Stu
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Registered: 3rd May 00
Location: Madchester UK Drives: 2014 BMW M135i
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If you have read How Car Engines Work, you know about the valves that let air into the engine and let exhaust out of the engine. You also know about the camshaft that controls the valves. The camshaft uses rotating lobes that push against the valves to open and close them. This animation from How Camshafts Work can help you understand how the camshaft opens and closes the valves
It turns out that there is significant relationship between the way the lobes are ground on the camshaft and the way the engine performs in different rpm (rotations per minute) ranges. To understand why this is the case, imagine that we are running an engine extremely slowly -- at just 10 or 20 rpm, so it takes the piston seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but imagine that we could. We would want to grind the camshaft so that, just as the piston starts moving downward in the intake stroke, the intake valve would open. The intake valve would close right as the piston bottoms out. Then the exhaust valve would open right as the piston bottoms out at the end of the combustion stroke and would close as the piston completes the exhaust stroke. That would work great for the engine as long as it ran at this very slow speed.
When you increase the rpm, however, this configuration for the camshaft does not work well. If the engine is running at 4,000 rpm, the valves are opening and closing 2,000 times every minute, or thirty to fourty times every second. When the intake valve opens right at the top of the intake stroke, it turns out that the piston has a lot of trouble getting the air moving into the cylinder in the short time available (a fraction of a second). Therefore, at higher rpm ranges you want the intake valve to open prior to the intake stroke -- actually back in the exhaust stroke -- so that by the time the piston starts moving downward in the intake stroke, the valve is open and air moves freely into the cylinder during the entire intake stroke. This is something of a simplification, but you get the idea. For maximum engine performance at low engine speeds, the valves need to open and close differently than they do at higher engine speeds. If you put in a good low-speed camshaft, it hurts the engine's performance at high speeds, and if you put in a good high-speed camshaft it hurts the engine's performance at low speeds (and in extreme cases can make it very hard to start the engine!).
VTEC (which stands for Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to effectively have multiple camshafts. As the engine moves into different rpm ranges, the engine's computer can activate alternate lobes on the camshaft and change the cam's timing. In this way, the engine gets the best features of low-speed and high-speed camshafts in the same engine. Several of the links below go into the actual mechanics of the VTEC system if you are interested.
Several engine manufacturers are experimenting with systems that would allow infinite variability in valve timing. For example, imagine that each valve had a solenoid on it that could open and close the valve under computer control rather than relying on a camshaft. With this type of system, you would get maximum engine performance at every rpm range. Something to look forward to in the future...
Taken from.............http://auto.howstuffworks.com/question229.htm
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Martin_C
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Registered: 27th Jun 03
Location: Ayrshire, Scotland
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or, just watch this 
http://www.youtube.com/watch?v=AcT_ZyY3F0k
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Dee
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Registered: 19th Sep 01
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This has explained a lot
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Robin
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Registered: 7th Jan 04
Location: Northants Drives: Clio 182 Cup
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Cam timing in that .gif is all wrong.
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Martin_C
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Registered: 27th Jun 03
Location: Ayrshire, Scotland
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its a twin v-twin, except not in a v 
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Nick-S
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Registered: 3rd Mar 04
Location: Leigh. Drives: RS Megane 230 F1 Team R26
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at this post, vtec does sound gud tho atleast
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abdus
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Registered: 23rd Feb 06
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Jenko_Sport
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Registered: 25th May 06
Location: Stoke-on-Trent
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Link!
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chrisj_88
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Registered: 22nd Sep 06
Location: Dewsbury
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cheers stu, was expecting a load of sarcastic answers, but cheers for a proper answer buddy
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Olsrey
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Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
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Vtecs arent actually that fast . . . . . .
Raced a 2.0 vtec civic older shape (p reg i think) and he said it was having to work it quiet hard to keep up with me but he fucked me off down a massive straight lol. bare in mind at the time i was in a standard x14xe with a crappy cone filter!
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ChrisBoom
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Registered: 6th Dec 06
Location: Highland
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quote:
Originally posted by Olsrey
Vtecs arent actually that fast . . . . . .
Raced a 2.0 vtec civic older shape (p reg i think) and he said it was having to work it quiet hard to keep up with me but he fucked me off down a massive straight lol. bare in mind at the time i was in a standard x14xe with a crappy cone filter!
I guarentee someone will tear you to shreds about that comment. I wouldnt know myself, never driven a civic, but someone will shoot you down for that.
CTRs and 106 GTIs are god.
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Olsrey
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Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
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Yea they will but only me and that guy know what happened and as a result of the race we have become good friends lol!
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ChrisBoom
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Registered: 6th Dec 06
Location: Highland
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quote:
Originally posted by Olsrey
Yea they will but only me and that guy know what happened and as a result of the race we have become good friends lol!
Excellent
Nice corsa btw, dying for a 1.4 sport now haha
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Olsrey
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Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
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quote:
Originally posted by ChrisBoom
quote:
Originally posted by Olsrey
Yea they will but only me and that guy know what happened and as a result of the race we have become good friends lol!
Excellent
Nice corsa btw, dying for a 1.4 sport now haha
funny that, im looking for a 1.2 8v  ... j/k lol. Im looking for a sport around T reg with x16xe in it so i can do it up 
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ChrisBoom
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Registered: 6th Dec 06
Location: Highland
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quote:
Originally posted by Olsrey
quote:
Originally posted by ChrisBoom
quote:
Originally posted by Olsrey
Yea they will but only me and that guy know what happened and as a result of the race we have become good friends lol!
Excellent
Nice corsa btw, dying for a 1.4 sport now haha
funny that, im looking for a 1.2 8v ... j/k lol. Im looking for a sport around T reg with x16xe in it so i can do it up
Haha, mine is totally fucked, rotten, so on the hunt for something a bit better. Whats the 1.4 like with the dblias?
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Olsrey
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Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
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really nice lol, so nice ive made my mate turn towards a corsa rather than a crappy 206
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Fash_Sport
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Registered: 11th Jun 07
Location: Gloucester
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To be fair i couldn't even here the vtec kick in (as mate owns one and he says hear can't here it?) it was probably a 1.4 with an induction kit and exhaust.
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topshot_2k
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Registered: 1st Dec 03
Location: Northampton Drives: Pug GTi-6
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VTecs lack torque
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P1CK4D
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Registered: 19th Jun 06
Location: Around Essex Somewhere
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quote:
Originally posted by topshot_2k
VTecs lack torque
How ever much this is true, how do they still do good in races when I thought its the Torque that wins races? My mate has a 1.8 type r lump in his eg civic which should be about 197bhp/ 142 lb/tq or something around those figures, totally standard. anyway and he ran a 14.3 yet mine 20xe corsa, running 151 bhp / 147 lb/tq and I couldnt do better than a 15.3. I dont know how, but they work and they work well IMO.
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topshot_2k
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Registered: 1st Dec 03
Location: Northampton Drives: Pug GTi-6
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limited slip, weight, tire setup, driver reactions?
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P1CK4D
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Registered: 19th Jun 06
Location: Around Essex Somewhere
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Both have LSD's, Weight is close enough, Same tyres and profiles, driver reactions - I believe we both done the best we could I really dont know, Torque's supposedly wins races and then theres Honda? :confused:
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Fro
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Registered: 20th Jun 06
Location: Rainham, Essex Drives: A3 2.0TDi Sport
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spoons civic is an F'ing animal though 
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P1CK4D
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Registered: 19th Jun 06
Location: Around Essex Somewhere
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quote:
Originally posted by fro-dizzle
spoons civic is an F'ing animal though
Yeah I know! 
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Stu
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Registered: 3rd May 00
Location: Madchester UK Drives: 2014 BMW M135i
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quote:
Originally posted by chrisj_88
cheers stu, was expecting a load of sarcastic answers, but cheers for a proper answer buddy
Nay worries at all pal!!!
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Jamie
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Registered: 1st Apr 02
Location: Aberdeen
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You dont talk about Vtec
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