help with speed density

malik641 · Jan 11, 2004

I know that with certain modifications with a speed density 5.0 you have to adjust the computer to what you added. I just wanted to know what modifications require adjustments. Any info is greatly appreciated

87AODGT · Jan 11, 2004

malik641 said:
I know that with certain modifications with a speed density 5.0 you have to adjust the computer to what you added. I just wanted to know what modifications require adjustments. Any info is greatly appreciated

Just stay away from really big cams that would kill the vacuum, and don't even bother with a supercharger or turbo, besides that you can run a decent cam and whatever heads and manifold you want, any exhaust setup, and nitrous is also fine on speed density

astronut1885 · Jan 11, 2004

You can't adjust a speed density computer. Most minor mods, like exhaust are fine, but big things like heads/cam/intake need a mass air conversion. Speed density is set up so that at certain RPM, the engine is fed a certain amount of fuel. That is fine on a stock motor because that fuel level is tailored to the amount of air used by a stock motor, a nice balance. When you begin to improve airflow, you throw off that balance. The same amount of fuel is there, but you have more air, you are running lean. When you upgrade to a Mass Air Flow system, it fixes the lean problem. A MAF system reads how much air is going into your motor at a given time, and supplies enough fuel to match. So rather than a set RPM/fuel ratio, you have a direct air/fuel ratio. This allows you to go as crazy as you want with the motor, as long as your fuel system can keep up. Hope I answered your quesiton.

tmoss · Jan 12, 2004

You can do heads/cam/intake on speed density, you just have to keep the cam below certain limits - 220° duration and 114° lobe seperation. I am putting an Explorer intake & 65mm TB, 24# injectors, GT40P NMRA prepped heads, MAC 1 5/8" shorties and possibly a cam in my 88 SD car and tuning will be done via fuel pressure. You can tune an SD computer, but you have to purchase a tuning tool/software like the Tweecer to do it.

CobraGT87 · Jan 12, 2004

astronut1885 said:
You can't adjust a speed density computer. Most minor mods, like exhaust are fine, but big things like heads/cam/intake need a mass air conversion. Speed density is set up so that at certain RPM, the engine is fed a certain amount of fuel. That is fine on a stock motor because that fuel level is tailored to the amount of air used by a stock motor, a nice balance. When you begin to improve airflow, you throw off that balance. The same amount of fuel is there, but you have more air, you are running lean. When you upgrade to a Mass Air Flow system, it fixes the lean problem. A MAF system reads how much air is going into your motor at a given time, and supplies enough fuel to match. So rather than a set RPM/fuel ratio, you have a direct air/fuel ratio. This allows you to go as crazy as you want with the motor, as long as your fuel system can keep up. Hope I answered your quesiton.

you must still be living in the dark ages . I ran H/C/I/N20 on SD with 0 probs, even on a 347 at one time. many people also run blowers too, plus SD CAN be tuned like TMOSS said.

I worked with SD for a good 10yrs and know what it likes and doesn't like..
read up on it. That info is just as bad as the old myth that 347's burn a ton of oil and don't last

The Shape · Jan 12, 2004

I have also read that stock for stock the SD cars were faster than the mass air cars. Don't know how much truth there is to that though

88STANGCONVERT · Jan 12, 2004

If you will take the word on here of anyone, listen to TMOSS and COBRAGT87 when it comes to SD.

COBRAGT87,
Mr. Speed Density, I was wondering if you were still around. Your knowledge of SD is amazing. I have some questions for you, I will PM you on them if you would not mind.

MadMatt5oh · Jan 12, 2004

The Shape said:
I have also read that stock for stock the SD cars were faster than the mass air cars. Don't know how much truth there is to that though

Yup. thats true

CobraGT87 · Jan 12, 2004

88STANGCONVERT said:
If you will take the word on here of anyone, listen to TMOSS and COBRAGT87 when it comes to SD.

COBRAGT87,
Mr. Speed Density, I was wondering if you were still around. Your knowledge of SD is amazing. I have some questions for you, I will PM you on them if you would not mind.

you can PM me anytime, or you can catch me on AIM under the same SN as here. I'd be happy to help.

I've been here & there. Been busy at the home & tweaking on the car and the wife's 4x4 also, but i'm still around =)

Take Care,
Scott

88STANGCONVERT · Jan 12, 2004

CobraGT87,
Thanks alot, I really appreciate it. You are the MAN when it comes to SD and I trust what you say can be done on an SD car. I will have some questions for you soon, I am just now getting all my stuff together and I am very greatful that you are willing to help.

TrophyHead · Jan 12, 2004

Hey did you speed density guys see this?http://www.mustangworks.com/articles/electronics/CraneInterceptor.html

Not sure if its worth it.

malik641 · Jan 15, 2004

i read that the reason for the stock sd was faster than MAF was because the air/fuel mixture was more accurate....but ill let cobragt87 take this one on if he feels.

tmoss · Jan 16, 2004

There is more than one factor that may make that true on an idividual basis, but it is known that the SD fuel curve was leaner than the MAF fuel curve which was a little richer, hence slightly better power. BUT that is a genralization and may not apply to every case.

GT Trooper · Feb 21, 2004

MAF Conversion Question

CobraGT87 said:
you must still be living in the dark ages . I ran H/C/I/N20 on SD with 0 probs, even on a 347 at one time. many people also run blowers too, plus SD CAN be tuned like TMOSS said.

I worked with SD for a good 10yrs and know what it likes and doesn't like..
read up on it. That info is just as bad as the old myth that 347's burn a ton of oil and don't last

What's up,

I'm in need of information regarding if I really need to do a MAF conversion. I have a 88GT vert with Cobra intake, Canfield heads and a mild cam. The car has stock exhaust which I will be changing to long tubes and off road exhaust. In case you are wondering I bought the car like this two months ago. Currently it runs fine but I'm wondering with the exhaust mod, will it effect how the car runs and is it really necessary to do the conversion. In the forum you guys state that an SD car can be tuned and I'd like any assistance you can offer on that as well. Any info you could give me would be greatly appreciated.

Thank you very much,
Emmitt

MadMatt5oh · Feb 21, 2004

Exhaust shouldnt affect anything as far as pissin off the SD

CobraGT87 · Feb 21, 2004

GT Trooper said:
What's up,

I'm in need of information regarding if I really need to do a MAF conversion. I have a 88GT vert with Cobra intake, Canfield heads and a mild cam. The car has stock exhaust which I will be changing to long tubes and off road exhaust. In case you are wondering I bought the car like this two months ago. Currently it runs fine but I'm wondering with the exhaust mod, will it effect how the car runs and is it really necessary to do the conversion. In the forum you guys state that an SD car can be tuned and I'd like any assistance you can offer on that as well. Any info you could give me would be greatly appreciated.

Thank you very much,
Emmitt

Emmitt,
The cam you have will determine if you need to convert or not as thats the main issue with SD as good vacumm is essential. Do you know the spec's of your cam? If so, please list them so I can give you more help. Your exhaust mod won't hurt anything, nor the heads, intake.

I don't know what Inj's your running but based on what you listed, the 19's will still work fine. Once you hit around 330FWHP, then it's time for 24's, or kick up the FP on the 19's to approx 45-50 psi. SD also run's best with a 180 T-stat, so don't go higher or lower.

Let me know,
Scott

help with speed density

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