People on this board always seem to say that
a speed density runs harder the a MAF.
Why? They were not rated at any more hp.
My understanding is that when you reach
a certain amount of hp through modding
that then one is better (I forget which)

------------------
88 IROC the best RS ever made!
well except for the BC4s

 

MAF is better when you UP the horsepower considerable. SD will need a chip to run as good as a MAF would with the same mods. And YES Speed Density cars were rated at higher horsepower.

------------------
92 Z28 L98 350
---------------
Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

MAF is better once you start modding. I thought the differences in horsepower throughout the years was due to subtle exhaust changes and minor cam changes am I wrong???

------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

I disagree Blade. After a certain unknown point, the MAF sensor becomes more of a restriction in the intake than the benefit of the info it provides to the ECM. Speed Density is a straight shot right into the throttle blades with no restrictions. Plus the computer can handle a lot more information and spit it out a lot faster.

MAF isnt as sensitive to vacuum, therefore you can run a larger cam with it. But all of the aftermarket ECMs are speed density. Why do you think that is?

------------------
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

If you got a MAF, stay w/ it.
It would be a waste of good money (not to mention time) to swap for a SD. If you do, you might as well go w/ something like a holley or accel computer.

And a MAF if I recall flows over 720 CFM.
Unless you are breaking into low 13's or high 12's, it will not be a restriction.

------------------
Michael Graeber

My Garage

1)83 Z-28 T-Top: Full cage, 9" w/ lad.bars, Midwest Engine Tech 406sbc,Strip Dominator, Demon Carb, Phase VI Chevy Bowtie heads, .630" Crower roller set-up, 1 3/4 coated Hookers 3" true dual exhaust th400, fuel cell & still not running

2)89 Formula WS-6 305 TPI Auto For the road: minor motor, more suspension stuff. MODS

 

Most of the aftermarket systems are speed density because they would rather not spend the extra money on a relatively expensive MAF sensor. Why do you think Chevy went back to MAF (as well as MAP) on the 94 - 97 LT1 and 98 - up LS1)?

=)



------------------
Edwin
1986 IROC, 1992 Body Kit, 1989 5.7 IROC Engine, Crane Cam, 3" CVX Exhaust, ADS Superchip, 24# FoMoCo Injectors, Gutted Cat, AFPR (45 psi), Airfoil, 3.42 Gears, MAF Screens removed, Gutted Airbox, K&N Filters

 

I think it was Chevy High Performance that did an article on MAF vs. SD sensors. They said the MAF was okay until you started doing mods. The MAF won't support more than 300 hp max. The SD sensor was created for higher HP engines and that is why they changed. I will go try to find that issue to clear this up.
Vman

------------------
1989 Camaro RS
2.8 V6
K&N's
700R4 tranny
Cragar Street Pro rims (old Series 30)
Pioneer DEH-P3000

1969 Camaro SC
350 HO from a Vette
Turbo 350 tranny
In the process of being restored

 

My SD Iroc has responded very well to mods without a chip change. It wasn't until late July that I got a chip for it from Ed Wright (stage 2 version). Granted, I haven't put a cam or heads on, but things like ignition upgrades, ignition control (MSD 6A), AFPR, very free flowing exhaust and conical K&N on the throttle body, it respnded very nicely.

------------------
"Clear your mind, relax, and float downstream."

 

Question: What is Speed Density, and MAF?? What are the main differences, and what is better??
(I keep seeing people talking about this, and I would like to be able to follow)
Thanks



------------------
Godti
'89 Trans Am (Red)
305 TBI 5spd

 

Question: What is Speed Density, and MAF?? What are the main differences, and what is better??
(I keep seeing people talking about this, and I would like to be able to follow)
Thanks



------------------
Godti
'89 Trans Am (Red)
305 TBI 5spd

 

MAF=Mass Air Flow Sensor. It measures the amount of air coming into the throttlebody using a "hot wire". This little tiny wire that you could break by getting a hair on does all the work. When you turn the car off, the wire heats up to like a thousand degrees nd burns off all the tire smoke and Grand National exhaust that you sucked in and got on it. This is all i feel like typing..sorry. Speed Density is this other thing for punks..=) actually, don't really know how SD works but I do know that MAF sensors like to set off error code 34 and be gay. hope this helps

------------------
-Red '88 IROC 5 Speed TPI
-Dual Friction Centerforce Clutch
-Accel 300+ Racing Ignition
-Accel 300+ Pro Sleeve Plug Wires
-Accel U-Grove Plugs
-Flowmaster Force II 3 Chamber Cat Back Exhaust
-Hypertech Chip
-Hypertech Airfoil
-Removed MAF Screens
-Gutted Air Box
-Best E/T 14.90, 60 ft. 2.17, 1/8th mile 9.61(bald tires, SES light on)
-Best MPH 92.7(bald tires)

 

The MAF system uses a sensor in the intake ducting like Yarnboy described to measure the incoming air into the engine. It has a hairlike wire that changes its output voltage in response to heat. The more air flowing across that wire, the cooler it is, and the engine responds accordingly.

The MAP system uses a vacuum sensor mounted to the passenger side of the plenum. It measures the amount of vacuum in the plenum. When you step on the gas pedal, the engine sucks more air into the cylinders, which increases the vacuum in the plenum, and the engine reacts accordingly. But changing the cam or the heads will change the amount of vacuum in the plenum. Too great of a change will confuse the MAP sensor, and thats where the rumor of "MAP systems dont respond well to mods" comes from. MAP systems are also called Speed Density.

A MAF sensor will only flow 720 cfm if you hack the hell out of it, cut the screens out, and grind down the cooling fins. Most people only remove the screens, which allows the MAF to flow about 500-600 cfm.

 

you would only need to switch to MAP if you have a 383 or bigger and like said before if you make more than 300 horses. i have MAF and dont have any problems , changed cam full exst, afpr and many other things

 

OK, I knew I had a MAP sensor. So Speed Density is just another name for it? I want to build a 350, what would you recommend, MAF or MAP?? Also, you said hack the hell out of it to get it to flow 500-600 cfm, do you want smaller numbers??

------------------
Godti
'89 Trans Am (Red)
305 TBI 5spd

[This message has been edited by Godti (edited October 04, 2000).]

 

Guys, I really think a MAF sensor is capable of supporting over 300 horsepower.

Here's one way I know of to determine whether or not your MAF sensor is a restriction. With a scanner, take a data capture during a WOT pass and monitor MAF readings. The maximum airflow reading of the MAF is 255 gm/s. If your engine can pull 255 gm/s, than the MAF is probably a restriction. Otherwise, there's no reason to ditch it. I'm pretty sure this is a valid test.

 

Kevin, correct me if I'm wrong, but at WOT under load the engine has substantially less vacuum than when at idle. This is one of the reasons the fuel pressure regulator increasses pressure when you disconnect the vacuum line, to simulate WOT. The ECM then takes this vacuum value, and the intake air temperature and looks checks a table in the PROM to determine the mass of air being consumed by the engine at that time. It calculates the mass air value instead of directly measuring it like a MAF system does. Because of this, MAF systems should theoretically respond to mods better than SD systems, at least until the MAF becomes a restriction.



------------------
Edwin
1986 IROC, 1992 Body Kit, 1989 5.7 IROC Engine, Crane Cam, 3" CVX Exhaust, ADS Superchip, 24# FoMoCo Injectors, Gutted Cat, AFPR (45 psi), Airfoil, 3.42 Gears, MAF Screens removed, Gutted Airbox, K&N Filters

 

- A correction on how SD works. The ECM uses vacuum and engine rpm to reference a value on an airflow map. It then decides, based on this value how much fuel to inject. It never measures airflow directly, so any changes to the stock airflow or vacuum cause the map(lookup table) to become inaccurate. Even changes in altitude affect the accuracy of the airflow map.
- While the stock MAF sensor has a limited range of airflow it can recognize, there are aftermarket TPI-compatible MAF's that flow a lot more than the OEM unit.
- 700 cfm is not really a restriction. You would need to make in excess of 500 hp or 6500 rpm before you would need more than 700 cfm. The reality is: because of the restictions in the intake system, even if your MAF flows 700 cfm, it is difficult(if not impossible) to deliver, that amount of flow to the combustion chambers.
- the reason most aftermarket ECM are designed for SD is packaging and price. The MAF sensor needs more room in front of the TB than a similiar SD setup. And the cost of the MAF sensor(and it's frailty) has discouraged a lot of aftermarket ECM manufacturers. In my research I have found one company(Electromotive) that makes an ECM for MAF equipped engines.
- I think the fact that GM switched back to MAF is vindication of that systems adaptibilty and accuracy. Although the SD equipped third-gens had a slightly higher advertised output, GM never attibuted the gain to the switch to SD. The official line was that a less restictive exhaust('89 - on dual-cat) and lighter pistons('90 - '92) were the reason for the 15 hp increase from '88 - '90.
- both SD and MAF respond well to prom's with fuel and ignition curves tailored to the particular cars' mods. While the MAF ECM's are more tolerant to internal changes, you are still not getting optimal performance if you are using a stock PROM with a slightly modded engine.

------------------
He who hesitates,... is lost!

 

Nice signature 871LEIroc BUT its B4C not BC4 and if you have a IROC thne its a Z-28 not an RS
anyway Speed Density and Mass Airflow both have there ups and downs I favor Speed Density the only reson that it "dosent respond well to mods" is due to that your incressing the flow of the engine and the computer dosent know that. The mass airflow sensor is a resriction and is Costly to repalce all you have to do to get SD to mod well is get a prom burner and make your own then the proformance ganes are all about Speed Density and With a prom burner you can tweek more power out of a stock motor by makeing the PROM more radical. now speed density runs on a lot more then just manifold vacume theres the Throttle positon sensor reads DUH throttle position-Coolent Seneor=engine temp-manifold air temp sensor=incoming air temp-map sensor=manafold vacume=O2 senseor=amount of unburnt oxogen in the exst. gasse- The computer takes in all this info and calculats the fuel your engine needs now if you have inressed the flow of the motor then there is more O2 in the chamber making you lean now the O2 sensor compensats some but its not enough for major mods.

------------------
Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 383 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)

 

91B4C,

You are quite correct in stating that the speed density ECM doesn't rely solely on vacuum and rpm to make it's fuel and ignition calculations(which would be as erroneous as saying the MAF ECM relies solely on the MAF sensor for those calculations). But the vacuum and rpm are the main sensor inputs it uses to reference it's lookup table. Other sensors, chiefly the O2 sensor, allow it to make minor corrections(trim) via the Block Learn Multiplier and the Integrator. For the sake of simplicity I didn't get into intricate details on the complete inner workings(and admittedly I still have a lot to learn on that subject).

I agree with you that burning your own PROMs is the best way to maximize your engine's efficiency(both for SD and MAF ECM's). However, most of us don't have, or don't want to commit, the financial resources necessary to burn our own PROM's. And there is also a fairly steep learning curve(of which I am SLOWLY ascending). Definitely a bit more involved(mentally anyways) than putting on a pair of headers or a set of runners.

I don't agree that an aftermarket MAF is an expensive investment(typically cost from $150 to $250), especially when measured against other "performance" parts such as the lower manifolds(approx. $400), runners($300+), bigger TB($300+) or a good quality exhaust system($600 - $1000+). Of course the MAF sensor is a vital part of the system, but I think a lot of folks don't want to spend the dough unless it makes a huge difference.
While a higher flowing MAF will deliver more cool air to the intake, it won't make as big performance gains as other aftermarket parts.

And again, even if you mod your stock MAF to flow 700 cfm, the intake sytem will prevent that amount of air from actually reaching the engine(which is true of SD engines too).

Both systems have thier pro's and cons, and there are some darned powerful examples of each. Rather than bicker about which is the superior system, I think each owner should learn how to maximize the efficiency of what they own, while realizing there are different ways to get the same results. Because I own three MAF engines, that is what I will spend my time learning about. But I realize that there are limitations to that system, as much as there are limitations to SD.

------------------
He who hesitates,... is lost!

 

91B4C Jacob- okay i got the rpo code wrong, B4C. I chose my username, 871LEIroc,
in memory of my previous 87 IROC, which was a Players race car. 1LE didn;t exit then, but if it had, my car would've been a 1LE.

Secondly, my 88 IROC. I say best RS made jokingly, because it's a TBI, and has the
factory 15" Z28 wheels, just like the Camaro RS. But I have the "wonderbar, steering box and suspension ect from the Irocs.

Obviously your B4C is alot better then mine but mines better then the rest of the RS's.
I will adjust my sig.

 

B4C Jacob,

I got the RPO code wrong. I jokingly say the best RS ever made, because it's a TBI, like the RS and has the factory 15" Z28 wheels, like the RS. But I have the steering box, wonderbar and suspension of the IROC.

My username is in memeory of my old 87 IROC
(TPI 5speed) which was an ex-players race car. IF the 1LE option had existed in 87, mine would've had it. I'll change my sig though

------------------
88 IROC the best RS ever made!
well except for the BC4s

 

B4C Jacob,

I got the RPO code wrong. I jokingly say the best RS ever made, because it's a TBI, like the RS and has the factory 15" Z28 wheels, like the RS. But I have the steering box, wonderbar and suspension of the IROC.

My username is in memeory of my old 87 IROC
(TPI 5speed) which was an ex-players race car. IF the 1LE option had existed in 87, mine would've had it. I'll change my sig though

------------------
88 IROC the best RS ever made!
well except for the BC4s

 

well I was just pointing that out a lot of guys on here would rip a newguy a new a$$ for something like that. and Im not saying that SD is better then MAF but I just favor SD to MAF 1. cus I have it 2. with not having a MAF sensor i will never have to replace one (saves some $$$) any how I was just trying to help out. I know that the SD cars run of mostly map sensor But it does take more then that to work the system. I had a Bad coolent temp sensor and my car wouldnt start with out using the gas even then it would idle at like 450 thats how big a differance one sensor can make

------------------
Ya sure it is just an RS

B4Cyaa

1991 RS B4C
Former Nebraska Highway Patrol Car 1 of 3
305 TPI
WC T-5
Four Wheel Disk Brakes
Only Options
Rear Defrost
Am-Fm Radio
Red-int White-exe
One BA Of A 350 In The Works
Mods
Dynomax Cat Back (to hold me over till I got the $$$ for the Borla)
best 1/4mile Run of 14.92@94.83
with 145,000 on her