...for our garage at AMP. I have no idea where to start. Seems like there are a godzillion companies selling kits. Would mostly be used to test power gains on some parts we're creating for 1st gen crx's, but the ability to dyno RWD too would be nice.
Thoughts?
Here's what I know:
Dynojets are liars, and make everyone look like they have more peak power than they actually do. And, their graphs don't always accurately reflect the true power/torque curves.
Mustangs are heartbreakers, because they give much more accurate real physics power output and it's ALWAYS lower than what the customer "just knew" it had to be making.
In reply to WildScotsRacing:
This would be more for showing "This modification made this percentage of a gain/loss in power" than providing dead-nuts accurate hp/torque numbers.
What the number is has little relevance.
How that number changes as you change the vehicle is what matters.
So reliability and repeat-ability are paramount.
To this the environment where the dyno is installed becomes as much a factor as the dyno itself.
Temperature Humidity Elevation O2 levels all have a major influence on the number produced.
Data acquisition, a 3 gas analyzer, and other instrumentation is needed to verify results. Also data recording, storage, and backup if you are serious.
Count on spending about double (or more) of the cost of the dyno on peripheral instrumentation and environmental control.
Other factors, like how the car is secured to the dyno can affect results as well.
Don't forget to include "environmental" cleanup considerations for your install, capturing escaping fluids quickly simply and economically is fairly important. As well as fire safety!
In reply to WildScotsRacing:
They are all only as accurate as the operator who sets them up....and should really only ever be used for back to back gains like the OP intends to.
I'd say the biggest question is if you want an in ground or rack mounted one. A 2wd one will allow everything except AWD cars.
In reply to Smarta$$ McPoopyPants:
Sounds like you want a mustang dyno or one of the hub dynos. You dont care what the number says as long as they are accurate and repeatable
So the biggest split between dyno types is load-holding vs inertial. Inertial dynos (such as the classic Dynojet 248) measures power by measuring the rate at which it can accelerate a known mass (the big, heavy drum that the wheels roll on). The advantage to this is that it is cheap, simple, and when operated properly is very repeatable and consistent. If you want to be able to compare numbers between two different dynos, then a Dynojet is the way to go -- this is why NASA uses dynojets for all of their power-to-weight based dyno classes.
There are a few downsides to inertial dynos -- they're big and heavy, and they store all of the energy from the dyno run in a flywheel (the roller), which you then need to dissipate properly after the run is over (there's a drum brake out of a train attached to it). If you don't do it properly that energy can be dangerous, which is why there are all those youtube videos of dynojets throwing cars across the shop. The biggest downside though, is that they can only do sweep runs, so you have to make all of your tuning fit into that pattern.
Load-holding dynos, OTOH, couple some sort of brake to the engine's output. There are a few distinct subtypes (eddy current, hydraulic, etc), but they all work by having a controller that measures RPM and varies the brake loading to keep that RPM at some expected value. They can simulate a dynojet "sweep" by raising the target RPM slowly over time, hold the engine at a fixed RPM and measure how much power it's putting out, or even do a "backwards" sweep where they pull the revs down by increasing the load. They're much more flexible than a Dynojet, and often smaller and lighter, but they're also typically more expensive and require calibration.
I've seen used Dynojets for $15K, nothing else even comes close to that price. That's cheap enough that I've occasionally thought about buying one with a couple friends, the main problem is that I don't have a shop to put it in. If I was getting seriously into the tuning business, I'd look at a Dynapack (hub-mounted, hydraulic dyno) but they're a lot more expensive. I've used them and they're really nice.
Every dyno reads higher than every other dyno, unless it's your car - in which case the reverse is true. I don't care how accurate your dyno is or who made it, you will be told it reads high.
Seriously, no matter what you get, there will be bitching and internet experts.
If you're running other people's cars, a drum dyno is a lot easier to use. You can get cars on and off quickly. A hub dyno means a certain amount of screwing around to bolt it on.
I would STRONGLY recommend getting one from a big manufacturer. Dynos are like kit cars - there are a million out there, and mostly are powered by hopes and dreams. Also, expect to spend a bunch of time screwing around with it trying to chase down weird power spikes and the rest.
Dyno history at FM:
Dynojet (one big roller). Easy to use, consistent, had trouble picking up engine speeds sometimes. Couldn't do steady state tuning, sweeps only. The mass of the drum was the resistance. The four post lift to get the car on the dyno was actually pretty handy at other times. Sold it, it's still working at someone else's shop.
Rototest. High-end scandinavian unit that had all sorts of abilities. Used hydraulic pumps for load and strain gauges to measure torque directly. Very accurate and quick, pulled engine speed from the wheel speed and gearing. Could run for hours at a steady state, great for testing cooling systems. Had some odd behaviour when trying to do sweeps on big turbo cars due to closed-loop load control. Very finicky from a computer standpoint, any power loss meant it was difficult to get back up and running again despite the on-board batteries. It eventually died when one of the embedded NT boxes refused to boot up. Took forever to hook up a car. Didn't even have its own software for comparing runs, I had to write my own.
Dynocom: Drum dyno, very quick to hook up. Grooved drums means it makes a ridiculous racket and tears up tires. Has limited eddy brake capabilities for resistance, but you can't overwork it. Has had constant problems that "have never been seen before" and are constantly being blamed on installation despite the fact that we've done everything they say and more. Currently requires quite a bit of hand-holding from the operator to make sure the runs are even partially representative and we can't do steady-state. Cannot recommend.
I miss the Dynojet. Everyone who doesn't have one rags on them, but they're the standard for a reason. The Rototest was great for testing cooling systems and anything that required steady state, but it was a princess.
Customers will expect sweeps. The only complaint I have about the fixed speed tests is that they're unrealistically high load, especially on high power cars.
codrus wrote: Load-holding dynos, OTOH, couple some sort of brake to the engine's output. There are a few distinct subtypes (eddy current, hydraulic, etc), but they all work by having a controller that measures RPM and varies the brake loading to keep that RPM at some expected value.
As noted in my post, if you want to be able to brake the engine, find out what the duty cycle of that brake is. Our eddy current dyno has some real limitations in terms of duty cycle, our old hydraulic one did not. It was actually pretty clever - the hydraulic pressure was used to run two 40 hp fans that pulled air across some radiators. So it used the work from the car to cool the fluid and it also helped move air to cool the car.
Keith Tanner wrote: As noted in my post, if you want to be able to brake the engine, find out what the duty cycle of that brake is. Our eddy current dyno has some real limitations in terms of duty cycle, our old hydraulic one did not. It was actually pretty clever - the hydraulic pressure was used to run two 40 hp fans that pulled air across some radiators. So it used the work from the car to cool the fluid and it also helped move air to cool the car.
Yeah, the only brake dyno type I've used more than once is the Dynapack. They are water cooled, you can either use them as "total loss" (just run a hose through them and let it pour down the drain) or keep a big drum of water next to the dyno. If you do the drum, then after a couple hours of dyno work that water can get pretty warm. :) I have never run into duty cycle limits on them.
As a dyno rental customer, I really like Dynapacks. The software is a bit weird, but it's powerful, consistent (at least on a single dyno -- not so much between different dynos), and almost foolproof. A lot of shops require that the dyno operator drive the car on the dyno, because they're worried about you applying the car's brakes at the wrong time and launching it into the air. Dynapacks, OTOH, many of the shop owners will spend 5 minutes showing you the software and then walk away and go do something else.
There are definitely a bunch of ways things can go wrong on a Dynojet 
Of course, sometimes those shop owners are also protecting their expensive tool.
Check out Land and Sea units Dyno-mite. dyno-mite They have some great reading on different types how and whys etc.
Very few shops are able to make these pay off for them. Most of the shop owners I've known who bought them thinking it'd make money for them sold them after a few years.
Unless you've got a big tuning business and need the dyno to work with I'd skip it...
Can you find a shop close by that already has a dyno and will let you rent "tuesday nights after 5 pm" or something like that for $250/month?
You might be able to 'rent' a dyno for a very low price.
Robbie wrote: Can you find a shop close by that already has a dyno and will let you rent "tuesday nights after 5 pm" or something like that for $250/month? You might be able to 'rent' a dyno for a very low price.
I know someone who has a tuning business and gets his dyno time this way. It works very well for him and the dyno owner.
I've had my car run on three dynos, two different DynaPacks and an in-floor DynoJet. After running the car on DynaPack #1 it was run on a DynJet several months later with the exact same setup and similar weather. The DynaPack read "411 hp" and the DynoJet read "325 hp", a difference of about 20%.
I get that dynos are simply tools used for tuning, but what bugs me is that these very expensive tools differ by 20%? I suspect the DynaPacks was the optimistic one because given the car's weight, it performed like it had 300-something hp instead of 400-something. FWIW, the two DynaPacks (in different shops) produced virtually the same reading. In this day and age of microsecond timing and precision six places past the decimal, it's amazing that the units differ by so much. Yes I get it that it in part depends how the operator sets it up, but given that both DynaPacks had the same reading makes me wonder if they're just "optimistic" by design... okay, but 20%? Really?
In reply to kb58:
Yeah, agreed. I would expect the HF dyno to be off by 20%, but not a brand name.
It seems you should be able to get closer than 20% by using some data logging software and knowing the actual weight of your car. Just do a run in 2nd gear to keep it mostly legal, but you should be left with time between each RPM (converts to acceleration), and the weight of the car, which should get you to HP at each RPM you measured for (ie every 10 RPM or 25 or whatever).
Thank you SO much for all the great responses. All this great info at least gives me a starting point.
Keith Tanner said: Dynojet (one big roller). Easy to use, consistent, had trouble picking up engine speeds sometimes. Couldn't do steady state tuning, sweeps only. The mass of the drum was the resistance. The four post lift to get the car on the dyno was actually pretty handy at other times. Sold it, it's still working at someone else's shop.
After reading this ^^^
And watching this:
https://www.youtube.com/watch?v=Tq1dMgsw9AU
...I'm thinking the dynojet is probably the best option.
At the risk of sounding like a moron, I'm confused about the comment regarding using the 4-post lift to get the car on the dyno.
Smarta$$ McPoopyPants wrote: At the risk of sounding like a moron, I'm confused about the comment regarding using the 4-post lift to get the car on the dyno.
The DynoJet is a very large unit because of the drum. Some people choose to set it on the floor rather than in the floor. They build a platform around it and use the 4-post to get the car up on the platform
Yup, that's what we did. Would have been a hell of a hole to put that thing in. Made it easier to remove when we sold it, too.
The current dyno is in a hole, but it's also considerably smaller than the big Dynojet was.
In reply to Keith Tanner:
This is a big concern for us too. We rent the garage from AMP, so cutting a ginormous hole in the floor is probably a no-no.
Any chance you have a pic of your old setup? Email is fine, if that's easier.
Here's one of our record-setters on the roller. 39.2 wheel hp!
FWD testing.
Using the four post lift as a lift.
pushrod36 wrote:Robbie wrote: Can you find a shop close by that already has a dyno and will let you rent "tuesday nights after 5 pm" or something like that for $250/month? You might be able to 'rent' a dyno for a very low price.I know someone who has a tuning business and gets his dyno time this way. It works very well for him and the dyno owner.
That's what we do, too. It makes way more sense to rent dyno time than to buy our own, and the shop we rent from uses it for several hours per day so it makes sense for them to own one.
It's a Dynojet, too. As noted, they aren't any good for steady state work but they are at least very consistent.
We did used to have a Land & Sea engine dyno. Operating that was interesting, in that changing the way the sweep was run would really affect output. I made a Pontiac 455 gain something like 50 or 80ft-lb just by sweeping it down instead of up 
We ran it total loss from a 1000gal container of water. Ambient water went into the brake, extremely hot water came out...
My latest dyno sheets. Does yours print in color?
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