Skip navigation

Customer:  Jody H

Car: 2006 Pontiac Grand Prix

Story:  The owner of this car was like most of our customers in that their goals in getting the car tuned were to fix the God awful shifting the car had, & hopefully pick up a little extra power at the same time.

So, first things first.  Here is what the car ran as the project commenced.

152 whp & 181 ft/lbs.  Assuming a 20% drivetrain loss that works out to be approx. 190 hp & 226 ft/lbs.  Pretty much exactly what GM rated the Series III 3800 at.

After reviewing the datalog from the above run, a considerable amount of knock retard was noted, so the car was filled with 91 octane fuel and run again.  Approx. 4 deg. of knock retard was eliminated with the 91 octane fuel, & the power output climbed accordingly to 160 whp & 184 ft/lbs.  An increase of 8 whp & 3 ft/lbs.  Crank numbers are now approx. 200 hp & 230 ft/lbs.

Next order of business will be a K&N drop in replacement filter.  I’ve always been curious as to whether the drop in filters really offered any performance benefits, so this is a perfect opportunity to find out!

The results of a brand new K&N drop in filter are in!

Reviewing the datalogs show that peak airflow increased from 21.14 lb/min to 21.62 lb/min showing a definite improvement in airflow.  Interestingly enough, a further reduction in knock retard of almost 2 deg. was also noted.  The net result is now 164 whp & 188 ft/lbs, an improvement of 4 whp & 4 ft/lbs.  Crank numbers now translate to 205 hp & 235 ft/lbs.  Also note that the hp curve doesn’t drop like a stone past 5400 rpm anymore.  Evidently the stock filter was a significant restriction beyond that rpm.

So we currently have picked up 12 whp & 7 ft/lbs with almost no modifications!

The next modification is going to be a little more involved.

This is a pcm from an ’05 Grand Prix from the local salvage yard.   The ’06 models have no options for tuning them, however the ’05 models do & the pcm’s are a direct replacement for the ’06 models.

So after enduring the hour long security relearn procedure required when replacing the pcm in these cars, tuning commenced!

Most notable improvement is that the car no longer feels like its lugging around in 1 gear too high all the time now (because it no longer is).  Changes to the shift strategy have made the car much more “lively” to drive than it used to be with nice quick shifts.  It is also much more responsive to downshifting, not requiring the driver to almost put the pedal to the mat to prompt a downshift anymore.  These improvements alone would make the tuning worthwhile!

As for the results in power production, a bit of a mixed bag there.

With the stock pcm in the car, the Virtual Dyno results were erratic at best due to inconsistent fueling & timing.  If all the stars aligned, the car would generate a decent pull (such as the graph above).  More often than not though it wouldn’t.  After being tuned, the car now generates very consistent results every time.

A few things to make note of.  The peak torque numbers didn’t change much from the “better” of the stock pcm runs.  However look at the improvement once past peak power.  Whereas the car would fall on its face past about 4700-4800 rpm with the stock pcm, the car continues to pull hard all the way to the shift point now.  At the shift point on the above graph there is a 21 whp difference between stock & tuned!  Needless to say the car feels significantly stronger now, and generates virtually identical results every time.

Unfortunately  that is all the power this car is going to make until the tiny stock 18 lb/hr injectors are upgraded….they are maxed out on a basically stock car.

The owner has started tracking the fuel economy of this car on & can be viewed here.

When viewing the fuel economy details, keep in mind that this car is driven almost exclusively in town….& the owner has no concern for fuel economy when she is driving it!

Update Apr. 25, 2014

So this winter here in the snow belt (with all the road salt that goes along with it) finally finished off the OE mufflers on Jody’s car.  After cutting off the rotted out OE mufflers we had a look inside & were a little surprised with what we found.  Looking at the exterior of the mufflers would lead you to believe that the factory exhaust system was a decently sized system with dual mufflers sized at 1 7/8″ inlets & 2 1/4 inch outlets……that would be be more than adequate for the power this basically stock 3800 V6 was making.  However looking into the mufflers once they were cut free revealed a bit of a surprise!


Those pipes that looked decently sized from the outside concealed 1.3″ tubes inside the mufflers (pictured above)!!!!  Doing the math, we find that those 1.3″ pipes give an area of  of 1.33 square inches each…2.66 square inches for the pair of mufflers.   That area is comparable to a single 1 7/8″ I.D. pipe.  That is a little on the small side!  Had we known we were going to find this, we would definitely have put our back pressure gauge in the car before cutting the mufflers off to see how bad this system really was!

Those mufflers are history now though, so onwards & upwards!  A pair of Dynomax Super Turbos have replaced the old mufflers that measure a true 2 1/4″ in & out vastly increasing the exhaust area.  Surprisingly enough, the new mufflers are as quiet as the originals, if not even quieter…an added bonus!  Time to see what the datalogs & Virtual Dyno reveal about the car’s performance.

Update Apr. 27, 2014

So today we got some time to take the car out to gather some data on how the car was liking the new mufflers & also to see what Virtual Dyno had to say about them too.

As for how the car is liking the mufflers, datalogs from when the car was tuned several years ago showed an area in the rpm range from about 3900-4400 rpm that had consistent knock retard in the 4-5 degree range that just would not go away without removing a TON of timing.  The very first run with the exhaust uncorked showed the knock retard to be gone for all intents & purposes.  Running knock free showed up in he Virtual Dyno results too.

Tuned vs Tuned with Dynomax Mufflers


Peak numbers improved nicely by 4 whp & 9 ft/lbs of torque…..the torque number is the real pleasure.  At 4300 rpm, there was as much as a 13 ft/lb increase in torque! Definitely worthwhile opening up the exhaust on this car.


Update Feb. 9/2015

Lately we’ve been evaluating some new software…..Track Addict.  We happened to have Jody’s Grand Prix available today, so we elected to go out & use Track Addict to time some 1/4 mile runs with the car.

As usual the car performed perfectly & turned in a 1/4 mile run of 14.92 seconds, 1/8 mile of 9.59 seconds!  Of course it was pretty cold today, so correcting that pass to a more normal temperature of 75 deg, alters the time to a 15.43 sec.  That represents a significant improvement from the 16+ seconds these cars run stock!




Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: