[QUOTE]Originally posted by scottrnelson
[B]It might not be engine knock, it might be the vibration of the heat shield next to the engine.

 

I believe he's refering to 14.7 as the air/fuel ratio. @14.7, the car is getting dangerously lean.
Going up a hill that steep in too high a gear (4th), at that low an rpm (3000), you need to apply fairly heavy throttle to try to get up that hill. This then becomes a high load, low rpm or "lugging" situation. Lugging any engine is BAD, BAD, BAD!

 

Well I spent about six months trying to figure out what was causing the sound I was hearing and one of the few reasonable explanations was very light detonation. It didn't really make sense to me, since more throttle made it go away rather than increase. I had figured that since the engine must have a knock sensor to allow it to run on lower octane gasoline, it might be right on the edge of detonation. In any case, I now know that my car makes a sound when the vibrating heat shield hits a metal pin and I don't worry about it.
[QUOTE]Originally posted by xviper [B]... you need to apply fairly heavy throttle to try to get up that hill.

 

What exactly does lugging an engine do that is bad for it? .
I am under the impression that as the rpms drop the oil pressure decreases. The amount of oil available to the rod and main journals of the crank decreases and at some point ( very low rpm ) the pressure from the combustion chamber transmitted down the rod will be greater than the ability of the thin film of oil cushioning to keep the bearings from contacting the journals. When the bearings contact the journals bad things start to happen and in short order the bearing faces and crank journals are changed, forever changing your engine.

 

Sideways,

That's the best description I've heard yet of the problems that can occur from lugging an engine. Thanks.

 

Back to the 14.7:1 thing. 14.7:1 is not lean or rich. it is reffered to as the stoichiometric ratio. this is the ratio at which all the fuel blends with all oxegen in the air.
It makes sense, cause it takes 14.7 lbs of air to burn 1 lb of fuel.

All cars are designed to stay damn near this ratio because when the manufactures started to install 3 way catalytic converters the engineers discovered that the A/F ratio must stay close to 14.7:1 in order for the converters to be effective in reducing exhaust emissions. If the ratio goes rich (numerically lower than 14.7) then Hydrocarbons and Carbon Monoxide levels will rise, while NOx emissions will decrease.
If the A/F ratio becomes lean (numaerically higher than 14.7) then CO and HC levels will decrease, however NOx emissions will increase.

Now from a performance point of view, slightly rich (14.5-14.0:1) will produce more power, but will also produce more HC and CO.


Just thought I'd clear that up

 

Sidways---Lugging an engine is trying to make the engine run under heavy load at low RPM causing ping, knock, detonation, warning signs, it all the same really, whatever you want to call them. The engine lugs because the computer is trying to retard the timing to prevent detonation but can only retard it so far. when the timing is retarded it looses power, so it advances it a little, then the knock sensor hears the engine knocking, so it retards the timing again. Its an on going cycle till a lower gear is selected or the load is taken off the engine (such as cresting the hill)

The oil pressure theory may sound good but, it is really different. The oil pressure of all but race engines stop building oil pressure around 2k-3k RPM. The pump picks up the oil then the oil is just dumped by a relief valve back in to the pan. the reason for this is simple. The rule of thumb for a race engine is 10psi of oil pressure for every 1000 RPM. In a race car this is fine, too a point. In a street car like the S, reving to 9k RPM that would put close to 90psi in the oil ing system. And all but race filters would burst at that pressure. in a street car it is normal to see close to 40-50 tops, however there are exceptions.

I think I have explained this right, if not feel free to correct me if im wrong

 

The leaner an engine runs, the hotter the engine runs. Yes? No?

 

Hmmm... simplified...

In an engine the pressure due to combusion should raise at the same time the cylinder goes down and relieves the pressure. (The fuel burns over time, not all at once). When you lug an engine, the cylinder isn't expanding fast enough and the pressures rise too quickly. This results in very high connecting rod compression force and therefore heavy bearing oil squeeze-out when oil pressure is relatively low. Given the lightweight pistons and the fact the S2000 is tuned for high RPM, I try to keep it above 3000 RPM or else feather the throttle to maintain my speed when below.

 

xviper---yes