Disc Brake Hold Off & Prop Valves
hello again, i know its running rich because the plugs are fuel fouled and the exhaust will run you out the the shop in about 5 minutes. lol
OK now we are getting somewhere.
That stink,
if it burns your eyes,
is NOT running rich; NOT rich.
You will not get rid of it by doing any carb adjustment, by itself.
Well actually it is rich but not for the reason you might think.
So my next question is this;
does the stink burn your eyes?
refresh your screen, I am editing as I go.
you said;
Full MSD ignition. Set at 32 degrees advance @2000 rpm. Full tub w/cage, 4 wheel disc break. It's a complete street car.
Do a compression test and post up the results.
What is the coolant temperature at idle?
What is your local elevation?
Do you recall what the installed centerline of the 292cam might be?
Is that the 292/292...... the 108Lsa cam?
Are your roller rockers adjustable?
What sparkplugs are in it?
Do you recall what the ring-gaps were set to? Does the engine mysteriously lose oil level?
Are you running a PCV?
As for the PCV System;
You MUST run a PCV plumbed to the underside of, and between, the Primary Throttle blades. If your carb is NOT set up for this, and it was mine, I would drill and tap the intake as close to that position as I could.
If your carb has a port at the back, between the Secondaries, I suppose you could, with a 4-corner carb use that, and since I have never run a 4-corner, I guess I would try it.
But,
with a regular carb, my experience is this;
Running the PCV off the back is guaranteed to make the idle-exhaust stink, as the rear cylinders run lean. The tendency is to richen the Primaries to get fuel back there, but now the Front cylinders run too rich. So you end up going from bad to worse. So I just never run that configuration.
Additionally I never run the Booster charge hose to just one of the rear cylinders.That charge hose, with the 292 cam is constantly shuttling air as the vacuum at low rpm is so low, so then whatever cylinder it is plumbed to is having it's airflow constantly being upset. You can plumb it to that rear port on the carb, if you have one there. If your carb does not have one back there, then drill and tap the intake PLENUM in/near that location. This will smooth the signal to the booster as well. DO NOT Tee the PCV and the Booster charge line together. Make sure your valve-cover Breather is well baffled in the cover and to avoid the mess on the VC at WOT, I run an enclosed-type breather with a fat breather hose on it looped up and over so any oil trying to get out, runs back into the breather and at shut down, drains back into the engine. If you are running the factory type air-cleaner housing, then use the factory system. But with a 292 cam you should be running fresh air from above the hood or from the front of the car, either works on the street.
The PCV is NOT an option.
If your engine is mysteriously losing oil level, with no visible external evidence, I can guarantee you that she is sending it out the tailpipes. You gotta fix this because more than half of the times that I run into burning eyes, that oil is a major contributor to the cause of it.
In some cases that oil loss is from fuel-wash on the cylinders from a too-rich low-speed, and/or Part Throttle circuit. To combat that, I run what some say is a too small MJ, but my 10.5 PV comes in early enough to cover the loss of fuel, and I never feel a lean hesitation. This strategy also gets me great fuel mileage in steady-state running.
To prove oil-burning just swab the inside of your Tailpipes. Do not confuse Soot from oily residue. I just taste it.
BTW
your tailpipes should not be sooty with the MSD ignition system.
Your tailpipes should NOT be black at all, rather tan to white-ish but not full-white. Black might be OK as long as it is not sooty. It should take a fair bit of pressure to swab blackness out on your fingertips.
Full-white is too lean and dangerously close to a melt-down.
Other things that can cause oil-burning are; the oilrings stuck in the grooves, tapered cylinder walls, out of round cylinder walls or gouges in the cylinder walls, baggy oil-ring gaps, lousy umbrella seals, and excessive cylinder oiling coming from the rod-jets. You do not need 20W50 oil either, 10W30 is just fine. The Second compression ring is NOT an oil-ring and does a lousy job of removing it off the walls. It's not even a good second compression ring,lol.
So if you are loosing oil, find out the cause and fix it. Nothing can really be done with the stinky exhaust until you have proved it ain't burning oil.
After that, yur not gonna like me, cuz you are gonna have to sacrifice some low-rpm timing.
I know, I know; all that timing makes the little 292-cammed 340 more peppy at lower rpms, but 32* at 2000rpm is just too much and way too early. And if you don't have a Vcan, or if it's hooked up to manifold vacuum. you are gonna like me even less.
From an earlier post;
Full MSD ignition. Set at 32 degrees advance @2000 rpm.
I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.
"" To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.
To get the cruise timing, I modified the V-can to 22* by filing the stops partly off. I think you can do this to any 70s V-can. My Eddy-headed 367 liked over 56* of cruise timing.
There, that will get you started.
Your 340 may, of course, have slightly different requirements. ""
This is the timing I ran on my 292/292/108, with excellent results.
You can argue all you like, lol, but the stink will not go away until the Idle-timing is down around 14* plus/minus 2*, AND the carb adjusted as per the Transfer-slot synchronization technique; BOTH together.
Now, like said, your 340 might be slightly different.
Here's how you can know that the low-speed circuit is right;
Number one; no more stinky exhaust, lol
2) after the warm up, you can put her in first gear and she will idle down to 550 while pulling herself and NOT get jumpy, until about 500rpm. If your 292-cammed 340 will not pull herself at 550 rpm in First gear with a Manual-trans, the low-speed circuit is not right. The first thing to try is
LESS idle-timing ! My 367 does that with 5 measely degrees of advance. The more advance that you give it, the more powerful the engine will become, and the power pulses will hammer the driveshaft and the car will get more and more jumpy until you are forced to clutch it, and start over.
3) with the car in first gear and rolling, she will take throttle right away with no stumble,hesitation, nor a sag of any kind. It may not take WOT, I'm not saying that, but you should be able to drive away briskly like it was an automatic.
4) you don't care what the plugs look like after idling all day. You have an MSD; if the fire goes out on the first spark, the MSD will just keep on relighting it. You cannot tune that cam to an AFR of any kind at idle, so let it be what it will be... If you keep leaning the idle out, to try to clean up the plugs, you will only create other issues.
Ok a brief explanation;
All Four-Stroke Internal combustion engines have exactly one best place for peak cylinder pressure to occur to put the most amount of energy into the crank. This is variously said to be 25 to 28 degrees AFTER TDC Compression. ALL your timing systems are, from the factory, or were before the smog era, designed to peak at that spot. Now, it is your job to find it, and design your ignition system to do it.
However, you cannot run that at Idle because your big fat 340 will be TOO powerful, the rpm will runaway on you.
Want proof?
Go out and warm up your engine, then grab the Distributor and start advancing it without checking the timing. Keep advancing it until the rpm no longer rises. NOW check the timing at the highest rpm. What did you get? I have seen numbers deep into the 30s and even into the 40s and occasionally into the 50s if the rpm runs over 2200rpm. Put your timing back.
Whatever number you got, that is the amount of advance your engine was HAPPY about at whatever the rpm got up to, AND in all likelihood was in the window of creating peak pressure at the magic 25 to 28 degrees AFTER TDC. But obviously, you cannot drive it like that. But you can engineer your timing systems to get there at that rpm and the engine will be very very peppy there and get great fuel economy at that peak pressure setting.
If you advance the timing more from there, the peak pressure will arrive too early and slam the piston/rod onto the crank , doing a lotta pushing but less actual work. This is hard on parts and in some cases produces audible detonation which if allowed to continue will break parts.
If retard the timing from there; the engine will not achieve it's full potential, as the expanding gasses chase after the descending piston. You can use this to your advantage to soften the power at low-rpm, and specifically at idle. For those that have automatics and low-stall convertors, such a powerful idle only serves to cause the trans to bang when going into gear, and the engine immediately loses rpm as the TC drags it down.
The point is this, ask 20 guys where to set the idle-timing of your 292 cammed 340 and they will almost invariably give you a high numberr and then you spend the rest of the summer trying to tune it........... like I did. Forget that chit.
Let the engine tell you what the timing should be, by setting the T-slot sync, and using timing to set the rpm. Just retard the timing from your 20* until the engine stalls and then give some back, lol. With a manual trans, that's all there is to it. wait, you have a 4-speed right? Lemmee go check.
Oh no! you said 3500 stall, lol. Well then
who cares about the idle-timing........ so long as she doesn't bang or stall going into gear..... right?
On the street .....Wrong!
You still want the low-speed operation below stall, to be enjoyable; so everything I have said to this point still applies, except you can run more low-speed timing because, the engine is never required to be under full-load below stall, so detonation is less of an issue. BUT, the idle is still pretty important, so basically, nothing much has changed.
So how do you get that "more low-speed timing? "
That's what the Vacuum advance is for.
After your basic advances are established you can use the V-can to fill in the rest, below stall .
Go out and map your advance curve, having disconnected the Vacuum advance. Just take the rpm up in 400rpm steps and record the amounts. You need to do this so that when you make changes, you will know if you are going in the right direction.
Next repeat the test with the V-can back on line.
Next repeat the exercise, still with the Vcan on line, but just twist the distributor at say 2000rpm, and keep it there while simultaneously advancing the timing.This will require you to close the throttle as you go.
When the rpm no longer climbs from 2000, read the timing and record it. Then repeat this at every 400 rpm until you hit 3600rpm.
Now plot the numbers on graph paper, and compare the results.
The first set is what you got for Power-timing.
the Second set, is what the engine can muster for Part-Throttle.
The Third set is what the engine wants, with no load on it. How close are the lines?
After about 3600 all open-chambered iron-headed SBMs want about the same POWER TIMING of ~36*, while closed-chamber alloy-heads seem to be happy with 2 to 4 degrees less.
Your job, as the tuner, is to try to give the engine what she wants for as many conditions as you can. Your job is NOT to force timing on her. On the street you will not, by the seat of your pants, feel 3* short of optimum, so don't sweat the shortage of 3 degrees. Rather be alarmed if too much timing causes detonation. This must not be allowed.
Here's the bottom line;
I don't have a dyno, but I have watched dozens and dozens of tests, and the result seems to always be the same. The last two or three degrees at WOT, are worth no more than 7hp at the peak! Less is the norm. How often, on the street, is your 292-cammed 340, gonna be at WOT AT ~5300, in a gear that does not spin your tires. If the tires are spinning, you already have more power than the suspension and tires can handle.... so is 7 hp gonna ruin your day?
I hardly think so, lol.
BTW
5300@WOT, with 3.55s is about 45mph in First, maybe77 in Second, maybe 112 in DRive, lol, with 27" tires. In other words, for most of us, when the tires stop spinning, we have already been speeding for quite a while. So really, First gear is the only gear that is gonna run up to the PowerPeak, and the tires are usually still spinning, so no you will never miss those 7 hp.
So having come to that assessment, you can confidently build your timing curve to add the amount of PowerTiming, to whatever Idle-timing your engine is telling you to try. Suppose the engine want 14* and the PowerTiming is gonna be 34*; this means that the mechanical system has to provide 34 less 14 = 20* How easy is that!
The next part is not as easy, and goes back to the above quote, which I will repeat here;
I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.
"" To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.
Once you have modified your distributor, you repeat the "What have I got Test" and plot the new no-load numbers then compare them to what the engine wants. Are you closer? There may be some rpms that you are and others may not be close at all, but what you are looking for is the shape of the existing curve to the desired curve. Then you bring your V-can back on line and see how close you are to the desired line, then modify IT ! lol, to get as close as you can.
This is a lot of work and takes a lot of time and you really only want to do it once, so it behooves you to get the idle right before you do anything else..... I gotta tell ya, nothing gets me going than hearing a car idling around the parking lot, with a great tune in it, cuz I know how hard that can be.
And when it mine doing that with a 4-speed, well, I can safely say, I like that tune, and I like that AJ guy, lol.
Ok that's it for today, I got some chores to do.
refresh your screen one last time.