K24Z3 endurance build - Vegas
 

New thread to document It's conversion from turbo BP and AZ6 for S1 to K24Z3 & Quaife sequential for endurance racing. Focus will be on AER, Lucky Dog Racing. Possibly some NASA WERC, Champcar EC class and maybe WRL if we travel east with it.
Vegas was originally built for Supermiata S1 class, finished late 2018. Raced a bit early 2019. Won Super Lap Battle Unlimited RWD in 2018 with it (boost turned way up). S1 (220whp turbo) class never really took off the way S2 (140whp N/A). We tried to future proof
it by including connections for lights everywhere, radios and such in the scratch built harness. Cage is sorta like an FIA cage, far more robust than a traditional Spec Miata style floor mounted 6pt cage.

For enduro, we knew we could improve on the turbo BP and AZ6 drive train. As solid as the turbo kit proved, to total system was still mot as bombproof as we would want for enduros. The AZ6 also a liability in that regard. Beyond that, fuel consumption was the Achilles heel of that drivetrain config. In S1 trim, it was too fast for pretty much any budget enduro series so we didn't need all the power it was making. So we decided to switch from E85 to pump gas, fit a 11.0:1 K24Z3 motor and bolt it to the Quaife, This should drop us from about 16 gallons/hr in S1 trim to about 10 gal/hr and be more reliable to boot. We figure 180whp at around 2200 comp weight should put us in the right window for enduros. One key strategic goal is to be able to run the maximum 2hr stint length on one tank. We'll be slightly short of that, but can probably stretch it out by short shifting if we find ourselves with a gap to 2nd place late in a race.

We're using the Kmiata kit for the K24Z3 swap. The Quaife needs a low MOI clutch/flywheel assembly to allow two pedal driving. By two pedal, we mean flat upshifts and clutchless, blipped downshifts. To downshift, you left foot brake and tap throttle to unload dogs while shoving lever forward. Clunk! Like butta. Being able to shift up or down, anywhere at anytime, instantly and without upsetting the car or worrying about a mis-shift makes driving smoothly so much easier. We decided to design and make our own proprietary flywheel to mate the K24, Kmiata adapter and Quaife our existing 7.25" Racetwin clutch.

We plan to run the exhaust down the pax side, deleting the PPF. We'll make our own trans & diff supports. The PPF becomes a failure point in endurance racing, hanging low and vulnerable. Only needing a 2.5" exhaust at our power level makes routing a bunch easier. Aero will be pretty much the same as S1.
We should be able to run a smaller oil cooler. The huge Setrab we have now is overkill for a K24 on gas running stock redline. By raising the vent tube in the gas tank, we can squeeze a full 15 gallons in their including the filler neck. We have been doing that since 2010.

https://cimg7.ibsrv.net/gimg/www.mia...f311b8c79f.jpg

K24 7.25" Racetwin flywheel & clutch
 

https://www.miataturbo.net/suspensio...-trans-102233/

The flywheel we're making to be able to use our existing 7.25" Racetwin clutch.

https://cimg0.ibsrv.net/gimg/www.mia...6a1d2772d8.jpg
https://cimg8.ibsrv.net/gimg/www.mia...cc0b3aadd0.jpg
https://cimg9.ibsrv.net/gimg/www.mia...40256f310c.jpg

If the quaife bolts in place of an AZ6, does that mean this flywheel could be used with a k24z3 and an AZ6... :fael:

Looking forward to seeing this come together!

Yes, of course.
If if you are interested in one when we do the production run, send an email to info@949racing.com and ask to be put on the list. The only plan to make 10, five of which are already spoken for.

Are you guys going to be doing the same kind of oil pan/ oiling system modifications as on Deviate?

I think the PPF only becomes a failure point when you cut a very large notch out of it :giggle:

Excited to see this all come together though, especially the clutch/flywheel, good shit there.

No need. We're not revving it nearly as high. V-Tec requires a lot of oil volume, no so much pressure. OEM K oil pump cavitates badly when spun well past OEM redline. Long oil tube also has poor .cf. Keep revs lower and it's not much an issue.
PPF bolts and frame hang low and get hit when/if the car goes off track. Particularly vulnerable when car drops two and high centers on track edge. We have seen PPF failures in sprint and enduro. Aside from the lower flange on a Racing Beat header, the F&R PPF bolt heads are the lowest points on the chassis. Ditching the PPF make service easier as well as making exhaust routing far easier for a K.

While I understand the desire to eliminate the PPF because of the transmission and other plans, but the Mazda solved the issue with the bolt heads (before removing it as a cost reduction) with just an aluminum wedge forward of the bolt heads. Been using one of those PPFs on an enduro car for years with no bolt head damage.

A bit more detail on our plan and overall race strategy. We wanted to build a car that could run at the front of the fastest class but still go 2hrs on a tank. Depending on the series (fuel tank rules), this is basically impossible with the OEM tank. No way to get down to the 12-13 lbs/hp or so we will need and only burn 7.5 gal/hr. Most of the faster cars wining Champcar and LDR are fast but not running 2hrs. We won't be able to either so at least its a level playing field. I think LDR allows an aftermarket fuel tank so the possibility remains of dropping a 24 gallon fuel cell in the pax floor. For Champcar we're in EC no matter what so we might as well. We'll get it running with the stock tank first though. Then we'll asses our competitiveness and see if a full cell is warranted.

Still the lowest part of the car by far. The load from any impact goes into the PPF. I can see both side of the rationale, I'm choosing to ditch it.

Isn't the goal of 180HP a little low considering the 09 TSX the Z3 comes from is listed at 201HP? What is your intended engine management? Are you planning on keeping the NB Diff (assuming you have an OSG in there) or move to a Getrag or RX7 unit?

Very interested in how this turns out, and i'm sure there will be a lot to learn from this thread.

180whp vs 201bhp. focus is efficiency. Won't be surprised if it comes in over 180whp though.

Just doing some though exercises with the part of the team that has remained active in enduros the last few years. Don't fixate on power for this project, we're not. We have the luxury of tuning up or down as needed. As you know, there is such a thing as being to fast in budget enduro, depending on the series.
Goal is to have BSFC as low as possible. So free flow intake and exhaust, pump gas, perfect oil and clt temps and a careful tune. On paper at least, we should be able to match the gal/hr of the best BP engine Miatas but have another 50whp or so.

As mentioned earlier, we'll see how the package works in race situation. If its too slow and the fuel economy isn't making up the difference, we'll turn up the wick. I think it'll make about 210whp on gas as is. Cams would bring that to 225 or so. But we hope to be competitive with a junkyard motor, revving it to 7400 for best BSFC. We'll see.

Haltech 2500 ECU. DBW, sequential shift stuff, Vtec (yo)
OEM diff with Supermiata tuned 3.9 OSG. Utterly bomb proof at 400whp with the cooler so no concerns in the 200whp range.

Our test car make 180whp on the first pull with a 2004 TSX basemap, and in 30 mins of tuning we had it making 206whp. There should be some more in it with a bit of intake length tuning, plus our engine is a $300 junkyard block with over 150k on it. I'd expect a fresher engine to do a bit better.

Yup. We published what we think we can run at strategically, not the peak it will be capable of. I'm sure cams, valve springs, E85 and leaning on it would net 230whp or so, but that's not an rock solid, high economy enduro config.

The discussions on the private Team FB group are to have a long list of maps to choose from in the lap top that travels with the car. From about 160whp with 6800rpm redline to Kill, in 15whp increments :D

Please tell me where you've found cams for this motor. Bisimoto had some on the website but they're gone now...

I was more concerned about the diff ears, but if it hasn't snapped in Vegas after the buttonwillow jump, I guess it should be fine.

This gives me high hopes for my 60k mile motor...

I haven't even looked at cams because I doubt we will ever explore that area. Healthy junkyard motor will meet or power goals. My point was just that we are aware that more power is easily available if we need it.
It's scrambling everyones thoughts that our power goals are so modest. BUT ALL THE POWERS!!

https://supermiata.com/Kmiata-differential-gussets.aspx

Yes LDR allows fuel cells, nothing over...22? 24? Just to keep people from making 500hp and running full 2hrs by just running giant tanks. Not the most effective or restrictive cap but it is what it is. We ran close to 200hp and a few tweaks to the filler with great success, there were times we wanted more, but a few cautions would keep us on schedule. Green flag for 2 hours straight is what we couldn’t do, and why we decided to put a cell in the trunk. I think I already rambled about this on FB though, but im bored on the dyno.

Were you monitoring EGT? I'd be interest to see what lambda/equivalence ratio, ignition timing, and EGT you're running. I'd run the highest RON fuel available with the lowest ethanol %, which will provide the best balance of energy density and knock toughness. OEM fuel enrichment on newer North American market cars requires running stoich, unless you need to enrich for component protection. Euro6D is already requiring RDE (real driving emissions), so in order to pass CO, they're basically operating at lambda 1.0 continuously. Also it's quite common in racing to have different fuel enrichment maps- economy to full power. The Haltech 2500 allows for a second map, so you would at least have the option to change strategy mid race.

Enrichment will have a yuge impact on fuel consumption. Control fuel and IG to run ~900C at cylinder head outlet by leaning her our and relying on your knock control system, as much as you dare, to run close to knock. This is one area where the OEM engine controls far outpaces the aftermarket (ignition control, knock detection accuracy, exhaust temp prediction). IG will have the greatest impact on exhaust temp. It's an iterative process: Lean out 0.05 lambda, advance to knock, check temp, repeat. I wouldn't run a stock K above 930C sustained, at least for endurance. I also wouldn't even bother trying this unless you can run steady state on a dyno and map each gridpoint.

One thing that is coming out of RDE is DBW throttling. Since they're running stoic, or very minimal enrichment, at peak power, the DBW is being closed at high engine speed to control exhaust temps. Also keep in mind that engine speed is not a friend of fuel economy - downspeed when possible. This has as much to do with the driver as it does with engine architecture and calibration. Audi's LMP1 was famous for extreme fuel economy measures even as far as banning left foot braking to reduce time on throttle and also coasting into the brake zone. Not useful for qualifying, but the driver plays a big part in endurance racing to turn the available fuel into the most efficient lap times.