FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Tom Gahman on February 18, 2023, 09:26:31 PM
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I would like to know what I should try to achieve in afr readings, generalizations. I have been dealing with a "running warm "problem last summer/fall and I think I made progress, but it got too cool to tell or really drive it more. I installed an AEM wide band with the o2 in the right collector. The little bit I was able to drive it it was way lean.I adjusted the idle to 13.8-14.5. Cruise is alittle leaner,and if I jump on it hard it goes lean off the scale! It may come back towards richer a little but by now I have to keep my eyes on the road.
I have a new in car vacuum gauge witch reads higher than the value I used to select my power valves, so that may help.When it gets warmer out and I can drive it some more and I get used to what I am seeing on the gauges, I will make some changes.I'm thinking more main jet to bring cruise into line and power valve channel restrictions for wot(less restrictions).
The carbs are a pair of 1850's on a M.R. intake,Edelbrock heads,CJ size valves,CJ crank,Auto tech pistons,
.017 427. cam is 258@.050 .6-.610 lift. 20 initial with 35+- total. 108 lobe separation.
car is a 64 Galaxie ,close ratio top loader and 4:86 rear gear.
Mainly looking for guidance on afr ranges,but any tuning tips will be greatly appreciated. Thanks, Tom.
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When you stomp on the gas, you should be looking for an AFR number in the 12-12.5 range. If you are leaner than that, you are probably down on power in addition to inviting detonation. If your exhaust system is perfect, with no leaks, and the O2 sensor is installed in a good location (not 6" from the tailpipe, for example), you should be shooting for about 14.5:1 at idle and around 13.5-14.0 at cruise. However, if you have exhaust leaks, OR if you have a pretty big cam installed, the idle and cruise A/F numbers can be pretty much meaningless. A big cam will fool an O2 sensor, and so will an exhaust leak. Even with a big cam or exhaust leaks though, wide open throttle readings are usually pretty accurate. These are just my observations from running on the dyno and on the street with a few different engine combinations, and wideband O2 sensors with either a Bosch or an NTK wideband oxygen sensor - Jay
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Given the cam you have, your a/f ratios are on the wrong planet.
Here is a bit I wrote:
https://www.afscarbs.com/post/multi-carbs
You will likely need a rich no load ratio to run decently in gear.
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Jay and Drew, thanks for the reply. Drew,the idle mods I understand,but if I'm lean at wot,why do I make pvcr smaller? Not being argumentative,just want to learn and understand.Also could you expand on"your ratios are on the wrong planet".Do you mean yes, way too lean? again just want to understand.Thanks again,Tom.
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A/F gauges are great tuning tools. They are in a couple cars here. I have learned not to expect to tune to supposed ideal numbers for every 100 rpms of engine operation. Some can achieve that but one could also drive themselves nuts trying to accomplish it.
If you are mashing the throttle and it stays lean you will have to sort that out. With the gear you have in that Gal I think you plan on lots of pedal stomping. If it is just a momentary blip in the number and the engine does not stumble at all it just might be the sensor/gauge can not keep up. The transition phases such as cruise to WOT can be tough to make perfect from a numbers standpoint but if there is not a hesitation it might not be worth the effort to try to change it.
That big cam can make for some dilution at idle and lower rpms. I have a cam similar to yours but more cubes, 92 degrees of overlap. That can make it tough to find a sweet spot A/F number in lower operating ranges. If you tune to a number for cruise and the car is surging you will have to pay more attention to how she is running than the gauge number and richen her up.
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Yes it gets run hard,it actually seems to run pretty well,though I drive right through where most street problems occur. If it gets just a little bit warmer out and they don't put any more salt down I'll start working on it again. I just ordered a new vacuum gauge and I'll start some more carb mods and see what happens. Thanks for the suggestions. Any other tips or suggestions would be appreciated, thanks,Tom.
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Are you certain from recent power runs that the secondaries are opening? If there is any doubt you can place a paper clip over each vacuum pod’s actuator rod. Place the clip at very top of rod up against the bottom of pod. If the secondaries are opening, after a rip you will find the clips down at the bottom of the actuating rod. If not open the pods up to learn which springs are inside them.
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I will give that a try,I do believe I have the lightest springs in now. Thanks.
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Jay and Drew, thanks for the reply. Drew,the idle mods I understand,but if I'm lean at wot,why do I make pvcr smaller? Not being argumentative,just want to learn and understand.Also could you expand on"your ratios are on the wrong planet".Do you mean yes, way too lean? again just want to understand.Thanks again,Tom.
Yes regarding idle.
Your WOT gauge reading needs more investigative work.
I rarely see stock 1850s used for 2x4 show lean at power unless secondaries are flopping open prematurely. Normally the opposite.
As often stated, wideband is a tool for tuning.
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FWIW, I did some of Drew's mods on a pair of 1850s on a tunnel ram. I did have some launch and +6000 issues but that later turned out to be an ignition issue - Mallory high end box breaking down. I have not re-installed that setup to test with the updated 7AL-3 setup. It's now 180 miles to a Test-n-Tune so I'm loathe to mess with my bracket setup LOL. When the car did hit well I found that purple springs in the secondary cans did not seem to create any bog sensation. His article is spot on, especially the synchronization of the primary barrels. I use a 1:1 and if they get a little out of sync the idle will start rolling.
I have also run dual Ed 600s on a 302 with a tunnel ram. I had good response with those - jetting was "one step" (per the tuning book) rich on primary & secondary, both carbs and #33 shooters. The Innovate I used at that time read 12.5~13 as I recall. I doubt I have that data as it was on a Windows XP laptop. Not sure I even have that PC still.
I'd do some street testing of the duals with the Innovate but I run nearly straight VP110 leaded race gas so not sure how long the O2 sensor would put up with that. I do not leave it in the car - only set up for testing, then remove the equipment.
IMHO - I would use an A/F gauge for initial tuning and setup, the put it back in the box. Unless you are going to spend time at way differing altitudes, once you get the car set for best performance you're not going to mess with it. The 650DP on the Falcon 351C was jetted 20 years ago and have never been changed. I race from altitudes ranging from around 3000' MSL to around 500' MSL.
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Thanks Drew and Falcon, I don't plan on leaving the gauges in after I'm happy with it. I have read Drews article in the past and I printed it out, its in my carb book,but I think I only was working on the idle at the time.I'm sure I'll get it figured out. Thanks again.