All the Optimas are dual terminal units which don't bolt into a C4.
Ok.
You guys got me on this one...don'tcha love it?
Let me restate...
The proper Redtop and Yellowtop Optimas are dual terminal units which do not bolt into C4s earlier than 1989 unless the left side hood-latch-mount-to-frame-rail brace is modified.
The problem is that the OE battery was side terminal only and the positive top post on a Group 75/86 DT battery is too close to that brace and can ground on it. That causes a huge short and possibly a battery explosion.
There are a variety of "bubba-DIY":bash fixes for this and I've seen most of them...taking a hack saw to the positive top post, wrapping a rag around the brace, putting half a tennis ball over the top post, wrapping the top post with tape....none are good solutions.
The only safe solutions are 1) not using a DT battery, 2) modifying the brace for clearance (see:
Extreme Battery - Corvette Product Reviews) or 3) in the case of the few gel cells which can be turned on their sides, laying the battery down, modifying the battery hold-down and changing the cable lengths.
As for 84-88 C4s, I have not personally attempted to fit a DT battery to anything earlier than 89. On cars earlier than that, it might be possible that brace is different or doesn't exist on those cars, in which case a DT battery would fit. Also, typical for 89-96 cars is a Group 75 battery. If a battery that's shorter in length were put in the C4 battery box and positioned more towards the driver's left, the positive post might be relocated to offer safe clearance. Problem with that might be that the smaller battery will be inadequate under some conditions such as cold weather or starting with an already partially-discharged battery.
I'll add that based on my experience with Optimas...today, the product (which was sold to Johnson Controls by its originator several years ago) does not have the quality it did when it first came on the market. IMO Optima is very well-marketed but is overrated quality-wise and are no better in performance or durability that some standard wet-cell batteries. If value is an issue, you're better off with a "normal" type battery, such as a Delco, Interstate, Die-Hard etc. If price is the primary factor in a battery purchase, in my experience, Costco is hard to beat for low cost and reasonable quality.
All that said, if you want the best performance and durability with price being secondary, my experience is that there's only one choice and that's the Odyssey Battery.
Up until just recently, the only Odysseys available for C4s were Group 75/86 dual-terminal units, but about 10 days ago, Odyssey introduced Group 75 and Group 78 side-terminal batteries.
I've ordered two of them for testing and will report back to the CAC using the product review section. I anticipate that these new Odysseys will perform just as well as the Group 75/86 I tested a couple years ago for the above listed review.
