general dyno questions

[foghat]

Hey all,

I want to get a baseline dyno run before I install my mods.

I have a couple general questions:

1. I am at about 3500ft. How will the numbers I see on the dyno compare to someone who was at, say, sea level? Is there some sort of correction factor so everyone is comparing the 'same' numbers?

2. I currently have winter tires on my car. Is it a bad idea to do a pull with winter tires?

I spoke to the shop with the dyno and the guy said that it is fine. But depending on the speed rating (which I don't recall right now) of the winter tires, he may have to do the pull in a lower gear than he normally would - not sure if this would affect the end results or not.

Thanks.

[Alexim]

+1 on the correction factor.. I'm still in doubt about this, since I'm also at 3000ft and around 95F...

[Freon]

1. What are you wanting to know? What the car would do at sea level? What it actually does?
This is especially debatable on turbo charged cars. The car may target load or absolute manifold pressure, so it may make about the same ACTUAL power at elevated altitude. Applying a correction factor on such a car will lead to inflated numbers at altitude. Some car may target the same boost (gauge) pressure. If so, the car will make less power at altitude, but not as much of a drop as a naturally aspirated car.
Some turbo cars may act as either of the above, but will eventually tail off at higher altitude. How high, and how fast it drops off you'd either have to try to measure or look at the tune.

There is no good answer here. Again, part of it goes back to what you want to know. Do you want to know actual power, or some uneducated guess as to what the car would do if you were at only 1000ft? I tend not to like correction factors on turbo cars unless you know precisely how the car adjusts absolute pressure based on barometric pressure, then you should use a specially calibrated correction for that car only.

SAE correction is a joke.

2. I'd ask the dyno operator.

[foghat]

Originally Posted by Freon

1. What are you wanting to know? What the car would do at sea level? What it actually does?

You see all kinds of dyno numbers thrown about here. I appreciate different dynos = different numbers (and no car is exactly the same). But, consensus seems to be, stock car dyno's at ~270-280. FBO ~380-400.

While there is mention of the type of dyno (and how that may affect numbers), I have never heard mention of the altitude the run was done at.

Like you mention, I know altitude affects FI less than NA, and our dme, to a certain extent, tries to compensate for altitude so that performance is as equal as can be regardless of altitude - but as I understand it, this is not 100% effective.

So really what I am trying to determine is if I should expect to see the same numbers (assume same car) on a dyno at 3500 feet as I would at sea level. i.e. will the 'consensus' numbers apply to me?

Now I know if there is not any correction applied, then I would expect to dyno lower. But since I never hear about what altitude a given run was done at (yet there is this consensus to what a car with given mods should make), I am not sure if there is maybe some standard correction that everyone uses to make comparing numbers a little more apples to apples. And yes I appreciate you can't really compare numbers from one dyno/car to another, but still, these general numbers are out there and seem to be widely accepted.

[foghat]

And more to my point/confusion:

You will see threads here how that dyno number is way too high for mods done or 'your numbers look pretty low for those mods'. But never does altitude that the runs were done at come into question. So I am just not sure.

[Freon]

Solution? Don't place much confidence in random people on the internet commenting about particular dyno numbers being high or low.

Just taking your "270-280" as a range of a stock car does not seem nearly wide enough. I'm just another schmuck on the internet, but I'd just switching from a dynojet to a mustang dyno will yield far more change than 10hp. If I was forced to say, I would the difference would typically be more like 30hp.

I think you're trying to misuse the tool. A dyno sheet is good for comparing with your friend's M3 that just ran on the same dyno an hour early that day, or to your own car last week before you installed downpipes. People WANT to compare dyno numbers to people all over the US or world, but that WANT rarely manifests in reality.

[foghat]

Fair enough. And ya, my stock range may be out - but again dynojet vs mustang dyno yields different numbers. This known and accepted. But there is never any mention of altitude. I guess I don't understand why, as I thought it could play a significant role in what the end numbers look like.

I know a dyno is best used as a tool to measure the deltas in the mods/tuning you do to your car and not for comparing to others. Still one can't help but do it and feel like something is not right if their numbers do not fall within the 'generally accepted hp range' for a given mod.

Guess we will see what my numbers look like once everything is delivered.

[Alexim]

Originally Posted by foghat

Fair enough. And ya, my stock range may be out - but again dynojet vs mustang dyno yields different numbers. This known and accepted. But there is never any mention of altitude. I guess I don't understand why, as I thought it could play a significant role in what the end numbers look like.

I know a dyno is best used as a tool to measure the deltas in the mods/tuning you do to your car and not for comparing to others. Still one can't help but do it and feel like something is not right if their numbers do not fall within the 'generally accepted hp range' for a given mod.

Guess we will see what my numbers look like once everything is delivered.

Have you actually dyoned yet???
Try to dyno with both corrections and no corrections do we can see what the difference is...
I read on the n54tech forum, a post that Terry did, on how to dyno your car.. At the end he says, always choose STD correction, so I'm guessing most people dyno with that sort of correction...

Here's the link...

http://www.n54tech.com/forums/showthread.php?t=488

[JZWBMW]

I have been dealing with this issue for years, some cars seem to be close and some seem to read high. The best thing to do is get a base line and then see what your gains are over stock.

This will not be exact as the turbo has to work harder to make the same power at elevation as it does at sea-level, so there is the potential to see less of a gain over stock when you are at elevation.

Get on a dynojet as most people dyno on this type of dyno and the weather station will change with the atmospheric conditions and keep your CF power the same from day to day.

The only way to know for sure is to take it down close to sea level and get a dyno there to compare to your CF numbers. I have actually seen numbers be higher at sea-level than the CF numbers at elevation. Losses in the 15% on a FI car are not uncommon from what my data shows and I have tons and tons of dynos and airmass readings. If you get a data logger, you can see what airmass you are flowing and I have seen a 70 grams per second increase from 6000' to sea-level.

Here is my stg 1 135 with just my own tune on it and then I compared it to the JB4 and got similar peak numbers, but my tune held a little better power from 5k to redline.

JZW

[foghat]

Good info. Thanks. CF = Correction Factor?

When you say stage 1, what does that mean? Tune only? And what do you mean by weather station? Is that some correction feature of the dyno?

[foghat]

Originally Posted by Alexim

Have you actually dyoned yet???
Try to dyno with both corrections and no corrections do we can see what the difference is...
I read on the n54tech forum, a post that Terry did, on how to dyno your car.. At the end he says, always choose STD correction, so I'm guessing most people dyno with that sort of correction...

Here's the link...

http://www.n54tech.com/forums/showthread.php?t=488

Thanks for the link.

No Dyno yet. Will be doing one for:
- stock
- Cobb ots for stock 93oct
- Cobb ots for fmic, dp, full exhaust, dci
- pro-tune for fmic, dp, full exhaust, dci