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-   -   K20A VTEC breakdown (https://www.superhonda.com/forum/showthread.php?t=124797)

05 tC 04-29-2003 05:19 AM

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.

https://www.superhonda.com/photopost/.../k20a2cams.jpg

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.

https://www.superhonda.com/photopost/...kseriesvtc.jpg

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:

https://www.superhonda.com/photopost/.../k20a3cams.jpg

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 high-RPM (short) runners in use, and on the bottom, you can see the low-RPM (long) runners are in use.

https://www.superhonda.com/photopost/...a3srunners.gif

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.

* * *

Sources of pictures and information (good reading material):
http://www.leecao.com/honda/vtec/index.html
http://www.hondata.com/techk20general.html

Here are some bigger pics of the two different heads:
http://ephatch.com/forum/attachment.php?postid=92101

ProspeedCTR 10-25-2005 05:03 PM

GREAT WRITE UP!!!!

ABCsR2EZ4Me 10-25-2005 07:08 PM

That is so informative. Now I understand why people keep wanting to swap the k20a2 head onto the k24 blocks. Makes total sense now.

revtune 11-04-2005 02:20 PM

It should also be mentioned that the extra power in the base RSX might also be because of the fact that it lacks balancing shafts. The Civic Si has balancing shafts built into its oil pump, the base RSX uses an oil pump like the RSX-S. So the intake may add a bit of power, and the lack of balance shafts possibly adds a little more.

EP3Driver 11-04-2005 04:53 PM

Thanks for the info. I have a k20A2 car myself. 2004 Civic Si. Yeah it only redlines at 6800 which really sucks. Question. Doesnt hondata let you redline up to 7800? My friend has a K20A2 also, got him hondata, programmed it and boom, redlines at 7900. So the K20A2 engine isnt really a i-v t e c h or dohc, its really v t e c h-E. Call me stupid,ijuts want to be sure for myself.

joeu 11-05-2005 09:22 AM

Thank you for cool information, man I learned lots today, now I know why my accord can't spin wheels like my camaro, I think Vtec is the way to go for everyday car (but thats me).

Joe

mad-ass 11-05-2005 09:24 AM

Quote:

Originally Posted by EP3Driver
Thanks for the info. I have a k20A2 car myself. 2004 Civic Si. Yeah it only redlines at 6800 which really sucks. Question. Doesnt hondata let you redline up to 7800? My friend has a K20A2 also, got him hondata, programmed it and boom, redlines at 7900. So the K20A2 engine isnt really a i-v t e c h or dohc, its really v t e c h-E. Call me stupid,ijuts want to be sure for myself.

i think you are haveing confusion with engine codes.

K20a - DC5/EP3 Type-R motor
K20a2 - RSX-S
K20a3 - RSX base, civic Si motor.

why do you ask such question when your firend already did it and probably have shown you this to you?

DOHC - Dual Over Head Cam
it's VTEC, not VTEC.H

K20a3's setup is "i-VTEC-E"

this wasn't mentioned, atleast not pictures. the exhaust cam shaft fround in K20a3[Si] only has one lobe, which meaning it only has one level of exhaust valve opening. you can look at this as more like your norman SOHC engines found in older generation of Accord[F23a1, F22b, F22a's] and all Non-Si Civic. so what you get in the 02~04 Civic Si is a Echnomical DOHC engine. you can kind of compare K20a2 and K20a3 to B18C1[GS-R] to B18b[LS, GS], made for gas saving, not for performance.

read the links provided at the end of the article. should get your understanding cleared up :)

EP3Driver 11-05-2005 01:13 PM

O my bad for the spelling, I was in a rush and didnt think. I meant the K20A3. I was asking the question just to clear my understandings some more. Anyways, that helped me. Thanks.

gsrboy171 11-06-2005 01:02 PM

Quote:

Originally Posted by EP3Driver
O my bad for the spelling, I was in a rush and didnt think. I meant the K20A3. I was asking the question just to clear my understandings some more. Anyways, that helped me. Thanks.

you can change the head on your motor to a K20a

rockintheEKoupe 11-07-2005 05:24 PM

Well Figgen done. People like you make this site worthwhile. and you can swap to a K20a on any K20.

mad-ass 11-07-2005 09:00 PM

Quote:

Originally Posted by rockintheEKoupe
Well Figgen done. People like you make this site worthwhile. and you can swap to a K20a on any K20.

and K24 ;)

_suleman 11-08-2005 07:55 AM

well damn, now i want a k20head.

accordjtstyle 01-28-2006 05:52 PM

VTC question
 
Great Thread. Very nice writeup. However...Could someone please explain how the VTC works? I did a little research and noticed that the K20A2 has a 50 degree cam and that the TSX has a 25 degree cam. Meaning it can adjust the cams up to 50 total degrees in advancement or retardment? Thats crazy? Anyone know how much it normally adjusts? With K-pro you can swap the cam gears, but are you able to tune it?

Thanks.

and yes I know. Back from the dead. But best info i could find.

nojdmsadness 01-29-2006 06:42 PM

:clap very informative

red.gsr/itr 02-02-2006 01:09 PM

rep! nice and informative. thanks!


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