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Discussion Starter · #1 ·
While I've been on and off about getting a system together to datalog my gm/sec so that I could figure out my exact VE, I stumbled onto some worthwhile data.

A 231 CID engine at 3,000 RPM at 100% VE is going to pump 201 gm/sec..

After looking at some misc data logs with DS, I saw a run that had 244 gm/sec at 3,000. Which means that combo, at 3,000 RPM was at 121% VE.

At 5,000 RPM one needs to be moving 335 gm/sec to achieve 100% VE.
 

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Doc1of7 said:
While I've been on and off about getting a system together to datalog my gm/sec so that I could figure out my exact VE, I stumbled onto some worthwhile data.

A 231 CID engine at 3,000 RPM at 100% VE is going to pump 201 gm/sec..

After looking at some misc data logs with DS, I saw a run that had 244 gm/sec at 3,000. Which means that combo, at 3,000 RPM was at 121% VE.

At 5,000 RPM one needs to be moving 335 gm/sec to achieve 100% VE.
Doc,
your figures just happen to match cfm. Does 1 gram/sec=1 cfm then?

cu in x rpm x %ve (100%=1.00, 80%=.8,etc), divided by 3456=cfm
 

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Discussion Starter · #3 ·
Let's try this again:
(and showing the math)

From:
http://www.sy-klone.com/support/CFM_conversion/index.html
200 CFM = 6.45 KG/Min
200 CFM = 6,450 gm/min
200 CFM = 107.5 gm/sec
1 CFM = .5375 gm/sec

231 CID engine at 4,500 RPM
116 x 4,500 = 522000
522,000/1728 = 302.8 CFM
302.8 x .5375 = gm/sec

302.8 CFM = 162 gm/sec (100% VE)

Several data logs that show ~255 gm/sec at about ~4,400 RPM

255/162 = 157% VE
 

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Doc1of7 said:
Let's try this again:
(and showing the math)

From:
http://www.sy-klone.com/support/CFM_conversion/index.html
200 CFM = 6.45 KG/Min
200 CFM = 6,450 gm/min
200 CFM = 107.5 gm/sec
1 CFM = .5375 gm/sec

231 CID engine at 4,500 RPM
116 x 4,500 = 522000
522,000/1728 = 302.8 CFM
302.8 x .5375 = gm/sec

302.8 CFM = 162 gm/sec (100% VE)

Several data logs that show ~255 gm/sec at about ~4,400 RPM

255/162 = 157% VE
302.8 cfm is correct for 232 cu in. 231cu in x 4500rpm x 1.0/3456=300.78 cfm

don't know about grams, its why I asked. My initial question is answered-
"1 CFM = .5375 gm/sec"
correct?
 

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Doc, follow me, find holes.

Oem computer/maf will max out at 255 gr/sec.
255/.5375=474.4 cfm, right?
474.4 cfm at 1 atmosphere (n/a), so in effect it would be-turbo'd ve x 474.4
I will assume/guess 160% ve, or 1.6 x 474.4=759 cfm
759/2.1=361.4 hp @ 0 vacuum/pressure (increased ve is represented in the 759 figure). 2.1 cfm is the amt of air required for one hp @ sea level/0 depression.

I could calculate the cfm @ a given vacuum between the maf and turbo, but it's not relevent to my point.

If these cars make the obvious power they do, w/stock maf, how does the computer calibrate beyond the limits of the maf (neighborhood 365hp)?

There has to be something I'm missing. I'm going to bed.
 

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Discussion Starter · #6 ·
wmsonta said:
If these cars make the obvious power they do, w/stock maf, how does the computer calibrate beyond the limits of the maf (neighborhood 365hp)?
It doesn't.
The code pegs at 255, that's all it can read to.

But, you can trash the calibration of the MAF, so that it just pegs at 255, and generates a given PW/ DC (for a given amount of HP), or adjust, the TPS/ RPM, PE % enrichment settings, so that you have the right amount of fuel for whatever HP you're making.

Clearer...
 

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Yeah, what Bruce said. The stock MAF calibration was/is good for the stock horsepower, plus a little. Beyond that, you don't measure the air flow, you just add fuel and up the boost. In "the old days", you did that by trial and error, watching the O2 readings and the knock gauge, while raising boost and fuel pressure. (and keeping your fingers crossed) Now, there are lots of tricks that let you measure the air flow at levels way beyond stock, or at least control fueling with more logic.
 

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To the both of you, thanks for the replies.

My reasoning was flawed. Doc is right on-255gr/sec is the max. After about 230-240hp the maf has to come out of the calibration. Actually both of you are right.

So, the maf is not necessarily a restriction, but cannot be used for fuel tables.

I think the next time I travel to the flow bench, I'll have my maf flowed. Or has somebody already been there/done that.

Follow me again. After stock hp the fuel curve is an educated guess. Spark would be set to boost, hence the different levels of street chips. Aftrmrkt systems (FAST, etc), because of their higher capacity can use direct feedback for fuel/spark, etc?
 

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Discussion Starter · #9 ·
wmsonta said:
So, the maf is not necessarily a restriction, but cannot be used for fuel tables.

I think the next time I travel to the flow bench, I'll have my maf flowed. Or has somebody already been there/done that.

After stock hp the fuel curve is an educated guess.

Spark would be set to boost, hence the different levels of street chips. Aftrmrkt systems (FAST, etc), because of their higher capacity can use direct feedback for fuel/spark, etc?
Years ago, Mike Pitts ran some dyno tests when the first Felpro ecms were in the works, and he found a 30 HP lose with the stock MAF in the system. He was running the two systems back to back for HP comparisons.

It's been done, and the results posted. The Airflow reporting of the stock MAF, is very close to right. The *error* seems to be an attempt to allow for some *leakage* from the PCV system. A search for GNJones231, and MAF might get you the posting about it (I'm not for sure on the name).

Some guesses, are pretty educated, and some guys have A LOT of experience behind them about what their car likes.

It's all about resolution/ granularity of the code....
The finer the it is, the closer you can taylor the fuel and spark. In an effort to make them user friendly a lot of the aftermarket ecms, fall short of what they could do resolution wise. I'll admit to being kind of a nut on ecm code.. I've spent a lot of time (with a friend of mine) rewritting the TR code to operate as I want it to. The stock stuff, basically, is really good stuff.

It's all rather moot now, with the MAFTPRO being available. It eliminates the MAF, and converts the system to being MAP based.
 

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Thanks.
 

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ive been reading this thread for 2 days and still am lost lol
 

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Doc1of7 said:
Years ago, Mike Pitts ran some dyno tests when the first Felpro ecms were in the works, and he found a 30 HP lose with the stock MAF in the system. He was running the two systems back to back for HP comparisons.

It's been done, and the results posted. The Airflow reporting of the stock MAF, is very close to right. The *error* seems to be an attempt to allow for some *leakage* from the PCV system. A search for GNJones231, and MAF might get you the posting about it (I'm not for sure on the name).

.
Doc,
I just finished your recommended searches, M. Pitts evidently did not post on this board. I am however contemplating a new direction with my meek/oem gn. When my "to do" list gets to GN, I expect to bear resemblance to the ChrisGarret of old.

The GNJones231 search was great, as carbs really cannot compete today in my preferred discipline. I want to take the time to thank you again.

Given your .5375gm/sec=1cfm, I am off to determine the max measurable airflow of the LT1/LS1 maf's.
 

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Discussion Starter · #13 ·
wmsonta said:
Doc,
I just finished your recommended searches, M. Pitts evidently did not post on this board. I am however contemplating a new direction with my meek/oem gn.

Given your .5375gm/sec=1cfm, I am off to determine the max measurable airflow of the LT1/LS1 maf's.
Sorry, it was at GNTtype.

The ZO6 MAF is good for 505 HP, in oem form. I'd guess, there's still a lil on the table. That's to the *stage* of running 32 PSI on a 3 bar sensor, IMO.

Nothing *meek* about the oem ecm. It's just a matter of what you're willing to do to optimise it. If you really study it, the aftermarket guys are still chasing GM, the most they can offer is ease of tuning, at the expense of *cruder* code. As the aftermarkets evolve they'll be getting more and more oem like.
 

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Discussion Starter · #14 ·
ajt86 said:
ive been reading this thread for 2 days and still am lost lol
Ask some guestions...

VE, is the actual airflow though an engine as compared to what the engine would normally pump, with 100% cylinder filling. So the most basic part of this thread, is that with the engine being a 4 stroke it takes 2 engine revolutions to pump all the air that an engine can. So to look at the original math:

231 CID engine at 4,500 RPM
116 (CID) x 4,500 (RPM) = 522000 (cubic inches of air)
1 cu. ft. of air = 1728 cu. in.
522,000/1728 = 302.8 CFM

Is that any help?.
 

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Doc1of7 said:
Sorry, it was at GNTtype.

The ZO6 MAF is good for 505 HP, in oem form. I'd guess, there's still a lil on the table. That's to the *stage* of running 32 PSI on a 3 bar sensor, IMO.

Nothing *meek* about the oem ecm. It's just a matter of what you're willing to do to optimise it. If you really study it, the aftermarket guys are still chasing GM, the most they can offer is ease of tuning, at the expense of *cruder* code. As the aftermarkets evolve they'll be getting more and more oem like.
My CAR is meek/oem and will stay that way. I am, however, daydreaming about closed loop timing/fuel up to/including WOT.
 

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Doc,
If I used a larger maf than my car could max out, I should be able to closed loop tailor the fuel map all the way/including WOT?
 

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Discussion Starter · #17 ·
wmsonta said:
Doc,
If I used a larger maf than my car could max out, I should be able to closed loop tailor the fuel map all the way/including WOT?
One of the problems with big MAFs is that they get really bad at reading low airflows. One of the *rumored* problems with the Raptor set-up, was a poor idle. Yes, it can be done, ie using various AFRs at various loads and RPM in closed loop. What would be *nice* is using a NB, and WB, then in the Stoich areas, having one sensor to double check the other. That way if one is going out the other would catch it. Using one sensor for WOT IMO, is kinda scarey, at least with the 2 sensor set up you're somewhat sure about things being OK.

One other concept you might think about is using the boost sensing harness, and then using the MAF, and timing IAT tables, use the MAP input to correct the timing, and MAF. Or better yet, use a Translator, and then the boost sensing deal, the late MAFs already have their own temp compensation in them.

Hmm, but then again, all this will mess with the LV8 calculation, and you'll have to play with it's *scalar*. (Timing is based on LV8, not gm/sec).
 

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Doc1of7 said:
One of the problems with big MAFs is that they get really bad at reading low airflows. One of the *rumored* problems with the Raptor set-up, was a poor idle. Yes, it can be done, ie using various AFRs at various loads and RPM in closed loop. What would be *nice* is using a NB, and WB, then in the Stoich areas, having one sensor to double check the other. That way if one is going out the other would catch it. Using one sensor for WOT IMO, is kinda scarey, at least with the 2 sensor set up you're somewhat sure about things being OK.

One other concept you might think about is using the boost sensing harness, and then using the MAF, and timing IAT tables, use the MAP input to correct the timing, and MAF. Or better yet, use a Translator, and then the boost sensing deal, the late MAFs already have their own temp compensation in them.

Hmm, but then again, all this will mess with the LV8 calculation, and you'll have to play with it's *scalar*. (Timing is based on LV8, not gm/sec).
After reading twice, I got a large part of it. Based on your gm/sec=cfm, i'm allowed to calculate, I would only need a maf w/335 gm/sec capability. I don't expect my gn to make 300hp. Oem @approx 15#.

I would have to hire the programing(sp). I don't know if I could trust a narrow band O2 @ WOT. I have never used a wide band for closed loop part throttle.

When this daydream gets labor intensive I should pass it up. Their are no schedules/goals for the gn,

Thanks again Doc.
 

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hey doc

thanks so much for explaining- never really thought about it. :cheers:

ill just sit back and read and soak it in and ask some questions after im done reading all the posts- thanks again doc and wmsonta
 

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Here's a graph of some VE data I took over 10 years ago on my pretty much stock 87 GN. The only mods are an upgraded fuel pump, a catless Hooker exhaust, and alky injection. The data is taken with a one of a kind synchronous
data logger I made a long time ago that reads the sensors direct at a maximum rate of about 500 samples/second. Hope this helps...

Dave
 
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