SPEED DENSITY QUESTION??

[86droptop]

I`m getting ready to install a typhone intake and a bigger throttle body. My question is, how does the computer (speed density car) gather info for the increased air flow, so it can adjust the fuel flow. I know on MAF cars it gets it from mass air flow sensor, but i`m not sure about speed density.
Thanks

 

[crunchie12268]

I think it is with your MAP sensor and some other small sensors placed on the manifold. If you get a typhoon intake don't go larger than a 65mm t/b.

 

[86droptop]

can you explain to me how the MAP sensor works.
Thanks

 

[ss93cobra]

Speed density systems work off of throttle angle and manifold absolute pressure. It has internal pre-set tables for throttle body blade angle that assumes that since throttle is at a certain %, then fuel should be such and such. Does that make much sense? Kinda like, since incoming air is at "a" on the tables, then fuel should be "a" also. There's much more technical ways to describe function, but I'm trying to keep it simple to understand.

 

[bryanrevans]

86Droptop Can you post your results from this upgrade?I too plan the same mods!!!!I had a 89 tb and upper so I swapped cause I had to check the injectors.It has loped since.And idles erraticly.What I thought was a bad injector was a bad map sensor!!!!!!!

 

[86droptop]

If I understand you correctly then it will be getting the same amount of fuel with the new manifold and throttle body as with the stock one, because the throttle blade will still be in the same relative position,
. Is this correct, how can I increase the fuel flow
Thanks

 

[bryanrevans]

Better pic!!I think!!

How about a class on how to post pics on here?????

 

[87'GTstang]

If I understand you correctly then it will be getting the same amount of fuel with the new manifold and throttle body as with the stock one, because the throttle blade will still be in the same relative position,
. Is this correct, how can I increase the fuel flow
Thanks

Pretty much. In another example, think of it as a multiplication table. As an easy correlation, say if the throttle blade is measured by the TPS as 10% open, and the MAP sensor reads the vacuum in the manifold as say 6" of Hg, then by the ECU's tables that would call for 60 lbs/hour of fuel. It is in no way like this but is an easy example. The part when the SD system will have a problem is when stock values are no within spec. Like when the engine goes WOT with the new intake and TB, the airflow would be substantially greater than stock and will partially confuse the ECU. So in terms of MAF versus SD, MAF is much more forgiving and conforms instantly for air/fuel trim curve demands wheras SD must learn over time. It won't be as accurate as MAF metering, but it can learn to an extent and adjust a little - but airflow at WOT is completely the computer's guess and is not correctly known. So potential could easily be limited with SD in factory-form.

 

[87'GTstang]

Is this correct, how can I increase the fuel flow
Thanks

As for fuel delivery, there's isn't a whole lot you can do. For one let the computer adjust and see how it likes it. Second is to get a custom-burnt chip for the computer to basically give it new air/fuel trim curves - this can get costly if you continually modify and I would not reccomend it unless you are done with modifying and my first suggestion doesn't work so well. Lastly, convert to MAF.