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Customer.  Wayne D.

Car.  2008 Colorado Crew Cab Z71 2wd, 3.7L auto.

Story.   Wayne brought his truck to us in the hopes that the poor shifting manners & lack of bottom end torque could be resolved.  His complaint was that the truck just simply didn’t have the torque to pull the truck at all when the torque convertor was locked at speeds below 80 km/hr.  He also didn’t care for the very sluggish shifting performance of the truck either.

Modifications.  Other than a K&N drop in replacement filter Wayne’s truck is as it left the factory.

Numbers.   After resolving the issues that Wayne brought the truck to us for, we spent some time spicing up its WOT performance too.   With the factory calibration, Virtual Dyno generated results of 199 whp & 193 ft/lbs.  Not bad for essentially being completely stock & running on 87 octane.  Final results after a few tweaks came in at 207 whp & 197 ft/lbs…again pretty decent result for a completely stock truck on 87 octane.

A comparison of stock versus tuned shows some pretty significant improvements at certain points.

Update September 3, 2012.

Wayne has reported that his average fuel economy has improved to 11.2 L/100.  Better  fuel economy is always a nice added bonus!

Update May 24, 2013

Last weekend Wayne brought his truck down to do a couple of dyno runs with the Z71.  Apparently in the Colorado community it is a common mod to remove the snorkel from the airbox where it passes into the fender.  The thought being that the opening is now much larger allowing for more airflow.  Both Wayne & ourselves like to see genuine data to support whether  a mod is beneficial or not, so we decided to test this one out.

When he arrived, we took the truck out & ran it with the snorkel in place as a baseline for that given day. As usual, the truck ran dead nuts consistent with what it ran when we tuned it last year.  We then returned & removed the snorkel & went out & ran the truck again….results below.   Red plot with the snorkel in place, blue plot with the snorkel removed.

Snorkel Mod Dyno Results

The truck lost torque across most of the rpm range, as much as 6 ft/lbs to the wheels at certain points!  It would seem that removing the snorkel likely killed some velocity in the intake tube costing power.  Needless to say, Wayne re-installed the snorkel after the second run & will not be removing it again!

Update Aug 24, 2014

Back in the spring of this year Wayne discovered that his Colorado had developed a cracked exhaust manifold…..apparently a pretty common problem with these trucks.  The decision was made to install a header on the truck rather than put another manifold on that would likely crack again eventually anyway.  After doing some reading he decided that a header from OTTP would be the one installed.

Wanting to be as accurate and objective as possible in terms of evaluating the header’s performance we took the truck out prior to removing the old manifold & did a baseline dyno run using Virtual Dyno.  The reason behind doing this rather than just using the dyno results from when we tuned his truck revolved around the newly installed tires on his truck.  The original General tires had been replaced with a much heavier Michelin LTX M/S 31X10.5R15 tire (absolutely fantastic tires by the way!).  The part where this gets intriguing is that adding weight to rotating assemblies like rims, tires, brake rotors etc impact a vehicle’s performance at about a ratio of 8 to 1….meaning adding 1 pound of mass to a tire for example is equivalent to adding 8 pounds to the vehicle weight.  If we start doing some math we see that Wayne’s new tires are 8 lbs heavier each tire…..8 lbs * 8 = 64.  64 * 4 tires = 256 lbs.  Adding 8 lbs to each should have an impact on the truck’s performance similar to adding 256 lbs to the vehicle!!!  Doing even more math we can calculate that 256 lbs represents 6.8% of the trucks 3747 curb weight.  Therefore, adding these tires should negatively impact the truck’s dyno numbers by 6.8% roughly.  If we look at the dyno results from when we tuned Wayne’s truck it made 207 whp & 199 ft/lbs.  Subtracting 6.8%, the truck should make roughly 193 whp & 183 ft/lbs with the new tires on.  Theory & math is all great, but at the end of it all, we wanted a genuine baseline to measure the header’s performance with.

Header Baseline

Turns out our math wasn’t very far off!  With the new tires installed the truck put down a baseline run of 187 whp & 183 ft/lbs.

The installation of the header was a pretty straightforward bolt on affair.  Fit was exceptional, a very good quality piece.

After the installation was complete, we went out to do a follow up dyno to evaluate the performance of the header without any adjustments to the tune at all.

Baseline vs Header Installed No Tuning

Those results look pretty dismal!  Gaining only 6whp above 5000 rpm???

What the graph doesn’t show is that there was such a dramatic increase in airflow that the pcm was referencing cells in the timing map that were stock, not the optimized timing we normally run on these trucks!!

After altering the timing map to rectify that problem the results became much more impressive.

Baseline vs Header Installed

Power output climbed to 212 whp & 200 ft/lbs after our tweaks, representing a gain of 25 whp & 17 ft/lbs from the baseline run!!!

It would seem the combination of this header with the appropriate tuning are a very potent combination!


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