Hobbywing Max4 - EZRUN 70125 - Speedmaster P2 build


New member
Hi all - I've started making some progress on my build and all the information here has helped a lot so i thought i'd post up what i have.

I'm using the P2 supercharger as it requires lower RPM which I though would be easier to manage.
When delivered i found the bearings a little noisey and as noted here are only rated to 22,000 RPM.
I've since remade the shaft from precision ground 10mm round bar. I've changed to HTD 5M15 pulleys to allow some testing with different ratio's
The HTD belts are rated around 80m/s i think and were suitable for the desired motor RPM. It should also be slightly more efficient / generate less heat than the original T5 solution.
I made a taper lock to fix the pulley to the shaft and its working quite well. I made bushings to suit new bearings. I chose 6800ZZ that are rated to 38,000 rpm and everything rotates much more smoothly now. The bearings have a lower dynamic load rating than the original but i haven't noticed any issues so far. I have room to double stack them if needed.
I've mounted the motor "upside down" to try and reduce the package height of the whole assembly. I've used 2 x 6mm sections and 1 x 10mm section of aluminium flatbar to space the motor up for belt alignment. The motor is recessed into the top plate 4mm.

I'm currently using 2 zee 6s 9000mah packs for testing but seeing more voltage droop at high power than I'd like. I still need to go over connections and clean up anything there but I think i need another 2 packs to reduce the load per pack. This runs through a 3 phase isolator I picked out of the scrap.

I'm using an arduino board to control the ESC because I eventualy want to tap the CANBUS in the car to drive it. I'd like to use shaft speed to set targets but unsure how i'll manage this. Might be able to get motor speed from the esc and use that?

I've got the hobbywing OTA adapter for the MAX4 and successfully pulled the logs to the desktop. I've worked out what all the data is except 2 additional values not shown in the app. Just need to figure out how to script the conversion to csv. I'm learning as I go though and enjoying it.

Next steps
Eliminate as much voltage drop as possible.
Investigate further battery options
Testing current draw at different drive ratios to see what the motor prefers - I have 20t on the shaft and 24, 28 and 32 available for the motor.
Housing for the belt drive.
Maybe some flow testing to benchmark to the vortech map. I've thought about using a cheap MAF for this othwise i'll go down the now standard restrictor method.

The peak motor RPM below was 35,300 so 42,360 impeller RPM at 10,584watts. The current spike on ramp up was 308.2A / 11,126W. It was very much a hide behind something and see whats going to fail moment.
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I like how the motor is for packaging. very good looking setup. pulleys look bigger too, to my very uneducated eye, the bigger pulley with bigger belt getting the same ratio looks more durable. hopefully it gives you good numbers.

the idea of a maf on the inlet side while testing seems interesting, as long as you could log the data. not exactly sure what it would tell you, but if you could leave it installed for on a running engine log, be cool to see that airflow vs test bench data.
Re the MAF I really just want a way to confirm the amount of air that its acutally flowing at what RPM and i don't have a flow bench at hand. This would help see where this unit sits compared to the actual vortech. I think it's going to come down to just fitting it and starting out easy though...
Hey, progress has been slow actaully. Been struggling to get any time but some little bits happening. I've started to check positioning in the engine bay which looks ok actually.
Started on a MAF sensor mount to be welded to a new intake pipe. Got a blow off valve to be welded to the same pipe.
I found a new arduino board with integrated can module and will start to figure out control based on throttle position. Longan labs I think it is. I looked at a kaizenspeed control module but this was cheaper for the sake of the experiment.
Once the intake pipe is done ill try and get everything mounted so then some actual testing can begin.
I havent sorted the additional fuel management yet but I think ill try and get 0.5 or 1psi to not push the factory ecu too far and keep an eye on knock correction while I figure out the rest.
Not as much progress as I'd like but it's still going.
This looks great - when you get things working, definitely let me know and I'd love to make a video with you featuring your build. I also like your packaging of the motor, btw.
damn nice, what exactly is that thing in the middle with a switch? was this the isolater? looks neat to connect through it
The switch is a 3phase isolator I got out of the scrap bin. It isolates all 4 contacts so makes connecting the batteries a bit less sparky. Not sure if it will make it final install but it's nice and handy on the bench.