Do fuel mixtures change when driving or freerevving? - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
General Tech Have a question that is not covered by one of the other categories? This is the forum for all other items not specifically covered in other categories.

LinkBack Thread Tools Display Modes
post #1 of 2 (permalink) Old 09-07-04, 02:36 PM Thread Starter
Jim Mock You Rock
Join Date: Jul 2004
Location: sYDNEY
Age: 48
Posts: 1,766
Do fuel mixtures change when driving or freerevving?

I was just wondering if fuel mixtures change say if your checking them in park and takethe revs up compared to if they were under load?

useless is offline  
Sponsored Links
post #2 of 2 (permalink) Old 09-07-04, 03:18 PM
Registered User
TruBlu351's Avatar
Join Date: Apr 2003
Location: Newcastle
Posts: 2,398
Re: Do fuel mixtures change when driving or freerevving?

I wouldn't tune my engine using free-revving to determine the correct mixture/jet air fuel ratio. It's under true load that the check needs to be done (ie: on the road or a dyno). The carby has several fuel circuits inside that won't work unless fully loaded up therefore giving a false reading for the regime you're after (car acceleration).

The engine will accelerate free-revving in park quite easily, throttle plates barely open and therefore pulling in less fuel. The mixure or air fuel RATIO could be close, "Less fuel + less air" vs "more fuel + more air". I'd say it would be slightly leaner though.

Air fuel mixture could be quite different at WOT and having FULL fuel flow through your jets/main metering system and ALL throttle plates fully open. Free revving will also have a higher manifold vacuum than a loaded situation, where it will be close to or on zero when loaded up. This has implications with power valves opening up etc and the secondaries opening up if you're running a vac sec carby. What will be markedly different is the cyclinder temperatures at a loaded WOT. Cruise AFR is about 14.7:1 and full power should be richer at about 13.2 to 13.5:1 (engine dependant).

As long as you're not blowing grey smoke (rich) or pinging its head off (lean) you're somewhere in the middle. No substitue for the sensor gear on a dyno for EXACT numbers. Can also check your spark plugs after a run.

XE Falcon
393 Tremec TKO 9"
TruBlu351 is offline  
Sponsored Links

  Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > The Garage - Tech Forums > General Tech

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Similar Threads
Thread Thread Starter Forum Replies Last Post
Florida Highway Patrol now using Mercury Marauders GMACK24 Ford Crown Victoria | Mercury Marauder | Grand Marquis | P71 2 12-14-04 05:54 AM
US:Ford begins producing fuel cell fleet in Detroit Stacy94PGT Ford Worldwide News 0 08-10-04 05:19 AM
Ex-cab: Petrol still not working w/ new fuel pump Tragilgas General Tech 15 02-01-04 08:31 PM
Latest EPA report says vehicles gain power but not fuel economy Stacy94PGT Ford Worldwide News 0 05-12-03 10:00 AM

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome