The double throttle exists for one reason only--to keep joe public from redlining/boosting his FD while the engine is still cold. For most of those on this forum, it's not necessary.

Once removed, you have one less restriction in the intake path, and less useless clutter in your engine bay. There is no re-tuning needed, and the map sensor is not affected at all.

When my dad bought his near-stock R1, I noticed that it seemed to be faster than it should be, given it's lack of serious mods. Turns out that the previous owner had removed the double throttle and deleted the coolant through the throttle body. He was running on the stock ecu. My dad ended up dynoing 290 rwhp with only intake, dp, cb, and pfs piggyback at 12 psi.

A few of you said that the reason to do this is if you’re going single or non-sequential. Is there any detrimental consequences for doing this mod with stock sequential?

"Have not seen these tables in the 1994 factory workshop manual. Would appreciate gaining knowledge from your experience. Reference? Link?"

You need the datalogit to see and adjust both of these tables.
One of them is adjustable with the PFC commander.
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"Is there any detrimental consequences for doing this mod with stock sequential?"

NO problem. As I said the purpose of the mod is to increase air flow through the throttle body by removing a source of restriction and turbulance.

here you go chuck, this is one i did for a customers car!! welded, ported and "polished" (really just smoothed out a good bit).
-J

I fail to see how it does this, if it works as advertised. My impression is that it only "slightly delays" (Mazda's words, manual page F-137) the opening of the double throttle butterfly until the MAP sensor can catch up; it does not prevent fully opening in order to inhibit full power. Apparently when cold, the A/F ratio cannot richen quickly enough to prevent hesitation when suddenly accelerating, without the aid of the double-throttle being temporarily closed. But this would not prevent one from redlining the engine when cold, unless Mazda's statement is false. Are you saying that the explanation is wrong, and that the double-throttle opening depends only on coolant temperature, and not on the PCME terminal 30 just delaying its voltage change temporarily for benefit of A/F ratio under acceleration when cold? Our car uses the stock ECU. It sounds as if these tables were not generated by Mazda but rather by the Apexi people. Is that correct? If so, how does that relate to the double-throttle operation on a stock engine, or to elimination of the double throttle altogether?

The double throttle prevents boost above 7 psi when the water temp is below 176F.

The Apexi uses the same tables as the stock ecu, while adding a few controllable options (oiling, boost control, fan settings, etc).

As cobbled together as that mod was it's unfortunate that we see as bad or worse nearly everyday. Someone butchers one of the car's systems and insists it had to be done to "improve performance". :wallbash:

it's the one system I regret removing...

using a haltech ECU...I wish I still had it [DT] to increase low end torque with a single turbo.

Re-wire the system to open around 3psi boost...when I start suppling fuel to the secondary ports, why give them air without fuel???

but that should be discussed in another thread.

I agree, at least on stock/rechipped ECU's. When I removed mine, it immediately introduced the "cold car hesitation". I only removed mine as my Charge Control solenoid failed and I used the DT solenoid to replace it. In hindsight, I wish I would have just bought another solenoid.

Aha... I wondered why Mazda would have added it if they had not found it necessary. My bad, though, for interpreting "temporarily" to mean fractions of a second, if the valve is only sensitive to coolant temperature. Surely the MAP sensor cannot have that much delay!

With the PFC, even though the stock transistion duty cylce % is set at a 40%,
it actually logged at 47-48%. I set mine down to 30% and it now logs at 37% and the engine responce is so much better. This and more info about this was posted by me on the PFC forum. This summer I plan to experiment with the secondaries coming on sooner and closer to the point of the secondary throttle opening up.
But opening up does not say how wide they are opened.

You could try something similar with your Haltech.

^I would but I've been advised not to add double throttle back into my UIM...and I've haven't been sold a good unit yet.


I didn't realize the PFC added options to the double throttle control...that is the coolest thing I've heard the PFC doing.

I believe it's a combination of both water and air intake temp. I have an air intake temp sensor on my stock my fd. My double throttles wont open till a specific air temp. If the air is too cold, the throttles wont open regarless of engine temp. I can't remember the specific air temp mine open at.

Not making excusses, just stating a fact. Though the job wasn't done to your satisfaction, it still worked.

Your lack of low end was nothing to do with the elimination of your DT. It has everything to do with your single set-up and decreased intake air velocity at lower rpm's. What info did you get that info from?

In the Fd & Fc's throttle body, the secondary throttle plates have a mechanical delayed opening. In very light throttle, only the primary ports are getting the air flow. Mazda engineered the TB this way to help with the intake air velocity in low rpm's. The higher intake velocity better helps the air fill the combustion chamber (which is most imortant in a NA set-up). Regardless if your engine is NA, turbo, or supercharged, the more air you can cram in the combustion chamber at any given rpm, the more bang you will get when the fuel ignites, therefore giving your engine more leverage against the rotors and e-shaft. This is how you get more torque.

The DT is nothing more than Mazda means to control boost when the engine is cold and air intake temp it too low. That's it. Once some of you guys began to understand how a NA rotary works, then you will truely understand how power is made.

^I know it has nothing to do with removing the system...

I wish it was still installed so I could modify (hence, why I said re-wire/plumb) it to increase the intake air velocity at lower rpm's and boost by forcing EVERYTHING thru my primary ports.

trust me...I fully understand.

^ I see what your saying but, it's still not going to help you much if you did that. Think about what's going on inside the engine. On a stock Fd with sequencials, when the DT open after the engine gets warm, they stay open. They do nothing else. They don't open and shut when you apply throttle. When they are open, your bottom end doesn't change on bit. It's the delayed opening of the secondary throttle plates ( and only these plates) that's responsible for helping with your bottom end. If you want to furthure delay the secondary throttle plates, they can be adjusted to open later, but you will loose some top end because now the plates wont fully open all the way unless you get creative in modifying them.

Look at the guys who go non-seq? They loose a ton of botton end simply due to a lack of air velocity in the bottom end all because of slower spooling of the turbos.

I'm talking about making the double throttle plates act almost like AUX ports on an N/A. This is why I said... Which they keep the 5/6th ports closed until there is enough air flow...when closed they are there to increase the air velocity in the smaller secondary ports.

there are a few people who are running this type of thing...reason behind my regret [removing DT], is I didn't know such a thing could help and I was just all about removing things.

Well good luck with your experiment.

Not to mention you could potentially get better atomization of your fuel...

(I don't know if atomization is the word I want to use, but you could get a better distribution)

Velocity is usually more important volume capability. Air momentum is a large determining factor in the capacity of the intake charge.

hence why the na rotarys have the 5/6th ports. the control this velocity to tune for optimum performance through the entire rpm range.

So what is it? A tradeoff between keeping the DT control and associated better low end torque or removing the DT altogether and increasing high end Hp through less flow perturbances in the intake tract?

Help me understand ;)

Crispy