A/F ratio numbers

Well,
Another woe of the log runners is how much fuel run is effected by the cars ride height. With my 61 which is set up with air ride I was having issues with the front cylinders running fat and the rear 3 running lean. I have a tri power set with headers dual outs. I have the system running through a FAST tech dual A/F meter. To run the rake that I like I was getting more fuel delivered to the front end but once I raised the front of the car fuel delivery balanced out and my numbers were very close to balanced. Simple fix is to reset my ride height and level out the engine at the trans crossmember. Since I have a progressive set up my only other option ins to run a synched set up to ensure that all cylinders are getting a more balanced delivery of fuel.

That's a fascinating observation.

If you look at the intake log on one of our heads, it slopes down from back to front (Cyl 6 to 1). I guess this is so the log is level when the engine is installed properly (tilted down in the back).

Is the intake log on your engine level when the A/F ratio is balance across the cylinders?

very fasinating, I didn't think the log would ahve that kind of effect, but as it does to your tri power, I wonder how much worse it would be on a 2bbl mount. Thanks for sharing, keep us updated on the leveling challenge, maybe you can take pictures with a leveler on the front and rear of the log when it's all 'equal' for a good quick rule of thumb for others.

Guess I'll be doing O2 Bungs on both exhaust pipes.

on another thought, where are the unequall numbers in rpm range, the reason being is if ti's idle, maybe all you need to do is pull out the idle mixture on the rear carb to fatten it up? or open the throttle more than compared to the front... IDK just throwing ideas like clay pigeons...

The great thing with running the FAST A/F is that I can record runs to data log info as to what my ratio numbers are throughout an RPM range. I had been told that our logs had a tendency to run a bit lean in 5/6 cylinders. When I transition to all carbs open on load runs and fuel is being delivered from all 3 carbs my numbers are good. To find out where I need to be I simply ran a level across the center carb throat. This is an easy fix. When I installed my T5 I added some spacers to raise up the trans about a 1/4" I will just remove it to drop down the trans to ensure that my center carb is perfectly level. With the air ride I can also influence some things as well.

Guess I'll be doing O2 Bungs on both exhaust pipes.

This is more of a question than offer of help (but both). Doesn't the vehicle 'tilt' front to back with excelleration and breaking (real noticable on fast starts and quick breaking) and THAT effect this 'out of level' you mention? What about cornering or other 'off gradients'?

I've seen some mention a tune with this O2 sensor, Kevin. We sell all sorts (& prices). I assume the "wide band" O2 sensor is what is used in this application. Any suggestions on which model/manafacturer? And what type of 'gage' is it hooked up to to read? Need seperate power to activate?

Thanks.

Mostly noticed my numbers off at idle or city driving where I was primarily running off the center carb. The unit I went with was the F.A.S.T unit. I can read then bank individually or average them out which will fool you on the numbers. Running them in a dual mode I can see how the 123 / 456 banks are reading.

I'm ignorant (uninformed) and not real technical yet have seen some mention a diagnosis/tune with an O2 sensor. I assume the "wide band" O2 sensor is what is used for this application. Any suggestions on which model/manafacturer? And what type of 'gage' is it hooked up to to read? Need seperate power to activate the gage itself?

Thanks

Hmm. Interesting stuff. Four things.

1.Regards mechanically progressive external linkages, I'm not a believer based on the evidence, as they create many issues on smaller sixes. Offenhauser and Edelbrock systems fix the problem with poor idle quality from an unbalanced set of triple carbs on a V8, and are fine for V8's running the centre 2-bbl carb. But for a triple 1-bbl six, I'd say the situation's reversed, with 20 inches from cylinder 1 to cylinder 6. If you just locked the throttles, you'd have even float levels, and probably gain about 10 more horsepower. A/F ratios should level out. In essence, a triple carb system can be run like a Hüsker Dü developement, http://upload.wikimedia.org/wikipedia/c ... go.svg.png

with three seperate members playing together to result in one coincident form. I'd use another narrow band O2 sensor to measure average a/f on the fly, and the FAST set-up to to measure cylinder 1 and cylinder 6. Take a Canon A495 camera like I do, and then drive for 25 minutes recording voltmeter readings on the narrow band, then come back and download cyl 1 and 6 from FAST. Then you'll find what level of variance you have. Then go to locked 3-bbl set up,and you'll have a pretty good indiction of what the outer secondaries were dojung to you a/f ratio.


2. If you did static dyno runs with a tilting dyno, you'd find that the A/F ratios would vary only past 4°angle, or about 7%,and then go ballistic from then to about 19°(35%). It varies with cross fall and long fall.

3.The air fuel ratio is influenced by air flow in the engine bay, float level, and transient fuel delivery. A progressive linkage which opens at 60% throttle will always be subject to swinging float level and fuel delivery changes, and they are, in my opinion, not likely to be related to even a 5° degree lean in any direction. To change from a factory fuel float level of 1.575" for a Weber just by by angling the carb, or the car, its all the same.


4. The working range of gradients on a highway is way greater than what you can generate on an air ride suspension. There is no way to make it level without grounding out. The when you make a car lean 5°to 10° when banking it hydraulcially or by cornering, it starts looking wickedly sick, like a Citroën with its hydraulics off. So your carburation has to work on upslope, downslope, hard left, hard right, full noise quarter mile.


Background: The standard carb is designed to be level on a perfectly level plane, but most roads have a 3% to 14% (2°-8°) crossfall and longitudinal, they can be as steep as 35% (or 19°).

To get the engine and gearbox to reach the hypoid bevel on the crown wheel, the engine is set to a 6%-7% (3.5° to 4°) degree level. The engine is sloping back to reach the axle. Most rear drive Fords, even with independent rear suspension are normally set up that way. Carbs are generally able to cope 8% (5°) of slope from standard without fuel delivery changes, which allows for a hotmix asphaltic cement and concrete highways 2% to 3% normal camber to clear water, and up to 10% cross fall camber to keep linehaul trucks on the road. Normal long ways gradients are 0 to 11%, with some resulting long and cross fall gradients resulting in spot crossfalls of 14% max. Spot steep gradients of roads vary. We have the technically steepest street in the world down here (Baldwin Street,19°or a 35% slope). See http://en.wikipedia.org/wiki/Filbert_St ... _Francisco) and http://en.wikipedia.org/wiki/Baldwin_Street,_Dunedin

Just a thought - has anyone ever used the outer two carbs as the primaries, and the middle card as the secondary (e.g., drive off of carbs 1 and 3 normally, and have carb 2 come in progressively)?

Xctasy you are the dude. I am almost ready to drop the $$$ on an aluminum head so I can run an more effecient EFI set up. But still having fun playing with my current set up. Don't get me wrong the motor is still running strong and pulls like a mutha. Just still learning what it needs. I still need to figure out a way to maximize the vacuum advance. right now just running mechanical advance.

Ideal power happens when you use the Weber carb chart to size square inches of carb or throttle body venturi area to the size of each cylinder. Organised Racing always restricts the maximum areas of this to restrict power. Power boats, speedway, touring cars, NASCAR, World Rally Championship, Formula 1,2 and 3.

Stick with what you have, and optimise. The trick to making the tripower work is ultimately finding a way to support stable A/F delivery. Based on the single runner design of the Ford i-6 log head, I'm pretty sure you cannot make a progressive linkage evenly supply a/f, as the normal centre carb a/f supply is suddenly air hammered by the secondary outer carbs. In EFI intakes, they use resonance boxes to cope with situations like that. In tri-power V8's, the intake has three 2-bbl holes to contain and direct the flow. With the three 1-bbls, the mixtures collide at sundry times, creating unstable flow. That is the reservation I have with the Edlebrock and Offy, that they are okay for a stock engine, but really finicky when you start to cam it up when still using a progressive linkage.

If aggressively roller cammed 188 cubic inch Turismo Carretera (English: Road racing, lit., Road Touring) Ford Falcons can make a stunning 380 hp at 9500 rpm with just one IDA 48 with two 37 mm venturis, 9.35:1 compression and just 3.3 sq inches of carb venturi, then so potentially can yours with just 3.07 sq in.

After all, you've got better fuel distribution.

Only issue I have is that to make power, you have to get way more aggressive with that cam profile. At 5100 rpm, your running at air speeds above 190 feet per second (at a lowly 85% volumetricefficiency) requires a different camshaft stratergy than if you were able to run three 2-bbl carbs with twice the area. 60 to 85 feet per second is the ideal speed for any independent runner system,and power increases 25% when air speed is reduced by half to that level. That means that specific power requires 25-50% less revs when you increase the venturi areas 100%.

The '66 Shelby GT350 Clone Historic C with stock 2-BBL 500 Holley and 289 can make 352 hp at 6700 rpm at 452 feet per second and just 2.97 sq inches of venturi. Aspirations index is (289*6700)/352, or 5500,

In Australia, cross flow guys run big 750 cfm double pumper 4-bbl carbs with massive cams to get 375 hp at 7500 rpm out of 250 i-6s, but cams are really intense roller profiles with 256 degrees at 50 thou, 0.650" lift. Air speed in that situation is 219 feet per second, and there is 6 sq in of venturi exposed at wide open throttle, aspirations index of 4991.

The ACTC Argentine Turismo Carretera cars are running at 376 feet per second with 3.31 sq in, aspirations index of 4742.

All have custom cams which are designed around making the package increase cylinder filling,but the engines have poor aspirations indices.

What you compare that to is totally stock XR6 engines. A really mildly cammed EFI Falcon can make 268hp at 5250rpm from just 243 cubes, or 216 hp at 4600 rpm from the same cubes. Air speed is 129 and 151 ft/sec, aspirations indexes of 4762 and 5176 respectively. They are tame engines, which if the low air speed tune could be duplicated would then make the TC 188's power at 7500 rpm rather than 9500 rpm, or the 289's 352 hp at 4700 rpm rather than 6700 rpm, or that 375 hp 250 engines power at 5500 rpm, rather than 7500 rpm. 25, 35 and even 50% more power with no extra effort. Put another way, a TC 188 with 487 hp at 9500 rpm, a class C with 528 hp at 6700 rpm, a 250 X-flow with 511 hp at 7500 rpm. This is matching the time honoured Weber Independent runner carb sizing with the sensational work the American cam industry has made on cam optimization.

That's what pulse tuning does..it gives the most horsepower for the least revs. As you nail the tuning, you end up with more power with less revs. The epitome of power is the NASCAR 350 V8 or AVESCO 302 V8'S. Each has aspiration indices from 4100 in a restrictor plated Winston Cupper to 3650 in a free to air EFI. Restrictor plate engines with 800 feet per second air speeds, yet still making 650 hp at just 8000 or 7500 rpm. Its all down to the cam profile, compression ratio and head flow. Unrestricted, the specific power goes right up 13%. An 850 hp at 18 000 rpm 183 cube Formula One engine can't even match the hp per rev per cubic inch because its effectively restrictor platted too.

Soldmy66":2sk098ro said:

Just a thought - has anyone ever used the outer two carbs as the primaries, and the middle card as the secondary (e.g., drive off of carbs 1 and 3 normally, and have carb 2 come in progressively)?

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I wanted to bump this. I would be very curious if this has ever been done and, if so, how it performed. It would seem easy enough to do; no?