Engine: 1.8L I4
Injection: Port injection (stock 1990)
Description: I upgraded the engine to a 96, 1.8L and am currently using the stock 1990 computer for spark, and idle control. I have the Megasquirt and the stock computer sharing a single temp sensor. Surprisingly, the stock computer uses the suggested 2.2K pullup to +5v that the Megasquirt (for Mazda) requires. There is some temperature error, since the +5v in the stock computer differs in voltage to the Megasquirt -but it works well enough. I have been tuning with a diy widband o2 sensor. Everything works well, except low temperature startup idle. Since this is a summer car, I have not fixed this. There were a couple of issues making the newer coil packs work with the 90 computer- If you are considering upgrading engines, while still using the old computer, then drop me a post for further details.
Rather than purchase a supercharger kit, I decided to cobble together a system on my own. This allowed me to do things a little differently (I think better) and have saved a bunch of money as well.
The system is built around a Ford Thunderbird M90 supercharger and a Conquest intercooler. I basically copied some of the parts provided with aftermarket kits, and figured out the others. (I have access to a machine shop). In order to get things to fit, I had to lower the rad, move the swaybar, move the aircleaner to under the fender, plus numerous other small adjustments). I built most of the pieces last year, starting the install in the late spring, and finished a couple of weeks ago.
I am using 86 RX-7 440cc injectors, flowmaster exhaust, modified stock header and stock cat. (I like things reasonably quiet)
My current pulleys produce 11psi of boost max. â€“I like the supercharger because boost is instant and comes on at fairly low rpms. -6psi@2000rpm, 9psi@3000rpm, full boost by 4000rpm.
I still have quite a bit of tuning to do. -with the stock ignition settings, the system won't knock up to about 8.5psi (running 94 fuel, and a peak a/f ratio hitting 11.5:1). (I have a bypass valve, that I can wire to limit boost) I will need to adjust the timing to run full boost, and haven't decided how I am going to do this just yet.
The megasquirt has worked great, and I have found Megatune and the log visual viewer, to be excellent tuning tools.... thanks Guys! Also, thanks to Dave J and Lance for their tuning suggestions!
I will repost in late fall when things are dialed in.
Its time to put the car away for the year, so I will have to wait until next spring....
These acceleration (20-60mph) and horsepower(2500-6700rpm) curves were derived using a gtek competition gmeter. These hp numbers are a little lower than what a dyno would report, due to additional losses, such as aero drag, front wheel rolling friction, and transmission losses (2nd gear vs 4th gear)
This megasquirt file is for 440 cc injectors, and provides an AFR of about 12.5:1
Went to the dyno, on the hottest spring day on record here, some 90+ degrees....torque is good, but hp was lower than expected, since boost was falling off above 3500rpm (turned out belt was toast) and iat was some 35d higher at 6500rpm than 3000 rpm (not enough air moving over intercooler)
afr numbers measured and printed are 1/2 point higher than the actual afr.
-changed the 55mm TB to a dual 48mm corvette unit.
-fabricated new intake piping from TB to air cleaner using styrofoam as a mold.
-new belt tensioner, and upped boost from 12 -15psi
since I started with MS, I have added a 3 small pcb's, to accomodate additional circuitry (for WI, IAC & custom ignition). Although this has worked ok, I wanted to integrate this onto 1 board. (new board on left, old on right -note sophisticated method for mounting 3 small pcb's )
in car video of a 3rd gear pull
latest under the hood pic.