LIFE WITH SIRS

B

BMW RACER

New member
Looks like we're stuck with the 29mm SIR. I'm not happy about it, but I'm willing to give it a try. I'm on the list with Raetech to trade in my 27mm piece.

Any thoughts out there as far as mounting this thing? Obviously after the air mass sensor. How far away from the throttle should it be? Can we modify the wiring to move the AMS foreward? Can we run the air filter out through the hole below the left headlight? I'm thinking nope.

What affect will it have on the stock crankcase vent system?

Just thinking out loud.
 
John,

I highly suspect that the reason the SIR in front of the MAF causes the problems that is does is that the there is a large velocity gradient in the middle. I'd say one would need to mount the SIR about 9-15 diameters ahead of the MAF, or you could use a flow straightener to make the intake tube shorter. Next factor to consider is any acoustic harmonics between the SIR and the valves. Actually the best way to deal with this factor is the same as what BMW has on the stock air box, a side branch oscillator. This is a chamber mounted perpendicular to the air flow that changes the natural resonant frequency of the intake tract. If you want to discuss this further and in more detail please feel free to pm me, I'd be glad to offer any help I can.

James
 
Looks like we're stuck with the 29mm SIR. I'm not happy about it, but I'm willing to give it a try. I'm on the list with Raetech to trade in my 27mm piece.

Any thoughts out there as far as mounting this thing? Obviously after the air mass sensor. How far away from the throttle should it be? Can we modify the wiring to move the AMS foreward? Can we run the air filter out through the hole below the left headlight? I'm thinking nope.

What affect will it have on the stock crankcase vent system?

Just thinking out loud. [/b]
Click to expand...

John, this is how I'm going to mount the SIR:
Air Filter=AFM=SIR=======TB (AFM needs to read clean undistrubed air)
I think (this is wat I was told by someone who tested a SIR) there should be enough wire to move the AFM (AMS) forward of the SIR & towards the Air Filter. I'm wait for my car to get finished and the SIR to come in. This is as far as I can comment on. I was going to see if we can't keep the location of the air filter where it is now, just behind thne left headlight. I would think you like to keep the SIR as far away from the TB as possible, like just behind the AFM. I was also told the the car will be running rich and you won't be able to tune with a adjustable fuel reg., this means burning a new chip. I'll be able to tell you more when I get on the dyno with the SIR. If you guys want to go PM feel free.
 
I am not the expert you guys need, sorry, but my comments are free, so I thought I'd share them.

I think that extending the harness will prove problematic legally. But it is pretty long as is so it might be fine. I also think that gaining distance between the SIR and the TB is a good idea. I would look into it. From what I saw, the AFM needs to be upstream of the SIR, but there may be methods to make it work vice versa.

I might try to make the tract longer by bending the intake tube down, then back up between the SIR and the TB. Not sure if that will help, or is even possible, but I'd look at it if I had a BMW.

In tuning, I would consider steps to make sure I had a good broad tq curve. The car that we tested with showed good A/F ratios, but I imagine that is a case by case thing, as he had a custom chip.

After getting the thing to run the best it can on a dyno, I would think about gearing, if needed.

I know, most of this is obvious, but I'm just trying to help.
 
Jake.

Good ideas, right now I'm waiting for the restrictor to get here.

My next race is May 5th. I'll keep you'all posted.

Thanks.
John
 
Dave.

Since we can only move the AMS as far as the wiring will let us.
Is there a distance at which SIR stops having an adverse affect on the AMS if it's installed in front of the AMS?

Also I have a question for the "rules nerds"

Does the wiring loom have to remain in the original location? I'm thinking probably yes (IIDSYCDIYC) But flexability in that area yould help with moving the AMS.

Thanks

John
 
Dave.

Since we can only move the AMS as far as the wiring will let us.
Is there a distance at which SIR stops having an adverse affect on the AMS if it's installed in front of the AMS?

Also I have a question for the "rules nerds"

Does the wiring loom have to remain in the original location? I'm thinking probably yes (IIDSYCDIYC) But flexability in that area yould help with moving the AMS.

Thanks

John
[/b]
Click to expand...
John, I am not gonna quote any rules here but I think anywhere the stock portion of the loom can plug in would be OK. I had thought of the possibility of running a hose across the front tof the engine and back to the stock location and putting the MAF on the end. I think the tubing is free these days and the additional length may alllow the MAF to work correctly with the SIR. This is just a thought but the proven (dynoed)deal is Airfilter====MAF====SIR===TB...
 
John, I am not gonna quote any rules here but I think anywhere the stock portion of the loom can plug in would be OK. I had thought of the possibility of running a hose across the front tof the engine and back to the stock location and putting the MAF on the end. I think the tubing is free these days and the additional length may alllow the MAF to work correctly with the SIR. This is just a thought but the proven (dynoed)deal is Airfilter====MAF====SIR===TB... [/b]
Click to expand...

Joe, in your opinion, doesn't it seem logicial that with the SIR the engine should run rich since the AFM is reading good volume and clean air but the SIR is shutting down the air, thus the computer is throwing more fuel into what is actually less air? Am I looking at this correctly?
Thanks
dj
 
Joe, in your opinion, doesn't it seem logicial that with the SIR the engine should run rich since the AFM is reading good volume and clean air but the SIR is shutting down the air, thus the computer is throwing more fuel into what is actually less air? Am I looking at this correctly?
Thanks
dj
[/b]
Click to expand...
if the sir is shutting down the air, then the air will stop going through the maf and it will read the correct amount of air. air has to go somewhere...if it can't get through the sir, then is won't get past the maf either, even if the maf is in front of the sir. it is a "sealed" system.

in theory....
 
if the sir is shutting down the air, then the air will stop going through the maf and it will read the correct amount of air. air has to go somewhere...if it can't get through the sir, then is won't get past the maf either, even if the maf is in front of the sir. it is a "sealed" system.
in theory.... [/b]
Click to expand...

So if I read you correctly, if the maf is reading less air then it is telling the computer to put less fuel to the engine thus creating a lean condition? Does this sound right? If this is correct then engine should start going lean from about 3500- 4000 rpm up.
 
I may be incorrect, but, I don't believe that the MAF will read correctly because it was designed to work in the 4 inch(or so) air intake system, calculate velocity, and determine volume with respect to that area. With the velocity being considerably greater due to the restriction readings will have to be adjusted accordingly.
That is why the MAF doesn't want the SIR in front of it, as it will direct the airstream only on the middle of the wire. Causing way out readings.
This is just a SWAG(Scientific Wild Ass Guess). I pick up my E36 this coming weekend and am looking to learn all I can, and help where ever possible.
Thanks
 
So if I read you correctly, if the maf is reading less air then it is telling the computer to put less fuel to the engine thus creating a lean condition? Does this sound right? If this is correct then engine should start going lean from about 3500- 4000 rpm up.
[/b]
Click to expand...

not really. maf is reading less air because less air is going into the engine through the sir. this leads to computer putting less fuel in to try to keep the mixture at the correct ratio based on the maps in the computer. this is where the custom chip is critcal and just playing with an adjustable fpr isn't very effective.

of course, i am not a professional engine tuner, but i hung out with one during several tuning sessions on my car last year.... :D
 
not really. maf is reading less air because less air is going into the engine through the sir. this leads to computer putting less fuel in to try to keep the mixture at the correct ratio based on the maps in the computer. this is where the custom chip is critcal and just playing with an adjustable fpr isn't very effective.

of course, i am not a professional engine tuner, but i hung out with one during several tuning sessions on my car last year.... :D
[/b]
Click to expand...
I wonder who that might be? ;) I think I'm understanding this a little better. From what I've heard your enginer tuner/ builder should get his 29 mm SIR this week. I had him burn me 2 chips last year and only 1 will be any good (the one without the FPR) lol. Damn is that a long day for me if I have to go to his dyno again to get another chip burnt (620 miles round trip). He's such a unique and likable guy would be worth it if I had too.

I may be incorrect, but, I don't believe that the MAF will read correctly because it was designed to work in the 4 inch(or so) air intake system, calculate velocity, and determine volume with respect to that area. With the velocity being considerably greater due to the restriction readings will have to be adjusted accordingly.
That is why the MAF doesn't want the SIR in front of it, as it will direct the airstream only on the middle of the wire. Causing way out readings.
This is just a SWAG(Scientific Wild Ass Guess). I pick up my E36 this coming weekend and am looking to learn all I can, and help where ever possible.
Thanks--------------------
Chris Leone
E36 ITS underconstruction
Remember half of the people you call friends are considered below average.

SWAG--------Good one Chris! Man did you pick a good time to do a E36 ;) .
This is a reason maybe not to mount the SIR to close to the MAF but not to close the TB either. I know there is only a limited amout of space to mount everything needed.
 
If you could move the SIR upstream far enough to allow the velocity to return to normal (fill the tube) you could run the SIR out front and likely not see the thing until it goes sonic. This is why the location between the MAF and the TB seems best at this point the airspeed will remain constant through the tube and the MAF until the air stalls at the SIR. I believe at this point the It will act like an over rich revlimiter since the MAF will have seen then air before the stall. I think the problem we are having getting our arms around this is that it is not like a FPR that screws up the airflow. The Idea is this type of restrictor is allowing all the air the engine can actually use until it goes sonic. Even at this point the leanest we should get through ECU control would be stoich on a stock program.
 
I believe thats why we see formula/ sports racers using any restrictor in front of everything and use an airbox of sorts, for attenuation or cleaning/straightening the flow of air, as well as acting as a "holding tank" for a decent supply of air. Leaving sub sonic supplies for the engine. It would be nice to have that kind of room available!!
 
I am not sure you don't have room if your creative. I don't think it will net much of anything but I think you could run enough tube to run the SIR out front.
 
Thinking in terms of Cubic Feet per minute, we know that your engine uses hundreds.....(think about a 650 holley on a Chevy, that makes twice the HP) so, if you are flat down a straight for 20 seconds, you'll use a lot of air, LOL. A lot more than any box can house.

If you are doing experiments in this area, I imagine that the concept will be to get the speed of the air stabilized and smooth across the hot wire resistor.

My understanding of the genious of the hot wire design is that it automaticaly adjusts for all changes in the conditions. Basically a current is sent thru it, and the resistance is monitored. The computer seeks to maintain the temp of the wire. More air flowing over it, whether due to speed, incresed density due to temp, or incresed density due to barometric pressure will couse the computer to adjust. The adjustment is merely then translated into a fuel need.

In testing, I think the SIR, when placed in front of the MAF, presented a stream of very high velocity air/turbulence, that had not slowed and smoothed, to perhaps one section of the wire, and the wire was over cooled, so to speak, causing the computer to assume that it needed to add more fuel. Thats why we saw issues with black smoke, and CEL triggers relatively low in the rev range.

The safest thing to do is place the MAF upstream in clean flow, but I think that a closer study could yeild a different arrangement with the SIR upstream.

Again, I'm not an engineer, just reporting what I saw, and just trying to help.
 
Thinking in terms of Cubic Feet per minute, we know that your engine uses hundreds.....(think about a 650 holley on a Chevy, that makes twice the HP) so, if you are flat down a straight for 20 seconds, you'll use a lot of air, LOL. A lot more than any box can house.

If you are doing experiments in this area, I imagine that the concept will be to get the speed of the air stabilized and smooth across the hot wire resistor.

My understanding of the genious of the hot wire design is that it automaticaly adjusts for all changes in the conditions. Basically a current is sent thru it, and the resistance is monitored. The computer seeks to maintain the temp of the wire. More air flowing over it, whether due to speed, incresed density due to temp, or incresed density due to barometric pressure will couse the computer to adjust. The adjustment is merely then translated into a fuel need.

In testing, I think the SIR, when placed in front of the MAF, presented a stream of very high velocity air/turbulence, that had not slowed and smoothed, to perhaps one section of the wire, and the wire was over cooled, so to speak, causing the computer to assume that it needed to add more fuel. Thats why we saw issues with black smoke, and CEL triggers relatively low in the rev range.

The safest thing to do is place the MAF upstream in clean flow, but I think that a closer study could yeild a different arrangement with the SIR upstream.

Again, I'm not an engineer, just reporting what I saw, and just trying to help. [/b]
Click to expand...

Damn I think the CRB should tell us how thay want us to mount for it to be legal. With all this expermentation don't we deserve a little more time to make this damn thing work? Hell it's been 6 years, what another month or 2?

Jake, I'm not sure if there was enought room to get the sir forward enough to not cause turbulance to the AFM. Bending tubing like a header system might work but the bends would have to be perfectly smooth with absolutely no kinks.
 
Well, if it were me, I'd run to the Home Despot, or the bLowes, (kidding) and pick up some PvC plumbing parts to "prove/disprove" the theory parts of it. I think you can fab up a pretty fast set of parts, with some rubber hoses and some U and 90 degree bends to try a bunch of different configurations out before dyno time.

Then on the dyno, you can just swap the parts out to get some quick direction.

I'd love to take credit for such a concept but I have seen some very bright engineers do it to make sure that their theory matched reality before commencing with more time consuming methods. (One guys dyno results were strong enough that he actually raced the "mock up" for a while before finalizing it)
I have developed a relationship with my local NAPA store, and they allow me to "putter" around the back area looking for the weird bends of pipes and hoses I might need for whatever project I am working on. Look at large truck radiator style hoses as well.

Once you have what you think is the final direction, you can get fancier with the right silicone hoses and such.
 
You must log in or register to reply here.
Back
Top