Ok ok can't you just predetermine how much the pre-TB needs to be open (getting everything installed minus the second throttle cable). You should be able to start the vehicle and adjust until charger noise is heard. At this point you can just determine how much more rotation is needed for the pre-TB and then machine a pulley with slightly less diameter than stock so that both open fully (smaller = less arc length = less travel). This is just my interpretation without actually fiddling with anything.

 

Well we have machined the TB pulley based on calcs... and the pre-work that Barby did. However, there's still adjustment in the cable slack that you can use. I my case, I think it requires adjustment of the idle stop screw to close the plate, then make sure we are getting good travel with the cable.

It's on the agenda for the next few days. As it stands, the car is driving well... just need to tune the noise a bit.

Dave,

 

For balancing the two throttles, I found it worked best when:

1) Adjust the SC TB stop screw to open the butterfly as much as possible
2) Start the car
3) Temporary shim the IM TB to 1500rpm
4) Gradually close the SC TB stop screw until a deformation of silicone couplers is seen caused by a vacuum between the two TB.
5) Open the SC TB stop screw until the deformation goes away
6) Remove the shim

After I did this I measured the travel of both TB cables from idle to WOT to get the relative difference and calc'd the pulley diameters required.

7) To ensure the two throttles continued to move together I had to adjust the cables a couple of times to take out the stretch.

 

Barbycar, if you don't mind me asking: Where in the T dot are you getting the custom throttle cables made up? I have an extra TB lying around and may tackle this project (I do so very much miss the stock feel and idle of the car).

 

Staffa, we had a local contact through miataphiles who was able to get the cables made up. I think there might be a desire for more than yours as well, since we have a few other cars who are piecing together the dual tb stuff.

Unfortunately, I don't have the cable length handy... And barby's at the gap this week....

Dave,

 

Get hold of Jo at Dynodragon. He's on 'philes board and has my drawing.

 

Alright I am working on the DTB mod. In doing so I had an idea. My sc kit has the relocated IAC valve on the firewall. This means that one tube runs from the intake pipe (pre SC throttle body) and the other heads from the IAC to post TB. The idea I have is to run a single tube from the intake pipe to post SC TB to bypass the SC TB plate. I am thinking that this would eliminate the need to crack the SC TB because air will be able to bypass. This will also hopefully make installation easier because you can match the opening of the two TB's. What to you fellow SC'ers think about this idea?

 

Even though it seems like a good idea on paper, it will be more hassle than it is worth, and negate any advantage the dual throttle system will offer.

The problem is the increased volume the IAC has to deal with. Corrections made by the ECU and executed by the IAC will neither be timely enough, nor they shall have enough authority to deal with such volume.

The best place for the IAC is its original location on the IM TB, where it can have instant control on idle speed.

 

Sorry, I guess I didn't get my point across. I plan on returning the IAC to the original TB. However, the way it currently is that the IAC is on the firewall. Two lines run to it so that it can control the air getting past the SC throttle plate. What I am getting at is joining the two lines (basically looping a vacuum line from just after MAF to the other side of the SC throttle plate. Basically bypassing the IAC in the current setup (would be as though the IAC is fully open) while utilizing the IAC in the original location. Air will bypass the SC throttle plate this way. My only concern is that diameter of the tubing will not allow enough flow.

Here is the link to the Moss SC install instructions if you want a clearer picture (page 22):

http://www.mossmotors.com/graphics/p...gCard_INST.pdf

 

Here is an image of what I am getting at (only pic of my setup that I had):

 

So my IAC is on the stock TB, with the hose presently running to the pre-blower intake, post mas.

Your remote IAC was originally there to help with the idle dip, which you are removing with the dual tb's.

You could potentially use the air meter (on the blower tb) to help with the idle, but in Barby's case I believe he's simply closed it. I don't have it on mine with the 4-rib... so it's a non-issue.

Dave,

 

I know you have to crack the pre-blower throttle plate to allow air to populate the intake system. Will running the tube from pre-blower throttle plate to post blower throttle plate (only asking because nipples are there) possibly eliminate the need for cracking the pre-blower throttle plate. I'm going to use the IAC in the stock location (eliminate the firewall IAC) and route all vac lines to the intake manifold. I am just trying to utilize an already existing air passage. My understanding is that the throttle plate must be cracked so that the IAC in the stock location has a air volume present to be passed to the engine so the engine doesn't suffocate at idle. I think this passage could be a viable alterantive to the cracked plate, but I would like your thoughs.

Sorry, for poorly getting my idea accross to you all.

 

If you are using the stock NB IAC then it does not have any external porting once mounted on the stock TB. It pulls from the crossover tube and introduces it behind the throttle plate. If you are going to mount it on a remote (ie your firewall) position then you might as well leave it where it is - I think Godless Commie's comments then apply.

 

steelrat: what are you referring to when you say you have a hose running to the pre-blower intake. My IAC does not have hoses runing to or from it (In stock location)???? It simply sits under the throttle body and allows variable air to pass through the two square passages.

 

I looked at several of those options too. For some reason I could never get enough air to bypass the throttle plate using those nipples to allow reliable idle. The largest diameter I tried was 3/8" and it still would not idle without the throttle plate cracked. The difference in the amount of crack with and without that bypass was about 2 turns on the stop screw. I decided the extra leak potential with the bypass was not worth it and just added the extra crack.

 

He has a '95 - totally different IAC.

 

Ok I appreciate the input but either I am slow and am not getting what you are saying or I am just not getting my idea across. So here goes my last try to explain before I go home tonight and take better pics and possibly even try my plan (worst case scenario engine does not run). I don't plan on using the remoted IAC at all (consider it gone). I will be using the IAC on the throttle body in the stock location. All I am trying to get at or suggest as an idea is to connect the two hose that run to the remote IAC valve so that air can bypass the pre-SC throttle plate while it is closed (also let any air surge bypass back across). I'm thinking this may have the same benefit as cracking the throttle plate to let the air pass. Well if it still is not clear I will take some better photos tonight.

 

I understand you.
Here's the problem:
When you substitute a plumbed bypass instead of utilizing the "cracked butterfly" method, you end up with a fixed amount of bypass air.
The whole idea behind cracking the plate is having a "variable" which you can adjust till you get it right.
Trying all sorts of different diameter hoses, adapters, etc, will be pretty unpleasant, to say the least.
And, if you still have to crack the plate a bit to make up for insufficient bypass, you will be back all the way in square one.

I really get what you are trying to achieve, but adjusting the throttle plate is both simpler, and a sure thing.

 

Godless: Thanks I get what you are saying now. Yes, the adjustability is obviously a positive benefit to fine tune the setup. I guess this variability eluted me in my thought process. I still might give it a try since its not hard to route the line. Maybe I strike gold, but most likely I will be fiddling with the cracking of the plate.

 

Ok, hopefully this is my last post about my idea. Well I just finished hooking it up in this manner and running the bypass valves line to the rear of the IM. The car started up perfectly fine with both TB's closed and after idling for a couple seconds at 1500 rpm dropped down to 1000 rpm (stayed constant at this point). The afr's were high 14's - low 15's. Since the throttle cable was still attached to the blower's TB I thought I would press it to see if there was any difference. In doing so I heard the whine you all spoke of. Since the idle was steady and afrs were where they should be I think I will try leaving it like this and link the second throttle cable (still working on the cable went the $3.99 CT route but most likely will go custom made). I will also try to make the opening in an eccentric manner to get good throttle response. Sorry I can't post a pic but I believe some of you got the idea.