Toymods Car Club Inc: Tech & Conversions => Compression braking

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oldcorollas
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003

Re: Compression braking	Thu, 06 November 2003 03:40

Heyall, just to be a real pain in the arse.. and to clarify... compression braking is a diesel thing... since they always injest the same amount of air, and inject fuel as the throttle, so when you are not injecting fuel, the engine is still pumping thru and compressing lots of air, creating a retarding force and slowing it down, hence "compression braking" in a petrol motor, when you take your foot off the throttle, there is much less air actually going into the motor, since the butterfly is closed, so you aren't actually compression braking. in fact, it's more like vacuum braking, since the power stroke is now a vacuum stroke.... also the bigger you valve overlap, the less effective this will be... take 250 race bikes as an example.... so it's a mixture of vacuum and friction braking..kinda scary that when not making power, a car motor takes so much energy to spin around!!! oki, so what does it do? burns clutch when engaging (unless you rev match?) reverse loads the drivetrain (prolly not that much of a prob, unless you already have cracks in the gear teeth) the rods get 2 tension loads per cycle (intake stroke and power stroke) as opposed to 3 compression loadings and 1 tension (compression, power, exhaust strokes vs intake stroke) the oil pump is still spinning away so no probs with that.... about the only real issues are that the clutch wears if you are dumping it to get the braking effect, but if you are just letting it pull up the car when already in gear, less drama. and the main real problem is that of accidentally over-revving the motor on the downshift... a few seconds at 1-2000rpm over redline = very bad for component lifetimes.... if you have good brake bias, you will stop faster using the brakes than the engine (in a RWD car). and if you stop faster using engine braking (in a RWD car), then you don't have enough rear bias. in a FWD car, engine braking can be quite effective blah blah, back into my hole Cya, Stewart [Report message to a moderator]

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