Mick, The heat shield has caused quite a dramatic change by the looks of it and I guess if your design is that effective then that's to be expected with the fine tuning req'd to get the best out of that type of engine. I used heat shields in the rally car usually only at sea level and with fairly similar effect. What we changed from running in altitude as opposed to sea level was to run with the heat shield, used 2mm bigger chokes and .10mm bigger main jets and run +2/3 degrees static advance, usually higher at night. We mainly used a 66 degree cam in Canberra and a 72 degree cam at sea level and the Artie Jackson engine produced very similar hp. We had the most dramatic change if we run the Canberra setup at Bega (sea level) and not so evident the other way around.
Now you're using a bigger cam again (one that we didn't particularly like on dirt) as it was too peaky but I'm thinking that it could be far more sensitive to air density than either of the smaller cams as it's at it's peak velocity for a short period of time (very much dirt racer thinking and not so critical for a circuit car.) I wouldn't change too much at once, perhaps if you can get hold of a set of 38mm chokes to try out, fit 160 main jets and up the static timing a tad (watch pinging of course but a 76 cam shouldn't ping at all under 11:1 CR on 98 octane) and see what happens from there. good luck on the weekend, regards Terry -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of mick ralph Sent: Tuesday, 29 January 2002 7:49 PM To: [EMAIL PROTECTED] Subject: weber heat shield Part 2 Today I made up and fitted the heat shield and took the car for a run up the motorway for a couple of hours. Some very interesting first impressions... 1. The carbs are cool to the touch after an hour on the freeway....normally quite hot 2. Fitting the brackets to the underneath exhaust studs is a real pain!!!!! 3. The motor seemed really dead ie down on power I got blown off by a porker 924!!! 4 Fuel consumption was noticeably way down. I reckon a 1/3 less than normal! Questions If the carbs were running significantly cooler, could this upset the jetting? What sort of change might u expect ie richer or leaner? Would it affect low rev range or high rev range? Might it run leaner is the question I guess? Relevent settings twin 45dcoe Venturi 36 Main Jet 150 Air correction jet 150 Emulsion Tube F2 Idle Jet 45 F9 Pump Jet 40 Plugs BP6EY Std B/B electronic dissy - no vac advance 15 BTDC 76 degree cam Big valves etc etc Cheers Mick --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/[email protected]/ ---------------------------------------------------------------------
