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5 minute(s) of a 64 minute read
4-17-2013
Yep! 9.2 static. After blowing a few and also running 12 :1 with an SC12 supercharger at 5 psi. ( Which was very torquey but nowhere near the sting I wanted) I decided that easy drivability in heavy traffic was smarter. The set up I had with 12:1 and the cam was getting hard to live with as I could'nt keep the speed limit of 60 kph if the blower was on. Crazy hey? 3rd or 4th at 60 kph, the little 404 was " nup! I'm goin' man, git me outer here!". The turbo is much faster but civilised. Typing this I recall I wanted to go more static with the new set up with my new design cam but I't is easier for me to dial in 2 deg advance on cam timing. The old engines actually failed from poor ignition control, detonation and preignition but not from high compression. It was engine oil exploding before or during combustion. I speak the bitter truth as I learnt ( read that, relearned and remembered early trade teachings) and studied a few engineering sites and publications. Poor oil control from engine breather and rings will confuse the engine tuner and at times the engine will be tuned to run allowing for detonation caused by hot oil. The anomaly is, when cold there is less oil entering and it is not at a temp high enough to be very volatile. Different matter once it gets over 90 C. though. A big issue with rings and broken pistons is material and hone pattern depth before bed in.
Chrome faced rings will not bed in unless the compression is very high. No good for us they will let oil past them almost straight away. Cast iron rings or Moly faced iron rings, gapped correctly is a great start.
Ring gaps make or break the fun of it all. From SAE Int. the standards for ring gaps is very interesting. The 2nd ring gap needs to be a lot less than the top. If the piston breaks as in Tamo's machine , it begins to indicate high pressure build up between the two rings. That makes them vibrate and flutter, then crack goes the land, before or after a ring breaks as well. Indipendant of boost or compression numbers.
So what I've learned, and am trying to share without sounding arrogant, is engine oil and breather control is the number 1 issue before building any engine. . Stop any oil vapour before it gets to the inlet, make sure that vapour returns as liquid oil back to the sump and control that oil with accurate and correct ring selection, gaps and hone. ( Rotary engines inject oil in for lubrication. Engine blows them up, specifically designed oils like Silkolene, Motul don't explode in that enviroment.)
The engine rings bed in quickly using run in oil in about 20 hours, this way. Bitter experience!
I do have Dani. cams data somewhere but Lordy Lordy, Uncle Jed. Ifferrin' y'all kin git me the figures of bore stroke and cam timings we can work something out here, without me checkin' under Ellie May's.........................................................................................................................
..chair!
That is the business, Rabin.
I'm going to "vent" me old crank case now, so here she goes!
The idea is to vent the OHC at the top of the engine and with a T piece from the crank case as well. It will make the gas work out some of it's energy on the way to the vent/filter which is mounted above the engine. ( Gravity is useful here.) Consider the P 200 as a condenser for oil vapour. Any gas, which should only be air , oil vapour and a tiny amount of blow by, must push it's way through the filter medium to get out. Energy is released, oil falls into the base and gets plumbed back to ideally the sump, below oil level. Then the outlet can go to the air filter. One can use a PCV, say from a Rover which screws into the manifold. Plumb it to a T piece in the hose going to the air filter. A small vacuum source is also important as it helps evacuate the crank case when the engine is cold. Moisture in the air can become ice cream in the oil from no other reason than it not being vented well enough. A vac source does this and keeps the oil clean, too. Many racers use a belt driven or electric vac pump to pull a vac. under the rings so they seal better. I've found using a PCV valve also helps the idle quality, too. The French use a metered orifice in most engines but a quality PCV, ( Positive Crankcase Ventilation) valve is much better.
Strange things float around in a mechanic's head.
