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Old 03-22-2008, 05:36 AM   #18 (permalink)
AXMonster
British Ecomod Hypermiler
 
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Join Date: Mar 2008
Location: South Coast, England
Posts: 101

The AXe - SOLD - '97 Citroen Citroen AX 1.1i 5 Door
90 day: 46.78 mpg (US)

Foci - '03 Ford Ford Focus Tdci Ghia Estate
90 day: 64.37 mpg (US)
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Quote:
Originally Posted by RH77 View Post
I've heard to warm up the car (WAI at full temp, if equipped), advance the timing until you hear a knock, and back it off a degree or 2.

Someone step-in if I'm mistaken...

RH77
Absolutely correct. All vehicles (without knock sensors) are mapped to DBL (Detonation Borderline) -2, which is as you say the knock point -2 degrees.
However, they are mapped on the worst reference fuel at the worst conditions. We probably won't be driving at those conditions (although the WAI is bad for knock) so you can probably advance the timing by a few degrees until incipient knock is heard (about one knock every second or two) then back it off by a degree. This is your engine's DBL-1, which may be quite a bit advanced over the stock setting. High octane fuel will help get this higher, although there is usually a cost involved over regular gasoline.

To hear knock you should be familiar with the sound you are listening for (sounds like two hammers being hit together), or fit a knock meter or det cans (either electronic or a length of bundy tube).

Home made det cans with metal bundy tube can be made with a length of tube long enough to go from the engine block to the driver's seat, passing through a hole in the firewall. The block end needs to be flattened and drilled to bolt onto the block about 1/3 of the way down the block in the centre. Then route the tube through the engine bay and bulkhead (without touching anything) to about head height by the driver's seat. A piece of rubber hose can be fitted on the end of the tube and split into two at any point, then fed into a pair of ear defenders with holes drilled to feed the hoses in.
The aim is to be able to hear the engine combustion noise without hearing all the surrounding noises.
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1997 Citroen AX 1.1i SPI
2003 Ford Focus 1.8 Tdci estate
Ecomods: See my garage



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