HOME FORUM RULES CONTACT
     
   
   

Go Back   CLASS RACER FORUM > Class Racer Forums > Stock and Super Stock Tech


Reply
 
Thread Tools Display Modes
Old 03-09-2014, 03:29 AM   #11
pbp1
Junior Member
 
Join Date: Mar 2013
Posts: 78
Likes: 11
Liked 18 Times in 5 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

MAF sensors do a very good job of measuring airflow but their weakness in a race application is that they are only accurate over a very narrow range so it would take a sensor/housing designed specifically for the application. In the case of stock and super stock, we are flowing much more air than a stock engine therefore we have moved out of their effective range. Also, since these classes are throttle body limited, anything in the airstream before the throttle body is undesirable. In stock or modified street vehicles, Mass Air systems do a great job. They just have no place in this type of racing in my opinion.
pbp1 is offline   Reply With Quote
Old 03-09-2014, 09:27 AM   #12
Ed Wright
Veteran Member
 
Ed Wright's Avatar
 
Join Date: Mar 2005
Location: Sand Springs, OK
Posts: 8,132
Likes: 896
Liked 389 Times in 168 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

I think MAF is a better deal. I work with GM's factory systems every day, and the MAF system is much more forgiving for weather, elevation and engine combo changes. Different manifolds, headers, collectors, going to Denver, seldom require any tuning changes.

On many cars, (like mine) where would you put it? Going to put an air filter on it? The GM (don't know about Ford) sensors have heated wires. They glow red when running. They have to remain perfectly clean, or the calibration changes. Then you usually end up with elbows in the ducting to accommodate an air filter. You can't have dust, and who knows what else in Louisiana (Joke) cooked on those heated wires.
Speed Density done correctly compensates pretty well.
__________________
Ed Wright 4156 SS/JA

Last edited by Ed Wright; 03-09-2014 at 09:29 AM. Reason: Still can't type...
Ed Wright is offline   Reply With Quote
Old 03-09-2014, 12:25 PM   #13
ken robinson
Member
 
Join Date: Dec 2001
Location: tomsriver nj
Posts: 437
Likes: 37
Liked 163 Times in 68 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

For odd ball combos (2.3 ford turbo)that do you do for a cal map to start with if one is not available ? Or do most of the company like FAST have a start up cal map on file you just need to call when ordering the the ecu .
ken robinson is offline   Reply With Quote
Old 03-09-2014, 12:53 PM   #14
RacingRicki
Sponsor
 
RacingRicki's Avatar
 
Join Date: Sep 2005
Location: Colorado
Posts: 106
Likes: 0
Liked 0 Times in 0 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

David,

You mentioned a racer that is running in speed density open loop. If it is open loop, how is it that the ECU is compensating for air changes? I thought open loop meant that there was no compensating going on.

I run the "classic FAST" system in Alpha-N mode open loop. With that setup, closed loop would use the o2 sensor to correct the fuel. In open loop it doesn't. How is this different with speed density? Does speed density use the o2 sensor at all?

Also, I was told that even though I run in open loop Alpha-N that there are tables that I can't see that are compensating for barometric changes much like a carburetor does naturally. Is this true?
__________________
RacingRicki
RacingRicki is offline   Reply With Quote
Old 03-10-2014, 01:59 PM   #15
pbp1
Junior Member
 
Join Date: Mar 2013
Posts: 78
Likes: 11
Liked 18 Times in 5 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

Ken, one of the beauties of Speed Density is that since it is really based on airflow, it is relatively easy to start with a basic VE table and run it in closed loop and tune it in based on the O2 correction that you see in your datalogs. There are a lot of baseline tuneups in our C-Com software to chose from and while none of them are specifically for a 4 cyll, it would be very simple to start with one of those and make a few changes to give you a close starting point. I would be glad to put a tune together for you, send me a message if you are interested in this.
David Page
FAST
pbp1 is offline   Reply With Quote
Old 03-10-2014, 02:50 PM   #16
pbp1
Junior Member
 
Join Date: Mar 2013
Posts: 78
Likes: 11
Liked 18 Times in 5 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

Ricki, Closed loop is a separate consideration.

For those who aren't familiar with the term, Closed Loop is a process where the system compares the actual Air/Fuel ratio read by the O2 sensor to your programmed target A/F ratio and makes corrections to the fueling based on the difference. In Open Loop, the system still reads the Air/Fuel ratio from the O2 sensor but it does not make any corrections.

You can run Alpha-N in Closed Loop or Open Loop and you can run Speed Density mode in Closed Loop or Open Loop.

The compensation I am talking about is not really a correction. In speed density, the air pressure and temperature are taken into account "on the front end" of the ECUs fueling calculations. In Alpha-N mode with FAST systems, there are corrections made in the ECU behind the scenes for Air Pressure as long as you have a MAP sensor plugged into the harness with the hose barb of the sensor open to the atmosphere and an Air Temp sensor plugged in. Even in Open Loop, these corrections are going on behind the scenes without any input from you. If you do not have a MAP sensor or Air Temp sensor in your system, the ECU just assumes standard temp and pressure and you are using the system like a mechanical carburetor of mechanical injection.
pbp1 is offline   Reply With Quote
Old 03-10-2014, 10:18 PM   #17
partsbob67
Member
 
Join Date: Apr 2005
Location: rohnert park,ca
Posts: 409
Likes: 9
Liked 37 Times in 10 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

so which would make more consistent power in a stocker combo batch fire or sequential in your opinion ?
__________________
bob beals 7244
partsbob67 is offline   Reply With Quote
Old 03-10-2014, 10:44 PM   #18
pbp1
Junior Member
 
Join Date: Mar 2013
Posts: 78
Likes: 11
Liked 18 Times in 5 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

Sequential injector operation offers the most precise fueling. That being said, as injector duty cycle increases (meaning the injectors move closer to just being wide open), the difference between bank to bank operation and sequential operation diminishes. Now, selecting a large injector that will operate at a lower duty cycle gives you the room to "time" the injector open time in relation to the opening and closing of the intake valve. Operating in sequential mode also gives you the ability to add or subtract fuel to or from individual cylinders to find an optimum balance of Air/Fuel ratios from cyll. to cyll.
Now these are very small potential gains and there are no hard, fast rules to go by. If you have unlimited time and are willing to spend the time on the dyno testing every possible combination of injector size, injector opening timing, and individual cylinder corrections (and the XFI 2.0 system allows all of this) then I am certain you could find some power.
That being said, I have seen racers run their systems in bank to bank with great consistency and run in the 1.25 under range any time they want.
I guess the short answer is that it is likely that you can find some power gains by switching from bank to bank to sequential but there is no guarantee that the gains will be worth the investment required to properly test to find the optimum parameters.
I have not seen any evidence that sequential fueling offers any more consistency over bank to bank.
Now, sequential definitely offers better idling, drive ability, and part throttle operation so if I were running a stocker, it would definitely be in sequential mode.
pbp1 is offline   Reply With Quote
Old 03-11-2014, 07:59 AM   #19
SS3718
Member
 
Join Date: Sep 2006
Posts: 128
Likes: 5
Liked 28 Times in 14 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

David, I just wanted to say thanks for sharing and taking the time to post on this topic. As a current FAST customer, not only do you have a great product but the customer service that you provide is second to none and this post is yet another example of the service/tech support that your team provides.

Thank you and see you at the track in 2014,
Nick Morris
SS 3718
GT/FA
SS3718 is offline   Reply With Quote
Liked
Old 03-11-2014, 08:26 AM   #20
Rich Biebel
VIP Member
 
Rich Biebel's Avatar
 
Join Date: Jun 2007
Location: Northern New Jersey suburbs
Posts: 2,273
Likes: 25
Liked 510 Times in 200 Posts
Default Re: EFI, Alpha-N vs Speed Density fueling Strategies

How do you add a cam sync sensor to a GM LT-1 from the mid '90s ?

I raced one and used bank to bank but my Accell Gen VII could run in sequential. I ran a crank trigger with a gutted optispark dist.and was not sure how to add a cam synch sensor.

I struggled to tune my car on my own and really needed a pro's help and some dyno time.....running in sequential sounded like it would make more sense.....
__________________
Rich Biebel
S/C 1479
Rich Biebel is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 06:43 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © Class Racer.com. All Rights Reserved. Designated trademarks and brands are the property of their respective owners.