The History of My Car & Engine

from Rally Bashing Hack to Weekend Racer

So after rebuild #5, I was getting sick of throwing money at fixing the engine and replacing pistons, I would rather be buying a bigger turbo, or fitting a bigger exhaust, stuff like that.  I had been sticking with cast pistons because I knew they were structurally strong enough to handle the cylinder pressures and loading of a properly tuned engine.  They are also much cheaper, at about $200 a set, compared to about $1200 for a set of forged pistons.  

Detonation is what breaks pistons.  Detonation will break both cast and forged pistons, forgies will just be more resilient as they are stronger, but if the detonation is bad enough, they will break too.  Therefore, if you tune your engine right, with the right air/fuel ratios, and right ignition timing, if you keep inlet temps under control, and make sure you have high quality fuel in the tank, you should be okay with cast or stock pistons.  

I really enjoyed circuit racing and decided the only way I could continue was to fit EFI, and that would give me a safe and reliable tune so that cast pistons could still be used.  I did a lot of research on this, and couldn't find any instances of cast pistons failing simply due to high cylinder pressures, not at my relatively low power levels anyway.

I bought an EFI manifold from a late 90's model Holden Rodeo and a Microtech MTX-8 computer which could run sequential fuel injection as well as direct fire ignition (one coil per cylinder).  I bought a distributor from a Mitsubishi TP Magna that has two hall effect sensors built in.  One senses each cylinder reaching TDC, and the other measures TDC of piston # 1 only.  You need both of these sensors to run direct fire ignition.  Its so the computer knows not only when to fire a coil, but which one to fire.  I got the magna dizzy housing machined a little bit, then had the dizzy shaft grafted to the Gemini dizzy shaft so it mounted up as per standard in the stock gemmy timing cover.  

The manifold had to be modified a fair bit to fit, grinding clearances and cutting bits off here and there, but the stud pattern is the same as the Gemini head, so it slides over the gemmy inlet manifold studs.  The injectors were also pretty big, at 330cc each.  These turned out to be big enough to run 15psi of boost on my engine.  The inlet runners are pretty big, bigger than the carby manifold runners, and the throttle body is also a decent size, 60mm in diameter.

My Nissan Pulsar fuel pump was showing signs of giving up under the stress of running at the 47psi fuel rail pressure now with the Rodeo EFI manifold.  So I bought a new Bosch VL Turbo fuel pump.  Dont be fooled by what everyone tells you, the VL turbo and NA pumps are not the same pump.  The turbo one flows more fuel at the same fuel pressure.  The part number is 0 580 464 070, the turbo pump has threaded electrical connections with little nuts on them, whilst the NA pump has electrical spade terminals, just like the Pulsar pump I was originally running.  The NA pump is probably an 0 580 464 008 or similar, there are heaps of different Bosch external EFI pumps from factory cars that look similar.  A true VL turbo pump looks like this.

My clutch had been slipping a little bit with the last engine combo, particularly when trying to launch hard (burnouts maybe??), so I bought a 5 puck ceramic button clutch plate and used the existing RPM heavy duty pressure plate (the yellow bit).  This is a pretty good clutch combo for the money, the RPM kit was about $150, and the 5 puck clutch plate was about $140, Daikin brand I think.

I was also thinking of ways to keep engine temps a bit lower, so I fitted an RX7 oil cooler just under the radiator, with a sandwich plate between the oil pump outlet and the oil filter.  I needed to use a short oil filter now, and the EFI V8 Commodore filters are a perfect fit.  This has helped with temps, now they never get over 96deg C, unless there is a problem.  Typical temps for my engine whilst racing are 90-94 degrees.  You see see both the oil cooler and intercooler here.

It took a while to get the computer to fire up the engine, the fuel maps were way out, and the exhaust kept filling with fuel, then igniting, giving an almighty back fire.  At the time, I had no idea what sort of injector pulse widths I needed to start the car.  The maps in the computer were for a GSR Lancer and had really long injector pulse widths in the fuel maps, they must have smaller injectors than 330cc as my engine just kept flooding with the same pulse widths. I flattened a few batteries too.  Nearly cooked the starter motor.  

Anyway, finally got it running, and did all the tuning myself on the road with my narrow band oxy sensor measuring a/f ratios.  I knew by trail and error that I could run 15psi of boost with the stock injectors, as if I would up the boost any higher, the air/fuel ratios would start to lean out.  I think they were reaching 100% duty cycle.  So I got a set of 500cc RX7 series 5 injectors, which almost were a straight swap for the 330cc Rodeo items.  No more fuel shortage!

The wheel spin problem became much worse.  I could crank in a lot more timing advance at low rpm, this coupled with the low rpm torque of the G200 meant that it was really responsive down low, and would wheel spin very easily with the single spinner open centered diff.  Whether it be in straight lines or through corners, the RHS rear wheel would loose grip very easily.  So I decided to chase down an LSD option.  It was really hard to find one, but I eventually did, and booked it in the following week to get it fitted at G & E Differentials in Keysborough on the outskirts of Melbourne.  

I had a week to kill, and a mate had got the diff locked in his girlfriend's Toyota Corolla, so I knew basically what to expect, but was keen to see how a locked diff would feel in the Gem, so I got a spare centre welded up the weekend before (CIG locker) and took it for a spin.  After leaving rubber all over the streets, and getting dizzy from going in circles, I decided that locked diffs are for crazy people, or for straight line racing only.  If you are partly turning a corner, and give it too much curry and break into wheel spin, the whole car will spin around pretty easily, and quite quickly.  Instant oversteer.

I got an early model Commodore 6 cylinder LSD centre fitted to my diff, this literally bolted in, same axles, etc, just fitted my crown gear from my original diff centre to this new one.  I got it reconditioned before install, and fitted with heavier springs so that it engages sooner and harder as wheel slip is detected.  They are a cone style LSD, and its a bit weak for my engine, often it still slips so that only one wheel spins, but for the money, there aren't any better options.  

I really need something larger for optimum traction.  From a strength point of view, I have only ever broken two diffs, and the spider gears went in both of them.  I have not had a trouble with this LSD diff, so its probably stronger overall.  It was from a 6 cylinder car.  The handling/traction improvement was great, I could take a corner at high speed and accelerate out of it, without massive oversteer like the locked diff.  The car was a lot slower through corners with the single spinner diff, and I couldn't accelerate out of corners very fast, it was really hard not to wheel spin.  Now I can if I try, but not accidentally.

I Did a few races around the tracks at Calder Park and Phillip Island.  Hadn't been on a dyno yet, so ran it pretty conservatively with rich mixtures and only 15psi of boost.  Once again, it was awesome.  Overtook pretty much every car in sight on the straights, then some of them would catch me through the corners.  I needed better tyres and suspension.

Now that the back was over steering a lot, I had to get used to it with the extra power of the EFI set-up.  I had one small mishap where I spun half way through a corner and ended up boot first into a concrete wall at Calder.  I put the power on too early coming off the second corner after the main straight, it boosted up and I ended up spinning and kissing the wall.  After it hit, the car flicked around and my front right wheel crunched the wall, bending the stub axle and breaking the disk rotor off the hub section.  It was a cold morning when I took the photos below, ice on everything.  I painted the damaged area to stop it rusting.  It didn't matter that much, because the panels were replaced anyway.

This required a brand new rear quarter panel and rear beaver from Holden, and a new paint job, which was nice.  Needing to replace the damaged brakes on the front, it prompted me to look at brake upgrades and after this I put my option 2 brake kit on, which worked better than I could have hoped. 

I had also fitted a bigger Selby swaybar on the front end, and splashed out and bought some Yokohama Advan A032R race rubber for each corner.  These are awesome tyres.  They are often referred to as a "grooved slick", which I know is a contradiction, but they are a soft sticky grippy compound.  You can see the tread pattern in the pic below, the brakes fitted in the photo are my option 1 kit.

Tried to do a few G-Tech runs on the drag strip, but did it before I bought my race tyres or started mucking around with the diff, it was like trying to launch hard in the wet.  Wheel spin!  I couldn't recorded any decent times, I actually had better times in the early turbo days, even though now I had much more hp.

EFI itself doesn't make power.  EFI simply sends a signal to fuel injectors to provide enough fuel to get the desired air/fuel ratio.  A carby can do this too.  However, EFI has some other benefits.  Usually, to fit EFI, you use an EFI manifold like I did, which flows more air than the old carby inlet manifold and 32/36 Weber I was using.  This increase in air flow does make more power.  Therefore, if you had equal air flows, you could make the same power at a particular engine RPM with either EFI or a carby. 

However EFI can also give you the correct air/fuel ratios over the entire operating range of the engine, which means better fuel economy, better throttle response and part throttle power, as well as reliable full power air/fuel ratios, under all conditions, such as taking corners hard, and probably even upside down.  The carby will struggle to give the desired air/fuel ratios over the same range of engine operating conditions (load and rpm).

I had some pretty rough intercooler piping, I wanted to do it right, but I also wanted to drive the car, so I took some shortcuts.  Nothing dangerous, it just didn't look all that nice with heaps of rubber bends and hose clamps everywhere.

I took the car to the dyno to get the computer fine tuned and see how many ponies could be found at the wheels.  I knew it was more than before, it just felt better overall, more response, more power through the whole rev range.  The computer also controlled the new direct fire ignition system which included timing adjustments with respect to RPM, boost, air and water temp.  This in itself gives much better part throttle response and lets you accurately map your ignition timing.

So dyno run # 1:

It made 125hp @ wheels.  (90kW @ wheels).  This boost was chosen to start fine tuning the computer with.  This was a bit more power than the carby set-up, but with similar air fuel ratios and ignition timing, I didn't expect the EFI to make much more power.  I was hoping that the EFI manifold would be able to flow more air than the old carby and inlet manifold at higher power levels.  It made a bit more power now, but to properly check this, I needed to turn up the boost to where the carby set-up was causing a flow restriction.

Dyno run # 2:

It made 197hp @ wheels.  (147kW @ wheels).  Not wanting to push it too far, I was pretty happy with this result, so we left it there.  We just did a bit more tuning with the fuel side of things to get some cruise economy and adjusted the accelerator pump settings to get crisp throttle response.

Once again, I cant recommend highly enough the importance of getting your car tuned properly, with the help of a dyno, or at least a wide band oxy sensor.  I was running too rich, and I knew I was rich, but I was loosing a lot of power because of it.  We leaned it out to about 11.8:1 to make this hp, so it would have made a bit more at around 12.5:1 probably, but temps would have increased and more chance of detonation.  It never felt as quick as it did after I left the dyno workshop, and part throttle and mid range power was up, it was much 'crisper' overall because it wasn't getting bogged down with extra fuel from my overly rich tune.

The engine always pulled hard to about 5500rpm, then the power seemed to taper off sharply.  It would rev higher, but wouldn't keep pulling.  I knew that the existing 2.25" exhaust and super turbo muffler were probably the bottleneck now.  I also knew from previous inlet air temperature testing that the turbo is pretty much at the end of its efficiency at this boost level of 19psi.  Diminishing returns mean more boost will make a lot more heat, which is not good for a circuit racer.  So I had a few plans to take it a step further.