Alright, I'm confused...I've now heard two distinct opinions on what can be done with the stock computer and speed-density setup.

Opinion 1: go ahead and convert to MAF. It's more adaptable, more tolerant of changes, and a lot of people I know whose opinions I trust through long experience tell me to go ahead and do it.

Opinion:2 speed-density can be modified. Cams, intakes, throttle bodies, heads, etc...can all be changed. The stock computer stays in place with all its sensors and works fine, and is in face better than MAF. This was the opinion of Ryan at fordfuelinjection.com.

So, is there a better way? I understood that speed-density used base tables to calculate airflow, and changing any of the parts mentioned in Opinion 2 causes massive problems with driveability. So my questions are these: who has modified their speed-density with intakes, heads, throttle bodies, etc, and how does the truck run now? I mean, honestly...there HAS to be a better way here, and I'm tired of feeling like my 351 has less power than a beat-up Escort.

 

By the way, if anyone has gone with a stand-alone or programmable computer, what did you choose?

 

He told you that you could make all those changes and not modify the stock SD computer or that you can change things and use a chip for the SD computer?

 

here's the quotes - verbatim- from the e-mails i received:

"As for your build up:
3" single Exhaust
Edelbrock Performer intake
56mm throttle
Comp Cam 35-255-5
World Roush 180 heads
As long as you don't over bore too much you can use the stock
computer."

now, needless to say, this sort of blew me away, so i sent an e-mail back to clarify on how adaptive SD is, and received the following:

"as long as the cam doesn't screw with the vacuum, O2 sensor is
new, the comptuer can learn up to 25%."

25%. okay, so it can learn things. it can adjust. that's good. i don't know that the throttle body, cam, and heads are within any sort of 25% range from stock.

so to answer you, NJ, i can make those changes with the stock SD computer. and that goes against everything i've heard from the people i trust. that's why i'm wanting to learn what everyone on this forum thinks on the issue, because we're the people that are actually doing this stuff and living with it day to day.

 

thats pretty cool. I am glad to hear that. I'm sure he knows his stuff. I have read his posts on other boards

 

Hey InLoveWithGreta
yea, I say this before, but I ended up posting on the other thread instead. Sorry that I didn't reply here too. I forgot to mention that, before I had changed over to MAF, I had put on Edelbrock upper & lower manifold, Edelbrock throttle body, Edelbrock mild rv cam, K&N FIPK, and had the engine bored .30 over. A whole lotta power. But there was some hesitation in it to. There is a long story, But it lead me to go ahead with the conversion. I'm sure I could have put in a chip in the orriginal set up. But, on my rig I don't think just the chip alone would have helped.

Another thing to consider is that Speed Density runs on what's called bank firing. Which is where cylinders 1 thru 4 injectors are fed then 5 thru 8 are fed, this through out the firing order. The Mas Air Flow set up, runs on what's called sequential firing. which is where each cylinder acts like a single cylinder X 8 (or 6 for those v6 motors)

Again, I hope this helps

 

every bit of information helps. right now, i'm starting to think that i may be able to sneak a few mods in under the computer's nose, and let her figure out what's going on...seems like as long as i don't screw with the vacuum, there is some adaptability that can be used.

 

Most mods aren't going to "mess with" the computer. Heads, headers, K&N, cam (as long as it's not too radical). But if you stroke it you just changed the displacement and SD can't compensate for that because it's set up for a certain displacement and it is only estimating how much air your putting in the engine and putting in the "correct" amount of fuel to go with it. MAF is actually measuring how much air is flowing into the engine so if you stroke it or supercharge it it knows how much air is going in and is capable of giving it enough fuel to maintain a proper fuel/air ratio.

 

well that's just the thing that bothers me. no, i'm not changing the displacement...a healthy 351 is all my truck needs. but since the computer is estimating the airflow, it then becomes a question of whether or not it can adapt to the increased airflow that heads, cam, intakes and throttle body will provide. if it can adapt, great! i save a lot of money. if not, i just killed my gas mileage, which is really good right now. oh yeah, and the engine might not run, either. but all the responses are helping, because i'm starting to get a list of "this will work" items...

 

Don't forget your truck has always "estimated" air flow and did it without a problem. This is where the O2 sensor comes into play. When you are flowing a little more air because of the mods you made it will be running lean and the O2 sensor will tell it so. This will change the signal to the injectors telling them to allow a little more fuel. This is minor even though you can see a big improvement from these mods. But from what I've read and what I've been told from the experts if you change the displacemnt you are now talking about a lot more air and fuel and if you try to just rely on the O2 sensor to keep it all running good it won't work. I know of a couple guys on another board who have 351W with speed density, cam, high flowing heads, headers and they run great. I'm rebuilding a 351 to swap into my Bronco right now and I have the Edelbrock truck/EFI cam (#3782), Trick Flow twisted wedge heads (just came in the mail today), roller rockers, and I'm putting on headers and 3" exhaust, and I'm keeping the SD.(I just need to find a 351/E4OD/SD computer) It worked for these other guys so I'm sure it'll work for me too. Hope this helps some, I learned of this recently too. Good luck with your build.

 

thanks for that...i'm glad to know it works. right now i'm thinking really hard on the AFR 185 heads, a moderate grind cam from Comp Cams (suggested by several people), the edelbrock intakes and something around 60mm for the throttle body. i'm staying with 1.6 rockers and not chaning the internals of the engine whatsoever, and probably strapping some JBA's on in place of the exhaust manifolds and letting it all out through a single 3" with a high flow cat. i might split it to duals after the muffler to give a nicer look but still keep my backpressure. i may end up going with cast iron heads instead of the aluminum AFR's, depending on the flow numbers and quality. i honestly don't need to spend the money on the aluminum heads because it's a truck, after all... BTW, i've seen several computers on eBay for SD Broncos, so you shouldn't have a hard time finding one.