Supercharger Dual Throttle Project
 

I'm looking for help with a supercharger project. I'm copying a dual throttle body install from the UK onto my 2000 with MP62. I have a Big Throttle Body at the charger inlet and the stock TB on the inlet. I'm trying to find a coupe of silicone tees to connect up a recirculation valve and I figured who better than a bunch of turbo experts. Does anyone know of a company that makes odd-ball sizes of silicone? Specifically I want 2-3/4" inlet and outlet with 1" side port and 2-1/2" inlet and outlet with 1-3/8" side port. My searches have found nothing so far.

(I'm in Toronto, Canada)

I think I understand your question. How about getting a metal coupler between two hoses and have your desired fitting welded to the coupler.

That would be an option but I really wanted to use the tee(s) as the "couplers" between two other pieces:

a) Outlet of AFM to BRP Sleeve (2-3/4")
b) As a sleeve over the metal cross-over pipe with a 1-3/8' hole in the cross-over pipe. (2-1/2")

Try these guys out: Intercooler Pipe Fabrication - Silicone Intake Systems Auto Parts

Yup, found them. They have silicone tees but not the right sizes and don't do custom work. But thanks for the suggestion.

I've also tried these without success.
Silicone Vacuum Hose - StylinMotors.com, StylinMotors Inc.
Blow Off Valve Adapter Hose, BOV Adapter Hose, BOV Hoses, Blow Off Valve Hose, Blow Off Valve Hoses
Turbo Hose — 90° Elbow with 1" Nipple— Silicone

You could try to make your own. I remember seeing a how to a while back but I don't remember if it was on mr2oc.com or here.

DIY Custom Silicone Couplers - DSM Forums
Here's the link

You're over-complicating your setup. There is no good reason to run dual TBs on a supercharger. I've run a s/c with the TB in front of the s/c and in it's stock location....using one in conjunction another only voids the other one being used.

Point taken.
I've been running my s/c in the normal configuration for a couple of years and I only have one goal in mind - to get rid of the idle dip which on a cool morning in Toronto causes stalls at traffic lights until the engine warms right through. Reports from the MX5nutz in the UK report the DTB WILL do this.

Great link, thanks.

Oh boy, I can see me getting into all kinds of trouble from the missus if I try to do that in the kitchen.

Plenty of evidence to the conterary in the UK....

In my experience running a charger unthrottled is deafeningly loud and extremly unplesant. Having two throttles removes this and solves all idle and throttle response issues.

You can also have any IC pipework route you like which means a DIY around the rad option is feasible.

...my wildest dream.

It's not hard to accomplish to be fair, all you need is a throttle cable and a 2nd TB :)

Got both of those - the car is away for the winter so it won't get tested until spring.

I've been following the threads on MX5Nutz and a few of us in Canada are waiting on the kit from PJB to arrive. I ordered tees from Turbohoses, not exactly the right size but I'll adapt. I'd be interested in your thoughts of using a recirc valve or just cracking the blower TB at idle.

Your time and money are better spent on a better fuel management system. Which will also cure this problem. And instead of adding an intake restriction and reducing hp, will increase your hp through optimized timing and fuel.

Ha reducing HP? That I seriously doubt.

Engine management can help for sure, but you can't kid physics, a smaller intake track is better period, end of.

Re the recirc valve, I ran without one for a bit and it was fine till I took it on track and kept blowing charge pipes off....

Regarding physics
 

"but you can't kid physics, a smaller intake track is better period, end of."

HP X 1.62 = airflow in CFM

stock miata size

55mm TB flows 317 cfm

317/1.62 = 195 hp at the crank.

With 17% drivetrain loss thats means you have a restriction at anything over 162 wheel horsepower.

Don't get me wrong reducing intake track total volume will help throttle response, but if that's your focus do it by using an air to water intercooler to shorten up the piping. Don't use a diameter of pipe or tb that is too small to flow the air you need without causing a restriction. I presume you're shooting for more than 162 whp, and this project will cost you hp.

I'm already at 220 and know someone pushing 280 ... The extra tb made no noticable difference in power, a/w I tried it's ok nut can't cope after a few laps on track , it's also still a longer intake tract...

You can band theory about all you like, in practice it works!!!

I thought you couldn't kid physics?!?

Just cuz your butt can't discern the lost 5 hp doesn't mean they're not gone.

You can't I have a short intake tract and a great idle etc ;)

is the TB. Any smaller than the dummy TB? if it is it's marginal at best.

Besides 5bhp for OEM drivability and fantastic throttle response? Nothing to think about there. As you just said you can't even tell a 5bhp loss ;)

I'm starting to see your guys point. A junkyard throttle body is a whole bunch cheaper than a $1000+ fuel management solution. And if it works at 220 and you don't need a whole bunch more why not. A miata with anywhere near 200 whp is a ton of fun.

As I say there's a guy over here with just under 280 with dual TB's and it's perfect...

It's really not going to effect power much

Any chance you can post some pics or link to some of these projects? I'm curious to see how it looks.

Great dialog guys, thank you.

I'm running 95/65 pulleys on the MP62 so max boost is 5.5psi on my gauge - so probably, what 175-ish whp?. No intercooler at all - baby steps. There are guys here running more boost than me w/intercooler and fuel management and they have the same idle problems because of the long intake tract.

Once I can get the idle and throttle response back close to stock (ie not stalling when cold) then perhaps I'll be ready to up the boost, add intercooling and management. Or maybe not, my car tracks all day and sits in summer traffic with no heat problems - shaving a few seconds might not be worth those headaches to me.

Of course that might change when I drive Steelrat's car - the other guy from Toronto doing the DTB Mod - with more boost and management and IC.

There's a whole bunch on mx5nutz.com. Here's one of the threads. Dual Throttle Kit - MX5Nutz.

Seeking opinions on the vacuum side of this project.

The recirc valve is mounted to a BOV tee at the outlet of the blower. It needs a vacuum line.

Adding the second throttle body means the blower bypass valve vacuum line cannot be hooked up to the blower outlet any more.

There is only one unused vacuum port on the inlet manifold and it is smaller than either the recirc or the bypass ports.

So,
If I use this smaller inlet manifold port and run a line to both the recirc and bypass valves is their response time going to be greatly affected by the flow restriction of the smaller port?
or,
Do you see any problem adding a tee off from the brake booster hose? (on North American cars the brake servo is engine hotside)
or,
How about removing that inlet manifold port and drill/tap for a larger port - or leave that port and drill/tap elsewhere for a larger port?

Am I overthinking this? It's winter here and the car is in storage so I can't test until spring.

*caution, I have no idea what you're talking about*

I believe BEGI uses a tee in the brake booster line for something, their instructions may be available online.

Massively so.

Just get a plastic 'T' connector used in windscreen washer jets etc and use one of the sources on the intake manifold.

Pics from the install so far.
Picasa Web Albums - Wendinator - Dual Throttle...

Comments:
I wanted the Recirculation valve on the intake side to catch the start of the pressure pulse from the stock TB closing but it was a space/mount/plumbing mess hence the blower outlet mounting.

I want to keep the added volume in the vacuum system to a minimum so I'm thinking of plumbing into the brake servo line to keep the run short.

The Recirculation valve is not supported by any brackets - to allow more engine/frame relative movement - it's a fairly large unsupported weight which might oscillate, guess I'll know better when I fire it up.

You had to know I couldn't wait until spring.....vac lines connected to intake manifold, battery reconnected, started first crank and she purred like a kitten.

But, what a strange noise that recirculation valve makes. Maybe it's the 50/50 vent/recirc. I ordered FM's deal of the day (3 Feb) BOV which is a full recirc capable. Other than the BOV noise, all is good so far - at least sitting in my underground parking spot it is.

Though Doppelganger didn't run 2 TB's, he did have a valve to relieve the pressure between the SC and the IM's TB. I think he let the additional air bleed to atmosphere.

What is the benefit of having the recirculation valve blow the air back into the initial intake tract? The SC TB should already be closed if the recirc valve has kicked in. Theoretically the MAF has already read that air as incoming, but the split second it was already needed for fueling has come and gone. The only thing I see happening is you have a pressurized (albeit lightly) intake tube which may impact incoming MAF readings (possibly negligible, but you get the idea). Why not let it blow in the wind?

Forgot to say that it looks like a clean implementation. Fingers crossed for you on maiden voyage!

My understanding is not vast but my belief is:
1) SC TB cannot be fully closed since air for idle is required by the IAC in the stock position.
2) Dumping the previously metered air - for which fuel calculations were done at the ECU - means that new air the MAF sees will cause new calculations at the ECU resulting in a short term too rich fuel/air at idle and Black bumper syndrome .

Thank you. I'll report after the event.

Car is still in the parking garage but i just had to tinker - you know the feeling.

I fitted the FM Deal of the Day recirc BOV and I wanted to check for it being closed at idle. It was, but there is a massive leak from the outlet port to the vacuum line (enough that the supercharger bypass valve won't actuate unless I blocked the BOV outlet). I refitted the other FM 50/50 BOV and it does the same although to a lesser extent. This cannot be right, can it? Do I just have two bad valves?

Out of curiosity where are you getting the signal for the bypass? When I moved the throttle with my m45 i had to move this line pre-tb which i imagine you would have to do for a dual setup as well.

So, you moved the TB to the inlet of the supercharger, yes? Are you sure the by-pass pickup went pre-TB? That would place it in the almost ambient intake tract. If yours is indeed pre-TB then your supercharger bypass valve spends the majority of its time closed. Your supercharger is working way harder than it needs to be all the time. It should be open until vacuum drops (as you mash the pedal for example) at which point it closes and you go boosted.

The Bypass valve needs to see vacuum. Before the dual throttle install my pickup was in the outlet plenum of the MP62. After the dual install my pickup is off the inlet manifold. i.e. the bypass vacuum line should always be on the vacuum side of the last throttle.

Sorry brain fart. I meant post tb with the tb in the stock location. Sounds like you have it at the same port i use. My bov leaks a lot of air out at idle but since i have a ms i dont care. I have a 2 port greddy knock of adjusted to hold peak boost when needed but at other times vent any excess pressure. One thing i did find is the bypass on the super and the bov didnt like sharing a vaccum line with eachother or anything else.

I took the car out for a quick test drive in the 9C sunny weather today (before the snow comes back next week). I have to say I'm a little (a lot?) disappointed. The car is waaaay down on power and makes the most amazingly annoying noises that seem to come from the supercharger outlet. (Like a dog howling down a plastic drainpipe).

The only good thing is there's no idle dip.

I know there's not much info here to go with but any thoughts from the guys that have made this work?

I'm much happier now.

I bought a Forge recirc valve (MSM fitment) after finding lots of leaking with the others I have (lesson learned!). Put a check valve in the recirc line to stop intake vacuum through the Forge bypassing the blower at idle and overrun. Tuned the throttle body relative opening by camming the throttle wheel. Found an unused vacuum port under the intake (part of connection to the Vics) and used it for the blower bypass valve so bypass and recirc valves are independently connected to the vacuum plenum in the intake.

Connected a calibrated digital pressure gauge (0.5psi increment) which showed max boost 6psi (so more than 6, less than 6.5) - my old Autometer analog gauge which I loaned to a buddy used to show 5.5psi.

Driveability is excellent. Throttle response time is virtually stock and no idle dip.

I need a few more miles before I pronounce this a complete success but it looks good. Can't wait for AutoX season to start....

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 have is the stiffer throttle pedal.
I'll try it with one coilspring removed from the TB. See what happens.

I will also post pics when I have a chance to take pics during the day.

What do you guys use for the second throttle cable? Is it all DIY, or are there kits out there to start at?

You can use an OEM throttle cable and modify one end. It depends on your preferred cable routing.
The trick is the interface between the cables. As Godless Commie pointed out, cracking the supercharger throttle means that there is an exaggerated difference in cable travel length between idle to WOT of each throttle. He had an interface wheel made up. I drilled an oversize hole in my wheel which gave me the ability to cam it and compensate for the difference.

I removed one coilspring from the stock TB.
Made no difference in the way the butterfly operates, but the pedal is much lighter now.

I removed one spring rotation from each throttle and it feels nice and stocky.

Dyno Dragon Parallel wiring

Mods please move to sticky, I don't have access.

Thanks Barbycar!

I just installed a relay powered from the underhood fuse box, and spliced into & ran the 12V signal from the primary fan as a trigger to that relay for the second fan. Second fan and the relay share a common ground, bolted to the chassis.
Five minute job, $3 relay.

The relay is in the lower right part of the picture.

has anyone ever tried...
 

mounting the dummy throttle body to the S/C inlet and leaving the stock throttle body in it's original position, as opposed to using the second throttle body? Would using the dummy throttle body in combination with the existing air intake piping be quiet enough?

This is probably a dumb question, but thought I would ask

Jim

yes plenty of times, its VERY VERY VERY loud

I figured that was the answer, but it didn't hurt to ask

I've heard it described as being like an Apache helicopter's 20mm cannon.

Stock TB location is pretty loud. I know since i have my car set up that way.

So finally got the dual tb installed on the weekend....

Running without any recirc at this point, however, I think I'm going to try one.... I'm wondering if extra boost the stock 4-rib pulleys the bypass valve will be enough.

Stock idle, is a wonderful thing. If you add load (turn the lights on, or whatever else, it doesn't dip or do anything.)

So after working with Barby's car we've modified the pulley wheel for both throttles to help make sure the offset is included. At this time, it seems to be working well with the two stock TBs that I'm running. With the new TB in the stock location, I had to adjust the idle set screw after the install. But given this was from another car, I'm not surprised. The blower TB hasn't been adjusted, but I'm curious if I need to adjust the stop a little higher or not yet.

Also I've found that I needed to add the restricter pill back into the bypass. Originally I had it removed to help with the boost/off-boost transition, back when the kit was new. I found at this point, the faster transition was hurting the near 0 vac was making it stumble a bit on grades without going into boost.

Also finding I have to relearn the car, the throttle response, and more importantly just the little things like decel are completely different.

At this point I'm thinkin' all hotsides should be dual tbs... <G>

Dave,

Two things:
Fix that vacuum leak on the signal modifier.
Try the signal modifier at 2" vacuum and reduce the volts.

I finally got to autox my dual throttle setup yesterday and everything ran perfectly. I forgot how much of a PITA it was having to deal with throttle dip. The car now idles perfectly and transitions much quicker. It is a pleasure to drive again.

Vac leak is a work in progress. <G> Need to get the new pressure switch first. Second.... the switch I have/ordered works the same, in 0.5-1psi on boost....

The voltage for the clamp was set properly before, but I can throw a DVM on it and see to make sure it hasn't shifted. <G>

Dave,

Steelrat I've got a few questions for you.

1) Did you buy the extra TB pulley from the UK supplier or are you using the existing pulleys (i.e. does the TB in the stock location have an additional pulley mated to it)?

2) What did you do about a throttle cable between the two TB's? Did you get a custom made cable?

3) What do you mean when you say you modified the pulley wheel? When you mention offset are you referring to an eccentric pulley configuration (pulley axle not in its center)?

I can answer these for the Rat

1) The pulley is a rough mockup of my redesign of the UK pulley. It is an additional pulley. Once we know that everything is good - a few miles travelled and some autoX runs we'll get a few production quality pulleys made.

2) The throttle cable is made up locally in Toronto to my dimensions and runs around the rear of the engine.

3) The modification was to machine two different radius on the same pulley face allowing the supercharger TB to be cracked open at idle and having both throttles hit WOT together.

GodlessCommie did something similar by having his second pulley be a reduced diameter. See above in this thread.

I had to have a reduced diameter..
I have the BBK big throttle body on my SC, and that butterfly requires a lot LESS cable movement as compared to the stock pulley.

It would seem at the moment the two stock TBs have the same sort of limitation, since you always need the blower tb open a little....

Need to check the throttle position adjustment. My blower might be set "too" open at idle from trying to get it to idle properly with the IC + one tb.

Dave,