Little. Yellow. Different. Better. GST's boost pill will cure what ails us. Or will it?
During our baseline dyno pulls of Project Evo X, Bryan Medway, Evo tuner at GST Motorsports, immediately noticed that the air-fuel ratio was leaner than either of us liked. The strange part is that although no changes had been made, it was about a half-point leaner than it was at its previous tuning session. Either our car had changed (unlikely but possible) or this AFR sensor was reading higher than the other one.
Nevertheless, I didn't want to take any chances, so I had Bryan richen it up to about 11.5:1 AFR. Better to be safe than to run over your own crankshaft, I say.
It would prove a highly influential decision. Once Bryan added the fuel, the entire torque curve dropped about 15 lb-ft. And for nearly an hour and a half, he toiled away trying literally every possible tuning avenue to recoup the lost output. Fortunately, ECUflash allows him to upload a new flash to the ECU in a matter of seconds, allowing him to quickly evaluate a number of changes. It was all for naught, as the car was proving insensitive to Bryan's attempts to tune around the now-richer AFR.
Then Bryan installed the GST boost pill.
The GST boost pill (left, in above pic) would allow us to run more boost, as the factory wastegate duty cycle was already maxed out in our current state of tune. Installation is a breeze--you simply remove the hose at the compressor discharge and pop out the stock pill. Press in the GST pill and reassemble. Couldn't be easier.
Then it was back to the dyno. Thanks to the pill, boost now arrived sooner in the rev range, but it seemed that increasing the boost wasn't producing any more power. In fact, a 2 psi increase in boost resulted in a hair less power than we were making before.
The reason for this is due to fuel octane. California's best pump gas is 91 octane, and it simply doesn't have good detonation resistance. By adding boost, we had to run less ignition advance. And turbo cars looove ignition advance--every little bit adds a lot of power when you're talking about highly boosted cars like the Evo.
Also, adding boost is undoubtedly adding a lot of backpressure on the poor stock turbo, which was never intended to be worked as hard as this. Backpressure contaminates the cylinder's contents during the valves' overlap period and further erodes detonation resistance.
His hands tied by crummy fuel and an overworked turbo, Bryan dialed the boost back to where it was. After a few more tweaks to the tune, here is where Project Evo X ended up:
The richer AFR cost us a bit of midrange. On the plus side, the turbo hits harder now and our peak power is very similar to before. Furthermore, the richer AFR provides cooler exhaust gas temperatures, which will make things easier on the engine until we can find an AFR sensor we trust
By the looks of things, we'll need less exhaust backpressure before we can unleash any more power out of Project Evo X.
Jason Kavanagh, Engineering Editor
billt9 says:
04:10 PM, 03/ 8/09
How much does this car cost now, $60,000?
ice1874193 says:
06:14 PM, 03/ 8/09
^ u obviously dont own an evo....mods are on the cheap for mucho HP
slickersdrip says:
06:32 PM, 03/ 8/09
So gut the cat and don't post about it and you'll be fine?
spdracerut says:
06:56 PM, 03/ 8/09
People have been getting GSRs for about $32k OTD. IIRC, this car has a cat-back exhaust, intake, larger intercooler, new IC piping, and cams. That's roughly $2500 in parts.
billt9 says:
08:34 PM, 03/ 8/09
ice1874193... chances are most people don't own an evo... huh, huh.
kitw says:
09:51 PM, 03/ 8/09
Weird.
My car, tuned by Bryan and with the GST boost pill, did great on 91 octane. GST's dyno is obviously different than this one, but one can look at the shape of the curve. My curve held a lot more torque above 5000 rpm. Sounds like your injectors are maxed out with the additional VE of your cams.
sealclubb3r says:
06:18 AM, 03/ 9/09
I wonder if using octane booster would make a difference.
church123 says:
07:57 AM, 03/ 9/09
Jason does your car still billow out black smoke at high rpm like a stock EVO X?
cwmoo740 says:
04:34 PM, 03/ 9/09
You should find out how much power you can make on 100 octane. The local gas station in Saratoga, CA (about an hour south of SF) sells 100 octane gasoline, but for $7.99/gal. There has to be somewhere in LA you can get it. Still sounds like you'd need to upgrade the turbo and reduce backpressure to get enough boost to maximize the power from 100 octane though.
By the way, if you're trying to make this thing ridiculously fast, when is the new turbo coming?