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Posted: Sun Aug 27, 2006 10:38 am 
Getting Side Ways
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Posts: 625

Joined: 6th Nov 2004

Ride: R32 GTR

Location: Brackistan
VIC, Australia

I dont bother with the limiter in my car, it runs out of puff at 4500rpm so its better to go down a gear earlier.

Re the damage freerevving, yes it is much more stressful on the engine but not because the pistons are "slapping" in the cylinder, its more stressful on the conrods and bearings.

I'll try explain why the engine is at most stress at at the 10 degrees TDC when free revving - Visualise the crankshaft spinning with a conrod attached to it. In between 5-7 o'clock, and 11-1 o'clock the crank rotates the same amount. The biggest difference is the rod/piston speed is maximum when it is at 90 degrees angle with respect to the crankshaft, this only occurs at about 10 and 2 o'clock. This means the rod moves more than 50% of its travel in the top 180 degrees of rotation, depending on bore x stroke of the engine, anywhere from 60-80% of the piston stroke is the top 180 degrees. So maximum loads are placed around TDC where maximum speed change occurs.

Why does less damage occur when the engine is redlining while under full power compared to more damage while under free-revving?

easy - Upper cylinder pressures counteracting on the force of the piston needing to change direction. When free-revving there's not much pressure at the top to both compress and force the piston down at the point of the flame front hitting the piston. Rememeber the crankcase is close to atmospheric pressure while the upper cylinder is in a vacuum when free revving. At wide open throttle (foot to the floor) there is a lot of air and fuel in the upper cylinder which helps reduce bearing and conrod loads, on the compression stroke the upper cylinder pressures are similar to the lower cylinder pressures and on the power stroke the change of direction is assisted strongly by the flame front.

Heres an excellent 2 page article with pictures explaining this in much more detail:
http://e30m3performance.com/tech_articl ... /index.htm

You can see on the first page that the piston has travelled half way down the cylinder even though the crankshaft has rotated a lot less than 90 degrees from TDC.

Hopefully this makes some sense and explains more why the 4 litre fords hate revs compared to the shorter stroke jap engines.
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Posted: Sat Sep 02, 2006 12:29 pm 
Getting Side Ways
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Age: 31

Posts: 4849

Joined: 19th Feb 2005

Gallery: 1 images

Ride: BA Falcon Suzy Across

Power: 178 rwkw

Location: melbourne
VIC, Australia

so this would be hell for the engine then?

http://s115.photobucket.com/albums/n281 ... ALTED1.flv

 

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Posted: Sat Sep 02, 2006 1:13 pm 
Getting Side Ways
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Age: 30

Posts: 597

Joined: 8th Sep 2005

Ride: EL XR6 Hybrid

Location: Canberra
ACT, Australia

f**k hell man, thats off the tacho :shock: I'd never do that to my own car lol.

 

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Posted: Sat Sep 02, 2006 2:15 pm 
Getting Side Ways
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Posts: 625

Joined: 6th Nov 2004

Ride: R32 GTR

Location: Brackistan
VIC, Australia

That's just tacho overshoot :p
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Posted: Sat Sep 02, 2006 5:49 pm 
Getting Side Ways
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Age: 32

Posts: 1112

Joined: 18th Jan 2005

Location: MAFFRA
VIC, Australia

used to change gears in the ea at 6000 all the time,they love the revs

 

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Posted: Wed Sep 13, 2006 9:26 pm 
Getting Side Ways
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Age: 50

Posts: 912

Joined: 22nd Mar 2005

Gallery: 1 images

Location: FNQ
QLD, Australia

The Cruise Control system actually has a cutout function - if rpm is registered at 5000 or 5500 - something like that - the cruise control disengages.

Workshop test for auto car is to: you guessed it - with cruise control engaged, drop it into neutral!! I don't recall whether there's a test for manual - maybe not, as the clutch pedal is supposed to trip a switch to disengage the Cruise Control - and excepting a situation where the gearbox jumps out of gear - not considered a likely possibility I suspect - the only way a manual Cruise Control could rev the car out would be if the clutch was pushed in.

Having done a manual conversion I don't have that clutch cutout switch - I find cruise control very handy for highway overtaking - just do a quick gearchange to the next gear down (without touching the accelerator) and she does the initial pickup very nicely so if I then follow up with mashing the accelerator .... wheeeeee!!! Works as well as auto tranny kickdown for overtaking. Could be nasty if I missed a gear - which I haven't done....... yet.

 

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Posted: Wed Sep 13, 2006 10:15 pm 
Getting Side Ways
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Age: 33

Posts: 2058

Joined: 25th May 2006

Ride: ef xr8

Power: 229 rwkw

Location: Perth
WA, Australia

could be worse....

Could have knocked into Reverse

 

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Now N/A (permanent Lag) - AFR 165's, Comp XE270 cam, 1.6 RR - 269 rwhp 14.1 @ 102mph.

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Posted: Wed Sep 13, 2006 10:32 pm 
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revers doesnt f**k the gearbox though :P well in commodores atleast...our vys goine from drive to reverse (bro being a f**k d***head) and its still driving fine ;)

 

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Posted: Wed Sep 13, 2006 10:49 pm 
Getting Side Ways
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Age: 30

Posts: 4609

Joined: 29th Jul 2005

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Ride: BOXCAR

Location: Launceston
TAS, Australia

mitch_anderson wrote:
revers doesnt f**k the gearbox though :P well in commodores atleast...our vys goine from drive to reverse (bro being a f**k d***head) and its still driving fine ;)


not for much longer by the sounds of it

oh and BTW its impossible to knock it into reverse without pushing the button

 

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