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2ndGenTeg · 09-14-2001, 10:56 AM

A quick crash course for anyone unfamiliar with VTEC:

VTEC stands for Variable Valve Timing and Electronic Lift Control. The premise is that at low RPMs and at idle, a less aggressive cam grind is necessary to prevent "loping." Ever hear a pro drag car staging up at the gates? Sounds like it's about to stall. It's because he's running aggressive camshafts, and since the cam is spinning more slowly at idle, the intake valve is still open after combustion has completed. That's what causes loping. At higher RPMs, a more aggressive grind is desirable. The idea is that you want to cram as much air and fuel mixture (A/F) into that combustion chamber as possible, so that when it's ignited you get as grandiose an explosion as possible. So what is good at low RPMs is bad for high RPMs. So what do you do?

If you're Honda, you invent VTEC. What VTEC does is simply to employ different cam grinds at different RPMs. A less aggressive grind at low RPMs for a smooth idle and low to mid range power, and a more aggressive grind up high to produce that high end pop. At a strategically placed "VTEC crossover point," the camshaft switches grind from the less aggressive to the more aggressive.

What determines this point? Hours and hours dyno testing and tuning. If it is set too low, the more aggressive grind will kick in early, bogging down the engine (think "loping" at 3500 RPM). Too high, and the engine is missing out on valuable time it could be spending with the VTEC engaged. So all those fools who spent $400 on a VTEC timer running stock camshafts just so they could get their VTEC to kick in earlier- they're idiots. They just cost themselves a ton of midrange power. The stock crossover point is optimized for stock camshafts.

So when is a VTEC timer necessary? Easy- when you're no longer running stock camshafts.

If you want big power all motor, you go with one of the big players in the cam game- Toda Spec B and C, or Jun Stage 2 and 3, and you accept no substitutes. All (or at least 95%) of the 225+ all motor whp B18s are running these camshafts.

How does this relate to VTEC crossover point? Well, the VTEC grinds on these cams are so aggressive, that the VTEC point needs to be moved up- way up- usually to 6500-7000 RPM. These cams will also make power to 9500+ RPM (READ: Built motor). Run these in conjunction with high compression pistons (at least 10.5:1), and you'll have yourself an all motor wonder. And this, friends, is where torque in Hondas comes from.

09-14-2001, 10:56 AM	#8
2ndGenTeg 4th Gear Join Date: Aug 2001 Location: Boulder, CO Age: 43 Posts: 830	How VTEC works, and why it lives at high RPMs A quick crash course for anyone unfamiliar with VTEC: VTEC stands for Variable Valve Timing and Electronic Lift Control. The premise is that at low RPMs and at idle, a less aggressive cam grind is necessary to prevent "loping." Ever hear a pro drag car staging up at the gates? Sounds like it's about to stall. It's because he's running aggressive camshafts, and since the cam is spinning more slowly at idle, the intake valve is still open after combustion has completed. That's what causes loping. At higher RPMs, a more aggressive grind is desirable. The idea is that you want to cram as much air and fuel mixture (A/F) into that combustion chamber as possible, so that when it's ignited you get as grandiose an explosion as possible. So what is good at low RPMs is bad for high RPMs. So what do you do? If you're Honda, you invent VTEC. What VTEC does is simply to employ different cam grinds at different RPMs. A less aggressive grind at low RPMs for a smooth idle and low to mid range power, and a more aggressive grind up high to produce that high end pop. At a strategically placed "VTEC crossover point," the camshaft switches grind from the less aggressive to the more aggressive. What determines this point? Hours and hours dyno testing and tuning. If it is set too low, the more aggressive grind will kick in early, bogging down the engine (think "loping" at 3500 RPM). Too high, and the engine is missing out on valuable time it could be spending with the VTEC engaged. So all those fools who spent $400 on a VTEC timer running stock camshafts just so they could get their VTEC to kick in earlier- they're idiots. They just cost themselves a ton of midrange power. The stock crossover point is optimized for stock camshafts. So when is a VTEC timer necessary? Easy- when you're no longer running stock camshafts. If you want big power all motor, you go with one of the big players in the cam game- Toda Spec B and C, or Jun Stage 2 and 3, and you accept no substitutes. All (or at least 95%) of the 225+ all motor whp B18s are running these camshafts. How does this relate to VTEC crossover point? Well, the VTEC grinds on these cams are so aggressive, that the VTEC point needs to be moved up- way up- usually to 6500-7000 RPM. These cams will also make power to 9500+ RPM (READ: Built motor). Run these in conjunction with high compression pistons (at least 10.5:1), and you'll have yourself an all motor wonder. And this, friends, is where torque in Hondas comes from. Last edited by 2ndGenTeg : 09-16-2001 at 05:06 PM.