New Air Cleaner Housing

[L31MaxExpress]

Well I can say without 100% a doubt the Spectre 4" MAF housing is garbage. The metal tube is not a problem, the cheesy thin plastic adapter warps, the metal screw inserts that hold the MAF fail and the setup becomes an unfiltered, metered air leak. I started noticing my fuel trims spiking up and found the MAF barely hanging in place. I will try to remember to get a picture of how it failed, but just a warning to guys considering using it in their builds.

I was going to order an inexpensive universal aluminum 4" LS cartridge MAF housing (I saw numerous examples under $50 just a couple of months ago) but they seemed to have dried up availability wise, perhaps due to the EPA. I refuse to pay $300 for something like the Lingenfelter or Haltech MAF setups merely because those companies want to gouge Corvette owners. I did some digging around and GM offers the newer Express 6.6L L8T air box for the newer vans brand new with a new filter included for $83. Luckily it comes with the mounting provision for a cartridge style MAF sensor. Pretty nice looking factory air box compared to what GM put on the older vans and for good reason, the L8T is a 401 net hp engine even in the vans. GM did a better job on the L8T vans to ensure the full power of the engine was not reduced unlike the 5.7L and 6.0L vans that were choked by the factory air inlet and MAF. I snagged a couple of pictures of a used but identical airbox being offered on Ebay for more than 2x the money of the new GM part. The pricing for the GM airbox honestly surprises me but I am not complaining at all. It will be here in a few days, I will figure out the mounting(looks like GM kept the same mounting points as any 01+ van), then get the ducting squared away and likely have to work on the MAF table a bit. I do like that it will keep somewhat of a factory appearence underhood.

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[Supercharged111]

What have your observations been in terms of restriction with the stock MAF housing?

 

[L31MaxExpress]

What have your observations been in terms of restriction with the stock MAF housing?

It was 5 KPA increase at the factory shift points with the stock 350 going from the stock MAF to a Granatelli MAF years ago. That was with the TB lip already deleted, all the stock ducting and a K&N in the factory 97 air box. I later duplicated the Granatelli MAF with the stock MAF and ended up modifying about 10 of them for different vehicles. The same MAF was used on the F/Y car LT1, the early LS1s as well as the early Vortec V8s. The TB lip delete, Granatelli/Ported MAF and K&N made the WOT MAP increase from 89 KPA to 97 KPA with the stock 350 at stock shift points. The MAF change kept the fueling right at lower rpm and leaned it out ~5% at WOT which at the time on stock tuning with the stock MAF it was running around 11.5:1 at the tailpipe. The MAF reading went from about 240 gms/sec with the stock MAF to 218 gms/sec with the modified MAFs.

I already had the 4" MAF and ducting on the 350 prior to swapping in the 383. I now see nearly a 10 KPA drop at WOT due to the extra restrictive vortec van air hat. The manifold starts building noticeable vacuum around 2K rpm and just keeps building the higher it spins. I feel the Indmar manifold and 90mm TB swap that is coming soon will fix that.

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[L31MaxExpress]

So the math I spit balled when I said 5% change was a bit off. I just used a percentage difference calculator. The airflow was a 9.6% lower reading and leaning out from 11.5 to 12.5 was an 8.3% leaner mixture at WOT. It was probably a little richer than those numbers though as I did not have a wideband on it back then and those numbers were from a tailpipe sniff on the dyno. MAF change was an 8 hp gain peak to peak and more like 15 hp at fuel kill from the combined effects of airflow and leaning out. I have always made 2nd gear pulls to fuel kill to keep the driveshaft in this pig.

Later when I tuned the van, I leaned out the PE multiplier and corrected the MAF transfer curve.

 

[L31MaxExpress]

Well scratch the airbox change. The one I ordered arrived damaged. It was still in decent enough shape to mock up. It is too tall to allow the hood to close and the air outlet duct is jammed against the firewall. I still needed a solution for the MAF. The 4" LS7 MAF loses a lot of resolution compared to one that is slighy smaller. Jabbing a LS7 MAF into a 3.5" tube would work, but I would be spitballing a MAF curve by graphing HZ vs Dynamic airflow off my dialed in VE tables which is totally doable, but I wanted an easier way out. Looking at the various MAFs in place on both the GenIII and GenIV, I picked one for a 2007-2009 truck, G8, SS or Caprice. The MAF physically reads to 15,000 hz but the GenIII platform tables stop at 12,000 hz. The MAF I picked hits 512 gms/sec at 11,800 hz. The MAF curve is much more linear than even the GenIII truck stock MAF. I feel it will be a good match with the HZ vs Flow limits in the GenIII computers. That MAF is only slightly smaller than a 4" MAF as well and uses the same connector as the LS7 although I will need to swap the power and ground wires in the connector.

 

[L31MaxExpress]

The MAF I picked has a nice flow straightening vane and lamnier flow screen that should make for a nice, stable, clean signal. In addition to being able to read from as low as 1 gm/sec to as much as 512 gms/sec while using almost the entire frequency range of the GenIII PCM. One could almost not ask for a better, more accurate reading MAF for the application. Another nice part about that MAF is it looks factory. Another benifit for this MAF, is when I swap to the E67, I can plug the stock MAF curve right in.

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[L31MaxExpress]

Gen IV style G8/SS and 07-09 truck MAF is on and I programmed the PCM with a G8 MAF curve. Fueling is extremely close now and the slight tip-in hesitation I have had for a long time is gone. The MAF signal is extremely clean with this MAF. I need to add about 3-4% to the area around idle but above idle it is showing fuel trims between -1 and +1 across the board. Does not get any closer than that.

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[L31MaxExpress]

I drove it a bit and it is pretty close just driving around. That being said WOT is a bit off. I made a quick WOT pull from a slow speed to ~80 mph. At WOT the MAF is under-reporting airflow a bit and somehow the 383 ran 37° (OOPS!!!) of WOT timing advance and 13.25:1 AFR (commanded 12.0:1) without knocking on 93 pump gas (luckily it is cool and humid here today). I will be adding a bit to the MAF curve where it starts leaning out. In the logs the short term fuel trims jumped up to +15 right before I gave it enough pedal to go into PE, so I know where it starts to go lean and I will bump the whole curve up from there.

 

[L31MaxExpress]

The adjustment I made to my hood latch and rubber bump stops for the hood seems to have helped my IATs considerably as well and the slight misalignment of hood and fenders is barely noticeable. The gap between the hood and grille help get cooler air to the airbox. The IATs drop to near ambient very quickly after I start to move now and they are basically ambient cruising 30+ mph. Such a small, quick tweek that seems to have a great benifit. I may yank the hood seal and see if that helps as well.

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[Moofus02]

The adjustment I made to my hood latch and rubber bump stops for the hood seems to have helped my IATs considerably as well and the slight misalignment of hood and fenders is barely noticeable. The gap between the hood and grille help get cooler air to the airbox. The IATs drop to near ambient very quickly after I start to move now and they are basically ambient cruising 30+ mph. Such a small, quick tweek that seems to have a great benifit. I may yank the hood seal and see if that helps as well.

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I love those vans. Expedited with a 98 1 ton 5.7 4l80 bare bones work van no air no cruise no tilt. Had 420k miles when I quite using it. They pull a trailer nice and ride great