Sharing Some Dyno Facts

[Canyon707]

I had and interesting conversation with Gary from X-Metal regarding my latest dyno run after my new throttle body installation. Here is what I was told and I beleive that is is 100% accurate. You cannot dyno your car one day and then return to the dyno shop and get the same results on a different day. Reasons are ... Temp, humidity, tire pressure, where the car sits on the dyno drum, the strap tension, gear selection, fuel, ( many gas stations now are using a blended gas so the get a taxcredit of .50 per gallon sold. There were other things mentioned as well we chatted for an hour or more. So the deal is get your base run on the dyno. Leave your car in the same position on the dyno make your changes and then retest this will give you more accurate test results. Comments more than welcome.

 

[rcl4668]

I had and interesting conversation with Gary from X-Metal regarding my latest dyno run after my new throttle body installation. Here is what I was told and I beleive that is is 100% accurate. You cannot dyno your car one day and then return to the dyno shop and get the same results on a different day. Reasons are ... Temp, humidity, tire pressure, where the car sits on the dyno drum, the strap tension, gear selection, fuel, ( many gas stations now are using a blended gas so the get a taxcredit of .50 per gallon sold. There were other things mentioned as well we chatted for an hour or more. So the deal is get your base run on the dyno. Leave your car in the same position on the dyno make your changes and then retest this will give you more accurate test results. Comments more than welcome.

I agree that to be truly "scientific" about dyno runs that would be ideal. I am just not sure that it would be entirely practical. For example, I will be installing some mods (headers and exhaust) that require a certain number of "break in" or "learning" miles. Thus, there is no way I could keep the car strapped to the dyno in the same position as I would need to drive the car 500-1000 miles before redynoing with the mods. My only hope is to redyno the car when ambient temp and humidity is roughly the same.

/Rich

 

[steponz]

What about the gas issue...... I notice more and more gas stations by me are switching to 5% ethanol...

Would this be worse to run in the car????

Joe

 

[britospeed]

Nothing is 100%...but, Use a load bearing dyno, not an inertia dyno. Also make sure that the dyno has an automatic weather station. If not make sure that the operator enters the weather data right before your runs. Also make sure that the operator uses the same correction factor. On the load bearing dyno ask when the last time the load cell was calibrated as this can skew results. On higher horsepower cars it's a good idea to use 2 different rpm pickups eg. roll speed and either ODB2 or an inductive pickup. That way you can see if your getting wheel spin which will affect your results.
I could go on but you get the idea...
Michael

 

[B767DRIVER]

I had and interesting conversation with Gary from X-Metal regarding my latest dyno run after my new throttle body installation. Here is what I was told and I beleive that is is 100% accurate. You cannot dyno your car one day and then return to the dyno shop and get the same results on a different day. Reasons are ... Temp, humidity, tire pressure, where the car sits on the dyno drum, the strap tension, gear selection, fuel, ( many gas stations now are using a blended gas so the get a taxcredit of .50 per gallon sold. There were other things mentioned as well we chatted for an hour or more. So the deal is get your base run on the dyno. Leave your car in the same position on the dyno make your changes and then retest this will give you more accurate test results. Comments more than welcome.

That is the best case scenario. As Rich said, It is not always practical...

 

[Canyon707]

I think the best answer is on the drag strip. make 10 runs and look at the times and speed traps. Planning wed night drag racing at Infinion in Sonoma Ca. next month. My issue was just this the new Tb on the dyno gave me 1 additional Hp and 9 lb less torque. Was I disappointed yes but it feels stronger and the curve is better. Really not sure this guy really knows how to set it up on the dyno. I did add a K and N cold air package to this and removed my RSI intake which had two intake tubes to the TB tubes thinking since the Tb had only one opening I would get more from the K and N. Well thats the story.

 

[DMan]

Yea, I've always used trap speed in the quarter as another measure, less impacted by traction than ET. 10rwhp should be close to 1mph increase, I'm told. I have the XMetal on the shelf, if I installed and pulled lower, with weather correction on the same baseline dyno, I'd be a little bummed, but not completely til I got to the track & saw what happened. If no increase in mph or even slower, than with the two measures being disappointing, I'd be, well ... disappointed.

Let us know the track results, obviously I'm very interested in your results.

 

[mike & juli]

Chris: I also believe that to be correct, makes 'logical' sense, right? We have our car back at our tuner's this week for a 'fine-tune' that we didn't get to a year and 1/2 ago...so, yes, our results are gonna be different than they were then...it was like 95 degrees at that time, VERY high humidity...now it's barely 30 degrees and arctic air all week. The pulls should be BETTER this time around. We'll know more after this weekend. Same dyno, but yes, different season/day = different results. Agreed. ~juli
http://forums.viperclub.org/srt10-srt10-coupe-discussions/611050-re-viper-romarracing.html
(This is where our Viper is right now)

 

[mike & juli]

What about the gas issue...... I notice more and more gas stations by me are switching to 5% ethanol...
Would this be worse to run in the car????
Joe

Good question, as here Hess gives you NO choice in the pumps (we don't use Hess for our high-performance cars though, we use Mobil or Sunoco up here)...and they have 10% ethanol POSSIBLY added it says on all the signs on the pumps. Wonder also the effect.
~~juli

 

[CarDude]

Good question, as here Hess gives you NO choice in the pumps (we don't use Hess for our high-performance cars though, we use Mobil or Sunoco up here)...and they have 10% ethanol POSSIBLY added it says on all the signs on the pumps. Wonder also the effect.
~~juli

Here in Colorado it is 15% ethanol in the winter to reduce CO2 emissions. On the other hand, E-85 (15% gas) may get worse miles per gallon, but the octane levels are much higher, so if the car can use the higher octane (based on tune) it could actually make more HP. But then again what do i know...I am a software developer.

 

[mike & juli]

Here in Colorado it is 15% ethanol in the winter to reduce CO2 emissions. On the other hand, E-85 (15% gas) may get worse miles per gallon, but the octane levels are much higher, so if the car can use the higher octane (based on tune) it could actually make more HP. But then again what do i know...I am a software developer.

Well, you know more than I do!! So far, we have NO ethanol in our high-performance cars. By the time we have to fill up again, probably all pumps around here will give you no choice...they WILL have ethanol....so will be interesting to see how it impacts our HP...we're not that concerned about fuel efficiency (teeheeeee). ~juli

 

[Canyon707]

Yea, I've always used trap speed in the quarter as another measure, less impacted by traction than ET. 10rwhp should be close to 1mph increase, I'm told. I have the XMetal on the shelf, if I installed and pulled lower, with weather correction on the same baseline dyno, I'd be a little bummed, but not completely til I got to the track & saw what happened. If no increase in mph or even slower, than with the two measures being disappointing, I'd be, well ... disappointed.

Let us know the track results, obviously I'm very interested in your results.

I will post that when I do it for sure. I am going to try the mustang dyno. there is one in town but, my thoughts are I have no base on the mustang but, curious about it and about the operator I am not sure if the dyno jet guy has a real clue on his machine Gary also said with my 3:73 gears I should do the run in 5th gear.

 

[DMan]

The mustang dyno will definitely show lower numbers, like a superflo, about 8-10% the say.

I've never heard of dyno'ing a car in 5th, I've dyno'd several cars with 3.73 gears & the T56 tranny in stangs, always in 4th. You'll have a lower hp # with 3.73 vs 3.07, but dyno'ing in 5th seems like it has to be wrong.

 

[Joseph Dell]

I only partially agree with Gary. There are always variables. But you could also argue that the oil temp, coolant temp, outside temp, etc... need to also all be the same for a 'perfect' match.

The dyno itself (at least MOST of them) take a temp and barometric pressure reading BEFORE each pull (it is actually data recorded in each pull) and it creates a 'modifier' for your power output. In fact, the reason people use SAE as their dyno measurement value is b/c the SAE calculation ADDS correction factor when needed and SUBTRACT when it isn't needed.

The drum weight of a dyno (which goes into the correction factor) is unique and precise on EACH dyno. so if you went to two different dynos the same day you may or may not get identical readings. probably not.

But if you go to the SAME dyno twice in one year then any noticeable modification will show up on the 2nd trip regardless of the time of year.

RE: D'man's 'what gear' question, you want the dyno to pick up as close to a 1:1 ratio as possible of the engine... so 4th gear is the best option in a viper. if you dyno in 3rd, you (in theory) will see the same readings. in theory.

I've got over 430 dyno runs on the same car on the same dyno over the past 9 years. I don't disqualify them because they weren't all runs on the same day.

The gas comment: I call BS on that one. That's pure crapola. but my .02 that it's crapola.

If you do a dyno run today, make a change, go back tomorrow, and the car runs better or worse, you can be pretty darn sure that the change was responsible. On the other hand, if you see no change or LESS power (Gen 2 TB upgrades on STOCK cars actually see this), then you can't blame the weather or the day... it's the modification or the combination of modifications working together.

JD

 

[mbccenter]

We change the headers on the dyno when testing to see HP gain. Same day and same conditions.

 

[Joseph Dell]

We change the headers on the dyno when testing to see HP gain. Same day and same conditions.

There is no doubt that minimizing the conditional changes gives a more accurate result. But there are just as many stories of people who dyno on a feb winter day and then come back on a hot June or July day and dyno the exact same power readings (no car changes).

I'm just sayin' izzall...

JD

 

[Canyon707]

It's interesting stuff you all have pros and cons here and good to hear all thoughts. Maybe my 04 is just not the motor I had hoped for then. new plugs, new wires, K&N air package, DC computer adjustment, X-Metal TB Corsa, 180 Thermostat. 3:73 gears, output on the Dyno Wed 451 hp and 471 tq down from 480 tq and up one hp. I am not happy with those numbers. Although the car is quick and runs great the numbers that I got from the mods don't add up to what I think they should be. As far as I figure I should just leave it alone. Although I was thinking about new heads I think I should let it be. Tell me about the M and M headers. I had RT cats but way to loud so I took them off.

 

[mbccenter]

Your 3:73 gears will show lower duyno numbers vs the stock 3:07

 

[fqberful]

Tell me about the M and M headers. I had RT cats but way to loud so I took them off.

I'm using M&M's, no cats, and those super long mufflers from a MOPAR perf exhaust. Not all that loud actually.

The initial dyno gain was about 37hp, 39ft/lbs tq. N/A car with just K&N, 172'thermostat, 3.55's, and B&G flash.

Thanks to Matt and Mitch for the awesome headers. And they do sound cool!

I did an X-metal TB on the dyno and didn't see any appreciable gains though it may take a little time for the PCM to adjust. I doubt I'll see much here though, but the throttle response is noticeably better.

 

[mike & juli]

Joseph: When you talk about the fuel/ethanol being crapola...what exactly do you mean? That it makes NO difference whatsoever that ethanol is in the gas? If SO, that's a good thing. We will be seeing our dyno results hopefully Saturday...VERY different than last dyno when humidity was so high, you couldn't even breathe, so NO air was getting into the car at that time...this time will be different....20's, dry air, but air nonetheless...we're hoping for a good tune!! ~juli

 

[Canyon707]

I'm using M&M's, no cats, and those super long mufflers from a MOPAR perf exhaust. Not all that loud actually.

The initial dyno gain was about 37hp, 39ft/lbs tq. N/A car with just K&N, 172'thermostat, 3.55's, and B&G flash.

Thanks to Matt and Mitch for the awesome headers. And they do sound cool!

I did an X-metal TB on the dyno and didn't see any appreciable gains though it may take a little time for the PCM to adjust. I doubt I'll see much here though, but the throttle response is noticeably better.

did you see less???

 

[Canyon707]

Check this out.......... dynoed about 7 runs on a Mustang Dyno with a few different parameters. All ran in the ball park 400 RWhp Tried 5th gear pull and it was stronger but dyno was limited to 150 mph so it didn' finish the run. I did notice more power and torque but it never finished. I understand that mustang dynos make lower numbers but, 400hp with my mods???? I can tell you it feels strange to try to make more power with these mods and get less. It ascutally *****. I am just not sure what the issue is or if I am being premature on this. How much time does it take the PCM to adjust to the latest changes? I don't want to swap back to soon (really not at all) DC did my PCM I think I will call him and see what he thinks. anyone Dyno on the Mustang it seemed like a pretty good setup and the guy was knowledgeable. We messed around with it for a couple hours. ( to no avail)

 

[Canyon707]

Your 3:73 gears will show lower duyno numbers vs the stock 3:07

I understand that 4th is based on one to one with stock 3:07 My 3:73 must kick it off quite a bit. I wonder how that is figured out. Like I had said Gary for X-Metal thought I should try it in 5th I did but the dyno shut down at 150 showing more power but, ended prematurely.

 

[mike & juli]

Check this out.......... dynoed about 7 runs on a Mustang Dyno with a few different parameters. All ran in the ball park 400 RWhp Tried 5th gear pull and it was stronger but dyno was limited to 150 mph so it didn' finish the run. I did notice more power and torque but it never finished. I understand that mustang dynos make lower numbers but, 400hp with my mods???? I can tell you it feels strange to try to make more power with these mods and get less. It ascutally *****. I am just not sure what the issue is or if I am being premature on this. How much time does it take the PCM to adjust to the latest changes? I don't want to swap back to soon (really not at all) DC did my PCM I think I will call him and see what he thinks. anyone Dyno on the Mustang it seemed like a pretty good setup and the guy was knowledgeable. We messed around with it for a couple hours. ( to no avail)

Think that's a good idea...call Dan Cragin from DC since he did the PCM...as we all know, he is also one of the 'greats' on here with his expertise. Does seem like you should be pulling more rwhp...I DO know adding the gears won't change the dyno figures from what I've been told by the experts. Did you also try asking Joseph Dell what he thinks? He may also be able to help from your dyno runfiles, if I may be so bold as to mention him?
Good Luck...juli

 

[wallbanger]

I agree that to be truly "scientific" about dyno runs that would be ideal. I am just not sure that it would be entirely practical. For example, I will be installing some mods (headers and exhaust) that require a certain number of "break in" or "learning" miles. Thus, there is no way I could keep the car strapped to the dyno in the same position as I would need to drive the car 500-1000 miles before redynoing with the mods. My only hope is to redyno the car when ambient temp and humidity is roughly the same.

/Rich

The reason rich doesn't have his headers on yet is because he is still sleeping with them

 

[Canyon707]

The reason rich doesn't have his headers on yet is because he is still sleeping with them

Don't feel bad Rich I slept with my TB, I think I should have kept sleeping with it also.

 

[rcl4668]

Don't feel bad Rich I slept with my TB, I think I should have kept sleeping with it also.

Feel bad? I thought everybody slept with their aftermarket parts before the install.

<Crickets>

/Rich

 

[Joseph Dell]

Feel bad? I thought everybody slept with their aftermarket parts before the install.

<Crickets>

/Rich

It depends on how expensive they were. I heard that sleeping with the Shifter was popular in some circles...

<crickets>

 

[FE 065]

Doing before and after roll ons with a bud that has a Viper or ? that's close in power to yours will let you see any loss or gain... That won't get you any HP numbers, but removes all the variables of a dyno and drag strip as long as the other car doesn't change anything..