Honda / Acura K20a K24a Engine Forum banner

1 - 20 of 94 Posts

·
Registered
Joined
·
929 Posts
Discussion Starter #1
K20A VTEC breakdown

--------------------------------------------------------------------------------

-Originally posted by Targa250R-



The K20A3 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, I've included the following information from a post I made elsewhere:

Allow me to evaluate. 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.

Here we see an image of 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.



Now here we see 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.

Here we see an image of 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).

Here is an image showing just how this dual-stage manifold works. On the top, you can see the low-RPM (long) runners are in use, and on the bottom, you can see the high-RPM (short) runners in use.



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 fucktard. 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.
 

·
Registered
Joined
·
2 Posts
Yeah great info . . . but

What about the K20A found in the RSX type R any news about that engine? I mean what does it have that the K20A2 (Type-S) doesn't?

Just wanted to know
 

·
Premium Member
Joined
·
456 Posts
Re: Yeah great info . . . but

K20EF said:
What about the K20A found in the RSX type R any news about that engine? I mean what does it have that the K20A2 (Type-S) doesn't?

Just wanted to know
No it's just like the A3 motor :lol:

No just playing its true VTEC.
 

·
Registered
Joined
·
1 Posts
so is this telling me that a A3 can never be modified to show "some" improvements. would like to swap to A2 but its like $4500 dollars right?

"some" meaning is there a good forum that talks straight A3 mods.....

thx guys this forum really is the shizzzzznt!
 

·
Registered
Joined
·
15,818 Posts
sustane said:
so is this telling me that a A3 can never be modified to show "some" improvements. would like to swap to A2 but its like $4500 dollars right?

"some" meaning is there a good forum that talks straight A3 mods.....

thx guys this forum really is the shizzzzznt!
More like $3000 www.car-parts.com go there and search for a 2003 RSX type-s engine

Also a few people in here are selling them for that much as well
 

·
Registered
Joined
·
13 Posts
Doo-Doo said:
i just learned something about my civic si and how its not really vtec.oh well.
I know how you feel man! Before I knew that I didn't have a high speed cam lobe I could have sworn that I could hear vtec in the high end. I was imagining things. I had to have the good stuff so I swapped a ported and polished type-s cylinder head on my stock block and now I have more vtec than I'll ever need! I highly recommend the swap if you want "real" vtec, not to mention low 14's instead of high 15's!
 

·
Registered
Joined
·
22 Posts
Is there any way to make the k3 a k2 / swap the heads, ofrmaybe replace the cams?? or is a total swap the only way to get it.

I was just gonna swap the motor and trany but then i saw a way to make the 5 speed a six speed for like 1 g, its in hinda tunning this month, so i wounder if i can just convert my k20a3 to a k20a2 set up for less then 3g. O and great post i learned alot abount how my car suxs, thanks. lol. :mad:
 

·
Registered
Joined
·
13 Posts
swapping the cams wont do it because on the type-s head both cams have 3 lobes and on the a3 head the intake side has two lobes and the exaust has only one. Even with cams the a3 head still doesnt have a high speed setting on either cam. The difference is huge when you swap to 3 lobe on both cams. Real vtec is so much different, it's so incredibly loud I love it
 
1 - 20 of 94 Posts
Top