k20a3 compared to k20a

[taffeta_wht_si]

I have a few questions about the difference in the block and head of the k20a to the k20a3. I have been pricing k20a engine internals to swap into my k20a3. Here is my biggest question though: Is the crankshaft the same in the k20a as it is in my si. I am looking to buy k20a pistons, rods, camshafts, springs, and valves. I just want to know if this is a safe swap to do into the k20a3 block and head? I know I am going to have to get a reflash and stuff. The reason I am not getting the entire k20a swap is $$$. This way I can piece it together. Just curious. Any help is greatly appreciated

[DavidT]

The A2 crank is forged...the A3 is not. The A2 crank is also balanced to 8k from the factory and the A3 is not.

On the cams and valves idea. In theory it's a good idea, but in reality it will not work. Your A3 head does not have the castings for the lost motion springs that are required for the 3-lobe per two valve operation of VTEC. So...your plan simply will not work.

You can beef up your bottom end because those parts are interchangable...but it won't do you much good without a good free flowing head :( That's why a lot of people do (Or are considering) the A2 head swap, the cams simply will not work on our A3 heads.

[taffeta_wht_si]

Thanks for the input. I am very new to the k20 (I was a big h series guy) so Im still learning the specifics. I have actually been toying with the idea of just getting an k20a2 head. I have had some people tell me there really isnt much diff between the a2 and a head. I dunno if this is for real or not though. But as far as the crank with it withstand the same revs as say the a2 crank

[taffeta_wht_si]

About the crank. I have heard that the k20a3 crank was tested up to 8300 rpm. Also what about hondatas reflash that takes it to 7700 rpm. I may end up just having to piece the whole thing together anyway but I guess I am just trying to see my options

[DavidT]

I'm sure it will withstand the revs...for how long? Who knows. It hasn't been put to the test yet :) To date I haven't heard of anyone breaking a rod because of over revving, I've only heard of valvetrain failure so I assume the A3 block will handle the revs for alittle while.

I was an h-series guy too :cool: Use to own a 2000 Prelude SH. Also incase you didn't know, the A3 has the dual balancer shafts like the h-series motors. The A2 doesn't, yet another reason to just go with a swap. The A2 was setup from the factory for high revving applications. The 03+ A2s uses the same valve springs as the 02-03 S2000s (Which has a 9k redline). The A2 motor is a superb balanced piece of art from the factory and it will withstand 8600+ RPMs all day long without hiccups.

If you're seriously thinking about going all motor. I'd just sell your A3 for around $3k or so and then find an A2 for around $5k and call it good. That's my opinion and others will vary :)

[myeverlovinsir]

The variation is that I have reved my ride into the 8+ rpm range on the A3 block many times and recently hit 9k (datalogged) at the track in 1st and 2nd gears without a problem. There are a limited amount of persons who are willing to test it that far, and for good reason. I don't intentionally want to blow my engine but feel a little more confident after a month of high revs at the track. The A3 block is capable of 9k but I would not try it with the A3 head. Just my .02 cents.

[taffeta_wht_si]

Thanks guys, Hey what setups are you guys running, I am assuming they are NA. myeverlovinsir you said that you ran high revs at the track. What times are you getting with your setup. The whole reason I am trying to figure this out is because I bought my si used about a month ago with 19,000 miles on it. Didnt figure there would be anything wrong with it so I didnt check that well. Well it turns the previous owner ran nitrous in it and messed up two of the cylinders. The car still idles perfect and is very clean but the compression on cylinders 2 and 3 is very low and I can hear a valve tapping on cylinder 3. So thats why Im trying to figure out where to go from here.

[myeverlovinsir]

Where to go? Get yourself a head swap or fix the valve issues. It sounds like you have a lemon and with poor compression in a couple of cylinders, they will need attention first. I will provide timeslips soon.

[taffeta_wht_si]

Originally posted by myeverlovinsir
Where to go? Get yourself a head swap or fix the valve issues. It sounds like you have a lemon and with poor compression in a couple of cylinders, they will need attention first. I will provide timeslips soon.

The reason I think they ran nitrous is because the spark plug in the 3rd cylinder had the ceramic melted and was bright white. I have been looking for a nicely priced a2 head swap but none yet. Just need to be in the right place at the right time. I`ll be watching for those time slips. Im eager to see em