I've posted in recent threads how to tune ignition timing on the street, as it pertains to turbocharged vehicles that have traction. This is the slowest of the tech forums on this site, so I don't feel like a dick telling you to read the first page. Your mind is primed to soak in some good stuff, you'll like doing it.
NA cars, if you aren't strangling the engine with a restrictive cam (my 12.5:1 CR D16Y5 Type-R with the stock HX cam, perfect example) are very simple creatures. B-series motors always make their best power at 30-32 degrees final timing, and make all of their power off of cam adjustments. Sometimes timing is a hair outside that realm but the power gain/loss is very minor. 90% of the mojo is in cam gear adjustments whether stock cams or aftermarket, which do have to be performed on the dyno as the changes are usually very subtle. That being said, every design of motor is different... stock cam NA D-series do not need cam adjustments, while stock cam turbo D-series ALWAYS do (typically retard it, you can probably seat of the pants it in a pinch). NA F-motors like the cam retarded 3-5 degrees - you lose zero bottom end and pick up a lot of top end. Turbo F-motors probably like it, too, but I've never tuned one. It's basically the same for every engine design, they are all a little different although single cams (whether SOHC, or OHV V8s) tend to like the cam retarded.
Also, NO ONE CLAYS THEIR MOTORS to know when piston-valve or valve-valve contact happens, so either you get them to sign a disclaimer that says they don't know what the clearances are and want you to adjust cam gears despite the possibility of lunching the motor, or you're a big asshole and refuse to touch the gears. The more reputable guys usually say no unless they know you and know you understand the ropes, or you're super cool and demonstrate you understand the risks. If you're going to tune other people's cars, sit down and have a long think about how you'd like to be treated vs how some people act despite how good you are to them.
Anyway, I deliberately got entirely off the subject of ignition for a minute on purpose. It's important, but only in the context of what is going on. For NA cars I spend very little time on timing, 75% of which is yanking it below 2500-3000 rpms to prevent pingies on high CR engines that are being strangled by the camshaft (95% of VTEC motors, since most aftermarket cams use ITR low cam profiles) and to set initial timing on the base cam settings. Then, I adjust cams. Typically two degrees one direction then two the other to see how the power shapes itself. Retarding the exhaust cam/advancing the intake cam creates more overlap which pushes the engine's sweet spot higher in the rpm band. Once I get the best overall power band, I go back and redo the timing. Most NA B-series can be done credibly (not perfectly) by listening for pings in the lower rpms and defaulting to 30-32 degrees final timing - but cam settings can not.
Dennis is very good (so is Sewell, to a lesser extent) at reading the "timing" mark on the plug ground strap. It's mostly a bottom feeder street tuner art for people whose cars are so shitty they can't afford an hour's dyno time - or high end $5000/day track tuner art for cars that will ring any dyno ever made and still have a ??thousand?? horsepower left on tap. I use it as a yardstick for whether or not I need a different temperature plug as I am a medium sized fish in a large ocean, and everything I do (save a handful of track-only cars) is best and most quickly done on the dyno - I don't disregard the concept, I simply do not need it. Goforth has a couple cars in the works that should ring a dyno, one will start as a real street build and progress to 10.5" Outlaw when the suspension is dialed in, and I'll learn it then. After that I imagine I'll do a few such cars before I do something else with my life.
My particular skill is reading the carbon trail on a piston face. It, not residues on the plug ceramic, is the most fragile thing in the combustion chamber and I'm pretty confused by why plug reading gets such attention. Burn quality, atomisation, ignition timing, crank ventilation problems, etc, are all expressed on the surface of the piston - as are AFRs, although in a circumspect fashion.
You don't learn this shit overnight, go out there and play with the shit for a bit.
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Topic: 2 questions/ about assemblers dissemblers and tuning theory. (Read 7145 times)