I'm sure your car is running just fine as long as the A/F is within nominal.

I've seen a lot of stock revups tested on the same dyno machine. (IE Dynapack at Church auto) and they are all within +/- 2HP. Assuming the ECU isn't in lazy mode, the repeatability is so good from engine to engine I seriously doubt there is any kind of weak engine issue.

$10 says your ECU was in lazy mode or it was simply the dyno you ran it on.

You could probably go back to that same machine tomorrow and see another 10+HP. It just happens from time to time.

 

Lazy mode... I have a hard time telling if it does that. I noticed on the dyno as the car kept gaining hp every run. Typically I'm used to seeing the 2nd run be the best, and the last just a little bit weaker.

 

ECU resets can sometimes help kick it back into performance mode.

 

I never have done the ecu reset during any of my mods. I always disconnect the battery and then reconnect it when im done. Does this work the same way or do I have to do that whole long list of things ha? Thanks.

 

Resetting the ECU using the pedals doesn't take as long since you have to disconnect the battery for like 10 hours for it to clear everything. They say you can pump the brakes to kill it also but I've never tried. I started using the proper method because I find that draining power to reset the ECU caused my car not to idle on a warm start. It took like a week to relearn how to idle.

 

Switching to 3.9 FD will not add HP. It will make your car faster but it won't show on a dyno. Correct me if I'm wrong peeps.

 

I can never seem to do the damn pedal trick to reset the ECU...

 

+1. Doesn't do a thing for power gain, just delivery. Effectivey, you're shortening your gears and rowing quicker. That's it... If you're planning on staying NA then go for it, otherwise it's kind of a waste.

 

Ive never seen proof of a 3.9 FD adding hp on an NA dyno, but a very respected member on these forums saw the opposite effects when going from a 3.5 FD to a 3.3 FD. He went from putting down 573whp to 54X whp, which is explained by the FD. Take it for what it's worth....

 

I didnt see any increase going from a 3.3 to a 3.5 on the dyno . It felt much quicker though

 

Oh I know the 3.9 isnt going to add any power wise, Im getting it because its going to accel quicker through the gears. All in all It seems like 300whp is going to be a waste of a goal to get to N/A. Pricing is going to be too much for what I have in mind. Question though, If I do the 3.9 final drive, will that have negative affect on a vortech s/c like it would on a turbo car?

 

Final Drive on the dyno WILL read the same. This is because the dyno operator will input the new final drive and after that it will adjust for the HP. So if you gain or loose hp on the dyno with the FD something else changed.

 

Not true-not all dynos have the option of inputting the FD/weight/tire size, etc...perfect example is the Dynojet, you starp it on, get an rpm signal and doa pull, only thing that can be changed is the correction factor.

 

My bad, I thought they all did.

 

That seems low, I dyno'd 248/221 with just a pop charger on a mustang dyno

 

I dynoed 260 whp and 234 wtq on K&N's Dynojet with just testpipes and popcharger.