MSefi.com read only forum (Jan.15,2018)

Has anyone ever done any experimenting with the sub throttles on many TBs rather than just ignoring them or removing them?

It is my understanding that they help with throttle response much like a CV carburetor does.

Robert

Is a sub throttle like the Ford SHO's had?

73Eldo wrote:Is a sub throttle like the Ford SHO's had?

Not being very familiar with FI car stuff (yet), I don't know about that, but the sub-throttles in my TBs is basically a second set of butterflies on the atmospheric side of the throttle plates, operated by a stepper motor and equipped with its own position sensor. They could possibly be mistaken for choke plates if it were a carburetor.

From what I've read, they are used to vary the geometry of the intake tract. A rapid throttle opening at low RPM can perturb airflow momentarily, which changes the mixture. As I understand it, sub-throttle plates allow the TB to react like a CV carb does, opening as the air flow increases.

Obviously, there is no facility for that in the stock MegaSquirt, but I wondered if anyone has played with them at all?

Im having trouble understanding how that would help on a fuel injected setup. Have any more info on this idea?

I only saw the SHOs apart in a junkyard but what it looked like is that they are 4 valve motors and 2 intake runners for each cyl. There was a throttle looking blade on one and the injector was in the other one. I assume that those 'throttles' were closed during low demand times and opened for high demand. I assume the result was sort of a variable intake.

Most of what I have found via Google is in review and spec stuff, rather than engineering details, touting why they use it rather than how it works. For example, this snippet from a review of the 2006 Vulcan 2000:

To provide sharp throttle response at any rpm, the Vulcan 2000’s electronic engine control unit (ECU) manages electronic fuel injection with its dual 46mm throttle bodies and sub throttle valves, as well as the iridium spark plug ignition system. The sub throttle valves provide the Vulcan 2000 Classic LT with smooth throttle response, while the highly sophisticated fuel injection system’s fine atomizing injectors deliver an ultra-fine mist of fuel/air mixture to the cylinders for greater combustion efficiency, increased power and optimum fuel economy.

Similarly for the Yamaha R1 (2004):

And, what makes the YZF-R1 system unique is the adoption of a motor-operated sub-throttle valve controlled on the basis of information about engine rpm and the throttle opening fed back via the ECU in order to provide excellent power control characteristics. The functioning of the main and sub throttle valves enables optimum control of the intake air flow speed. This enables optimized volume efficiency across the entire rpm range, thus resulting in the kind of outstanding low- to mid-speed drivability only digital control can provide.

There are also some mentions of sub-throttles in shift control and traction control applications.

Robert

Dont some bikes also have a throttle sort of thing in the exhaust?

73Eldo wrote:Dont some bikes also have a throttle sort of thing in the exhaust?

I know of two-strokes that do, specifically the Rotax RAVE valve, but never heard of it on a four-stroke.

I don't think I ever mentioned that the sub-throttle equipped throttle bodies I have are removed from a 2003 Kawasaki ZX636R. I presume there is more of this on factory EFI than I was aware of. Then again, I am quite a newbie to EFI.

Robert

Sub-throttles are mostly for bikes. Basically, they are designed to keep you from having super jerky throttle response (potentially dangerous on a 180+hp sub 400lb machine) by moderating the rider's input. Not really necessary on a car. A CV carb is similar in operation, except it is automatic. IIRC, some manufacturers actually used a CV design for injected bikes (a secondary slide opened by vacuum.)
Some cars have variable tract intakes, such as BMW DISA. A secondary butterfly will open to change intake runner length or effective plenum volume.
Some cars have dual throttle butterflies that open either as a mechanical pair with one smaller and one larger, the larger opening with more pedal input. Some are opened by computer or vacuum.
Some cars have a combination of these systems. A US model 1996 BMW 318i has both a mechanically connected pair of butterflies (one small one large) and a 2 stage intake tract.
MS can control something simple (the BMW in the example uses an on'off signal for a vacuum switch) but more tinkering on your part may be necessary to control a stepper motor.

Yamaha used (maybe still) an EXUP exhaust valve on 4 strokes. It was a barrel shaped valve at the collector. I know they used it on a YZF R1, at least for a while.

-Paul

designed to keep you from having super jerky throttle response

That makes sense, and explains the "drivability" leanings in the sales brochures.

Thanks!

Some versions of the Nissan CA like ca18det for JDM, have sub-throttles and 8 ports:
http://en.wikipedia.org/wiki/Nissan_CA_engine
Apparently they weren't sure about emissions in other markets so did not exported and rest of the world had to live without.

My 99' Cougar 2.5 Duratec V6 has a dual track intake with separate tracks for each of the 2 intake valves per cylinder. One of the tracks is blocked off with a butterfly that is opened with a solenoid at a certain load/rpm. The linkage on it broke and I wired it open as a temporary fix. I noticed quite a difference at low to mid rpm, would assume from decreased port velocity. Fixed it and it runs much better. Probably worth looking into if you have a similar setup and are going to use it on the street. The IAC code could probably be modified to work.