Steve, I knew that the online calculators could not possibly be off almost a full number of compression. I couldn't fault your actual math, so I knew it had to be something I/you were missing. Took me a bit, but I realized what it was. The swept volume that the piston displaces in the cylinder is 843.71cc, BUT the total volume of the cylinder includes what is above the piston at BDC. That includes the head gasket, deck clearance, piston dish, and combustion chamber. So using your numbers, 843.71 + 8.869 + 16.21 + 69 = 937.789. Divide that by what is above the piston at TDC, 106.08, and you get 8.840:1 SCR.
For what it's worth I have experienced my fair share of pinging with both carbed buicks as well as the efi gn. There have been only 2 causes that I have found. Incorrect timing or other issue with the distributor and low octane fuel. I've had horrible oil burners but they didn't ever have detonation issues . I damn near went Crazy with ping in my gn under boost and in the end it was low octane fuel. With the tt street chip 93 octane is not a recommendation its the bare minimum requirement or you will experience audible ping . 91 won't cut it. my gs is the same way . any thing less than 93 and she pings too. Granted that is easily adustable by turning the distibutor on the gs but I tune with 93 fuel for max performance. Today's fuel is crap and ethanol makes it even worse for our classics.
So is the pinging at part throttle only, or at wide open throttle too? Does the ping occur right away, as in before the engine comes up to temp? What is the engine temp when it’s 50 out? How are you measuring the temp, and have you checked another way to see if how you're measuring the engine temp is accurate? You mentioned “thermostat temp” but never put a number on it. Do you have access to some race fuel, like a 5 gallon pale of 110? 91 isn’t a lot, and a “stock BBB” of early vintage may not like it. If the results disagree with the theory, change the theory. Keep in mind that pre-ignition and detonation are 2 different things. That’s why I would like to see the spark plugs after seeing the top of the piston. Also, a picture of the cylinder head showing the valve faces in the combustion chamber may be helpful too.
Retarding a engines ignition timing on a motor who's cylinder pressure is already not good enough to pump out hot Exh gasses as required once a certain rpm / throttle opening is reached will only serve to compound the ping issue!
At this point, we have more questions than answers. I think we need to wait for the OP to get back to us.
Ok, I will try to respond to all of the advice! Yes, i checked total timing. I had it set about 26 to minimize pinging. After reading Larry's post on power timing your buick i disconnected the vacuum advance and have not used it for a while. As i mentioned i have tried 2 different balances and i have also used 2 different timing guns. It does not ping if I drive the car easy. Depending on the distributor it would ping earlier or later in the timing curve. When i had the stock HEI in the car it would ping when i hit about 3000 RPM under modest to full acceleration. The car has a 190 degree thermostat and runs at that during cooler temps (i have verified that with my hand held temp gun). The car doesn't ping when it is cold (i.e. hasn't warmed up to operating temp) but once up to temperature it pings regardless of how cool it is outside. I have tried octane booster, but not racing gas. That is an option once i get the engine back together. I am also willing to have the distributor professionally curved if that is what i need to do. I remeasured and remeasured the deck clearance yesterday at it is the same as what i posted the first day, approximately 0.075 inches. The only way to change that would be to change the pistons or deck the block...neither of which are likely to happen until the car breaks and i rebuild the engine again. I would love recommendations on how to clean the carbon off the pistons (and how to keep the carbon off the pistons!). Any other suggestions before i put the engine back together?
The only question I have pertains to how you are setting and checking the total timing. I would definitely not use the vacuum advance as it will only aggravate the pinging at part throttle. Are you using light springs to check the total timing? A very common mistake is to set total timing by revving it to 2500-3000 and thinking all the mechanical advance is in. It likely isn't with stock springs. So the timing may be advancing beyond where you think it is. You mentioned using 2 different distributors. The amount of mechanical advance is likely different between the 2, so they would need to be set up differently depending on the amount of mechanical advance in each one. Light springs are essential when you set total (initial + mechanical) advance. It's the only way to know that all the mechanical advance is in.
I indeed made a mistake in figuring out your compression ratio the other day, doing it the right way I come up with 8.95 to 1. Sorry for the confusion!
As probably mentioned limit bushing is probably missing so a whole lot of timing may be coming in over 3000 rpm.
Thanks all. Larry I did use lighter springs to check the total advance. I haven't plugged in the vacuum advance since starting this whole investigation. Is it probable that the piston deck clearance is a part of the problem? Either way I will put it back together and check timing again. Any thoughts on cleaning the carbon of before I do? I have tried three different distributors, two points style and one hei. I installed the brass bushing that came with the curve springs so I know it is there.
The .075 in the hole does not help things for sure. Zero deck is desirable because it makes detonation less likely because of better quench and squish. (Google it) Maybe use come cleaner like Seafoam and CAREFULLY scrape the tops of the piston. What do the combustion chambers look like? When I had the aluminum heads on my first motor (I did not install them), the installer did not use a valley pan under my intake. As a result, my PCV was siphoning oil out of the valley for a season. Oil consumption was noticeable, but not on the plugs. I finally figured it out, and installed a valley pan, but when I removed my heads to send them to my new engine builder, they looked like this, And the back side of my valves looked like this, That happened in 2000 miles or less.
I have not closely looked at the head, but will tomorrow. I spoke with TA and they recommended using a thinner head gasket (like the factory style). Is that something that may help?
That would be the steel shim head gasket which is .020 thick. That will bring you from 8.85:1 to 9.25:1 SCR http://www.taperformance.com/proddetail.asp?prod=TA_1725B I don't really see that helping any. What you really need is better pistons to get closer to zero deck. That's assuming that the .075 is what's causing the ping/detonation. I'm just not sure about that.
Steve. I am really enjoying this thread and subject. To stay in line with the original questions here. Do Buick 455 engines make that kind of power w higher compression and 87? With 0 deck or close to it? I have been playing w my car and some adjustments have put it in knocking/pinging range w pistons .035 in the hole. Which in turns uses the bore for part of the combustion chamber then. 73 engine w 73 heads milled . 0200 total I believe. .027 cometic gasket. I believe 170-175 psi on compression test. Just trying to learn here. This is a real learning thread. Thank you all.
Treeboy, Have a look at post #11 in this thread, http://v8buick.com/index.php?thread...-drivers-side-rocker-arm.357334/#post-3064177 Specifically, this quote from Jim Weise, "the problem with a 400/430 is that they must have a custom piston.. the off the shelf cast replacement stuff will result with the pistons being .070-.080 in the hole.. I have fixed those 430 engines from folks doing a "budget" rebuild, only to find that the thing pings so bad, it can't be used. So your going to be spending big money on a custom piston set."
