The History of My Car & Engine

from Rally Bashing Hack to Weekend Racer

I had always known about the benefits of an intercooler, and I finally got around to fitting one.  I had put it off till now purely because of the plumbing issue, and having to cut out holes in the radiator support panel.

I bought an RX7 series 5 cooler from Dalton Automotive and modified it to become a front mount unit.  Check this intercooler installation link.  I modified the carby air box so that the inlet was at the front, and I made a cone section to try and give the air a better transition from the round plumbing into the square box.  The old side inlet was simply blocked off.

I remember the first chance I got to drive it after fitting the intercooler, I set the boost back to 7psi and went around the block.  It made as much power on 7psi intercooled, as it used to at about 12psi non-intercooled.  I assume the reduction in inlet temps was the reason for this, but it made a really good difference.  Also as my fuel mixture was a little rich, and the colder denser air carries more oxygen for a given volume, this effectively leaned out my a/f ratios a little bit and I found more of a sweet spot which made even more power.

Its often the case with some mods that you cant actually tell what difference they made.  This was a really noticeable improvement, just like turning up the boost.

I also modified the distributor so that I had some mechanical advance again.  I know I wanted to run about 24deg total timing at 18psi of boost with my combo, but with the locked dizzy, the most I could run was 18deg, so this would give me a bit more power both on and off boost.  Check this link for modifying the ignition timing.

I had been trying to do a bit more fine tuning of the air/fuel ratios, mainly to get some fuel economy on the highway.  This was the benefit of using the 32/36, I had separate primary and secondary circuits in the carby to tune.  I could tune the primary for cruising economy, and the secondary for max power.

I managed to lean it out a bit whilst cruising, but was still a bit rich under full boost.  Carbys are hard to get right, and its always a bit of a compromise.  This is where EFI comes in handy.  So back to the dyno to check air/fuel ratios and the new power output with the intercooler.

Dyno run #1:

It made 150hp @ wheels.  This is less of an improvement as I was hoping for over the last dyno run, but there are a few possibilities for this.  It was a different day.  You have heard the expression "same shit, different day"?  Well with a dyno, its often "different day, different shit"!  

Fitting the intercooler, although of huge benefit, also introduces flow restrictions into the system, with the air having to flow through around 1.5metres of extra pipe work and the intercooler core itself.

I never measured compressor outlet temps, but if they were low enough, I could have increased the boost even further.  Something I couldn't have done without the intercooler.

I also feel that the 32/36 Weber was approaching its flow limit, and was probably becoming a bottleneck in the whole system at that stage, along with the crap muffler I was using.

This would be around 200hp at the flywheel though, not bad power results from this carby.  We didn't check air inlet temps, but the air/fuel ratio was still too rich for optimum power.  It might have made another 5 or 10hp with mixture and timing tweaks.

I never made it back to the drag strip, but it was about then that I started getting into circuit racing.  I took the car to Winton Raceway for a day of tearing down the straights, and braking hard before the corners.  

A few weeks before going to Winton, I had a bit of a drag (didn't measure time), and wound it out to a bit over 200km/h, then I tried to stop!  I had 100% stock brakes at that stage, and when I went to brake, I got some pretty bad brake fade about half way through the stop, and my brakes would have been fairly cool before this.  A tee intersection was fast approaching, and I thought I was going to go straight through it.  I stopped with the nose of the car about half way into the lane of the intersecting road.  I heard circuit racing was pretty hard on brakes, so I went and got a set of Bendix Ultimate pads before driving to Winton.  I also fitted a new set of shocks, as car was getting a bit "bouncy".

I was actually surprised how well the Ultimate pads worked.  I could do about 3 hot laps before the brake pedal would go to the floor, but I was using the gears a lot to help slow down.  I knew that if my car only had half the power, I probably could have raced continually because there would have been a lot more time between corners, and my speed wouldn't have been as high.  

It was a good day, and a bad day all at the same time.  I got a speeding ticket on the way to the track.  Had an awesome time racing, I was overtaking a lot of the other cars, going as fast as I could, I had just got some new 16" wheels and the handling improvement was great, better tyres too.  It was a hot day, over 30deg C on the track.  My engine was running a bit hot, I had just put a new 3 core radiator in and was running a 10" thermo fan, but the temp gauge was still a bit high.  To counter the higher track temps and engine temp, I was only on about 15psi of boost.  Then I blew the motor before the day was finished.  It had been about a year since I blew my last motor, at that stage, a year was a long time for an engine and me to stick together. 

It happened because carbys don't like to experience high lateral g forces, such as when cornering hard.  The fuel sloshes around in the fuel bowel, and you can uncover a main fuel jet if cornering really hard.  Also, unless you have a surge tank, you need to make sure you have plenty of fuel in the tank so that the pump is always submerged.  A combination of these two things meant that often halfway through a long sweeping corner, the engine would hesitate and splutter, like it was short on fuel.  

I felt this happen, but often just kept the accelerator applied as it was only for short periods that the engine would play up.  However this lack of fuel is a classical lean condition that promoted piston breaking detonation.  That's exactly what happened.  I'd blown another motor and had broken pistons.

Check out STAGE 10 - G200 EFI Turbo.