I have been trying to eliminate part throttle ping by changing the timing and have not been able to eliminate the problem. The pinging is most noticeable when the secondaries are opening up during gradual acceleration in second gear(TH400), but you can also hear it when I drop the hammer from a dead start. I have changed the timing a bunch of times trying to get rid of the ping. I backed it down to 4* initial and it still pings. Turn it up to 12* initial and it seems the same. The distributor has 20* mechanical advance and 8* vacum advance. I have also adjusted the vacum cannister in and out using the allen wrench but it does not seem to help... I have not moved the vacum limiting plate because I have not figured out how it works. Right now the timing is set at 10* initial and the car runs like a " Three Balled Tomcat" (GREAT), but I would like to get rid of the ping. Last winter I changed from a 2:93 peg leg to the 3:08 posi and changed the muffler shop exhaust out and replaced it with the 2 1/2" Torque Tech. I also changed out the distributor at the same time so I may have been chasing my tail because I changed so much stuff at one time... Bone stock 1970GS455 TH400 Open element air cleaner Daves Small Body HEI distributor with adjustable vacum advance 7044240 Quadrajet from TA Performance(boutght it from them approx. fifteen years ago so I dont know how it is set up. 3:08 Posi 2 1/2" Torque Tech exhaust I have tried AC44RTS plugs gapped at .045 and .030 Right now I have NGK UR5 plugs gapped at .040 93 Octane pump gas (Shell) The plugs look almost new after several hundred miles-no sign of detonation or anything else... I have never worked on a Quadrajet and dont know how to tell what jets it has in it but if you guys can walk me through checking/changing them I am game. I checked the secondary hanger is a K and the rods are AY. Thanks for any help or tips. Bert
Can you tell us what your actual (measured) compression ratio is? Do you know exact camshaft specs? As far as checking primary q-jet jetting, the air horn will have to come off to make the jets visable. Devon
Here are some good q-jet pages: http://vetteworks.tripod.com/qjet.htm http://www.geocities.com/wag1comet/quadrajet/quadrajet.htm http://peterpam.customer.netspace.net.au/quad.htm http://www.gmcmotorhome.com/tech/qjet/index.html Devon
Thanks for the links, that will help. As for the specs on the compression and camshaft, it is a bone stock 1970GS455. Thanks Bert
have you tried disconnecting the vac advance and plugging it? If that works you need to work on limiting the vac or mechanical advance. From your description it sounds like that's what's going on. You said right now you have 10* initial plus 20* mechanical and 8* vac. That adds up to 38 which is 4-6* more than you want.
My vote is timing and/or jetting. The true compression ratio of the factory engine should be fine with pump gas, unless it's actually been "blueprinted" to bring the ratio up to factory specs (they're usually quite a bit lower than advertised). Devon
Nope, 38-40* is about right with vacuum advance. He only has 30* total at wide open throttle. The first thing I would do is disconnect the vacuum advance and drive it around. Set the total to 32* Make some wide open throttle runs from 45 MPH, and from a stop. Does it Ping? If not, you may need to use a stock cannister and limit that. I have found that the Crane vacuum advance cannister spring may not be strong enough (that is what you adjust with the allen key) for a stock cam. There is too much vacuum. A stock cannister with a limiter plate may work better. The spring is stronger and pulls the vacuum advance sooner when you tromp on the gas.
oops, my bad. I stand corrected. :TU: I know better. I did offer the same advice about disconnecting the vac advance so I guess it wasn't all bad.
I will try that I will try disconnecting the vacum advance next weekend and see, that sounds logical to me. Can I replace the vac advance cannister without removing the dist? Bert
It's not to bad to do on the car. You have to rotate the breaker plate a bit to get at both screws, that's all. Devon
That's the first thing I'd change. You're drawing in hot underhood air; you should be pulling in cooler outside air. What temperature is your coolant? Ping any different when the engine is cool?
Based on what you describe here, I would guess that you have a mechanical noise and not a "ping". Of course I haven't heard the noise first-hand, but that is my guess from a distance. -Bob C.
Crane adjustable vac advance cannister? I plan on driving the car later today with the vacum advance disconnected to verify that the ping stops, meanwhile I was curious about the amount of vacum advance and the adjustability provided by the limiter plate on the Crane adjustable vacum advance cannister on my distributor. I was reading the instructions that came with the distributor and realized(remembered), that it also has an adjustable limiting plate that I can move to another position and lower the amount of vacum advance provided by the Crane vacum cannister, how much vacum advance can I remove by moving the plate? Thanks Bert
I know Dave sets the vacuum advances up for use with full manifold vacuum, never for ported, is your vacuum advance on ported or full manifold vacuum? Ported vacuum will cause part throttle pinging. I know the only instance Dave recommends ported vacuum advance is for engines equipped with, and functioning EGR (Exhaust Gas Recirculation) valves. I have a dozen of Dave's conversions, no problem with any of them. He sets the Crane advances up with the Crane stop plate for the degrees, on the other side of the pull pin from what Crane suggests, and for me, in all 4 of my Buick's, they work better that than where Crane tells us to mount them. Dave does the plate this way to separate the rate of advance, from the Allen screw in the hose fitting, from the actual number of degrees given. With the Crane method, the more you cut the vacuum degrees down, the higher the vacuum level you need to operate the advance., the less control you get from the spring/rate adjuster inside the cannister itself. On the Crane plate, there are small cuts. These cuts are two crankshaft degrees each, so, if you are seeing 8 degrees on the crank, the plate should be on its 4th cut, 10 degrees would be the 5th, 12, 6th, etc. You indicate the distributor has 20 degrees of mechanical advance, that, and 12 initial will give you the 32 degrees suggested above. The 8 degrees from the vacuum advance, on low load cruise, will give you the 40 degrees also suggested here. It took me about 5 of his conversions to get all this through my own thought pattern, but he kept teaching me, proved it to me, and that is the way it works best on all my engines. I'd suggest you call or e/mail Dave for more information, and leave both the Crane advance in place, and the plate where it is, in front of the pin, make sure the vacuum advance is on full manifold vacuum, and then, get the carburetor right. You can also ask Dave questions directly over at buickthunder, he is a moderator there. Regards, Milton
Re: Crane adjustable vac advance cannister? Bert, It's pretty simple. Dave mounts the limiter cam on the vacuum advance unit itself. All the cam does is block the pull pin travel. If you loosen the bolt in the middle of the cam, and rotate it, you will see that it allows varying amounts of travel. Measure between the pull pin and the cam, use feeler gauges, .086 is 8*, .104 is 10*, Each tooth on the cam is about 2* Dave probably already has it set to 8 or 10 * Your problem may be the spring inside the cannister. It may be too weak even fully adjusted so that the vacuum advance is not going away quick enough when you step on it.
I know Dave uses that specific Crane cannister because it has every setting the stock cannisters have, including the heaviest spring set you can get. I ask if the vacuum advance is connected to ported or full manifold vacuum? Should be full manifold vacuum. Regards, Milton
