Hey guys im recently going in for a dyno tune with my apexi vafc and ive seen some people lower the vtec all the way down to 4200, and im curious as to why that low? Ive heard of people losing peak power just because they want vtec as soon as possible. Wouldnt it be better to leave the vtec engagement as 6000? or is there a really good reason to lower the vtec to maybe 5500?

 

Ive had many upon many cars tuned, you can do a few things,

1) you set vtec really high in the rpm band usually giving you no gains but the in your pants feel is like wow as IT REALLY JUMPS up there but your losing the down low where it should have been

2) You set it too low and you gain nothing...........


3) You bring to a shop that dyno tunes and you set the vtec so that it gets you as straight and fluid whp curve as possible.

That is the only way to know, dyno test that whore!

 

with the variable valve timing. there are 2 cam profiles used. 1 below vtec and one during. both are optimized for certain rpms. engaging vtec early makes it hard to get af correct.

aka....leave it alone

(my understanding)

 

You should not feel any "butt kick" from the VTEC crossover. It should be a smooth as silk transistion. This is not the way most S2ks come out of the factory, and lowering the VTEC crossover point a couple 100 RPMs helps!

 

If your going to track it, otherwise not having any kick is borring in my opinion. The reason you want it smoothed out is to not get any supprises in the corners, it gives you more predictable power inputs. I have mine set to come on at 6100. I like the kick, but thats my prefrence and with my supporting mods It performs really well this way, because my Pre Vtec power curve continues to climb well into 6400 without any drop off assiosiated with a typically stock power curve. If I lower my Vtec it squanders the bennifit I feel I get.

In all out exceleration typically the higher Vtec engagment performs better I have found. On a track where you need some finess and less supprises, lower vtec makes sense. The way to deturming the proper Vtec point if you wan to lower it is to Dyno your car and look at where the tq line crosses the HP line. Right where they cross is where you set your Vtec engagement point, this on a stock S is between 5400rpm-5600rpm's typically, but I don't recomend it.

 

Dont go to low with Vtec or the car will bog I would leave it or lower just a tad the Dyno curve should be as smooth as possible . Tuning should eliminate the typical Vtec dip that occurs right around the cross-over point.

When you feel Vtec kick in it typically means the dip is more drastic (loss of HP is geater than it should be) thats why you feel the "kick in the butt" when Vtec engages.

 

VTEC at idle FTW!!!

 

Wow is this Honda-Tech? So much misinformation.

To get it right you have to get it dyno tuned, period.

2 (kinda) exceptions:

1) You go to the 1/4 mile and make pas after pass after pass and if you have the same 60' times all night you chose the VTEC setting that worked for you

2) You RR or AutoX and you drop out of VTEC so you bump it down a couple hundred RPMs to keep you in VTEC around the track

 

I've heard of guys running down that low but it was becuase they were Turbo. I don't know any other reason that would be bennificial to run that low. Iv'e experimented will my Vafc2 through its full range from 4000-7000 vtec engagement and well, let me tell you. On an NA car anything under 5500rpm and it is useless. Feels like the power curve just goes flat, the cylinders can't handle that much volume of A/F at that rpm. If you had bigger pistons you could squeeze out a bit more at lower rpm Generally. It works with FI because your forcing more air into the cumbustion chamber earlyer in the rpm then stock and they are just trying to maximize this through lower Vtec/more fuel.

The stock 5850-rpm really is the right rpm for a stock NA S2000. Its true that part of the jump you feel from the Vtec is because the lower cam is starting to go flat in the curve from fuel starvation. But that is only half of it, the other half is an actual increase in a power jump created by the increase in velosity this slight leaning before the big fuel relief happens at Vtec cick in. This charge helps carry the power jump well into the higher rpm range. When you lower the Vtec point to lets say the average low point of 5400-5600, it doesn't create the same "charge effect" I have experimented allot with my set up to come to this conclution. I utilize my Vafc2 of course but also my other fantastic tuning tool, my AEM widband AFR meter.

 

Any spicifics or is this just your general concensis from this collective thread? Because the only addition you made that wasn't mentioned already was your mention of the benifit of (lowering Vtec to keep from falling out) in sertan race senarios. I think this is a usefull reason, however there is what i feel a better spin on this that I will gladly add for you, since you seem to like to open your first additions to threads with insults.

My thoughts on the matter is to lower the decel change over point and keep the excel point higher to maintain max performance. This way you get the best of both worlds. Stronger pull from the higher Vtec point in exceleration but when decel for a turn, the vtec stays in longer for re exceleration in Vtec without down shifting (However if your skilled at shifting this isn't really much bennifit in most situations) But since we are discussing maximizing Vtec settings, i'll give them to you. For example, Mine as you know is set to 6100rpm engagment and my decel is 5800rpm disingaged. It works! Do you have anything else positive to add?