grassroots dynomometer

http://www.youtube.com/watch?v=heLMAMp_SCs&t=3m0s

A) That rules.
2) They would have a larger mass to accelerate, and would thus be able to do slower runs (better resolution) if they filled the tires with concrete.
iii) Hmm - I know where the rear axle subassembly from a trailer is for sale - Frame, 2 axles, 8 tires.

needs more bungee cords

WOW! that looks dangerous!

hilarious. Weld the differential, and hook up some giant mass to the diff input. calculate moment of inertia of the system and get high resolution rpm at the axle. use some maths and there's your diy dyno

Hilariously dangerous? For sure!

I'm not sure which is worse... the dyno, or the car...

ISTR that when concrete 'accidently' sets up inside one of those concrete trucks, they have to discard the cylinder. So you should be able to get one of those really cheap. ;)
Dig a trench big enough for the cylinder to sit horizontally.
Suspend the cylinder on each end on bearings.
Build a platform so that the driven car wheels run directly onto the outside surface of the cylinder. Add a tach to get cylinder RPM.
Calculate/measure the polar intertia of the cylinder.
Attach a cheap 4 channel data acqusistion system like this: http://www.dataq.com/products/startkit/di149.htm

Dyno your ass off!
(or, as stated, Hilarity Ensues)

P.S. Also pray that the cylinder doesn't somehow escape 'at speed'.

What's bad about an ls1 powered s13?

Taiden wrote: What's bad about an ls1 powered s13?

I'm guessing you didn't see the scary interior wiring...

Or the INSIDE-THE-CABIN rear mount turbo setup?

I dont know. I never liked distribution blocks for automotive wiring, but the more I learn about motorsports wiring, the more I become okay with them. The rear mount turbo is hilarious imo. I'm not going to trash on someones car, especially when it's a turbo ls1 s13 haha. Plus, I don't know if he's prototyping his wiring right now or not.

Seems like a candidate for a Darwin Award.......

in Soviet Russia.. dyno runs you.

erohslc wrote: ISTR that when concrete 'accidently' sets up inside one of those concrete trucks, they have to discard the cylinder. So you should be able to get one of those really cheap. ;)

A guy that lived on the same street as me growing up makes his living inside those cylinders with a jack hammer...Very rarely do they discard them they just stuff the drunk in the hole.

Ghetto-fab-ulous

44Dwarf wrote: A guy that lived on the same street as me growing up makes his living inside those cylinders with a jack hammer...Very rarely do they discard them they just stuff the drunk in the hole.

He must have been thoroughly deaf... those things are noisy enough without being confined to a small, resonant space.

92CelicaHalfTrac wrote: Or the INSIDE-THE-CABIN rear mount turbo setup?

Somebody needs to do that for LeMons. There was some scary lookin' stuff going on, the cut right rear tire and the damaged bodywork that caused it made my blood run cold. If that tire had let go on that homemade rig at WOT....

Ok.... how about some remedial (or advanced) formulas here... How does one calculate those things? I've always wanted to build a dyno using an old ford 9" I have sitting around and sending a driveshaft to some kind of brake or inertial mass.

How do I calculate that stuff? I can fine tune it by using some known power combos.

For instance, lets say we replace the tires/wheels on that truck axle with some massive 45" ingots of steel rod that weigh 3 tons. How do I calculate my output?

Brake stuff I'm not so sure. Mass moment of inertia is fairly straight forward.

http://emweb.unl.edu/negahban/em223/note19/note19.htm

http://en.wikipedia.org/wiki/List_of_moments_of_inertia

Honestly though, I would go ahead and make it, get all your electronics set up, and get everything done except for your mass moment of inertia constant... then take your car to a known good dyno, then throw it on your dyno and find MMoI making sure your torque numbers are the same. Calculate your MMoI first though and see how close it was.

To make inertia drum, could use couple of sections of concrete tube form, 5ft OD, 3ft ID, add some rebar rods, pour in concrete.
Even better, find a piece of "surplus" concrete sewer pipe of appropriate size, trim the broken edges true with concrete saw. Get some heavy duty pillow block bearings from McMaster-Carr with steel tube axle.
Tires can run directly on the outside surface of the drum.

92CelicaHalfTrac wrote: I'm not sure which is worse... the dyno, or the car...

Yes.