Modifications to cold-side M45 supercharger installation on a 1997 Miata
In 1999 I purchased a 1997 Mazda Miata. One of several modifications already made was a Jackson Racing supercharger kit.
This kit uses an Eaton M45 Rootes-type supercharger mounted on the left side of the engine over the exhaust manifold. Having driven stock Miatas and been underwhelmed by their power, I had already decided to install a JR kit when I found an appropriate car. Hence I was happy to buy one already modified.
However, the installation was not entirely satisfactory and the car had significant driveability problems. The primary one was a dramatic and annoying hesitation or "flat spot" when opening the throttle. Armed with the optimism of the inexperienced I went ahead with the purchase since the car was in fine condition otherwise.
There followed the better part of a year of measurements, experimentation, and modifications. This led to substantially improved but by no means satisfactory driveability. I got lots of advice and ideas from the Sebring SuperCharger Owners Registry, an active and very helpful newsgroup (SSCOR@yahoogroups.com) which I highly recommend to owners of supercharged (vice turbocharged) Miatas. But in the end it was clear that the major remaining problem was due to a characteristic of the stock Miata OBD-II Engine Control Unit: when the throttle is suddenly opened, it leans the mixture for several tenths of a second. Result: hesitation. At that time the only solution appeared to be going with an aftermarket ECU such as the Link. The $1500 price tag persuaded me to simply grit my teeth and drive the car for several years.
In late 2003 BR Performance in Mauldin SC (www.brperformance.com) began selling a kit which featured a replacement intake manifold and allowed moving the supercharger to the other side of the engine. Overall this seemed a very good idea because mounting the supercharger over the exhaust manifold wasn't a very good approach (but it was far less expensive) and there was a significant amount of volume after the throttle body which could contribute to hesitation. Early adopters reported substantially improved driveability, and late in 2004 I ordered a kit. It was delayed by parts shortages and by the time it arrived the installation window of opportunity had closed; the parts sat forlornly in the box until Dec 2005. I should point out that the parts were of very high quality and nicely machined. The instructions were clear and detailed. And BRPerformance has been generous with advice when I've needed it!
At the end of December 2005 I installed the kit and made several modifications which are detailed in the sections which follow:
1. I restored the EGR functionality, not included with the cold-side kit I bought. It may be available on newer kits and I think it is included with the M62 kits. In this area we need EGR to pass emissions tests. Adding EGR.htm
2. I installed a blow-off port in what I hope was a successful attempt to protect the supercharger from the effects of the engine backfiring into the intake manifold. With luck I'll never have to find out whether it works. Blow-off device.htm
3. After realizing that the BRP belt-tensioning approach was unsatisfactory, I replaced it with what appears to be a viable improved version. Idler modification.htm
I also installed an oil filter relocation kit from Moss Motors, but that was a standard installation and not detailed here. The oil filter, previously difficult to access from above with the stock intake manifold installed, became completely inaccessible from above with the billet BRP manifold in place.
The modifications as listed above significantly improved driveability, but it was still by no means satisfactory.
I then installed the Jackson Racing PowerCard which was included with the BRPerformance kit. It richens the mixture in response to manifold pressure/vacuum, and made a marvelous improvement in driveability! There is a very brief tip-in hesitation which I would still like to eliminate, but it's only a shadow of its former self. If I had installed a PowerCard while the supercharger was still on the hot side, it's possible it would have made sufficient improvement that I wouldn't have made the expensive jump to a cold-side installation. But from a mechanical point of view I'm a lot happier with this cold-side setup, and the supercharger is no longer being heated by the exhaust manifold.
With both tip-in and upper-RPM leanness either eliminated or greatly reduced by the PowerCard, I added a Bipes Auxiliary Control Unit to complement the J&S Safeguard detonation-protection unit. This setup seems to provide very satisfactory performance: I can run 12 to 14 degrees of static advance on 93 octane gasoline, the ACU pulls out about 8 degrees in the peak torque range, and the Safeguard takes care of occasional detonation. A cold-air intake setup will be added at some point, but for now I've got other priorities and the car is running very well.
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