you opinion appreciated!
extra points if you have experienced it; how did you identify it? :confused:

 

heehee, I'm fighting with that now (well maybe not TOO lean, but enough to make my car slower. we'll see for sure when I re-jet)
Hmm, I looked at my very light color plugs, the SEVERE stumble upon throttle input with the accelerator pump disconnected, and a temporary increase in rpm at idle when I put my hand over the primary air horn. That's how I came up with "too lean". :smash:

I like these quizzes! :D


[Modified by isosceles, 1:54 PM 6/9/2003]

 

Most people are too rich not too lean. I do regular plug checks. Often after a run down the expressway I will pull a few plugs and look for too lean. I like my plugs on the white side. I also run a oxygen sensor and try to run around 15-1 for normal cruising with the power valve kicking in to pass or up hills.
To solve the stumbling problem when the throttle is cracked I open up the squirters a little and make sure my pump cam is on the highest setting.
To me a lean motor will last alot longer then one running rich and my gas mileage will be up.

 

Vizard says he uses a Colortune to calibrate his oxygen sensor. 14.7:1 is white, leaner is blue :eek: and richer is yellow.
Says you can drill a hole in a header tube near the head and see the exhaust color, that will work too. :cool:
IMO a plug will not show blue because of the high temp. it works like a self cleaning oven and can not show "too lean" since the particles that show tan are vaporized.

 

On the dyno we find that max power is always around 12.8-13.0. After that the power will start to fall off and exhaust temp will shoot up. The readings are taken with extremly sensitive fuel flow meter and air flow meter to calculate A/F ratios. We also take exhaust temps at every cylinder with thermocouplers. We try to get them between 1230 and 1280°, with no more than 100° difference between highest and lowest cylinder. The problem with using a singe O² sensor is that you only get an average of all the cylinders. You can have one cyinder running extremely rich and another running extremely lean and still get the same O² reading.

These numbers are for a motor running at WOT not cruise speed for fuel economy.

If you want to drill a hole in the header and stand next to a motor that is under full load at 8000RPM to see the color of the exhaust, you are a much braver man than I am. :yesnod:


[Modified by Pete79L82, 7:37 AM 6/10/2003]

 

Pete
how much variation do you see on the dyno(350 chevy dual plane)
richest vs. leanest?
i've got 12%
is this common?
i use o2 sensors at each cyl. while driving WOT.
.
when i calibrate the sensor i'll just turn the idle speed screw until it switches to the main jet, near 2000, and watch for a white exhaust flame, then shut off, put the o2 sensor back in, start up and see what it reads.


[Modified by Matt Gruber, 9:00 AM 6/10/2003]

 

I agree with Norval. I pulled my plugs out last night after a nice cruise. All of my plugs are on the white side. My car is running better than it ever has. I can remember when I first started running my car with the unadjusted carburetor. It would burn your eyes if you let it idle in the garage.

A rich motor is washing the oil off the cylinder walls and in most cases will lead to plug fouling, poor performance and poor gas mileage. Every performance car around my area seems to run on the rich side. What they don't realize is they are missing out on power.

I believe a wise man once told me that "75% (conservative estimate too) of all muscle cars are run rich" ;)

 

once in 72-74 i ran too lean.
this was my 63 Valiant with my turbocharged slant 6. This car was experimental and i was always pushing its' limits.
The cas was impressive with 22 psi boost. Wanting more power i removed the turbo muffler and ran a straight pipe. That was in preperation for switching to a(non-holley, maybe an AFB, i forget) 4bbl
from a holley 500cfm 2bbl.
Well, 1st and 2nd gear were amazing with 30 psi boost :eek: When i hit 3rd, i soon heard an abnormal WOOSH sound :cry as the turbine blades melted off. :cry At the time i had no idea what too lean could do :confused: so i switched back to the 2bbl holley. with a new turbine of course. This is an example of why holley runs their carbs rich. it saved my butt back then (in the days before oxygen sensors)

 

When you can see the ribs showing ...... oh wrong subject never mind. :)

If you like to run it lean you better make your adj at the time the weather cond will give you the leanest running set up or you will be too lean when that occurs.

 

Norvalwilhelm - How do I see which cam is highest when the cam curves ends in the same height, can I go by the numbers on them?

Which cam is normal to begin with on pri/sec on a 850DP?

Fevre - In which weather do I get the leanest condition?

If I go steady at 60 mph, after how long time can I see the difference on plugs?

Me, a novice in his early carb career... :cheers:


[Modified by Lasse, 10:41 PM 6/10/2003]

 

Cold dry air contains higher % of O2 so it would cause the leanest cond. Seems that is when most people say their car runs the best so that does indicate most people are running rich during warm weather, when we are most likey to drive are vettes. Remember most cars are designed to run in a very wide range of cond so you have to expect that they would run rich in warm damp weather as opposed to cold dry weather.

 

Shane you are starting to sound like me. :)
Lasse. I don't remember if 1 or 2 is the highest setting. I make sure there is no play between the arm and and the pump but at the same time with full throttle make sure the pump is not bottoming.
I also drill the squirters out a little bit but sometimes the screw need help, but can't remember how I did it. If I looked at the screw in the squirter I could figure it out again. With my 2 x4 setup with 8 squirters I haven't touched them from factory.

 

The color tune plug is made of quartz and it does not change color . It is transparent and allows you to see the flame front as it travels across the combustion chamber . I have every type of analyzer you could imagine in my shop including infra red and I run dual o2 sensors on my car . The colortune plug can give very reliable info for tuning .

gman ase master certified

 

back 2 school 4 you :crazy: :crazy:

30lbs of boost?? melted turbine blades?? what were you running an oxy acetylene torch?


[Modified by Twin_Turbo, 6:39 PM 6/10/2003]

 

:lolg:
actually i was in college back then.

 

Guys thanks for yor input! I had no idea there was any interest in cruise jetting!
(that is about the only thing i could set right without an o2 sensor).
So i added a paragraph about it at the very end of my A/F article(in my sig link) :cheers:

 

http://forums.corvetteforum.com/zerothread?id=580485

 

This is TOO lean!



That piston was in a new motor for about 10 minutes of break-in time and 6 SECONDS of WOT dyno pull. That shows you how quickly a lean motor can be damaged.


On a dyno you can not use an O² sensot to tune a motor because they are not quick enough to react and I have never found one accurate enough to rely on. A dyno pull will generally be about 8 seconds long and O² sensors lag behind about 2 seconds of read time. They are probably great for a street car but not for a race motor.

As far as variations on a dual plane manifold, if you can get one to have exhaust temps within 250° from high to low it is pretty good. Because of the differences in runner lenght it is very difficult to tune a dual plane manifold for proper air/fuel distribution. They take a lot of work and a lot of trial and error flow bench time to get good equalized exhaust temps.

No motor has a totally flat fuel curve. Generally a good race motor will run lean (around 13.5 A/F) at off idle and low RPM, get richer(12.8 A/F) as the motor hits peak volumetric efficency (ussually the same RPM range that the motor hits peak torque at) and then will lean down (13.3 - 13.5) at higher RPM. A great deal of time is spent on jetting, air bleads, and booster size and positioning to get a flat fuel curve. To do this would be way past the needs of a street motor but what I am saying is you can't look at one RPM range and say that is your A/F ratio because it changes with RPM. If you are going to set A/F it is best to do it at the RPM band and throttle postion that you are in the most.

I agree that most muscle cars are run to rich. And it should be that way. Very few people (and I am not pointing any fingers or refering to anyone here) understand a carb enough to know how to properly lean one out without damaging the motor. Jetting is only a fraction of what is needed to do it correctly.
It takes an extremely rich mixture (under 10-1 A/F) to wash down a cylinder and do damage and at those A/F 's you will see black smoke out the exhaust.

A 12.5-12.8 A/F at WOT is probably the best comprimise of power/safety that most people should run on a street motor.

Pete

 

Pete
any idea of the A/F or EGT on that piston?
.
when you tried o2, where did you mount the o2 sensor? Did you try a heated sensor?
.
Good point on the fuel curve! Mine gets really lean on early WOT shifts. That could be a big problem if i was towing a trailer in the mountains. Might be why holley jets them so rich. :cheers:

 

Very interesting topic!

Can you use a lambda sond constantly when you add lead addition in the fuel, I've heard that the lead will destroy them in the long run?

I have found a buildscheme on this site http://www.markvanderkwaak.com/dbbp/tech-tips/mm.html and will try to build it.

Any comments about their accuracy for street use?


[Modified by Lasse, 6:34 PM 6/11/2003]