Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1903 Won't Respond to Tip-In Procedure
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.
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