Air/Fuel ratio, is there a quick answer? |
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Air/Fuel ratio, is there a quick answer? |
malcolm2 |
Feb 5 2017, 05:50 PM
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#1
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Advanced Member Group: Members Posts: 2,745 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
OK, I have been tinkering with the new-to-me AFM on my 1911cc engine all weekend. I have adjusted the spring about 20 teeth CCW to get to this point.
I have been using an A/F sensor and gauge. can someone tell me, or direct me to a chart/table of what A/F I should be shooting for on my daily driver. The last adjustment of the CO screw has left me here: I have always had a strange idle situation, so lets ignore that for now. any normal adjustments to reduce the idle at normal operating temp eventually stall the car. A problem for another post. (IMG:style_emoticons/default/blink.gif) the idle is high.... at 1200 the A/F is a smooth 12.2. I found a long hill and drove up it at about 3800 rpm and the A/F was 12.5. thoughts? |
Mark Henry |
Mar 5 2017, 07:55 AM
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#2
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Yes 15:1 cruise is too lean for an aircooled 14:1 would be the max and even then I'd want a good headtemp gauge to be sure they're not getting too hot.
That chart might be OK for a watercooled, but not aircooled. WC big advantage is they can control head temps way better than air cooled. Aircooled has a much narrower burn AFR range. This would be my aircooled chart; About 11:1 is the max for rich burn WOT power between 11.5 and 13 Max performance WOT 12.3 to 13 maximum Lean burn no higher than 13.5-13.7, nickies can run 14:1-14.3 The exception to the above is decel, AFR on decell is of no concern, of course it's a high reading, you just took away all the fuel, but no load so it's not producing heat. You can run richer than 11:1 without really hurting the engine, but your power and tune goes to poop. Anything over stoich you better have a damn good head temp gauge to monitor your temps, you are getting into dangerous territory. As you head temps go over 350f you will start to lose power as a heat soak condition starts to set in. Running 17-18:1 and you will have a hole in a piston PDQ. Basic rule on heat temp and heat soak is you can go over 350f on a long hill, as long as the temps recover on the downside. Once the temps are not recovering on the downside of the hill you have a heat soak issue. Even a cheap VDO gauge you can easily see this heat soak/no recovery condition. Head temps consistent 325f is about perfect, 350F is OK, but I don't want to see much more for long periods of time. On my LN nickies I don't see much over 300F unless I'm really hammering it on a hot day. |
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