Hey guys, I finally got the correct points distributor installed with only 16 degrees of mechanical advance. Initial is set at 14* so total is 30 now. I thought this would take care of pinging when over 3000 rpm. I use high octane 91-93, no ethanol fuel in a mild 455 engine. The carb was rebuilt last year, a qjet, I'm told it was slightly modified and is capable of 800 or 850 cfm but i don't recall exactly. The fuel filter was also replaced last year. The engine temp is 180F. Two other guys have noticed the pinging. I raced a coworker with a 2016 wrx today and we were side by side until the higher RPMs and higher speeds when he pulled away. He noticed the pinging and thought my car was flat at higher speeds but we both agree it has plenty of torque and gets off the line decent for street radials. I'm wondering if my mechanical fuel pump is the issue and it's too lean under the heavier loads? I don't think it's the carb, distributor or gas. Maybe plug wires and leads? Sent from my iPhone using Tapatalk
It could be as simple as spark plugs that have to high of a heat range, something to research. GL Derek
Not if the Q-jet is jetted/set up too lean. What is the part number on the Q-jet? I'd also like to know more about the static compression and cam choice. I'd do a compression check and see where the cylinder pressure is.
What compression? I had a '70 455 with stock pistons and stock '68 heads in my old '68 coupe, and even with a curved distributor it would ping or rattle at WOT, and bumping up octane for the track (and street) was my cure. Mix in some race fuel. Patrick
Oops! I meant the fuel pump reasons only! ou: You really need to read your plugs to get a better idea of what's happening.
I was told by several hardcore racer friends that to properly read plugs, it must be 1) with a fresh set installed, 2) a full on quarter mile pass, and 3) shut down immediately after the pass, like just after crossing the line. You REALLY don't want to keep winging it when it is pinging .. repeatedly doing so will cause damage. How old are all those rubber lines in your fuel system ? Are they ethanol-compatable ? If it were me, I'd drop the timing 2-3 degrees and see if that alleviates it (getting out if the gas at first sign of pinging ..) Rinse and repeat A temporary fuel pressure gauge will show you where your pressure is at .. record it with a vid camera or cell phone during the run as its too difficult to try and eyeball it while the adrenaline is pumping and your ripping through the gears. an AFR meter will show you the actual burn data during the run but you need to plumb in a O2 sensor into the ehaust
Thanks, I don't use ethanol at all. As for the cam, I have this documentation. The previous owner didn't know much about the car, he bought it from his dead friends wife. The car sounds like it has a cam in it and the yellow sheet below was in the console, but that's all the proof I have for a cam. As for compression, I haven't checked it yet. Sent from my iPhone using Tapatalk
Oops, tiny cam! I'm sure someone will drop by to do the math for you showing that there's probably too much cylinder pressure with your engine combo. This does fit your description of pinging during the powerband. [30* total timing shouldn't be too much for the Buick's chamber. If that number is correct, it's telling you something. Simply retarding it more isn't really the fix] As far as looking at plugs...I'm not asking the OP to put in a fresh set of plugs and abuse the engine by subjecting it to a long, full throttle run knowing it's pinging the entire way. ou: I'm suggesting that the plugs will already show things like incorrect heat range, timing indications, and possibly the telltale signs of detonation and it's severity... even if used a little while. If others can hear it, it's severe. You can see the timing and heat range indications on less than full length runs. Columbo always looks at the murder weapon. It would be better to look at that before you have to autopsy the entire engine :eek2: I would also verify that the dampner hasn't slipped, and to begin detective work on what it COULD have for compression. An idea of when the intake valve closes and how much cranking compression would be a good start. You could work your way backwards from there to determine the suitability of the combination. An AFR meter won't show actual burn data if there's misfiring or detonation. You still need to read plugs. They are a better window to the inside of the engine than people blindly guessing over the internet. Once you verify that you have a combination that could live...then you can make adjustments and steer the tuning in, maybe look at a fresh set of plugs, lol. Hopefully it all works out for you. :beers2:
I did some quick calculations. With a static compression ratio )SCR) of 9.5:1, the Dynamic Compression Ratio would be 7.88, and that is perfect. With 10:1 SCR, it would be near 8.3, and that is getting close to Race Gas territory. http://www.empirenet.com/pkelley2/DynamicCR.html
My stock 68 GS400 (un-rebuilt, original 90k mile motor) has the same problem. I started mixing in LL 100 octane non-ethanol avgas (50/50 at first) and the pinging went away. Plus, it starts much easier after sitting for a week. I no longer have to take off the air cleaner and dump gas in the carb to get it to start.
I've seen that too, and that is something I am unwilling to do with aluminum heads. I'd be too afraid of damaging the plug threads in the head.
I appreciate all the input guys. This is great. Here's the carb I have; pictured below. As for the pinging, I took it out at lunch with a friend. I hammered on it in hopes of hearing it and then letting off the gas as soon as I did. Well, I got up to 4200 rpm and didn't hear one ping. Nothing has changed since yesterday. Same fuel in the tank. Sent from my iPhone using Tapatalk
Good point Larry! Antiseize helps. I know it gets beat to death (pun intended), and I hope this can help the OP start with enough info to sort out the vehicle... DCR is a good "on paper" starting point. Water and air temps, eliminating incandescence such as plug heat range, sharp edges left in the combustion chamber and the width of exhaust valve seats, can have more influence to the formula of octane tolerance than trapped compression. Those are also good "on paper" starting points, but harder to obtain some info. That being said, you should have enough to begin looking at things. Looks like a fun car.
Anti seize also hampers heat conduction from the plug to the head. A big reason I use NGK plugs with their plated threads, no anti seize needed. I'd still be afraid to do it. Aluminum expands more than iron. Agreed, lots more to consider beyond DCR.
Stock jetting is .067 main jets and 41B rods. That may be too lean. I would ask Mark or Ken about that carburetor and see what they recommend. Secondary rods should be AY (.567 tips). A thinner rod like a BG or AX has .397 tips for more secondary fuel. That would be an easy thing to try.
Larry, I wasn't disagreeing with you, I don't like to pull them from a hot head either. Because of what I do...I have to though. You can feel when they don't want to unscrew and the anti-seize gets factored into the plug readings. I don't always use it either. Even if the most accurate solution turns out to be jetting the carb, I was offering how I solve that in order to prevent further damage...by verifying the mystery engine's specs before running it again. The problem being that on a 1-12 scale of severity regarding detonation, audible det. is at 10. The damage is already being done prior to that. A hot exhaust valve is harder to trace.
Guys, the original recommended spark plug was an AC delco r44ts. The second 4 is the heat range. I thought I read that they don't make this one anymore. What's the recommended heat range for a plug? Sent from my iPhone using Tapatalk
