Am I getting the runaround?? Dyno procedure - Team Camaro Tech
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post #1 of 5 (permalink) Old Dec 20th, 02, 07:08 AM Thread Starter
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I always seem to get the runaround when it comes to engine builders because I tend to trust everyone. Well, I find myself in another predicament that I want to prevent from turning ugly. I'm not sure whether I'm misreading my engine builder or not, so please give me some advice.
Here's my situation: I've had my 69 SSRS on the road for one year now. It ran great, but I felt as though I was losing power. I finally decided to pull the engine and trans due to oil leaks and the loss of power. I talked to a local gentleman who rebuilt a carb for me (who has what I consider to be wonderful work ethics as far as guaranteeing his work) and he recommended a local engine builder. After visiting the engine builder, I decided to have the engine dynoed as per his recommendation. I and a friend were there for the dyno, but what I found to be strange was that we found two dead cylinders (#5 and#8)on the first run. He said that it may be the wires or the plugs or possibly something internally. I had the engine tested just recently at another shop for compression loss and a rear wheel horsepower dyno. The test showed that everything appeared to be fine. The rear-wheel horsepower stood at 359h.p. They estimated that the engine was putting out about 400-416 hp at the flywheel. What I found to be strange was that instead of shutting the engine down and trying to locate the problem, he continued to make four more dyno runs. Is this standard practice or is it me?? I would assume that if a plug wire or plug was found to be bad, it would be replaced so as to get a true reading of the engines performance under normal operating conditions. When I asked him why this was not done, he told me that he wanted to see EXACTLY how the car was running when I took it out of the car. Well, to be completely honest, I can see making one or maybe two runs with two dirty plugs or two faulty wires, but not all four or five. Mind you, this dyno will cost me around $400!! Am I wrong?? Is there something I'm missing as far as a correct dyno process??

<LI>My everyday driver 69 SSRS.
<LI>My project 69 SSRS L-78.
<LI>My 69 RS project. [/list]
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post #2 of 5 (permalink) Old Dec 20th, 02, 07:42 AM
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I don't think you're wrong. And $400 for that is way high. I've done over a hundred chassis dyno pulls on my cars. If there's a problem you fix it otherwise you're risking further damage and at the very least beating on it for no reason.


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post #3 of 5 (permalink) Old Dec 20th, 02, 08:24 AM
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All of my dyno experience is with race car engines (DIRT Modifieds). The engine is always out of the car and usually off of a fresh build or rebuild. The going rate seems to $500 dollars for the day. As far as number of runs (commonly called pulls) We have done up to 50 in a day. Also every pull is backed right up with a second pull to eliminate and bogus information. I am a bit surprised the "dead" cylinder was not researched.

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post #4 of 5 (permalink) Old Dec 20th, 02, 08:56 AM
David Pozzi
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I'm no dyno expert but was going to buy one a while back. I did some research on test methods and data aquisistion for water brake engine dynos.

It may be he has a proven method of doing pulls that gives him a certain amount of accuracy in determining horsepower. He probably takes an average of the horsepower readings from the four pulls and compares that to later tests.
If you don't know what your power was at first, you won't know the effect of your changes.
If he does a lot of smaller engines, the power differences are much smaller and his testing methods will be such that he is trying to be as accurate as possible.
Dynos are not good at measuring very small HP differences that you get on small engines. Some dynos/test methods are worse than others (less accurate).
If he has a lot of manual guages instead of a data aquisition computer to save data, he may be reading different things like fuel pressure and exhaust temps, coolant or oil temps when running it. Any variance in oil or coolant temps will affect HP readings. He may have been doing added pulls to get the oil up to temp. He probably has a target oil temp and water temp to do his most accurate test pulls at.
There is an awful lot to dyno testing that isn't readily apparent.
The Superflow site has some good info on dyno testing and accuracy. Also here:

If it were my engine running badly on the dyno, I'd be wincing too.

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[This message has been edited by davidpozzi (edited 12-20-2002).]

[This message has been edited by davidpozzi (edited 12-20-2002).]

[This message has been edited by davidpozzi (edited 12-20-2002).]
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post #5 of 5 (permalink) Old Dec 22nd, 02, 03:11 PM Thread Starter
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Hi Guys,

Thanks for your assistance with this topic. I went back to his shop yesterday and I'm feeling a bit better about his intentions. I'm going to have him rebuild my engine rather than having a whole bunch of extra engine pieces laying around collecting dust. I did find out that my previous engine builder charged me for machine work that was never performed, so I'm going to pay him a visit and get things straightened out!! Thanks again for all the help. Paul

<LI>My everyday driver 69 SSRS.
<LI>My project 69 SSRS L-78.
<LI>My 69 RS project. [/list]
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