Well, I thought we were discussing what to do with an engine that was headed to be freshened up. I surely wouldn't rip open an original engine just "set deck at zero" as a vague claim if there weren't any issues with the motor. But when you are spending new dollars on an old engine, one is faced with lots of choices. These choices involve difficult selections between current fuel, future fuel quality, trips to buy racing gas and the planned use for the car. Originality is also a concern, but I surely wouldn't search out NOS main bearings, cause no one will ever see them. Many of these choices have only minor impact on the final cost for the engine rebuild. For instance, $200 on pistons vs $500 on custom pistons will be lost in the final price on an engine rebuild that you won't see completion of for less than $3000. I know the difference is a few hundred bucks. But I'm looking at longer term use of the car with fuels we can expect to buy.
To be sure, Pontiac didn't screw up when they set deck height for their production engines. They had different concerns. One was production tolerances, where avoiding collision piston to head (or valve) was essential and had to be avoided with the cheap OEM rods. If the deck height wandered from spec on a mass produced motor, it couldn't be allowed to clash into the head, even with some wear during the warranty period. These are production choices that engineers make all the time. Engineering choices made nearly 40 years ago don't have a lot of relevance for a motor being reworked today. Yes they did a great job back in the day, but that has nothing to do with 2007. This is especially true when the motor gets precise machine work from an accomplished shop rather than being manufactured en mass.
I figure we are talking about an engine that is headed for freshening up in a car that will be driven. I surely didn't suggest Jim tear apart his motor to make it "run better" with lower CR, zero deck and all that. Jim says he can buy decent gas where he goes. I expect he is fine where he lives. I can't buy good fuel around here in the nation's capital, without burning half a tank during the trip. Here, the gas stations dump octane boost into the tank when the county comes down on them for failing testing after complaints.
We're talking about choices for a new project. To me, that means the car needs to take fuels you can buy on the road, not what you can mix at home after a trip to buy racing gas that you store and mix at home. I guess there is racing gas around here somewhere if I search, but mostly I can buy 91 octane at best. Everywhere I go now posts notice that the fuel is contaminated with 10 percent ethanol. I would rather get 10 percent less fuel for my money.
Add to the concerns that the engine needs to be numbers matching so not machined to zero deck on the block is why I brought up special pistons. No's match dismisses notions of bolting up aluminum E-heads, milling the block to zero deck, or even installing other heads from the early 70's low compression smog engine where CR might be set where you want (need) it. I understand that, but in any engineering puzzle, you can't optimise everything at once. A milled '96 head or a later head won't numbers match this car. I really understand the concern.
On top of that, Vikki is determined to not mill metal from the original motor deck. I can understand that too, cause you can't put it back. That leaves piston design as the only option. There are folks who build one-off pistons, so lets look there. If that is out of the question too, there ain't any solution other than good fuel. I don't see good fuel in our future, without a lot of effort. Blueprint the motor, put gas equivalent to what we bought in 1968 and you're golden.
But life is full of compromises. You can put the engine back to blueprint specs, but if there is wear that doesn't clean up with a hone, it's .030 over already. Now the engine isn't no's perfect anymore. How many of them are left not worn? Worse, the engine has lost .030 and has only one more clean-up before it's trash. I never accepted bore it out as a remedy to get a bit of power through the small increase in displacement. These are tiny gains while limiting the functional end of life for the motor. But then I don't race, so to me it doesn't matter. I guess Chevy motors are cheap and this is a worthwhile choice for that last tenth. But we're not talking about the last tenth here.
I might be lost here, but I thought the puzzle was what is the best thing to do with a '68 motor without grinding down more original metal than necessary. And I thought this was a car to be driven often. That says you don't drive back home for more hundred octane or home mix of racing gas and 93. To me, that says drop the CR, deck the motor and only rework (grind down) what is necessary to make the motor run as planned. A good cam choice might help too, but I'm not started in my studies about cams.
Jim is pretty adamant about how good his motor runs. But he can buy good fuel, according to his own description, post 83024 where he says
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Never thought it had anything to do with the exhaust. Only that you can hear the ping better without headers. It's pump gas. I drive up to the pump/pumps. Just as soon as the racing fuel pumps disappear I'll have aluminum heads.
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Well, we are talking about fuel you can buy on the road, not what is available in a few choice locations.
There ain't racing fuel where I plan to drive MaybeI redefined the question with my own concerns and hijacked the topic, but there's not much high octane for "drive up" and "gas and go" around here. I stick with Exxon here because they are one of the few suppliers around town where 91 even works right in my vehicles. I expect it to get worse. Reworking my motor, what I can readily buy, vs what is possible plays a key roll in choices.
