MAF and injector size for homebrew using hybrid turbos

EdyJun · 03-01-2006, 02:32 PM

I am looking into what setup I may want for my homebrew S4 (K04/RS6, GIAC X, TCD, and EBC), trying to find a mathematical solution for MAF and Injector size in hopes to not have to do too much tweaking and also to keep the software close to what setup it was intend for.

73mm maf= 36.5*36.5*3.1416=4185.39 = Stock
83mm maf= 41.5*41.5*3.1416=5410.62= 29% larger than stock
85mm maf= 42.5* 42.5*3.1416= 5674.5 = 35.5% larger than stock
88mm maf= 44*44*3.1416= 6082.1376= 45% larger than stock
90mm maf= 45*45*3.1416= 6361.74= 52% larger than stock

349cc/min - S4 w/4bar (stock) 0% larger than stock
380cc/min - 36lb Bluetops w/3bar 8% larger than stock
390cc/min - S4 w/5bar 12% larger than stock
422cc/min - 36lb Bluetops w/4bar 21% larger than stock
440cc/min - 42lb Greentops w/3bar 26% larger than stock
481cc/min - RS4s w/4bar 38% larger than stock
488cc/min - 36lb Bluetops w/5bar 40% larger than stock
508cc/min - 42lb Greentops w/4bar 46% larger than stock
538cc/min - RS4s w/5bar 54% larger than stock
568cc/min - 42lb Greentops w/5bar 63% larger than stock

Am I just totally wrong in my thinking?

Edy

Blue2 · 03-01-2006, 02:54 PM

Mike2kS4 · 03-01-2006, 02:54 PM

88mm ID MAF housing combined with ~510cc worth of squirt is a great combination. Nevertheless there are variations in MAF curve due to sensor and intake type.

Bosch are less forgiving than hitachi with regard to MAF overrun due to the central mounting position of the Bosch sensor. But, the Bosch is more accurate because of this.

Intakes need to be smooth, avoiding any dramatic ID changes and isolated from engine-bay heat.

Mike2kS4 · 03-01-2006, 03:00 PM

You have to ask how fast you want to go and what your tuning philosophy is.

Mine is to run the largest injector at the lowest pressure possible due to the fact that injectors operate most effectively at a lower rated pressure as does the fuel pump.

That being said: a 90mm MAF and ~609cc of squirt (630cc injector at 2.8bar) is my choice.

Imolavirus@BuehnEngineering · 03-01-2006, 03:03 PM

pressure? I would think there's a happy medium to stay within......same thing would apply to duty cycle.

RMcQ · 03-01-2006, 03:09 PM

what is your fuel economy like? Is it bad only when hammering on it or does it get worse even when highway cruising?

EdyJun · 03-01-2006, 03:11 PM

EdyJun · 03-01-2006, 03:14 PM

Also, with too large of a MAF your TRUE MAF @ ideal will be way off when it comes to MAF reading, right?

That could cause some misfires I believe.

Mike2kS4 · 03-01-2006, 03:16 PM

I've run mine as low as 2.5bar with no problems, except that it wasn't enough fuel.

There are also sweet-spots in duty-cycle (80%-95% is good) and MAF (Over 250 g/s peak)

It's by no means a simple problem.

EdyJun · 03-01-2006, 03:18 PM

I want the most optimal for my setup with some head room for later. I will be running GIAC X (K03) and would be using it for day to day driving.

I guess what I am trying to say is that I like to keep the same setup/logic/ratio that GIAC X (K03) has but with hybrid turbos @ ~24 PSI.

Does that make any sense?

Edy

03-01-2006, 02:32 PM	#1
EdyJun Member Account #: 48484 Join Date: Dec 2002 Posts: 2,849	MAF and injector size for homebrew using hybrid turbos I am looking into what setup I may want for my homebrew S4 (K04/RS6, GIAC X, TCD, and EBC), trying to find a mathematical solution for MAF and Injector size in hopes to not have to do too much tweaking and also to keep the software close to what setup it was intend for. 73mm maf= 36.536.53.1416=4185.39 = Stock 83mm maf= 41.541.53.1416=5410.62= 29% larger than stock 85mm maf= 42.5* 42.53.1416= 5674.5 = 35.5% larger than stock 88mm maf= 44443.1416= 6082.1376= 45% larger than stock 90mm maf= 4545*3.1416= 6361.74= 52% larger than stock 349cc/min - S4 w/4bar (stock) 0% larger than stock 380cc/min - 36lb Bluetops w/3bar 8% larger than stock 390cc/min - S4 w/5bar 12% larger than stock 422cc/min - 36lb Bluetops w/4bar 21% larger than stock 440cc/min - 42lb Greentops w/3bar 26% larger than stock 481cc/min - RS4s w/4bar 38% larger than stock 488cc/min - 36lb Bluetops w/5bar 40% larger than stock 508cc/min - 42lb Greentops w/4bar 46% larger than stock 538cc/min - RS4s w/5bar 54% larger than stock 568cc/min - 42lb Greentops w/5bar 63% larger than stock Am I just totally wrong in my thinking? Edy __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

03-01-2006, 02:54 PM	#2
Blue2 Junior Member Account #: 24070 Join Date: Aug 2001 Posts: 936	I started with 85MM MAF (35.5%) and Bluetops@5BAR (40%)

03-01-2006, 02:54 PM	#3
Mike2kS4 Elder Member Account #: 38083 Join Date: Jun 2002 Posts: 12,104	That's the basic calculation to figure out if it will work with tweaks or not... 88mm ID MAF housing combined with ~510cc worth of squirt is a great combination. Nevertheless there are variations in MAF curve due to sensor and intake type. Bosch are less forgiving than hitachi with regard to MAF overrun due to the central mounting position of the Bosch sensor. But, the Bosch is more accurate because of this. Intakes need to be smooth, avoiding any dramatic ID changes and isolated from engine-bay heat. __________________ 2002 S4 Avant, 6spd. Bone stock. <a href="http://www.autospeed.us"> </a> Caveat: Any advice I express regarding potential tuning and such is purely informational. If your knowledge and abilities are not up to the task, no amount of advice can assist.

03-01-2006, 03:00 PM	#4
Mike2kS4 Elder Member Account #: 38083 Join Date: Jun 2002 Posts: 12,104	To apply this to your car is another issue... You have to ask how fast you want to go and what your tuning philosophy is. Mine is to run the largest injector at the lowest pressure possible due to the fact that injectors operate most effectively at a lower rated pressure as does the fuel pump. That being said: a 90mm MAF and ~609cc of squirt (630cc injector at 2.8bar) is my choice. __________________ 2002 S4 Avant, 6spd. Bone stock. <a href="http://www.autospeed.us"> </a> Caveat: Any advice I express regarding potential tuning and such is purely informational. If your knowledge and abilities are not up to the task, no amount of advice can assist.

03-01-2006, 03:03 PM	#5
Imolavirus@BuehnEngineering AudiWorld Super User Account #: 33927 Join Date: Mar 2002 Posts: 17,946	but can't you start to run into an issue of too large of an injector running at too small of a pressure? I would think there's a happy medium to stay within......same thing would apply to duty cycle. __________________ -Jacob ^^^CLICK SIG FOR BUEHN ENGINEERING WEBSITE^^^ <big><big>Website Here!!!</big></big> <big>Items For Sale</big>

03-01-2006, 03:09 PM	#6
RMcQ Elder Member Account #: 2021 Join Date: Mar 2000 Posts: 12,485	Not that this really is a consideration when you get to this point, but... what is your fuel economy like? Is it bad only when hammering on it or does it get worse even when highway cruising? __________________ + + = 451whp/472 ft-lb Full RS6 bastardized allroad quattro alive and on the road.

03-01-2006, 03:11 PM	#7
EdyJun Member Account #: 48484 Join Date: Dec 2002 Posts: 2,849	I am thinking of RS4 intake (Top) & RS4 accordion hose w/ 88mm MAF. How do you feel about that? __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

03-01-2006, 03:14 PM	#8
EdyJun Member Account #: 48484 Join Date: Dec 2002 Posts: 2,849	Imolavirus:Infected that is what I was thinking. (more) Also, with too large of a MAF your TRUE MAF @ ideal will be way off when it comes to MAF reading, right? That could cause some misfires I believe. __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

03-01-2006, 03:16 PM	#9
Mike2kS4 Elder Member Account #: 38083 Join Date: Jun 2002 Posts: 12,104	Yea, you can run into an issue if you try to run an injector rated at 3bar at 2bar... I've run mine as low as 2.5bar with no problems, except that it wasn't enough fuel. There are also sweet-spots in duty-cycle (80%-95% is good) and MAF (Over 250 g/s peak) It's by no means a simple problem. __________________ 2002 S4 Avant, 6spd. Bone stock. <a href="http://www.autospeed.us"> </a> Caveat: Any advice I express regarding potential tuning and such is purely informational. If your knowledge and abilities are not up to the task, no amount of advice can assist.

03-01-2006, 03:18 PM	#10
EdyJun Member Account #: 48484 Join Date: Dec 2002 Posts: 2,849	I want .... I want the most optimal for my setup with some head room for later. I will be running GIAC X (K03) and would be using it for day to day driving. I guess what I am trying to say is that I like to keep the same setup/logic/ratio that GIAC X (K03) has but with hybrid turbos @ ~24 PSI. Does that make any sense? Edy __________________ 2000 Audi S4 STG 3 FATS = 3.66 w/ 91 oct AIM: EdyJun 11 September 2001 In their honor. In their memory. <font color="red">---------------------------------------------------------- <u><big> <a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help) </a> </big> </u>---------------------------------------------------------- </font>

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode


Discussion Forums:	Advanced Search