stock cam. if i change my heads and intake will my speed dens. still work correctly?
Upgrading Heads And Intake Will Speed Density Work?
Rustbelt
21 - 40 of 49 Posts
Joined
·
164 Posts
so what everybody is saying is that i could do a set of head and intake manifolds but all i have to do is keep the stock cam. and it won't effect how it runs?
Joined
·
466 Posts
yes it should, if you keep the stock cam, but I'm asking what's the best cam I can use for SD
I've got some pistons with holes in them to prove this is a bad idea. The SD system is fixed, kind of like carburetor jets. It measures crank speed and air density (temperature and altitude) and mathematically determines the correct amount of fuel to inject. If you add more air to the equation by increasing valve size or lift or increasing the header or intake size, the EEC doesn't know it's pulling in more air, only how fast it's going. It determines the proper mixture based on the stock (read that tiny) intake components. This makes for a lean condition, the more air the leaner. Lean mixtures burn hot, and it's only a matter of time until your 302 becomes a hand grenade.
Ask anyone that does motor work on carbureted engines what happens when you make the engine breathe better but don't re-jet the carb. Or even jet it in Denver and then make a trip to LA.
Break down and get a mass-air conversion. You can find a used one for not a lot of $. Try Mustang Parts Specialties in Atlanta if you can;t find one anywhere else. Then you can do whatever you want to your motor.
Trust me on this. I speak from experience.
Ask anyone that does motor work on carbureted engines what happens when you make the engine breathe better but don't re-jet the carb. Or even jet it in Denver and then make a trip to LA.
Break down and get a mass-air conversion. You can find a used one for not a lot of $. Try Mustang Parts Specialties in Atlanta if you can;t find one anywhere else. Then you can do whatever you want to your motor.
Trust me on this. I speak from experience.
MAF conversion is easy. The hardest part is changing out the computer. It's installed inside the kick panel just in front of the passenger door. The cable has to be run inside the fender and come out somewhere around the three inch hole behind where the airbox is. It's kind of short to go far, but if you use a stock air tube and sensor it works fine.8t6gt said:
Here's how I ran mine. You can just see the plug and wire coming through the inner fender. This was a used system, cost me $300. I used a 80mm sensor calibrated for 30# injectors, and that cost more. But you don't have to do that, unless you really make it breathe good and get near 300 HP.
Any way you cut it this is cheaper than a new set of pistons. Unless you are looking for a way to convince Mama that you need a new engine. In that case, just go for broke! It won't last long with SD and you'll be well on the way to getting your new engine!
Joined
·
11,995 Posts
It won't be anymore off than it would be with a factory mass air conversion. The computer still computes, the difference is it realies on vacuum. I've run several speed density cars in the past. A gentleman by the name of Lee Rutter who was a big name in Mustang racing in the early 90s went deep in the 11s with a stock shortblock and speed density. The speed density cars also happened to be the fastest stock Mustangs and from what I've been told is because the speed density system processes faster which is why most aftermarket systems are speed density.JBIGBOOTSY said:
Joined
·
466 Posts
Alright, I really didnt want to convert to mass air, but I guess I have too, there's really no choice of cams?
You can make just about any cam work as long as it doesn't cause a valve to tap a piston, it's just a gamble how much too lean it'll run. With the stock SD set up in it's stock configuration if it breathes enough more air for there to be a noticeable difference in performance, regardless of how it does it, it'll burn a piston sooner or later. Guaranteed.
More air + same fuel = burnt motor.
You might be able to change out the injectors and mess around with the fuel pressure and that kind of thing to get the air-fuel mixture right, but unless you have the proper test equipment and expertise, you're just guessing, and one lean dyno run can blow your motor up if you guess wrong. Mass-air is no big deal to buy or install, a lot easier and cheaper than a set of heads and completely brainless to run. You will have to do most of the injector/pressure stuff even with mass-air if you want more than around 300 hp but mass-air takes the guesswork out of it.
Speed-density systems meter fuel based on a mathematical constant of how much air was drawn into Ford's test engine per revolution with the stock intake/exhaust capacity, at a given throttle position and crank speed and using a mathematically estimated air density. In other words, it's making an educated guess at how much air it's sucking in. Mass air measures the air coming into the engine and injects the right amount of fuel based on the actual amount of air consumed. No guessing involved.
I know mass-air seems like a black hole for cash that won't give you even a hundreth of a second, but it's a worthwhile investment if you want to go fast. Even Ford had the sense to give up on speed-density systems after 16 months.
Power to the Pavement!
More air + same fuel = burnt motor.
You might be able to change out the injectors and mess around with the fuel pressure and that kind of thing to get the air-fuel mixture right, but unless you have the proper test equipment and expertise, you're just guessing, and one lean dyno run can blow your motor up if you guess wrong. Mass-air is no big deal to buy or install, a lot easier and cheaper than a set of heads and completely brainless to run. You will have to do most of the injector/pressure stuff even with mass-air if you want more than around 300 hp but mass-air takes the guesswork out of it.
Speed-density systems meter fuel based on a mathematical constant of how much air was drawn into Ford's test engine per revolution with the stock intake/exhaust capacity, at a given throttle position and crank speed and using a mathematically estimated air density. In other words, it's making an educated guess at how much air it's sucking in. Mass air measures the air coming into the engine and injects the right amount of fuel based on the actual amount of air consumed. No guessing involved.
I know mass-air seems like a black hole for cash that won't give you even a hundreth of a second, but it's a worthwhile investment if you want to go fast. Even Ford had the sense to give up on speed-density systems after 16 months.
Power to the Pavement!
Joined
·
6,172 Posts
I dont doubt the abilities of SD, or what people have done with SD, It's just if he wants to change a cam and heads and intake, He will either have to get a chip, or go maf, a chip being the way I would go, Mass air is another, if he wants to put a cam in the car He is going to have to do one or the other, or deal with it not running right. A stock SD mustang with a cam and no chip will be slower than a stock mass air mustang with a cam and no chip.Darrell said:
Joined
·
11,995 Posts
You had other issues if you were burning holes in pistons. It takes alot to melt a piston on a naturally aspirated engine, especially a mild engine. I ran last year with a jet extension completely clogged. It was so lean that fixing the problem was the difference between running 10.1x and 9.70s. This was in a 700hp 7000rpm race engine. If that wasn't enough to burn a hole in a piston, I can't imagine what is. We've done head swaps on alot of speed density cars over the years. Burning holes in pistons is not an issue.Overkill said:
Joined
·
3,413 Posts
Yeah what they said....ridebmxfbm said:
Joined
·
11,995 Posts
Its not that I'm saying you are making up the fact that you destroyed an engine. I'm saying speed density has nothing to do with it. Who ever told you speed density caused it is wrong. Like I said, I've built several speed density cars and ran them for years. Speed density cars with head and intake upgrades run strong. Hell, they used to supercharge speed density cars back in the late 80s. I even put one together back in 95 with an alphabet cam and it ran great once I got past the idle issues which was compensated for by a bit more fuel pressure and an IAC adjustment plate. I know several people that own shops with dynos. Almost everything I put my hands on goes on a dyno. The number one reason for failure on a dyno is part failure and assembly error which is one of the main reasons to dyno a race engine, so you can break it in and make sure there are no issues.Overkill said:
All due respect, Darrell. I never said Speed Density causes problems, only that a lean fuel/air mixture burns up engines and that using the stock '86 - '87 Ford system on a modified engine can and will cause a lean condition. Sure SD works, been around a helluva lot longer than mass-air, at least as far back as the 1937 German ME-109. Using and properly tuning an SD system will surely cost at least as much in the long run as mass-air, and I think the original question had to do with saving money by using the stock system. It will take a bunch more expertise and equipment at a higher risk level to make SD work right. If you're getting 700 HP at 7000 rpm out of a small block Ford, then you know this is true. You are one of the very few with that kind of expertise, and I'll bet you charge out the ass for it. If you don't you should.
Darrell, I think we're talking about two different things. You are talking about speed-density as a particular type of fuel metering system, I'm talking about using a stock Ford system on a modified engine. Nobody told me my engine broke because of SD. They told me, and they were right, that a lean air/fuel mixture caused detonation and subsequent piston failure (the number one reason for engine failure - improper fuel metering, I was told). Using the stock '86 SD with a Trick Flow manifold and a good set of headers without increasing the fuel flow is what killed my engine. Actually didn't kill it, just burned one piston clean thru and made some hellacious divits in a couple more.
Sure if you have access to a real-live engine dyno and can use it to break in and dial in a race motor, speed-density probably is better. But if you're just bolting a set of heads to a block and adding a manifold and headers and hoping it works, I'd go with Mass-air. It'll give you a lot more room for error.
Darrell, I think we're talking about two different things. You are talking about speed-density as a particular type of fuel metering system, I'm talking about using a stock Ford system on a modified engine. Nobody told me my engine broke because of SD. They told me, and they were right, that a lean air/fuel mixture caused detonation and subsequent piston failure (the number one reason for engine failure - improper fuel metering, I was told). Using the stock '86 SD with a Trick Flow manifold and a good set of headers without increasing the fuel flow is what killed my engine. Actually didn't kill it, just burned one piston clean thru and made some hellacious divits in a couple more.
Sure if you have access to a real-live engine dyno and can use it to break in and dial in a race motor, speed-density probably is better. But if you're just bolting a set of heads to a block and adding a manifold and headers and hoping it works, I'd go with Mass-air. It'll give you a lot more room for error.
Joined
·
11,995 Posts
Ok, the detonation part I can see causing the damage. I guess I was misunderstanding your post. I wouldn't go as far as to say the speed density caused it and infact I highly doubt it. There are so many variables that can cause detonation. I just can't see how someone would tell you it was because of the speed density system. If that is the case why would this issue not be talked about alot more often? Like I said, I've assembled alot of factory speed density set ups and never seen a problem like that or any problem for that matter besides a minor idle issue in a cam swap SD car. I've been refering to the factory speed density system, not an after market system. Specifically 87-88. I've never messed with an 86 speed density system but I can't imagine its much different. In fact I'm looking for an 87-88 Mustang GT right now for my next project which is a full accesory 11 second street car and I want to use all production Ford parts and speed density.Overkill said:
I don't disagree that converting to mass air is cheap and easy. It certainly is fairly cheap and easy. I fully agree with that and it is the best thing to do for modified street Mustangs. I just took offense to the SD discussion because some of the things you were told I believe were twisted away from fact for various reasons.
Joined
·
466 Posts
so Darrel wat would be the best combo of H/C/I to install on my SD car in order to get to around 350rwhp maybe more
Joined
·
466 Posts
is it even possible to make that much power with the stock cam?
21 - 40 of 49 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
