My sons and I have had great experiences with 8th Gen Civic Si as daily drivers. My younger son's 2007 Si's engine developed a rod knock and we bought a slightly tired 2007 with no 3rd gear for its engine and swapped it in. So now we have a worn but rust free shell that we could sell, part out, or turn into a project car. It looks one option is a K24 swap, with a formula like this:
- Use a K24-A2 out of a TSX
- Remove the balance shafts
- Use aftermarket adjustable timing gears
- Use an Acura RSX oil pump
- Aftermarket tune of course
I'm too lazy to read every Honda forum, so I thought I'd ask the hive and see who can chime in with experience. I'm also curious about:
- Does removing the balance shafts and the oil pump swap just free up a few more HP, or is there more going on?
- Similar with aftermarket gears--does that just help change the timing more radically to pick up more top end?
And, third gear synchro issues are well known with these transaxles. The bad one felt like it was freewheeling in 3rd gear, so I'm thinking the synchro or something is keeping the gears from fully engaging . I'm assuming there are teeth on the gears as the gearbox is otherwise fine an no chunks of metal have been found. Anyone with experience fixing these?
Thanks for your advice!
The K20 oil pump shaves some weight and a significant amount of rotating weight. You're also not dumping oil into a balance shaft assembly without good reason (I can never tell the difference between K24s with and without balance shafts) the K20 oil pump is also better suited to sports car work than the integral pump/balance shaft assembly. Power, weight, oiling system efficiency.
K24s use a VTC gear that only moves 25 degrees. Fun K20s use one that will move as much as 50 degrees you'll want one that is mechanically limited to 40 degrees or so or to be very conservative with cam advance in the tune you can crash valves into pistons in a 2.4 with a 50 degree VTC gear.
Very easy trans to get inside of. If you have any familiarity with rebuilding manual transmission it should be a cakewalk. Replace the master with one from a 99 Civic SI, replace the slave with the one from a 2004 Civic Si, replace the clutch line with one from K tuned or similar. Run Redline MTL or MT85 in the trans.
In reply to Byrneon27 :
Thanks, these are the kinds of tips I was hoping for. Curious about changing the clutch hydraulics--they feel like butter on the stock Si's. Do you change them to get faster engagement/disengagement?
To get rid of the weird diaphragm valve thing in the 8th gen and up hydraulics. Think a BMW style clutch delay valve but more intrusive and not removable. If you're shifting quickly in one of these cars you're putting undue force on the synchro because of less than ideal clutch disengagement.
In reply to Byrneon27 :
Got it. I wasn't aware the 8th gen had that. My 10th gen Si had it and it was very noticeable and annoying. It was easily removed on that car.
If it's a street car I say keep the stock balance shaft oil pump system. If it's a race car or mostly spirited use then go down the k20a oil pump road. The vibrations from removing the assembly are noticeable and maybe it's my old age showing, but I wasn't a fan. I imagine the power difference is around 10-15hp and potentially more revs available? Not sure if there's ever been any real proper tests to confirm the power loss. My guess is you'll feel the difference only in vibes, power you won't feel at all. That said the 2.4 also doesn't gain power by being revved out like a 2.0 without installing proper cams. They fall on their face around 7k or just before if I remember correctly.
Timing gear upgrade is worth it but you need to be able to tune that system to be useful.
