I'm in the process of reading up on chip burning in order to burn my own chips. For my set up below, I had a local tuner burn a chip after hours on a chassis dyno. The motor, according to the dyno puts out 327 rwhp and 405 rwtq. Reality is, the best trap speed I've been able to get is about 108mph. I know I'm not getting what I should be getting out of this setup. In the process of looking at scan from my EASE scanner, I noticed that the MAF at around 5200 rpm is reading about 227 gm/s.(this is a TPIS ported, screen and heat sink removed unit) I read elsewhere that with the bigger cubes of the 383, I should be maxing out the the MAF. Since we all know a motor is an air pump, it seems obvious to me I need more air to be flowing.

Assuming that there is no blockage before the MAF, any ideas?

Thanks in advance.

 

Once you tamper with the MAF, it's calibration goes to hades.

If you know your max reading is 208 then just make your sure your calibration reflects that.

You have two choices on a serious motor,
Speed Density.
or
Speed Density.

What folks ignore is that the calibration of the MAF to ecm isn't linear. There are dips and valleys, and when you change the characterists of the MAF, all that changes as well.

Change the cam, or most any part of the engines breathing and you change the reversion characteristics, and the MAF needs to see that change calibration wise, if you want it to be correct.

 

Thanks Grumpy. I suppose I should try another MAF just in case. I'll have to consider the SD conversion.

 

MAP sensors are a lot cheaper and seem to be more reliable than MAF sensors. In fact, I seldom hear of a MAP sensor "going" and when you consider the number of TBI cars and trucks using MAP sensors, it kind of suggests it's reliability.

Also, you can probably use any GM 1 Bar MAP sensor for the conversion from a wrecking yard (the one on my Buddy's GMC Van was identical to my TPI car when we "swapped them" to test the MAP sensor...which turned out fine). The SD ECM is easily obtained from an early 90s 3.1 V6 Sunbird/Cavalier. Around here, the wrecking yards tend to charge the same price as the "core charge" the GM dealership charges for a new ECM (i.e. dirt cheap).

Then, you'll never have to worry about that silly MAF sensor again. Tuning VE tables is a LOT easier than most people think. And more intuitive IMO. I've worked on both MAF and SD systems and the moment you need to "touch" those MAF Scalar Tables (espcially the "upper boundary"), you really appreciate SD.

In all honesty, I spend MOST of my tuning efforts on spark anyway, regardless of MAF or SD. Fuel was/is actually a minor part. And if you get/make a WB O2 Sensor, "WOT" is a dream.

 

How did you figure out that you should be maxing the MAF? If you have the equations, please post them? I have never heard of this.
Thanks,
J

 

Thanks for he info Glenn.

Junk- It has been discussed here many times particularly with regards to the debate about the merits of Mass Air vs. Speed density. I have heard instances of people with set ups similar to mine hitting the max 255 gm/s limitation in the mid 4k rpm.

 

I've seen some guys peg em at 2,800 rpm.

 

Experience with a variety of setups. But, there is no "hard and fast" calculation because it all depends on airflow characteristics of the engine (and the MAF sensor itself - screw with the screen/heat sink affects the signal for a given flow).

Generally, the bigger the engine, the quicker you'll max the MAF. The more air the engine can flow, the quicker it'll max the MAF. Also, with TPI, if they CAN max the MAF, they will do it at lower rpms (because that's where they emphasize the air flow) than say a Miniram.

Minirams (which are "non-tuned") make it quite easy to predict at what RPM you are likely to max the MAF due to the linear nature of the airflow (compared to a TPI setup). I have a buddy with a 383 MAF Miniram and while he was "breaking his engine in", we noticed he was running 150 gm/sec @ 3,000 rpm. I predicted he would max the MAF around 5,000 rpm (3,000*255/150).

When he actually had his engine "broken in", we monitored his "WOT" run and maxed the MAF at 4,800 rpm (which would be consistent with the Miniram's greater efficiency at higher rpms).

 

Thanks for the info. Sounds like an opinion thing. Here is my opinion........your engine isn't large enough to max. out the MAF. You should be happy about this cause it means less work on your part.
J

 

Junk, it's definietely NOT an opinion. I have yet to see a well tuned 383 NOT max the MAF (they've all been 350+ HP). If one was to take the time to "do some figuring" they would find there's a direct correlation between the air consumed and the MAF.

But you are asking for a "formula" and, quite simply, no one has bothered to work one. Personally, it has no value to me (I'm already SD). I've already given a specific method of using an engines existing rpm/MAF readings to predict when a particular engine setup is going to max the MAF. This is generally how I "prove" that a new engine is likely to "max the MAF" and to allow a person to consider "alternatives".

But, since you are "keen" on some "formula", I will give you a hint. There is a relationship between air consumed and the MAF readings (provided you haven't "fubared" it or altered its relationship between airflow/voltage). And there is a relationship between air, gasoline and HP - someone so WANTING such a formula can easily derive one based on HP. Besides, HP is more useful for a person wanting to determine when they've maxed the MAF. But to obtain a certain HP, an engine MUST flow a certain minimum amount of air and gasoline.

Based on some of the engines I have played with, I think you'd be surprised how low of an HP level it is.

Just remember that if a person "alters the MAF" by gutting it, etc; they've altered the relationship between air consumed (HP generated) and Voltage of the MAF.

 

I have recieved my programmer yesterday and cant wait to start
tuning. I want to play around w/my MAF system for a while but
want to convert to SD some time this year.
I have read that you can get a 730 ecm from early 90s 3.1 cars
can someone tell me how hard it is to change the harness?
or do i splice my harness?
any/all info appreciated.

 

Glenn,
I understand what you are saying. It is like choosing a carb for an engine. One guy says 650 DP another says 750 DP. Who is right? The guy that has built more higher horsepower engines? Yes, there are equations. But they are really only for steady state flow, not for transients.
It sounded to me like the original post was saying something kind of like.....my motor should make more horsepower, but it isn't, and my maf is this.....
I think we all agree his MAF and ECM are out of tune due to the MAF mods. He could do a good tune on the MAF tables and other ECM stuff. But since he already knows that his engine maxes the MAF then why bother and just convert to SD.
Anyway, I am not really looking for some equation. I just ask that if he had it, please post.
Since it is not recommended to use a CAL tuned for one ECM in another ECM, then why do some people compare their peak horsepower ratings to other people's engine figures?
J

 

People (generally) figure that an engine making more HP MUST be faster than another engine. But this is not always true. The TPI is a great examplle with it's emphasised low-end TQ and low HP rating.

A lot of the dyno graphs posted by guys who have built some quick TPIs always show the same thing - a TON of low-end TQ but once their RPMs get aroudnd 4,500 rpm, their HP curve flattens like the Nebraska horizon.

Yet, that TPI motor is quicker than most cars with a similar HP/Weght. In reality, it's the TQ that got the TPI car moving. But, HP is the "yardstick" that everyone quotes to indicate an engine's potential performance. Just like a lot of guys will quote their pecker size to indicate their potential performance in love-making.

Interestingly, both are usually exaggerated.

 

That is funny. It is true though. So again, how can this guy figure that he should be maxing out the MAF?
J

 

Junk,

I assume I should max out the sensor because everyone else with a superammed 383 that I've ever seen post about this hits the 255 gm/s mark below the 5000 rpm mark. Now if the modifications to the MAF are what's causing the lower readings, I'll need to get another MAF. The AMF is a TPIS ununit with the screens and cooling fins removed. On top of that, it has at least 70k miles on it.

It's true that I feel I'm not making enough power on this combo. That's the whole point for the question in the first place. My setup is not putting out the power it should.


One question for everybody is - do I stay with a stock bosch unit or by the Wells replacement?

Thanks to all for the great feedback.
Glenn S.

 

Thought I would chime in here. Ported MAF and 383 cubes of fury huh...... I would guess that the stock unit was engineered with the cylindrical volume minus the heat sink volume in mind. With it ported wouldn't you have just increased the avaliable volume and therefore tricked the sensor into thinking that its seeing only a certain amount of air go by when there is a lot more going by due to the larger volume?

I wonder if it would be possible for some guru somewhere to re-write some sort of source code so that the MAF doesn't max out at 255g/s. Well... unless there is some inherent limit to an MAF sensor I guess.

Another thing you might want to do is make a custom intake system where the ribbed bellows are removed and a smooth, aluminum maybe for heat dissipation, tube is used. Also... I assume you are using the same intake as I am... the 2 Filter air-box. Have you cut out the bottoms of the filter holders or at least taken out the fins in there? You may be chokeing your engine instead of having a MAF problem.

Guess I brought up more questions than answers.

BTW, not everything can be done with tuning guys, some things ARE mechanical lol!