Replating Alusil cylinders with Nikasil
12-20-2013, 11:43 AM
#16
5th Gear
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I am listening very intently and trying to understand my options. I thought that at high altitude the tendency for detonation was diminished, thus allowing for a modestly higher CR.
12-20-2013, 12:09 PM
#17
Rennlist Member
From what I understand, the Mahle 3.4 MM P+C set with 9.8 CR are compatible with standard ignition; and if one wants to go wants to go with a dual ignition to allow a higher CR, it appears as if JE's 98 mm at 10.5 is the next step up. Is there something in between, or is there no reason to go with dual plug with a 98 mm piston?
12-20-2013, 03:12 PM
#18
RL Technical Advisor
From what I understand, the Mahle 3.4 MM P+C set with 9.8 CR are compatible with standard ignition; and if one wants to go wants to go with a dual ignition to allow a higher CR, it appears as if JE's 98 mm at 10.5 is the next step up. Is there something in between, or is there no reason to go with dual plug with a 98 mm piston?
While octane requirements do lower with altitude, so does the efficiency of air cooling as air density drops. Detonation thresholds are largely determined by cylinder head temperature so this must be factored when choosing what CR to run, especially when considering summertime weather.
For air-cooled engines, its prudent to be conservative since the consequences will be very expensive.
Mahle makes a special wedge-domed 98mm piston that was specifically designed for safe operation on single-ignition with 9.8:1 CR. IMHO, this is the wisest choice for engines running pump gasolines without having to compromise timing maps.
12-21-2013, 10:51 AM
#19
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Thanks to all for your input, especially Steve. This forum is a great place to learn and build a knowledge base that hopefully translates into avoiding missteps. Steve, are the 98 mm Mahle P+C sets readily available?
12-21-2013, 01:45 PM
#20
RL Technical Advisor
Always a pleasure,...
Indeed, those sets are available; just call me on Monday.
