Checking your engine performance on a chassis dyno?

[tnewland]

I am looking to gain some knowlege on using a chassis dyno to check the state of tune and power figures of my engine. What are the typical conditions of testing the vehicle? When should the operator of the test shut the engine down after reaching maximum power output? Should the test operator continue running the test after maximum power has been reached, if so for how long? Thank you.....

[Dwight]

I just got back from a chassis dyno tune today. The operator did one low rpm pull to check out everything. Wheel hop, vibrations, etc. then one pull to 3000, let her cool and made adjustments on my computer. Another pull to 5000. Cool time and adjustments, a couple of more pulls, one to 6000. He let it cool between pulls.
They should watch what it happens and take each pull a little higher in the rpm range.
Jon told me a story of a kid that drove his car to the dyno shop. On the first low rpm pull the new trannie cracked. When they checked the driveshaft, it had one bolt missing and the other three were loose. He and his dad had forgot to tighten them.
I have had my Cobra dyno'ed five times before. Some were just to see what I had. 3 or 4 pulls in 30 minutes, not much cool time between pulls.

The guy today did the best job.
Jon charged me 4 hours, $350 total.
This shop does 2 pulls for $50, which is the best price I have ever hear of.

We're going to take a few Cobras next month for a dyno day.

Should be fun

Dwight

[STL Mark]

Originally Posted by tnewland

I am looking to gain some knowlege on using a chassis dyno to check the state of tune and power figures of my engine. What are the typical conditions of testing the vehicle? When should the operator of the test shut the engine down after reaching maximum power output? Should the test operator continue running the test after maximum power has been reached, if so for how long? Thank you.....

The operator will monitor the engine performance and air/fuel ratio during the pull. When the engine quits making power he'll stop by taking his foot off the throttle. A skilled operator will not make a full pull unless the air/fuel ratio is proper or erratic. You will want to give your dyno guy a complete description of your build including cam specs if you have them, your carb, ignition, rev chip, and any problems you may be having such as hesitation. You may also want to have him pull your dizzy and check the gear first, as well as verify and adjust any timing issues.

A skilled operator will help you to solve your problems to make SAFE horsepower, and creep will break your motor.

[tnewland]

Thanks guys
So this particular operator not only brought it up to max power at 6500 RPM but he continued to keep his foot into the throttle until 7425 RPM where the max speed of the dyno shut the dyno down (the dyno printout said MAX SPEED !!! In big red letters), needless to say the bearings in this high dollar engine were hammered #1 rod bearing spun.

[tnewland]

............I gave the "creep" a 6500 RPM ceiling.

[STL Mark]

He ran your car 1000 RPM past your basic instructions?
Was he asleep or drunk at the wheel?
Do you have a rev limiter?
Do you have a print out of the pull?

It sounds like this idiot ruined your motor.
A print out that includes HP and TQ charts as well as air/fuel readings will tell the story.

[tnewland]

Yep, I have (3) seperate printouts from (3) pulls, two of which he went over the 6500 RPM limit given to him. The engine was an original 289 Cobra competition engine with original dual points (no limiter). He not only made the mistake once but twice. I also have a photo of the Smiths Chronometric tachs tatle-tale needle at 7400 RPM, taken after the "operator" was done.

[STL Mark]

Wow.
Your car is one of those new 289 Slabside cars right?

Hopefully some folks here we'll help you with your next steps.

If it was me I would do the following:
1) Never go back to that shop again - ever.
2) Find an engine real pro to tear that lump down and repair it.
3) Contact an attorney.

I don't know where you live, but if your were anywhere near St. Louis, Missouri (or felt like paying for shipping) I could hook you up with the best group I've ever seen. A group that is trustworthy and knowledgeable, with the only goal of getting right. I can provide you with numerous references of local Cobra owners that are very satisfied.

Fell for ya bud.

(weird - that's the second post today for me that I had to say that)

[tnewland]

Yep, pulled the engine and took it down to the builder he said he had never seen anything like the damage that was done. The biggest problem is the crank was a super special piece, original GT40 steel race crankshaft. I'm checking out the legal route now as I'm sire this is going to get expensive one way or another. Thank you for your help and guidance.

[STL Mark]

Document everything.
Have your builder document everything.
Ask him to make a complete set of notes with dates and times.

Get this guy.

[Jerry Clayton]

I disagree-----

People go to dynoes either to solve a problem or looking for that BIG number to brag about and generally its looking for the big number---

You went in there with out a rev limiter (which you are going to need for yourself or you'll be over revving that 289 pretty bad) and the operator had lots of things to watch----generally they'll be watching the O2 readings for mixture ---

And in Cobras, the tack/gauges are probably the worst arranged of any vehicle for seeing what's going on temp/pres/rev and drive the car.(its actually easier on a race track than in street traffic)

And----usually the limits of the engine are valve train related, not bearing issues----

And---you probably signed a wavier before they tied it down----

[lovehamr]

While I don't agree with Jerry that it's your fault, I AM surprised that you would have a bearing problem. If the 289 was properly built with all those special parts then 7400rpm should not have been a problem. And as Jerry did state, normally you'd experence an RPM related valve train issue, not bottom end. I've seen my Boss302s bounce off of 8k quite a few times with no ill effects and that is with mostly stock rotating parts. Of course they are Boss parts but certainly no better than what you described in your engine. In short, I'd be looking for another issue other than over-speed. Not saying that it had nothing to do with it, just that unless something else were amiss it shouldn't happen as you described.
JMHO, Steve

[Jerry Clayton]

He only mentioned ONE part---an original crank!!!

The dynoes are set up for a test range and the operator ran the car to that MAX SPEED ---I don't know what type of dyno this was on but probably a Mustang?

AND----you do want to run it past MAX power so you can compare hp/tq curves to determine shift point according to gear ratio spread---

If this 289 had an original crank, what did it have for rods, bearings(and size) oil system, and was it a 4 bolt main?

[tnewland]

Hi Guys
As I had previously stated I had instructed the dyno operator not to exceed 6500 RPM. The engine had 12:1 compression ratio and a cam profile designed to give the most power in the 6500 RPM range. The dash in the car is very well laid out with the oil presure and water temp beside the mechanical tach.
Jerry
So what I am to understand from your statement is that you are supposed to run the engine past where the engine makes it's highest figure and keep going until you've hit the max MPH speed the dyno is set-up for? To me this sounds like it would run the engine into the ground with possibly both severe detonation and oil starvation?
The reason I took the car to the dyno was that I had ignition break-up at 4000 RPM and was diagnosing the problem, it turned out to be a worn distributor shaft bearing. The distributor was replaced with a freshly restored original then the other two pulls were made that exceeded the 6500 RPM limit. My engine builder has stated that there are signs of valve float as well,

[Jerry Clayton]

You did NOT reach max speed of the dyno---they are mostly all rated up around 200 mph +-

The operator was probably watching the dyno readout for the numbers----your car guages were not a factor in this

The test range is part of the dyno set up and the readout you saw had nothing to do with the dyno but the test range the operator set up

Its your problem, not the dyno operator--unfortunate, yes, but you could of solved the ignition problem without a dyno

Again---can you tell me what kind of dyno??? mustang or dyno-jet?????

[tnewland]

Jerry
You sound like you know a lot about dynos, do you operate one? If the operator of this particular dyno stated that the max MPH of this dyno had been reached at 150 MPH and the dyno sheets have a large red "MAX SPEED !!!" printed on the front of it what leads you to believe that the max MPH had NOT been reached? Also as an operator are you NOT supposed to monitor basic functions (oil pres, engine temp, etc) of the engine during the test to identify any potential problems during the test? Wouldn't potential problems be displayed on the graph the operator is watching as some sort of inconsistency in the line of the graph? As the operator when is the test finished, after the max horse power has been reached and just as the graph starts to taper downward or are you supposed to continue on until the dyno shuts down irrelevant of what both the customer and the computer monitor are indicating? Is the dyno NOT supposed to be used as a diagnostic tool and a controlled enviroment to safely conduct controlled tests? It sounds lie from what you are telling me that I might as well had gone out on a public street and just mashed the pedal to the floor until I hit whatever speed the engine or car finally stopped at? I hope that you are NOT an operator of a dyno as you appear to be the same type of "operator" that STL Mark is warning about! What is the benefit of using a dyno if for no other reason than a diagnostic tool in a controlled safe enviroment?

[STL Mark]

If the engine was stumbling around 4000 it would have been as clear as a bell on the chart during the pull and there would be no need to run it through a full pull - or beyond. A skilled tech can listen to the engine, watch the gauges, and keep an eye on the computer screen all at the same time during a session to make sure that he doesn't blow your engine.

A skilled tech would have listened to your initial complaint, done a couple of test pulls (after checking timing and dizzy) to 4000 RPM or so (maybe), and if they looked good - he may have done a full pull. But he should never do a full pull unless the motor was making good numbers.

If your engine had any sign of erratic or otherwise unstable behavior at any time during a pull - he should have immediately stopped. And going beyond your instructions of 6500 RPM limit is simply insane.

[Jerry Clayton]

Tnewland-----

Let's separate a few basic things here---

First, If you said don't go above 6500rpm---I can't /won't comment

Why go above the max power rpm? Again, you would do this as that downward trend of the hp/tq curve is just as important as the upward curve toward the max---It will give you the basis for shift patterns / gear ratios---go past the peak rpm so on your upshift the engine doesn't fall too far below peak---if you need more explaination about this I will be only happy to help you understand it, but I am assuming that the idea of your build is to replicate a road racer---

You haven't said what type dyno he used---if you don't know, ok, if you do know there are some differances--On a Mustang dyno you enter certain things into the program and come up with a test window---during the run it will say on the moniter that it is running thru test, once thru the test it will say test ended---IF the run continues beyond the range it will say so--

Things to moniter---the operator will be monitering the dyno read out, not the car instruments--he can't look two places at once---so if your vehicle loses oil pressure someone else would have to notice it--

So you had a steel crank--what oil system, rods, pistons???
If you where running oem rods you were way over the bar way before 6500rpm--

We perform dyno services on several dynoes in the Chicago region and quite often do 3-5 on an average per week, sometimes multoples at the same location---My son, Corey does all the electronic tuning on the Nickey Camaroes and other builders cars, plus we are often recommended to Diablo and computer tuners customers to solve/straighten out issues--there are two Mustang chassis dynoes located in St. Charles,IL and other Mustang and Dyno-Jet facilities that call us out to help them out with the more complex vehicles.

I do the carb/ignition cars and on the computer ones while Corey is into the computer I watch over the whole test for issues such as smoke, leaks, temps,oil pressure, etc---

I'm sorry that you lost your engine, but also some were all over the dyno operator without knowing anything about what is involved in running a test.

[tnewland]

SLT Mark

An initial pull was done to 4000 RPM where the ignition problem was found, we put in a new distributor that had been tested on a distributor machine and he did a pull past our problem RPM to about 5800 RPM with no more trouble. The operator then decided to rest the dyno for a pull and did two more pulls, both exceeding my 6500 RPM limit and until the dyno safety MPH had been hit. On both of those pulls you can see the graph line breaking up after the max horsepower bell curve started downward all the way to the dyno shutting itself down.

[STL Mark]

Here is an example of a problem spotted on the dyno.
My friends car was "running rough" around 4000 RPM.
He told our dyno guy about it.
He did an initial pull - see the erratic set of HP/TQ lines.
They are broken at about 4300 RPM because the operator stopped the pull.

He then made some corrections to the car (sorry I don't remember what) and did another pull. That second pull where the lines meet about 5000 RPM corrected somewhat but his A/F ratio was off so he discontinued that pull as well.

The engine was never in danger during the session because the operator was paying attention and doing his job.