In the Gearing
The inter-gear ratios of the transmission dictate the required width of the engine’s powerband for peak acceleration. The upshift inter-gear ratio dictates where the engine’s RPM will fall when shifted from gear to gear. The 1-2-upshift inter-gear ratio is calculated by dividing the gear ratio of Second divided by the gear ratio of First. In the case of the Albins 4-speed drag ratio gearset that we are using, second gear is a 2.00:1 ratio while first gear is a 3.00:1 ratio. This upshift inter-gear ratio is therefore 0.667. Multiplying this upshift inter-gear ratio of 0.667 and the shift RPM of 10,500 RPM produces 7,000 RPM. Hence, the 1-2 shift at 10,500RPM drops the engine speed to 7,000 RPM as second gear is started. Third has a 1.390:1 gear ratio, so the upshift inter-gear ratio equates to .695. The .695 inter-gear ratio drops the RPM from 10,500 RPM in Second to about 7,300 RPM to start third gear. Fourth gear has a 1.09:1 ratio which produces a 0.784 ratio for the 3-4 upshift. Shifting from third at 10,500 RPM drops the engine speed to about 8,250 RPM for the start of Fourth.
Based on the gear ratios delivered by the Albins gearset, the ideal powerband would start at 7,000 RPM and continue through 10,500 RPM for power delivery to be optimized in every forward gear. Since this is a FWD vehicle and traction is limited, a power band that starts a little later (at a higher RPM) may not impede performance significantly as only so much torque can be delivered to the ground before the tires break loose. The amount of time spent in Second gear is likely to be just a couple seconds, so it’s the powerband required for peak performance in Third and Fourth that our most critical. For Third gear, our engine’s powerband starts about 700 RPM later than the ideal. As such, we’ll likely have to make some changes to start our powerband a bit earlier in order to realize the quickest performance on the strip.
Boost Curve vs. Power Curve
For the current combination, the engine’s gradual boost curve is directly affecting the torque and power curve shapes of the engine. While the 1.25 A/R turbine housing is likely the best choice for peak power, a smaller 1.10 A/R or 1.00 A/R turbine housing would allow the engine to reach its target boost pressure (40-42 psi) at a lower RPM. This will likely broaden the powerband of the engine while possibly trading off some peak power output due to higher exhaust backpressure. If the engine was already at the targeted boost pressure by 7,000 RPM and we still required a shift in the power and torque curves, swapping to a shorter duration camshaft could help shift the curves to the left (producing more power and torque sooner while potentially losing some power and torque at the very top end).
High torque output, excellent traction, high vehicle weights and high engine RPMs are some of the conditions that make clutch design difficult. In the case of our drag Civic, the vehicle weight is relatively low at 2,450 pounds with driver but the traction capabilities of the FWD on slicks is about on-par with an all-wheel-drive vehicle on street tires. Hence the amount of available traction is quite substantial and that means a good amount of load on the driveline will be produced before wheelspin occurs. As for the engine, 620 lb-ft of torque is also quite substantial. Combine these conditions with the fact that the clutch needs to properly engage and release at 10,500 RPM and the field of potential players gets dwindled down to two or three clutch systems that can do it right. Having great success in the past with the custom quad disc, carbon-carbon clutch used on our Project R33, we decided to look to Tilton for a solution. Thanks to the popularity of the Honda B-series engine, Tilton offers an off-the-shelf solution. The Tilton Cerametallic Clutch Flywheel Assembly (CFA) for the B-series is built around a billet-steel flywheel with integral gear. The integral ring gear eliminates a potential point of failure found on flywheels that have a pressured or welded ring gear. The billet steel flywheel mounts the 7.25-inch twin-plate OT-series clutch system to the engine. This clutch system uses two 4-pad cerametallic clutch discs along with the Tilton “GG” pressure plate. The 4-pad discs have a lower inertia than full-circle discs for quicker shifting. Torque capacity is rated at 840 lb-ft (about 35-percent above our engine torque output, providing a nice factor of safety). The entire clutch system and flywheel assembly weighs just 18.6 pounds. To reduce pedal effort, improve modulation and eliminate the problems that occur in the factory clutch hydraulics, a Honda hydraulic release bearing kit is also available. The kit provides the hydraulic release bearing, a Tilton ¾-inch bore clutch master cylinder and the necessary hardware and lines for the conversion. To reduce shock loads to the driveline, we also installed a Tilton flow control valve. The valve regulates the flow of hydraulic fluid back to the master cylinder when the clutch pedal is released from the floor and is traveling back to its regular position. Three different orifices allow tuning for just the proper amount of “clutch riding” on launch and between shifts for minimal driveline shock.
Transmission Gear Set
[pullquote]THE TRANSMISSION’S CLOSE-RATIO GEARING PROVIDES LESS RPM DROP PER GEAR THAN ANY FACTORY-AVAILABLE GEARSETS[/pullquote]To find a proper gearset for the B-series transmission, we had to go over and down under. Unfortunately, we went over what we originally planned on spending as the gearset retails for about $6,800 (due in part to our weak U.S. dollar). We went “down under” as we couldn’t find anyone in the Northern Hemisphere with a proven solution. Located in Victoria, Australia, Albins Performance Transmissions offers a Honda B-series dog-engagement gear set for drag racing applications. Designed to fit in the factory B-series transmission case, this close-ratio gear set is built from ultra high-strength billet alloy steel. Using helical cut gears, noise is reduced (compared to straight cut gears) while case deflection is better accommodated. A handcuff brace replaces fifth gear with the installation of the system. The gearset’s dog-engagement removes the fragile sychros out of the equation and allows for faster shifting. The transmission’s close-ratio gearing provides less RPM drop per gear than any factory-available gearsets for the B-series. On all of the factory Honda B-series transmissions, the RPM from a 10,500 RPM shift out of First, drops the RPM to 6,175 RPM (6,850 RPM on Del Sol trans). With the Albins gearset, five different final drive ratios are available. We opted for the 4.09:1 final drive which yields an effective 4.46:1 final drive ratio in Fourth gear. Estimating 5.0-percent of tire-height growth on the slick, 10,500 RPM in Fourth would be about 180 MPH. Based on our power-to-weight ratio, we should hit about 176-178MPH at the traps.
As Honda drag racers continued to push the envelope on power output, the limits of the 27-spline differential and axle setup eventually became apparent. To address the needs for additional power handling, The Driveshaft Shop engineered a Pro-Level 28-spline axle and differential solution. The 28-spline axles are 40-percent larger at the differential and intermediate shafts. On the outers, 33-spline CV’s handle all the power that can be delivered to them. The Pro-Level solution requires either a 28-spline spool or 28-spline limitedslip differential. We opted for the LSD and also had the ABS rings installed so that our MoTeC engine management system could read the wheel speed at each axle. With a retail cost around $3,750, the solution is not a cheap date. However, having axles that won’t break on a FWD vehicle is one of the best ways to help keep the vehicle from hitting a wall.
Wheels and Tires
To put the power to the ground, we selected a set of 24.5×9.5×13-inch M&H Racemaster slicks. M&H Racemaster has been an avid supporter of import drag racing since its infancy and its drag slick simply works very well. A set of Weld Wheels Magnum Import Drag wheels of the 13×10 (+0 mm) variety with custom OMF Performance beadlocks carries the front rubber. Matching 15×3.5-inch Magnum Import skinnies carry a set of 24.0×3.6×15-inch skinnies at the rear. Using this “pizza cutter” wheel and tire combination on the rear reduces rolling resistance significantly.
While the right pad and rotor combination can allow the factory brakes to make that single stop at the end of the quarter mile, the factory brakes are extremely heavy for such a task. Fortunately, Fastbrakes.com offers a lightweight drag brake system for the front of most Hondas you’d want to race. While the standard Fastbrakes.com kit sheds 15 pounds and uses a single-piston Wilwood caliper, we preferred to give up a pound of weight loss and run the optional two-piston Wilwood calipers. The two-piston calipers offer a bit more braking torque due to the increased piston area while also offering less drag on the brakes due to its design.
Near the Limit
To this point, there appears to be just one item reaching its limit. The Fuelab 41402 Prodigy Fuel Pump is conservatively rated to support 1,300 horsepower on gasoline. This is one bad-ass pump. If we were running race gas or perhaps even running at at lower boost pressure levels, this pump would easily support that number and then some. However, we are dealing with two factors that really limit the horsepower potential of a fuel pump. First, we are running E85 and that requires almost 40 percent more volumetric flow than gasoline for the same power level. Hence, if a particular fuel pump can support 1,300whp on gasoline, it can only support (1,300/1.4) or 930 horsepower on E85. Second, we are running a significant amount of boost pressure. Fuel pumps need to run at a base pressure plus the amount of boost pressure to deliver the proper amount of fuel to the engine. If our base fuel pressure is 45 psi, running 45 psi of boost pressure means that the pump is operating at a head pressure of at least 90 psi (maybe closer to 100 psi to overcome inertial and fitting losses). As pressure increases, the volume that a pump can supply decreases. In the case of the 41402, the pump can supply roughly 12,000 cc/min of flow at 45 psi or about 7,800 cc/min at flow at 100 psi. Since the fuel pump cannot match the needed delivery at 100 psi, fuel pressure drops. To compensate for reaching the flow capacity of the pump at that pressure, the injectors are run at a higher duty cycle to provide a safe A/F ratio. Fortunately, we’ve come up with a potential solution that will negate the need to add a second pump. We are simply planning to upgrade from our current “12-volt” to a “16-volt” battery and alternator setup. We asked Fuelab to run a test on the 41402 at both 13.5 volts (the charging/alternator voltage of a “12-volt” system) and at 18.0 volts (the charging/alternator voltage of a “16-volt” system). The lab results show that the 41402 goes from delivering 7,820 cc/min of flow (at 102psi) at 13.5 volts to delivering over 11,600 cc/min of flow (at 106 psi) at 18.0 volts. That’s enough to support over 1,300 horsepower at the wheels on E85. As a side benefit, the new “16-volt” system will also increase the voltage capacity of the current coil-on-plug ignition system. This should further reduce the chance of misfires and plug fouling.
The Master Plan
The Voltphreaks 16-volt lithium battery and Powermaster 16V alternator have just arrived. As soon as we get a chance, these items will be installed and the vehicle will be re-tuned to accommodate the increased fuel delivery capacity of the system. From there, we plan to do some further dyno testing with the smaller 1.10 A/R turbine housing. Hopefully, we will also be able to take a look at some ¼-mile datalogs with the current 1.25 A/R turbine housing in place too. From there, we’ll try to determine if a trip to the strip with the smaller A/R turbine housing is warranted. We are also planning to test the effects of varying the plenum volume on the Skunk 2 Ultra-series intake manifold.
Being able to run consistent 8-second passes reliably may take us in other directions as well. We have yet to dial in the suspension to maximize its ability to help the power get to the ground. We also haven’t started playing with custom camshafts to optimize the power curve. There’s plenty to do and plenty to learn. If you are interested in engine and drag performance, from a Honda or any vehicle for that matter, stay tuned.