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Originally Posted by cderalow
uh... no
they altered the cam profile from the previous fit yes.
but it was more to give it a similar profile to the R18/K24 in the accord, cr-v or element.
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That's the exact opposite, and is wrong. I have to repeat this so many times.
Quote:
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Originally Posted by vtec.net
On the road, the Fit's 1.5L SOHC 16-valve 4-cylinder (117hp@6600 rpm, 106lb-ft@4800 rpm, codename L15A7) has been fortified with "real" VTEC, meaning it actually has dual discrete lift profiles that the intake valves follow, and the difference over last year's "mild" VTEC motor (which switched between 3- and 4-valve operation) is immediately noticeable. On paper the differences don't sound like a lot (+8 hp, +1 lb-ft) but the new version of the engine makes noticeably more torque everywhere below 4000 rpms and above about 5500 rpms, and the difference can easily be felt.
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You don't need a DOHC engine to have separate lift profiles. There isn't a profile for each cam. Learn how VTEC works.
R18 runs on HIGH cam profiles by default, and LOW cam profiles when hitting v-tec. Under normal/aggressive driving, it runs at a high cam profile, where vtec isn't engaged. When "vtec engages", it switches to the low cam profile, and is preventing pumping losses due to premature intake valve closure--a benefit of the DBW system. (I put engage in quotes, because vtec doesn't exactly turn on--it's really just the syncro pin switching the cams to a different profile)
The activation of the economy-oriented low cam profile is contingent upon your driving style--hence if you're flooring it all the time, then technically it never even "engages" vtec.
This is why it's called i-vtec, but it's the reverse of how i-vtec works for the K20. Unlike the K20, the syncro piston in the R18 slides to engage the lower profile when the right fuel economy conditions are met, whereas in the K20 the syncro piston moves to engage the high profile when you're flooring it at higher RPMs.
A diagram to show how i-vtec works on the R18
It's the opposite of the L15A. The L15A has one lobe used for "low" cam profile. By default, the L-shaped rocker arm on the L15A drives both the intake and exhaust intake valves from the cam low-profile when v-tec is "off." When "vtec engages", it switches to the higher cam profile for power. It's the exact opposite of the R18.
*****Cliff notes:*****
R18 (Civic): high-cam normally, low-cam when v-tec "engages"; v-tec engages at
low RPM
L15 (Fit): low-cam normally, high-cam when v-tec "engages"; v-tec engages at
high RPM
K20 (Civic Si): low-cam normally, high-cam when v-tec "engages"; v-tec engages at
high RPM
Conclusion: L15A v-tec is like K20 v-tec.
Honda L-Series SOHC i-VTEC Engines for the new GD Honda Fit/Jazz