[timmy8784]

Hi all,

First off, I am not an expert when it comes to dynos and numbers, just understand the basics.

I completed a custom NPP exhaust on my SS recently eliminating the secondary cats and using magnaflow straight through mufflers.

Before the exhaust project, the shop threw the car on their dyno and it made 380rwhp. Now (2 months later) I brought it back to them for another run. Now I know different factors make a difference, but after 2 runs, it topped out at 302rwhp. Temperature difference then from now was 82 degrees then and 105 today. The shop is stating that the temperature change caused this drop but this seems quite ridiculous. What could be the cause of this massive drop? Can outside temp really affect that much?

Hoping someone with some more knowledge can chime in on this. Thanks!

[Blk16SS]

VERY possible too lose a few ponies do to heat soak but it sounds like something is wrong..

[RCF]

So, that would say take it back when it's like 40F and you'll see 500hp... total BS! From just the temperature change alone (assuming no other changes, and dyno runs done similarly), the HP difference would not even be 8hp, let alone 80hp!

Heat soak would be another matter, but 80hp is still absurd!

[STEVE41]

your car was heat soak, this is the same trick some shop will do to show a low # before any mods, after mods will show some crazy gain....lol you should be around 400rwhp WITHOUT heat soak.

[SomeGeoffGuy]

Did they give you corrected numbers? I thought they could punch something in that accounted for the temperature and barometric pressure. It might even say it on your graph. If both runs are corrected, then you have something wrong.

-Geoff

[timmy8784]

Originally Posted by SomeGeoffGuy

Did they give you corrected numbers? I thought they could punch something in that accounted for the temperature and barometric pressure. It might even say it on your graph. If both runs are corrected, then you have something wrong.

-Geoff

Nope, no corrected numbers.

They said we will have to try again when the weather conditions are similar to what they were the first time

[timmy8784]

So obviously there is an issue, would you lean on the side of the car or the shop doing the dyno incorrectly?

[nancygrl]

Yes temp, humidity, barometric pressure and altitude do effect the numbers, loosing 10 probably maybe a little bit more given the 23 degree increase in temp, but 80hp that seems like a lot.
Is your car is running the same as before? Runs smooth ?, getting similar gas mileage ?, oil life % ?, acceleration feel the same?, etc.??? Maybe there's an issue with their dyno and/or software ???
If it's possible maybe you can go to another place to get a 2nd opinion (and get corrected numbers). that may help narrow down if issue is with your car or their dyno.

[mjmenke]

Originally Posted by timmy8784

Nope, no corrected numbers.

Ask them to turn on SAE for both runs (or the older STP) correction factor and print them out. Both of these will correct for weather and give you a more consistent difference between each run.

(I've been able to do this with 3 different dyno shops)

[timmy8784]

Originally Posted by nancygrl

Yes temp, humidity, barometric pressure and altitude do effect the numbers, loosing 10 probably maybe a little bit more given the 23 degree increase in temp, but 80hp that seems like a lot.
Is your car is running the same as before? Runs smooth ?, getting similar gas mileage ?, oil life % ?, acceleration feel the same?, etc.??? Maybe there's an issue with their dyno and/or software ???
If it's possible maybe you can go to another place to get a 2nd opinion (and get corrected numbers). that may help narrow down if issue is with your car or their dyno.

It really doesn't feel any different to me (im hoping that I would've immediately noticed if it really lost 80hp)

It runs smooth, gas mileage is almost identical, oil change actually happened in between dynos, acceleration seems the same

[Spartan268]

Originally Posted by timmy8784

It really doesn't feel any different to me (im hoping that I would've immediately noticed if it really lost 80hp)

It runs smooth, gas mileage is almost identical, oil change actually happened in between dynos, acceleration seems the same

Something must have been off with the dyno then. Maybe it needed a re-calibration? Or someone fudged the settings up. Cause you would feel the 80rwhp difference in power when you stomp on it.

[nancygrl]

Originally Posted by timmy8784

It really doesn't feel any different to me (im hoping that I would've immediately noticed if it really lost 80hp)

It runs smooth, gas mileage is almost identical, oil change actually happened in between dynos, acceleration seems the same

Everything else being equal....Loosing 80hp, I know you'd be able to notice/feel that difference. That's like driving a 4cyl Accord vs 6cly Accord (90hp diff.) you could tell one is down in the power dept.

Even the difference between the different "correction factors" STD vs SAE-J607 vs SAE-J1349 wouldn't account for 80hp difference, 10-15 at best. I'd have to lean towards some setting or something not input correctly.

[timmy8784]

Originally Posted by nancygrl

Everything else being equal....Loosing 80hp, I know you'd be able to notice/feel that difference. That's like driving a 4cyl Accord vs 6cly Accord (90hp diff.) you could tell one is down in the power dept.

Even the difference between the different "correction factors" STD vs SAE-J607 vs SAE-J1349 wouldn't account for 80hp difference, 10-15 at best. I'd have to lean towards some setting or something not input correctly.

This is what im thinking. I find no way that the computer would do any sort of fuel adjustment due to a cat back exhaust install (someone else I talked to mentioned something like this)

[MAGAUSA]

Instead of focusing on dyno numbers, have you noticed an 80+ hp loss? You would.