i think you answered your own question.....swapping to mass air would be best....alot more can be done with the engine.....but....you can get close to those #s with speed density....free flowing exhaust....good filter....little head work??... it don't think you can swap a cam...without problems with speed density....good luck.
My 88GT ran 2 tenths and 1.5mph faster in the 1/4 mile before I converted it to mass air. Just some food for thought.. I understand why you are being talked into switching.. but if this is a Mustang code speed density computer and motor.. you should have 225hp to start with. Wringing another 25hp out of that thing does NOT require a damn MAF conversion.
Speed Density cannot adjust to certain changes in your engine the way mass air can. It cannot compensate for massive increases in airflow that come from certain things like aftermarket heads or superchargers.. or even some cams that you would think were mild enough. But exhaust and a little port cleanup could net you the 25hp your looking for.. and save you the swap-out. Now.. if you think you'll want more than 250 anytime in the near future.. you better find yourself a good computer tuner.. because you'll be needing a PCM reprogram for speed density to work right with major changes.
In closing.. (it must be late) I agree with the push to convert to MAF as long as your not doing it to simply gain 25hp.. because in all reality, you will probably LOSE hp doing it.. but have the potential to make much much much more.
P.S. the auto and manual code computers are basically the same. They have different timing curves and idle settings (takes more to idle an auto.. converter.. stuff.. things). Either will work in either car. Been there. Done that. Back in the day, alot of my street racing budies liked running the auto computers in the 5 speed cars..
I agree with the post above that if you are not going to make major or drastic changes in the future to leave it with speed density. However, if plans in the future include diffrent cam, heads, intake, power adder etc, do yourself a favor and upgrade to MAF.
I agree with vermin also. He just told you what I was gonna. stock speed density is faster than stock mass air. A my shop we did a mustang with a e cam, gt40 heads, edelbrock intake and larger throttle bodie along with the flows and k&n. It didn't want to run very well til converted to mass air. try bumping the fuel pressure up and advance the timing a little.
The biggest thing to keep in mind with Speed Density mods is the cam lobe seperation angle, keep it at 114 or higher and you'll be alright. I just built a 351W for my speed density '88 Bronco that turned out great, I used the Comp Cams speed density cam. Also ported E7 heads and lower intake, I was looking for a bunch of torque and that's exactly what I got. For more speed density info go here and ask Mr. Speed Density about your combo questions. http://www.50tech.com/forums/viewforum.php?f=1&sid=a6cd5a1e094cf6811b541f097ac7a0ba
P.S. - Forgot to mention I also installed 1.94 intake and 1.60 exhaust valves in the E7 heads, and had the bowl undercut.
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