Home Built Water Brake Dyno's 7

Maybe an inertia dyno?

optimum:

What is the max H/P & RPM you want to test.
Inertia dyno's are great for small low output engines, but be (WARNED)!!!!! you have to consider the peripheral speed of the flywheel,drum etc etc. Eg If you made your flywheel or drum, say out of 4140 you would have to limit your peripheral speed to around 140 M/sec or else your in big trouble.

If you are testing automotive style engines how about an automatic transmission with direct clutch mechanically locked. Torque arm at the output shaft. Regulate the torque converter oil filling. Cheap and doable.-------Phil

For those kind of HP #'s the torque absorption capabilities would exceed most automotive automatics. Why not rent dyno time if high capitol investment is the drawback?-----Phil

- lots of info on homebuilt dyno's.

optimum:
Can't see why buying a second hand water brake would be a problem if your playing with that sort of H/P & revs.

There is a small company in Salem, NH Land and Sea the web site is They were making variable pitch props of marine applications and found a new use for them, dynos this may lead you in the right direction

willeng, head me in the right direction for an affordable used unit.

xr7755

Not sure where you are?

Dyno-Dynamics of MELBOURNE have been advertising second hand dyno's. Trade-ins etc.

I picked up an old Telma eddy-current retarder for under a grand out of a truck at the wreckers. SCANIA trucks have these fitted as well as some tourist coaches. Some of these units are very strong to 2400 ft/lbs.
The retarder i bought will brake 1000 ft/lbs but needs to be geared a little to keep the rpm reasonable.
These are good for acceleration testing
I am currently building the engine bed etc now.

On the West coast of USA. I have seen some industrial engine dynos on the market before. But they don't handle the RPM's. It seems anything for auto engines is way over priced. I don't see that there is that much work in making them. That they should be priced like that. It's like anything else make them affordable and people would purchase them.

xr7755

I think like you,that it's not that difficult to make a cheap brake especialy with the materials we have today.
I think people often misunderstand what a brake has to do.
I was talking to some people a while ago about breaking engines, they were thinking that you need super strong frames huge braking cells etc, they nearly fell over with embarrasment when i explained that with one of our current V8 supercar engines 530ft/lbs of torque all you need in reality is a 10ft lever & hold 53lbs on it.
It would pay to look up the inventer of the water brake
William Froud this was in the late 1800s would you believe. He was braking navy ships with 116,000ft?lbs----about 380 small block chevs. RPM was a consideration then because of materials but now we haven;t got that problem.
There is an old article by David Vizard that i have in Hot Rodding Basics 26/june/1982---might be of interest.

Also there are papers that i have from Heenan & Froud LTD---worcester-England Publication No 526/2 shows the old basic design of the brake. I have other diagrams of the old principle workings of these if someone could tell me how to put them on the (bloody) computer i have a scanner.
The reason i picked the eddy current retarder is that at the time I couldn't work out how to do transient response testing with a water brake--not smart enough. I have recently worked out how this can be done--it's easy.

XR7755, check out this link

West coast location, not sure if it meets your other requirements or even if it is still available. Worth a look, anyway.

Other links applicable to DIY dynos are below…

You could directly measure the torque with a torqometer type torque wrench also. I saw a photo of a diesel engine being tested that way. The biggest hurdle is getting the power absorber. The measuring is the easy part.

DOOH!
Thank you for thinking for me! I had to draw it on paper to 'prove it' to myself. I do agree with the flaws on roller dyno's (they are good for tuning) and their inherit lack of consistance. I always have to laugh at(no to their face) people who talk to me about 2hp changes they had. One manufacturer solved this buy driving the pump off the axle directly. It is limited by because of the torque multiplication from the gear ratio of the axle. It is actually using one pump at each wheel (2 or 4 wheel drive)which adds complexity but also increases load capacity. Speed is less of a factor because of the vehicle's gear ratio. I was wondering if stepping the speed down through a 4:1 or 2:1 gear set and run multiple stages of pumps to handle the torque.
Thank you all for keeping me on track
Tim

xr7755
optimum

Seems as though there are posts missing so i'm not sure where we were up to, or if you've solved your dyno problems yet. If not i may be able to assist you in building your own water brake. Online or E-mail

Thank you, I dont know what happened to half of this thread but I have found some promise in a product I stumbled across. I will keep you posted.
Thanks,
Tim

I am in the process of doing something very similar to test kart engines. I am going to attempt to build a water brake and test stand like the land and sea one.

willeng
If you have any info that would help it would be great if you could share it.

Thanks

Luke Haddow

Luke
Whats your email address.

willeng

my email address is haddow@iprimus.com.au

Thanks