Homemade Engine Dyno

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: Homemade Engine Dyno

Post by Belgian1979 »

gmrocket wrote: Mon Jul 06, 2020 6:51 pm
Belgian1979 wrote: Mon Jul 06, 2020 12:53 pm
Keith Morganstein wrote: Mon Jul 06, 2020 11:47 am

The simplest is a step test where the engine is loaded to and stabilized at each RPM point. This is common with HD Diesel dyno testing.

True racing endurance engines will handle that type of testing.
Many hot rodded automotive engines wouldn’t last too long...
hm, a nascar engine might. Cannot see anything regular do this type of thing at say 7000 rpm for too long? The question is though if it is needed. As far as ignition timing is concerned (which would be the primary reason to tune on a dyno), most are at the maximum advance around 3000 rpm or so.
Most acceleration tests are 300 or 600 rpm stepped tests

The steady state test will give a different number

Is that what your asking ?
Obviously steady state will be different. But what counts is acceleration force over a given time. So the stepped test is what I think I was referring to.
Steady state is the most useful when tuning as you will want to hold the engine at a constant rpm while you vary the load. This means you have to have a computer that controls the load of the brake to keep the engine at it's set rpm to tune.
Last edited by Belgian1979 on Tue Jul 07, 2020 3:46 am, edited 1 time in total.
Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: Homemade Engine Dyno

Post by Belgian1979 »

PackardV8 wrote: Mon Jul 06, 2020 6:30 pm Isn't there a backstory about Jack Roush using generators to load his engines and selling juice back to the utility?

An even older backstory about someone buying a scrap military surplus generator with a failed 6-71, selling that for parts and using the generator as a load?
I think you would have difficulty controlling the output of the generator to the grid when you have an engine that goes up in rpm a lot. Not to mention that most generators are rpm limited...
Think about it, in a normal situation the engine speed is controlled by the frequency of the electricity and voltage, which both need to be constant.

The only recovery of energy would be in the form of heat imo. I can imagine that Rolls Royce would have used the heat coming from the dyno facility to heat the factory where the assembly took place.
Powertrip
Pro
Pro
Posts: 314
Joined: Sat Feb 10, 2007 11:09 am
Location: North West Indiana

Re: Homemade Engine Dyno

Post by Powertrip »

I have been casually looking into this, and it seems an inertia dyno set up might be the easiest/cheapest way for the do-it-your-selfer.
I've seen a lot of home made inertia dyno's for small engines and motorcycles, anybody build one for V-8's?
The price of progress is trouble.
BCjohnny
Guru
Guru
Posts: 1772
Joined: Sun Feb 26, 2006 6:07 pm
Location: Black Country, England

Re: Homemade Engine Dyno

Post by BCjohnny »

Powertrip

You'll be spinning a helluva lot of weight relatively to keep the rpm gain reasonable, obviously depending on the torque / horsepower curve of the V8 your testing

That's why it's more practical use brakes with diminishing load to control rpm gain rather than using pure inertia

The big inertia rolling roads have massive drums, obviously to help obviate the effects of gearing

If you go that route make sure the inertia absorber is well nailed down, otherwise it might resemble something out of Whacky Races :wink:
User avatar
Stan Weiss
Vendor
Posts: 4801
Joined: Tue Feb 20, 2007 1:31 pm
Location: Philadelphia, PA
Contact:

Re: Homemade Engine Dyno

Post by Stan Weiss »

What would you call a huge weight?

Picture is from the BLP Inertia dyno during the "Carb Test" The output below is from my software.

I original wrote this code to take OBD II data log data and parameters about the vehicle and calculate road HP. The OBD II data log data did not have great resolution so I got a lot of spikes and valleys. When used with this data the results were much better. I had to guess at the weight and distance. 335# @ a 12" radius seen to work well for this data set.

Stan

PS - Let me added - Other than the weight and radius the only other things needed are accurate measurements of RPM and time.

Code: Select all

Program Input
Car Weight = 335.0
Rear Gear Ratio = 1.0
Tire Diameter = 24.0
T Gear1 = 1.0
Tire Rolling Resistance = 0.0
Coefficient of Drag = 0.0
Frontal Area = 0.0
Percent Rear End Power Loss = 0
Tire Rolling Radius = 12.0
Power Loss 1 = 0
;         RPM    Time
ROad HP = 5000 0.0
ROad HP = 5100 0.131
ROad HP = 5200 0.262
ROad HP = 5300 0.392
ROad HP = 5400 0.523
ROad HP = 5500 0.654
ROad HP = 5600 0.785
ROad HP = 5700 0.917
ROad HP = 5800 1.048
ROad HP = 5900 1.178
ROad HP = 6000 1.307
ROad HP = 6100 1.435
ROad HP = 6200 1.563
ROad HP = 6300 1.691
ROad HP = 6400 1.82
ROad HP = 6500 1.95
ROad HP = 6600 2.08
ROad HP = 6700 2.211
ROad HP = 6800 2.343
ROad HP = 6900 2.475
ROad HP = 7000 2.609
ROad HP = 7100 2.744
ROad HP = 7200 2.882
ROad HP = 7300 3.021
ROad HP = 7400 3.163
ROad HP = 7500 3.309
ROad HP = 7600 3.457
ROad HP = 7700 3.609
ROad HP = 7800 3.765
ROad HP = 7900 3.925
ROad HP = 8000 4.089

Code: Select all

__Weight_=_335.0#____Radius_=_12.0_Inches

____________________________Rear_____Aero_____Rolling____________Rear_W__Accele___Time___Rate
__RPM______MPH___Velocity___Wheel___dynamic___Resist.__Elapsed____Horse__ration__Differ_Rev_Per
__________________ft/sec___Torque__Drag_-_HP____HP______Time______Power__in_G's__ential___Sec

_5000.0_356.999__523.599_____0.00______.000____.000____.0000_______0.00__0.0000__0.0000_____0.0
_5100.0_364.139__534.071___832.33______.000____.000____.1310_____808.24__2.4846__0.1310___763.4
_5200.0_371.279__544.543___832.33______.000____.000____.2620_____824.09__2.4846__0.1310___763.4
_5300.0_378.419__555.015___838.73______.000____.000____.3920_____846.40__2.5037__0.1300___769.2
_5400.0_385.559__565.487___832.33______.000____.000____.5230_____855.79__2.4846__0.1310___763.4
_5500.0_392.699__575.959___832.33______.000____.000____.6540_____871.63__2.4846__0.1310___763.4
_5600.0_399.839__586.431___832.33______.000____.000____.7850_____887.48__2.4846__0.1310___763.4
_5700.0_406.979__596.903___826.03______.000____.000____.9170_____896.49__2.4657__0.1320___757.6
_5800.0_414.119__607.375___832.33______.000____.000___1.0480_____919.18__2.4846__0.1310___763.4
_5900.0_421.259__617.847___838.73______.000____.000___1.1780_____942.22__2.5037__0.1300___769.2
_6000.0_428.399__628.319___845.24______.000____.000___1.3070_____965.62__2.5231__0.1290___775.2
_6100.0_435.539__638.791___851.84______.000____.000___1.4350_____989.38__2.5428__0.1280___781.2
_6200.0_442.679__649.262___851.84______.000____.000___1.5630____1005.60__2.5428__0.1280___781.3
_6300.0_449.819__659.734___851.84______.000____.000___1.6910____1021.82__2.5428__0.1280___781.2
_6400.0_456.959__670.206___845.24______.000____.000___1.8200____1029.99__2.5231__0.1290___775.2
_6500.0_464.099__680.678___838.73______.000____.000___1.9500____1038.04__2.5037__0.1300___769.2
_6600.0_471.239__691.150___838.73______.000____.000___2.0800____1054.01__2.5037__0.1300___769.2
_6700.0_478.379__701.622___832.33______.000____.000___2.2110____1061.81__2.4846__0.1310___763.4
_6800.0_485.519__712.094___826.03______.000____.000___2.3430____1069.49__2.4657__0.1320___757.6
_6900.0_492.659__722.566___826.03______.000____.000___2.4750____1085.22__2.4657__0.1320___757.6
_7000.0_499.799__733.038___813.70______.000____.000___2.6090____1084.52__2.4289__0.1340___746.3
_7100.0_506.939__743.510___807.67______.000____.000___2.7440____1091.86__2.4110__0.1350___740.7
_7200.0_514.079__753.982___790.11______.000____.000___2.8820____1083.17__2.3585__0.1380___724.6
_7300.0_521.219__764.454___784.43______.000____.000___3.0210____1090.31__2.3416__0.1390___719.4
_7400.0_528.359__774.926___767.86______.000____.000___3.1630____1081.90__2.2921__0.1420___704.2
_7500.0_535.499__785.398___746.82______.000____.000___3.3090____1066.48__2.2293__0.1460___684.9
_7600.0_542.639__795.870___736.73______.000____.000___3.4570____1066.09__2.1992__0.1480___675.7
_7700.0_549.779__806.342___717.34______.000____.000___3.6090____1051.70__2.1413__0.1520___657.9
_7800.0_556.919__816.814___698.95______.000____.000___3.7650____1038.04__2.0864__0.1560___641.0
_7900.0_564.059__827.286___681.47______.000____.000___3.9250____1025.06__2.0342__0.1600___625.0
_8000.0_571.199__837.758___664.85______.000____.000___4.0890____1012.72__1.9846__0.1640___609.8

_Averages__________________803.84________________________________995.48__________0.1363__737.2

Stan
JMark_BB.gif
You do not have the required permissions to view the files attached to this post.
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
BCjohnny
Guru
Guru
Posts: 1772
Joined: Sun Feb 26, 2006 6:07 pm
Location: Black Country, England

Re: Homemade Engine Dyno

Post by BCjohnny »

Not wishing to argue, and not run the maths (I'm not building an inertia dyno), but I'd imagine if using a solid steel disc you'd be looking well in excess of 1000 lbs at 12" dia

Apologies if I'm wrong but 335 lbs @ 12" seems shy, to me ?

Empirically :

IIRC a Dynojet car inertia roller dyno has a drum of ~ 3000 lbs + ..... it's obviously not solid but it runs a much larger diameter, and as PMI is relative to the square of the diameter, that's significant ...... even accounting for the effects of gearing ?

Also a large Telma has a static combined rotor mass of ~ 190 lbs, more than half the figure your suggesting, at a greater diameter of ~ 20", and they're not considered an undesirable inertial mass ?

I'm not saying it can't be done but IMO, the average guy trying to diy an 'V8' inertia dyno is dealing with not inconsiderable mass weights that might be a struggle to process & balance ......

The only way I could see it being done is having multiple machined discs on a common shaft ..... and if you then rig up a basic dog clutch engagement at the same time, you could tune the PMI to suit the power of the engine to be tested by engaging the correct number of discs you need to achieve the required rpm gain ?

But I could be wrong .....
gmrocket
Guru
Guru
Posts: 7622
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Homemade Engine Dyno

Post by gmrocket »

BCjohnny wrote: Tue Jul 07, 2020 3:40 am Not sure if the comment was directed at me, but ...... 'step testing' was the most common method used until the advent of computer controlled 'sweep testing' on brake dynos

It still has it's uses when ignition and fuel mapping

I only mention it in this context as a computer controlled sweep control system could double the cost of any diy system ...... you can initially prove your brake initially with a simple variac and diode bridge (if using an electric retarder), even get some meaningful readings, and then move on to a sweep control system if that's your goal
Sorry, I didn’t mean stepped...just Timed acceleration.

300 or 600 per second
User avatar
Stan Weiss
Vendor
Posts: 4801
Joined: Tue Feb 20, 2007 1:31 pm
Location: Philadelphia, PA
Contact:

Re: Homemade Engine Dyno

Post by Stan Weiss »

Stan Weiss wrote: Tue Jul 07, 2020 4:03 pm What would you call a huge weight?

Picture is from the BLP Inertia dyno during the "Carb Test" The output below is from my software.

I original wrote this code to take OBD II data log data and parameters about the vehicle and calculate road HP. The OBD II data log data did not have great resolution so I got a lot of spikes and valleys. When used with this data the results were much better. I had to guess at the weight and distance. 335# @ a 12" radius seen to work well for this data set.

Stan
BCjohnny wrote: Tue Jul 07, 2020 7:53 pm Not wishing to argue, and not run the maths (I'm not building an inertia dyno), but I'd imagine if using a solid steel disc you'd be looking well in excess of 1000 lbs at 12" dia

Apologies if I'm wrong but 335 lbs @ 12" seems shy, to me ?

Empirically :

IIRC a Dynojet car inertia roller dyno has a drum of ~ 3000 lbs + ..... it's obviously not solid but it runs a much larger diameter, and as PMI is relative to the square of the diameter, that's significant ...... even accounting for the effects of gearing ?

Also a large Telma has a static combined rotor mass of ~ 190 lbs, more than half the figure your suggesting, at a greater diameter of ~ 20", and they're not considered an undesirable inertial mass ?

I'm not saying it can't be done but IMO, the average guy trying to diy an 'V8' inertia dyno is dealing with not inconsiderable mass weights that might be a struggle to process & balance ......

The only way I could see it being done is having multiple machined discs on a common shaft ..... and if you then rig up a basic dog clutch engagement at the same time, you could tune the PMI to suit the power of the engine to be tested by engaging the correct number of discs you need to achieve the required rpm gain ?

But I could be wrong .....
Remember I am talking about weight at a given distance. The total weight may be greater, but the closer the weight is to the center the less force is needed to accelerate it.

Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
ijames
Expert
Expert
Posts: 849
Joined: Fri Jul 04, 2008 3:44 pm
Location: Laurel, MD

Re: Homemade Engine Dyno

Post by ijames »

BCjohnny wrote: Tue Jul 07, 2020 7:53 pm Not wishing to argue, and not run the maths (I'm not building an inertia dyno), but I'd imagine if using a solid steel disc you'd be looking well in excess of 1000 lbs at 12" dia

Apologies if I'm wrong but 335 lbs @ 12" seems shy, to me ?
Some comments from the peanut gallery: He said 12" radius, you said 12" diameter, and he said 335 lbs at 12" radius, not a 335 lb solid cylinder of radius 12". Think a hollow tube with all the weight concentrated at a radius of 12". Couldn't actually build it that way, but the equations just care about a point mass at the center of gravity radius (or a similar simplified tubular geometry) so I'm guessing that's why he phrased it that way. Yes, I should have quoted his posts too, sorry :( .
Carl Ijames, chemist not engine builder
carl ddott ijames aatt verizon ddott net
brentry
Member
Member
Posts: 128
Joined: Fri Aug 16, 2013 5:56 pm
Location:

Re: Homemade Engine Dyno

Post by brentry »

I have a small engine inertia dyno with performance trends software . There is a section in the software to tell you at what disc rpm(depending on disc size ) gets dangerous. Also calculates how much torque your disc can handle. Gives u a guideline
Give or take.
Few times i had no choice but to spin it,
Quit bit more disc rpm than the recommended .

A interia engine dyno for a car engine would be great. Great dynos.
I just dont see how to get around enormous weight needed, or the enormous height of the disc depending how you do it (i did check in the software)and how to get around hooking the engine to the weight. That would be big dog clutch i would think. Which mine has.
Best kind of dyno imho. Simple and dead accurate.
BCjohnny
Guru
Guru
Posts: 1772
Joined: Sun Feb 26, 2006 6:07 pm
Location: Black Country, England

Re: Homemade Engine Dyno

Post by BCjohnny »

Stan Weiss

Yes sorry misread, it was late and I'd had a couple of apple based beverages ......... but no excuse

Even at 12" r / 24" D, 335 lbs seems shy, in as much as :

I've not seriously researched inertia dynos, as I'm not building one, but am aware of the inertial effects relative to what I'm doing

From all the research I have done however casual inspection strongly suggests that relative masses much greater than being suggested here are empirically being used

You would, in this application of testing a 'V8', either have a very heavy smaller diameter weight, which has it's own obvious implications, or a lighter much larger diameter weight, which has obvious other implications, not least rpm ...... none of this AIUI is controversial or flies in the face of what is actually being done, instead of modelled ......

brentry
I just dont see how to get around enormous weight needed, or the enormous height of the disc depending how you do it (i did check in the software)and how to get around hooking the engine to the weight.
Yes, quite
ClassAct
Guru
Guru
Posts: 1024
Joined: Wed Dec 05, 2018 11:55 pm
Location:

Re: Homemade Engine Dyno

Post by ClassAct »

brentry wrote: Wed Jul 08, 2020 2:42 am I have a small engine inertia dyno with performance trends software . There is a section in the software to tell you at what disc rpm(depending on disc size ) gets dangerous. Also calculates how much torque your disc can handle. Gives u a guideline
Give or take.
Few times i had no choice but to spin it,
Quit bit more disc rpm than the recommended .

A interia engine dyno for a car engine would be great. Great dynos.
I just dont see how to get around enormous weight needed, or the enormous height of the disc depending how you do it (i did check in the software)and how to get around hooking the engine to the weight. That would be big dog clutch i would think. Which mine has.
Best kind of dyno imho. Simple and dead accurate.
Google Revolution dyno and look at that. Mike Laws developed the thing. If I had the budget I’d have one.
User avatar
Stan Weiss
Vendor
Posts: 4801
Joined: Tue Feb 20, 2007 1:31 pm
Location: Philadelphia, PA
Contact:

Re: Homemade Engine Dyno

Post by Stan Weiss »

ClassAct wrote: Wed Jul 08, 2020 9:09 am Google Revolution dyno and look at that. Mike Laws developed the thing. If I had the budget I’d have one.
The dyno sheet that I posted came from that dyno. I used the RPM and Time numbers from that sheet as the input to my calculations. At that time I exchanged a number of emails with Mike Laws about the dyno and software. I sent Mike a message about this tread. Hopefully he will drop in an add his expertise.

Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
Mike Laws
Pro
Pro
Posts: 485
Joined: Thu Aug 03, 2006 9:02 am
Location: Florida

Homemade Engine Dyno

Post by Mike Laws »

Thanks Stan for the heads-up on this thread.

One of the most important factors in race engine development involves acceleration. When vehicle dynamics are maximized, the engine that accelerates the vehicle (mass) the quickest from one rpm to another will always outperform vehicles with slower E.T.'s between the same 2 rpm points. F=MA. With this in mind; there is no better method of testing acceleration than an inertia dyno (ID). All other dyno's simulate acceleration. Some 'brake' dyno's do it better than others, but none do it as well as an ID. 6 of these machines were built. The first was relatively crude but proved the concept. It was built for less than $10k. The others were significantly more expensive due to the chosen markets and features desired by the end user. One is used by Nascar at their facility in Mooresville, another is at a Pro Stock shop, a couple are in the midwest at engine shops, there is one at BLP, although it's my understanding that it is not operational and I am unsure about #6.

I'm happy to answer questions about this.

Here is the patent info which shows the basic layout: https://patents.google.com/patent/US6918287B2/en
Mike Laws Performance
Belgian1979
Guru
Guru
Posts: 4576
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: Homemade Engine Dyno

Post by Belgian1979 »

In a dyno you're ultimately measuring torque. Torque is the result of force over a certain length lever. Force is force imo, no matter if it is the result from a weight you're accelerating or from a brake being applied to a certain amount where you are accelerating against.

A rolling road is the same as the real road. You can only accelerate it for a certain time and that's it. You cannot hold it a certain rpm to tune it. So why would you need a rolling road when you can do the same on an empty stretch of road (if that exists, which might be exactly the reason to use a rolling road in the first place :D ).

When you tune a drag race engine that only runs at one rpm, the maximum I can see that work. On something that needs to run at different rpms and loads not so much.

PS : in the US I can imagine that empty roads exist. Over here not so much.
Post Reply