Curious to know all your fuel set ups
01-28-2004, 08:44 PM
#1
1.0 BAR
Thread Starter
Join Date: Jan 2004
Posts: 210
Curious to know all your fuel set ups
I have a 98 prelude. Im installing a turbo and am planning on using DSM 450's, 255lph fuel pump, with a SAFC2.
I wanna know what maybe i should set my SAFC at? I know i should go to a dyno... But the closet dyno is about 4 hours from my house and i aint driving or towing my lude there. Thanks
I wanna know what maybe i should set my SAFC at? I know i should go to a dyno... But the closet dyno is about 4 hours from my house and i aint driving or towing my lude there. Thanks
01-28-2004, 09:42 PM
#3
1.0 BAR
Join Date: May 2003
Posts: 267
Re:Curious to know all your fuel set ups
for the lazy
2-4) What settings should I use for X size injectors with X amount of boost?
This is one of the most misunderstood concepts about using the AFC hack. Lets examine each part to determine your correct settings. To begin, please read question 2-2 before continuing. Now that you understand a little bit about injector sizing with an AFC, we can talk about settings. If you decide to use something other than 450cc injectors, you may want to start with lower boost settings (at the wastegate) and build up from there, keeping the same fuel compensation settings in the AFC.
This will give you the upper limit for the current injector size.
As for obtaining those settings there are a couple of things to explain. Fuel flow rate difference.
This is the difference in flow based on the stock injector flow rate. For a Honda, 240cc injectors are stock. If you increase to 450cc injectors, your flow rate difference is a 46% increase. How do we figure that? Simple math: percent_of_difference = ((240 / new_injector_size) - 1) * 100
Second, an AFC does not control fuel injector pulse duration. This means we cannot compensate for injector latency in the fuel table for our larger injectors. Injector latency describes the scientific characteristic of how long it takes the injector to physically open. The larger the injector, the higher the latency. Since AFCs do not control the pulse duration directly, we compensate with a fixed percentage subtraction, otherwise, we would run lean in lower RPMs, even though our fuel flow rate has been adjusted based on the exact percent difference. The scale for common injector sizes used is 5% for 440-450cc, 4%, 390cc, 3% for 310cc.. then subtract 1 percent per 500 RPM increase. This will give us are starting point. For a boosted application, running stoichiometric is dangerous because of the high volume of air. To "play it safe", you want to run a bit on the stoich/rich side, so we increase fuel flow by 1% per 1000 rpms, trying not to top out a 5% overall increase. Why 5%? ..because your fuel maps are still increasing in pulse duration. So you're increasing pulse duration, and percentage
of flow rate at the same time. You'll get rich, very quickly. If you have VTEC, enrich by 1% more over VTEC VTEC crossover.
So, lets apply everything we've learned, and come up with base settings for 450cc injectors.
1) 240/450 = 0.53
2) 0.53 - 1 = -0.46
3) -0.46 * 100 = -46
So we have a 46% difference, we add our 5% for injector latency compensation, which leaves us with these settings:
1000 - 40%
1500 - 40%
2000 - 39%
3000 - 38%
4000 - 37%
--- VTEC set to 4400 RPMs ---
5000 - 35%
6000 - 34%
7000 - 34%
8000 - 34%
Application of these ideals will find your AFC Hack producing the smooth, safe, reliable power.
2-4) What settings should I use for X size injectors with X amount of boost?
This is one of the most misunderstood concepts about using the AFC hack. Lets examine each part to determine your correct settings. To begin, please read question 2-2 before continuing. Now that you understand a little bit about injector sizing with an AFC, we can talk about settings. If you decide to use something other than 450cc injectors, you may want to start with lower boost settings (at the wastegate) and build up from there, keeping the same fuel compensation settings in the AFC.
This will give you the upper limit for the current injector size.
As for obtaining those settings there are a couple of things to explain. Fuel flow rate difference.
This is the difference in flow based on the stock injector flow rate. For a Honda, 240cc injectors are stock. If you increase to 450cc injectors, your flow rate difference is a 46% increase. How do we figure that? Simple math: percent_of_difference = ((240 / new_injector_size) - 1) * 100
Second, an AFC does not control fuel injector pulse duration. This means we cannot compensate for injector latency in the fuel table for our larger injectors. Injector latency describes the scientific characteristic of how long it takes the injector to physically open. The larger the injector, the higher the latency. Since AFCs do not control the pulse duration directly, we compensate with a fixed percentage subtraction, otherwise, we would run lean in lower RPMs, even though our fuel flow rate has been adjusted based on the exact percent difference. The scale for common injector sizes used is 5% for 440-450cc, 4%, 390cc, 3% for 310cc.. then subtract 1 percent per 500 RPM increase. This will give us are starting point. For a boosted application, running stoichiometric is dangerous because of the high volume of air. To "play it safe", you want to run a bit on the stoich/rich side, so we increase fuel flow by 1% per 1000 rpms, trying not to top out a 5% overall increase. Why 5%? ..because your fuel maps are still increasing in pulse duration. So you're increasing pulse duration, and percentage
of flow rate at the same time. You'll get rich, very quickly. If you have VTEC, enrich by 1% more over VTEC VTEC crossover.
So, lets apply everything we've learned, and come up with base settings for 450cc injectors.
1) 240/450 = 0.53
2) 0.53 - 1 = -0.46
3) -0.46 * 100 = -46
So we have a 46% difference, we add our 5% for injector latency compensation, which leaves us with these settings:
1000 - 40%
1500 - 40%
2000 - 39%
3000 - 38%
4000 - 37%
--- VTEC set to 4400 RPMs ---
5000 - 35%
6000 - 34%
7000 - 34%
8000 - 34%
Application of these ideals will find your AFC Hack producing the smooth, safe, reliable power.
01-30-2004, 10:48 AM
#8
1.0 BAR
Join Date: May 2003
Posts: 267
Re:Curious to know all your fuel set ups
Thread
Thread Starter
Forum
Replies
Last Post
