A bit of history (part 9) – Back on the road

Once Tony had finished putting the new engine together it was time for Matt to step in, his task was to make up a new exhaust section to run from the new turbo to the existing back box, and install the engine back in the car. As part of my continued concerns around heat management, I also asked him to put an oil cooler in the boot with thermostatic control.

The prior exhaust set up had featured a ‘screamer’ pipe, which vented the waste gate directly to atmosphere- very loud and impressive sounding, but ultimately a fail for track day noise limits…so this time I wanted the waste gate routed back into the main exhaust to keep noise down.

[Waste gate: this is basically a valve in the exhaust system upstream of the turbo, its purpose being to vent excess exhaust manifold pressure in order to limit the gas flow through the turbo, and hence control how much boost the turbo produces.]

I was surprised to learn that the exhaust back section I had (being an HKS design) was only 2.5 inches in diameter, whilst I had specified the rest of the exhaust to be 3 inches…but at this stage I was still wedded to the ‘look’ of the car I had imported back at the start, so opted to keep the HKS back section and taper the exhaust down to fit…not ideal.

Then Patrick opted to install the new electronics in the car for me, being the Race Technology data logger and digital dashboard, along with a new fuse box in the boot to manage the connections for the new MoTeC ECU. Dave Rowe then kindly came over and wired in the new ECU for me…

Matt did a really nice job of fabricating a dash panel to mount the digital dash onto so that it fitted in the standard Toyota clocks position, a nice piece of work and helped keep the inside of the cabin reasonably OEM looking. Likewise the data logger was hidden away in the cubby behind the driver/ passenger seats, and you could see the flashing light in the reverse mirror to confirm when it was doing its thing…happy days.

I had also been debating as to whether the boot mount intercooler I was using was up to the job of cooling the intake temperatures sufficiently, I was concerned that simply relying on two fans to push air through it wasn't enough...and I was considering a swap to a charge cooler instead. A charge cooler makes use of water to cool the air going into the engine, with a water pump and a radiator at the front of the car to cool the water.

The advantage in a mid-engined set up is that you get to make use of the massive amount of cooling available at the front end of the car, with the charge cooler still close to the engine...the obvious disadvantages being increased weight (as you now have a secondary water system on board), and added complexity (and hence additional stuff to go wrong).

My focus was really on maximising how the engine performed, so in the end I opted for a modified Radtech charge cooler system, with the main core mounted in the boot where the intercooler had been.

[What is an intercooler and why do we need one? The amount of torque an engine can produce is dictated by the mass of fuel and air that we can get in the cylinders to combust, the more we get in there- the larger the forces of combustion to push the pistons down, and so the greater the torque produced.

As temperature rises air and fuel expands, so at higher temperatures we are able to force less mass of air/ fuel into the cylinders as they have now expanded and are taking up more volume....so with higher air intake temperatures to the engine, lower torque levels can be produced.

The real issue with a turbo is that in compressing the air going into the engine (i.e. making boost), the temperature of the air increases...so we need to cool this air after the turbo has compressed it, before it goes into the engine, in order to maximise our power output.

In addition- remembering that one of the drivers of detonation is heat- a cooler intake temperature is only ever going to help reduce any propensity for detonation,]

Finally the day came in late October, time to run the new engine and start the mapping process…Dave (as always) asked me what I hoped to achieve, and I (as always) said something like let’s see what it will do and not blow up! I think this approach to tuning always gets better results as opposed to pushing for target power numbers, and putting the mapper instantly under pressure to make the motor do something it may or may not be capable of doing reliably.

The mapping day was quite painful, first of all we had to swap out the thermostat which was sticking, and then it developed a mis-fire, so a new set of spark plugs was required. That said I came away feeling very positive- the new engine seemed to be running solidly, and nothing broke…although we had run out of time.

Dave mentioned he thought he could hear a “bearing type” noise going on (note this for later!), and that the fuel pump sounded like it may be on its way out…so Patrick was going to take the car back to Rogue HQ and check over the wheel bearings.

In terms of results- the engine was coming on boost "reasonably" early- making full boost just before 4k rpm, and I thought I had seen ~380hp on the dyno during the day with about 1.8bar of boost and reving out to 7k rpm.

I remember coming away feeling super impressed with Dave’s no-nonsense, conservative approach to mapping, and I felt greatly reassured that we had taken no chances on the day, with everything feeling very well controlled.

Jump to a month later, and we were all back at the dyno to try again, and I was surprised to see that I had been mistaken in the results from the first session…the engine had made 280hp, not 380hp: significantly down from where it should have been. Oh boy, here we go again…

Anyhow, after getting over this shock- the second session actually went really well…Tony G was there and helped me retard the exhaust cam, which raised the power output. But peak torque was still kicking in a bit later than expected at ~4.7k rpm, and the torque curve had a strange double dip shape going on (despite Dave’s best efforts to map it out).

So we tried advancing the inlet cam, and suddenly everyone started smiling…torque increased, and the curve smoothed out. At 1.5bar of boost the engine made 345hp and 336ftlbs of torque at the hubs ( so approximately 400hp / 400ftlbs at the flywheel using our 15% transmission losses assumption).

It was amazing to notice how such a small movement in cam timing could make so much difference to how the engine worked, which in hindsight should have been obvious: the camshafts in the engine were still from Catcams, being very high lift and relatively short duration…the short duration meaning that any movement in their timing significantly changed the timing at which the engine could breath.

We then upped the boost to just under 2 bar, and the motor made 10hp less…we were now out of the turbo’s efficiency range, and the smaller turbine housing I had chosen was presumably throttling the exhaust gas flow. So my choice had (as expected) limited top end exhaust gas flow, and hence power levels, but the trade off being that boost kicked in lower down in the rev range.

The road test (in the wet) was “interesting”, and I seem to recall involved a lot of wheel spinning, but the early spool with (let’s be honest!) plenty of power, had made the car very fast on the road.

I was very happy with Dave’s feedback as well, which was that the engine felt pretty much bullet proof, and we didn’t seem to be close to straining the setup. It was also nice to see that peak exhaust gas temperatures across all four cylinders were ~850c (with the middle two running slightly hotter), pretty much perfect for what I was doing and nowhere near the 1000c levels we had started to see on the old setup.

At this point I actually got to take the car home, and I remember reflecting how much fun it was to drive now. If I was painfully honest, I did miss the mad rush as ferocious boost kicked in (even if that did make it less driveable), with this setup the car just went and it was only when you looked down at the speedo that you realised how fast you were going…far more driveable, but less scary!

I think this had already got me pondering a slightly larger turbine housing to see if I could get the scare factor back, but that’s another story…