1903 Won't Respond to Tip-In Procedure

[bry593]

This truck is my daily driver and I have put some miles on it since the beginning of this thread.  Noticed this morning my sticky throttle seems to be wearing in.  One less thing, eh?

New vac advance should arrive in a couple of days. 

[Cliff Ruggles]

"K" series rods are next to useless for tuning with the APT system. 

We offer a full tapered 45C instead, which tapers from .045" all the way to .026".

"K" rods only have .005" taper on the entire supper section of the rods then "step" clear down to .026".  If you look at where they start at in the actual orifice of the jets you'll see that you have very little actual room for adjustments for the entire travel of the rod with the APT screw.

When tuning the primary side determine the jet size FIRST.  Do this by climbing a hill or steep grade in a higher gear w/o the secondaries.  Once you nail down the correct jet size then use the APT for light load/part throttle tuning.

For the later SMAB APT carbs with very few exceptions .036" tipped primary rods will be the best choice.  I have tuned a few with .026" rods and dropped the main jet size down about 4-5 numbers to sort of split the difference between using .036" and .026" tipped rods, with good results.

Even with that said I only took that approach before we had the 50C rods made and  I didn't have a decent set of "M" series rods available for that particular build......

[bry593]

Thanks Cliff.  I will take that into consideration if my vacuum advance mods are insufficient to cure the ping.  I know that with the pedal to the metal, the vac should be all out, but I'm hoping for a miracle

Tonight I checked my initial timing and checked your vacuum advance curve.  Turns out, I must have done a parking lot adjustment because my initial was 12 degrees and was supposed to be 10.

Here is your curve as tested using a Mighty Vac and dial-back timing light:

4 in Hg = 0
6 in Hg = 5
8 in Hg = 10
10 in Hg = 18
12 in Hg = 18
14 in Hg = 18

So basically, you have a 9 degree that starts at 6 in Hg and is all in by 10.  I need the advance to be all in closer to 14 since my engine produces 14-22 at typical cruise loads.  Actually, a better way of looking at it is that I need the vac advance to start falling out at 12-14.  Don't want that advance under load.  This cam and compression is prone to detonation.  My new advance should arrive in a couple days and I'll run the same test on it.

Just for posterity, my current total cruise (2450ish rpm @ 75 mph) is 12 + 18 + 16 = 46 crank degrees.

[bry593]

Edit:  The Mighty Vac might read low by 1 in Hg.  I calibrated against my vacuum gauge and there was 1 unit difference.  Even so, that would mean your pod starts at 7 in Hg and is all in by 11.

If you didn't notice the vast majority of the time your engine is making enough vacuum to both apply the vacuum advance and the power piston would be DOWN no matter what power piston spring you'd have in it.

"K" rods only have .005" taper on the entire supper section of the rods then "step" clear down to .026".  If you look at where they start at in the actual orifice of the jets you'll see that you have very little actual room for adjustments for the entire travel of the rod with the APT screw.[\quote]

[bry593]

Edit:  The Mighty Vac might read low by 1 in Hg.  I calibrated against my vacuum gauge and there was 1 unit difference.  Even so, that would mean your pod starts at 7 in Hg and is all in by 11.

If you didn't notice the vast majority of the time your engine is making enough vacuum to both apply the vacuum advance and the power piston would be DOWN no matter what power piston spring you'd have in it.

Yes, this engine makes great vacuum.  But, it is a '71 3/4 ton truck with 76lb wheel assemblies and a 4.10 differential (locker, 10-1/8 ring gear).  It likes a bit of primary taking off.  Not unusual to drop to 10 in Hg.  I have the stiffest power piston spring + a brass shim. 

"K" rods only have .005" taper on the entire supper section of the rods then "step" clear down to .026".  If you look at where they start at in the actual orifice of the jets you'll see that you have very little actual room for adjustments for the entire travel of the rod with the APT screw.

Yes, similar to the 50M rods that come stock in the Edelbrock are 2-step.  If you hit the 6-10 in Hg range, my truck would suddenly come alive well before the 2ndys.  It is obvious when it reaches the step down and continuous length of .036".  Problem is that it is max primary flow range, and pre-WOT vacuum signal.  If you are towing and reduce vacuum enough to lift the needles to the step down, gas mileage is over... 

Please remember my application is not a hot rod.  It is a daily driver, 1971 truck that I can tow a tractor with when needed.

[Cliff Ruggles]

My gauge shows them just a tad higher as well, but I've dropped it enough times over the last 40 years it may not be dead nuts on the money either.

In any case I've been using them for decades on thousands of applications and never once had to switch to something else to cure any type of "tuning issue" related to ping.

Your problems are fundamental more than tuning, so efforts to split hairs with these things are more a "crutch" fix than anything else.

Not trying to be critical or put a big black cloud over the engine build, believe me I've been EXACTLY where you are before.

There are "camps" on the NET that advocate tight LSA and early closing intake, and some of those folks have names that are household words when it comes to engine building and parts selection. 

I don't give a chit about all that, but can tell you from doing this for a living for over 20 years full time and another 20 something years part time I have NEVER once been overly impressed with a relatively "small" camshaft on a tight LSA in a well thought out engine build.

Overlap is NOT your friend with these things, nor is early closing intake. 

Most of this "trend" started quite a while back when some very popular folks started advocating LOWERING compression to some sort of proverbial "brick wall" of 9.5 to 1.  At the same time they would recommend a short seat timing cam on a tight LSA to bring back the lost power.  I just about want to puke every time someone calls up telling me that's exactly what they've done with their "new" engine build and they are asking me to crawl thru the phone to fix it....not overly impressive for power, pings, etc, etc.

Yes, when you LOWER compression you LOOSE power (torque) at every RPM, all else being equal.  Problem is that tight LSA narrows up the power curve and makes higher peak power and it occurs earlier in the RPM range.  That move INCREASES dynamic compression with much higher "spike" in cylinder pressure down where the engine is much better at cylinder filling.

So when we go that direction we INCREASE octane requirements as peak VE it higher and sooner.  Peak VE is the point in the RPM range where detonation is most likely to occur.  What screws the pooch here is that IF you are evaluating engine power by the "seat of your pants" those builds superficially "feel" pretty strong, responsive, etc.  All you are feeling is throwing a LOT of power at you right off idle and in a narrow RPM range.  So that little "shot of nitrous" feeling fools the driver into thinking they have improved things and the engine is now making more power.  A higher compression build with tight quench, larger cam, wider LSA, later intake closing, etc will have a broad/flat/smooth power curve more like a locomotive.  Since there is not quick "spike" or rush of power anyplace it will be evaluated as not as good, when in reality the engine is making excellent average power over a broad RPOM range.  So the butt-meter tells the driver it's just not as good.

If we simply go to a larger cam and wider LSA, we flatten up the power curve and push peak power higher.  This does two things, lowers cylinder pressure over the RPM range and lowers octane requirements at the same time.  Since we've pushed VE higher, past that in a N/A engine it simply can't fill the cylinders better (more cycles per seconds) so no worry about ping past that point.

.......continued

[Cliff Ruggles]

As it relates to what you are doing here a recent customer called me for carb parts for his "new" engine build.  454 from a truck or motorhome, compression raised to a bit over 9 to 1.  Application is a HD truck mostly heavy work, towing, etc.

I asked about cam choice and he said that they had a custom cam ground on a really tight LSA, like 106 if memory serves me correctly, with the ICL at something like 100 or 102.  I said to myself WTF???  Being a nice guy and not wanting to be critical of others I didn't say much but knew it wouldn't be a good end result.  I did ask a little about it and got some long winded response about how articles in the "high performance" magazines from a "guru" with these things goes that direction and those engine make great power, walk on water, leap tall buildings better, blah, blah, blah.

Well, guess what......that customer is having all sorts of tuning issues and I've had to spend a good portion of my life trying to crawl thru the phone to fix them in recent weeks.  It's really not a bad thing for me, I get to sell MORE parts to help "crutch" tune a poor engine combination!.......FWIW......Cliff

[bry593]

Cliff,

Your 45"Custom" rod might work okay considering I lifted the 50C rods a bit to cure my cold weather lean hesitation.  In other words, I wasn't cruising at .050" diameter. 

%Change in fuel from 50C to 45C rods:
Rod   Jet           Cruise Rod     WOT Rod   Cruise Area   WOT Area   Cruise %   WOT %
50C    0.074      0.050            0.036        0.0023     0.0033      
45C    0.072      0.045            0.026        0.0025     0.0035            6.15%   7.85%
45C    0.073      0.045            0.026        0.0026     0.0037          11.02%   11.32%

I assume your 45C rod is a repop of the 45J? 

Most J rods are not available anymore.  At least not in the size I am considering.
45J 7043545 SMOOTH SINGLE TAPER TO .026
46J 7043546 SMOOTH SINGLE TAPER TO .026
49J 7043549 SMOOTH SINGLE TAPER TO .026

Some K rods are still available, but the step to a continuous .026 presents efficiency issues:
45K 17051345 SINGLE TAPER (0.045 - 0.039) & STEP TO .026
46K 17051346 SINGLE TAPER (0.046 - 0.040) & STEP TO .026
47K 17051347 SINGLE TAPER (0.047 - 0.041) & STEP TO .026
48K 17051348 SINGLE TAPER (0.048 - 0.042) & STEP TO .026
49K 17051349 SINGLE TAPER (0.049 - 0.043) & STEP TO .026
50K 17051350 SINGLE TAPER (0.050 - 0.044) & STEP TO .026

I was thinking I could probably keep the needles from rising to the step in typical day to day driving by going to a slightly less stiff power piston spring.  Maybe target half throttle load or something like that.

[Cliff Ruggles]

The 45C really aren't a "re-pop" of anything.  I had them made to taper much like "J" rods continuous from .045" down to .026" tips.

They have been selling very well.

As mentioned earlier "K" series rods are pretty much useless for APT tuning.  Right to start with the very top portion of the tapered section is in the actual orifice of the jet.  You really only get a few thou of metering area to work with using them.

I have many hundreds of used "K" rods here, never use them for any reason and just toss them in a drawer......

[bry593]

Swapped in the VC-217/VC1831/AR7 and measured the advance curve.  Have to say, it looks almost like your advance at the beginning, just seems to have a bit more travel for more total advance.

4 in Hg = 0
7 in Hg = 2
9 in Hg = 10
11 in Hg = 17
14 in Hg = 23 Max crank (11.5 distributor)

This fairly matches advertised spec: starts @ 6-8 in-Hg, 12 @ 14-16.  It is Standard Motor brand.

Your vacuum advance was marked VC-234/DV1862/AR31, and had the following curve (corrected by 1" Hg from previous post).

4 in Hg = 0
7 in Hg = 5
9 in Hg = 10
11 in Hg = 18 Max crank (9 distributor)

This VC-234 does not seem to follow advertised spec:  starts @ 2-4 in-Hg, 8 @ 6-8. 

Good news!  No more ping in the primaries.  Bad news, I have detonation on the 2ndys.  Oddly, it seems my 2ndys are delayed about 2-3 secs.  I don't recall a delay like this previously.  2ndy ping with rich AX rods, not helped by the Edelbrock "S" hanger.  That thing rides low.

Seems to want more primary WOT.  Maybe that is the cause of the seemed delay.  Not running as strong as it was when it was flooding out.  At that time, it ran through the secondaries fairly seamlessly.  Don't remember which needles I had in it at that time, maybe the 50M step needles.

[Cliff Ruggles]

Basic tuning guidelines and I've covered this on here and other Forums a few times.

Start out with known "recipes" for N/A engine combo's.  What we need to do first is to get close so the vehicle drives well without any detonation anyplace.  Detonation, especially at heavy or full load will damage or destroy the best engine build out there.

Tune JET size on the primary side first.  This assumes your "recipe" for idle/off idle fuel is where it needs to be.

Do this by climbing some steep grades/hills in higher gears w/o downshifting and without the secondaries.

Once you determine the most ideal jet size leave it alone, at least till much later in the equation and most likely you won't need to make any changes.

If you are also doing some distributor tuning tune TOTAL TIMING first.  Make sure the engine does not ping under any type of heavy load as this can damage the rod bearings, piston rings, piston ring lands, etc.

I like to start out a bit "fat" on the secondary side but may lean that up later.  Being a bit rich is always better than lean when it comes to heavy and WOT operation.

Anyhow, tune the APT system next.  Initially you want to start out a bit lean or rods pretty low in the jets then sneak up on the most ideal setting.  This part of the tuning may take several tanks of fuel and driving in various conditions to nail things down.  I may do some vacuum advance tuning here as well in later stages, but initially get the best results that you can.

Realize when tuning in the "normal" driving range that superficially a lean setting may show a slight improvement in MPG's, but overall I've found being lean on the primary side of the carb requires more throttle angle in many driving scenarios than it would if things were a little richer and overall everything else suffers.  Remember that the basic laws of physics apply here and it takes a given amount of energy to accomplish a specific task.

For WOT testing it is difficult if not near impossible to do it "by the seat of your pants".  It's even worse with some vehicles if they have poor traction as spinning tires flaws all testing.  It really helps here to use a dyno (engine initially) then the drag strip or some sort of timed/distance thing to real nail down the best tune.  Weather, head wind, air quality (DA), slight uphill/downhill grade and even how much weight is in the vehicle effect this testing pretty dramatically so once you get close it may take some time to nail down the best settings.

Continued.....

[Cliff Ruggles]

For the distributor you need to nail down initial and total timing.  Some engines will not tolerate a lot of initial timing or they will "buck" the starter on a hot restart.  So after you determine best total timing you may have to "adjust" the mechanical spark curve some if the initial ends up high enough it causes restart problems.

For spark curve I have never found to date that a super-quick mechanical curve getting ALL the timing in early works well for a well thought out engine build.  Engines with optimum compression for pump gas with well chosen cams and good flowing heads typically don't like, want, need or respond well to a lot of timing right to start with, nor will they like a lot of it early in the RPM range.

For vacuum advance, with a well thought out efficient engine build I can't remember ever going past about 14 degrees VA timing and most are fine with a bit less.  If you have a "low" compression engine and put a "hefty" cam in it forget the last statements, it's going to need a lot of timing everyplace to make up for poor dynamic compression and poor combustion efficiency.

Anyhow, this particular engine combo has a small cam in it and tight LSA.  This will spike cylinder pressure pretty high and early in the RPM range.  Unlikely you'll need to throw a lot of timing at it anyplace, even at light engine load.

For "basic" distributor numbers I usually start out with around 9-11 degrees of mechanical advance 18-22 at the crank.  A good starting point for initial timing is usually around 10-12 degrees so we'll be in the 28-34 total range right off the bench.  I usually set the VA up for around 10-14 and work from there.  The mechanical advance needs to start right off idle, but NOTHING in at idle speed or idle tuning will be difficult if not near impossible.

I'll add here that most of these "new" shiny billet offshore HEI's are HORRIBLE for that sort of thing to a point where I refuse to work on them here in the shop.  Many have low quality center cams/weights and the relationship between those parts has been "adjusted" to a point where by the time I put enough spring tension in them to keep some timing out at idle they delay too far in the RPM range for start and stop points with the advance curve.  Not tying to put a big black cloud over all of those parts, but quite a few I've seen here are JUNK and if you have good luck with them I'm happy for you.  I'll also note here that we don't know what old car bumpers the Chinese melted down any particular day to cast the gears from and I've seen enough of them chewed to nothing in 200 miles or so to NEVER want one in any of my engines!

One to better things.  So some good basic numbers for N/A engines will be 10-14 initial timing.  18-22 more mechanical, and 10-14 from the vacuum advance.   This puts total timing around 28-34 degrees and around 40-48 at cruise, or potentially that much depending on your exact cruise RPM and when the mechanical curve reaches full advance.  I like to see 2800-3200rpms for full mechanical advance with most of these engines.

Continued......

[Cliff Ruggles]

The above numbers have served me very well for decades.  I'd add here that I tune for a living, and still open up a couple Saturdays a month for custom tuning.  I've had vehicle brought here from as far as 2800 miles one way, but most are 200 or less.  It's ALWAYS the same thing, and fixing the issues are to go into the carb and distributor, usually the distributor first.  I yank out the POS MrGasket or other crappy spring/weight kit (EVERYONE buys that junk for some reason), get the distributor up to par then move on to the carb.  I'm about 98 percent successful to date, the few I couldn't fix I had to "crutch" but still got them to work OK.  The ones I couldn't nail down, guess what?  They had short seat timing cams in them on pretty tight LSA's and to much static compression for the CID and cam choice.......FWIW.......

[bry593]

Correct, Chinese distributors are junk.  The weights have no stop and it will advance to the moon.  I only use GM distributors and this one has the nice #41 weights. 

Agreed, aftermarket curve kits are crap.  Not sure why they didn't simply copy the original GM design including the correct size bushings.  Anyway, I steer clear of aftermarket everything when possible.

My total current cruise timing is:  10 + 16 + 23 = 49.   It can go a little higher since my mechanical is not "all-in" at 2400.

If I do encounter kick-back during hot start, a switch from manifold to ported vacuum would resolve it.

[Cliff Ruggles]

There isn't enough vacuum cranking to overcome the spring tension in any VA I've ever seen, so NOT part of the tuning for "base" timing.

As for "aftermarket" distributors the readers should know that there is NOTHING waiting for you with any of them, aside from not having to replace points every 20,000 miles or so.

I've dyno'd MSD billet distributors back to back against my stock HEI with a factory "990" module and coil and they gain NOTHING anyplace.  Matter of fact the runs showed a very slight advantage to the factory HEI.  Most likely because of the very PRESISE fine points on the reluctor vs the wide (and usually all rusted and corroded up because they didn't plate them) ones on the MSD stuff.

I'd add that I hooked up a 6AL box on the MSD for those pulls, still NOTHING over a stock HEI.

At the drag strip on back to back runs we swapped in an MSD billet distributor to replace a stock points distributor I had done for a good friend about 30 years back.  It was "locked out" and plate brazed down, we just used the points as a trigger.

To my surprise the car slowed down about .03-.04 seconds and LOST about .5 mph....hum?

An "old timer" later told me that the points provide a "natural" timing-retard at high RPM's and why we went a little quicker with them vs the MSD billet.'

Learn something new all the time.......