best air fuel ratio

[jmarkaudio]

What carb? What does it have for main air bleeds and what emulsion calibration?

Leaner mixtures make more power when the fuel is delivered with a sufficient amount of atomized fuel, when the mixture of air and fuel are homogenized well, when the fuel used vaporizes sufficiently for the application… these things ensure more equal distribution of air and fuel to the cylinders. Rich mixtures burn easier, but don't make as much power. When distribution suffers or the mixture is not well homogenized you end up with either a lean cylinder or lean and rich pockets. You either get a misfire or an incomplete burn, both lose power. Finding the balance for any engines key to running the best track times. As far as dyno versus track times, g-forces affect the distribution of fuel more than air, so that can be a factor on what calibrations need to be or what changes can be made to influence more equal distribution.

[bigjoe1]

This is another one of those things where your results may vary. The high out put engines I w ork with always have a two carburetor , tunnel ram intake set up.


JOE SHERMAN RACING

[1972ho]

If you are referring to my carb.it is a quick fuel Nhra legal SSR 780 VS with .032 high speed bleeds not
sure on emulsion.

[jmarkaudio]

If you are referring to my carb.it is a quick fuel Nhra legal SSR 780 VS with .032 high speed bleeds not
sure on emulsion.

I was commenting on rfoll's wide AFR swing. For your SSR 780 I have the calibration on it as I've had one through my hands. For the B/S Camaro it went on it needed a couple jet sizes up from the box, and when time permits staggering jets may help it more. Is yours a Stock car with a dual plane or a Super Stock with a single plane?

[1972ho]

It is a dual plane ford stocker intake,So do you remember which area of the carb. that you staggered the carb.when I ran mine in Vegas I had the lower numbered jetting on top and the higher numbers on the bottom.

[nickmckinney]

If you go lean you can lose a cylinder quick if things are not perfect as the sensor is taking the average and not the reading on the leanest cylinder. 13ish in the collector might mean 11:1 on the rich cylinder and 15:1 on the lean cylinder if you are having distribution issues. Also make sure the sensors read good by testing in a known good car, I have had 5 motors come back torched on the dyno or shortly after in where the readings were good but the reality was a blowtorch being set loose.

[1972ho]

Well it did make some of the plugs look like they were not been firing there are about 3 plugs that did not have any carbon on them the way they looked as if they were not firing So i'm kind of scratching my head on that issue.And on a couple of runs the racpak did show a couple of peaks and valley's after the 2,3 shift so i figure that those or misfires but overall the runs seem pretty smooth.

[jmarkaudio]

That is where individual cylinder O2's help, or just reading the plugs and giving it fuel where it needs. The following link shows what plugs looked like before and after staggering on a Big Block. Your Ford will have it's own needs depending on the intakes distribution characteristics.

viewtopic.php?f=1&t=36744&start=15

[RAS]

Lots of possibilities here. What is max power producing in the am may not be in the pm. Run an engine in Denver one day and the next in Chicago and get different results. Carbs need constant tuning. To be safe,(intimidated) I had an air fuel meter wired into my streetrod. 502BB with Accel 7 EFI. I prefer to let people like John Meaney keep my 'stuff' right. I fought carbs for decades and they won. Track tuning is surely different than street tuning. Our author is track focused and I'm not qualified with racing carbs. Sorry.

[Barry_R]

give it what it wants

True words.
One of the key beauties of EFI is the comparative ease of generating smooth, even A/F curves.
One of the risks/downsides to EFI is the ability to generate smooth, even fuel curves AND assuming you are "done" once you have them.
You tune for power & ET - not perfect A/F numbers.
Any proper tuning effort is two stepped - first you establish control, then you find out what the engine "wants"...

[treyrags]

Lots of possibilities here. What is max power producing in the am may not be in the pm. Run an engine in Denver one day and the next in Chicago and get different results. Carbs need constant tuning. To be safe,(intimidated) I had an air fuel meter wired into my streetrod. 502BB with Accel 7 EFI. I prefer to let people like John Meaney keep my 'stuff' right. I fought carbs for decades and they won. Track tuning is surely different than street tuning. Our author is track focused and I'm not qualified with racing carbs. Sorry.

A well tuned, efficient combination will not need nearly as much jetting change for altitude as most think, sometimes none at all - just a gear change. I've seen guys overcompensate for it many times.

[bigjoe1]

I totally agree with the last post, Most people make way too much change where perhaps NONE is needed


JOE SHERMAN RACING

[headman]

What I have seen is that the real strong, high HP per cubic inch engine can run leaner than the run of the mill engines, What might be good for a 1.50 HP/ cube is going to be overly rich for a 2.0 HP per cube. The more efficient engine will like a leaner jetting for best power. It shows up as a lower BSFC on the dyno. On serious race engines,I have seen over 14 to one air to fuel ratios.


JOE SHERMAN RACING

This makes complete sense. Anything else is just washing raw fuel through the engine, (that is not contributing to making heat).
If we are honest with ourselves, we dump extra fuel in just to be sure no cylinders go lean.
Hate to say it, but the Honda cars that have been on my dyno are at/ around 14:1 or leaner.
They use the fuel they burn to make power, not just to keep the cylinder temp in check and avoid detonation.

I expect the obvious is the 2.0hp/in engines are delivering a consistent mix to each cylinder, so no need to run rich to keep the leanest cylinder above 15:1

[fdicrasto]

Well it did make some of the plugs look like they were not been firing there are about 3 plugs that did not have any carbon on them the way they looked as if they were not firing So i'm kind of scratching my head on that issue.And on a couple of runs the racpak did show a couple of peaks and valley's after the 2,3 shift so i figure that those or misfires but overall the runs seem pretty smooth.

A possible scenario for stagger jetting assuming you have a dual plane intake. Follow the runners to the plenum and see if there is a correlation to lean or rich readings based on where the runners meet the plenum. Do the obvious,e.g. say cyls # 2 and #5 intake ports transition to the plenum under the left front carb butterfly and those plugs read lean; go 1 or 2 jet sizes up on that corner,rich? same plan. This should keep you busy and MAYBE get you some results. Phil D.

[john hennessy]

the first question i would ask is, "how equal are the chambers on the heads?"

next would be cam timing at the front of the motor compaired to the back, check all the cylinders to make sure that they are the same, if not adjust the lash accordingly, you want all the valves opening and closing at the same time, this i feel is more critical than max lift, unless you have a hydraulic cam, in which case i would set the cam timing to an average.

contact area of the valve seats should be the same cylinder to cylinder.

all the above factors cause poor fuel distribution.

if you know none of the above, then keep going ritch until it slows down, now you have an average fuel supply, now start a stagger jet program, jet up the lean cylinders one size and the rich down one size, then start from that up or down /rich or lean until best e.t. is achieved, then go up on all the jets one or two sizes and see if it goes quicker or slower, if quicker then go some more if slower drop down a size all round.

do keep checking the plugs, they are in the cylinders so they know what is going on.

when you have all this figured out, the atmospherics will change and you start again.