Lately I'm seriously considering doing a K-series conversion to my Insight. My logic: at some point the IMA battery will need to be replaced. If I lived somewhere more flat it wouldn't be a big deal to just bypass it, but Vermont's mountains make the car a bear to drive without assist. I'm approaching 250k miles on the engine with zero problems so far, and have no idea how many miles I can put on it. My transmission needs a "tabectomy", it grinds when downshifting into first and second. Undoubtedly the least expensive option is to just keep it running with factory parts, but I can't help but dream and it might be best to do this while the components I'm taking out still have value.
My ideal swap would be the drivetrain from one of Honda's more recent hybrids. However, nobody knows how to do this.
Next best would be a modern L15B out of the 2015+ Fit. This is the same motor as is in the 1.5T Civic, just without the turbo. These have an offset crank and a lot of low friction technologies. Despite the gearing they're pretty well tuned for economy. I could re-use the really tall ~3.2 final drive out of my Insight's transmission, or the entire transmission, since the Insight's engine is secretly an "L" engine too. Unfortunately the L motors are quite tall, the intake manifold tilts upward and sits on top of the engine (making it even taller!) and there are virtually no aftermarket options. So, I'm probably going K as I won't be able to make it fit under the hood.
My idea: Obtain one of the higher compression "K" engines with integrated exhaust manifolds which nobody wants. The king of K motors in my opinion is the K24W7 out of the 2015+ Acura TLX, with a mouth-watering 11.7:1 compression ratio and 182 ft*lbs of torque at 3900rpm, but the K24W out of the recent Accord and CR-V (at "only" 11.1:1) can run on 87 so that would be a decent option too.
Undecided on a 5 vs 6 speed. Weight and size may dictate that. However, whichever way I go, I'll likely have a custom ~3.4 final drive made for it, which would bring 65mph cruising RPM down to ~2200 with the Insight's stock tire size, lower if I go a hair bigger.
A shop in Florida has successfully tuned the older K20A2 motors to run at 19:1 AFR at part throttle, and reports in excess of 50mpg highway in the Insight body.
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Well, The K-Sight is a pretty nice car and we're not really drag racing it. But we have logged a couple of low 3 second 0-60 times using the Hondata K-Pro.
We have took it to some local shows as well as SEMA and have managed 57mpg without any issues.
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^ Mind you their low-3 second 0-60 is with a turbo, which I would not have.
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I have my K24 insight running at this point and have taken it on longer trips. The best I have gotten on a base map is 49MPG at an honest 85MPH for a 5-hour trip. This is with a custom final drive and the longest 6th gear available which drastically improves cruising rpm from 3700 to 2500. It was also on snow tires, haha. I plan to lean burn tune it soon to see if I can improve from there.
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49mpg at 85mph is actually quite close to what the Insight's stock engine gets, probably because it's running outside of peak BSFC at that speed.
Dry weight of the car is ~1850lbs with A/C.
Insight engine - 128lbs
IMA battery - 95lbs
Insight manual transmission - 56lbs
MDM + DC-DC - 20lbs? estimated
Total: ~300lbs
57:43 weight distribution
K-series 6 speed weight: 89lbs
K-series 5 speed weight: 87lbs
K24 engine - 283lbs
K20 engine - 275lbs
Total: 360-375lbs, plus maybe a bit more in brackets and alternator
I'd be adding ~100lbs to the car. More importantly, this will throw off the weight distribution, adding ~200lbs to the front and subtracting around 120lbs from the rear. Ideally I'd re-use the IMA power cables and migrate the 12v battery to the back of the car, maybe switch to an AGM battery for safety (and efficiency) reasons.
I've exchanged a few emails with a shop in NYC with a lot of experience with K swaps. We'll see where this goes.