What is the Purpose of the secondary throttles?

I have been toying with the idea of removing them because I was under the impression they where only used when cold to stop you WOT it. But I’ve you been playing with it and it looks like it shuts the Secondary throttle runners and slowly opens the closer you get to positive boost? (does that sound right?)

So in theory by removing them you are opening up your secondary’s on idle and low rpm? That said I’m not sure if that would Hinder the off boost power/response by removing (basically doubling+ the port volume?) or have I got this all wrong ?

 

How to Disable or Remove the Double Throttle

 

Yeh thats what i read but i'm aiming for as much low end/Mid range power as poss and looking at how mine opens / closes i don't see how it has anything to do with the cold running. I'm thinking its there to get the turbo spooled up as quick as poss (Primary runners are only used off Boost so the air speed would be higher?) maybe its so the Twin Turbo's Primary with its lower Volume has a bit of help (closes everything not being used?)

I don't think its there for Fun? and i don't like removing anything i don't fully understand.

 

Its primary function is:
What he means by this is that most people have not seen any difference with the cars performance if these are actually functioning and if they are not in working order they do tend to hurt performance.

Removal of them doesn't necessarily hurt low end performance/torque loss.
Many people have mentioned that it improves throttle response and their removal of their restriction improves airflow as even the provided link says that he has noted increase in boost creep

 

Thing is "The double throttle prevents you from using too much throttle before the car has completely warmed up" is wrong, when i looked it would still move the same amount and at the same Neg Boost etc if it was hot or cold.

I have just been chatting to a well known engine Builder who said he thought it was part of the Twin turbo system and was used to increase the off boost air speed through the primary runners for about town driving and fuel efficancy. nothing to do with On boost driving, because as soon as it hits 0 psi the secondary throttles are fully open.

But as with most things i've read its all just theorys and peoples hear say.

 

I tend to think the same as Grizzly- the double throttle moves the same amount no matter if the engine is warmed up or not. It cant prevent too much throttle under cold start running, as it moves the same amount no matter what engine temps are.

There's a lot of conjecture about what its real function is, but I would tend to think along the lines of it being used to reduce the size of the plenum, to increase air speed at lower rpm, to assist in throttle response. As the engine speed increases, it should open, increasing plenum volume, which would help with top end power.
Remember the old mechanical secondary Holley 4 barrel carbs- they bought the secondary venturis open mechanically with throttle input. Vacuum secondary versions pulled the secondary throttle plates open according to manifold vacuum.
You see this sort of thing these days with the "variable length intake runners" in newer tech cars- butterfly flaps open with electric motors, etc, to tune the effective resonant length & volume of the intake runners for various engine speeds. I believe this is just a crude early attempt on the FD- so crude, we may not recognize it as such :p
On a stock car, its probably good to keep. On something non-stock, the tuned length malarchy probably doesnt do much..

 

Its supposed to stop air surges on sudden throttle position change before the fuel duty cycle an catch-up (Causing you to run lean) according to the UK FSM. That being said..I've removed it on both my FD's w/o issues.

 

So in theory at low rpm (off boost) they should be dramaticly reducing the flow to the secondarys, so if this was left on would it help with a Half bridge's off boost low rpm driving issues?

This is just one of those things that you would have expected Mazda to bin with the end of Turbo2 but they felt it worth carrying over to the Twin Turbo? which is why i'm intrested

 

This is going to sound really sad but i fixed a Cam so i could see how they where working and drove round for a bit. LOL

Seems the secondary throttles dont open until you are close to 0 when you feed the power in slowly but if i floor it even in neg Boost they open almost Instantly. So next i'm going to drive it off boost for a bit and see if i can record acuratly the MPG then swap only the Upper Inlet for one thats been mod'd and try again. See if it does atualy make the off boost MPG better as its been sugested.

The things you do when your Board

 

First off, there's no big mystery or trick here. Simply hook your boost gauge up to the vacuum line to the double throttle and see what happens. I did that myself many moons ago .

The secondaries are either on or off - it's a simple solenoid controlling them, they're either full closed or full open, that's it.

The ECU keeps them closed until around 50 deg. C (if memory serves on that number) then opens them. That's it. It's to keep you from going full throttle with the engine cold and possibly to help cold mixtures, but that's it. When the engine is at operating temp they are open and stay open.

I removed mine when I put on my bored out throttle body. Noticed no difference in driveability or cold start driving. Of course, I could now go full throttle cold but I'm smart enough to know better .

If you'd like to test for yourself, T your boost gauge into the vacuum line to the secondary throttle actuator. Takes like 1 minute and you don't have to take anything apart. If you see vacuum, it's closed, if you see atmospheric (0), it's open.

Dale

 

Ok well thats odd, because when its cold it does exactly the same thing as when its warm? also the dont stay open when its hot, as i say they flick open very quick when you WOT but if you feed it in the stay shut upto 0. Could that be because of the PFC its running?

Also i'm getting really good MPG off boost (27mpg on a street ported Single) can you say 100% thats not going to loose some of that by removing the secondary Throttles?

 

Remove it, its for cold engine only. If its closed during a warm engine, the solenoid is probably faulty (or its possible the pfc does not control it, i'm not sure). It works off vacuum, if there is no vacuum, it will not close which would explain your opening when you give it WOT or boost.

If you don't believe it won't have an affect on anything from the members here that did this over 10 years ago. You can test if it affects anything by simply disconnecting the vacuum line and capping it (screw being the easiest) so you don't have a vacuum leak. This will keep them open all the time. After you realize it has no affect on anything, you can remove them to take advantage of the restriction removal. Going a step further, you can put a grinder on it to remove the material in the middle to reduce turbulence and increase plenum size....



thewird

 

Yeh i did all that on my T2 (fd upper manifold with the Secondarys removed and port matched etc) but at the same hp as my FD i was doing 19-22mpg around town and beleve me when i say this (i still have the Vid of it when i was checking) when i drive around town Off boost the Secondary Throttles are shut they open ither WOT or at 0, now i couldn't tell you if its been modified but what i can say is it doesn't matter if its hot cold inbetween it still does the same thing at the same time.

I couldn't tell you if there faulty but they don't look it to me? i will try blanking the vac pipe off and see what happens.

I know every one keeps telling me that when the engine is warm they should stay open all the time but mine don't. The question is this, why i'm seeing much better MPG off boost than all the cars with simalar mods?

 

You're getting the same "off boost" mpg as I am.

27imp mpg ~ 22us mpg

I have a streetported engine with bnr's and many other mods.

I still have the double throttle.

-Geoff

 

Because internet.

thewird

 

if it stays closed when warm then your vacuum routing is probably incorrect, they should default to full open even if you have the vacuum line disconnected to the actuator on top of the UIM.

it is mainly as said, to prevent cold engine WOT actuation to limit power until the engine is fully warmed up. when the engine is cold the internals are relaxed and it is not sealing fully and the coolant seals may be exposed slightly to the combustion chamber which can damage them if you run the car hard with a cold engine. when the engine is warm the housings to irons will virtually seal everything without much assistance from the coolant seals.

 

So what you’re saying is it should be open or closed? None of this flicking open under throttle etc.?

The reason i ask is i have just been looking at my fd and thought I’d check its all piped correctly and i even swapped the solenoid over for a brand new one i had knocking about. Nothing has changed? it still flicks open when its cold and you blip the throttle and its still closed when its idling at full operating temp? I even did as suggested and ran it with my Mityvac connected up and watched when the ecu opened the Secondary’s? I have even checked to make sure the Temp sensors etc are all functioning correctly but it wouldn't explain why it opens when cold etc.

I don't doubt what you are saying is correct but mine is not working as you suggest.

 

No i meant here in the UK, for some reason (probably down to mapping tbh or i am less heavy footed). The people with similar 450ish hp single turbos are not seeing any more than very early 20's to the gallon.

Yes i get you are using a different Gallon and climate etc but i don't like comparing Internet Figures to what i'm actually doing so i talk to people locally to me with simalar specs.

 

ok slightly diffrent question, Are the Primary ports diffrent timing just or the cold running/Idle when the secondary throttles are shut?

 

Any negative with not closing up the holes after taking out the butterfly? I see where some have put bolts in those holes, but I'm not will to take the risk of that guy coming out one day.

Based on thewird's pic it looks like the holes can stay?

 

^those bolts are obviously not just put in there, they're tapped and then threaded in. They're not going anywhere if done properly.

You'll need to close those holes otherwise, you'll have a boost leak.

 

I guess your right.. at a glance it didn't look like they open to the atmosphere, but obviously they would have too for the actuator to open them.