Guest Rick Johnson Posted December 2, 2003 Share Posted December 2, 2003 Guys, I spent copious amounts of time tuning this carb. The drivability is excellent, enrichment circuit comes in smoothly, and idle is consistent. No WOT bog and this jetting delivers the fastest acceleration of any jetting combination. MY main concern is at 3700 RPM the Air Fuel ratio is about 12/1, but by 5500 RPM the Air fuel ratio is a more desirable 13/1. Another Q-Jet carb I tested showed the same traits. Visit this page of my site and see if you can shed light on these findingsand compare my jetting specs to what you may have used. http://www.tootechracing.com/Quadrajet%20Notes.doc Anyone with real indepth experience tuning their EFI systems may be able to answer this: Has anyone optimized there EFI systems at each RPM point and found that the max power Air Fuel ratio varied with RPM changes, or does it remain constant as stated in Taylor’s bible? Added on 12-4-03 This may not be a good question because EFI probably can guarantee uniform fuel flow at each port and thus each cylinder where as carbs experience Air Fuel distribution variations in the intake. (see my post below) Carb guys may be able to answer the following: Has anyone taken the exact same engine and optimized both a Holley and Q-Jet to determine which makes more power? Quote Link to comment Share on other sites More sharing options...
johnc Posted December 2, 2003 Share Posted December 2, 2003 Has anyone optimized there EFI systems at each RPM point and found that the max power Air Fuel ratio varied with RPM changes, or does it remain constant as stated in Taylor’s bible? The max power air fuel ratio (AFR) will be the same for each cylinder at every point in the rpm band. The issue is not what the AFR should be. The real issue is how to get that ideal AFR in each cylinder at each point in the rpm band. If you are able to measure the AFR for each cylinder and your engine management system allows you to tailor fuel delivery for each cylinder then its just a matter of measuring and adjusting. But, only a few high end EMS systems allow that much tunability. Most of the time you're measuring AFR for a group (or all) or cylinders and adjusting the EMS to that "summary" AFR number making sure the leanest cylinder is running at something like 13 to 1. Other cylinders may be running richer and thus producing less power then the theoretical ideal. Again, its basically a matter of measuring, adjusting, measuring, adjusting, etc. until you hit a "summary" AFR that produces the most power while still keeping the leanest cylinder from detonating. And to (finally) answer your question, yes the "summary" AFR number will vary with RPM because of variances in each cylinder's actual AFR number throughout the rpm range. Quote Link to comment Share on other sites More sharing options...
Guest Rick Johnson Posted December 3, 2003 Share Posted December 3, 2003 AFR that produces the most power while still keeping the leanest cylinder from detonating. A noted carb tuner says he can get more overall power out of a Q-Jet. The main Air Fuel ratio difference is the Q-Jet is fatter at lower RPM's. Both carbs can be jetted to the same Air Fuel ratio at a higher RPM. TRY THIS LOGIC: It is probable that the distribution is more inconsistent between cylinders at lower RPM's. As RPM's and intake flow increases, the mixture consistency cylinder to cylinder should improve. (Taylor mentions something to this effect in his bible) Keeping in mind that we want to avoid the leanest cylinder from going too lean, maybe it is beneficial to have the overall mixture richer at lower RPM's to insure that no cylinder runs too lean. Then as RPM's increase and cylinder to cylinder mixture becomes more consistent, we can lean the overall mixture to the max power ratio of 13/1 because we do not have to worry about one lean cylinder. A Q-Jet will deliver this type of variable air Fuel metering in stock form. Well the only final proof would be a well documented test. Any takers??? Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted December 4, 2003 Share Posted December 4, 2003 any carb is a good carb if you know how to tune it.the reason for egt's on each exhaust port-to check for fuel distribution.carbs work better with more air velocity-low rpm's are a little rich to allow for this.the reason for efi is to improve low and mid rpm driveability.if you stab the throttle on a carb motor you lose manifold vacuem and motors ability to draw fuel.efi just pumps it in. Quote Link to comment Share on other sites More sharing options...
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