58mm throttlebody good for a bolt-on car?
01-15-2007, 11:03 PM
#24
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,696
All I know is that every tuner I've ever talked to said that removing the MAF screen was a good thing for the LT1s, but not for the LS1s. I read the article that GM high tech put out, and I believe it was called "putting your LT1 deep into the 13s with basic bolt-ons". I did everything that they recommended, including removing the screen and my car ran 13.49@106 in the 1/4 mile. I think the LS1 intake, different type of throttle body, and/or the size of the MAF sensor has something to do with not removing the screen on the LS1.
Interestingly, the C5 LS6 gained 5HP when GM removed the stock "screen" from the MAF in 2001 or 2002 (??). They felt that the symetrical inlet ducting of the LS6 was sufficient to provide uniform cross-sectional velocity, without the screen.
So much for that theory
Yes, the LT1's run "rich" from the factory, because GM programmed them for a target A/F ratio in Power Enrichment (PE) mode of about 11.7:1, which does not provide peak HP or torque, because its too rich. Removing the screen MAY lean out the high RPM A/F ratio, because it destroys the calibration of the sensing element, and causes the sensor to UNDER-report the air flow, which of course leans it out in PE mode because there is no O2 sensor feedback.
But statistically, about 1/3 of the people who pulled the screen saw truely amazing, SOTP HP gains (seldom confirmed by real data
), 1/3 felt nothing, and 1/3 found they had irregular idle, and in some cases reduced fuel mileage. Hence, rather than remove the screen, and take a 1:3 shot that you will get lucky and lean things out with a ghetto hack, you simply have your tuner (many of whom you apparently know) lean out the PE mode target A/F ratio, and get a guaranteed 10-15HP, without pulling the screen and screwing up the calibration of the MAF sensor. Hard to understand why any "tuner" would recommend pulling the screen, when he already knows how to pick up the HP by leaning out the tune.Its really pretty simple.
01-15-2007, 11:19 PM
#25
Registered User
Join Date: Jul 2006
Location: Ft. Lauderdale, FL
Posts: 177
When I first put my BBK 58mm TB on my car I felt more low end torque. That quickly went away as RPM's climed. My stock TB pulled better in the 3K and up range but the 58mm got me to 3K a little quicker but then would lose steam. Honestly, I liked my 48mm better. Thats all out the window now. BLEW IT UP!!
01-16-2007, 01:40 AM
#26
Registered User
Join Date: Mar 2006
Location: San bernardino
Posts: 68
The screen it there to straighten the flow, and to provide a calibration curve that matches the one that is programmed in to the PCM. The MAF is a hot-wire anemometer. Good design practice for such a device is to provide a straight, uniform cross-section inlet flow channel at least "10 diameters" (or, about 30") in front of sensing element, and several more "diameters" of straight, uniform cross-section ducting at the outlet of the sensing element. The stock LT1 ducting, and most CAI's, provide neither..... hence the use of the screen to redistribute the flow. The screen is there because of the inlet duct configuration.
Interestingly, the C5 LS6 gained 5HP when GM removed the stock "screen" from the MAF in 2001 or 2002 (??). They felt that the symetrical inlet ducting of the LS6 was sufficient to provide uniform cross-sectional velocity, without the screen.
So much for that theory
Yes, the LT1's run "rich" from the factory, because GM programmed them for a target A/F ratio in Power Enrichment (PE) mode of about 11.7:1, which does not provide peak HP or torque, because its too rich. Removing the screen MAY lean out the high RPM A/F ratio, because it destroys the calibration of the sensing element, and causes the sensor to UNDER-report the air flow, which of course leans it out in PE mode because there is no O2 sensor feedback.
But statistically, about 1/3 of the people who pulled the screen saw truely amazing, SOTP HP gains (seldom confirmed by real data ), 1/3 felt nothing, and 1/3 found they had irregular idle, and in some cases reduced fuel mileage. Hence, rather than remove the screen, and take a 1:3 shot that you will get lucky and lean things out with a ghetto hack, you simply have your tuner (many of whom you apparently know) lean out the PE mode target A/F ratio, and get a guaranteed 10-15HP, without pulling the screen and screwing up the calibration of the MAF sensor. Hard to understand why any "tuner" would recommend pulling the screen, when he already knows how to pick up the HP by leaning out the tune.
Its really pretty simple.
Interestingly, the C5 LS6 gained 5HP when GM removed the stock "screen" from the MAF in 2001 or 2002 (??). They felt that the symetrical inlet ducting of the LS6 was sufficient to provide uniform cross-sectional velocity, without the screen.
So much for that theory
Yes, the LT1's run "rich" from the factory, because GM programmed them for a target A/F ratio in Power Enrichment (PE) mode of about 11.7:1, which does not provide peak HP or torque, because its too rich. Removing the screen MAY lean out the high RPM A/F ratio, because it destroys the calibration of the sensing element, and causes the sensor to UNDER-report the air flow, which of course leans it out in PE mode because there is no O2 sensor feedback.
But statistically, about 1/3 of the people who pulled the screen saw truely amazing, SOTP HP gains (seldom confirmed by real data
), 1/3 felt nothing, and 1/3 found they had irregular idle, and in some cases reduced fuel mileage. Hence, rather than remove the screen, and take a 1:3 shot that you will get lucky and lean things out with a ghetto hack, you simply have your tuner (many of whom you apparently know) lean out the PE mode target A/F ratio, and get a guaranteed 10-15HP, without pulling the screen and screwing up the calibration of the MAF sensor. Hard to understand why any "tuner" would recommend pulling the screen, when he already knows how to pick up the HP by leaning out the tune.Its really pretty simple.
So why do all the after market MAF come with no screen
01-17-2007, 02:24 PM
#27
Registered User
Join Date: May 2006
Location: Lancaster, Pa
Posts: 537
I would say go with the 58mm and port the intake manifold to 58mm. That way, you will have what you need in the future should you decide to upgrade more. You will not hurt anything by using the 58mm. Just don't get any shavings in the engine when you port the intake. If anything, your performance will increase by porting and adding the 58mm.
01-17-2007, 04:47 PM
#30
Banned
Join Date: May 2003
Location: LA (lower Alabama)
Posts: 6,661
