locked out timing/any downsides on street cars?

[wjnielsen]

Hey Troy,

I ain't sayin' fine tuning doesn't get fine results... just that the big gains come quick, and easy and that you start working harder for smaller results as you get closer to 'ideal'.

Now, if we say that I get everything set up 'ideal' on my BBM on a 62 degree Seattle morning in May with 50% humidity, that might have my timing set at 36 degrees from 4500-6000 RPM where she'll actually spend time.

But that 36 degrees will probably not be ideal on an August afternoon in Atlanta... and might not even be ideal back later on that day in Seattle, after 3:30 PM when the temp has gone up to 80.

My point is that the gains start getting smaller, and unless you're running a very competitive class (and probably have budget for data logging, etc)...a lot of us guys might find bigger gains for less work by just setting the timing to a conservative value, and start looking elsewhere for the next few hundredths.

-Bill

[Troy Patterson]

Awe shucks...your on to it..
Yep,im the Aussie secret agent for them..

Oh right, what was I thinking. Never mind.


@ wjnielsen - gotcha. I am sometimes surprised at the gain from one or two degrees of timing on some engines while others I can swing the distributor as much as five degrees and realize no change in performance. I've seen a one jet difference on the dyno make twenty horsepower. Very surprising.

Troy Patterson TMPCarbs.net TMP Carbs

[MadBill]

When a wide range of spark or fuel makes little difference, I usually assume the cylinders are unbalanced in received AFR or required MBT SA, i.e., as one or two are benefiting, a couple of others are losing...

[Troy Patterson]

When a wide range of spark or fuel makes little difference, I usually assume the cylinders are unbalanced in received AFR or required MBT SA, i.e., as one or two are benefiting, a couple of others are losing...

Good point MadBill, hate those dual plane intakes and widely uneven header lengths.

Troy Patterson TMPCarbs.net TMP Carbs

[GREG K]

The threads that I have been writing in this post have not been telling you how to set up your idle timing and fuel settings, but rather they have been explaining how the engine works when you advance and lean a mixture at the same time, that’s all.

You generally don’t set up an idle on a performance engine like that, as like I said in one of them, it won’t take a load.

Generally with performance engines you have to deliver more fuel into the cylinders at idle because performance engines are not very efficient at burning a fuel load. This is not always associated with the word “performance”, but rather the way in which people set these types of engines up.
When you use a holley on a performance engine that has reduced manifold vacuum, you generally have to deliver more fuel at idle to get the gassed environment around the plug at firing time acceptable.Reduced manifold vacuum(like you get with large overlap) reduces the gassed fuel in the cylinder and increases the liquid fuel in the cylinder. This is not the way that is really desirable, as the methodology that you should try and use is one that increases the QUAILITY of the fuel load to the plug not the QUANTITY. When you increase the quantity, to get the gassed environment acceptable (by burning the light HC’s) you waste energy via fuel out the cylinder, and glaze bores and stuff…all bad stuff..
When you increase the quality of the fuel load to the cylinder you don’t waste as much fuel, but rather impart more energy into the crank, and not out the pipes.
Whenever you are setting up the idle fuel it is important to realise that you tune the ignition timing and the fuel load together, not one without the other.

So when you found that your timing had advanced itself and the engine didn’t like a load or didn’t run right, its because the cylinders had less vaporisation time of the fuel load. The cylinder has LESS vaporisation time, on top of the fact THAT IT DON’T HAVE MUCH TO BEGIN WITH AS AN ENGINE AT IDLE DON’T HAVE MUCH TO COMPRESS WITH THE THROTTLE BLADES SHUT.YOU DON’T GET MUCH COMPRESSION ENERGY. sorry ,the caps locked on.
Just stick your gas bench on ,tune the different ways and you will see what goes out the pipe with each tuning method,then see how that relates to what the engine likes and how it can take a load or not.

When you change the ignition timing point you are changing the amount of input energy that goes into the fuel load that’s in the cylinder. When you add or take timing away without doing much else, you are either making the vaporisation percentage of the fuel load higher or lower.
This is how the ignition timing and the fuel mixture are related.
The relationship between the two is very close.

When you choose the method of fuel QUAILITY you need to work with the t-slot fuel.It takes much time and effort on the engine,that’s why carbs out of the box untuned on the engine are generally not as good.The t-slot fuel effects the engine right through the rpm range.

[Shrinker]

To be at the top of the "tuning" game and a consistent front runner in competition one can't make assumptions.

Troy Patterson TMPCarbs.net TMP Carbs

And that gentlemen is why I have measured the gas content of our drag car engine idling with extremely lean AFR and advanced timing. I measured the gases 4 feet up from the collector outlet. I set the butterflys LIGHT TIGHT, it wouldn't run, I then proceeded to lean the IFR's and altered the T-slots so that it would run at 28 degrees timing and the engine could not be slowed down below 4000 rpm. I then measured the exhaust to find out where it was getting its air to run at such high Rpm from, and low and behold there was 18% oxygen concentration in the exhaust. The overlap of the cam was feeding the intake manifold with Oxygen because the mixture had insufficient fuel in the cylinder to reduce the O2 concentration to an unusable level and the atmosphere was also supplying the engine from the exhaust outlet . I ragged the end of the collector and the engine slowed dramatically but I couldn't get a good enough seal to stop it in the time I was willing to spend under the car. All 8 cylinders fed into the one outlet. The engine ran as though it had a standard camshaft with very smooth and perfectly even combustion, but it wouldn't pull a load of any kind.

[GMH323ci]

probably little off topic but there is some tuning pros on this thread i would like to ask a question,

i just got my LM2 single sensor to try tune/learn more about my own engine.

i just put the sensor in one of the tail pipes and at idle about 1100-1200rpm i have 20-21 afr's. showing lean, un burnt mixtures due to cam?
when i pick up rpm a little it goes about 12.5 afr's. rich

how do you tune a 14.7 afr idle if you have to much cam/overlap?

can i mount sensor in my x pipe to read both banks? is it ok to just put it in one pipe? and where is best, near collector?

cam is 252 @ 50 in a 323ci and i also have ignition locked at 32deg

[F-BIRD'88]

If the sensor is too close to the end of the pipe the afr will show a false lean as air is drawn in(and out) of the pipe at idle.

[MadBill]

To be at the top of the "tuning" game and a consistent front runner in competition one can't make assumptions.

Troy Patterson TMPCarbs.net TMP Carbs

And that gentlemen is why I have measured the gas content of our drag car engine idling with extremely lean AFR and advanced timing. I measured the gases 4 feet up from the collector outlet. I set the butterflys LIGHT TIGHT, it wouldn't run, I then proceeded to lean the IFR's and altered the T-slots so that it would run at 28 degrees timing and the engine could not be slowed down below 4000 rpm. I then measured the exhaust to find out where it was getting its air to run at such high Rpm from, and low and behold there was 18% oxygen concentration in the exhaust. The overlap of the cam was feeding the intake manifold with Oxygen because the mixture had insufficient fuel in the cylinder to reduce the O2 concentration to an unusable level and the atmosphere was also supplying the engine from the exhaust outlet . I ragged the end of the collector and the engine slowed dramatically but I couldn't get a good enough seal to stop it in the time I was willing to spend under the car. All 8 cylinders fed into the one outlet. The engine ran as though it had a standard camshaft with very smooth and perfectly even combustion, but it wouldn't pull a load of any kind.

So, just to be clear here Shrinker, you're saying that with the right IFRs, T-Slots, spark timing, etc. and with the carb butterflies virtually sealed off, you can run an engine to over 4,000 RPM, operating strictly on air sucked in through the exhaust system during the valve overlap period?

At 4,000 RPM, the engine rotates once in 0.0150 sec. and if the effective flow period of the overlap is 60°, the time available to pull fresh air from the open collector is 60/360 = 2.5 ms., so to arrive in time, the velocity over a distance of 4' will be 4/0.0025 = 1,600 ft./sec. That's about Mach 1.5.

Wow. What kind of manifold vacuum does that take?

(On second thought, perhaps that 18% O2 reading is not from 'slugs' of pure atmosphere being drawn in, but rather from a uniform mix of in-cylinder exhaust gas, in which case the engine is using only 3/21 or 15% of the available O2, the equivalent of operating on air at 98:1 AFR...)

[Matt Gruber]

some intake gaskets fail to seal, and those owners often complain of excessive oil use.
BUT, couldn't some suck air and rev pretty high?

[Shrinker]

Bill, If the atmosphere inside the pipe is 18% O2 and its close enough to the head then it doesn't have to be mach whatever to feed the inlet. I did exactly what i posted, I worked for a day trying to understand things about the engine tuning and modifying the carbys and then I had to repair them after. Why dont you go do it yourself, you could measure the air flow with your dyno's meter. I dont have one. There has to be air feeding the engine from the T-slot circuit so you have to take that small amount into account but its not enough to run the engine at 4000. But the important thing is I couldnt slow the engine down, the only way to slow it down was to enrich-en it back up,like normal.

I'm just telling everyone that at least I have done these things. How many others have? Own up please.

If you use a gas bench to take readings of engines running with hot cams and combustion problems you will find many examples of exhaust readings of 10% oxygen at no load say 2000 rpm with vast amounts of HC left over (8000+ PPM). Yes these engines need fixing, but my point is its not unusual to get a so called impossible burn if you only look at O2.
To do the test I did, you have to vaporize the fuel very fine and supply a lean than stoich mixture, the sum overall of the cylinder is partly intake feed and partly exhaust feed. If the cylinder used all the fuel the O2 content would be much less but it wasn't on my test. I dont know if a cylinder failed to fire on my test, I didnt have a scope at the time, Its possible a missfire could resupply O2 to the intake, All sorts of possibilities exist. I could only hear that it ran very smooth.
The fact is there was 18% O2 near the start of the collector on an engine running very lean at 4000RPM with 28 degrees advance with a 289@.050" cam, 15:1 comp, VP C14+ fuel.

The reason why I posted this in this thread is the only way to slow down that engine in the test without reducing the timing was to richen it up. This may not be the best technique for some street engines. Advanced timing at idle causes the engine to require a different mixture, depending upon individual circumstances that may not be best for engine wear or response.

[GMH323ci]

If the sensor is too close to the end of the pipe the afr will show a false lean as air is drawn in(and out) of the pipe at idle.

POSSIBLE, but i also put it in the tail pipe of the family car and reading was 14.7 exactly

[dieselgeek]

If the sensor is too close to the end of the pipe the afr will show a false lean as air is drawn in(and out) of the pipe at idle.

POSSIBLE, but i also put it in the tail pipe of the family car and reading was 14.7 exactly

Family car will have a more restrictive exhaust - what you are seeing is 100% to be expected and I see it all the time. What you can do is make a tailpipe extension with a ltitle restriction to find the right AFR at idle but, what I usually do, is tune "by ear" and maximize vacuum at idle and just use the wideband sensor for tuning when under load.

I used my first LM2 this weekend, and found it to be a real nice piece. The logging feature worked great for us.

-Scott