Megasquirt? MSD?
07-17-2007, 04:45 AM
#91
Rennlist Member
Idle ususally is about 4-10 degrees, set for max vacuum and stability with AFR around 16-18 to 1 depending on cams.
Cold start around 13:1 seems to work wll and take it out of cold start mode quickly...
Cheers,
Marc
Cold start around 13:1 seems to work wll and take it out of cold start mode quickly...
Cheers,
Marc
07-17-2007, 05:13 AM
#92
Instructor
Join Date: May 2004
Location: United Kingdom, Manchester
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OK This may sound totally stupid but as a starting point for using something like MS is it not possible to take the LH and EKZ maps and translate them from MAF to MAP. There must be a correlation between the two. Just a thought.
07-17-2007, 10:07 AM
#93
Three Wheelin'
Originally Posted by BrendanC
Yes, the MS does Xtau, which I believe is the way they describe the TPS and MAP blending. I think VEMS does as well. Its supposed to be really tricky to figure out, but the only way to tune engines a MAP will not work for (and hot wire is also not an option) - like yours.
Xtau on the other hand is a surprisingly advanced (for hobbiest oriented MS) accel enrichment method based on the premise that there's a certain amount of fuel clinging to the port walls at any given time. The Xtau algorythm uses a table much like the MAP table. It has constants for various rpm and vacuum conditions which the algorythm uses to formulate AE. When I had my Cobra I experimented with the beta versions of Xtau and wound up using it as my main AE, it seemed to have magical abilities to tune a very difficult fast reving big displacement ITB motor.
07-17-2007, 03:58 PM
#94
Originally Posted by Mike Simard
The Xtau is a unique thing different from the TPS/MAP blending. Yes MS can use different combinations of TPS or MAP for accel enrichment and as Louie suggested it just isn't as important as it sounds like it would be in real world conditions.
Xtau on the other hand is a surprisingly advanced (for hobbiest oriented MS) accel enrichment method based on the premise that there's a certain amount of fuel clinging to the port walls at any given time. The Xtau algorythm uses a table much like the MAP table. It has constants for various rpm and vacuum conditions which the algorythm uses to formulate AE. When I had my Cobra I experimented with the beta versions of Xtau and wound up using it as my main AE, it seemed to have magical abilities to tune a very difficult fast reving big displacement ITB motor.
Xtau on the other hand is a surprisingly advanced (for hobbiest oriented MS) accel enrichment method based on the premise that there's a certain amount of fuel clinging to the port walls at any given time. The Xtau algorythm uses a table much like the MAP table. It has constants for various rpm and vacuum conditions which the algorythm uses to formulate AE. When I had my Cobra I experimented with the beta versions of Xtau and wound up using it as my main AE, it seemed to have magical abilities to tune a very difficult fast reving big displacement ITB motor.
07-17-2007, 07:14 PM
#95
Three Wheelin'
Originally Posted by Z
Have you thought about where and how your IAT sensor is mounted? The sensor may be reporting a higher than actual IAT at closed throttle from the sensor body being heated, because of it's location under the hood, or because of absorbing heat due to being mounted in a warm and thermally conductive material. Under part throttle there's enough air flowing through the intake tract that the sensor gives accurate readings. At idle there's very little air going through there. Underhood heat will heat the body of the sensor, and that heat will affect the reading to a greater extent than when more air is going through the intake system. The ECU will think that the intake air is hotter than it really is. The result is that the ECU will supply less fuel because that's what would be required for the hotter and less dense air that it thinks is entering the engine. Since the actual intake air is cooler and denser than what the ECU thinks it is, the mixture goes lean.
With the car at idle, there's less airflow under the hood, which increases the problem. The IAT sensor being mounted in a warm metal duct or airbox will also contribute to the problem, because of the metal conducting heat to the body of the sensor. Mounting the IAT sensor in an a cooler area under the hood, mounting it into plastic or a plastic bushing, or insulating the body of the sensor that's outside of the intake air flow, and that's exposed to underhood heat, can help fix the problem. I don't know what kind of IAT sensor the DTA uses, but some styles of sensor are more suseptible to this problem than others.
With the car at idle, there's less airflow under the hood, which increases the problem. The IAT sensor being mounted in a warm metal duct or airbox will also contribute to the problem, because of the metal conducting heat to the body of the sensor. Mounting the IAT sensor in an a cooler area under the hood, mounting it into plastic or a plastic bushing, or insulating the body of the sensor that's outside of the intake air flow, and that's exposed to underhood heat, can help fix the problem. I don't know what kind of IAT sensor the DTA uses, but some styles of sensor are more suseptible to this problem than others.
I think the IAT sensor is mounted in a fairly good spot. The best would be right inside one of the TBs. That won't happen. It's in the intake air stream about 8" inside the air box from the opening. No more than 12" from any intake. Even at idle you can feel the air movement through the opening so it isn't in a stagnant spot. The air temp sensor is an open (fast response) type NTC Bosch originally intended for a VW. It is about 1.5" high with the little sensor element supported on thin plastic legs. It may pick up some heat from the hotter base. Although the air box is quite large, I can't see the air staying in there long enough to heat much. The air box is carbon fiber which is supposed to not conduct heat very well. The intake air temp (IAT) sensor reads close to ambient air temp when I'm moving, but does raise after idling for 3 or more minutes. The IAT will go to around 60C after a prolonged idle with ambient air at around 85F (30C). Using the air density formula that 30C rise in air temp, should make for about 9% less density which means 9% less fuel. However, to maintain the same AFR at 60C that I had at 30C, I have to increase fuel by 4%. The fuel is probably hotter too and I have no tunability with that, but fuel density doesn't change as much with temp as air density. My fuel rails are insulated to try and help stabilize fuel temp. I'm coming to realize that this is the way the engine and installation is and there isn't much I can do about it. In the EFI101 fuel injection tuning class I took, I remember the instructor said to not get too hung up on how the tuning compensations should be if it isn't working out. He said give the engine what it wants no matter what.
I don't know how someone could do a good job of tuning without subjecting the car to all extremes of both temperature, and pressure. That's going to take several months and lots of driving around. Which is about what it did take, and I'm not really done yet. Now if we had a sensor that would compensate for both air temperature and pressure, it would be a lot easier and more exact. Wait! That would be a MAF.
Here is a pic of the coolant and air temp sensors I used.
https://rennlist.com/forums/attachme...d=206412&stc=1
Coolant & Air temp.jpg
Last edited by Louie928; 03-18-2008 at 01:11 PM.
07-17-2007, 08:00 PM
#96
Nordschleife Master
Louie, with MS you can actually have the MS not take any MAP inputs until X RPM, so you could use that for just off tuning and up,
Although where you need the most help is at idle, as well with the brake booster, I had planned on running a vacuum pump and not trying to get the ITBs to power it, the HVAC would be plumbed into it as well.
Although where you need the most help is at idle, as well with the brake booster, I had planned on running a vacuum pump and not trying to get the ITBs to power it, the HVAC would be plumbed into it as well.
07-17-2007, 08:24 PM
#97
Three Wheelin'
Originally Posted by Lizard931
Louie, with MS you can actually have the MS not take any MAP inputs until X RPM, so you could use that for just off tuning and up,
Although where you need the most help is at idle, as well with the brake booster, I had planned on running a vacuum pump and not trying to get the ITBs to power it, the HVAC would be plumbed into it as well.
Although where you need the most help is at idle, as well with the brake booster, I had planned on running a vacuum pump and not trying to get the ITBs to power it, the HVAC would be plumbed into it as well.
Last edited by Louie928; 07-18-2007 at 12:26 AM. Reason: misspelled word
07-17-2007, 11:30 PM
#98
Nordschleife Master
Have you done any research on vacuum pumps at all?
all the ones I was able to find were a stupid price, I was thinking about hitting up a junkyard looking for one out of an older vehicle.
all the ones I was able to find were a stupid price, I was thinking about hitting up a junkyard looking for one out of an older vehicle.
07-18-2007, 12:55 AM
#99
Three Wheelin'
Originally Posted by Lizard931
Have you done any research on vacuum pumps at all?
all the ones I was able to find were a stupid price, I was thinking about hitting up a junkyard looking for one out of an older vehicle.
all the ones I was able to find were a stupid price, I was thinking about hitting up a junkyard looking for one out of an older vehicle.
Info on junkyard vacuum pumps. I bought a new one that cost a bunch of money to use. It was noisy, vibrated, didn't appear to be made very well, and it's still in the box. I figured I'd try to use the vacuum the engine generated and that has worked ok. With stock cams and using TPS for idle and low RPMs, you should be fine without the pump. Keep it simple.
07-18-2007, 01:55 PM
#100
Nordschleife Master
Louie, Thank you for the link,
I also dont need it right now but will in the future,
And for keeping it simple, that is the plan to keep the vacuum system as simple as possible.
I also dont need it right now but will in the future,
And for keeping it simple, that is the plan to keep the vacuum system as simple as possible.
