Hondata

Does the k series rev limiter cut spark and fuel or just fuel?

How stressful is hitting the rev limiter?

How stressful is hitting the launch rev limiter?

Fuel. Stressful. Depends on the rpm - below 7000 rpm is ok.

Hondata wrote:Fuel. Stressful. Depends on the rpm - below 7000 rpm is ok.

Is it something one should avoid on the dyno at all costs, or something that it's not going to hurt to hit once in a while?

I realize this is a pretty grey area to speak to, as any potential damage done could be very releated to the tune being ran and the stress already on the engine due to many factors, but can you potentially elaborate on how stressful and why it is so stressful to hit it above 7k. Is there fuel left over that causes a lean condition for a few puts?

Wayne

There is no problem using a fuel cut rev limiter. Gasoline will only ignite within a certain air/fuel range (about 25:1 unless the engine is specifically designed for lean burn). When the ECU cuts the fuel there is very, very little fuel in the cylinder - well below the amount that will ignite.

Engines don't like the vibration and harmonics set up from a rev limiter. Generally the higher the rpm the worse, but a 4 cylinder has certain engine speeds where the resonance seems worst (4500 rpm and 7000 rpm are two engines speeds that I have noticed). The rev limit will cut and then resume fuel multiple times very quickly, and will cause some stress at high rpm. The exact potential damage is hard to judge - many people drive on the rev limiter the whole time without a problem, but generally it is a good idea to avoid hitting the rev limiter, especially on a stock engine.

To soften the rev limiter I usually set the ignition timing as far retarded as possible before the rev limiter. eg if the rev limiter is at 8600 rpm, then I will change the ignition tables to have a row at 8350 rpm and then another row at 8600 rpm. At 8600 rpm I'll set the ignition timing to -10 degrees. Thus as you get within 250 rpm of the rev limiter then the timing gradually retards to 10 degrees ATDC and this will both give the driver more time to shift and also softens the rev limiter.

Great info, thank you.