Manimal's Honda K24 Swap 260z

[manimal]

It's been a long time coming, but the car finally runs in it's second iteration. I purchased it around 10 years ago when I had a few non-running projects thinking "buying another project that runs and needs work is a good idea". It stops running almost immediately, then a move disrupts the progress. Two years later a second move is motivation to get it to running since driving it into the garage is the only way it'll make it.

The moment I got it running again and had a rather scary drive around the block. Fuel lines dripping, brakes barely working, and really struggling to hold an idle.

Replaced the fuel lines and got it to run just enough to drive it up the steep single car driveway. Oct 2018, up on blocks for a refresh. Rust ended up being worse than I expected. The bushing/brake/engine/suspension refresh turned into disassembling it to the shell, leaving on the windshield in since it had a crack.

Over the next year I patched the floor panels and battery area. Replaced the OE "frame rails" with some 40x70x2.4mm box tubing. Made some "K" braces and a brake master cyl brace. Added plates for a strut/firewall brace.

Now in November 2019 I had a change which necessitated getting the car done by may 2020... Unfortunately the car was poorly done primer when I bought it and the PO had sanded through the paint in many places so surface rust was showing all over it. I decided to sand and do my best with Rustoleum Industrial primer, then paint, in late November-December. The results are meh, but I don't have to worry about it getting dinged and the plan was/is to make it my daily.

1

After the painting I sectioned the struts, fitted Bilstein VW rabbit inserts, retained the factory top hats, and added 2.5" adjustable sleeves + springs. The rest of the suspension/driveline was cleaned up, fluids replaced, new brake pads/rotors/master cyl, and front wheel bearings. Cleaned the fuel tank and replaced the vent lines. Also fabricated a 2.5" header back exhaust tucked up tight for ground clearance.

 

The car is an early '74 and has the stupid interlock system. I decided to remove it from the wiring harness. While doing this I also re-routed power for the headlights, running lights, wiper(honda motor swap there too), etc... No all of that is on relays and the combi switch is only supplying a few amps so it shouldn't burn up. This was my first time doing any electrical beyond a simple relay harness for an electric fan. Many hours were spent staring at wiring diagrams, tracing, and labeling.

reassembly

I got lucky and it started first try. Definitely didn't think that would happen considering all of the wiring harness changes. May 2020.


Moved out three days later and parked the car at a friend's shop since I didn't have space at the time...and it sat again. Worked on it a bit, but never got it to run as well as I had hoped. It was running the factory L26 with a pair of weber 32/36s. The motor was definitely a bit tired. I was facing another move to a much bigger city(late 2021) where I wouldn't have a garage, spare parking spot, or place to work on the car. I debated a few options like L28/old fuel injection, Ztherapy carbs on a rebuilt or better condition L24/6/8, megasquirt, etc... At the time there weren't any running engines within 200 miles and the above options all cost quite a lot for something still questionable. I considered a LS, but at the time believed that would have led to needing a rear end update as well.

Enter, the K.

[manimal]

RWD K swaps started showing up in social media a lot around this time. After running the numbers, I figured I could do the entire K swap for around the cost of a reputable built higher output L28, but then I'd have a lighter car, better transmission, more reliable running/starting, better mpg, and an engine which can be replaced at any point for <$1000. I was working for a company with the industrial tools a home fabricator dreams about, 4kw sheet/tube laser, cnc press brakes, professional 3d scanner, and a lot of scrap metal in many thicknesses/tube profiles.

 

***this is a very short summary of a 12-18 month project, more to come later***
April 2022 I moved the car to my parents packed garage and got to work with the 3d scanner. After reading a lot of forum posts I made a spreadsheet of what I thought I needed and started buying parts. The 3d scanner was incredible to use, though the entire process of scan to workable model oriented in space was a lot more involved than I expected.
Bye bye L26

Hello K

First test fit, many hours spent getting the alignment just right.

First test fit with the prototype mounts

The project involved many detours like a bike rack w/1.25" hitch receiver. Mainly due to the excitement of being able to build whatever I could dream up with sheet metal and tube, this project took 9-12 months longer than if the only goal was the engine swap.

Overlay of the K24 located in the model(yellow) vs the engine scanned in the car(grey). Pretty close, adjustment side to side/fore-aft was built into the mounts.

 

 

[manimal]

As of earlier this evening, right after I got it running/idling for the first time.

 

I've got a few full days the next week so I might not update this for a bit. I plan on cleaning up my wiring notes, spreadsheet of purchased parts, and collection of helpful links. I'll post all that in the next few weeks. I'm also going to be selling the engine/transmission mounts. I haven't decided on a price yet, but I do have a few sets welded and powder coated already.

 

Something I was very curious about during the process is the final weight of the car and what the difference between the L26 and K24 was. I weighed every major part and most of the minor ones, all of that will end up in a spread sheet eventually. I don't have automotive scales, but I do have two 400lb bathroom scales. To make this as accurate as I could I made three platforms the same height as the scales with a bridge board on them so the corner being measured is at the same height as the other three. As it sits with 4 gallons of gas and missing ~175lbs worth of body parts the car is 1860lbs. If those bathroom scales are correct it should weigh <2100lbs with a full tank. In a few weeks I'll have a chance to throw it on actual scales and get a much more accurate reading.

[manimal]

Drove it for the first time yesterday. Still more testing to do, but it didn't overheat.

 

A lesson for anyone K swapping with Hondata Kpro who doesn't have experience tuning is start with the provided TSX 04-05 91 octane basemap and the original 310cc injectors. This is my first tunable ecu engine swap. I tried to start with 550cc injectors using the stated base map with corrected injector size and voltage compensation numbers. It ran so bad and ended up throwing a P1166 code for a bad o2 sensor, even though the o2 sensor is a new OEM unit. I bought another new one and installed it, no change, though the P1166 code didn't come back. AFRs were crazy reading in the low 20's at idle. After making some adjustments to the fuel numbers based on the datalog it still ran terrible and had a high idle around 1350.

 

After messing with it for a few days and reading everything I could find I put the stock 310cc injectors in, loaded the TSX 91 octane base map, and it immediately started to idle around 950-1000. With some minor adjustments to the throttle stop it smoothed out, held close to 1000 idle, and had much more stable AFRs around 14.5-15. It still has a weird idle issue where when it warms up it like to idle around 1200. Sometimes after driving for a bit it'll idle at 1050-1100, other times when the temp is the same it wants to idle at 1300.

 

Still a lot more to do, but getting it out for a drive really helps the motivation on a very long project.

[HIWAY ONE]

Nice project!