We hate California 91-octane premium fuel. Apparently so does Project EVO. California gas is to fuel as Bud Light is to beer-less octane, more detonation. Although we used some of the best bolt-on parts available for the EVO, we were thwarted at every turn by California's urine-like fuel. Our results are disappointing compared to what tuners in other parts of the country are getting. Typically California gas strips 30-50 hp from a turbocharged car with modern fuel injection. Project EVO was no exception. We hate excuses even more than California gas, so we pledge to continue to develop the car until we get some more respectable numbers out of it.
In part one of our series, we squeezed more stick and balance in the corners of an already fine-tuned cornering machine without reducing its refinement as a daily driver. We also improved the stamina of its powerful brakes in anticipation of hard track use and more power from the motor. In part two, we attempt to squeeze more power out of the EVO's tried-and-true 4G63 engine.
From our baseline dyno runs, we knew we'd have a hard time with Project EVO. Strapped to XS Engineering's 4WD dyno in stock trim, we experienced a lot of variability when attempting to get a solid baseline stock power run. The EVO's knock sensor has a lot of authority over spark, mixture and boost, and with California's poor fuel, we were getting trace knock. The ECU tried to eliminate the knock, thus the boost and spark advance were erratic. So was the engine's power curve.
This is why. Ask any Californian with a turbocharged car about how bad our gas is. Our 91 octane usually means 2-4 psi less boost and/or 4-6 degrees less advance than other states' 93-octane fuel. We suspect the volatility rating of California gas makes it even more knock sensitive than the 91 suggests. Our 91 acts like what old 89 octane used to in terms of detonation threshold and EGT.
After many dyno runs, we picked 232 hp as our baseline. This number was approximately between our recorded high- and low-horsepower thresholds. Our run-to-run variation was as extreme as plus/minus 5 hp. First, we bolted on a Vishnu Performance Systems standard dump-back exhaust system.
We chose this system over Vishnu's more expensive turbo back and signature-series systems because the EVO has a pretty cool divorced wastegate turbine housing and outlet elbow from the factory. The wastegate discharge exhaust flow, which can interfere with the flow coming out of the turbine, is kept separate until it's smoothly merged with the turbine flow downstream. This minor detail is usually good for up to 5-10 hp and a few hundred rpm earlier spool so we didn't mess with this excellent bit of stock engineering. The more expensive Vishnu systems have a fabricated elbow/dump tube, which doesn't do much for power over the stock cast piece and costs more.
The Vishnu exhaust was nicely crafted from polished 3-inch TIG-welded 304 stainless tubing and came with everything we needed for a clean install, including spacers to lower the chassis cross brace to make room for the fat exhaust pipes. The exhaust features a free-flowing perforated core main and sub muffler. A high-flow cat with provisions for a rear-mounted OBD-II O2 sensor for no MIL light operation is also part of the exhaust package.
Another reason we chose the standard-grade exhaust is its modular construction allows us to delete the cat for race gas and track usage, which we'll test at a later date. The exhaust fit perfectly, which made for a smooth and easy bolt-on installation. The exhaust gave a smooth, deep throaty sound that wasn't too loud nor tinny.
Back at XS, we were again frustrated by the ECU's reaction to our fuel. The exhausts reduced backpressure and the added power it allowed gave the ECU fits, greatly increasing the power variation. We'll be conservative and say the gain was more than 8-peak hp to 240.6 hp, but had maximum gains of 12-15 hp in most other places in the powerband. On some runs, if we wanted to cherry-pick, the car belted out 30-more-peak hp than stock! Damn gas. Despite this, the exhaust wins our bang-for-the-buck award.
Next up was AEM's cold-air intake, which is usually a proven power adder. But consistent readings again were thwarted by the 91 octane. The AEM intake is a lightweight aluminum short-ram design with an open-element cone-type filter that uses an aluminum shield to block hot air wash from entering the engine compartment. It's hard to beat the stock EVO system because it has a large filter element, big airbox and a cold-air ram.
AEM dyno-tunes the length and diameter of each application for best power. We registered a 4-hp gain up to 244.5 hp, with general gains of up to 7 hp over a wide part of the powerband, from 3300 rpm on up. The AEM intake also produced even more dyno variation.
Our theory is that these mods were improving cylinder filling and thus tickling the knock sensor more. Due to run-to-run power variation, it was difficult to confirm this gain as a solid one, but this was a conservative non-cherry-picked run. The AEM intake made a throaty roar when the throttle was applied and you could really hear the compressor bypass valve at work, popping and hissing like an open blow-off valve.
Our next mod was Unorthodox Racing's Ultra S underdrive pulley set. The EVO application is a three-piece set consisting of a crank, alternator and water pump pulleys. The Unorthodox pulleys gain power two ways. First, they underdrive the crank-driven accessories with a lower drive ratio, thereby cutting parasitic loss. They're much lighter than stock, reducing the amount of power needed to spin them up to speed.
The Unorthodox pulleys cut nearly 5 pounds of rotating weight off of the car's reciprocating mass. Other tuners have confirmed these pulleys usually net a 6-whp gain, but we couldn't honestly pick out a gain in the mass of variability in our dyno runs.
The car did rev faster and felt faster. We've always experienced good gains with Unorthodox's pulleys before so we'll have to ignore our data and take other tuner's word for it.
We blame it all on the gas and the hyperactive knock sensor. For 4G63 builders, removing the front damper and replacing it with an underdrive pulley is controversial. Many respected 4G63 builders don't recommend this. Since the 4G63 is an internally balanced engine and we've never had a problem with any Unorthodox pulley, including very high-horsepower and racing engines, we're not worried. We'll keep a close eye on bearing life when we tear into this engine later.
We installed a pair of Unorthodox Ultra Series adjustable timing sprockets, which we found to be the lightest on the market. After a round of dyno tuning, we gained 1-peak hp up to 245.7 hp, but as much as 11-hp more after the peak, effectively flattening the powerband and giving excellent top-end pull by retarding both the intake and exhaust cams by 4 degrees. Of course, this was a conservative run and we were still plagued by considerable run-to-run power variation.
Next, AEBS supplied a set of Tomei Pro-series cams with valve springs and a set of AEBS lightweight titanium retainers. The Tomei cams are a short-duration, high-lift design featuring a lift of 11.5mm and a duration of 260 degrees, with recommended lobe centers of 110 degrees on the intake and 115 degrees on the exhaust. After the cams were installed and broken in, we changed our oil to Motul 300V synthetic in 15-w50 for protection even under severe track use. We also used a genuine Mitsubishi oil filter.
With fast valve action caused by the lift with this short duration, Tomei springs are mandatory with these cams. The cams' short duration makes for a nearly stock idle, with no loss of bottom-end power and good driveablity.
The cams and exhaust tie for "best bolt-on mod," dramatically increasing power above 4500 rpm with no loss in power on the bottom end. We experienced a peak gain of 8 hp, now up to 253.7 hp with a peak gain of 14 hp after the power peak. Unfortunately the dyno operator only took data to 7000 rpm on this and subsequent runs when our prior data went to 7500 rpm. If we extrapolate our power curves to 7500 rpm, our peak gains would be estimated in the 25-hp range. Of course, we selected a conservative run to report these gains and still suffered run-to-run variability, although the cams slightly reduce this variability.
To suppress the detonation and changes in boost pressure and spark advance, we installed an Aquamist water injection system. Usually water injection doesn't produce gains unless the engine is tuned around the water, and/or the boost pressure is increased, but we wanted to see the water's effect.
The Aquamist system is unique in that it uses a high-pressure 130-psi pump and atomizing nozzles that provide a fine spray of mist vs. a stream of water. The pulsating effect of the pump produces a variety of sizes of water droplets. Fine drops vaporize right away and provide charge cooling. Bigger drops reach the cylinders and suppress combustion and detonation. Water injection is very useful in road racing and does a great deal to keep the engine's temperature down and ensure reliability.
We used a Hobbs pressure switch to trigger out water injection at about 10 psi of boost. The Aquamist system can be tuned by changing nozzle size and nozzles, from .5mm to 1.0mm, in .1 mm increments. We used a .7mm nozzle to start with. When water is injected into an efficient turbo engine without any tuning changes, a power loss of around 10-15 hp usually results. We were expecting this and that's what we got.
We lost nearly 11 hp to the water, but what's interesting is that with the elimination of detonation, all of our power runs are now very consistent. Since we know the water is working to stop detonation, in our next installment we'll tune the engine and water injection system to exploit what can be done with very poor quality gas.
Finally, we readjusted our cam timing, running the exhaust cam straight up and the intake cam 2 degrees retarded. We were rewarded with an 8-hp gain up to 262 hp with no loss of power anywhere else in the powerband.
The combination of cams and timing gears is awesome, with 16-peak hp more and, if our dyno operator had revved it to 7500 rpm, we suspect a peak gain of 50 hp could've been had at high rpm. When the cam timing is optimized, the Tomei cams are the best single mod we applied to Project EVO.
All in all, we gained 30-peak hp, with a minimum of 3-hp right off of idle and a maximum estimated 50 hp at 7500 rpm. Our maximum verified gain is nearly 40 whp. This is seemingly impressive, but we're disappointed.
Other EVO tuners have reached 300 whp with similar mods, but with higher-than-stock boost levels and 93- or 94-octane fuel, we can't turn up our boost without detonation. Considering this, we're not doing so bad.
Our bad gas is hampering our goals. In our next installment of Project EVO, we'll tweak the ECU and tune around our water injection system in an attempt to reliably get more than 300 whp on 91-octane gas. We'll be back, crappy gas and all.