Tips on how to dyno a Viper....

[Sean Roe]

Hi Guys,

We answer questions all the time about dyno testing and thought we'd share with you our procedure. We do this to produce the most repeatable and best numbers we can. Anything less than this will typically not yield the best results.

When doing a dyno test, you need to do a few things to prepare beyond the normal mechanical check of the car.

1. Check for full throttle. This typically means removing the carpet mat.
2. Check oil level. Do not fill beyond max.
3. Check rear tire pressure and set to 36 psi.
4. On the way to the dyno, punch full throttle a few times, even if it's just momentarily in order for the PCM to see / learn what you're about to do on the dyno. Otherwise, your first pull could show a little low.
5. Put a fan in front of the car and raise the front of the hood up for better airflow.
6. Have the dyno operator set the smoothing to 2 or 3 before the pull, not after.


Hope this helps everyone.

Sean

 

[Tom Welch]

Sean,

Great tips! Here are a few others that folks could use;

1. Remove the air filters from the airbox.

2. Throw a few bags of ice on top of the intake manifold. This will not really increase power, but it will help maintain consistancy as your engine warms up during testing.

3. Reset the computer after the first pull. This is done by disconnecting the battery wire under the "Red" cap on the PCM..just behind the windshield wiper fluid tank(on 96 and newer)

4. Start pulls at about 2800 RPM. Starting the dyno "sampling" at too low or too high rpms will net lower results.

5. Avoid "spiking" at the end of the pull. The little spike on the dyno sheet is not reflective of your acutal horsepower and usually benefits the car unrealistically. Avoid spikes by letting off the accelerator before you end the sampling.

Tom

 

[99 R/T 10]

Question for you guru's, if there is no fan and the hood is not up, how much lower will the dyno numbers be? Thsi is going to be a greatly informative thread!

 

[Marv S]

How about 4th gear?

It would be nice to get this dialed in as a comprehensive instruction and put in:

http://www.viperclub.org/menus/index_how_faq.htm

 

[Vipersrule]

3. Reset the computer after the first pull. This is done by disconnecting the battery wire under the "Red" cap on the PCM..just behind the windshield wiper fluid tank(on 96 and newer)

Does this help after making modifications such as a new exhaust and smooth tubes?

Or will the Viper PCM figure it out on it's own?

 

[KenH]

Great thread!

How about the correct attachment points for the tie-down straps? The one time I dyno'd my car, they seemed to have a hard time deciding where to strap to and I couldn't give them any guidance. They ended up using the A-arms, but I think that afterwards I read you should not use these points.

--- Ken

 

[slaughterj]

A thought on a point by Sean and a point by Tom:

Since my Viper is a daily driver, I like to know its performance as close to how it is set up on a day to day basis (Pilot Sports set at 30psi, air filter in the care, etc.), regardless of the activity I am doing, whether it is on the street, on a road course (but for changing the brakes), on a drag strip, etc. Consequently, I don't intend to change tire pressure or remove the air filter when dynoing. However, I do "blip" the throttle before dynoing, because typically it will have been applied vigorously while driving , though the car is usually siting an hour or so while the group is working through those awaiting dynoing.

 

[99 R/T 10]

A thought on a point by Sean and a point by Tom:

Since my Viper is a daily driver, I like to know its performance as close to how it is set up on a day to day basis (Pilot Sports set at 30psi, air filter in the care, etc.), regardless of the activity I am doing, whether it is on the street, on a road course (but for changing the brakes), on a drag strip, etc. Consequently, I don't intend to change tire pressure or remove the air filter when dynoing. However, I do "blip" the throttle before dynoing, because typically it will have been applied vigorously while driving , though the car is usually siting an hour or so while the group is working through those awaiting dynoing.

Hey slaughterj,
I believe the reasoning behind the opening of the hood, using the fan and taking out the filters is to better simulate the forced air that WOULD be coming in from foward movement that your not getting during the dyno.

Mike

 

[utahviper]

I think the reason that the tire pressure is at 36lbs is to give an accurate reading on the dyno. You don't want the tires to flex when they are on the dyno.

 

[GONABITE]

Not having a fan in front of the car is a major no no, you would notice a great lose of power without it. Always do pulls in fourth gear as the ratio is 1:1. And using the A-arms as a tie down point is the correct procedure.

 

[Marc Lublin]

I seem to recall that where you position the tires on the drum also affects the #'s (A little in front, centered or behind) but I don't know which is best for the best results?

 

[slaughterj]

A thought on a point by Sean and a point by Tom:

Since my Viper is a daily driver, I like to know its performance as close to how it is set up on a day to day basis (Pilot Sports set at 30psi, air filter in the care, etc.), regardless of the activity I am doing, whether it is on the street, on a road course (but for changing the brakes), on a drag strip, etc. Consequently, I don't intend to change tire pressure or remove the air filter when dynoing. However, I do "blip" the throttle before dynoing, because typically it will have been applied vigorously while driving , though the car is usually siting an hour or so while the group is working through those awaiting dynoing.

Hey slaughterj,
I believe the reasoning behind the opening of the hood, using the fan and taking out the filters is to better simulate the forced air that WOULD be coming in from foward movement that your not getting during the dyno.

Mike

They always have a fan set up, which is cool (pun intended), and I can see that simulating the air as you're going down the road, but if you dyno it with the air filter out, then (a) how do you know your K&Ns or S&Bs are any better, and (b) how can you say your dyno # legitimately without saying "air filter removed"?

 

[slaughterj]

I think the reason that the tire pressure is at 36lbs is to give an accurate reading on the dyno. You don't want the tires to flex when they are on the dyno.

More info please! I can also see the argument that if you are sitting around for a while before dynoing, that your tires get cold, thus more like your baseline psi, rather than the increased psi you'd have if you were driving around, therefore you should add air. But (a) what a pain in the @ss and (b) instead, go light 'em up out front of the place before dynoing