Embedded Files
Difficulty: 5/5
Time to install: 2-3 Days on and off?
Disclaimer: I'm rating this a 5/5 in difficulty. Is it really that hard? No, but some people dislike DIY stuff. If it doesn't work, can you just return to the original setup? Sure, but only if you're familiar with how this supercharger actually works and you're comfortable with removing and installing it yourself. If you paid to have someone else install it, maybe think twice. Needless to say, it'd doable with very common parts, nothing fancy.
I’ve come up with a Hotside, Big Throttle Body, Dual Throttle Body mod I hope can be adopted by anyone still using this setup (if there's any of you left). There are many clever variations in the monster DTB thread, but often required things I couldn’t do, people with skills didn’t know, parts I couldn’t buy, or work I was too lazy to organize. Out of sheer dumb luck, I found an inexpensive one that solves the two major problems:
1. The correct throttle wheel sizes so they open in tandem.
2. Getting the throttle body cables in the right positions. This often required additional throttle wheels or pullies. Not needed here.
TLDR version
TLDR version
Buy an OEM throttle body that supports two throttle cables – typically available on Automatic Miatas. That’s what I did. Or:
I’ve read using early NA TBs too. I think YMMV depending on your IAC setup. I don’t know enough about them.
Search for “shapeways DaveyC Miata adapter”. Haven’t used it either, but seems sound.
At the Hotside SC intlet, purchase the Ebay knockoff 75mm Throttle body for a 1996 V6 Ford Mustang (starting at $35 shipped from Hong Kong). The throttle wheel is about the same diameter as a Miata OEM, so they open at the same rate. The secret sauce is in the throttle wheel. Unlike other Throttle Bodies, the wheel’s mounted to the butterfly shaft by a nut. That allows you to switch the wheel around to the necessary orientation.
The Long version
The Long version
Enough time stuck in the house prompted me to create direct steps that were easy to follow, and could be generally be done by anyone with some rough DIY skills. I was curious why some people were having better or worse results, so I took the dive and pretty much hit every snag along the way…
My original setup:
MP62 Hotside supercharger
Dummy Throttle Body on Intake Manifold
Pre-charger, BRP-designed, BBK Big Throttle Body adapter that includes a flow valve
IAC installed on Big Throttle Body
3” Intake made of silicone elbows 135, 90 and 45* and couplers.
Intercooler w 2.25” pipes
New setup:
TVS900 Hotside supercharger (courtesy of Tom at FFS)
Pre-charger Generic Ebay Big Throttle Body replacing Edelbrock or MAC BBK – you still need the BTB adaptor from your prior kit.
OEM Mazda Throttle Body from an Automatic with IAC located back.
TurboSmart Kompact Plumb Back BOV
Same 3” Intake, with additional 1” hose to route excess boost
Same Intercooler w 2.25” pipes
Final result:
Single Throttle Body, Pre-charger Experience
Idle was decent, in California, temperate weather. On the “colder” mornings (50*-ish?), needed to give it a little throttle for about 10-30 seconds and once warm, no dip. Once warm, idle didn’t dip, but the behavior was a gradual drop down to 1000, then a quick drop back down to 950 – almost like having a very heavy flywheel. I think this “success” was mostly due to the BRP Throttle body with integrated flow valve. My theory is that it basically choked the air flow enough, so idle had to “float” back down to 900rpm, giving the IAC enough time to really zero in on target idle.
Single Throttle Body on IM Experience
For the past few months, I also ran in a single throttle body configuration. I locked open the Big Throttle Body, replaced the dummy throttle body on the Intake Manifold with an OEM. Idle was rock solid, but drivability was a bit jerky, power delivery fine at WOT, mid-throttle delivery felt like a bucking car – all boost or no boost. And the noise - even on the “quieter” TVS charger was bad. Part of this is aggravated by the 3” intake, it acts like an echo chamber. Like, people stopping to gawk at the car and “Walking Dead” intro with flocks of crows scared off, half way down the block.
Tools Needed
Tools Needed
Beyond basic hand tools, here are other things I needed:
Drill, or better, a Drill Press for the few holes you’d need.
Rotary Tool/Hacksaw to make a few minor cuts in Home Depot aluminum bar.
A file to smooth things out
A soldering iron to add a cable barrel to both ends (although they do make cable ends with screws).
Shopping List:
The OEM TB noted prior.
2nd, OEM Throttle Cable.
Generic Throttle Cable kit – Just to poach the other mounting end and a throttle cable barrel. I used a generic Venhill kit, whatever’s cheapest, measure the whole for your barrel
Generic Ebay 75mm TB noted prior
Silicone Coupler with 1” Tee for Bypass valve. Size dependent on your IC outlet.
Bypass valve - 25mm Turbosmart Kompact Plumb back or equivalent
Revotec 25mm sealed barb (SST25K). Probably cheaper alternatives, but I don’t really know the terms to search for. Used to puncture silicone couple after maf for the return.
1” / 25mm hose to connect from bypass valve to Revotec. I think I used about 3 feet.
1” / 25mm aluminum couplers and 90* hose bends based on your layout. I used 2 of each.
Valve Cover to Intake/Idle plumbing (Optional, but highly recommended to suppress noise)
Two 3/8" NPT, 90* Hose Barbs - a 3/8" barb will provide a maximum 850RPM. A 1/2" barb will let you idle up to 1250RPM
3/8" NPT Tap/Die combo (and a drill bit for the pilot hole)
One hose barb tee connecting valve cover hose to the two barbs noted above.
Aluminum Bar from Home Depot
Step 1 - Secondary Throttle Cable
Step 1 - Secondary Throttle Cable
OEM TB on the Intake Manifold, pretty obvious. On throttle, the new cable pulls towards the front of the car.
Step 2 - Routing Diagram
Step 2 - Routing Diagram
Diagram of the DTB cable. When throttle is applied, the SC throttle wheel needs to pull towards the firewall. This is why most aftermarket TBs require pulleys or an additional wheel. They open by pulling BACK, towards the flange.
Step 3 - eBay Throttle Body
Step 3 - eBay Throttle Body
Here’s the solution – generic Ebay TBs simply hold the throttle wheel to shaft via a nut. We’ll remove it, and flip the wheel around.
Step 4 - Simplify
Step 4 - Simplify
Remove the wheel and flip it. Make sure to wind the spring up appropriately. It won’t completely turn yet. We need to do some very minor grinding. BTW, you can grind off this part, you don’t need it, and the space is tight.
Step 5 - Modify Original Throttle Stop
Step 5 - Modify Original Throttle Stop
Here it is, wheel mounted backwards, spring wound up. Wheel hits the original throttle stop. Just grind the 4mm or so to let the wheel clear.
Step 6 - Throttle Stop or New Plumbing?
Step 6 - Throttle Stop or New Plumbing?
You still need a little air to let the car idle. This can be done in two ways:
Method 1 (Recommended - Not Pictured, but in Video) Drill and tap two 3/8" NPT holes - one prior to the throttle body butterfly, and one on the throttle body adapter after the butterfly. Then put in the 90* barbs. Set it up just like 0:19 seconds in on the Youtube video. This yields the least amount of noise, and you don't need to crack the butterfly at all.
Method 2 (Pictured) Cut, Grind and file a throttle stop, from some aluminum. One hole lines up with the BTB’s mounting point. The second is purely to mount an adjustable bolt, allowing you to crack the butterfly for idle purposes. I tapped it so a bolt can be adjusted. Frankly, all that was necessary was thickness of a bolt head anyway. This method will yield the noise level in the first part of the Youtube video. Still a little noisy, but tolerable.
Step 7 - Throttle Cable Bracket - Preview
Step 7 - Throttle Cable Bracket - Preview
Here’s a sneak peak of the bracket. Measure your desired length, bend it somewhat like a Z. The length will depend on the space available, and ensuring it doesn’t bend against brake lines. Some very minor brake line bending may be required (maybe 5mm at most).
Step 8 - Throttle Cable Bracket Mount
Step 8 - Throttle Cable Bracket Mount
Test fit the bracket. At the TB end, drill your mounting hole, mark the cut-off, so the other end lines up with your throttle cable path.
Step 9 - Cutting/Bending Bracket
Step 9 - Cutting/Bending Bracket
On the other end, cut a ½” slot to hold the new Throttle Cable. I used a ½” drill bit, and rotary tool to cut it, then filed it smooth.
Step 10 - Aligning Throttle Bracket
Step 10 - Aligning Throttle Bracket
If you did it right, it’ll mount like this; the throttle cable nipple will line up with the throttle wheel guide.
Step 11 - Aligning Cables
Step 11 - Aligning Cables
Back to this pic. I checked for general length and spliced the two throttle sheaths together, so I had threaded mounts on both sides. I installed the BTB and bracket up to my SC, rotating the wheel for clearance. Mounted the cable, and checked for firewall clearance to avoid abrasion. On the IM side, I clipped the steel cable to size. There are two types of replacement barrels, screw clamp types and standard solder. I chose the latter, because I like to solder. The OEM steel cable was a bit thicker than the universal kit, so I had to drill it out a little larger. Stuck the cable in, added solder to lock it into the barrel.
Step 12 - Adding the BOV
Step 12 - Adding the BOV
With your throttle cable in, give the pedal some strong pushes, ensuring it’s strength. If your barrel fails, you can still drive the car home, but your SC butterfly will create a massive air obstruction. I won't bore you with the rest. Silicone Tee on the IC outlet with BOV, here are the few parts I used to route it back to the intake after the MAF.
Vacuum Line Notes
Vacuum Line Notes
Vacuum lines for both the Bypass valve and BOV are after the TB on the IM. I had to keep them on separate sources. When on the same vacuum source, I couldn't ever get the idle and transitions at 0 vacuum to play well.
Hose for Bypass Valve connected to back of IM, same vacuum source as my Boost Gauge and Electronics
Vacuum line for BOV connected to a separate vacuum source after the Throttle body, on a separate vacuum source. I noticed it had to be as short as possible for the best behavior. I put it on a tap on the throat of the IM
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