what does a vtec do
- Thread starter daves106
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Not going to pretend i know the details, but this site explains it...
http://auto.howstuffworks.com/question229.htm
http://auto.howstuffworks.com/question229.htm
scrob said:In layman's terms, the engine takes off using 8 valves (more torquey and faster off the line) then at around 5500rpm the other 8 valves kick in for lots of top end grunt and mega acceleration
Nah they're always 16v lad, its just the valves open more at higher revs.
RickyB
RMS Regular
A vtec is a twincam engine with 16 valves. Up to 5500rpm the engine uses one cam that opens the valves to a certain limit. Once over 5500rpm it switches onto the second camshaft (like a highlift cam) making the valves open fully and then it revs it head off to about 9200rpm. U can hear and feel the switch over taking place.
GT Sam
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class engine. would love a vtec!! but cant cause of the ins grr
One cam shaft with different lobes. When running below vtec revs, the engine acts just like any other, with the low rpm cam controlling the valves. When you hit about 5500 revs a rod connects the lairy cam to the valve followers, lifting them much higher. Not too sure how the rod appears though, probably to do with the vtec solenoid.
No mate, the DOHC means Dual-Overhead-Camshaft - there are two cams which sit parallel to each other. One camshaft is for the intake valves and one is for the exhaust valves.
For each set of valves, there are 3 cam lobes. Only 2 are utilised at low rpms, while the third is a high-rpm lobe . The engine is set up so it runs a mild cam profile before vtec. When you hit vtec (for example, around 5500rpm on a Civic VTi), the oil pressure changes in the engine and pushes a metal pin through the valve rockers. This effectively connects the 3 cam lobes, but they now follow the profile of the high rpm lobe, which opens the valves longer and for a wider duration. This equates to more fuel and air and thus more power.
It works nicely
Gaz
For each set of valves, there are 3 cam lobes. Only 2 are utilised at low rpms, while the third is a high-rpm lobe . The engine is set up so it runs a mild cam profile before vtec. When you hit vtec (for example, around 5500rpm on a Civic VTi), the oil pressure changes in the engine and pushes a metal pin through the valve rockers. This effectively connects the 3 cam lobes, but they now follow the profile of the high rpm lobe, which opens the valves longer and for a wider duration. This equates to more fuel and air and thus more power.
It works nicely
Gaz
Bronk said:
On the SOHC Vtec like the LSi, there is only a single camshaft and thus only the intake valves change profile - not the intake AND exhaust like on the dohc. It still uses the oil pressure to activate a pin which binds the valve rockers. In day to day driving, this means a much less agressive changeover and ultimately, less power. You still feel a bit of a peak when you rev the engine out but its not the kick in the back you get with a dohc.
Gaz
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