K20A2 vs K20A3

[Spikedoll]

The K20A3 used on local version DC5 GSR does not have a standard DOHC VTEC valvetrain as we know it from the B-series engines - the K20A3 should actually be called a "DOHC i-VTEC-E" engine, because it uses a VTEC-E cam setup. The K20A2 is the "real" DOHC i-VTEC engine, utilizing the standard DOHC VTEC cam setup we're all familiar with. To help you understand the differences between the K20A2 and K20A3 engines.

Let's start out by defining some terms:

 

VTEC - Variable valve Timing and lift Electronic Control. At low RPM, a VTEC engine uses a normal cam profile to retain a smooth idle, good fuel economy, and good low-end power delivery. The VTEC mechanism engages a high-lift, long-duration "race" cam profile at a set RPM value (i.e., ~5500RPM on the B16A) to increase high-end power delivery.

 

VTEC-E - Variable valve Timing and lift Electronic Control for Efficiency. This system isn't really VTEC as we know it. At low RPM, the VTEC-E mechanism effectively forces the engine to operate as a 12-valve engine - one of the intake valves does not open fully, thus decreasing fuel consumption. At a set RPM value (i.e., ~2500RPM in the D16Y5), the VTEC-E mechanism engages the 2nd intake valve, effectively resuming operation as a normal 16-valve engine. Note: in a VTEC-E engine, there are no high-RPM performance cam profiles; this engine is supposed to be tuned for fuel economy, right?

 

VTC - Variable Timing Control. This is a mechanism attached to the end of the intake camshaft only which acts as a continuously variable cam gear - it automatically adjusts the overlap between the intake and exhaust cams, effectively allowing the engine to have the most ideal amount of valve overlap in all RPM ranges. VTC is active at all RPMs.

 

i-VTEC - intelligent Variable valve Timing and lift Electronic Control. This is a combination of both the VTEC and the VTC technologies - in other words, i-VTEC = VTEC + VTC. Currently, the only engines that use the i-VTEC system are the DOHC K-series engines.

 

Now this is where things get tricky - Honda uses the term "DOHC i-VTEC" for two different systems: The first system is used in the K20A2 engine of the RSX Type-S. The second system is used in the K20A3 engine of the Civic Si.

 

The First System (K20A2):

 

This system is pretty close to the older DOHC VTEC engines. At low RPM, the K20A2 uses a normal cam profile to retain a smooth idle, good fuel economy, and good low-end power delivery. At 5800RPM, its VTEC mechanism engages a high-lift, long-duration "race" cam profile to increase high-end power delivery. The only difference between this i-VTEC engine and the older VTEC engines is the addition of the VTC system. The intake camshaft has the automatic self-adjusting cam gear which continuously optimizes valve overlap for all RPM ranges.

 

The intake cam lobes of the K20A2. Notice there are 3 lobes; the two side lobes are the low-RPM profiles, and the center lobe is the high-lift, long-duration profile which engages at 5800RPM. Basically the same setup as the old VTEC engines we are familiar with.

 

The VTC mechanism - the gear on the end of the intake cam that adjusts valve timing (overlap) automatically on the fly.

 

This system is used in engines powering the JDM Honda Integra Type-R, Civic Type-R, Accord Euro-R, and the USDM Acura RSX Type-S and TSX.

 

The Second System (K20A3):

 

This system does not really conform to the "DOHC i-VTEC" nomenclature, as Honda would like us to believe. As I mentioned in my previous post, it actually should be called "i-VTEC-E," because it uses a VTEC-E mechanism rather than a standard VTEC mechanism. At low RPM, the VTEC-E system effectively forces the engine to operate as a 12-valve engine - one of the intake valves does not open fully, thus decreasing fuel consumption. At 2200RPM, the VTEC-E system engages the 2nd intake valve, effectively resuming operation as a normal 16-valve engine. There are no high-RPM performance cam profiles; this engine is tuned to balance fuel economy and power, rather than provide pure performance. On the intake cam, there is the VTC mechanism which basically is an automatic self-adjusting cam gear used to continuously optimize the valve overlap for all RPM ranges. This being a VTEC-E system - and not a true DOHC VTEC system - is the reason the K20A3 redlines at a measly 6800RPM, while the K20A2 is able to rev all the way to 7900RPM.

 

The intake cam lobes of the K20A3. Notice there are only 2 lobes - there is a nearly round one used only for the low-RPM disabled intake valve, and then there is the regular lobe used by the other valve at low-RPM and by both valves at high-RPM:

This system is used in engines powering the USDM Acura RSX base, Honda Civic Si, Accord 4-cylinder, CRV, and Element.

 

Special note: The K20A3 engine used in the Acura RSX base has a slightly different intake manifold design from the K20A3 engine used in the Civic Si. The RSX engine uses a dual-stage manifold, similar in concept to the manifold of the B18C1 in the old Integra GSR. It uses long intake runners at low-RPM to retain low end power, and switches at 4700RPM to a set of shorter intake runners to enhance high-end torque. This accounts for the extra 9 ft-lb of torque in the RSX (141 ft-lb, vs. 132 ft-lb in the Civic Si).

 

Myths:

 

1. The i-VTEC engine engages VTEC gradually, and not suddenly like in the old VTEC engines.

 

Wrong. The i-VTEC engine "engages VTEC" at a single set RPM, like always. Whoever started this rumor is a fxxktard. Read the definitions above.

 

2. VTC engages at a set RPM.

 

Wrong. VTC is always activated. Read under "VTC" above.

 

3. The K20A3 engages VTEC at 5000+ RPM.

 

Wrong. Technically, there is no "VTEC" (as we think of it) in the K20A3 engine - it uses a VTEC-E technology, which engages at 2200RPM. Read under "The Second Sytem" above.

[YellowFlash]

wow...i learn alot of new things.

[Jeffrey]

No wonder my CRV does not have any resemblence to my previous VTEC (B16A)- in terms of providing the high RPM power surge!

[Atlantis_boi]

Very gd write-up I learnt something frm it

[W210k]

The K20A2 engine is the real VTEC McCoy to me. Only thing is that its engine response may be considered 'peaky' by the non-racing types.

 

Similarly, Toyota's VVTL-i BEAMS engined models have 2 sets of tune too. One for the race-bred and the other for the street.

 

I wonder why Kah Motor does not currently bring in any of the Honda models with K20A2 engine? Though niche market, I think there will be sufficient interest to support in SG.

[Stivo]

:) finally someone cleared the lights!!

 

I have told actually asked the SE before regarding this 7 or 8 months ago but they assured me K20A3 is the same as K20A2 and in fact better, i am very sure at that time before i went to Honda. We actually disassembled a K20A3 engine block and was shock to find that high cam gears are not in there!!

 

Hmm...marketing!!!

[Flaser]

What about the K20A1 engines used on the Stream? Are they similar to the K20A3?

The Stream 2.0L also comes with dual-stage intake runners.

[Silver_z]

I recently went to Kah Motors and the SE dare to argue that the K20A3 has high cams like the B-Series engines, when I told him that the A3 is only switching from 12 valves to 16 vales unlike the A2 which switches from low to high cams. KNS! Thats why I say PIs are better than Authorized Dealers. They use the Authorized Dealer tag to make them look more knowledgeable, when in fact they have no clue of what they are selling.

[Maxxtotal]

no wonder the last and current VTEC on normal cars has so-so power.

 

does this apply to MIVEC also? the MIVEC nowadays also no significant power, unlike the older days when the can achieve 100bhp/l just like the VTEC

Edited May 4, 2006 by Maxxtotal

[Yc86]

another interesting readup can be found here:

http://www.leecao.com/honda/vtec/index.html

 

i thought the "i" in i-VTEC means intake, not intelligent?

as quoted from another site:

 

i-VTEC introduced continuously variable camshaft phasing on the intake cam of DOHC VTEC engines. The technology first appeared on Honda's K-series four cylinder engine family in 2002. Valve lift and duration are still limited to distinct low and high rpm profiles, but the intake camshaft is now capable of advancing between 25 and 50 degrees (depending upon engine configuration) during operation. Phase changes are implemented by a computer controlled, oil driven adjustable cam gear. Phasing is determined by a combination of engine load and rpm, ranging from fully retarded at idle to maximum advance at full throttle and low rpms. The effect is further optimization of torque output, especially at low and midrange RPMs.

[Spikedoll]

bro sorry..me not so sure abt mivec ...maybe u can checkout mitsubishi clubs in sg...hehe

[Atlantis_boi]

does this apply to MIVEC also? the MIVEC nowadays also no significant power, unlike the older days when the can achieve 100bhp/l just like the VTEC

 

Tat was the Mivec found in the Lancer MR. V.gd power. The Mivec found in the Dc3 Colt is much more mild, more like for fuel efficiency

[Maxxtotal]

yes yes, the previous gen Lancer MIVEC 1.6

 

and Galant VRM 2.0l, 200bhp 200NM

[Vblaster_w211]

K20A is the traditional VTEC high cam action high rev NA engine, as used in Type R DC5.

 

K20A3 is used in Type S and GSR DC5. It lacks VTEC high cam, but is very economical as when lower than 2200 rpm, it'll operate 12 valves, and only open 16 valves when revved higher. Some variants in sportier rides, like those in Type S and GSR has a variable intake that switches between short and longer air intake manifold path. It also sustains the opening of valves more aggressively when revved on the intake side, whereas the K20A is active on both in and out.

 

Although lacking true high cam action, try a ride on a properly tuned K20A3 DC5 and you'll realise it's quite different from Civic 2.0, Stream 2.0 etc.

[Flaser]

Edited May 6, 2006 by Flaser