The dual throttle body thread

[POPSTOY]

Originally Posted by ACBlessing

Does FFS make an adaptor or method of remote fitting the IAC that can be used for a hotside?

I believe they do. Bob

[Steve in VC]

Originally Posted by ACBlessing

Does FFS make an adaptor or method of remote fitting the IAC that can be used for a hotside?

Yes, it is a bracket with two hose barbs.

[ACBlessing]

Hmm, it seems then that anyone could adapt this to their current hotside for better performance. I'll ask Tom about it tomorrow. So, then a relocated IAC seems an appropriate add on to the dual TB mod. Anyone have a picture of one? Twenty eight posts and not a single picture of anything yet.

[Reverant]

I got the IAC relocation kit to use with my throttle bodies; I got the kit from Moss (its part of the MP62 Supercharger kit but you can get the parts seperately). I think I paid ~180 four months ago.

Dimitris

[Godless Commie]

Hi, my name is Godless Commie, and I have successfully done the dual throttle mod.


Why did I do it?

I have a hotside S/C, with a TDR IC. That spells extra throttled volume, many times over the stock.

Hotside setups indeed utilize a remote IAC valve, which means more "vacuum volume", by way of extra plumbing.
That, coupled with the excess throttled volume and the parasitic and variable loads on the engine seriously overtaxes the IAC valve, which was designed to respond to a much smaller throttled volume.

I had my stock throttle body on the shelf, anyway. A large, 75mm BBK throttle body suits the requirements of the MP62 blower.
While the car had amazing performance, I seemed to battle an ongoing idle quality problem:
The car would start fine, and once everything was nice and warm, the idle would shoot to 1600-1700 rpms. Or, I would have a hard time keeping the engine running in the winter, following a cold start.
Or, it would just hunt a couple of times, and die.
Man, I was a heel and toe maniac for a while.

(For the record, coldsides do not have this problem due to the massive difference in throttled volume.)

So, I started searching around. The logical solution seemed to be the dual throttle mod.

Let me tell you this befor I go any further: Just do it. Do not even think twice. If you have a hotside SC, waste no time. Start gathering parts, plan your work, have someone do it, but do it.

I want my car to be "civilized", meaning excellent parking lot manners, smooth take up, rock steady idle, and a ferocious beast when I get on the go pedal. Like a Maserati.

Before the mod, all I had was a ferocious beast. Now, it wears silk gloves.

The logic is too friggin' simple:
Keep your pre-blower TB (no matter what you have got there. Then, just add a stock TB on the intake manifold. In other words, remove the dummy TB, and install the stock one there. It will have all the flow you need. I will not go into the math here, but trust me on this. (You will be pushing compressed air through that stock TB.)

Oh, get a can of carb spray and clean the TB before you install it.

Then, you need two things, a second throttle cable, and a new cable pulley to operate that cable.
One caveat, though.. The throttle cable needs to have two cylindrical ends on it, just like the way the stock cable terminates on the TB pulley.

Just go to a bike shop. They make all sorts of cables, and I am sure they can bang one out for you in five minutes. I paid less than 20 bucks for mine.
The pulley is easier even, if you have two stock TBs. Just visit your local wrecking yard and yank one for a couple of bucks.

If you happen to have a 75 mm BBK like I have, (I am so glad I was good at analytical geometry in high school, like 30 years ago) the outer dimension, where the cable rides, should be exactly 42mm.

I will post detailed pictures as soon as I can.

Oh, you need to get creative and fabricate a bracket for the second cable. It took me all of 15 minutes to make that. Simpler that you would think.

Before I forget, The IAC and the TPS need to be mounted on the stock IAC valve on the intake manifold, so the idle corrections could be performed. The reason why the TPS needs to be on this location is simple, as well. The pre-blower TB gets adjusted whenever an adjustment is necessary, and is left "cracked" for reasons I will explain. There is no need to keep confusing the ECU with new settings every time an adjustment is made.

Do not start the engine yet.

So, once all the hardware is mounted, the first step is to manually "crack" (read: open) the pre-blower TB a bit. Here, "a bit" means opening it as if you were setting the idle at, say, 2000 RPM. You need to do that so the blower can breathe.
Then, adjust the slack on the second throttle cable, so it is perfectly snug, with almost no slack in the line. Move the stock TB like you are revving the engine and let go, both should slam on their stops simultaneously. (The engine should be off)
Likewise, full throttle should be just that on both throttles.

Start the engine. You may hear funny noises, politely ignore all that.
Once the engine is warm, make sure you have perfect idle. 850-900 RPM.
Then, start adjusting the pre-blower TB, very small adjustments, till the funny noise goes away, just to the point where the whistling stops.
Rev the engine to about 2500 RPM, and let go. There should be no hesitation (assuming you have no other problems like timing, etc). Make vary small adjustments, if you have to.
Go drive the car just as you always do.
When you are back, pop the hood, and with the engine off, move the stock butterfly and observe correct operation.

Then, try to forget about all you have done by the next time you get in your car.
Be amazed at how it drives, and enjoy.

[Godless Commie]

Originally Posted by ACBlessing

Hmm, it seems then that anyone could adapt this to their current hotside for better performance. I'll ask Tom about it tomorrow. So, then a relocated IAC seems an appropriate add on to the dual TB mod. Anyone have a picture of one? Twenty eight posts and not a single picture of anything yet.

The IAC has to be on the stock TB, which is mounted on the intake manifold.
A relocated IAC defeats the purpose of the mod.

[Godless Commie]

Originally Posted by Fletcher

I've never heard of "the dual throttle-body mod".
What is it supposed to achieve (besides, you know, having two throttle-bodies) ?

Does it give more power? Does it give better throttle response?

Is there any reason to do it apart from being able to say you've done it?

I had never heard of that till I had a supercharger, too.

It actually achieves a lot. (See my long post above)
It does not "give" more power, but you get a much crisper throttle response.
The reasons are are also stated above: rock solid idle, perfect cold and hot starts, no dips, no problems..

And, yes, there are plenty good reasons for doing it.

[Steve in VC]

Originally Posted by Godless Commie

Hi, my name is Godless Commie, and I have successfully done the dual throttle mod.


Why did I do it?

I have a hotside S/C, with a TDR IC. That spells extra throttled volume, many times over the stock.

Hotside setups indeed utilize a remote IAC valve, which means more "vacuum volume", by way of extra plumbing.
That, coupled with the excess throttled volume and the parasitic and variable loads on the engine seriously overtaxes the IAC valve, which was designed to respond to a much smaller throttled volume.

I had my stock throttle body on the shelf, anyway. A large, 75mm BBK throttle body suits the requirements of the MP62 blower.
While the car had amazing performance, I seemed to battle an ongoing idle quality problem:
The car would start fine, and once everything was nice and warm, the idle would shoot to 1600-1700 rpms. Or, I would have a hard time keeping the engine running in the winter, following a cold start.
Or, it would just hunt a couple of times, and die.
Man, I was a heel and toe maniac for a while.

(For the record, coldsides do not have this problem due to the massive difference in throttled volume.)

So, I started searching around. The logical solution seemed to be the dual throttle mod.

Let me tell you this befor I go any further: Just do it. Do not even think twice. If you have a hotside SC, waste no time. Start gathering parts, plan your work, have someone do it, but do it.

I want my car to be "civilized", meaning excellent parking lot manners, smooth take up, rock steady idle, and a ferocious beast when I get on the go pedal. Like a Maserati.

Before the mod, all I had was a ferocious beast. Now, it wears silk gloves.

The logic is too friggin' simple:
Keep your pre-blower TB (no matter what you have got there. Then, just add a stock TB on the intake manifold. In other words, remove the dummy TB, and install the stock one there. It will have all the flow you need. I will not go into the math here, but trust me on this. (You will be pushing compressed air through that stock TB.)

Oh, get a can of carb spray and clean the TB before you install it.

Then, you need two things, a second throttle cable, and a new cable pulley to operate that cable.
One caveat, though.. The throttle cable needs to have two cylindrical ends on it, just like the way the stock cable terminates on the TB pulley.

Just go to a bike shop. They make all sorts of cables, and I am sure they can bang one out for you in five minutes. I paid less than 20 bucks for mine.
The pulley is easier even, if you have two stock TBs. Just visit your local wrecking yard and yank one for a couple of bucks.

If you happen to have a 75 mm BBK like I have, (I am so glad I was good at analytical geometry in high school, like 30 years ago) the outer dimension, where the cable rides, should be exactly 42mm.

I will post detailed pictures as soon as I can.

Oh, you need to get creative and fabricate a bracket for the second cable. It took me all of 15 minutes to make that. Simpler that you would think.

Before I forget, The IAC and the TPS need to be mounted on the stock IAC valve on the intake manifold, so the idle corrections could be performed. The reason why the TPS needs to be on this location is simple, as well. The pre-blower TB gets adjusted whenever an adjustment is necessary, and is left "cracked" for reasons I will explain. There is no need to keep confusing the ECU with new settings every time an adjustment is made.

Do not start the engine yet.

So, once all the hardware is mounted, the first step is to manually "crack" (read: open) the pre-blower TB a bit. Here, "a bit" means opening it as if you were setting the idle at, say, 2000 RPM. You need to do that so the blower can breathe.
Then, adjust the slack on the second throttle cable, so it is perfectly snug, with almost no slack in the line. Move the stock TB like you are revving the engine and let go, both should slam on their stops simultaneously. (The engine should be off)
Likewise, full throttle should be just that on both throttles.

Start the engine. You may hear funny noises, politely ignore all that.
Once the engine is warm, make sure you have perfect idle. 850-900 RPM.
Then, start adjusting the pre-blower TB, very small adjustments, till the funny noise goes away, just to the point where the whistling stops.
Rev the engine to about 2500 RPM, and let go. There should be no hesitation (assuming you have no other problems like timing, etc). Make vary small adjustments, if you have to.
Go drive the car just as you always do.
When you are back, pop the hood, and with the engine off, move the stock butterfly and observe correct operation.

Then, try to forget about all you have done by the next time you get in your car.
Be amazed at how it drives, and enjoy.

Very nice writeup, with the details that will keep novices from freaking out.

Thanks,
Steve

[ACBlessing]

Thanks for contributing GC. Can't wait to see your work! You make it sound easy but I guess that's your talent for explanation. I don't think anyone in the thead so far has done a DTB so please spare not detail nor photo, even if it seems insignificant to you.


I your first line, you say "Hotside setups indeed utilize a remote IAC valve..." but later say the IAC must be mounted to the intake TB. I take it you mean the intake TB is the "remote" location for the IAC?

For a typical hotside SC install, the dummy TB is mounted to the intake and the IAC is mounted directly beneath it just as it was when the stock TB was there. The stock TB then gets mounted to the SC and the TPS goes along with it (along with running the TPS wiring to its new location which was a pain).

With DTB, the dummy TB is removed and a real TB put in its place, the IAC mounted beneath it just as before but now the TPS must be moved (again) from pre-blower TB, back to the new TB.

I know it's basic but I wanted to be clear.

Okay, about the pulley. The NB's TB pulley is pressed in whereas the NA's is bolted on and can be removed. I suppose I can get another NB pully, make an aluminum spacer and bolt them together. Then I won't have to worry about getting the diameter correct.

I don't know what a "75mm BBK is."

As per the cable, I take it there are two ways to route it. Both in parallel and one in front of the other. I like the parallel idea and I think that's what you run. I read that a bike shop can make one and the barrel fitting must be present to connect it to the TB pulley but is there any secret to the cable housing length? How would I mount that cable to my DIY bracket? Wouldn't a universal automotive throttle cable be better because it is the fitting to mount to a bracket?

Actually, I'm overthinking it all right now. I'm sure your photos will answer a lot of questions so I'll wait for those.

I do want to know more about larger TBs like a Ford Mustang's but I'm not going to even attempt it until I'm adept at this basic DTB. I just don't see how a Mustang TB would even mount much less what to do about a throttle position sensor and IAC.

[Tom@FFS]

Alex, The reason to move the IAC on a hotside is that it is currently mounted on the dummy throttle body. Located there it sees boost during boost. The instant you lift, the boost goes to vaccum and the IAC needs to take a stab at setting the idle "target". The odds of that happening are slim. When you move it off the DTB, it no longer sees boost and the world, although still imperfect (still not a Coldside, doncha know? ), is waaay better. The internal spring(s) no longer have to unload all that unwanted force and have time to react in those few milliseconds to stop the droop/stall condition.

That's my story and I'm sticking to it.

[Steve in VC]

Originally Posted by ACBlessing

Thanks for contributing GC. Can't wait to see your work! You make it sound easy but I guess that's your talent for explanation. I don't think anyone in the thead so far has done a DTB so please spare not detail nor photo, even if it seems insignificant to you.


I your first line, you say "Hotside setups indeed utilize a remote IAC valve..." but later say the IAC must be mounted to the intake TB. I take it you mean the intake TB is the "remote" location for the IAC?

For a typical hotside SC install, the dummy TB is mounted to the intake and the IAC is mounted directly beneath it just as it was when the stock TB was there. The stock TB then gets mounted to the SC and the TPS goes along with it (along with running the TPS wiring to its new location which was a pain).

With DTB, the dummy TB is removed and a real TB put in its place, the IAC mounted beneath it just as before but now the TPS must be moved (again) from pre-blower TB, back to the new TB.

I know it's basic but I wanted to be clear.

Okay, about the pulley. The NB's TB pulley is pressed in whereas the NA's is bolted on and can be removed. I suppose I can get another NB pully, make an aluminum spacer and bolt them together. Then I won't have to worry about getting the diameter correct.

I don't know what a "75mm BBK is."

As per the cable, I take it there are two ways to route it. Both in parallel and one in front of the other. I like the parallel idea and I think that's what you run. I read that a bike shop can make one and the barrel fitting must be present to connect it to the TB pulley but is there any secret to the cable housing length? How would I mount that cable to my DIY bracket? Wouldn't a universal automotive throttle cable be better because it is the fitting to mount to a bracket?

Actually, I'm overthinking it all right now. I'm sure your photos will answer a lot of questions so I'll wait for those.

I do want to know more about larger TBs like a Ford Mustang's but I'm not going to even attempt it until I'm adept at this basic DTB. I just don't see how a Mustang TB would even mount much less what to do about a throttle position sensor and IAC.

75mm BBK is a 75mm throttle body, used in front of the SC, the stock is fine in the stock location.

[Hamid97]

ACBlessing,

With the old BRP SC hotside kits, a "BTB" or Big Throttle Body was available as a power adder to the stock kit. Typically around 70 or 75mm in size. They were Mustang throttle bodies that were slightly modified. Actually, I think they were barely modified really. Just a small cut on the throttle cable wheel is all I noticed. They also had two different brands of throttle bodies that were used. The BBK throttle body was a good quality unit, then they started using Mac throttle bodies, which wern't as good. I have a Mac unfortunately, but honestly it has been working without any issues for 5 years. With the BTB kit, you also needed a bored out throttle body adapter plate which was sandwiched between the Throttle body and blower. The original plate had a veeeery tiny opening, and therefore it made a good 10hp or more by increasing the size of the hole to fit the BTB. Lastly, BRP also offered the DTB or dummy throttle body to be polished as well to also increase flow. They would eliminate the lip on the DTB and created a smoother transition into the intake manifold.

-Hamid

[Godless Commie]

Ok, pics, as promised..

Here we go:

This is a close up of my cable pulley assembly.
Since I have two very different kinds of throttle bodies on my engine, I had to calculate angles and amount of cable pulled, etc. Long story short, the outside diameter of the second pulley (where the cable rides, the groove I mean) is exactly 42 mm.)

I welded a steel "ring" (actually a housing of sorts) on the original pulley. the aluminum pulley was then press fit in that housing. Works great. There are a few more detail pics of the pulley setup.

[Godless Commie]

Here is the pulley up close, from a different angle:

(I moved the vacuum line for the fuel pressure regulator out of the way for clarity.)

[Godless Commie]

Here are a couple shots of the bracket for the second cable:

I just used a piece of sheet metal, cut a groove to accept the new cable, and incorporated it into the existing bracket with a couple of nuts and bolts. Painted black.
(Never got around to painting the pulley assembly)

[Godless Commie]

Here's another shot of the pulley & bracket:

[Godless Commie]

So, the throttle cable goes around the engine at the back,




I mean, it's this one:

[Godless Commie]

... all the way to the pre-blower TB.

Notice both ends of the throttle cable are adjustable.

Note: To measure your cable length, use some extension cord. Lay the extension cord as accurately as possible between the two TB brackets, paying attention to the actual routing as you choose. Once you are satisfied with the routing, and that nothing binds, measure the extension cord, and you will have the exact length of the cable sheath. Then tell the guy whoever is building your cable you want a cable with two adjustable ends, and add one inch to your measurement (so the total length of the sheath, including the adjustable ends will be one inch longer than what you have measured on your engine) and you will have a perfect fit.

As for the steel cable itself, you have to make an allowance for the amount of cable that wraps around the pulleys, as well. Best thing to do is have the guy crimp just one end, and give you the cable and the barrel end separately. That way, you can crimp it in place once you are perfectly satisfied with the length (Leave the cable adjusting nuts in the middle for this step). Do not take this step for granted; too much or too little cable may exceed the sheath's adjusting range).

[Godless Commie]

Before I forget, please ignore my cable routing setup. Yours may look entirely different than mine. It probably will. What matters here is the fact that the cable has got to get to the TB somehow. And it has a bracket. Just connect the dots.

Here's my setup from another angle.

THE CABLE BETWEEN THE THE TWO THROTTLE BODIES MUST BE FREE OF SLACK.

[Godless Commie]

Here's a trick I found pretty helpful..

With two TBs, you will be pressing the gas pedal against two sets of return springs. This could be inconvenient, especially in cases where one switches between cars often, or where more than one person may drive the car.
Just use needle nose pliers to carefully "nudge and release" one of the return springs on the pulley. Look at yours, and you will see two sets of springs, wound together side by side. Once you are done, it will look like this:

[Godless Commie]

And, here's a wide shot of the engine bay, for posterity.

[ACBlessing]

Godless, thank you so much! I'm really starting to understand the whole thing and it seems easy enough to do. I realize there are other cable designes out there but I'm going to stay with the parallel design because it makes the most sense to me. The brackets should be super easy to make at home and I'm going to try to find who can make a cable for me. I wonder, do motorcycles have that kind of cable? I doubt a bicycle cable can endure much use.

Now, I realize your setup involves a throttle body that's different than a stock Miata so you had to calculate the second pulley's diameter (42mm) to work with a stock pulley. While that is nice to have, I think most people starting this mod, such as myself, will probably keep it simple with a second Miata TB with the knowledge that one day, I could go with bigger, bored out TBs from another maker along with adapter plates (and so on) in order to squeeze some more performance. That is a tempting upgrade path but for later.

I see that you made a pulley out of aluminum, welded a spacer of sorts to the stock pulley and pressed it in. Since I have another Miata TB, I won't have to have a custom pully like yours but rather, just another Miata pulley, a spacer and a little welding. OR, I could have one aluminum pulley made to accommodate two cables which I think would be better.

If I did this, I think I could make it slightly larger than stock for a bit crisper response. They sell larger pulleys for NA throttle bodies but not for NB, understandably because the NA throttle body pulley is bolted on whereas the NB TB is pressed. So my challenge will be to make a custom pulley that will press in. I wish someone with a machine shop here would step up. If I can't do that, I can certainly just do the spacer/extra stock pulley route with a couple spot welds.

Thank you again for posting the info and pictures. It is really making me excited to do this project and a bit more relaxed now. No picture of your Miata with Istanbul in the background?

By the way, that is a very ambitious meth injection system and interesting fuel pressure regulator.

[Godless Commie]

Wow! How did I miss your post?

For starters, if it is a crisper throttle response you're after, do not go with a larger diameter pulley:

It takes more cable to rotate a larger pulley for a given angle, and you may run out of pedal travel before the butterfly reaches full throttle.

And, I have tons of pics of my car with Istanbul in the background.. I'll post a few.

Yes, my water injection setup is something I happen to be proud of..
I have a 10 liter tank setup which is completely concealed. Does not take up any precious usable volume in the car that way.
I also like the direct port injection idea.
All I do is remove the nozzles and clean them in an ultrasonic bath every month or so. (I use a vinegar/water solution).

For more info on the water injection setup:
http://www.miataturbo.net/showthread...light=stealthy

[ACBlessing]

GC, thanks for the reply. I've decided to get another junker, NB TB and drill out the pulley. I was going to get an NA TB and remove the pulley because it is bolted on instead of pressed in but after looking at some pictures, it looks different. It might be the same diameter but it won't work for my "pulley sandwich" idea. I'll post some picts when I'm done of that.

Okay, so now I have the extra TB and pulley worked out. I just lack the cable and bracket. Why couldn't I just use another NB throttle cable and cut the length and sheath to fit? I'm going to fab my bracket soon as well since I can't find my stock one anywhere.

I don't want to detract too much with the water injection but thank you for the link to your fantastic work. I have an Aquamist system to install still and I had been pondering the idea of their 4-port distribution block and now I'm convinced it was a good idea after seeing your work.

I had also been pondering tank placement and was going to route the remote fill to the fuel lid area so we think alike. What cought me as a surprise was your sticking the tank in the tunnel which is super nice but I question if it's good to have a tank horizontally mounted instead of vertical.

[r2t2]

Just a bit late to the party , but GC's comments DID supply the missing pieces to my DTB upgrade. So a to GC! My last little niggling issues were fixed with my moving the Bypass valve vacuum line to the intake manifold from the vacuum nipple that is just aft of the SC.

Here a few pics of my install using PBJ's kit.