Posted: Thu Apr 08, 2004 11:17 am
That makes sense Brad. Never the less, because the CHT does drop to 70 ohms..or can, that is generally why I ballast to the reading right around 200 ohms during hot weather (about 125 ohms).
With high ambient temps in Texas and Oklahoma, the air temp sensor can quickly stay maxed out, and is not enough to correct the mixture. The problem is the metal thread installed in the steel manifold. Like everything else, it banks heat, and stays at one temperature regardless of ambient air passing over it. I have been experimenting with an insulated bushing for it to fit into, but I havn't had a chance to actually run it yet.
Depending upon how tightly your system is adjusted, "mucking" with the CHT has agreat deal of affect on the fuel mixture and running. Its not a tool to find extra HP, but if its control levels are not in synch with where your system is adjusted...it will lose you a bunch of the HP your engine should have. In extreme cases, you can damage the engine itself.
The factory stock levels of adjustment of the MPS, and the factory control levels of fuel pressure are not always, enough by themselves in my experience, to always offset the stock "vagueness" of the CHT, especially in the range of temperature extremes where I live and drive. I agree, most fine running adjustments should be done with the MPS. When that adjusting process begins to be pushed out of upper end enrichment range, it should be done with fuel pressure. All of this is assuming that, the CHT and the ambient air temp sensor have not been already pushed to the end of their useful adjustment limits (which you noted was 100 ohms for CHT).
I have found many people adjusting their fuel mixture and mps response, with the CHT maxed, when in reality, a reading of a 100 ohms or so higher would more accurately reflect the current ambient air temps, head temps, oil and engine temp. This would falsley reflect that the engine is running at maximum warmed up temp (say...350F head temps, 185F oil,)...when in fact the head temps may only be 275-85F and the oil at 150F or so...with an ambient of say 85F.
That means that if you adjust things to run perfectly at this range, and the CHT is maxed, simply because the heads ARE past 210....when you actually do reach head temps of 350, oil of 185...and ambient goes up a hair, you will be too lean.
It have found makes much finer adjustment to give a fixed extra amount of resistance to the CHT, before you adjust the MPS. It slows the process of the CHT maxing out, down a little. The only reason I have been piddleing with a variable version of this, is because I have found that at the two main temperature extremes in this region, it works better to have a winter setting and a summer setting for the ballast....and because as you noted, having too much ballast (which would pump the resistance up over 400 ohms) may give difficult starting in cooler weather due to being over-rich. My personal engines don't have that problem with the extra ballast. Partly because of much better than stock injector balance, partly because of better than stock fuel pressure stability and partly because of careful tuning of the MPS. Most stock tuning tended to idle a hair rich. Add to that cool weather and extra ballast,and most stock tuned engines will effectively flood.
On note....having a much better ignition than what the car came with really helps all of this. Ray
With high ambient temps in Texas and Oklahoma, the air temp sensor can quickly stay maxed out, and is not enough to correct the mixture. The problem is the metal thread installed in the steel manifold. Like everything else, it banks heat, and stays at one temperature regardless of ambient air passing over it. I have been experimenting with an insulated bushing for it to fit into, but I havn't had a chance to actually run it yet.
Depending upon how tightly your system is adjusted, "mucking" with the CHT has agreat deal of affect on the fuel mixture and running. Its not a tool to find extra HP, but if its control levels are not in synch with where your system is adjusted...it will lose you a bunch of the HP your engine should have. In extreme cases, you can damage the engine itself.
The factory stock levels of adjustment of the MPS, and the factory control levels of fuel pressure are not always, enough by themselves in my experience, to always offset the stock "vagueness" of the CHT, especially in the range of temperature extremes where I live and drive. I agree, most fine running adjustments should be done with the MPS. When that adjusting process begins to be pushed out of upper end enrichment range, it should be done with fuel pressure. All of this is assuming that, the CHT and the ambient air temp sensor have not been already pushed to the end of their useful adjustment limits (which you noted was 100 ohms for CHT).
I have found many people adjusting their fuel mixture and mps response, with the CHT maxed, when in reality, a reading of a 100 ohms or so higher would more accurately reflect the current ambient air temps, head temps, oil and engine temp. This would falsley reflect that the engine is running at maximum warmed up temp (say...350F head temps, 185F oil,)...when in fact the head temps may only be 275-85F and the oil at 150F or so...with an ambient of say 85F.
That means that if you adjust things to run perfectly at this range, and the CHT is maxed, simply because the heads ARE past 210....when you actually do reach head temps of 350, oil of 185...and ambient goes up a hair, you will be too lean.
It have found makes much finer adjustment to give a fixed extra amount of resistance to the CHT, before you adjust the MPS. It slows the process of the CHT maxing out, down a little. The only reason I have been piddleing with a variable version of this, is because I have found that at the two main temperature extremes in this region, it works better to have a winter setting and a summer setting for the ballast....and because as you noted, having too much ballast (which would pump the resistance up over 400 ohms) may give difficult starting in cooler weather due to being over-rich. My personal engines don't have that problem with the extra ballast. Partly because of much better than stock injector balance, partly because of better than stock fuel pressure stability and partly because of careful tuning of the MPS. Most stock tuning tended to idle a hair rich. Add to that cool weather and extra ballast,and most stock tuned engines will effectively flood.
On note....having a much better ignition than what the car came with really helps all of this. Ray