I've raced k20 civics for years. One particular car/engine combo has spent many a lap spinning at 9000rpm and the engine is completely bone stock.

Seriously, I couldn't begin to count the number of times that car has gone over 8500rpms. Lots of nasty, high-rev downshifts for maximum engine braking...

K20 has a 13mm shorter stroke they can rev all day long. I wouldn't be taking a k24 99 mm stroke to 9k to often unless it was a drag only race motor with light rotating assembly

Yes the long stroke has a few rpm limiting factors. The piston speed at 9K rpm exceeds that of F1 engines, not good for longevity or performance. The longer stroke allows for a wider power band, so performance at sub 8K rpm with the K24 motor is still better than the high rpm K20. I have a K24a2 ready to rock my world as soon as I have the kit.

What mods are done to your k ?

I will be running a basic stock TSX engine with the supporting mods for the swap only for the first year. I have a second motor that will be modified once any kinks are ironed out for the second round. It will stay non turbo, but compression, head work, cams, and probably ITB's are in the works. At that time some transmission mods and sort out a gear for the diff will be in order. The car will be sub 2000 lb.
Photos

Sweet about the same game plan as me but I'm gonna go forced induction after it's all sorted out, kraftwerks or turbo

Saw dave out racing the kmiata at Gridlife this last weekend. Car is amazing.

Pics or ban.

Pic from the weekend:
https://www.miataturbo.net/attachmen...ine=1401804634

He was also at Mid Ohio yesterday with Autointerests and was looking pretty quick. 1:45s on 225 NT01s. He was telling me he already has 4 trackdays and 2500 street miles on the development car with zero issues. It is awesome to this all coming together.

Its killing me, but somewhere I found a very good discussion of the K24s properties with regard to high RPMs. It went way beyond just calculations of stroke vs. RPM to get an average piston speed. It looked at the (very good for a stocker) rod angles of the K24. What I took away from it was that for a 99MM stroke, the K24 is very capable of reving out of the box. It was on K20a somewhere.

Now I need to do some research and see if anyone is throwing K20 cranks in K24 blocks and very long rods for really good rod ratios. Maybe yes. When the 2.1L 4G6X engines appeared the full-on drag psychos loved them. The much more headroom and stability meant that much more playtime with basketball sized turbos. Plus the cylinder filling characteristics mean you can get jiggy with cam profiles to take advantage if you want to go all $pecial. I just don't know yet if that's possible/being done with these.

The K24's rod ratio is 1.55
Its not terrible, but I wouldnt call it good. Most of the other Honda engines in that rande (D16, B20, etc.) are typically only revved to around 8k unless its a drag car.

I started putting this together a while back but never got around to adding much more than Honda and a couple Mazdas.
https://www.miataturbo.net/attachmen...ine=1401837750

Does anyone have access to the original pics?

Rod ratio is a REALLY small part of the equation. The F2T has close to an "ideal" rod ratio. Mazda made an F-series motor with a 2:1 rod ratio (seriously), and it sucks dick.

Here's a couple data points for that chart:

F2/F2T - 1.68
Long rod FE3 - 1.92 (FE crank in F2 block, G6 rods, F2 pistons, Fe3 head. Or keep it SOHC for full retard status)
F8/F8 DOHC - 2

Ohh me me lets add:
KLDE/G4: 84.5 74.2 2497 137.82 1.14 1.86 9.5 7500 170 68
KLZE: last four numbers are 10.0 7600 200 80

I think you have the redlines backwards. ;) The ZE on a stock ZE ecu will spin to 7600rpms.

Ahh ok, I wasn't sure. I thought it was 7000 to keep the retainers from breaking.

Yeah this car is already silly amounts of fun on track. And its still 100% street car mode with the Koni/GC setup. No other performance mods besides the swap, wheels, and tires.

Only 217 whp right now too, revving to 8000, but I did swap in a 6 speed with the 4.3. I was reviewing some footage from the long weekend and will post it soon.

Lots more development for the car, just trying to keep it a fun street/track toy that can show off what a basic weekend warrior K Miata can do. Xidas, a wing, and 30 more whp should do the trick...

So how does the new 6spd combo compare to the old setup with this swap?

It's pretty good considering the 8000rpm redline. But I think this combo is better for a k20 revving to 8500-9000. I think I'm going to put in a 4.10 and that will be perfect for most tracks.

Just an update the B16B's redline is 8500 not 9k, C5 is 8400 and C1 is 8200.

Anyone grabbing a kit for a RHD miata yet? or maybe a direct over head shot so I can guage somethings.

Keep up the good work!