I decided to throw the car on a dyno yesterday since a friend was doing his car as well. My last dyno was about 8 months ago where I pulled 200-203whp. All of the sudden last night I did 3 runs and got 175whp

I've been trying to come up with a reason why. I've blamed the dyno, the operator, blamed my sc belt, and everything else i can think of. The car feels as fast as it ever has. While i admit that my butt dyno is not the most sensitive thing on earth, id like to think i would pick up on a 25-30whp loss...

I have ran on that same dyno several times throughout my modding process. I have always gotten good numbers....and the setup on it was supposed to be identical to my past runs. My friend went right after me, and his numbers were what he expected.

Since this was a spur of the moment run, I did have a full tank of gas with a pint of seafoam in it (to clean up the injectors etc). I am not sure if that stuff can mess with octane levels, or the ecu, etc. My SC belt is 8months old...i just looked at the tensioner, and there should be a hole showing on the tab...there is not, its completely hidden. However on my pulls i was putting down 16-17psi.?

I'm really baffled. I have an appointment next week to run on a different dyno to see if the numbers repeat themselves. At least i was only charged half price...since i got such poor and unexpected numbers....

any guesses or suggestions ??

 

If you dont have a hole showing I would replace the belt, even if you are getting boost, it is just proper maintainence at this point and eliminates a possible source of the problem.

 

It can be boost leaks...Or Belt..

 

But if he's pumping 16psi, there's no boost leak, lbh.
I'd blame the dyno. I was at a dyno in Dallas that was reading 25hp down on previous readings for similar cars, or so the story went.

 

I want to do the dyno first, and see if my results repeat themselves, but after looking at my tensioner, i dont want to risk it. i'll be putting a new belt on tomorrow.

 

Dynos can be heartbreakers.

This is exactly why I really don't care what numbers a car will put down on the dyno. Even just a minor calibration error with the dyno will totally mess up your numbers.

1/4 mile times, trap speeds, 60' times are much better ways to compare vehicles.

 

Have you been to the dealer within those 8 months? Maybe your car was reflashed and your tune is gone.

 

This says it all. If he was REALLY down 30hp, you'd darn well feel it. Even the WORST calibrated butt-dyno can tell when your car is down 30HP. I wouldn't look too hard for issues with the car, personally.... I'm betting the dyno is off...

 

Blame the dyno.

 

If his friend wasn't there then you couold say blame the dyno. but he did have someone else to compare to on the day.

 

Well maybe..........
Is this the first time for the friend on the dyno? Many first timers do not have a properly calibrated butt dyno and do not have an accurate expectation of what they should be getting.

So, if the friend had gone before, and the same day as the car in question. Then made some minor mod with a well documented hp delta, and then hit those numbers.............. OK, the dyno is exonerated.

Otherwise, the dyno is still in question and the likely culprit.

 

I went first. and my friend...first dyno ever, went right after me. He has a 2008 mazdaspeed 3. which, according to him and his forum, should get 236ish whp stock. he has a cai and put down 248whp. He was happy with his results.

I think i should blame the sea foam in the tank, my belt, and the dyno/operator lol. new belt is going on this evening. Appt. on a dynojet is scheduled for next week. I will update accordingly as I hopefully come up with answers.

 

Well then good luck with that appointment and hope you get things sorted out. From your description of the amount of hole showing on the tensioner, you definitely need a new belt. Go for the Napa 060535 if you have a 15% or smaller pulley and you will be assured of no slippage.

 

oppss I missed the 16 PSI

 

What about weather, humidity and barometric pressure (don't care what you've read, forced induction cars are affected). I don't know about where you live, but dyno numbers can vary greatly when comparing summer and winter running. 8 months ago here, it would have been 80s-90s and a million% humidity. But right now, it's cold and dry.

Furthermore, there could be a bunch of little changes here and there. Weather, dyno cal., sc belt, fuel in the tank, dirty air filter, dirty intake, old oil change, old plugs, old wire, old coil, more wear-n-tear on the motor. All those little changes will add up to a lot.....maybe a 30hp lower reading, and because they happen over time, you're desensitized to it. First off, I'd say get to stage zero. Make sure you're car is in tip top running order before you start dynoing the crap out of it. Be methodical or you'll be chasing your tail.

 

Could the first dyno # have been off (your 200+ run)? If it was high, and now something is reading a bit more correct, there could be your answer... Just thinking out loud.

 

GOOOOOD point.

Though he says he's dyno'd several times throughout the modding process... and has gotten consistently "believable" numbers...

 

Make sure you get the proper sized belt for your pulley! Otherwise you will be having the same problems down the road. Most will suggest the 539 NAPA belt for a 15% pulley.

It does sound like a dyno error.

 

I thought it was the 535 for a 15%?

Ooops,

 

Yeah, it's the 535. That's all I've ever read. There are charts on here somewhere. I'm running ther 535 FYI.

 

that's what I get for trying to help.........yes the 535 is the right belt for a 15%

 

the dyno is "supposed" to correct for all the humidity/temp changes....which i dislike. However every time I run on the dyno it has been cold. It was probably 30 degrees during last weeks runs. Oddly enough the time i did a 203whp run was in 95 degree heat with 90% humidity in mid summer down in North Carolina. The run in NC was for a RMW tune and the only time ive ran on a different dyno. Since that dyno/tune dyno about 8 months ago, I still think id notice a 30whp loss. and your right, i did error in just throwing the car on the dyno just all the sudden. Im sure my filter can use a cleaning and already discovered the belt needs replaced.

that wasnt my first dyno run. the 200+ run was what i did last summer. (my most recent pull until last weeks low one) I have ran the car on a dyno after each mod i did. I got an intake, then dyno'd. Got a pulley, then dyno'd. Each time the numbers seemed to be in line with the mods I was doing. Im back right now, below the dyno numbers I put down when i had just an intake and pulley. Which is unfortunate since i now have cat-back and an RMW tune.
If this recent dyno is the "more correct" reading.....well, id sure hate that. pulley, intake, cai, and rmw tune, and only come out with 170ish whp? ouch

fortunately, the dragstrip opens next month. thats where i can throw all these numbers and dynos out the window. If i can still beat or hang with my friends mazdaspeed 3, i'll be happy.