Dual throttle setup - no more idle issues!
 

I just finished my dual throttle project today..

My problem was matching the wire travel between the two TBs.
I have a BBK BTB (big throttle body) on the S/C.

I measured wire travel on both TBs. Stock requires 3.5 cm from closed to fully open, and the big one takes 2.75 cm.
I found out that the stock pulley rotates 75 degrees. (One would assume the full motion would be 90 degrees..)

3.5 cm wire travel at 75 degrees needs a pulley which is exactly 42 mm in diameter (where the cable rests) mounted next to it to provide 2.75 cm of travel.

So I made some drawings based on my calculations, and had a machine shop turn a pulley for me with the correct diameter and offset.
I mounted this pulley on the stock TB, and had a "wire shop" build me a custom throttle cable.
The cable sheath is 95 cm. Has adjusters on both ends, and the cable itself is about 135 cm or so. Cost me 20 bucks to have it made.

The next step was to modify (extend) the existing cable bracket on the IM to allow for the offset on the new pulley.

I did not use a BOV or a recirculating valve.
The trick is to crack the SC butterfly open a bit. Imagine setting your idle at 2500 rpm. That much. (Stock TB has authority on idle, anyway.)

The big butterfly has a very aggressive opening/closing rate, which is a definite advantage.

Adjusted both cables so there is no slack, and made damn sure WOT on the stock TB is actually WOT on the other side, too.

Turned the key, the car started and immediately settled into factory idle. It took a couple of very minor adjustments on the SC butterfly to smooth things up.

Revs instantly, has great pick up, punching the throttle idling down the road in second gear smokes both tires forever.
I have a 130/65 pulley combination, BTW.

I took it out on a nice, long and SLOW test drive after dinner. Very civilized behavior overall, drops down to idle perfectly from all RPM levels, and has perfect throttle response. I got on the gas a few times, and no problems whatsoever.

I am very happy with the results. No idle related problems any more.
Should have done this a looong time ago.

The only concern I had was the stiffer throttle pedal with the resistance of two sets of throttle bodies.
I removed one coilspring from the stock TB, and got a nice and soft pedal again.

This is a must for all hotside S/C setups IMHO..

And, here are some pictures:

https://www.miataturbo.net/picture.p...pictureid=1144

Very nice work!
Do you still have your car and SC?
I´ve got a 1,8 - 94 with the idle issue. I also have DTB´s and I run an AEM f/ic and I have the coldstart idle drop issue. The AFR is showing very lean on cold idle. Anyway, I read your posts on idle issues on FFS and I´m going to have a look at the MAF tomorrow to see what direction I´ve put it. I think I was pretty obsessive with noting the direction, but it wouldn´t be the first time I´ve been wrong.

Cheers for the information!

Good stuff. This needs to be done with a turbo car.

Yes, he still has the car and the S/C.

Dual TB is a bandaid for not installing MS2 with the GSlender firmware...

Have you actually tried it?

im just being stupid. But I was impressed by GGreg's idle videos after he switched firmware and tuned out his idle issues with a hotside single TB with large FMIC.

I know as much about superchargers as I do about your mom.

The idling issue is almost non-existant with the M45 supercharger. One of the first cars I tuned was an M45 2001 1.8 with the TDR intercooler. No idle problems. He then switched to an MP62, same intercooler and piping. Idling went to hell.

shouldnt have been so greedy!

I still have my MP62, as well as the DTB.
Idle is perfect. DTB is not a bandaid.

I also have some serious newfound power. A single test run with the new pulleys netted me 16.5 psi at 6500 rpm. Didn't dare to take it all the way to redline for a couple reasons.

I'd have to agree in part. I was able to tune out the slight idle droop of my MP62 and 9lb flywheel on my 1.8L with just the MS1 idle control. The draw of the low profile projector headlights was enough to kill the engine at night pulling up to a stop. But with normal headlights and knowing how to tune the MS now, I would not add the complexity of dual throttles.

Holy cool necropost.

That was a pretty cool mod! Never had an idle or throttle response issue on the M45 with hotside throttle body only.

I'm curious why you don't just run it with one as a blow-through? Trying to avoid a bov? Tried that myself with the M45 and it had some severe driveability issues, so I assume those would be same on a 62?

Horrendously loud.