FDNewbie

iTrader: (10)

Heath, that was slick hehe. Made me smile

FDNewbie

iTrader: (10)

I spoke w/ Steve Khan about this for a bit the other day, and while he told me there are obvious benifits, it looks like it's quite some tricky...and he also told me something I didn't like at all...that in virtually all MAFs, you have a 15% hp loss due to restriction...he said that held true even when you get larger MAFs, simply because of the design (the heated rod being in the middle), and hence, that's why Mazda Japan switched back from MAF to the SD system when they made the 3rd gen. Looks like my hot idea in theory isn't so hot in action...

su_maverick

oh well, ya live ya learn....

jimlab

I have a lot of respect for Steve, but not when he says things like that, if he did indeed say it.

RotorMotor

iTrader: (5)

yeah i find that hard to believe.... 15% loss from the restriction of a wire? he must have ment with the conical ones.

jimlab

If that's the case, then BPU Supras would see a huge jump in power just by switching to the HKS VPC and eliminating the MAF sensor... but they don't. Any gains they get from that mod come from the single turbo that usually accompanies it or from the rudimentary fuel tuning, since stock twin Supras run very rich as a rule.

Most people don't know it, but during the time that my V8 project has been in progress I've owned several other cars, including a BPU+ Supra that I even went so far as buying a Pro Torque converter, RPS T64 single kit, HKS VPC, HKS FMIC, and injectors for before changing my mind, selling everything, and buying the Z06. I came this || close to being one of the 600+ RWHP Supra guys.

FDNewbie

iTrader: (10)

Well maybe I misunderstood him...maybe it's 15hp....I dunno, since I regard Steve one of those guys who really know what they're talkin about... So it's prob. something mixed up on my part.

RotorMotor

iTrader: (5)

jim, my grandma has a saying... "**** or get off the pot" i think it applies to you

jimlab

I thought you were going to say something about more money than sense.

J.S.J

I am thinking the map is there as a back up and for barometric pressure. This would truely be a nice set up. The complacated part surely would be programing. God knows if it were easy it would be out there. What does the Rx8 use? Surely its maf.

bureau_c

The RX-8 uses a MAF, which everyone who wants to go forced induction is bitching about. The thing (at least in the 8) appears to have a lot of variability in output that makes the car difficult to tune, and it has also proven to be susceptible to problems (presumably changes in airflow characteristics) caused by simply changing intakes.

jds

jimlab

That's the RX-8's stock EMS you're talking about, not an aftermarket EMS. Why should we care what limitations the RX-8 has?

The Lingenfelter twin turbo package for the C5 makes 750+ horsepower (with the aid of 427 CID) through a MAF-based EMS. The Halltech twin turbo package for the Z06 makes 625+ horsepower through the stock MAF-based EMS on a stock engine. MAF sensors are not the limiting factor, obviously.

bureau_c

Merely answering a question from earlier in the thread and pointing out something I found ironic.

Out of curiosity, the Haltech Z06 setup that uses the stock MAF...do they have to add a MAP sensor as well? I'm curious how they adapt a MAF based on the stock airflow characteristics (I'm assuming they use a decent chunk of the stock output range of the sensor to cover the stock min and max expected airflow) to the drastically increased airflow of a turbo system. This is probably obvious, but its come up time and again in another discussion on the RX-8 board, I'm not sure how its generally dealt with.

jds

jimlab

No. To my knowledge, all MAF-based systems also have a MAP sensor, even for naturally aspirated applications.

Kento

The biggest disadvantage with MAF sensors is that they respond best to smooth, even airflow. The sensor unit needs to be placed in an intake tract area where it is less likely to get large, quick variations in airflow, and/or be used in engine applications where it won't encounter these types of intake airflow situations beyond its capabilities. Which means that at very light throttle cruising rpms where the turbos aren't creating boost, intake fluctuations can give it fits. This is why they're often placed in front of big intake plenums or some sort of intake chamber, so that the sensor is physically isolated from the actual air that's entering the cylinders. Also, the more cylinders you have, the more even the airflow in the intake plenum will be through the cross-section of the intake runner, which is why they apparently work well with the Lingenfelter C5 and Halltech Z06 applications.

However, I'm not sure how a small engine like the 13B-REW would be with regards to intake fluctuations, even with the turbos in the intake tract. Which may be the reason why Mazda decided to go with MAP instead.

jimlab

In a forced induction application, the MAF sensor is totally isolated from the engine and intake plenum, because it is mounted on the non-pressurized side of the turbos or supercharger. Fluctuations in pressure level (on/off boost, etc.) would not affect it.

Kento

Note that I said "even with the turbos in the intake tract." Fluctuations in pressure level really don't matter; it's any rapid fluctuations in airflow. Simpy being mounted on the non-pressurized side of the turbos doesn't necessarily isolate it from any and all rapid intake airflow fluctuations. While a turbo certainly blocks most intake fluctuations, the seal on the turbine blades isn't airtight. You need to ensure that the airflow through the whole plenum where the sensor is located is consistent.

I'm not saying it can't be done. Just offering up a possible explanation why the FD doesn't use a MAF-based system.

jimlab

And I'm poking holes in your explanation.

MAF sensors work just fine on other turbo-equipped cars like the 300ZX and Supra. In my opinion, Mazda did it to save a buck, nothing more. They had a car that was already going to be high priced because of the extremes they went to in order to reduce weight, and they cut corners in places they probably should not have.

Kento

Well, I'd have to agree with you there.

DaleClark

iTrader: (55)

The 2nd gen RX-7's had MAP sensors, but they're basically the vacuum advance for the timing. Many non-turbo cars with MAF sensors don't have a pressure sensor of any kind. If they do, it's a internal pressure sensor on the ECU for barometric pressure - nothing with a vacuum line running to it.

Dale

DaleClark

iTrader: (55)

Mazda's supplier for the '8s hotwire MAF seems to have some variation in quality control - some are leaner, some are richer. But, it still should be able to be tuned out with an E-manage or the like. I know Greddy's putting the final touches on their '8 turbo kit, which uses an E-manage for fuelling.

I believe a lot of the problems from people putting on intakes stems from small vacuum leaks - even a tiny vacuum leak with a MAF will cause driveability problems. But, that is a factor.

Dale

jimlab

I was talking about modern cars...

XxJMF02xX

2 things. One the speed density system is not as precise as the MAF system but it instantly responds. Air that passes the MAF sensor takes time to reach the engine by then the throttle plate may have closed but in speed density system the pressure changes almost instantly resulting in less time difference between when the change in airflow occurs and when the ecu figures it out. So the speed density system would actually respond to sudden changes like boost spikes better.

The second thing is the MAF sensor is an obstruction in the airflow, allbeit a small one. For this reason there are conversion kits for Hondas and the like to convert to the speed density system. I've heard of people converting from MAF to speed density but never the other way around. I guess the grass is always greener though right.

XxJMF02xX

sorry repost

jimlab

Do you have any proof of that, or did it just sound good at the time?