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VTEC Controller: Lower RPM's vs Higher RPM's

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Lotus_Esprit

Contributing Member
Joined
14 September 2004
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185
noob alert - please dont flame but please educate.

alot of my friends and I were talking about vtec and how some people buy a vtec controller or sometimes buy a chip to induce the vtec to come earlier in the lower rpms. One of my friends on his Si, has the vtec kick in at 3500 RPM's. I think on the stock Si its at 6000 - 6500 RPM's. I know DOHC vtec opens up the intake and exhaust valves bigger but is there any gains in an earlier induce vtec? has anyone done this on their nsx?
 
Lotus_Esprit said:
noob alert - please dont flame but please educate.

alot of my friends and I were talking about vtec and how some people buy a vtec controller or sometimes buy a chip to induce the vtec to come earlier in the lower rpms. One of my friends on his Si, has the vtec kick in at 3500 RPM's. I think on the stock Si its at 6000 - 6500 RPM's. I know DOHC vtec opens up the intake and exhaust valves bigger but is there any gains in an earlier induce vtec? has anyone done this on their nsx?
Click to expand...

Tuner after tuner has tried to improve NSX performance by moving the VTEC engagement point around and it has not resulted in any substantial benefits. The consensus is that the most effecive VTEC engagement point for the NSX is the one Honda decided upon. Other cars including other Hondas might be different, however.
 
so what you are saying is that even at lower RPMS, for example at 3000 rpms (DOHC VTEC) when the intake and exhaust cams open wider for more air and better exhaust flow, there is no power gain at all?
 
Lotus_Esprit said:
so what you are saying is that even at lower RPMS, for example at 3000 rpms (DOHC VTEC) when the intake and exhaust cams open wider for more air and better exhaust flow, there is no power gain at all?
Click to expand...

Yes. At 3000 RPM the NSX engine doesn't need as much flow. It will actually hurt performance. It's best performance below 5800 RPM is with the more restrictive valving. After 5800 RPM the engine's profile is better suited for the open valving. Other cars may be different but Honda seems to have done the math on the NSX.
 
You really can't beat the stock torque curve of the na motor as honda built it.Sure you can gain some hp in midrange and top with i/h/e more so on the 3 liter cars but unless you want to start iem(internal mods) there is not much more useful performance out of the stock motor na.Why should you care though ,you will be peeling rubber in your 2 liter lotus:wink:
 
I'll be done with school in 3 months, then out to the real world of work. i've been doing research on the forums about the nsx gen I. i see they are going around 22k - 40k+.

Im thinking getting a nsx around 25-30k plus i want the lovefab turbo kit (to much youtube). comparing a nsx turbo against supras TT and 350z TT, the nsx lightweight just pwns them all even if the nsx has lower hp. what really sells the nsx to me is the mid-egine layout. im a big fan of mr cars. they have the best traction of all layout and best handling. them titanium rods do sound expensive..:biggrin:
 
the whole point of vtec is to optimize the cam profile for a particular RPM. why would you want to have the high RPM profile engage so early?:confused:

(btw, each stock connecting rod is 1000 bucks.)
 
Synthesis said:
the whole point of vtec is to optimize the cam profile for a particular RPM. why would you want to have the high RPM profile engage so early?:confused:

(btw, each stock connecting rod is 1000 bucks.)
Click to expand...


alot of rice boy racers around here like to engage their vtec civics at lower rpms (3k-4k rpms) and they are claiming its a big improvement. Im not quite sure its a big improvement, maybe because of the low litres but on the other hand my cousin told me that its better to leave it stock or set it up at the point of maximun hp without vtec and then engage the vtec. the later sounds right but i guess its one of them urban legend on vtecs. :tongue:
 
good question.

we have done a handful of vtec controlers.

on the rsx & TSX i know for a fact that if you change the Vtec point to 3200 you'll see increased in TQ and HP through out the rpm band.

also not just that, the HP usually drops or stops accelerating before the stock vtec point and then jumps up once vtech hits.

when you change vtec engagement point to 3200, the power is smooth across the board with no dip or jumps. at points right before vtec engagement we have seen 15HP difference, which is a big deal in drivability.

NSX vtec is very smooth, personally have not done a vtec controller on the nsx but from the dyno, there is no dips you can smooth out.

why dont you give it a shot? vtec controllers are dirt cheap now and wiring is pretty easy.

happy motoring

Rob
 
The biggest difference between the NSX's VTEC engagement and the civic si's is that the NSX doesn't rely on the VTEC to give it a surge of power. If you actually look at the dyno of a NSX, there is no HP/TQ spike during the VTEC engagement point where as other cars sich as the Civic Si and S2000 do have a spike due to the VTEC engaging. What the VTEC does do for the NSX is prevent power from dropping as it travels to the redline.
 
Bump for an old thread, has anyone come up with conclusive results since 2008?
 
vtec effectively switches between 2 cam profiles in the car... you have to remember the target buyer for the civic/ s2000 buyer. on those there is a dip in the power curve before the vtec switches to the 'racy' cams, so that the driver can go 'wow, vtec is kicking in' much like a turbo overcoming lag and kicking the back of the seat.

on the nsx the engineers 'aligned' the 2 cam power curves so that vtec switches them when they are giving the same power, thus smooth clean power delivery, better for performance and control, but lacking in the 'oooh vtec kick' effect. its there, just better in an NSX, up to 8000rpm nice and smooth
 
Generally speaking lowering VTEC a lot will not improve performance at all. Sure a couple hundred rpm up or down maybe, but not much if at all. VTEC engagement point should not be noticeable at all on a dyno chart, the torque curve should be smooth. If you see a dip in torque immediately after VTEC then it is likely too early. If you see torque dropping or holding steady, and then immediately rise after the VTEC engagement then VTEC is likely engaging too late.
 
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Thanks KO, I forgot about that thread. I don't know if it only makes power in turbo cars but it would make sense that it would for NA cars too. It would be a kick in the pants instead of the progressive rise in power of the stock car if it works. Some may not find that preferable but I don't know if I'd mind it. I think my tuner is just going to do what he thinks appropriate anyways but I will discuss it with him and report back. Hybridtheory may be right though. The more I find out, the more the only sensible solution to a power quest is a turbo.
 
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My understanding to make it simple is that if there is a pretty noticable diffrence in power when vtec engages then u may set it lower but like the nsx its not very notciable expecially when i compare it to my k20si so its basically where it should be at. The idea being that if there is a big increase in power when it hits then it was prbly starving for air when it hit. But at the same time if u go to early you will loose power in the low end hence having the smaller lobes in the first place. Which is basically what i see hybrid said
 
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My tuner said it wouldn't do any good basically. Makes sense since the car has been out for 20 years and we would know by now if it worked bc Comptech probably would have done it long ago.
 

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