Theory of operation

[RichHawk]

Tom,
I'm contemplating buying a coldside 190hp SC from you (95 Bone stock with AC and Power steering). I have a friend that works in the forced induction industry. Despite being completely jealous of his job, I do trust his opinions, and he is most likely going to be at my side during the install of whatever SC kit I choose. (incidentally he's thinking a Hotside MP62 with his Water meth injection IC)

So of course some questions:
Knowing that the 5th injector cools the charge through evaporation of the gasoline, how does the system as a whole account for the extra gasoline without going completely rich? You've written that the JRPC can give the main 4 injectors a longer pulse(more gas) but not restrict the normal ECU pulse signal to shorter pulses. So does it mean that the 5th injector, to adequately cool the charge, really supplies most of the additional fuel needed for boost?

Of course I haven't done the math, but it looks as if the evaporative cooling of gasoline at 135btu/lb (Methanol is 475btu/lb and water is about 970btu/lb.) would require 5-8 times as much mass flow as the equivalent water or water-meth injection to get the same cooling capacity. This worries me that at low boost( guessing here) the system would be bordering on massively overrich, or excessive intake air temperatures......

Also brought up by my FI friend is why such a large Throttle body? 75mm can flow enough air to feed 500Hp V8s.

Thanks for the responses,
Richard

[Tom @ Fast Forward]

The stock ECU is designed to go to atmospheric pressure and add fuel. When you boost the engine, the stock ECU doesn't even attempt to keep up. The PC-Pro adds fuel for all that extra (~80-90WHP). It takes very little fuel (~5% of the total fuel) to do the cooling. All we do is turn up the PC-Pro a little less and let the 5th injector do the last 5%. The stock injectors also run out of fuel around 200WHP in any case so, if you exceed that, you need the fuel from the extra injector to make up the difference anyhow. That fuel has to come from someplace.

I don't know about low boost as the base system makes 8-10PSI and a lot of the kits are well beyond that. You don't need to cool the charge very far. Only enough to kill the ping. We typically run 12:1 A/F pre-cat. That's not very rich. The main injectors are also adding cooling to the air as it enters the combustion chamber.

The stock TB is about 55mm. A lot of my competition uses the stock TB. I found that the stock TB was costing us ~15WHP so I wanted a larger one. The BBK 75mm was a really good TB so I used it. Probably could have gotten away with 65mm but didn't see a good 65mm that I liked.

The 75 must be a pretty good choice. I sell a bunch of them to hotside owners that want more power and they get it. The object of the game is to eliminate pre-blower pressure drop. Blowers make good boost but poor suckers.

[Griff]

Don't BBK do a 65mm ?

I have seen various complaints about poor idle / town driveability with BRP's BTB... and IIRC theirs was only 70mm.

Has anyone complained about yours ?

[Tom @ Fast Forward]

None. Takes two passes at adjustment of idle after install about two days apart. Just time for the ECU to learn and compensate. After that, no problems that I am aware of.

Hopefully some of the owners will pop in and add to this. We have fixed the idle control on a couple of BTB hotsides. To the best of my knowledge, they work now as well.

With the footprint I need, BBK only makes a 70 and a 75.

I'm curious why you want a smaller TB?

[Kyp J]

2001 Coldside originally from BRP and now becoming a FFSC (not significantly different to begin with) as soon as I get a good fueling card (either by the ELF being fixed or PC Pro becoming available whichever comes first).

No idle issues, just a cold engine stumble that the PC Pro should fix. I think most of the idle issues were with the hotsides.

[Gord96BRG]

I've got the Coldside with 75mm BBK throttle body on my 96; I'm also running 440cc injectors right now (ran 550cc injectors for a while too) and a Link ECU. With the big throttle body and even big injectors, the idle is as good as stock, if not better. Same goes for off-idle response and cruising around town driveability, at least as good as, generally better driveability than stock.

[raceskier]

Another stock Coldside. The cold idle is a bit fussy, but I don't think you can pin that on the TB. Once warm, excellent transition from idle and of course throttle response. The only downside I can see to the 75mm TB is the somewhat non-linear throttle response. Everything happens in the first 50-75% of pedal travel. You get used to it quickly though.

[RichHawk]

With the footprint I need, BBK only makes a 70 and a 75.

I'm curious why you want a smaller TB?

I can't come up with a single reason a larger TB would be a bad thing with a blower. Except for the cost associated with it (And that's merely an assumption that the 75mm TB costs more). I fully understand the less restriction = more power concept. Don't get me wrong I LIKE the bigger throttle body, as long as it doesn't cost an additional $200 for bling factor alone.

[Tom @ Fast Forward]

There was roughly $5 difference in my cost between the 70 and 75. I think the 65 might have saved another $15.

[bogey]

My recent install on my 96 of the FFS Coldside idles perfectly. I was a little concerned before installation based on my experience with my other car.

I also have a 97 with BRP HotSide and BTB that does not idle well at all. What kind of adjustments are needed to correct the idle droop on the Hotside?

I agree with raceskier that the throttle response is a bit abrupt. It is like turning on a switch. Full power is suddenly there! Is there an adjustment to control how fast the bypass valve closes?

[Tom @ Fast Forward]

Bogey, Where is the IAC valve mounted on the hotside? It should be remote mounted like the coldside.

After a couple weeks, you will get it down how to roll on the throttle. The bypass valve already has a restrictor in the nipple to slow it down. When you put the pedal to the metal, it makes almost the same torque no matter what RPM.

[bogey]

The IAC is attached to the bottom of the adapter on the intake manifold. It is "remote" from the TB which is on the supercharger on the hot side (though I don't think that is what you mean by remote).

One difference is the size of the air line running from the IAC. The line is rather large (1") going back to the hotside of the engine and under the supercharger.

On my coldside, I used a reducer from the 1" down to small 3/8" hose where it ties into the T.

Could the size of the hose affect the performance of the IAC?

Where should it be mounted?

[Tom @ Fast Forward]

I can send you a bracket and plate to put it on the firewall someplace like the coldside. It should plumb one hose to the BTB (or the adaptor at the back side of the MAF) and the other to the BTB adaptor (pre blower). It is difficult to get decent idle when one side of the IAC is tied to the intake manifold. The IAC should never see boost. Let me know.

Then you need to make a simple block off plate to block off the dummy TB where you remove the IAC valve.

[BlownMX5]

Tom, is this possibly the same thing I was telling you about on the phone last weekend (when I was installing my auto-tensioner), but I thought it might have been the TPS? My IAC is mounted on the DTB, post-blower. That is how BRP designed it. My car idles OK, but doesn't return to idle well. If I take my foot off the gas with RPMs more than about 1500, it will droop to about 300 RPMs and stumble, then either stall or return to normal idle.

[bogey]

So is the IAC acting as an air bypass that goes around the throttle butterfly valve?

Open when cold and closes when it gets hot?

[Tom @ Fast Forward]

Pat, The 94-97 is touchy about TPS adjustments. After 97, the Miata no longer had an adjustment. The ECU simply figured it out. 94-97 have a contact that makes when the TB closes to tell the ECU that it must be time to try and idle. The way you described your problem sounded like that switch wasn't making. After you confirm that it is, then work on adjusting the idle. My instruction manual describes the same method that the Miata service manual describes as to how to set the switch. Most important is to set it so that your insure it always makes when the TB plate closes.

If your IAC is mounted on the dummy throttle body, that could be a second problem as that is a hard place to get it to idle. Lastly, is the TB idle adjust. After a couple days of driving, disconnect the electrical connector at the IAC valve. If the idle drops, adjust the stop screw on the BTB to bring it up. If it rises, adjust the stop screw to drop it. After the engine is warmed up, you should be able to disconnect the electrical connector on the IAC valve and not have any idle change. You might have to make the adjustment twice but then enjoy forever.

best thing you can do to a hotside with the IAC on the DTB is move it and blank off the DTB.

Bogey, the job of the IAC valve is to correct for changes in air density. Theoretically the TB plate always come back to the same position at idle. That allows for a given CFM of air. However, when the air is cold it has more O2 and when hot, less O2. The engine, at idle, also gets air through the MAF, hose to the drivers side valve cover and out the PCV valve to the intake manifold. That is also a variable as to how much O2 based on oil vapors and how far the PCV valve opens, etc. As those two air intake vary, the ECU needs a variable source of air it can control to add more or less air to correct for the proper flow for proper idle. At "Normal", it needs to be in the center of it's travel so it always has room to go either direction. If improperly adjusted, it will sit at one end or the other and you will have poor idle (droop or hang).

The 94-97 adds another complication to all of this as the IAC valve has a built in thermal valve. If you don't run the two radiator water lines (in and return) the thermal valve (Normally open that closes when it gets heated) will always leak a fair amount of air and that leads to another source of uncontrolled air that the IAC has to overcome. You MUST connect the two water lines on a 94-97 IAC.

Hope all of that helps.

If you still have idle problems, Mazda makes a "restrictor" that you can put in the driver's side valve cover hose that lowers the amount of air going in there and out the PCV valve. The Mazda part number is B61P-13-986. Direction doesn't matter. Just pull the hose off the driver's side valve cover, stuff it in an inch or so and replace the hose. They are only a couple $$. If you have trouble getting it from Mazda (special order part probably), let me know and I'll drop one in the mail to you.

[BlownMX5]

best thing you can do to a hotside with the IAC on the DTB is move it and blank off the DTB.

Aha, but I have a BTB which you can't mount the IAC on, that's why it's on the DTB, now I remember. I guess I could go back to the STB. Hmmm... more power/good idle, more power/good idle... I'll take more power for 200, Alex :rolleyes:. I'll double check the TPS adjustment and maybe settle for a slightly higher idle RPM, I guess. Also, I'll pick up that restrictor and see if that helps.

Pat.

[Tom @ Fast Forward]

I have the parts and can put together a kit for you to move the IAC someplace else. It would take a bit of work on your part. you would need to make a blank off plate or get one from James. Then you would need to tap a hole into the TB adaptor if there isn't one already. John just did it to his hotside and I believe it is working well now.

[bogey]

Thanks for the explanation. I need to get more familiar with the HotSide setup. I am still trying to figure out the plumbing on it.

[Tom @ Fast Forward]

If it will help, I can make a sketch of how the hotside 'should' be plumbed. How yours 'is' plumbed depends on what day of the week it was made. ;)

Basically, the nose end of the IAC and the driver's side of the valve cover should connect somewhere between the MAF and TB. The barrel end of the IAC, Brake Boost and Cruise control should connect to the TB adaptor (between the TB and supercharger). The remaining vacuum lines can either stay on the IM or connect to the TB adaptor (preferred).

[BlownMX5]

If it will help, I can make a sketch of how the hotside 'should' be plumbed. How yours 'is' plumbed depends on what day of the week it was made. ;)

Basically, the nose end of the IAC and the driver's side of the valve cover should connect somewhere between the MAF and TB. The barrel end of the IAC, Brake Boost and Cruise control should connect to the TB adaptor (between the TB and supercharger). The remaining vacuum lines can either stay on the IM or connect to the TB adaptor (preferred).

I already have the blank-off plate and a gasket, they came with the BRP kit. There is a collar between the MAF and the TB that provides vacuum for the big hose that goes to the nose end of the IAC and another for the valve cover hose. The brake boost is still connected to the intake manifold and my CC is removed. So I'm challenged to imagine how the rest of it would work, to move the IAC to pre-blower. Are you saying that it would just "hang there" and interact with the TB via a hose?

[twooldto]

Hey Pat, I have some pics of my IAC install on my hotside 62. They are in the {install tips} post.

John

[Tom @ Fast Forward]

On our hotside, we have a "Tee" on the BTB adaptor. The small hose you see on this side goes to the cruise control. On the far side, you can just make out the hose that goes to the IAC.

http://www.FastForwardSuperchargers.com/Hotside/Hotside-BTB.jpg

And another one like that on the bottom of the BTB. The two barbs on the BTB feed the IAC and driver's side valve cover and the two on the BTB-A (shown) feed the IAC and CC.

We then mount the IAC on a bracket and plate and connect the hose from the BTB and the hose from the BTB-A. In this picture, the hose from the BTB goes to the barb closest to the firewall and the hose from the BTB-A goes to the other barb.

http://www.fastforwardsuperchargers.com/Hotside/HS-BTB-1.jpg

[BlownMX5]

And it works the same way on a '94 (John's is a '99 and that doesn't look anything like my IAC)? Also, wouldn't I be able to omit the 2nd fitting on the bottom of the TB since I already have that collar that feeds the IAC and valve cover? The "collar" I'm referring to is mounted between the MAF and the flex hose going to the TB. It has two pipes exiting it that the hoses connect to. It is sufficient, isn't it?

Man, it must be nice to have your throttle linkage right out in the open like that. I can barely see my idle stop screw, much less get a wrench on it.

Pat.

[Tom @ Fast Forward]

Same bracket, different plate to accomodate the different IAC. Your IAC plate would have one barb out the bottom to feed into the BTB-A. The hose from the pipe/collar you mentioned will feed directly to the IAC. You will also need to feed the water lines to the IAC.

[bogey]

I can send you a bracket and plate to put it on the firewall someplace like the coldside.

I am interested in getting the bracket for the IAC. Do I need to tap a hole into the TB for the line, or is there are place I can Tee a line to?

[Tom @ Fast Forward]

The incoming air will still come from the collar down by the MAF. The same place it did before. The return hose needs to go to the TB adaptor (between the throttle plate and supercharger). If there is hole there, you will need to drill and tap 1/4 NPT. I can supply a TEE to go there (for the IAC and brake booster) or a small distribution block that you can use for the IAC, brake boost and cruise control (if you have cruise). Let me know.

In any case, you won't need to drill/tap the TB, just the adaptor.