Improving the hacked maf theory!

[Steeliez]

I was driving home a couple nights ago and had this weird revelation...

Ever wonder why the theoretical pipe diameters for hacked mafs ran so lean when you straped them on the car? Its not because a hacked maf is inaccurate, its because we are rediculously unobservant...

The actual maf sample tube is an obstruction of the flow at the exact point where the air is being metered....thus, the area of the obstruction that is caused by the sample tube should be subtracted from the area that you wish to change by a factor of 370/270.

If this is not done, then what you basically do is assume that the obstruction that counters the original maf's flow will increase in size by a factor of 370/270 as well, but this is not the case! The Maf sample tube does not change size, so it shold be removed from the equation all togather. What you REALLY want to change by a factor of 370/270 is the area around the maf sample tube in the pipe. so in order to compensate for the unchanging obstruction value... we must change the equation a little bit:

2(sqrt(370/270((pi x radius of original maf^2)-A)+A)/pi)= new ID (in inches) of new maf pipe!

Where A = the area of the obstruction of the maf-sample tube.

To the best I can measure, the A value is ~1.25 sqare inches. Thats probably only accurate to the 1's place honestly...but using that as the assumed obstruciton area, you get a theoretical value of about 2.767" ID. Better Measurement of the sample tube will yeild a more accurate pipe size, but the math is no longer flawed at least! Also note that this will yeild a stock n/a afr, which is going to be a bit too lean for anyone who isnt running alky/H2O injection on a turbo setup(hence why orion had to bumb up ihs Base Fuel pressure to get into ~12:1 afr's...stock maps dont generally make 12:1 afr's to my knowledge) ...but we can richen it up mathematically as well and get a theoretical pipe size afterwards. Its an exciting time to be a maf hacker

[Nismo_Freak]

Sounds fun and all, but then again Z MAFs are so expensive these days compared to engines.

[D Money]

maxima mafs are the same size as 300zx mafs and plentiful at junkyards

[MarkEmark]

I was driving home a couple nights ago and had this weird revelation...

Ever wonder why the theoretical pipe diameters for hacked mafs ran so lean when you straped them on the car? Its not because a hacked maf is inaccurate, its because we are rediculously unobservant...

The actual maf sample tube is an obstruction of the flow at the exact point where the air is being metered....thus, the area of the obstruction that is caused by the sample tube should be subtracted from the area that you wish to change by a factor of 370/270.

If this is not done, then what you basically do is assume that the obstruction that counters the original maf's flow will increase in size by a factor of 370/270 as well, but this is not the case! The Maf sample tube does not change size, so it shold be removed from the equation all togather. What you REALLY want to change by a factor of 370/270 is the area around the maf sample tube in the pipe. so in order to compensate for the unchanging obstruction value... we must change the equation a little bit:

2(sqrt(370/270((pi x radius of original maf^2)-A)+A)/pi)= new ID (in inches) of new maf pipe!

Where A = the area of the obstruction of the maf-sample tube.

To the best I can measure, the A value is ~1.25 sqare inches. Thats probably only accurate to the 1's place honestly...but using that as the assumed obstruciton area, you get a theoretical value of about 2.767" ID. Better Measurement of the sample tube will yeild a more accurate pipe size, but the math is no longer flawed at least! Also note that this will yeild a stock n/a afr, which is going to be a bit too lean for anyone who isnt running alky/H2O injection on a turbo setup(hence why orion had to bumb up ihs Base Fuel pressure to get into ~12:1 afr's...stock maps dont generally make 12:1 afr's to my knowledge) ...but we can richen it up mathematically as well and get a theoretical pipe size afterwards. Its an exciting time to be a maf hacker

Looks like we gots one of them there thinkers on our hand

Good observation/contribution, esp for a n00b!!!!

[Steeliez]

Sounds fun and all, but then again Z MAFs are so expensive these days compared to engines.

True that... But if we were to get to the point that the hacked maf was bulletproof(assuming thats possible ), then made a writeup that even a MORON could follow...that would be an awsome tool for the intermediate modder. Its cheaper and has a better fuel curve than an rrfpr and its ALOT easier on the injectors... cant be all bad right? Then again, there could be some fatal flaw in the hacked maf doctrine...but who knows untill we try it, right? Its the hacker's way!

Im about to do a little testing with a wideband once I figure out how the damn thing works....sounds retarded, but I cant plug the bosch lsm11 or whatever into the plug on the back...yet its the only O2 sensor that works with the fool thing...fancy that! Just gotta do some slodering, but I need to find a pinout first. I guess I could take a multimeter to it, but its a DAMN nice WBO2, Id hate to screw it up... Anywho, Ill be back with results soon hopefully!

Thanks for your support guys, there are some cynical bastards out there on other forums and Im just glad you guys are willing to conside a new idea before handing me my *** on a platter for trying to make something work... : sorry.

[Steeliez]

The math gets long and drawn out, so Ive only done it for Ideal ratio: 14.7:1. That corrosponds to a 6.36943% concentratoin of gasoline in the cylinder. Assuming that we are somehow able to get EXACTLY (+or- 1% of the crosssectional area or so) the right size maf-pipe, then we can follow the stock fuel map until you hit boost. Then, our nifty fpr raises fuel pressure 1:1. So at say, 8 psi, that would raise fuel pressure to 51psi (43 + 8) Following the flow equation :

newflow=oldflow x sqrt(newpressure/oldpressure)

where you hit 8 psi, then your 370cc injectors will act like ~403cc/min injectors because of the pressure increase. because the fuel cocentration in the cylinder and the injector's capacity are directly proportional to eachother, we can set up a nifty ratio! turns out that (6.36943% gas conc.) / (370cc/min) = (6.93751%)/ (403cc/min). 6.93751% corrosponds to a 13.41:1 ratio@ 8 psi where the stock map would put it at 14.7:1. Does anyone know about what the stock fuel maps put the afr at @ about 3000 rpms? If anyone has a AFR graph from a stock engine, Id love to see it. Couldnt find one when I seached..

A 12.5:1 afr corrosponds to a 7.41% concentration. You would need you 370cc/min injectors to pump out 430.4 cc/min to get that kind of ratio. That corrosponds to a fuel pressure of 58.2 psi. (This is all relative to a 14.7:1 afr on the stock curve again). So, 58.2 psi-the 8 psi that the fpr will account for ar 8 psi boost give you a new base FP of 51.8 psi, which, again, will yeild about a 13.4:1 afr.

SO! with the idea maf size of 2.767" ID, you would theoretically need to bump your fuel pressure up to aobut 51-52 to get a remotely safe afr (12.5) once you hit boost.

These numbers seem to be RIGHT in line with the results of orion's old setup at 8 psi. " I used 2.75" ID with more fuel pressure to tune it to high-11 A/Fs. ~54psi base pressure"(zerothread?id=78124)

His pipe is for all practical purposes the exact theoretical size, only, he is tuning to high 11's (lets assume 11.75:1) instead of 12.5:1. Thats a 7.843% concentration...That would corrospond to a 65 psi fuel pressure...at 8 psi, the frp would raise it by 8, so his base would need to be set at right about 57 psi. The 3 psi differance likely is due the the fact that the AFR on the stock curve is a little richer than 14.7 where he gets full boost of 8 psi.

Id say were getting closer! a 3 psi fuel pressure margin of error is way cooler than an unexplained .1" ID differance! It will be alot easier to prove with a good afr graph of a stock ka... but its a good start! Plus, that 2.767" ID is pending on a better measure of the A value described above...and although its not much at all, the .017" differance makes a almost noticable differance in the math once you realize that it makes a ~.31 square in differance in crosssectional area... GOOD TIMES TO COME! SORRY for the long post...just excited.

[95_240sx]

Wow...I have a headache now.

I love my standalone

Rick

[Nismo_Freak]

maxima mafs are the same size as 300zx mafs and plentiful at junkyards

And resolute half the power.

[Nismo_Freak]

Wow...I have a headache now.

I love my standalone

Rick

You're such a noob, doing things the correct way is teh ghey in the KA-T community!

[:: orion ::]

...then we can follow the stock fuel map until you hit boost. Then, our nifty fpr raises fuel pressure 1:1. So at say, 8 psi, that would raise fuel pressure to 51psi (43 + 8) Following the flow equation :

...

where you hit 8 psi, then your 370cc injectors will act like ~403cc/min injectors because of the pressure increase.

...

SO! with the idea maf size of 2.767" ID, you would theoretically need to bump your fuel pressure up to aobut 51-52 to get a remotely safe afr (12.5) once you hit boost.

These numbers seem to be RIGHT in line with the results of orion's old setup at 8 psi. " I used 2.75" ID with more fuel pressure to tune it to high-11 A/Fs. ~54psi base pressure"(zerothread?id=78124)

Couple things here....

1) A+ for effort...we only learn new things as we dream them up and try them out.

2) The math in that last post of your, and the 1st (concerning the size) is convenient that the #s work, but not 100% correct for the reasons stated - FOr example:

We run a 1:1 regulator becuase you have to increase fuel pressure under boost (or decrease it under vacuum) b/c the PRESSURE DIFFERENTIAL across the tip of the injector needs to remain the same for flow to be constant...so where you're saying that at 8psi our 370cc injector flows like a 403cc...is wrong. It flows 370cc, thanks to the nifty 1:1 FPR.

8psi more fuel pressure is needed b/c the injector is trying to spray fuel into a PRESSURIZED intake manifold...so we needs 8 more pounds of fuel pressure to overcome the intake manifold pressure and make the injector still flow the rated 370cc...if we had no 1:1 on there, it would flow LESS...so the increase in fuel pressure does not increase flow...it makes sure flow is CONSTANT.

...

Now, with respect to the size...

While the numbers work out conveniently, it's not that cut-n-dried in the application.

I has to make a shim to decrease the ID of the MAF and add fuel pressure...that "tuned" it for WOT only...I ran rich at idle and under cruising. Since the MAFs voltage curve is NOT linear, we can't determine the exact size needed.

I can tell you that if you use a 2.6" ID MAF, it probably won't blow the motor...and 2.875" is too lean - That's about as exact as we can get.

One pipe size will NOT get you good cruising A/Fs AND proper A/F at WOT...this is a crude, compromised tuning solution...and won't be perfected.

So, like I said...the thinking here is good, but theory and actual application are quite different.

To determine anything, we need to test and test some more...we need empirical evidence. I've provided enough starting point to get a KA-T running cheaply...it's up to you guys to try it out, report your results...then after a bunch of guys come back with results, we can look for trends.

- Brian

[Steeliez]

That is a damn good point... I never considered the fact that the injectors would have to have proportionally he same pressure to deliver the same amt of fuel. It all makes since why the fpr is stock equiptment on a N/a car...that should ahve been a flag right there...

So without the use of some tuning or a rrfpr, the hacked maf becomes a bit more crude... You either sacrifice milage out of boost or safety At boost... huh. Well lets see... If nothing else, then the hacked maf could be coupled with a lower ratio rrfpr to put less stress on the injectors, right? I mean, if you are running the 270cc/min injectors with stock maf, you pretty much need a 10:1 rrfpr to be in remotely safe a/f's...but you wouldnt need to raise the fuel pressure nearly as much if your injctors are rated at 370cc, correct?

Perhaps a straight hacked-maf isnt the way to go on an intermediate-level budget setup, but a combination of a low ratio rrfpr in conjunction with the hacked maf and 370's? That would also allow for a bit of boost-relative a/f tuning if you were to be able to bleed the referance line of the rrfpr with a mbc or something...

I appreciate you calling me on the massive flaw in my idea of the funcionality of the fpr man...I would have been hosed if I expected the 1:1 raise in fuel pressure to cause a change in injector flow capability when it obviously won't.

So the new gameplan is to look into the use of a rrfpr in conjunction with the hacked maf... Im almost starting to see why people think the hacked-maf is a lost cause...almost;)...

Also, is it best to have a steadily declining a/f from the onset of boost untill you reach full boost, or to have it jump staight to the 11.5-12 from 1 psi on? I have heard slightly mixed opinions about this in different threads... any pros/cons to either side? Thanks again for your support guys...

[virus77]

factor in the price of a rrfpr plus injectors and you have to modify your mafs, its just smarter to go with a piggyback that lets you tune aswell.

[HolyShiznit]

I understand doing things cheaply and I understand that good information is out there. But my "cheap" 1st kit was still SAFC II/Z32 MAF/370cc set-up. It's just safer, cleaner, and less headaches. *shrug*

[Not_a_sr]

you guys ever heard of C&L performance?? they dont offer anything for the nissan market. but for mustangs they offer what we consider a hacked maf. might beable to intrested them into the market if there was enough intrest.