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Location:
Northwestern Sydney
Registered:
August 2002
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Compression braking
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Wed, 05 November 2003 22:19
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I've got into a bad habit of compression braking lately in my brothers car and was wondering what sort of damage this is doing to the engine? should I change my driving style 
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Location:
Brisbane
Registered:
July 2002
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Re: Compression braking
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Wed, 05 November 2003 22:29
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If it was your car, i'd tell you to stop. Lucky it's your brothers 
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: Compression braking
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Wed, 05 November 2003 23:03
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I want to get out of the habbit BEFORE my car gets rebuilt
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Location:
Melbourne, Australia
Registered:
July 2002
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Location:
Sydney
Registered:
February 2003
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Re: Compression braking
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Wed, 05 November 2003 23:51
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do you mean only compression braking?
redlining without brake or something?
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Location:
Canberra, ACT
Registered:
May 2002
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Re: Compression braking
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Wed, 05 November 2003 23:53
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from what I gather compression braking only does damage to an engine at higher revs, i.e booting it up to 6-7k and compression braking then..
Correct me if I'm wrong..
-Andrew
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: Compression braking
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Wed, 05 November 2003 23:55
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No not compression (engine) braking near redline but from around 3-4.5rpm, Stopping at lights, cornering etc.
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Location:
Canberra, ACT
Registered:
May 2002
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Re: Compression braking
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Thu, 06 November 2003 00:00
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I don't think at those revs it will do any damage at all.. I know when I took my driving test they frowned on compression braking but I hardly think that was to preserve engine life..
-Andrew
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Location:
Adelaide
Registered:
August 2003
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Re: Compression braking
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Thu, 06 November 2003 00:04
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I admit I used to slow down like that too, but if you're worried about it, look at it this way. What would you rather: having to replace your clutch and engine, or having to replace your brake pads? I know what I'd prefer.
Cheers,
Tim
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Location:
Perth
Registered:
May 2003
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Re: Compression braking
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Thu, 06 November 2003 00:49
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i love compressions its good in the wet cause you can kick the car our and plant it to set your self up for a nice drift 
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Location:
Melbourne
Registered:
October 2003
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Location:
Adelaide
Registered:
May 2003
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Re: Compression braking
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Thu, 06 November 2003 02:04
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my dad told me when i was ten to change down through the gears, use the engine to slow. he taught me about double clutching heel toe etc, he is an engineer, i dont think he would give me bad advice, and the fact that he was encouraging engine braking in his car so it cant be bad
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: Compression braking
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Thu, 06 November 2003 02:25
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| Timmy Turbo wrote on Thu, 06 November 2003 11:04 |
I admit I used to slow down like that too, but if you're worried about it, look at it this way. What would you rather: having to replace your clutch and engine, or having to replace your brake pads? I know what I'd prefer.
Cheers,
Tim
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Replace engine.......Hmmmmm
1G-Gte
18R-Gte
3sge
It would give me a reason
more concerned with problems in the engine rather than wear.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Compression braking
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Thu, 06 November 2003 03:40
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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
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: Compression braking
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Thu, 06 November 2003 04:05
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Ta stew, You've outline my worries. just to clarify my brothers car has shithouse brakes hence engine braking.(and bad habbit).
If when engine braking the throttle is closed and the engine is revving down from lets say 5500rpm is there any detonation worries?
Damn just answered my own question 
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Compression braking
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Thu, 06 November 2003 04:14
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oh, one other thing.
when you use the engine to brake, you also generate higher than normal vacuums in the intake manifold, which can/will lead to oil being sucked in past the intake valve stem seals, so some smoke may by produced, the oil will be washed thru the cylinder by the petrol nect you accelerate, so not so bad, but could be a bit smokey....
detonation?? possibly, but not the same as under power. if you suck in enough oil, then it can burn, particularly when the vapor pressure of the hot oil is high re;lative to the manifold pressure... more likely to just be smokey tho...
Cya, Stewart
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Location:
Sydney
Registered:
May 2002
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Re: Compression braking
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Thu, 06 November 2003 07:17
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bah the only thing you need to worry about is the sudden force put on the drivetrain.. say good by to g/boxs and diffs... bt ofcourse thats only if you dropping it back hard enough to make the drivetrain "bang" real wheels lock etc...
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Location:
Sydney
Registered:
January 2003
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Re: Compression braking
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Thu, 06 November 2003 07:38
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When learning to drive my instructor & parents encourgaed this "compression braking". To be honest in my day to day driving the car doesn't see 4500RPM all that much(if at all), I always downshift when braking, about 2000RPM, to me it feels like a more controlled stop, your using the engine and the brakes. All that said if you were working in the higher rev ranges I reckon its gotta be bad for your car(for the above listed reasons), but at loe RPM, ie 2000 I(non-mechanically) cant see a problem.
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