Idle air motors addressed , letter # 31796

P

Protech Racing

Well-known member
The rules state that all air must enter through the throttle body . All ECU cars use some sort of throttle by pass to control idle. The letter addresses that oversite with" must retrain OE throttle system or be eliminated entirely ".
 
No one is allowed to view other members' letters, other than its status. Which is not particularly useful (even to the letter writer...)

I retrain mine to rollover.

This is a good point, however. What keeps someone with a fully-tune-able ECU from opening the IAV bypass during full throttle? Not that it's a lot of airflow...

And, given you can't stop it (or scrutineer it), what do you do about it? Is it worth adjusting weights to accomodate the possibility? You'll need to deep-investigate the advantages of each individual implementation if you're going to...

In the end, it's probably "warts and all." Or ban that evil "fee-yoooll injection dragon" straight to hell!

GA
 
Sorry, Thought it might already have been addressed. I sent a letter also. You know every car with an idle air bypass screw is just as illegal as a car with an electronic idle air valve. (Miata, Mk 1 & Mk2 VW, to name a couple) The issue I have is with a wide duration camshaft, the high idle required to keep it running using open throttle butterfly doesn't kill a hot engine at shutdown. A factory idle control valve shuts off the air and the engine stalls.
 
david boles":1qx0r445 said:
Sorry, Thought it might already have been addressed. I sent a letter also. You know every car with an idle air bypass screw is just as illegal as a car with an electronic idle air valve. (Miata, Mk 1 & Mk2 VW, to name a couple) The issue I have is with a wide duration camshaft, the high idle required to keep it running using open throttle butterfly doesn't kill a hot engine at shutdown. A factory idle control valve shuts off the air and the engine stalls.
Click to expand...

Are you saying the stock vw throttle body is illegal? Or just using it as a comparison to the electronic.

Also, killing fuel and plugs should shut off the engine, no? From a safety standpoint.
 
I drilled a .200 hole in the throttle plate ,and screwed the idle screw all the way in to be legal . My idle air motor hose is removed and plugged to be 100% legal .
I tried useing the bypass hose for more air /faster back in the ITB days. Waste of time , idled at 2300.
Of course the dat acc system was a VHS camera strapped to the cage , pointed at the tach and dash mounted WOT light and brake light indicator. Not great data. I still have the camera , ,might have a porn tape in it:). I had a client that was part of a group that made a few movies. "Backside to the future" and "Buttsizer, King of rears" Funny stuff . I used to work on Deloreans . Not the one in the movie I dont think tho.

Thanks to Matt for usefull addition to the tthread. I put that with the rest of your useful post ..
Yeah , I flunked out of engineering school for english. whood da thought it . ? Do ya know how hard it is to mispeel all these words today with autcorectum ? If it 's not all underlined in red I go back to fix it mo better.
 
I'm confused. Are there cars where the IAC is drawing air that does not come through the throttle body?
 
planet6racing":27whhugs said:
I'm confused. Are there cars where the IAC is drawing air that does not come through the throttle body?
Click to expand...

"All inducted air must pass through the throttle body and be subject to control
by the throttle butterfly."

IAC's bypass the butterfly, that's the bugaboo
 
planet6racing":1dfrbbb7 said:
OK, thank you.

Does it matter? (asking for a friend...)
Click to expand...
depending on how large someone decides to modify their IACV, it could be significant enough to cause a power increase.
 
Yep, I took my IAC off. And there is a plate there now. 'Cause that is how I read the rules.

Another fellow's father was telling me I should have the ECU open it during full throttle.

.
 
If the throttle body ID is the same diameter on both sides of the butterfly, (and the IACV intake galley is located in the throttle body ahead of the butterfly) then it wouldn't account for any added airflow at WOT, only at idle and possibly at part throttle. If the IACV intake is not in the throttle body, then you would have additional airflow at WOT. Still, the rule would need to be clarified to avoid any tech shed drama.
 
That appears to be what's going on here.
Every fuel injected car I've worked on and paid attention to (a handful of Nissans over the years), the IACV is separate from the throttle body and sucks air from behind the MAF. So it's metered for fuel but not passed through the throttle body.

Newer cars like my Toyota that have a throttle by wire use the throttle body itself for idle control.
 
Jason, I'm not saying that your throttle body is illegal, just an example that I'm familiar with. The problem that initiated my letter to the CRB is my MK3 VW has a factory original idle air control motor that is not part of the throttle body. It is a real pain to get it to idle with a high duration camshaft without the idle control. It either idles at 3500 RPM or stalls if you close the throttle butterfly a small bit. The idle control valve controls it nicely. As Mike said in an earlier post, the amount of air that they bypass would be insignificant at wide open throttle.
 
DCOE%20Idle%20Circuit.gif


Note the idle circuit of a DCOE Weber. The wording of the carb section of the PCSis slightly different to the fuel injection throttle body section, but nonetheless the Weber (and other carbs) technically violates it by allowing a small amount of air to bypass the venturi and throttle plate.

I'm sure that no one ever worried about this, same as the VW Mk1/2 idle bypass screw, since the systems are stock and the orifices tiny. I have a 1990s Ford V6 however that has an ECU controlled bypass with passages a good half inch in diameter.

If we are going to change the wording and then enforce it, let's make sure that the older FI TBs and carbs don't get caught up.
 
Here's the best photo I could find of a KA24DE intake manifold showing all of the guts and relative position of everything.

Note the idle circuit has a completely separate air tube- roughly 1/2" diameter- coming from the intake tubing. it completely bypasses the throttle body and everything about it. all of the idle hardware is at the back end of the manifold, same for the EGR. what's the total airflow capability from that? It's surely more than zero, but likely not 'significant'. Of course that's one case of many many engines eligible for Prod...
 
RX7's have 2 separate valves that actuated to allow air in past the TB. In the ITS days we did dyno testing with them open to atmosphere and picked up nothing.
 
If high velocity air is passing over the bypass (when wot) would the air flow not create a vacuum on the by-pass that is greater than the intake manifold vacuum? Fluids was not my best subject so I don’t recall. I would think some tests or calcs at least could shine light on any illegal benefit. If you wouldn’t just “have a bad vacuum cap” I wouldn’t think an internal vacuum leak would be beneficial either.
 
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