Quote:
Originally Posted by lucas240sx
With it sitting at 140 deg right now.....my rpm is at 1000 with -14 vac
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this doesn't tell anybody anything. 140 degree Fahrenheit is still cold, and cold rpm will vary depending on the wax element in the throttle body cooling loop. If you read the FSM It will explain that sr20det have this wax element for raising the idle of a cold engine, which means your idle could be anywhere from 900-1400rpm in between that. The vacuum seems low. Do a compression test, and write down the exact numbers the best you can (132.5 for example).
Once the engine is warm it should be steady around 850rpm with an OEM camshaft. I dont know what the FSM says about it (I never read it) but once the engine is warm if you follow the above procedure for setting it around 850rpm it should be fine if there are no more air leaks (if the plumbing holds 10~psi of pressure verified).
the reason you do not want excessive high idle is because it absolutely demolishes your fuel economy. The reason we do not want the engine to drop below 800~rpm is because the engine bearings require a certain amount of minimum rotation speed from the crankshaft or else wear will occur. When I cold start, my idle stays around 900rpm and because I have an OEM piston I can drive right away (no boost until the engine is fully warm) to maximize economy you need to spend as little time at exactly idle sitting still as possible. Drivability will suffer if you limit cold start rpm, but drivability is a very minor attribute to me, I am most interested in economy and so use a minimal acceleration enrichment and minimal rpm whenever possible, and also a 15.0-15.2 air fuel open loop cruise area.
My injector duty at 60mph is exactly 6%, and with the turbine disconnected it is 6.5%. There is some measure of fuel economy found with spinning the turbocharger as you cruise, if it is sized for the job. If there is any leak, the turbo will need to spin faster, which means more turbine rpm, which means more exhaust gas pressure resistance to the engine, which diminishes fuel economy and power, as well as pushing the turbo to the right on it's map and limiting max power. A large enough leak will destroy a turbo (imagine you disconnected the compressor outlet from the engine and just ran it open. The wheel would spin so faster it will likely explode) It is therefore imperative that for maximum power and fuel economy, and to minimize turbocharger wear, every molecule of air that exits the turbocharger's compressor makes its way into the engine somehow and does not leak out. This is why we pressure test the entire region to 10-18psi (or more if you need more)