Buying a used Dyno - featuring fundamentals

Hey all, looking at buying a used Mustang emissions dyno with the intent of tuning cars with it.

The only model number I can find is in the included photocopied manual and its a Mustang I/M 100-8. Its from 2004 and I can't find any info specific to this dyno anywhere on the google yet. I know emission dynos generally have a low hp rating and this concerns me a little. I am poised to get this dyno for peanuts so even if we have to spend a little money on it thats ok with me. Owning a dyno is a pretty out of reach dream outside of something like this, I'm also a huge nerd and would be interested in this kinda stuff even if I was buying a brand new dyno.

The rollers look good, bearings don't have play, there is some rust from sitting but nothing we cant deal with. It spins freely and quietly and the Eddy current absorber measured 4.17 k ohms (need to double check what I wrote down) and generates a small AC voltage when spinning it.

So the hardware seems fine, the controller is a little more complex. The previous owner modified it years ago, it appears to have a new load cell and has an additional controller and some wiring but I'm not completely sure what it does yet. It also seems to be missing a speed sensor, not sure where its usually mounted but I expect on the shaft next to the absorber. The manual says its limited to 200 hp "max absorption" ; is that a constant rate or peak? Its only got a 8.6" (219mm) diameter roller, which isn't large.

Onto the fundamentals. I understand the basics of how eddy current absorbers work, what I'm having trouble finding out is how they are rated for torque and watt ratings specific to dynamometers. Heat and tire contact patch are the limiting factors to power handling, does this mean the dyno can't sustainably hold more then 200hp or max ramp run 200 hp? that would be a make or break for me, or more likely require changing the absorber.

When an eddy dyno does a ramp WOT power run, does the braking just ramp in to simulate wind resistance, vehicle weight etc?

If I were to get rid of the existing controller situation can I just get a new controller from Mustang or a more DIY friendly one like YourDyno.com and wire it up good to go? Not sure how to calibrate it to the weight of the roller or the power of the absorber (if any of that needs special calibration) as I'd like accurate power figures.

I am also a little lost whether an eddy current or water absorbers are better, I thought eddy were faster reacting but cant handle sustained load as well (depends on the water cooling situation for water brakes) but this is kinda irrelevant to me as this dyno will likely stay Eddy current.

And lastly is RPM limits just a function of balancing? or can you spin the Eddy current brake faster then designed? Or is that also a heat issue?

I've googled quite a bit, read a bunch of threads on here (HP forums are a more trusted source then 98% of the internet) and watched the How To Choose A Dyno webinar which all were helpful. Any input or correction to my understanding is welcome.

The cars I usually deal with are under 500 HP and I think I can handle sub 200 hp sustained load when doing cruise and low throttle opening steady state tuning. Hoping this can work out well, even if it requires some elbow grease

I will try and upload some photos tomorrow.

Where are you located in Canada? I'm in BC & purchased my Mustang new quite a while back, somewhere around 2008.

I would like to upgrade the software & it sounds like you are headed that direction. Maybe we can chat.

Generally if they dont specify or dont give a separate hot and cold absorber rating I would say it is likely to be a "warm" rating. So, it will hold a bit more when cold for a single pull and its capacity will fade away as heat soaks. The temperature effect is large, a graph from Land and Sea's 150Hp retarder is below.

With only 8" rollers you are not going to get much more into the rollers anyway and you have little inertia effect to take advantage of.

Speed will also likely be a limitation with the small rollers. The max RPM on most eddy brakes is due to the cast iron rotors, just like a cast iron flywheel will explode on a car engine if you rev it too high. My rollers are around 11" dia from memory and I limit my brake to 4000RPM since it is 20 years old (i think it was 4400 when new), so I'm limited to about 210kmh road speed.

@ctdls we are located in coquitlam BC, whereabouts are you?

@adam@link_ECU appreicate the response; if it is a 200hp warm rating thats not as bad as I thought. Does the documentation from Land and Sea state what temperature then used for the warm and hot curves?

Hoping that the 200hp rating, and the 150hp rating of the Land and Sea are the continuous? like it can hold or stall that hp for a reasonable amount of time (more then a ramp run) for steady state.

I had suspected balance had something to do with it. Looking at mustang's catalogue they have many options and speed and hp dont seem to directly correlate to roller size. Their smallest roller dynos in the performance section are rated for 900hp and 1200 hp and I'm guessing thats ramp run top hp not steady state.

Realistically I wont be running crazy hp cars on it, and for steady state tuning in the cruise areas I think 200 hp is plenty. At our current tuners dyno on an 18" wheel in 4th gear we dont really exceed 110 Mph. I will have to measure and do the math to see what RPM the brake will see... thoughts?