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Ok, here's two observed phenomena involving my supercharger's operation. Let's see if anyone can explain the theory that underlies these observations:
Mileage, at highway cruise, went up several mpg, about 5 actually.
Engine vacuum, at idle, jumped from 19 in/hg to 25 in/hg.
'Splain away,
F=MA
Sounds like you fixed a vacuum leak when you installed your supercharger. Probably didn't even know you had a vacuum leak....
Actually, I created one. On a speed density car, in order for the MAP sensor to not see boost, a one way valve and downstream hole in the vac pipe to the MAP are required.
I just took the SC off and the vacuum signal returned to 19, put it back on, back up to 25.
F=MA
Vacuum is just a measurement of intake restriction, the blower must have added some intake restriction, causing the vacuum signal to go up. 18-20 inches is a typical number for a stock n/a 5.0L.
As for theories, more than likely, the added vacuum signal is causing the eec to look up the timing numbers for a lower load than before, and the added timing is very beneficial to MPG.
I doubt the increased mpg is related to the blower itself, I have to agree, to pick up that much you must have corrected something wrong like a vacuum leak, when you did the blower install.
Good explanation on #1. However, I've had the blower on and off for various reasons, without changing anything else plus, I've owned the car for many years so, I know its quirks. The mpg increase is in some way, directly related to the blower install, since it goes back to normal expected with the blower off then increases after it goes back on.
I've tried to eliminate as many variables as I can.
F=MA
It's a 5 pound Paxton on a stock SD 5.0.
I have been thinking about this for some time about the mileage getting better w/ the S/C installed and came up w/ still another theory:
The S/C is adding air, thus making it run leaner under part throttle conditions = better mileage. Since you run Speed Density the computer has no idea it is getting more air as it would w/ MAF.
What do ya think?
Seeing as the S/C is adding more air, wouldn't the density of the air within the plenum be higher, thereby telling the ECM to add the proper amount of fuel to maintain the correct stoichiometric ratio? I'm not an expert on Speed Density systems, but isn't that how they work?Quote:
Originally Posted by JPJP
It is a mixed bag without seeing a log on the car running but I would say the car runs leaner at idle and none boost conditions causing the MPG increase. Since Speed Density uses a fuel map based on a NA car and with the additional air flow the engine sees but the computer does not your running leaner. The same problem when you go into boost on a Speed Density car and the car always has a lean spike and when using a ram air kit on a 5.0 that is Speed Density it always was leaner which helped power. The Ford computer was running rich on purpose to compensate for different selling markets that had different climates.
I have a 1990 f150 302 with e7 heads and sn 92 paxton pushing about 7 psi. I put the one way valve in to my map sensor just to see if there was a difference. It wouldn't even let the truck idle. So I done it with just the ford checkvalve and when you gave it gas it would cut out (run out of fuel) I have a fmu and boost-a-pump and an adjustable fuel regulater. im running about 48 to 50 psi on fuel. Is this normal or maybe a bad map sensor. I do have 1.7 rollor rockers and flat top keith black pistons. with 19lbs injectors.Thanks Sorry to hike the threadQuote:
Originally Posted by F=MA
I would get a used MAP sensor to try. It sounds like a bad unit or a vacuum leak.
Ok I tried that and it made a little difference. Can you contact me by pm or e-mail when you get a chanceQuote:
Originally Posted by speedytang
PM Sent