Installing an air straightener

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hackish
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Installing an air straightener

Post by hackish » Wed Jan 16, 2013 10:15 pm

Given the tight engine compartment in the Lotus proper location and orientation of the MAF sensor is a definite challenge. Abrupt turns before or after the MAF sensor can cause inconsistent readings as the airflow of the engine changes during varying load and RPM. The more power the engine makes, the more airflow and more chance that turbulence around the MAF sensor will cause it to mis-register.

Turbo kits are a prime example where at a fixed RPM you can have a significant range of airflows. Since the factory computer uses the airflow (and temperature) measured at the MAF sensor to calculate the required fuel, accurate measurements are absolutely essential. If the intake piping is not properly designed you will find significant hesitations and lean spots and despite making adjustments in the VE map it is impossible to achieve a consistent mixture. In the case of a popular turbo kit these areas of turbulence are also accompanied by an audible noise at the air filter.

From a design point of view, the Lotus MAF housing is slightly under 3" in diameter and a straight piece of pipe 5-6x the diameter is required to achieve an accurate measurement. A review of the engine bay will quickly reveal that there simply isn't enough space! Enter the air straightener. This is generally a honeycomb structure that forces the air into a consistent and even flow. Air straighteners are found in many OE applications to ensure accurate MAF readings.

Although the same procedure has been used a number of times on the Force Fed turbo kit, this example involves the piping for an aftermarket supercharger kit. The kit consisted of a very short run to the throttle body which was followed by a supercharger and air to water charge cooler. Turbulence from the throttle body caused poor idle quality and very inconsistent fuelling during cruise and part throttle operation. Fortunately, the straightener from a GM MAF was available and a good kit. GM produced the same unit for millions of vehicles and a quick trip to any local scrapyard will reveal a number of serviceable units from the mid 1990's on.
maf2.jpg
maf2.jpg (391.62 KiB) Viewed 8619 times
As you can see above the air straightener was removed from the GM MAF housing. This required cutting the factory aluminum housing away to leave the straightener element. The element itself is rather delicate so you do need to exercise some care in cutting away the housing. We cut it in 6 pieces so the aluminum MAF housing was easy to remove and the glue used to anchor the air straightener fell away with ease.
maf3.jpg
maf3.jpg (319.36 KiB) Viewed 8619 times
The outside diameter of the supercharger kit's MAF housing was 3" as was the air straightener element. Since the housing was made of a very soft aluminum alloy (meant for mandrel bending) it was relatively easy to use an exhaust pipe bender to flare the inlet large enough to accept the air straightener element. The cone air filter was flexible enough to fit on the enlarged part and the taper guaranteed that the air straightener would never be able to travel down the pipe toward the supercharger.
maf1.jpg
maf1.jpg (191.13 KiB) Viewed 8619 times
The modification cost $30 using spare parts and took well under an hour from start to finish. Since the MAF housing was the same length and the cone air filter re-used it still fit as designed but the running problems were almost entirely gone!

hackish
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Posts: 588
Joined: Wed Jan 05, 2011 1:49 pm

Re: Installing an air straightener

Post by hackish » Wed Jan 16, 2013 10:24 pm

What models did the MAF come on... Here is a probably incomplete list of vehicles you could check:
Buick:
Century 3.1L
1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Rendezvous 3.4L
2002, 2003, 2004, 2005
Roadmaster 5.7L
1996, 1997, 1998
Skylark 3.1L
1996, 1997, 1998
Chev:
Astro 4.3L
1996, 1997, 1998, 1999, 2000, 2001
Beretta 3.1L
1996
Caprice
1994, 1995, 1996
Express Van 4.3L, 5.0L, 5.7L
1997, 1998, 1999, 2000
Impala
1994, 1995, 1996
Lumina (sedan) 3.1L
1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
Lumina APV 3.4L
1996
Malibu 3.1L
1997, 1998, 1999, 2000, 2001, 2002, 2003
Monte Carlo 3.4L
1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Silverado C1500, C2500, C3500
1997, 1998, 1999, 2000
S10 Blazer 4.3L
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
S10 Pick Up 4.3L
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Tahoe 5.7L
1996, 1997, 1998, 1999, 2000
Venture 3.4L
1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Envoy 4.3L
1998, 1999, 2000
Sierra K1500, K2500, K3500
1997, 1998, 1999, 2000
S15 Jimmy
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
S15 Sonoma
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
Safari 4.3L
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Savana Van 4.3L, 5.0L, 5.7L
1996, 1997, 1998, 1999, 2000
Yukon 5.7L
1996, 1997, 1998, 1999, 2000
Pontiac:
Aztek 3.4L
2001, 2002, 2003, 2004, 2005
Grand Am 3.1L, 3.4L
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Grand Prix 3.1L, 3.4L
1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
Montana 3.4L
1999, 2000, 2001, 2002, 2003, 2004
Trans Sport 3.4L
1996, 1997, 1998
Oldsmobile:
Achieva 3.1L
1996, 1997, 1998
Alero 3.4L
2001, 2002
Bravada 4.3L
1996, 1997, 1998, 1999, 2000, 2001
Cutlass Supreme 3.1L
1994, 1995, 1996, 1997, 1998, 1999
Intrigue 3.5L
1999, 2000, 2001, 2002
Silhoutte
1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004

Depending on the scrapyard you may even be able to unscrew the air straightener section and pop it for to purchase the unit for even less money.

-Michael

hackish
Site Admin
Posts: 588
Joined: Wed Jan 05, 2011 1:49 pm

Re: Installing an air straightener

Post by hackish » Wed Jan 16, 2013 10:30 pm

maf4.jpg
maf4.jpg (188.37 KiB) Viewed 8617 times
It is important to make sure the unit you get is as pictured on the left, not a cheap aftermarket unit pictured on the right (it has only a screen, not a honeycomb air straightener element.

-Michael

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