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

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Arvada

Pang

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

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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.

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Gemini

Toilet Market for Toto Toilets - Best Flush Toilets

Prelude97

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1993 Civic cx *11.92 @ 118 stock ls*
2003 cbr600f4i
1994 Plymouth Sundance

Bryson

VTEC + BOOST = OWNZ JOO.

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

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91 CRX - Time attack/Trials race car
99 Jeep Cherokee (D60/14FF, turbo'd)- DD and tow rig

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.

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2004 Subaru WRX STi
-12.52 @ 109.5 with 1.78 60' at Bandimere
2002 Subaru WRX
-12.92 @ 106.3 with 1.96 60' at Bandimere

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.

BluByU

I'll disconnect it and sell it on Ebay.

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"Brown" Alex
07 WRB STI w spt basics
93 Rodeo full code 3 package

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.

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myshtern

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