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  #31 (permalink)  
Old 04-13-2010, 11:09 AM
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I am familiar with the basic functions of diagnostic tools, I was a technical instructor for the last several years prior to my retirement. I was actually attempting to show a method usable that someone less technically adept might be able to utilize. I believe I did recommend a wide band sensor, most heat delivered during oxidation is at about 14/ 1 but best horsepower is at around 12/ 1. I have seen guys replacing expensive components costing way more than a meter due to lack of understanding. I also do the answer man thing on a couple of Mercedes Benz boards as thats where my background lies, 40 years working in and running shops in So Cal. I looked at the Holley web site and that carb should be jetted perfectly for the engine described with a slightly possible issue with overlap effecting the vacuum signal for idle fuel. this is all fun for me as my carb/ dyno days are long past so this is memory lane for me. I'm building a 406 sbc with a home made hilborn/ megasquirt set up currently for a 26 T roadster I'm building so I use postings here for some domestic info from time to time. I appreciate your responses with any info, I'm sort of an info freak of sorts. As for wide open throttle responses I had a client several years back that had a new AMG CLS 550 MB that we chipped, overdrove the supercharger, installed tuned headers and other stuff anyway we were near 600 on the ground and he came to me asking abut an improved cam grind he found. I asked when he last drove it accrosed town at WOT and he responded never as it was too darned fast so I replied why do we want more horsepower? He decided to leave it as built. Thanks again for the response.
Bill

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  #32 (permalink)  
Old 04-13-2010, 12:33 PM
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Getting useful information from reading spark plugs on a street driven
engine is almost imposable.

One example: if the plug is white and clean, you could think it needs more
fuel even though the air fuel ratio is perfect for light load driving. Run
the engine at WOT for a period of time and the once good tune up is no
longer whatís needed.

Another example: the plugs discolor rather quickly, you could think itís too
fat when in fact the air fuel ratio is perfect. The fuel that colored the plugs
came from excessive idling with plenty camshaft of overlap. Or suppose it
is fat, what circuit needs tuning?

The wide band is a good idea, this would allow you to tune each individual
circuit on the carb.

As for the miss, I suspect it's an ignition problem maybe something simple like
a plug thatís fouling out. The air fuel ratio has to be way off to cause a miss.
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  #33 (permalink)  
Old 04-13-2010, 02:50 PM
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I used an Innovate LC-1 to tune in my qjet and it worked perfectly. Before that I tried the narrow band sensor with the volt meter and it did not work at all. I understand that the narrow band sensors are only accurate at 14.7. With the LC-1 I was able to record all my driving conditions from idle to WOT and can watch when I tap the accelerator and the squirt causes a rich reading on the gauge. I agree that reading plugs is very difficult but it does have some value. I recently did a trip of 45 minutes and had it all recorded on the computer. It was very helpful and told me I needed to up the jet size a couple more to get leaner cruise and better part throttle.
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Old 04-13-2010, 04:12 PM
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well guys thanks for more help. As far as installing an o2 censor my dad has a welder but it will be some time yet till I can get with him to weld a bung in for me but till then I have to look at plugs and see how things goes. Carburetor should be pretty close to where it should be but I need to now tune this thing to run on full manifold vacuum wich will help me with a nicer cleaner idle and that will have a effect on my plugs as well.

My cam has a tiny bit of overlap I think about 5 degrees at .050 but thats all. I will hook up my timing light Thursday and get things rolling from there. I want to do just one thing at a time as stated above. The missing problem was there before the spacer was put on too its just in the last month since it got warmer out it got to be more.

Also on the choke part is your motor running richer at 1500 rpm then with the choke cable pulled then when you just hold your gas pedal down at 1500 rpm then? I am a little confused on that one. I will only use my choke during the winter time period. Hoping to get some nice results from full manifold vacuum at idle. How do I know if I have a adjustable vacuum advance? I know they take a 3/32 allen wrench and turning it all the way out clockwise will give it the most amount of advance correct?

Even if i stick in an allen wrench will I still really even know if its that kind? If not no big deal I can pick one up at advance auto parts. I also got a msd street fire ignition box will that help me out as well?

Thanks again guys.
Eric
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  #35 (permalink)  
Old 04-13-2010, 04:15 PM
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Tuning

I ran a chassis dyno tuning both carbed and fuel injected engines, it isnt all that easy to be accurate. In those days we still used a co machine so the combination of the dyno and co reading was spot on. Watching the firing lines under load was extremely helpful as well. I later worked on a USAC midget race team and reading plugs running alchy is near impossible. You need an eye loupe and you actually observe the threads on the plug.
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  #36 (permalink)  
Old 04-13-2010, 04:33 PM
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Eric, reading your last post makes me feel you might be in a bit over your current skill level. Maybe you should get your dad to give you a bit more assistance with this project. I'm not sure but you may well be adjusting the dwell with an allen inside the distributor. If thats the case you are really going the wrong way to resolve your problems and should perhaps hold off till dad's around. As for the choke, think about the name..... choke. It reduces the amount of air allowed into the carb by restricting the opening. With a greater engine speed the air demand is increased while the air supply isn't so the fuel supply is amplified into the engine. Imagine the air pressure at sea level.... 14.7 lbs. In the center of the carb or the venturi area there is a much lower pressure with engine running, thats what the venturi does. Now imagine a small tube running from the fuel bowl to the venturi area. The fuel bowl has atmospheric pressure on the fuel so the pressure on the fuel pushes fuel down the tube to the lower pressure in the venturie area. Thats how fuel is delivered to the throat of the carb. The jet used is the restrictor in the tube that decides how much fuel is delivered. when you close the choke you actually lower the pressure in the venturi by restricting the air supply even greater causing a larger disparity between the too ends of the tube. This is easier with a chalk board but it's all I have at this point. So with all that being said, don't use the choke any more than absolutely needed. There is a automatic choke available for that carb, you might consider that as a possibleoption.
Bill
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  #37 (permalink)  
Old 04-13-2010, 05:17 PM
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This is turning into a really good discussion.

Bill, I'm enjoying your expertise. I have been tuning street and drag race cars
for nearly 35 years, no wide band or co readings. We use the track timers to
tune by. I work on three areas, idle quality, 60 foot times and 1/4 mile times.
Our run times are normally with-in 0.02 seconds from run to run, so its fairly
easy to get a feel for what it likes. Plugs are good for reading main jet air fuel
ratio for a couple of runs, after that they aren't much help, too many factors
could effect the readings. The plug porcelain on a well tuned drag race
engine is white. Here's the guide I use:

http://www.empirenet.com/pkelley2/sparkplugreading.html

Eric, this is good information on reading plugs, remember the plugs here
are from different operating conditions (all WOT) from yours and these
readings are taken with no idle time (click off at the finish line and pull
plug for reading).


Mertz, I need to correct my statement about reading plugs, it's useful and our
only look inside the combustion chamber. I have never seen anyone that
could look at a plug after street time and know for sure that the main jets
were X sizes too big or small. It's just not that easy.

Last edited by automotive breath; 04-13-2010 at 05:27 PM.
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  #38 (permalink)  
Old 04-13-2010, 05:33 PM
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eric,
different fixed vac adv units deliver different timing added curves/totals and different adjustable units have different curves/totals depending on the screw setting...

step #1 is find out where you are at "now" for how much is added...
(may well be just the right amount added where it is now set)
may well be to much to be used hooked to manifold

base + cent (all in) + vac adv (at high Hg no load) = total timing (typically anywhere from 46 to 53 degrees)

we know you base plus full cent is set for 34* so once you know the total timing just subtract 34 from the total tells you how much the vac adv is adding...

thursday read the timing total at 3500 and 4000
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  #39 (permalink)  
Old 04-13-2010, 05:51 PM
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Thanks, I am actually enjoying all this silliness. Working as a tuner when someone is paying a boat load per hour made me want to utilize all I had to get it right the first round. I nearly bought myself a dyno to open a pure performance tuning shop in my area. The carb laws are so tough anymore the fines would make it impossible so I go fishing instead. The newer computer driven systems require the wide band stuff to get them right, people want them to do more than go like hell for a minute, can you imagine that. The sbc I'm putting together will do around 475/ 500 but the torque is what I'm after in this project so I'm shooting for a lower hp with a ton of torque. You know smaller tube headers, 202 closed chamber heads etc. The car will be around 2100 lbs so it should scare the crap out of the new owner and never see over 6000. Retirement is a terrible thing, I just can't afford having this much spare time..LOL
Bill
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  #40 (permalink)  
Old 04-13-2010, 06:02 PM
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Quote:
Originally Posted by Bill Adkins
...The sbc I'm putting together will do around 475/ 500...
...the car will be around 2100 lbs...l
The power to weight ratio is what's scary! Best suited for straight line driving.

What you think about the plug reading link?
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  #41 (permalink)  
Old 04-13-2010, 06:12 PM
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The link, I love it. It's saved in the computer ..... along with a hundred other hot rod links. I still feel it may be a tad beyond a number of folks here as well as other boards but it's way kool. I try to give people stuff thats easily digestible that leaves little to enterpritation . It's so easy to blow a other wise perfect engine up over a lack of understanding and I always felt I worked for the car, the owner just payed the bill......LOL
Bill
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  #42 (permalink)  
Old 04-13-2010, 06:41 PM
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Quote:
Originally Posted by Bill Adkins
... it may be a tad beyond a number of folks here...
The number one problem people are having on this site is fouled spark
plugs, it must sweeping the nation!
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  #43 (permalink)  
Old 04-13-2010, 06:48 PM
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It's not difficult to determine that plugs are fouled, the secret is from what. If people left engine mods to those that are professionals there would be a lot less problems due to changes made. As a rule a set of cylinder heads with a matching carb for street driving shouldn't need a ton of tweeking but when an engine is built from pictures in a catalogue then Katey bar the door cause all hell is on the way. I usually ask someone what it is they're looking for or what they want it to do. Once that is decided then the process begins. Anyway its a lot more fun than politics
Bill
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  #44 (permalink)  
Old 04-13-2010, 10:22 PM
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Bill, with a combination like Eric's, how would you determine how
much ignition advance it needs at idle and at cruse RPM?
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Old 04-14-2010, 12:14 AM
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He has a sbc with closed chamber heads/ 64cc and I would imagine flat top pistons so cr should be between 10 and 11/ 1. 89 octane would work with 35 total lead. Depending on the distributor set up he will likely start around 15 btdc at idle. I like to bring centrifugal in early as it brings up the torque curve, Most any high output engine has a poor vacuum signal so vacum advance looses some of its effect. Maybe 10 degrees I would imagine but to be honest on engines I have built for performance I don't commonly use a vac advance unit. I regret having sold my distributor machine yrs back. I also spent near 15 yrs running sand rails in our winter in the desert and built a lot of different small displacement engines for the group I ran with.
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