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Old 03-11-2008, 01:15 PM   #1
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Dyno tune or 'street' tune??

Having had both types of tunes I think I can address this subject fairly objectively.


First, the street tune is head and shoulders over stock: no question at all and this is WITH or WITHOUT bolt ons. You will be happy if it is done by a competent tuner.

Second the dyno tune brings out the idiosyncratic 'likes and dislikes' of your car and you can usually pick up both mid range, which is where you live, and max power over the street tune. What impresses me is the mid range that you pick up.

I have seen two identical cars with the same 'thumbprint' computers receive the same street tune and both did well but when dyno tuned, each car "wanted" something else; that is to say, each responded better with a change that only the dyno could verify. What is really odd is how dramatically different the wants of a particular unit could be even though they were both basically the same vehicles down to all the bolt ons etc.

So, if you have the opportunity it will serve you better to get your car dyno tuned: or so I think.

This info and $30 gets a decent bottle of bourbon . . .
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Old 03-12-2008, 10:26 AM   #2
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Tuning a vehicle properly on just the dyno is a tall order unless you have a real load control dyno. Dynojets and the like just don't cut it....more and more professional tuning shops are finding this out every day.

Street tuning is perfect for idle and off idle operation as well as specific speed and acceleration bands. Street tuning sucks at high speeds or any other dynamic that has the driver/tuner breaking laws and endangering themselves and others. Street tuning can not address measurements of power/torque and thus cannot accurately, beyond SOTP, determine the sweet spots on timing and A/F requirements.

Bottom line is to have a professional tune your car on state of the art equipment and road tune as well.

One other thing...mail order tunes without data logging back and forth to optimize are a waste of money and time. And, paying more than ~ 100-150 for such service is the equivalent to a $1,000 oil change.

Just my $ .02 worth.
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Old 03-12-2008, 11:21 AM   #3
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So what are the "better" type dynos?

Ken
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Old 03-12-2008, 12:33 PM   #4
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They are called absorbtion dynos. They have some type of brake usually electric or water that puts load back on the drum so you can do steady state tuning. You can do road simulations also and it is much more accurate than tuning with just a max hp run. You can do a peak number run just like an inertia machine but it's more accurate across an unlimited number of vehicles. Most shops have inertia dynos that are only good for sweep tests meaning start at a target RPM and run up to another target RPM and it'll give you the peak numbers based on it's best calculation, if you break momentum the run is over. I don't want to get into a disagreement on here but inertia machines aren't really accurate because they don't take into account different variables that are important and constantly changing across a wide range of vehicles. An absorbtion machine can put the exact amount of load back on the drum as the vehicle is putting it to it, giving a more accurate reading. It doesn't need to take into account vehicle weight, driveline mass and things of that nature, all it knows or cares about is what you are putting to it.

By the way, B&P Performance is getting an Eddy Current machine in case anyone was wondering.

Ed
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Old 03-12-2008, 02:51 PM   #5
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Street tuning and data logging is good but, as indicated, you can't go 140 on the road while tuning for a multitude of reasons.

What my observation has been is this: use a quality dyno ( don't want to get into brands here) and tune the car as you will see intermediate and WOT gains of HP and torque. Then you must drive and data log the car as this allows you to come as close as possible to a perfect tune. Jeremy always data logs a tune be it a street tune or a dyno tune - - we just feel the dyno is a decent tool for some applications that are not practical on the street.

Also, it is my understanding, and yes, I could be wrong, that Dynojet also has a program that will allow cars to go through various driving scenarios.

Regardless, a dyno is in my personal opinion a good tool for a tune - - - I know first hand it is great for drag cars too!!
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Old 03-13-2008, 03:07 PM   #6
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I have a nice answer but it is in a PDF format and I am basically to computer illiterate to know how to forward it.
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Old 03-13-2008, 06:13 PM   #7
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DE Vette,

OK, you set the hook - - - will do my dyno homework and address your comments - - may be this weekend but I will not let it go unanswered.

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Old 03-13-2008, 06:40 PM   #8
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You got it, I can't wait to hear what you find out. I was going to buy an inertia machine but after doing my homework I found the absorbtion unit to be a much better tuning tool and much more accurate over a wide range of vehicles. Don't get me wrong, inertia machines are not junk by any means they are good for before and after to see gains, but as far as tuning it can't really be done spot on. I'd love to see that pdf if you can email it or PM it to me somehow.

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Old 03-13-2008, 08:42 PM   #9
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De,

Before I make the post I can tell you that Dynojet makes both and one is a combo of the two - - - I will spill all the beans shortly: hell, maybe I will learn something.
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Old 03-14-2008, 07:18 AM   #10
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Olddog,

Most manufacturers make both, it's just that the absorbtion type is double the price compared to an inertia machine. An absorbtion machine can do everything an inertia machine can do and be more accurate while doing it. It can also do other type of things necessary to tuning that an inertia machine can't do. Pretty much the equivelant of road testing a car. I'm still up in that air about that though, I really don't think there is a substitute for real on road data. I guess I'll find out when I get the machine and compare log files from what I have on the road.

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Old 03-14-2008, 07:34 AM   #11
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DV,

I agree and I hope to get the dyno differences post to you today - - I hope. Otherwise but me and it will get done by Sunday.

We have found that the dyno is a tool that is very close to the street and when the car is data logged for 20 minutes of different driving few changes are needed from what was learned on the dyno - - - remember, you can do part throttle driving on the dyno too.

later . . .
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Old 03-14-2008, 11:06 AM   #12
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I can illustrate the difference for ya...


Load dyno tuning can hold the engine steady at any RPM, at any load, and at any throttle position for any length of time = tuning every cell in the fuel and timing maps.

Inertia dyno tuning accelerates from low rpm to red line in about 8 seconds = tuning PE and spark tables at something less than full load.
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Old 03-14-2008, 11:20 AM   #13
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That's what I've been trying to say.

Ed
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Old 03-14-2008, 11:20 AM   #14
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Paradigm,

From what I have gleaned so far it is a bit more complicated then that - - I should have the info I collected into some sort of post by Sunday.

All I personally know is this: we begin on the dyno and end up data logging on the street for about 20-40 minutes and it works quite well.

What I am going to post are the differences which are not as simple as presented by anyone - - I should learn something from this myself.
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Old 03-15-2008, 07:43 PM   #15
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Well, here it goes from what I have been able to find out.

**Remember my background was cardiac pacing/defibrillating** I am not an ME. I am an enthusiast and I do work with a lot of 8000-9000hp cars and boo coo 1300 hp cars. Being only half stupid I have absorbed a bit, not much, just a bit. I own a 420 rwhp car and race a 827rwhp car **not sure what it makes on methanol**.

There are two types of dynos: Inertia type and electric type load dynos. Now lets look at them.

An inertia dyno operates with large steel rollers that contain a FIXED mass which can never change. Basically it's operating principle is Newton's Second Law which states: Force= Mass x Acceleration ((An aside here, we developed our new roll cage padding using Newton's second law)) Back to the dyno, based on the time required to accelerate the rollers allows you to measure force. For HP, inertia dynos take the force in lbs and multiplies it by speed of the roller in ft/sec which effectively yields HP.

A good inertia dyno CAN NOT have any operator influence on the power reading: the power to the drums is what is displayed. However, you can get three readings: real time, corrected or SAE corrected. 'Real time' means the actual power you are making for that pull and it allows the temp, barometric pressure, humidity and air pressure to give you a raw number. As such, if you make a pull on a 50 degree day with 30% humidity and a pressure of 30.2 you will get a high HP. The same car on a 95 degree day, with 80% humidity and a barometer of 29.6 will give you a much lower number.

To correct for conditions the operator can change to a 'standard correction factor' which takes the readings and converts them to a fixed temp etc. He can also choose to use a "SAE correction factor' which is a bit more astringent. Either way, you want to use a correction factor. You want apples with apples when you are looking for changes.

Now for some mythology about inertia dynos. Once a roller is rolling it stays at that speed unless throttle input is changed; as such, if at a slower speed and you accelerate partially or WOT you can plot the power change as you must still rotate this mass beyond where it was being held at a fixed speed.
It is not a WOT only tool.

The other class of dyno is known by various names: eddy current/electric type load/power absorption dyno (PAU) - - these are all the same basic operating system. These dynos use rollers of very little mass which is usually not known, so to present a physical load on the vehicle it needs to absorb power. Typically these units are electric coils using eddy current technology which acts like a giant brake which measures torque. The brake incorporates a strain gauge or torque cell but the strain gauge does not know the difference between 50 lbs. or 200 lbs. It must be calibrated and this allows for a margin of error. **Ever make a mistake with math?** This margin of error would apply to any eddy current dyno even the Dynojet series of inertia & eddy current dynos. And it gets more interesting: assuming the strain gauge is perfectly set the operator must enter certain parameters about the vehicle being dynoed that determines the rate of acceleration the dyno allows. It is imperative that the parameters that are germane to your vehicle be accurate. It has been said that some eddy current operators will tune the dyno and not the car. NOTE: I know of NO dyno shops who intentionally fudge parameters with these type dynos BUT it can be done.

I think, personal opinion here, you want a constant fixed measuring stick that is free from operator influence via mistake etc.

Now if you must do you complete tune from the bottom to the top ENTIRELY on the dyno then the eddy current dyno is most beneficial. However,remember the accuracy is dependent on the operator's proper setting up the unit.

No matter what kind of dyno you use, you should always, if possible, data log some parameters on the street to check against your dyno readings.

It has been suggested that you should get as much info about your car if you use an eddy dyno from the operator **timing. IAT, MAF etc.** Now take the car to an inertia dyno and check the same parameters. YOu may get an eye opening.

What is the most important factor in dyno tuning is the tuner: ECM tuning is an art form or a discipline that requires special tools (software) and the ability to interpret data correctly regardless of the dyno used - - this is the MOST important factor. NOTE: This is probably the most important piece of info on this post.

I will close by saying that Dynojets are primarily inertia dynos but they do make inertia/load type dynos as a combination and have been doing so for five years. These dynos can be operated in either mode or as a combination of both modes.

Most buy the inertia dynos and not the combos and I am sure it has to do with cost and time for set up etc.

OK - - you guys owe me as this was a pain in the ass!!
'
If you have questions go to Dyno Dynamics, Dynojet, Mustang or what ever dyno you have questions about: don't come to me.
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