The History of My Car & Engine

from Rally Bashing Hack to Weekend Racer

So after rebuild # 4, I was a bit wiser, I stopped pinching pennies, and went to a dyno workshop.  I was also getting sick of replacing broken pistons.  If I had spent the money in the first place, I would have saved all those broken engines, and would have had more cash in my bank account.

We played around a bit on the dyno, wound up the boost a bit and measured inlet temps at the carby air box.  I can recommend that anyone tuning their own engine should at least get a power run done on the dyno to get air/fuel mixtures checked, and maybe a quick play with the ignition timing, as you could be way out with your guestimations, and plus you also get to know how much power you are really making.

So dyno run # 1:

It made 90hp @ wheels.  This is less than I was hoping for at the time, but it all makes sense now.  The air/fuel ratios were too rich at 11.5:1, the inlet temps at only 7psi were pretty hot at 90deg C, and it didn't want to rev out properly, we thought at the time that it was due to the spark plug gap being at 40thou, probably a bit much.  I cant remember if we adjusted this before continuing, we did a few more runs though.

Dyno run # 2:

It made 105hp @ wheels.  Inlet temps rose to 120deg C, this was considered too high so we thought we would try spraying some water/methanol mix into the turbo inlet.  

We rigged up a jet from the carby spare parts box, and used the windscreen washer bottle.  Mixed up a 50/50 mix of water and methanol, and manually varied flow by kinking the hose.  Agricultural, but it was only for testing purposes.

Dyno run # 3:

It made 120 hp @ wheels and the inlet temps had dropped to about 90deg C again, which is the temp I had at 7psi of boost.  This was a great power improvement, however the engine seemed a bit "boggy" due to too much water/methanol flow.  We didn't have a proper jet to inject it, it wasn't a mist at all, and limiting flow by kinking the water line didn't work very well, as the pump supply pressure wasn't very high.  So to get a decent spray into the compressor inlet meant the amount of water/methanol was too much for this boost level.

Dyno run # 4:

It made 130 hp @ wheels and the inlet temps were around 100deg C.  The water/methanol injection was working well, Still had the hose kinked.  Air/fuel mix was still too rich, and the air box on the carby was starting to leak at the rubber gaskets.  I hadn't cut the gasket out very well between the carby and airbox, and you could see the water/methanol coming out from the gasket under boost.  

Dyno run # 5:

It made 140 hp @ wheels and the inlet temps were starting to climb too high again, around 120deg C.  We couldn't hold the engine under load for long for fear of detonation at these temps.  This was showing the turbo was starting to become pretty inefficient at these boost and air flow levels.  The water/methanol injection was working well, I think we didn't kink the hose anymore at this boost level.  Air/fuel mix was still too rich, and the air box on the carby was leaking all over the place. 

I came away from there pretty happy, knowing that I had built a decent motor, assembled everything myself, put together the turbo set-up myself, and now it was making some decent numbers.  These were about the same power levels as a stock Holden 253ci V8.  The car felt pretty quick too.

This also shows how we increased power from 90hp@wheels to 140hp@wheels and didn't touch the carby jetting, and it gave nearly the same a/f ratios.  So once you get a carbys jetting right, varying amounts of air flow (power levels) don't always demand re-jetting.

I went home and made a few more changes.  I made new gaskets for the air box to try and eliminate any leakage.  I made a decent jet for the water/ methanol injection and installed a VDO boost pressure switch to turn it on at about 12psi, not too early, or else it tended to bog down the engine.  If I switched it on at lower boost, you could tell when it switched on as power would drop off.

It was flowing the right amount for 18psi of boost, but too much for lower boost levels.  I normally drove around on about 15psi though.  I actually bought a higher pressure pump to replace the stock washer bottle pump hoping to get more of a mist than a stream from the jet, but it didn't make a noticeable difference.

Back to the drag strip, 17psi of boost, dizzy locked at 17deg, absolutely no traction, kept spinning the wheels through 1st and 2nd gear.  I had the same old crappy hard tyres on the back.  They were 225's, and fat looking things, but they were simply too hard and I couldn't take off very quick.  I had to slip the clutch a lot so as not to break into too much wheel spin.  

The best time I could get was a 14.7 second pass @ 170km/h.  The trap speed was up, and I knew other cars doing that trap speed (~106mph) were doing 12 second passes.  But they had the right suspension and slicks, I didn't have either.  Some decent rear tyres would have made a big difference though.

So wheel spin city.  I did go through a diff and 5 speed at this stage, the high horsepower must have got to them.  Probably too many attempted drag starts, as that puts an immense strain on the drive train.

Check out STAGE 9 - G200 Blow Through Turbo - Intercooled & Modified Points Distributor.