LIFE WITH SIRS

The "attenuation volume" issue is precisely why the SIR sits way out on the front of the airbox, where we have seen it in F3, FIA sportscars, etc. - or so I've read. Remember that air is a fluid - it flows and eddies and stuff. I can see how it might confuse things, putting the SIR close enough in front of the MAF that it in essence creates a blast of increasing-velocity air from that little hole.

Particularly if I didn't have a bottomless engineering budget, I'd be tempted to build the biggest airbox possible, and use the SIR as the inlet. Put the filter between the SIR and airflow sensor, to leave things as much like the OE MAF is used to seeing them, absent the restriction, and count on the flexibility built into the system to cope with some of the variables that remain, short of sonic velocities being reached at the SIR.

K
 
The "attenuation volume" issue is precisely why the SIR sits way out on the front of the airbox, where we have seen it in F3, FIA sportscars, etc. - or so I've read. Remember that air is a fluid - it flows and eddies and stuff. I can see how it might confuse things, putting the SIR close enough in front of the MAF that it in essence creates a blast of increasing-velocity air from that little hole.

Particularly if I didn't have a bottomless engineering budget, I'd be tempted to build the biggest airbox possible, and use the SIR as the inlet. Put the filter between the SIR and airflow sensor, to leave things as much like the OE MAF is used to seeing them, absent the restriction, and count on the flexibility built into the system to cope with some of the variables that remain, short of sonic velocities being reached at the SIR.
K [/b]
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You can't put the air filter between the sir and maf, the rule states all air must enter through the sir. If you put the air filter between the sir and maf you would be drawing in air that would not be going through the sir, making it illegal.
[/QUOTIt's on page 40 of the GT section of the GCR, called the "GTCS"
it says:

QUOTE
GTCS 17.1.2.F.4.i.10. Single Inlet Restrictors
a. The intent of this rule is to have a sealed system from
the Restrictor to the Intake Ports of the Cylinder Head.
All of the air entering the Intake Ports shall pass through
the specified Restrictor. Modification or addition to any
part of the Intake System that allows the introduction of
air into the Intake Ports that has not passed through the
specified Restrictor is prohibited.
b. The Engine Air Intake System must be fitted with an
aluminum air restrictor. The Intake System is defined
as an assembly of parts, including but not restricted
to: the Restrictor, Restrictor Housing, Ducting, Filters,
Air Box, Velocity Stacks, Throttle Body, Carburetors,
Manifold and Manifold Gasket up to the Intake Ports on
the Cylinder Head.
c. The Restrictor must be round in shape. The maximum
ID of the Restrictor is listed on the vehicle’s spec line.
The Restrictor’s maximum ID must be maintained for a
minimum length of 3mm. Restrictor mounting/placement
within the intake system is free, but must allow
accessibility for measurement. It is acceptable to have
some minor disassembly of the intake system to provide
access to the Restrictor for measurement. Measurement
device and restrictor shall be similar temperatures when
used.
d. Sealing the Restrictor from its supply of air must cause
the engine to stop within 4 seconds. This check is to be
made at an engine speed of approximately 2500 rpm.
The sealed airbox must withstand this test. Pressure
sensors present inside the intake system must be
disconnected during this check.
e. All GTL cars that have either an IR or SIR size (restricted)
listed on their spec line shall utilize an SIR for National
competitions.

So, all air goes through it.
 
With all due respect, I disagree.

Here's the pertinent quote:

QUOTE
GTCS 17.1.2.F.4.i.10. Single Inlet Restrictors
a. The intent of this rule is to have a sealed system from
the Restrictor to the Intake Ports of the Cylinder Head.
All of the air entering the Intake Ports shall pass through
the specified Restrictor. Modification or addition to any
part of the Intake System that allows the introduction of
air into the Intake Ports that has not passed through the
specified Restrictor is prohibited.[/b]
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So the key is that all air that gets to the intake ports has to pass thru the SIR.

So having the SIR in front of the air filter is fine, as long as the box is sealed that houses the air filter and the SIR. And it has to pass the 4 second rule.

Fab away!
 
I've seen SIRs mounted through the middle of the front of the car, right out where the main radiator intake opening is located. But they also had a custom low mounted radiator to accomodate the plumbing.

It seems kind of frustrating to be required to use this "trumpet" somewhere in the intake tract and not have any flexibility with respect to the location of the MAF with respect to the wiring loom.

Maybe the solution is to mount a "unicorn" horn way out in front with the SIR at the end. Don't follow too close though, you'll cut down on the airflow to the engine. :D
 
You can't put the air filter between the sir and maf, the rule states all air must enter through the sir. If you put the air filter between the sir and maf you would be drawing in air that would not be going through the sir, making it illegal. ...[/b]
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Um ... huh?

That doesn't have anything to do with anything. All of the air goes through the SIR, then all of the air goes through the filter, then all of the air goes into the engine. You street car filters all of the air that the engine breathes, right? I'll bet that the air goes through some kind of snorkle or intake hole before it gets to the filter, and that the intake tract is essentially sealed between that hole and, well, the end of the exhaust pipe for all practical purposes. Think SIR instead of snorkle hole and you're there.

That, and a couple decades of SIR-controlled Formula 3 cars - all of which do exactly what you claim isn't possible - MIGHT be some evidence that it is.

I don't have the faintest idea what you are talking about.

K
 
Um ... huh?

That doesn't have anything to do with anything. All of the air goes through the SIR, then all of the air goes through the filter, then all of the air goes into the engine. You street car filters all of the air that the engine breathes, right? I'll bet that the air goes through some kind of snorkle or intake hole before it gets to the filter, and that the intake tract is essentially sealed between that hole and, well, the end of the exhaust pipe for all practical purposes. Think SIR instead of snorkle hole and you're there.

That, and a couple decades of SIR-controlled Formula 3 cars - all of which do exactly what you claim isn't possible - MIGHT be some evidence that it is.

I don't have the faintest idea what you are talking about.

K
[/b]
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K,
I was thinking of a in line air filter and not using something like stock air filter box which would seal it from taking air from anywhere but the SIR. Building something like this to meet the 4 sec rule and keeping inside the engine compartment & legal could be an answer, It also will be a lot of time for experimentation. Maybe I can drop my car off with you and let you piss around with it. :D I should get it done by May 1st, this year, right? ;)

My next question is what would the air filter box do other than cut down on turbulence that would be created by the SIR? It seem to me that we spend money getting rid of the air filter boxes to use K&N cone tyoe filters for better flow. Anyone have a tuned header system for this? :D Hell a 100 hours of testing (including Dyno time) and you might be able to sell 2 or 3 of these. If you would want to keep your K&N cone type air filter would the SIR also work as well 1/2 between the AFM and TB. If you have to thein of air like a fluid isn't it best in a straight line?
 
Good morning campers!
Just a quick note to any E36 racers who are going to try the SIR deal. We have to be ready to race in one month! Not sure about you, but I haven't even got my 29mm SIR from Raetech yet.

I've written to SCCA asking for more time to install, dyno, burn chips, re-dyno and then track test the car with the SIR. I'm not talking about optimising the whole deal. I'm just talking about making the car raceworthy without risk of damaging the motor. If we get enough people writing maybe we can get a little more time.

Please write to: [email protected]

Thanks.
 
I emailed off a letter this morning John...NO confidence it will do any good...but...it's done.

Good morning campers!
Just a quick note to any E36 racers who are going to try the SIR deal. We have to be ready to race in one month! Not sure about you, but I haven't even got my 29mm SIR from Raetech yet.

I've written to SCCA asking for more time to install, dyno, burn chips, re-dyno and then track test the car with the SIR. I'm not talking about optimising the whole deal. I'm just talking about making the car raceworthy without risk of damaging the motor. If we get enough people writing maybe we can get a little more time.

Please write to: [email protected]

Thanks.
[/b]
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should have ours on friday, then to dyno. if everything works as advertised we'll do some track testing at roebling's test day.
 
Just to let you guys know, I have posted on our own forum (ITAC) about this. I think that there is support for an extention from 4 members, but as we don't have a con call with the CRB for weeks, I am not sure what we can do. If I can get a clear majority to support, perhaps we can send the CRB an ITAC request.

But, I'm new on the ITAC, so I'm not sure if thats an approved procedure, and even if it were to be, whether the CRB will agree.


Would a month be a helpful period?

Just thought you should know that your thoughts, letters and the situation isn't being ignored.

(And that I appreciate the letters that are reasonable and well thought out, as opposed to those that call us morons, LOL. )

(As a side note, I don't know who reads the letters along the way, but the CRB does occasionally stop in on the ITAC board and very occcasionaly posts a comment.)
 
Just to let you guys know, I have posted on our own forum (ITAC) about this. I think that there is support for an extention from 4 members, but as we don't have a con call with the CRB for weeks, I am not sure what we can do. If I can get a clear majority to support, perhaps we can send the CRB an ITAC request.

But, I'm new on the ITAC, so I'm not sure if thats an approved procedure, and even if it were to be, whether the CRB will agree.

Would a month be a helpful period?

Just thought you should know that your thoughts, letters and the situation isn't being ignored.

(And that I appreciate the letters that are reasonable and well thought out, as opposed to those that call us morons, LOL. )


(As a side note, I don't know who reads the letters along the way, but the CRB does occasionally stop in on the ITAC board and very occcasionaly posts a comment.)
[/b]
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Jake, I've had the pleasure of emailing thoughts on these matters to, let me say, who I think, someone of importance up in the SCCA. It is refreshing that someone like him takes the time to actually listen. Even though we don't 100% agree on everything, I think he is open minded and sincere, I'm sure he hopes things work out for what only could and should be better racing. I don't know for sure if my engine is built well enough to be competive. With my SIR otw I guess it's time to find out after testing, etc. etc.. I think 1 more month would be enough if the SCCA would grant us that. But if they don't, all we can do is get ready, test with what we have and know, then go for it. Either way, I've come this far, I'm stubborn and I want to see if this thing will work.

BTW JAKE, WHO YOU CALLING MORON!!!! ;)
 
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.
[/b]
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Yes, *however*...

One of the big issues is how the restrictor affects throttle transients and response. If you have a large enough volume intake tract, you can provide a "reservior" of air that can be tapped prior to pulling large flow through the restrictor. Think of it as an accumulator in hydraulic terms or a capacitor in electrical...

BTW- this is also why you want the Air Flow sensor (be it MAF, Vane Air, or other) to be in close to the stock location if using the stock computer. If going custom (which I pray you guys are), you can play a little. For carb guys, it's like changing intakes to one with a large volume under the carb- you need more pump shot because it takes the pressure "signal" longer to get to the carb jets... This is a MAJOR advantage of custom programming in ECU's- you can easily manipulate not only the amount of accel enrichment, but also the duration and other factors...
 
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