Yesterday we installed a set of Stillen high-flow catalytic converters (HFCs) onto the 350z that received the Injen Intake system and the Unorthodox Racing lightweight pulley last week.  We’ve seen how these HFCs have improved the power band in the past on other cars but it’s always nice to back up good results.  Again, this car is equipped with a Nismo exhaust system, unlike the other car with these mods which has a Bassani exhaust.

The Stillen high flow cats are a high quality piece but as with all exhaust modifications where the stock catalytic converters are removed we were interested to see if there would be any increase in exhaust rasp.  As you remember this was a small issue that we had to resolve on the red HR car that had the Bassani true dual system with an x-pipe.  The Nismo system is much different, it comes from the cats into a 2.5″ to 3″ Y-pipe (stock is 2″ to 2.5″.)  From there is a single 3″ pipe, with resonator, back to a factory style (but larger diameter) rear muffler.

This car with the HFCs installed exhibited almost none of the rasp that has become associated with the dual exhaust cars.  While the exhaust note was very nice, you can see from the dyno graphs that this car was a few horsepower short of the Bassani 350z.  The cars were dyno’d on different days but all the results are SAE corrected to get them on as even a playing field as possible.  In their uncorrected forms, both of these cars are putting down over 300hp to the wheels. Very impressive.

Below you can see the run comparison with and without the HFCs.  The Stillen cats gain around 10hp and 10lb/ft of torque at the wheels throughout the rev range.  That’s certainly power you will feel on the road which makes this change almost mandatory from a performance aspect.

Here are the graphs that show this customer’s entire power gains over the past week or so and the comparison between the this car and the earlier Bassani equipped car.

We are trying to get the ball rolling with a header and camshaft comparison for the HR engines and maybe an turbo install in the near future to show all of you what is really possible with all available modifications.  We can’t wait to make more “RELIABLE” power from the HR series.

Link:  Other HR related posts

The VQ35HR engine in the ’07-’08 350z just continues to impress us here at Z Car Garage.  This last generation of the VQ35 responds so well to bolt on modifications that the sky is the limit when it comes to producing normally aspirated horsepower.  Yesterday we bolted on another Injen intake system and an Unorthodox Racing pulley to accompany the Nismo exhaust that was already installed on this customer’s car.

The Injen intake now grabs air from in front of the radiator almost directly in the high pressure air stream.  The quality and appearance of the intake is top notch and fit and finish is up to the standards of a company that has been around as long as Injen.  The pulley from Unorthodox Racing is a high quality piece machined out of aluminum and is supposed to weigh around seven pounds less than the stock piece (8.25 vs 1.32lbs.)  We actually weighed both pieces and found the stock pulley on this HR to weigh only 4.8lbs, go figure.  Maybe they had two on the scale?  Anyways, the pulley is the stock diameter so all benefits come from reduced rotational mass rather than an under-drive system.

They dyno results were right were we expected them to be, but that doesn’t make them any less amazing!  While the main horsepower gain comes on the top-end, there are notable gains throughout the mid-rage on the torque side of the equation.  From looking at the graph you will also notice that the modifications cause the torque curve to not drop off as quickly past 5,500 rpm.  The car now makes twelve more foot-pounds of tourqe at peak horsepower, you will certainly feel that in your butt dyno!

Since the two modifications were carried out at the same time I can’t say for sure how much of a difference the crank pulley alone made, but if you look back at the first Injen intake we did on an HR you will see what the intakes did by themselves on that car.  I know, different day, different car,  but can be used as some sort of a comparison.

We are patiently waiting to see more aftermarket suppoort for the HR engines to see what sort of power we can extract.  I want to see cams, intakes, new headers, and more ideas that I’m going to save for our shop to make.  Hopefully more is on the horizon.

Baseline dyno and stock pictures:

We are all aware that the HR version is at the top of the hill as far as the 3.5L engines go.  But now we have some hardcore proof of how strong this engine is with just a few bolt-ons.  This car belongs to a good friend and customer of ours and it is now starting to put down some serious power.

Earlier this year Z Car Garage installed a Bassani cat-back exhaust system with cross-over pipe.  The baseline dyno for the new mods (high flow cats and intake) was done with the exhaust system installed.  The Bassani exhaust post on My350z.com can be found HERE.

The Stillen high-flow catalytic were first on the list to be installed after today’s baseline dyno.  They installed in about a half hour with no real complications.  Then our Innovate wide band O2 sensor was then installed to monitor the air/fuel ratio.  Off to the dyno!  The gains we saw were a pleasant surprise and we are very happy with the overall result.  This mod also brought out some more roar in the Bassani system.  It sounds mean…

Next on the list for this morning was the new Injen Intake System for the VQ35HR engines.  This new system uses twin POP style filters and drastically moves the location of the filters all the way down and into the front radiator opening in the front bumper.  This move ensures that tons of fresh, high pressure, air will be crammed into the filters.

As you can see form the graph above we also picked up some massive whp gains from the intake as well!  In uncorrected form this car put down over 300hp to the rear tires, WITH ONLY A FEW BOLT ONS!!  All of the dyno graphs listed here are SAE corrected to even things out.

This post should brighten the days of more than a few HR owners who cringed when they heard of the imminent release of the new 3.7L engine.  Only time will tell how much more normally aspirated horsepower we will make with this engine but you better believe that we have more HR parts on order as I write this.  Can you say experimental ECU tuning?  Ummm… I love the smell of power in the morning.

All three runs below: (click for larger)

More Photos After the Read More

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