Mass Air Flow vs. Speed Density

Mass Air Flow vs. Speed Density

With SD the area you want to watch for is the cam. Once you go over 220* duration@.050, then your idle can become unstable and can start surging etc. SD likes High lift, low duration cams, since it relies on vacuum. Most people switch to MAF when going with much larger cams, but if you stay within reasonable limits, SD will run just fine & hard. My 347 runs great with SD although I have pushed the cam limits a bit far with it, but I knew what to expect and with some fine tuning it's not that bad for ME. With SD, heads, intake, gears, blower, N20, all the goodies can be used and have no problems with it. MAF will give a more precise A/F reading to the computer since it reads & adjusts BEFORE entering the motor where SD reads AFTERWARD’S, and thus MAF gives you just a slight better off idle throttle response, a more precise A/F metering, and doesn't rely on vacuum in the way SD does, but I’ve also seen many MAF cars encounter surging problems (modded or not), unstable cruising modes etc as well, all the things that many claim is an SD problem. If you have done any in depth research you'll find many people still have SD with blowers etc and have absolutely NO problems. SD has a better fuel curve at higher rpm than does MAF (until MAF is tweaked or modified) Early 87 5.0’s had a little more aggressive cam than what was used in the mid 87-89 5.0’s which then were changed again in 1990. If the date code on your 87 5.0 HO is before 4/87, then you have this odd cam. It’s not widely known about this oddball cam. The difference being it had 276/276* vs. the later 276/266 cams, plus a slightly more aggressive ramp rate. This particular cam works extremely well with 1.72 RR’s, giving you a total lift of .475 and duration@.050 of 209*, and a 115.5 LCA. It pulls very hard right up to 5800 RPM with good exhaust, intake and reasonable gearing (3.55’s or better). I am currently trying to find the Ford Part# for this cam as back in 1992 I read in a Ford Motorsport parts book the different part numbers for each cam. The reason I mention this cam is simply because it came only in early SD 87’s.

Don't get me wrong now, there comes a time when MAF IS needed, unless you go DFI (Digital Fuel Injection) and with that, you can tune your motor till your hearts desire. I have discovered that having even a basic off the shelf computer chip (Module) help with minor idle issues. Some off the shelf chips will increase your advance rate in the distributor, alter your fuel curve, richen up the motor at WOT as well as add 4* to your total timing which other than a small boost in HP & TQ also allows you to keep your stock setting of 10*, thus making it easier on your starter motor to turn over the motor. I have heard all the rumors about many aftermarket chips doing nothing and being a complete waste of $$. I’m curious if those people who make these claims have actually dyno’d their cars before and after the chip install for absolute verification. Personally, I highly doubt it. I cannot speak for all of the manufactures out there as I have not tested them. I can only speak for the Hypertech Brand, which I personally used for 4 yrs and had the motor & car tested for what changes occurred. This is where my information comes from as listed above. I was pleased with the overall results of the chip, although I think pricing is a bit high for any off the shelf chips.

1 key note here, I always recommend a custom cam AND a custom chip when using SD and a moderately modified motor, but it is not necessary with just basic mod’s such as intake, heads, headers, gears, exhaust and roller rocker arm’s. SD also is more sensitive to fuel pressure settings; TPS settings, idle settings, as well as all your sensors, so make sure they all are in good working condition.



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