kind of extra grunt.

yes but there is a switch point at which the cams lock or "vtec kicks in", and there should definitely be more noticeable power from this point on. sure its not as noticeable in the k20 as it was in the older b series engines but thats probably where the term comes from

 

[coyote_dc5]

Absolutely, which means it's either working or it isn't. Not sure there is a half way house i.e only working 50%. You'd know for sure if it wasn't engaging as you'd be a good 50-75hp down which brings you down to standard 2.0ltr n/a car power which would be very noticeable

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[kyle'87]

Thanks for the advice I've got the aemv2 air intake and an aftermarket exhaust that was fitted before I bought it, want to go back to original exhaust trying to source one just now

I will be putting my OEM exhaust up for sale later tonight as I just fitted my Spoon B pipe and N1 backbox.

Drop me a PM if you want to know more, or wait for the FS thread.

 

[Crazylegs]

yes but there is a switch point at which the cams lock or "vtec kicks in", and there should definitely be more noticeable power from this point on. sure its not as noticeable in the k20 as it was in the older b series engines but thats probably where the term comes from

See I don't see a noticeable power change, the car does of course make it's power higher up in the revs but the only gear I really see a major increase in power in is 4th, in all other gears once over 6000rpm or whatever point VTEC comes in the car accelerates quicker that I do agree with. I don't feel a kick of sorts, the engine obviously makes a better noise but no boot in the back like I imagine a forced induction car would give.

Perhaps I'm just thinking about it too much. Mind you my old B20 EK9 was mapped for VTEC to come in a lot lower down the rev range and you could certainly feel it in the B20.

 

[wj51fut]

See I don't see a noticeable power change, the car does of course make it's power higher up in the revs but the only gear I really see a major increase in power in is 4th, in all other gears once over 6000rpm or whatever point VTEC comes in the car accelerates quicker that I do agree with. I don't feel a kick of sorts, the engine obviously makes a better noise but no boot in the back like I imagine a forced induction car would give.

Perhaps I'm just thinking about it too much. Mind you my old B20 EK9 was mapped for VTEC to come in a lot lower down the rev range and you could certainly feel it in the B20.

The VTEC on a K20 is less noticeable than on a B or H series engine. Honda designed these engines so that the torque curve dipped just before VTEC. Then when the cross over happened it was more noticeable as you got a surge of torque in one hit.

The K20 is different. The torque curve is a lot less and is more balanced. So when the cross over happens it won't give you the same feeling as the B or H series engines.

VTEC will only engage once all the parameters are correct. Oil level, oil pressure, cross over point (6k) and more than 70% throttle. There are other things it measures too like A/F ratio and crank and cam sensors.

VTEC is not a gradual thing either. It literally is a cross over. The two cam rollers lock together to form one large roller in which the middle cam lobe is used as it has a longer/higher duration. Effectively we have 16 valves 16 lower power cam lobes and 8 higher power cam lobes. This is done instantly once the parameters are met giving you VTEC.

If you see the picture below you have from top to bottom;

Cam shafts with the three lobes
Three rollers - these roll across the lobes and the tappets
Underneath the middle roller is a lost motion assembly. These take up the slack when VTEC isn't engaged. They are basically big springs.
And then the valve heads



In between the rollers are little poles and springs. Once VTEC is activated these poles slide across to lock the three rollers together. The engine then uses just the longer/higher duration cam lobe and so VTEC engages.

Simple but very effective, reliable and strong.

Hope that helps

Adam

 

[C&S Evo7]

imo you should be able to feel the change over , while it is smoother than some other hondas its still there, the biggest thing you will notice is the change in induction noise.

 

[coyote_dc5]

imo you should be able to feel the change over , while it is smoother than some other hondas its still there, the biggest thing you will notice is the change in induction noise.

Above certainly applicable if your factory map however if you have aftermarket map with k100/pro then often the power curve is linear so the feel of cross over is less pronounced so it could be you have a hondata map

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[Crazylegs]

I'm fairly sure I don't have Hondata, have never taken the ECU out though mind.

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[Matt-r8]

If you want a good but simple explanation on How VTEC works, then watch the show where they did up the Orange S2000. Something like wheeler dealers it was called. That had a knackered VTEC solenoid (Blocked gauze filter) so they explained what it did.

 

[BenLAST]

As already said, with a standard ECU and no map there is a small power/torque drop just before VTEC to make it more prominent. With KPRO/K100 this is eliminated to achieve the smoothest and best power delivery.

I think OP should get a video, would help a lot!!