Honda k20 Intake for P1
#37089 from Ryan Szyjakowski · Not recommended · Minutes (2024-12 Fastrack)
Thank you for your letter. The Club Racing Board does not recommend this change. The P1 class will be discontinued effective
1/1/25 and no rule changes are planned in P1 before the end of the year, but the P1 rule set will be incorporated with minor
changes in the rule set for the new Prototype class and the spec line for the Group CN Honda K20A-FD2 engine will be carried
forward. Please note that since 1/1/24, the P1 Group CN spec line has allowed competitors to make unlimited internal
modifications to the Honda K20A-FD2 engine while continuing to require the stock intake manifold with the stock 64mm single
throttle body, and this specification will be continued in the new Prototype class. The requirement of using the stock intake
system as the "restrictor" for the internally modified K20A-FD2 engine is based on information provided to the CRB which
indicates that the Single Inlet Restrictor (SIR) typically used on P1 cars with automotive-based engines is incompatible with the
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K20A-FD2's intake layout on Group CN cars. On-track data obtained from a Group CN car using the Honda K20A-FD2 engine in
unrestricted form (with unlimited internal modifications and aftermarket individual throttle bodies) established that the car was
an overdog compared to other P1 platforms, and accordingly restrictions were imposed on the K20A-FD2 engine. The CRB
obtained dynamometer data for an internally modified K20A-FD2 engine using various types of intake restrictions, including the
restriction provided by using the stock Honda intake manifold with the stock 64mm single throttle body. The dynamometer data
indicates that an internally modified K20A-FD2 engine using the stock 64mm single throttle body intake system produces
horsepower comparable to a 2500cc engine with a 30mm SIR. While various factors limited opportunities to set a representative
qualifying time during the official Runoffs qualifying sessions, the CRB has access to lap times recorded during the unofficial test
days, and these records show that the qualifying lap time attributed to the Group CN car as evidence of the need for a
competition adjustment is not indicative of the car's true potential. In addition, a Group CN car using the Honda K20A-FD2
engine in the form permitted by the P1 spec line (with unlimited internal modifications and the stock 64mm single throttle body
intake system) has demonstrated lap-time performance similar to that of an Elan DP02 using a 2500cc engine with the same
driver in West Coast SCCA events. Also, weight data obtained from that car shows that it is reasonably close to the Honda K20A-
FD2 spec line's minimum weight. The CRB will monitor performance in the new Prototype class and will make adjustments as
necessary based upon AiM data collected during on-track sessions.