Speed Density Limitations

02 281 GT

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Feb 3, 2009
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I'm looking to see what the limitations of the speed density ECMs are. I have a 1990 Grand Marquis that is my daily for which I would like to build a new motor.

This car will just be my daily driver and will never see a track. I'm looking to give it better power than the tired LoPo 5.0 can offer. At the same time, I don't want to just do an HO swap (something that is popular among people who modify these things) when I can do at least an Explorer swap.

I got my hands on an ECM from a 1990 Mark VII. This will allow me to retain cruise control as it's a computer-controlled function on 1990-1991 panther bodies as well as the Mark VIIs. This is a speed density setup. I'd be interested in just doing a MAF upgrade if A9P computers weren't going for at least $250/ea everywhere I look for a used computer that may or may not even still function. I could spend a little more than that and get a DIY MS kit, but I'm not looking to get that deep into things just yet. It'd like to keep it all plug and play for the sake of simplicity and frugality.

Would an Explorer engine/intake, 65mm TB and an XE258HR cam be too much for the speed density computer to cope with? I know the speed density system is dependent on good manifold vacuum for reference with the pre-programmed VE tables, which is why I would go with the 258 grind that has 114° lobe separation; not far off from the stock HO 115°. It's a very mild cam; I'd rather go with this one than a stock HO cam as a new HO cam is just as much as an aftermarket piece. I'm really asking if the GT heads and Explorer intake/throttle body would flow too much for the SD ECM.

I have very little experience with ECMs and any heavy modding, so any advice y'all can give would be appreciated. Thanks.
 
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I'm looking to see what the limitations of the speed density ECMs are. I have a 1990 Grand Marquis that is my daily for which I would like to build a new motor.

This car will just be my daily driver and will never see a track. I'm looking to give it better power than the tired LoPo 5.0 can offer. At the same time, I don't want to just do an HO swap (something that is popular among people who modify these things) when I can do at least an Explorer swap.

I got my hands on an ECM from a 1990 Mark VII. This will allow me to retain cruise control as it's a computer-controlled function on 1990-1991 panther bodies as well as the Mark VIIs. This is a speed density setup. I'd be interested in just doing a MAF upgrade if A9P computers weren't going for at least $250/ea everywhere I look for a used computer that may or may not even still function. I could spend a little more than that and get a DIY MS kit, but I'm not looking to get that deep into things just yet. It'd like to keep it all plug and play for the sake of simplicity and frugality.

Would an Explorer engine/intake, 65mm TB and an XE258HR cam be too much for the speed density computer to cope with? I know the speed density system is dependent on good manifold vacuum for reference with the pre-programmed VE tables, which is why I would go with the 258 grind that has 114° lobe separation; not far off from the stock HO 115°. It's a very mild cam; I'd rather go with this one than a stock HO cam as a new HO cam is just as much as an aftermarket piece. I'm really asking if the GT heads and Explorer intake/throttle body would flow too much for the SD ECM.

I have very little experience with ECMs and any heavy modding, so any advice y'all can give would be appreciated. Thanks.
In my very very limited opinion...it should work. There were a few similiar combos in the mustang pre-MAF world. Not sure if that particular ecu has different "tuning" parameters. Do you have a fall back vehicle to dd? Could try it and if it doesn't work...go MS? Just have some possible (more) down time.
 
In my very very limited opinion...it should work. There were a few similiar combos in the mustang pre-MAF world. Not sure if that particular ecu has different "tuning" parameters. Do you have a fall back vehicle to dd? Could try it and if it doesn't work...go MS? Just have some possible (more) down time.
I still have my '95 Mustang to drive when I need it, so yes. Thanks!
 
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I think if it were me, I'd put together the list of part for the build then head over to my favorite cam website (whichever that may be) and fill out their cam sheet.

Let those dudes know what your parts and EEC are and let em do the rest.
 
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I used to think the factory SD computers were useless as far as accepting mods, but my buddy has an SD f150 with an F cam that gets 16 mpg.

With that said, you can find A9x computers for way less than you mentioned. If it were me, I'd swap to a MAF harness if I wanted trouble free PNP function that I wouldn't need to mess with
 
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