Boost effects on VTEC

[myshtern]

Hi guys,

I've got a question.
I have heard some people say that VTEC is bad when you are running high boost (more than 10psi). Some people say it has no effects.

Can someone give me a clear answer. If it is bad on the engine, can someone explain why in detail?

Thanks
- Alex

[Pang]

not bad at all. Why do I keep hearing about this. Who is going around spreading the ghey word.

[stu]

Some people think that having VTEC creates some tuning block that you can't get around, it's mostly a myth though. You could say the same thing about OBD II cars.

[Prelude97]

not bad at all. Why do I keep hearing about this. Who is going around spreading the ghey word.
:werd:

[Bryson]

VTEC + BOOST = OWNZ JOO.

Thats all you need to know. Now that I think about it, that would make a good sticker... :P

[davidm_sh]

The only thing I ever heard about VTEC and high boost (8+psi) is bad becuase VTEC was designed and operates on the principal of a NA engine and therefore has quite a bit of valve overlap (exhaust and intake valves being open at the same time). With this it is harder to pressurize the cylinders with high levels of boost since some of that boost is escaping out the exhaust ports when they are open, briefly, at the same time as the intake ports.

The only downsides I can see to this the turbo has to work a bit harder = spin faster = potentially more back pressure to a point. But honestly the turbos most people use on the 1.6-2.0L hondas are SO big with nice LARGE exhaust housings that the back pressure point is probably nil.

The only upsides I can see is you probably get all the exhaust gas out of the cylinder with the intake and exhaust valves open at the same time = a cleaner, more pure, and denser charge to fire off on the next stroke.

I think it is probably only an issue more for people running REALLY high levels of boost 20+psi on drag cars becuase then they start to reach the limits of the turbos capabilities and they don't want to have to have the turbo work harder to try and fill the cylinders with pressure.

Someone please correct me if I am wrong... it has been a while since I had a VTEC engine.

[STIBungy]

Yup, that's what I've read in the past about turbocharging VTEC engines. I'm sure with the right set of turbo cams, you can minimize the overlap. Or hell, disconnect VTEC altogether. :D

[BluByU]

I'll disconnect it and sell it on Ebay.

[rmcdaniels]

I run 10 lbs -w- VTEC and I believe overlap is an issue. I put on some adjustable cam gears and took it to the dyno. A few pulls later I found that +4 degrees of intake timing and -.25 degree of exhaust timing made a huge difference. Not only did I make more power, but throttle response was much quicker (night and day) and power delivery was much smoother. I don't recommend anyone else use those settings (my engine is very far from stock), but a quick trip to the dyno should be sufficient to determine your own settings.

[myshtern]

so you are just saying it makes it a bit harder to tune right?

[rmcdaniels]

I'm not an expert on this, so somebody please slap me if I'm wrong here, but I believe that valve overlap is a normal and necessary part of NA engines, especially small 4-cylinder engines. When you make changes to the intake and exhaust, it changes the effect of your existing overlap (read http://web.tampabay.rr.com/redroby/3liter/exhaust.html for some interesting info). That's true if you have VTEC or not. I would guess that your VTEC lobes, because of the RPM range they are designed to operate at, might have more overlap than your non-VTEC lobes, which is actually a good thing under normal operating conditions.

Adding a less restrictive exhaust and forced induction will change the effect of your overlap, so if VTEC lobes have more overlap, then there will be a greater apparent overlap effect when they come online, and too much overlap can be a bad thing. The other side of this is that VTEC lobes are much bigger, so the valve opens much wider, allowing more gases to flow in VTEC mode, which is a good thing because more lbs/min=more power.

There are different ways to deal with the overlap issue. disabling VTEC is one, but with stock cams I'd rather keep those big lobes in there (my VTEC kicks in <3000 RPM if I am under boost), so I changed my cam timing to change my overlap. I probably still have some overlap, but not as much as I used to. However, because I have a less restrictive exhaust and FI, the apparent overlap may be the same, because remember, changing the exhaust or intake can increase the effect of the overlap you have. Changing the overlap also affects drivability, my idle isn't as smooth as it used to be (I also have an 8.8 lb flywheel and 8.4/1 compression), but it isn't too bad. The car is my daily driver and it generally only dies when I let off the gas 1-3 times/week, usually while I am still rolling so I can just disengage the clutch quickly and bring it back to life. For me, the gains in power and the nice smoothly rising HP line on my dyno graph are worth it. The thing to remember about changing cam timing is that each intake/engine/exhaust combo is different, so the only way to make sure you get it right is to tune it on a dyno, although from what I have seen, a few degrees of intake advance and a fraction of a degree of exhaust retard are generally what you are looking for in a FI VTEC setup.

[cherrybombcivic]

hey rmcdaniels, where the hell is that quote in your sig from about "the brother in law phil" ? it sounds so familiar!

[rmcdaniels]

hey rmcdaniels, where the hell is that quote in your sig from about "the brother in law phil" ? it sounds so familiar!

It was from an article on the Internet about bad opening lines for stories. That one came from a high school english teacher and was one of a bunch of funny ones the teacher had gotten over the years. I think I linked to the article from www.ilovebacon.com. Bacon rules!

[Bryson]

Don't disable the VTEC. Only full race setups should do that.

the smaller cam lobes will keep more torque in the lower RPMS, and the larger lobe allows the engine to make more power with boost.

If it makes good power N/A, it will make good power boosted.

I've seen 616HP on B16 with ITR cams with VTEC. If thats not proof enough for you, then I don't think I can convince you.

[myshtern]

616HP on a b16. can someone say lag?

[ryanman]

I'll disconnect it and sell it on Ebay.
:rofl: :rofl: :rofl: :rofl:

[Mark_H]

FWIW I run between 14-15psi on my ITR motor, stock head/cams/camgears. So far so good, 400whp :)
Mark

[Mr.VTEC SiR]

i have heard these rumors myself and Im not quite sure what to belive anymore. Personally i have heard that NON-VTEC engines are better for boosting, but not from a very good source (my brother).=)

[JYNX]

dont boost a honda because theyre gay.

[myshtern]

dont boost a honda because theyre gay.
Dont talk on this forume because you're gay

[JYNX]

im not gay, im flaming.

[Skaterkid]

And you suck at Flaming.

[JYNX]

i meant flaming gay.

And look at this fucking fag. Oooooo, i gots the fast NA converted to turbo car ever! I run a whopping 15.7!

[JYNX]

And by the way your Mods suck on this site and should be fired. I should have been banned a long time ago.

[stu]

We don't ban people often. We usually just let them pretend they are witty and fresh for a while, then they realize that they're not and leave. How far along are you in the process.

[Skaterkid]

i meant flaming gay.

And look at this fucking fag. Oooooo, i gots the fast NA converted to turbo car ever! I run a whopping 15.7!
Like I haven't ever heard that one before :rolleyes:

[JYNX]

You guys have a mod names stu? Probably some inbred motherfucker from Kentucky. No wonder hes incompetent.

[stu]

lol.

[myshtern]

You guys have a mod names stu? Probably some inbred motherfucker from Kentucky. No wonder hes incompetent.
ha
that was pretty witty in fresh - he is in the early phases

[rmcdaniels]

ha
that was pretty witty in fresh - he is in the early phases

He is weak, needs some serious troll school. Maybe he should check out http://www.highaltitudeimports.com/f79-troll-archive.html for some tips.

[Mr.VTEC SiR]

lol.
that guy JYNX sounds like a complete fucking retard...hehe