Someone school me on Speed Density...

ratio411

Founding Member

Apr 21, 2002

3,870

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Pensacola FL

Nov 9, 2007

#1

• Nov 9, 2007

• #1

I have a SD 5.0 engine.

My understanding is that too many changes will freak out the SD.
I want to use a 393w and keep it EFI.

I guess my basic theory is that if I use larger injectors, that should fool the SD.
Is that right, or am I totally off base?

The computer doesn't know there are larger injectors to compensate for more air going in. I am hoping that it would think it is firing stock size, the larger size should add more fuel. The CID will bring in more air, and the computer feels warm and fuzzy. I just have to choose the injector size very carefully.


Now that you have read my madness, you probably see I know nothing about EFI.

If I am wrong or missing something, school me!

Thanks
Dave

 

vristang

15 Year Member

Mar 31, 2005

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Seattle

Nov 9, 2007

#2

• Nov 9, 2007

• #2

Getting what you have described to work would be VERY time consuming, and there would likely still be issues that could not be compensated for...


My advice would be to either
1. convert to maf, and just run a calibrated MAF meter for you ecu and injector size.
2. Get a custom tune (via the J3 port) for your SD ecu.

There aren't many shops that will tune stock SD ecu's. The tweecer does support a couple of the SD ecu's, if you want to try tuning yourself.

A stock Ford Mustang MAF meter/ecu/injector setup will work pretty well on a mild 393w.
I ran an X3Z with a C&L MAF meter and 30Lb injectors for a while, and the car was tolerable.
A custom tune with a tweecer corrected many of the issues.

jason

 

tkareno

New Member

Aug 9, 2007

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clinton ct

Nov 9, 2007

#3

• Nov 9, 2007

• #3

your best bet is to convert to maf i am going to soon

 

Darkwriter77

Resident Ranting Negative Nancy

5 Year Member

Jul 1, 2005

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Apache Junction, AZ

Nov 9, 2007

#4

• Nov 9, 2007

• #4

:Word:

You'd have a LOT more time and money wrapped up into trying to make the SD air/fuel setup work than you would by simply upgrading to a MAF conversion (around $300, less if you get the parts used) and then getting a calibrated MAF sensor to match the injectors you're putting in.

Only reason I don't plan on upgrading my '86 GT to MAF is because I don't have any serious enough build-up plans for the forseeable future that would necessitate it - at most, I might throw on some ported E7 heads/intake and a bigger TB, which I'm sure the stock SD computer and 19# injectors could handle.

 

88-378

Member

Aug 10, 2007

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Alpharetta, GA

Nov 9, 2007

#5

• Nov 9, 2007

• #5

One of the fastest stangs I ever had was speed density. But you can only go too far.

Get an A9L and convert.

 

ratio411

Founding Member

Apr 21, 2002

3,870

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Pensacola FL

Nov 10, 2007

#6

• Nov 10, 2007

• #6

How do larger injectors act compared to stock?
Say 19 vs 24, for example.

Would the only difference be amount of fuel dispensed?
Would the computer see any difference in voltage draw, or anything else?

What is it about larger injectors that freak out the SD system?

 

baldy1

New Member

May 5, 2005

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Portsmouth Va

Nov 10, 2007

#7

• Nov 10, 2007

• #7

http://fordfuelinjection.com go to that site and you will learn a alot about EFI it is a very good site.

 

ratio411

Founding Member

Apr 21, 2002

3,870

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109

Pensacola FL

Nov 11, 2007

#8

• Nov 11, 2007

• #8

That was a good read about sensors, and their functions.

I still have questions about how different injectors work and what the computer recognizes about them.

 

TrickFlowd

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May 17, 2003

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Sayre, PA

Nov 12, 2007

#9

• Nov 12, 2007

• #9

I have a Pro-M mass air for sale if your interested. I have to check to see what injectors its cal'd for. I think 24's though.