2007 G35 Intake Project

Finished up my air intake setup on my G35 this afternoon after replacing the a/c compressor this morning. A/C clutch coil failed on it after 215K.

I was already running the HPS silicone intake hoses. I ordered a cheap intake setup from Amazon about a year ago but did not like the aluminum tubing and the way they heat soaked. They had terrible transitions and necked down the MAF sensor openings to about 2.25" which is smaller than the factory MAF housing. Car ran well but ran rich on the stock tune. I had pulled them off and put the stock air boxes on with K&Ns. I finally got the itch to let the VQ V6 have that awesome intake howl they have. I ordered a pair of 2.75" MAF housings about 3 months ago that were finally delivered this morning. I used the heat shields and filters from the cheap intake kit. I fitted it all up. Have a little tuning to do on the MAF tables but it runs very well. Fuel trims are running about +10 to +14 at the moment. Have not been WOT but the car accelerates much more smoothly now. I love the way this little high reving 6 sounds. It has equal length headers, high flow cats, 2.5" custom built exhaust with a X-pipe and 4 magnaflow mufflers into 4" tips. Quiet when you are cruising along but really opens up when you get into the throttle. Cruising around town checking out the a/c repair this evening it was knocking on 20 mpg. I even ran it up to 5,000 rpm a couple of times in 1st and 2nd gear at about 1/2 throttle leaving a couple of traffic lights. Not bad for a ~380 hp V6 with a 5spd auto and 3.91 gears in a heavy 4 door sedan.

A/C repair was a complete success. With an Oreilly's Murray reman compressor and charged with R152a it is cooling down to 34°F with the a/c fan on high speed and the climate control temp set to 60°F. It will freeze you out of the car after 5-10 minutes. Compressor is running quietly too. Much quieter than the 215K mile one even though it too was still blowing ice cold up until the clutch coil failed. Thats with a 25% underdrive crank pulley as well.

This was the air intake tube setup the way they shipped. It was a $124 system. Great buy for the heat shields and filters. The piping bumped to 3" after the 2.25" MAF section and those flimsy thin silicone couplers reduced it back to 2.70" at the throttle body. The HPS hoses are 2.70" ID and the new maf housings are 2.75" OD. They fit perfectly and the air flows smoothly through the system now. The MAF reading has never been very smooth at idle on this car. I am thinking of ordering a pair of 6:1 MAF screens for it to see if it will run more smoothly with them in place.

Amazon kit installed on a G37. I like my install with the heat resistant silicone intake hoses better. Much less flashy under the hood and much less heat soak. Intake air temps stayed under 110°F rolling around town this afternoon. With ceramic coated headers and around town driving those metal tubes would nearly scald your hand after 30 minutes of driving around town.

This is the exhaust setup I am running. 2.5" dual on a 3.5L engine because it spins 7,800 rpm on the big end and likes to breathe. Car was instantly far more responsive after the exhaust and high flow cats went on. OEM cats may have been partially plugged after ~200K as the catalyst beds were rattling around in the housings.

And the equal length, merge collector shorty headers. These alone after the exhaust setup added 20 ft/lbs in places of the powerband in the low-midrange. Did not gain alot of peak power (9 hp wheel), but I am not spinning the thing 7,000+ all the time. These gained torque across the whole powerband from 2,000 rpm and on compared to stock. Give me the torque gains any day. Compared to the stock un-equal length tubular manifolds these make the engine sound much smoother to my ears. These were another amazon buy, open box special for $200 to my door and a reputable brand.

Car made 296 RWHP and 270 RWTQ untuned with the HPS Intake hoses, K&N filters, headers and 2.5" exhaust. Air/Fuel ratio in the low to mid 12s. Gains of 26 HP and 28TQ. There were a few areas it made as much as 40 ft/lbs more in the midrange.

These are the stock manifolds. I think the longer equal length primary tubes and the nicely designed merge collector are responsible for the torque gains. A couple of small changes that make a huge difference. At first glance they look alot alike. Not until you put a tape measure up to the primary and realize it is 50% longer than stock and the stock ones have up to 2" of variation in length between shortest and longest although the short one and long one are on opposite banks.

Where the real power came from in this little V6 after adding headers and high flow exhaust. I modeled the engine with Engine Analyzer and spent about 4 hours modeling various intake and exhaust cam position changes for best WOT power. Then used some cam knowledge and a little experimentation to figure out what the car liked best at light and mid throttle. Woke it up at every throttle position and fixed an annoying part throttle rough running condition this car has always had around 35-50 mph in Overdrive. Car would shudder noticeably in that speed range while driving uphill. The OEM programming had a massive amount of overlap programmed into it at light throttle and that RPM. Lots of internal EGR going on with the stock tune, not nearly as much now. I did keep a substantial amount of exhaust cam retard where the car cruises at 60-70 mph at light load. Fuel economy was better with more overlap there and since it is turning 2,500-3,000 rpm at that point it runs smoothly. However go uphill and I am quick to lose that exhaust cam retard for more torque. I can pull a long 7% grade without it downshifting to 4th now.

Intake cams can be advanced as much as 45°. Exhaust cams retarded as much as 30°. It was very apparant that the Nissan engineers hit their power goal with this engine and could have gone alot higher once I dug into the cam phasing tables. Engine modeling had a simple result. More engine speed = more exhaust cam retard for peak power. I am running as much as 15° more exhaust retard in the 7,000 rpm range and the engine LOVES it. 15° extra cam retard models out to be a 40 hp jump over stock cam position. Difference between making 340 hp and making 380 hp! I also modeled flow numbers of a ported set of heads, ITBs and long tube headers with open exhaust. It was showing the stock cams capable of 430 HP @ 8,500 rpm!

Prior to any changes this car put down about 270 hp and 242 tq at 165K miles. Before the air intake changes, with the HPS hoses & K&N filters in the stock air boxes it made 326 hp and 282 tq at 210K miles. May not seem impressive but thats a gain of 56 hp and 40 tq at the wheels through an automatic trans on a little 3.5L engine that has not been opened up beyond the plenum and valve cover gaskets and that was only for spark plugs and replacing leaking valve cover gaskets. There were places in the powerband the car is up 60 ft/lbs of torque compared to stock. I put the 25% underdrive on after the last round of pulls. Those have had a very repeatable 5 hp and 5-7 tq on other 3.5HR and 3.7VHR engines.

I always thought it was a shame that R134a was chosen over R152. Where'd you get it?

Quote:

---

Originally Posted by sherlock9c1

I always thought it was a shame that R134a was chosen over R152. Where'd you get it?

---

Same place I have for years. Duster air cans.

So my next mod is going to have to be a set of 3.7VHR injectors I have laying around. They are about 60cc higher flowing. After I added to the MAF table some this morning the car is hitting 101% duty cycle above 6,500 rpm. WOT afr is 13.2 to 13.4 which is exactly target. Thow in a cold, dense day and it will run out of fuel at WOT. The 3.7VHR injectors have proven adequate for 340-350 wheel HP in a 3.7.

I know someday I will have to do the timing chains, guides and water pump in this car. Considering having some head work done and installing a stiffer set of valve springs. Porting the lower manifold and upper plenum. At the same time may also do the upgraded oil pump gears in a new pump housing. Can crank it up to about 8,200 rpm without hurting the lower end. I think it could hit 350-360 wheel with that. Then again I have seen pistons that I can put in the block with a 3.7 crank and rods. 12:1 3.7 would run very nicely. I think this car could run bottom 12s or even high 11s with a 370-380 wheel HP 3.7.

Finally got around to doing the valve cover gaskets this evening. Also changed the ignition coil boots and swapped in the 3.7 injectors. Need to adjust the injector K constant a little because its running a little rich but it runs so smoothly. Engine is spotless internally after running synthetic oil the past 70K miles or so. Between reducing the overlap in the cams at cruising speeds and running a bottle of Techron last tank the intake valves and ports are spotless. They are cleaner now than when I did the plugs at 178K. The fuel trims went about rich by about 8%. The MPG was displaying 30.2 mpg on a little 30 mile trip I took that was a mix of 65-75 mph highway and some residential streets at 30 mph with a couple of redlights mixed in. With that 8% higher flow rate its was running about 27.5 mpg. I got on it from about 60 to 85 mph and it downshifted to 3rd, wrapped the tach up to about 6,000 rpm and flew to 7,500. Car literally jumped forward and took off.