Text by Michael Ferrara | Photos by Richard Fong
Excerpted from DSPORT Magazine # 131
After years of preparation, the DSPORT KA vs SR challenge has finally begun. DSPORT’s DynoJet chassis dyno served as the battleground for the first melee. The rules were simple: deliver the maximum effort on the dyno with 91-octane pump gas. After maxing out on 91-octane, runs could be made with the assistance of a water/methanol injection system. Boost could be set as high as it could safely be run for the gasoline quality. With the same turbo, same compression ratios, same engine management and same tuner on both engines, we were eager to see which engine would reign supreme.
THE DYNO TEST
Both vehicles started with a full tank of 91-octane from the same gas station. The goal was to tune each of the vehicles to make the most power possible with a safe engine calibration. To be “safe” the tune would need to be free of knock while maintaining an air-fuel ratio that wouldn’t result in a meltdown. Koji Arai of Auto Talent has probably tuned more vehicles on the A’PEX Integration Power FC than anyone else in the country. Hence, it made perfect sense to have him tune the vehicles on DSPORT’s DynoJet eddy current chassis dyno.
INFO REFRESH
Both engines were built to have the same compression ratio and both engines are running the same turbocharger and wastegate combination. The KA24 engine has been bored to 90mm and uses the factory 96mm crankshaft. This delivers a final displacement of 2,443.2cc. The “SR23” has been sleeved and bored to 90mm, while the stroke has been increased to 91mm. Our SR23 delivers a final displacement of 2,316cc. As such, the KA24 has a 5.5-percent advantage in displacement. That advantage should be in line with a similar torque output advantage.
When we flow tested both the KA and SR cylinder heads, both heads had very comparable intake flows. However, the exhaust flow of the ported KA cylinder head versus the ported SR cylinder head showed flow numbers that were 10-to-15 percent higher at mid to high lifts. To the SR’s advantage, the S15 cylinder head incorporates Nissan’s Valve Timing Control (VTC). This system essentially advances the intake camshaft a fixed 20 degrees until a higher RPM point dictated by the ECU retards the intake camshaft back to its zero location. A crossover point of 6,700 RPM seemed to work best on the SR in its current configuration.
The Garrett GTX 3076R turbocharger was able to reach peak boost at 4,350 RPM on the built KA24 engine with 91-octane pump gas. The maximum average boost pressure was right at 23 psi (1.6 bar). Peak torque came in around 5,000 RPM and stayed flat until 5,500 RPM. Peak power was delivered from 6,600 to 6,900 RPM. While a spike of 502 horsepower was measured at the wheels, the graph showed a consistent 490 wheel horsepower figure. That equates to 575 horsepower at the flywheel or 3.7 times the original output. The turbocharged KA24 is now producing just over 235 horsepower per liter on 91-octane pump gas. That is an extremely impressive feat by any standard.
KA24: WATER/METH ASSISTANCE
With the Devil’s Own water/meth system, we chose the largest 630cc/min nozzle and set up the system to deliver full flow by 23.5psi of boost pressure. The system was also dialed in to start injection at 21 psi.
With the assistance of the water/meth injection, boost would exceed the pump gas curve starting from 4,100 RPM. So an additional 250 RPM of response was realized. The maximum average boost pressure was pushed up to 26 psi (1.8 bar). From 4,600 RPM through 6,400 RPM, the KA24DET was able to deliver over 450 lb-ft of torque. Peak torque came in at 5,100 RPM. Peak power came in at 6,300 RPM. Peak horsepower checked in at 554 ponies on a much smoother curve. This was a legit gain of over 60 wheel horsepower. The new peak power equates to 650 horsepower at the flywheel or 4.2 times the original output. The turbocharged KA24 is now producing just over 265 horsepower per liter on 91-octane pump gas with the assistance of the water/meth injection. Again, that is extremely impressive by any measure.
With our stroked and poked SR23, the Garrett GTX 3076R turbocharger was able to reach peak boost at 4,600 on 91-octane pump gas. The maximum average boost pressure was right at 22 psi (1.5 bar). Peak torque came in around 5,000 RPM and stayed flat until 6,200 RPM. Peak power was delivered at 7,400 RPM, just before the rev limit which we set at 7,500 RPM. That equates to just over 600 horsepower at the flywheel or 2.4 times the original output. Our SR23 is now producing just over 260 horsepower per liter on 91-octane pump gas. Hence, the SR23 is an exceptionally efficient platform.
SR23: WATER/METH ASSISTANCE
With the Snow Performance Stage-III water/meth system, we chose the largest 625cc/min nozzle. Richard mistakenly set up the system to deliver full flow by 27psi of boost pressure. A better selection would be to have the flow at full strength by 23psi. The system was also dialed in to start injection at 15 psi. Unfortunately, these settings put the SR23 at a bit of a disadvantage.
With the assistance of the water/meth injection, boost would exceed the pump gas curve starting from 4,200 RPM. So an additional 400 RPM of response was realized. The maximum average boost pressure was pushed up to 26 psi (1.8 bar), but boost began to slowly drop off starting from 6,000 RPM. From 4,750 RPM through 6,100 RPM, the SR23 was able to deliver over 450 lb-ft of torque. Peak torque came in at 5,100 RPM. Peak power came in at 6,300 RPM. Peak horsepower checked in at 533 ponies on a much smoother curve. This was a gain of just 20 peak wheel horsepower, while midrange gains were nearly 55 horsepower. Chances are that different setting on the water/meth system might have allowed for larger power gains. The new peak power equates to 625 horsepower at the flywheel or 2.5 times the original output. The SR23 is now producing roughly 270 horsepower per liter on 91-octane pump gas with the assistance of the water/meth injection. However, this figure may increase to the 280 horsepower-per-liter range with the water/meth system reconfigured.
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