mods and speed density

jester111 · Mar 29, 2004

hi
what are the typical problems associated with modifications and speed density vehicles? how do you fix these problems without going to mass air?
Im going to rebuild the motor since its coming out( cant leave well enough alone) im thinking of porting the stock heads upper and lower intakes and also install an e303 cam, does anyone out there have these mods done to a speed density car and how does it run for you? One more thing I was looking at my throttle body and saw there was a lip inside, im woundering if you can bore this out and install a larger plate or waste of time?

HISSIN50 · Mar 29, 2004

as long as you dont go crazy on the cam, you should be ok. might try searching. there is some real good specific info in some threads in here (same topic idea. SD vs. mass air, etc), with what cams work and what ones dont. i cant remember off the top of my tired bean.
good luck.

IMissMy93Fox · Mar 29, 2004

The thing with speed density is that when you start doing things that aren't basic bolt ons... like a cam you usually need to get a custom program burnt. I'm not sure if you'll have to with an e cam but it's something you'll want to look into.

Michael Yount · Mar 29, 2004

Speed density uses a MAP sensor - manifold absolute pressure. It sits on the firewall, and a vacuum line connects it to the manifold so it can sense pressure in the intake. The same sensor in a mass air car is called the BAP sensor - barometric absolute pressure. It's NOT hooked to the manifold in a mass air car, and simply senses barometric pressure.

Simplistically, the speed density system looks at temps, throttle position, rpm and manifold pressure, and calculates (estimates) how much air is entering the engine, and from that it determines how much fuel to inject. It's fairly sensitive to changes that impact manifold pressure/vacuum. Many cams (including the E303) will cause a big change in idle and low speed vacuum levels. It's not uncommon that with common mods, and E303 cam will reduce idle vacuum from a stock reading of 18-20" down to 11-13". Less vacuum at idle means there is MORE absolute pressure in the intake. More pressure there (less vacuum) and the engine thinks more air is flowing than actually is, and it therefore injects more fuel than it should. Once the car goes into closed loop and the O2 sensors start to provide signals, the system can trim back the excess fuel, but there's a limit to how much adjustment it will make that way.

So, when you start changing cams, heads, manifolds on speed density cars you just need to know that the more you alter the pressure in the intake from the what the designers designed it for, the more difficult you make it for the system to provide accurate amounts of fuel. There are people running the E cam, but generally it's considered to be right on the edge of what you can get away with if you want decent low rpm/street manners. It depends a lot on the other components as well, and the way you install the cam. Advancing it on the install usually helps to increase idle vacuum levels a bit, so that can help too. See if some of the speed density gurus can chime in and give you some more counsel.

Generally, if you stick with improved flow in the manifolds and the heads, and leave the cam alone, the speed density system should manage just fine. Just be careful with the cam choice. Why not leave the cam stock and throw a set of 1.7's on it if you want a bit more 'cam'? In any event, the E is recommended to used with different heads, intake, exhaust and gears -- so unless you really know what you're doing with your porting, it doesn't sound like a good match for your other changes anyway, not to mention how the SD is gonna react.

Having said all that, hook up with the SD gurus out there. The system can support certain mods quite well - and there are plenty of really quick SD cars on the prowl. You just have to know what the limits are.

88stangmangt · Mar 29, 2004

Michael Yount said:
Speed density uses a MAP sensor - manifold absolute pressure. It sits on the firewall, and a vacuum line connects it to the manifold so it can sense pressure in the intake. The same sensor in a mass air car is called the BAP sensor - barometric absolute pressure. It's NOT hooked to the manifold in a mass air car, and simply senses barometric pressure.

Simplistically, the speed density system looks at temps, throttle position, rpm and manifold pressure, and calculates (estimates) how much air is entering the engine, and from that it determines how much fuel to inject. It's fairly sensitive to changes that impact manifold pressure/vacuum. Many cams (including the E303) will cause a big change in idle and low speed vacuum levels. It's not uncommon that with common mods, and E303 cam will reduce idle vacuum from a stock reading of 18-20" down to 11-13". Less vacuum at idle means there is MORE absolute pressure in the intake. More pressure there (less vacuum) and the engine thinks more air is flowing than actually is, and it therefore injects more fuel than it should. Once the car goes into closed loop and the O2 sensors start to provide signals, the system can trim back the excess fuel, but there's a limit to how much adjustment it will make that way.

So, when you start changing cams, heads, manifolds on speed density cars you just need to know that the more you alter the pressure in the intake from the what the designers designed it for, the more difficult you make it for the system to provide accurate amounts of fuel. There are people running the E cam, but generally it's considered to be right on the edge of what you can get away with if you want decent low rpm/street manners. It depends a lot on the other components as well, and the way you install the cam. Advancing it on the install usually helps to increase idle vacuum levels a bit, so that can help too. See if some of the speed density gurus can chime in and give you some more counsel.

Generally, if you stick with improved flow in the manifolds and the heads, and leave the cam alone, the speed density system should manage just fine. Just be careful with the cam choice. Why not leave the cam stock and throw a set of 1.7's on it if you want a bit more 'cam'? In any event, the E is recommended to used with different heads, intake, exhaust and gears -- so unless you really know what you're doing with your porting, it doesn't sound like a good match for your other changes anyway, not to mention how the SD is gonna react.

Having said all that, hook up with the SD gurus out there. The system can support certain mods quite well - and there are plenty of really quick SD cars on the prowl. You just have to know what the limits are.

man knows his stuff

ninety15.0 · Mar 29, 2004

hahaha yea he does...everytime i read one of his long posts i learn something...keep it up bro you are making this whole forum smarter hahaha!!

Michael Yount · Mar 29, 2004

"Typing" was the single most important class I took during any of my formal education.

TrophyHead · Mar 29, 2004

http://www.50tech.com/articles/display_article.php?catid=4&id=8
Here's a good article.

I'd be a little weary with that cam choice. You could put RR's on the stock cam like Mike mentioned.

Not sure how this works but.......I think you can advance/retard your stock cam. Retarding it means better low end. And advancing it means better high end. Right?

smellmygas · Mar 29, 2004

i have an e cam...ported stock heads, bigger throttle body, SD of course, im doing fine right now, there are small surges nothing too big or anything that scares me too much. from what i heard my engine should be all over the place but its handling pretty nice, really only revs up randomly up to like 1400rpm, i read some of the threads that people posted in and i may have just discovered that the intake hose goign to the vaccum tree may be plugged in my car...for you knowledges...is that bad and should i fix that right away????? please tell me!
but id say you might as well try sticking to SD, im waiting it out till it gets bad, i dont really feel like spending 400 if not more on converting to mass air

CobraGT87 · Mar 29, 2004

Michael Yount said:
Speed density uses a MAP sensor - manifold absolute pressure. It sits on the firewall, and a vacuum line connects it to the manifold so it can sense pressure in the intake. The same sensor in a mass air car is called the BAP sensor - barometric absolute pressure. It's NOT hooked to the manifold in a mass air car, and simply senses barometric pressure.

Simplistically, the speed density system looks at temps, throttle position, rpm and manifold pressure, and calculates (estimates) how much air is entering the engine, and from that it determines how much fuel to inject. It's fairly sensitive to changes that impact manifold pressure/vacuum. Many cams (including the E303) will cause a big change in idle and low speed vacuum levels. It's not uncommon that with common mods, and E303 cam will reduce idle vacuum from a stock reading of 18-20" down to 11-13". Less vacuum at idle means there is MORE absolute pressure in the intake. More pressure there (less vacuum) and the engine thinks more air is flowing than actually is, and it therefore injects more fuel than it should. Once the car goes into closed loop and the O2 sensors start to provide signals, the system can trim back the excess fuel, but there's a limit to how much adjustment it will make that way.

So, when you start changing cams, heads, manifolds on speed density cars you just need to know that the more you alter the pressure in the intake from the what the designers designed it for, the more difficult you make it for the system to provide accurate amounts of fuel. There are people running the E cam, but generally it's considered to be right on the edge of what you can get away with if you want decent low rpm/street manners. It depends a lot on the other components as well, and the way you install the cam. Advancing it on the install usually helps to increase idle vacuum levels a bit, so that can help too. See if some of the speed density gurus can chime in and give you some more counsel.

Generally, if you stick with improved flow in the manifolds and the heads, and leave the cam alone, the speed density system should manage just fine. Just be careful with the cam choice. Why not leave the cam stock and throw a set of 1.7's on it if you want a bit more 'cam'? In any event, the E is recommended to used with different heads, intake, exhaust and gears -- so unless you really know what you're doing with your porting, it doesn't sound like a good match for your other changes anyway, not to mention how the SD is gonna react.

Having said all that, hook up with the SD gurus out there. The system can support certain mods quite well - and there are plenty of really quick SD cars on the prowl. You just have to know what the limits are.

Michael, Don't your fingers ever get tired from your very nicely detailed LONG explanations? LOL J/K

Yes, the Cam is the key with SD. it's all about the timing events of the Cam, choose those correctly and an SD car will run like a raped ape.

Scott

mods and speed density

jester111

New Member

HISSIN50

"How long does it take to get help in here?

IMissMy93Fox

New Member

Michael Yount

Mustang Master

88stangmangt

Active Member

ninety15.0

New Member

Michael Yount

Mustang Master

TrophyHead

smellmygas

Member

CobraGT87

Mr. Speed Density

Similar threads

mods and speed density

New Member

"How long does it take to get help in here?

New Member

Mustang Master

Active Member

New Member

Mustang Master

Member

Mr. Speed Density

Similar threads

Privacy & Transparency

Privacy & Transparency