dyno conundrum

[hoveringuy]

So I've been going to the dyno fairly regularly to keep tabs on the changes I've been making to the motor. The last pulls in May were very encouraging as I was approaching 220 hp.

I went back this weekend after some changes and was DOWN at least 25hp across the board!

Changes:

(1) Swapped Hall crank sensor and the conditioning board for a native VR sensor

(2) Replaced dead-head fuel rail with a flow-through rail

(3) replaced M50 throttle body with a 20% larger one.

(4) replaced OBD2 cats and muffler with 2 1/2" exhaust, Borla center and Dynomax muffler.

Here's the wildcard. The dyno was "upgraded" from a 2 wheel drive Dynojet to a all wheel drive Dynojet. The operator swore that it measured the same as the old one and showed a before-and-after with the same car and identical looking plots.

So, am I really down on power or is the dyno the problem?

Car feels fine. A/F ratios are fine.

[Mike The Bavarian]

was the dyno calibrated correctly?

[hoveringuy]

was the dyno calibrated correctly?

According to the owner it was.

[Mike The Bavarian]

weird. maybe try going to a different dynojet?

[LivingLegend06]

was there a large difference in atmospheric conditions?

[gregslow318i]

how does the ass dyno compare?

[hoveringuy]

how does the ass dyno compare?

My ass dyno is large and flabby. The Dynojet was cold and very firm.

Car seems to drive fine, I'd love to be able to do a 1/4 et.

Matt at TRM believes that the chart is too perfectly symetrical for it to be a mechanical issue.

The whole thing really pisses me off..

[u3b3rg33k]

Go back to your prior setup, dyno on new dyno. then dyno again after switching mods back. Eliminates the dyno as a variable.

[e46s54dr]

I'm no dyno expert but I'm sure my butt dyno will definitely feel a 25 horsepower deficit. You should know your car better than anyone? Does it feel like it's not performing as it should be?

[LowR3V'in]

Over time losing 25hp might not be real noticeable but
-/+25hp is night and day. :0

[hoveringuy]

I'm no dyno expert but I'm sure my butt dyno will definitely feel a 25 horsepower deficit. You should know your car better than anyone? Does it feel like it's not performing as it should be?

The car feels fine. I wouldn't have guessed that it's down 25hp, but on the other hand I always have trusted the dyno

Plan is that I will verify each element individually. Fuel pressure. crank signal waveform and timing. Then I will take it to a shop that has the two wheel drive version of the Dynojet.

I will also mail the files to Dynojet for their opinion.

[hoveringuy]

Would this make a difference (different gears!)?

[justin_l_]

Different gears as in different gears for the pull?
I have seen that cause different results first hand.

[Mike The Bavarian]

that would make sense...if you dynod and only ran it in say 3rd gear and your max power was around 220ish then say if you dynoed in 2nd or 4th it'll be pretty damn different

[e46s54dr]

I've also heard that using different gears and rpms on the dyno will give a slightly different read. Dynos are like science experiments, it's best to keep the control variables controlled or close as possible to get the most accurate reading.