MP 90 FWD Project Updates

[AleroB888]

I run a similar setup on my Datsun...And Raven, NO a standard blowoff valve will NOT work with a positive displacement supercharger. They really can't move enough air. I had mine taco the throttle plate a few times trying to use one.

The current setup on my Z is a Q45 throttle body on the inlet of the M90 super, A/A intercooler across the front of the core support, Ford 65mm Crown Vic throttle on the inlet to the intake manifold, and into the engine. I had to make a custom throttle roller that had two different diameter pulleys on it to synchronize the throttle openings. This solved my throttle damage and blowoff issues, along with adding quite a lot of drivability to the system.

Using just the throttle on the inlet of the supercharger, I had idle problems due to the very large throttled volume. Using a throttle on the intake manifold and trying to blow through it, I damaged throttle plates on a regular basis, even with two 1" blowoff valves, then again, with two 1.6" blowoff valves, then with the two 1.6" valves plus the internal bypass valve in the supercharger.

Using both throttle plates also cuts down a LOT on the highway cruise noise.

The best solution I have arrived at so far is the following:

Ford Airbox->Ford 70mm MAF->Q45 throttle->M90 supercharger->Big Frontmount intercooler->Ford 65mm throttle->Intake plenum

Of course, I'm running a 2.8L inline six and Megasquirt, the MAF is for flow monitoring only and has no engine control. With supercharger and head porting and some serious supercharger case reconfiguration, I am seeing 520CFM inlet flow at only 5.5lbs of boost. IAT's are about 110F at full boost in 80* heat. It scoots.

Putting an additional large throttle body ahead of the supercharger had occurred to me, but I wasn't sure if that method would react fast enough. It definitely would run quieter. Do you get a vacuum reading in the intercooler pipes at idle?

I am stuck using a MAF in this setup, which complicates things. I also left the MP 90's internal bypass valve stay active in the system.

Right now, standing start acceleration is great, but there are a couple of rpm ranges I believe there might be a little flat spot. Like if I floor it from 45 mph for example (could just be the ambient heat, too). But I can get 5 psi peak boost at 50% open throttle with a quick jab of the pedal, which surprised me. I have had a couple highway cruises with probably a dozen WOT runs letting the throttle plate snap shut, and so far no play in the MP 90's driveshaft coupler. The ultimate wear test would be to let the boost psi peak to maximum, then quickly let off the gas pedal, and do it several times in succession. I'm not sure if my test setup is ready to withstand that. In a perfect world, I'll have it down to Beech Bend in a couple months.

The next thing I will attempt is redesign the blower inlet, and investigate noise suppression. The two holes in the hood are no help there, but great for cooling!

[Xnke]

I am not using a blowoff at all anymore-Just the bypass integral to the supercharger. By using the throttling valve on the inlet of the supercharger, you dynamically control the compressor and remove the need for the blowoff valve.

Install the MAF upstream of the supercharger. As long as you are not running a blowoff valve, AND the bypass valve doesn't screw with it, it will do the job just fine. There is no need to blow through the MAF-It doesn't give a damn about pressure, only flow rate. If the bypass valve screws with it, put a 90* turn between the MAF and the throttle, but leave as long a section of pipe as you can between the MAF and the throttle. Put the MAF right at the air filter, if you need to-that's how all Fords are done.

[AleroB888]

I am not using a blowoff at all anymore-Just the bypass integral to the supercharger. By using the throttling valve on the inlet of the supercharger, you dynamically control the compressor and remove the need for the blowoff valve.

Install the MAF upstream of the supercharger. As long as you are not running a blowoff valve, AND the bypass valve doesn't screw with it, it will do the job just fine. There is no need to blow through the MAF-It doesn't give a damn about pressure, only flow rate. If the bypass valve screws with it, put a 90* turn between the MAF and the throttle, but leave as long a section of pipe as you can between the MAF and the throttle. Put the MAF right at the air filter, if you need to-that's how all Fords are done.

I have a couple of 75 mm throttle bodies laying around, as well as a TCE 68 mm billet one made for my engine, so I just might try that out (at the blower inlet). And it would be easier to sync the two throttle bodies, since the crank levers are the same. However, the inlet casting I'm using now will not allow enough space to bolt on without completely redoing (and lengthening) the intercooler piping, etc.

In my case, I was hoping to eliminate the heavy inlet casting and gain a less restrictive inlet to the blower at the same time. But if I have to waste too much space with noise silencing though, I should definitely try throttling the blower. The parts I've used so far are what I had laying around. The BOV is a 58 mm Ford throttle body from a salvage yard.

The advantage of having the MAF sensor downstream of the intercooler tubing is if you get a bad air leak upstream such as a coupler popping off, it remains drivable. And I believe this positioning can tolerate using a smaller diameter MAF sensor.

[robertisaar]

And I believe this positioning can tolerate using a smaller diameter MAF sensor.

not that I'm any kind of expert on this particular subject, but it makes sense to me. a smaller area at a higher pressure can flow the same amount of air as a larger area with less pressure.

[Xnke]

No, it can't.

it's a MASS FLOW sensor. It does not measure pressure, it does not measure volume, it measures mass flow. As long as the sensor doesn't restrict the flow rate, it doesn't matter at all how big or small it is. Calibration, though, would matter. A larger sensor diameter is almost always going to be calibrated to a greater flow rate.

[robertisaar]

perhaps reworded, it will flow the same mass of air with a larger pressure differential compared a larger area with less differential?

[Xnke]

Yes, but that larger pressure differential means more losses through the meter, as well as the meter not actually *metering* more air.

[AleroB888]

Finally got the nerve to do some scans on this thing. For ambient temps in the mid 80s, it did quite well. The "all data loaded" mode on the histogram shows no Knock Retard (KR) anywhere. That was a welcome surprise, and may be the best I've ever got under similar conditions. IAT was taken at the MAF inlet, not in the UIM as I prefer to do.
PSI peaked at about 11, and charge temp rise at the IAT sensor was 16 degrees:



The engine wear and tear has caught up with us, as the ongoing misfires I've had on #1 have gotten worse, and #3 and #4 are starting to join in. So it's been intermittantly throwing P 300 and P 141 codes, usually before it warms up. A couple times I did get a flashing SES, which after a short time things seemed to pop back into place and it ran "normally."

[AleroB888]

^ Well, maybe it's not as bad as I thought. Turned out I had a bad fuel pressure regulator. Replaced it with a stock 55 psi unit, and no flashing SES for 2 days. She really peps up once the ambient temps go below 80. Need to get a scan of the upshift into 3rd, which had a KR problem before. I think it needs a trip to the track