SD vs MAFless--which is better for MPG's
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From: Sutherlin OR
SD vs MAF--which is better for MPG's Ok, so I've read-up on both SD and MAFless and understand most of the pros and cons. Question is, which has seemed to produce the best fuel economy? (gas ain't cheap 
) Any thoughts on this and why?
) Any thoughts on this and why? Last edited by kbracing96; Oct 4, 2005 at 01:10 PM.
. I was just coming in here to change it
I think what you mean is speed density closed loop verses speed density open loop.
If both are tuned to hit stoichiometric at all temps and manifold pressures, there would be no difference between the two. But since this is the real world Closed loop speed density (no MAF, but active O2 sensors) will do a better job at holding the motor at stiochiometric (14.63 A/F ratio), which could give you better fuel economy.
But...and this is a big but...if you really were sharp with your tune, you could tune your speed density open loop (no MAF, no O2 sensors) to command an A/F ratio LEANER than 14.63 at cruising speeds. In theory, you could command the A/F ratio to be 15.5-16.0 at light throttle cruising speeds and pick up 2 additional MPGs on the open road. This is not for the average tuner though and a wide band O2 sensor is a must. FWIW, I run my car in speed density closed loop. I get 28 mpgs on the highway, even at my power level.
If both are tuned to hit stoichiometric at all temps and manifold pressures, there would be no difference between the two. But since this is the real world Closed loop speed density (no MAF, but active O2 sensors) will do a better job at holding the motor at stiochiometric (14.63 A/F ratio), which could give you better fuel economy.
But...and this is a big but...if you really were sharp with your tune, you could tune your speed density open loop (no MAF, no O2 sensors) to command an A/F ratio LEANER than 14.63 at cruising speeds. In theory, you could command the A/F ratio to be 15.5-16.0 at light throttle cruising speeds and pick up 2 additional MPGs on the open road. This is not for the average tuner though and a wide band O2 sensor is a must. FWIW, I run my car in speed density closed loop. I get 28 mpgs on the highway, even at my power level.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
