interesting subject , but like the English says it is Manifold Absolute Pressure that changes on the engine .and what is measured . It knows nothing about external atmospheric pressure . It needs pressure inside, above true zero ( always a ( - ) gauge pressure between 0 and -15 psi gauge )
You simply effectively step on gas more— throttle is open more to get oxygen mass you need for the power desired? FI / O2 sender fixes AF ratio off MAP which should not change for a given oxygen/ air mass flow*.
But in a carb what pushes gas through a jet is only the atmospheric pressure?
I always had trouble visualizing this as a kid — you imagine a “suction” (?whatever that is) but really it is weight of air pressing down on gas( i think ,almost got it at 81). So that is less at high altitude , carb goes lean , due to less gas at same vacuum , nothing to do with oxygen % etc . Same reason you can only lift water in a well 28’ with vacuum ( weight of water column with 14.7 psi air weight pressing down on it makes it rise up in pipe , but only to 28’ with perfect vacuum( which is no air pressure)
One would think FI , always looking at O2 sensor post combustion would fix this anyway ,,but close calibration requires flow of air to be closely known ( *various schemes for that ) and MAP is a critical input to determine that and so fuel needed — nothing to do with altitude? MAP is set by throttle and rpm , lets computer figure out gas
It dies not have a barometric psi sensor directly on modern FI ?
Carb however has a big problem , as already lean with ethanol .It was calibrated for real gas . I do not know about 300 carbs ( and what follows takes time ) but we should go up on jet .
I did go through this on slant six 1920 Holley 1 bbl ( great simple carb !) it would pop back at wot occasionally and just felt always unhappy, hesitation off idle etc My driver . Think it came with # 52? jet ( I think Holley numbers are close to drill size in thousandths) and area of a jet would track radius squared , so ( too long to get into here) using AF for ethanol mix vs gas convinced myself that 2 steps up should help . 54 I think ( memory is auugh) . That is 1.16 increase in area to a 54 . say ~10 % more gas flow, more hp will happen too . Note how critical jet size it is… Thing runs like a top , gas mikeage went up !! 75 - 100k miles later 67 dart convert . We need to figure this out on rams ?
The idiots who run Massachusetts now blindly follow the land of fruits and nuts ,being incapable here of any original thoughts that do not include tax —-so everything is ethanol laced .
—- How burning many more total gallons of fuel ( A/F physics) and destroying food grown with diesel to then make ethanol ( when Brazil fills the world market with it cheap , from sugar cane ) helps the environment ( net) escapes this engineer. Politicians must be really smart. About getting $ to constituents , who get $ to politicians who take it from me . BS baffles brains , as is currently on vivid display jg On Nov 3, 2024, at 8:27 PM, Rich Barber <c300@xxxxxxx> wrote:
Not a 300 subject. Responding off line, but no. Rich From: RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx>
Sent: Sunday, November 3, 2024 5:03 PM
To: Rich Barber <c300@xxxxxxx>; 'Nick Taylor' <nicksgaragesd@xxxxxxxxx>
Cc: 'Carl Bilter' <cbilter@xxxxxxxxx>; 'John Grady' <jkg@xxxxxxxxxxxxxxxxx>; 'Donald Verity' <chryslerdon@xxxxxxx>; 'John Nowosacki' <jsnowosacki@xxxxxxxxx>; 'Chrysler 300 Club International' <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: Re[2]: {Chrysler 300} Distributor overview I read as the pressures change the volumes of mainly nitrogen displaces oxygen changing the ratio.
The composition of air, including the percentage of oxygen, stays relatively the same at all altitudes. Further: <image001.jpg>
The percentage of oxygen in air is approximately 21%. Explanation: Air is primarily composed of nitrogen (around 78%) and oxygen (around 21%), with trace amounts of other gases like argon and carbon dioxide. Rich B. As your air density goes down, the s less percentage of oxygen at12000 feet 13.2 percent, and almost 22 percent at sea level.
Our ’05 Hemirango has an MAP sensor to adjust for barometric pressure. (Manifold Air Pressure) Except when it doesn’t. It adjust timing and fuel to meet the prevalent air pressure. Twice on Trail Ridge Road (12,000 ‘+ SLE) the map sensor failed requiring us to limp into Boulder for a new sensor (twice) I imagine it is a spring and bellows and the spring breaks or the diaphragm fails when overranged. When working, the system stayed drivable on premium corn gas, but lost power accordingly: The standard atmospheric pressure at 12,000 feet is 19.029 in Hg, which is about 40% lower than the air pressure at sea level. On the way to the Reno meet (Donner Pass 7,239’ SLE) towing our 300K, it Got-R-Dunnn without blowing out the MAP sensor, but downshifting way down. Helpful to have the Trailer Towing Package with higher differential ratios (4WD, just in case), fifth gear lockout and springs. Coming down, the electric trailer brakes satisfactorily assisted the four big rotors on the Hemirango. Rich Barber (Living at 120’ SLE and enjoying the warm high pressure pollution-laden air 40 miles east of San Francisco). Wishing all peace and good will this week. Does octane booster help? On Sun, Nov 3, 2024, 9:02 AM RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote: I can tell you what happens at 5000+feet in altitude with today's gasoline. Not good.
John, I have 2903s on my G not E-brocks, no ported carb vacuum. I just have E-brock electric chokes on the 2903s. Someone probably has Edelbrocks on their F or G with both ported and manifold. What have they experienced? ------ Original Message ------ Date 11/2/2024 6:36:50 PM Subject Re: {Chrysler 300} Distributor overview agree with Don , they are good distributors great even. Leave those alone . Comments on electronic refer to switching out the whole thing —- that vacuum bearing rusts too but can usually be freed up , concentric bearing on that unlike pin in plate of lesser designs does not change dwell with vacuum advance Correct — no ported carb vacuum , yet has vacuum advance? on manifold vacuum ! crap idea that was must cause lots of issues including lack of idle stability ( on ram ? never) . Chev corvette dual quad had that too . must have been the good idea of the day in 1958 . Copy GM And therefore lots of vacuum on idle advance ? yet fsm is no vacuum connected when you set it . No where is this setup addressed except in one ram bulletin it says ” there is no spec for idle timing with vacuum connected ( revisit discussion of idle timing on rams— its all over the place once vacuum is on ) yet how it is Carl has ported vacuum carbs I think .. did he hook up the ported ? or manifold? On Nov 2, 2024, at 7:18 PM, RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote:
There is no ported vacuum advance on 2903S carbs.
The dual point IBS 4011 has a bearing on the upper part of the shaft just below the tach drive gear. Dwell changes are not caused by the bearing or lower bushing. I've seen a few that needed a new bearing, but have never changed the bushing. If there is a anything bent it will be the shaft that the points cam rides on. They are supposed to be lubed regularly, but seldom are. The other issue with these is the bearing on the points plate. The vacuum advance is connected to the upper plate. These get gummed up and stop moving. The plate has to come apart to fix or you will have no vacuum advance. You need it on a street driven vehicle, if you want any kind of gas mileage. possibly nothing wrong with your dizzy bushes , at that low miles, easy to measure it per fsm . messing with it may make it overall worse . Cant be “leaning tower” , on main bore? - it would spin in a conical arc , hit all around —- you could measure runout if bent ( which is more likely at top , that skinny post or in advance parts . Maybe precision straighten upper skinny part of shaft if bent , easy . The only way you know max advance is to measure it , methods 2-3 very risky and ill defined , it does not vary car to car , there is a single correct number , all that is worked out when they did curve , especially the max . It is all in by about 3500 rpm w no vacuum ,,easy to know ,—check it there — then initial setting falls where it does . Can't say anything about it if vacuum snd mechanical are both active ,or set by ping etc . Depends on gas , load on motor etc way more than degrees .Max degrees very important with 10 :1 and todays gas ; you cannot always hear ping , if you do its a problem I think someone put cap on not seated right once , (?) tore things up , maybe bent shaft ( or bad cap ) — I am sure you went through all that I get DO get keeping it original , — love points, no issue , but you do keep original problems , maybe add new ones like widespread junk replacement capacitors from china ( aluminum can, black rubber cone on wire= watch out ) (= intermittent poor spark, drive you crazy ) Got me twice. Comes and goes , no start etc . Original high quality capacitor from mopar with copper strap was probably perfect when pulled out too . vs peaceful perfect running ride every time, no vague skip etc etc . No “ what is that” or that flex wire that goes bare and shorts or dropping little screws you can barely see , in sideways . no thanks ; unless truly solid reason, concours etc points ? the best , !!! but cant set right without dwell meter ,,but SO critcal — they move when you tighten the screw ps you aware there are two heights of rotor , two heights of cap that match? not sure of year of change but can get crossed .with disaster result Later ones are often tan and taller Thanks John, for the usual thoughtful analysis and experience. After 63 years and 80K+ miles, I can't really complain about my original distributor needing a rehab (though my 55 and 57 Chryslers never did), so if I can get the thing fixed with new bushings/bearing/shaft/whatever, I'll put it back in and not go down the path of any other modifications. I've owned the car since 1998, and been pleased with its performance all this time, so original configuration and changing points every 6 to 8 years is fine with me. I'm only using this stock single point unit as an interim solution because it was a one wire drop in, allowing me to still enjoy the car while waiting for the repaired original to return to its rightful place, so I won't be converting it to dual point or electronic anything. I've always used 3 methods for setting/adjusting my timing, sort of as a confirmation/comparison of all the methods against one another. 1. Good old fashioned timing light and marks under the hood (hopefully the damper hasn't rotated at all over 63 years) 2. Vacuum gauge approach attempting to set for maximum value at idle (compare with timing light) 3. Test drive under load heading up a nearby road with a nice incline that would induce pinging if too much advance for the ethanol-free 91 octane I am able to run down here in TX. Even at TX highway speeds of around 75 mph, I don't approach 4000 rpm, so I don't think I'm approaching any 'all-in' advance that is 'dangerous'. The odd part (to me) about my original distributor is that it only makes the rotor hit the side of the cap on three of the studs that are right next to each other in sequence, and nothing anywhere else under the cap, almost as if the entire shaft is now like a leaning tower of Pisa and not just randomly moving around from a bad bearing/bushing like I would expect. Anyhow, the new cheapo unit comes with a 'lifetime' warranty, and I'll hopefully not need it for all that many miles so I can have it on hand if/when I need to drop it in to my Hurst, which is still on it's original 54 year old dizzy. ;-) when looking at non tach drive B block distributors, one really should look at common mopar performance upgrade kits to a stock orange box electronic . or same thing used , from millions of 440 R B blocks Way outperforms any point distributor , no maintenance and all new parts . service pieces are in every napa . But generally very reliable . Standard auto parts brand seems good stuff Quality of an all new MP distributor is not what it was , i got one that ate its bushings — shipped with no lube on them , so —put oil on the bushings . looks offshore made , but does the job . All new bushings and you get an all new shaft with correct fit — that really matters . New vac can . By the way , not sure what rebuilding process really is , ( check out- exactly) as “all that wears” that matters imho is the shaft bushings and so they often need changing , very critical on points ,but less so on electronic pickup . —- which is resistant to gap changes (inherent in the way it works ) sometimes the main shaft gets worn undersized only in the bushing section , so new bushings wont fix that . been there . Cant use undersize bush as you cant get unworn part of shaft through it (where not reduced) Longer or slightly relocated bushes may work ( did that ) but setup then is not at 100% long term . Looking back , a lot of work , not worth it . Changing points , rotor and capacitor is not “ rebuilding” if shaft is shot where bushings are . But cleaning and lubing advance helps . vacuum diaphragm fails a lot too , check with mity vac = why on this , non tach RB app , a new MP one and electronic makes sense Keeps it mopar . Good for 100 k no touch or worry Once you to go aftermarket, lots of hype , thin wallet , lots of unique parts and problems Related , converting to modern electronic tach lets you use kit on FGH , stock tach is a dancing inaccurate joke ( there - I said it!) wrong advance curve likely too with aftermarket . Don't touch advance without accurate light , unless you want hole in piston .Cant “ tweak” “by ear “ without data where you are . ? 32 degrees max mechanical all in ? On Nov 2, 2024, at 8:32 AM, RICK AND DEBBIE CLAPHAM <rixpac@xxxxxxx> wrote:
I will look in my Sun machine, maybe have a spare IBS 4011, I did recently find a Rebuilt K distributor.
Not sure you got my other email. I had great luck with joes distributor in Ohio. Specialized in mopar stuff. He’s done a F one, and a 58 golden commando one for me. So, I went to Rock Auto just for kicks, and they had a single point "standard performance" distributor (out of stock on D14 dual point "performance" unit recommended for 'U' code 440 engine from 1970), which came with points, condenser, cap and rotor installed and ready to drop into the engine, all for $100. I ordered it and it came yesterday. I installed it in my G, and the car started right up, so I adjusted the timing a bit and took it for a test drive. There was no noise coming from inside the cap like there is on my original that has the rotor slicing its way through 3 of the plug wire studs. There was no 'skipping' in the 55-65 mph range like there was with the original, either. There was also no pinging at all, so I dialed in a bit more advance, since I bet the advance curve is less aggressive on the single point unit than on the IBS-4011 normally used with the camshaft of a G. I can totally live with this level of performance (and lack of tachometer functionality) until I can find a place that can rebuild/repair my original unit. With that being said, does anyone know someone who rebuilds/restores distributors? I found a listing in Hemmings for a guy named Jim from Special-Interest-Autos.com who advertises all kinds of tuneup parts available for sale, and the ad also states that he does 'restorations' of distributors. His listing is under Chrysler/Mopar parts for sale, as well as under Dodge parts for sale. Apparently he is from Rockwall, TX, which is a bit over 2 hours away from my location. I've traded voice mails with Jim, but have not spoken with him 'live' yet to discuss in detail my particular distributor and his ability to find parts to refurbish it (or what the cost would be). Any other advice/recommendations of repair folk for Autolite distributors would be appreciated. -- --
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