L15A7 Valvetrain CAD Models
Onshape was used to model the various rocker arms of the L15A7 valvetrain:
These models are based on measurements taken directly from the rocker arms I have in hand and plan to use in the car. The arm ratios are 1.7:1 and 1.8:1 for the intake and exhaust rockers respectively.
The Aluminum portion (light blue) of the rocker arms was assigned to be Aluminum alloy 2024, which is a common alloy where fatigue resistance is necessary. All steel portions (dark blue) of the rocker arm were assigned to be Stainless steel alloy 17-4. Though this steel alloy assignment may not be entirely accurate, the density is comparable to other high strength steel alloys.
As a sanity check, I weighed the synchronization piston from the secondary intake rocker arm and found it to be 6.72g. It measured 8.91mm in diameter and 13.50mm in length giving a density of 7.98g/cc. This is a +3.0% difference to the 17-4 alloy.
Valve Springs
| Spring | Rate (N/mm) | % of OEM | Spring Free Length (mm) |
| OEM Intake | 23 | 100.00 | 48.3 |
| OEM Exhaust | 14 | 100.00 | 55.0 |
| Supertech Intake | 44 | 191.30 | 46.5 |
| Supertech Exhaust | 44 | 314.29 | 46.5 |
| Brian Crower Intake | 35 | 152.17 | 51 |
| Brian Crower Exhaust | 35 | 250.00 | 51 |
| Rated Spring Conditions | |
| Rated Intake Spring Load (N) | 449.65 |
| Rated Exhaust Spring Load (N) | 315.00 |
| Rated Average Intake Spring Load (N) | 343.04 |
| Rated Average Exhaust Spring Load (N) | 257.81 |
Assuming the same installed heights, the different valve spring rates coupled with the different valve lifts and free lengths for the intake and exhaust side lead to a different load pattern than described by comparing the spring rates alone.
| Valve Side | Measured Installed Height (mm) |
| Intake | 39 |
| Exhaust | 42 |
Normalizing the peak spring loads to the OEM case for both the intake and exhaust sides resulted in the following two tables:
| Stock Cam Spring Loads | |
| OEM Intake Spring Load % | 100.00 |
| OEM Exhaust Spring Load % | 100.00 |
| Supertech Intake Spring Load % | 188.37 |
| Supertech Exhaust Spring Load % | 213.71 |
| Brian Crower Intake Spring Load % | 175.53 |
| Brian Crower Exhaust Spring Load % | 205.56 |
| CAT Cam Spring Loads | |
| OEM Intake Spring Load % | 101.02 |
| OEM Exhaust Spring Load % | 100.00 |
| Supertech Intake Spring Load % | 190.33 |
| Supertech Exhaust Spring Load % | 255.62 |
| Brian Crower Intake Spring Load % | 177.08 |
| Brian Crower Exhaust Spring Load % | 238.89 |
Valvetrain Loads
Based on the gas loads provided in this research paper, the tappet and camshaft loads were calculated for each rocker arm assembly while the engine was at redline with VTEC active. The main deviations from the paper above are the inclusion of the force required to accelerate the rocker arms about the rocker shaft and using a sinusoidal description of the valve movement. The calculation for rocker arm force due to acceleration was conducted with the rocker arm’s moment of inertia and the angular acceleration required to displace the valve by the lift specified in the data sheets provided by CAT Cams.
Due to the duration numbers on the camshaft being quoted for at least 1mm lift, the acceleration on the valve was calculated with full_lift – 1mm as the linear displacement of the valve. Initial seat load was calculated based on installed height + 1mm compression to account for the initial conditions of the camshaft.
The frictional component from the valve stem – tappet contact was less than 2.5% of the total load on the tappet. Because of this and full load in the Z direction being worst case, all of the tappet load was placed in the Z direction for FEA.
Loads were calculated based on maximum engine speed.The redline RPMs considered are 6800RPM for the case of a stock L15A7 and 6300RPM for the CVT equipped LEA1.
To begin, the mass of each valvetrain component was measured both for the stock L15A7 setup and the aftermarket valve side components.
| Rated Loads @ 6800 RPM | |
| Rated Intake Spring Load (N) | 1214.34 |
| Rated Exhaust Spring Load (N) | 731.09 |
If rated load is considered to be the load which was calculated under nominal conditions approved by Honda, the table below describes the percentage of rated load for each configuration.
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