Why We here at Speed Gems Love the GM Automatic

When it comes to cars, most everyone has their “favorite flavor”, whether that be Ford, Chevy, Mopar, or something different all together, there is never a wrong answer. Despite any bias, there is always something to admit the other guys does better. Chrysler is well known for their documentation, allowing us to know exactly how a car had come off the assembly line, adding huge value to them as collectors. Possibly one of the most important parts of hot-rodding came from Ford with the introduction of the flathead V8’s allowing cheap power from early on. The flathead may be one of the most important pieces of hot-rodding history, but if there was anything to challenge it as the most important, it would be what Ed Cole, and his team of engineers came out with in late 1954.

The small block Chevy, and for this purpose of this article, the small block Chevy engine pattern, has been one of the most consistently used and abused engines for the past 70 years. When it comes to us at Speed Gems, that is a great thing because it makes it that much easier to make all these cool kits for you guys! The beauty is, take your 265, ditch that Powerglide, and in its place bolt in that brand new from GM Performance 4l60e, get a transmission controller (check out our partner US Shift) and away you go with your new overdrive unit, about as easy as it gets. Now of course, most of those 265 engines did not have starter provisions drilled into the block, so you may need our CH501 kit to have somewhere to mount that starter, but point being, that pattern has stayed (almost) unchanged all the way up to today, in 2026 production models.

Can you bolt that brand new 10L80 to that same 265? Well, sort of, they do bolt together but you’ll run into some issues with spacing (more on this later), and with the transition to the Gen V V8 small blocks, the 10’o clock position hole has been ditched for a shifted 12 o’clock position hole that is different from the LS transmissions before them, that is somewhat different from the Gen 1 small blocks… But believe us they are functionally the same. The 4 lower bolt holes, dowel pins and locations of all these other holes are still all the same, it’s just a matter of what ones are being used in what application. To avoid being longer winded than this already has, being able to design off one set of criteria, and be able to work with transmissions ranging from the 2 speed Powerglides, all the way up to the incredibly stout 4L80e, makes the GM automatic transmission the perfect candidate to design adapters around. This paired with the fact that there have been more than 100 MILLION small block Chevy’s made in that time, not even including the big block which shares the same pattern, and there are plenty of these transmissions, in every variation available.

While it is great that the SBC pattern makes easy work for us to design around, we have to also thank all the other divisions of General Motors for having different pattens before being mandated to the second GM corporate pattern, the BOPC pattern, developed by Pontiac and being a staple until the 1980’s. Because of their independence, we get all the great and unique engines of the 50s and early 60s. It would be nice if those just had one consistent pattern, but because they don’t, we have adapter’s to pair to all these different small block Chevy transmissions.

Such a big part of the philosophy of our adapters is to give an option to upgrade outdated, hard to work on (and find parts for) and in some cases just flat out bad transmissions. Again, with transmissions like the TH350, they are simple, readily available, and when it comes to transmission swaps, durable enough to handle most engines that may need a compact replacement.

From Buick Fireball Eight engines, Packard inline and V8’s, Studebaker, Kaiser Willys, even maybe a Ford or Mopar V8, we offer all sorts of kits to go to the small block Chevy V8 transmissions. What makes this great is the pattern doesn’t change, we know our general torque converter patterns, the torque converter set back spacing, and a few different ways we can make adapters and just like that we have a great start for an adapter. The simplest, if space allows, would be a crankshaft adapter, a GM style flex plate and starter, and short of a few measurements on the engine, our kit is complete. Now, of course it is a lot more complicated than that, but all the “dirty work” of research and planning is already halfway done. We don’t have to spend the time to do these measurements on both ends, customers don’t have to search in junk yards, Craigslist or Facebook marketplace to find a limited or expensive transmission, they can find one of the millions made for the small block Chevy’s and pick the transmission that meets their budget. Whether that is the

TH350 sitting in the shed the past 30 years, or the freshly built Bowler 4L80e, it’s not hard to find one, and they come in all sorts of budgets. Now, is this somewhat true for something else, say the small block Ford transmissions like the C4, 5, 6, AOD and others? Of course, but there are fewer of those made. They have their benefits, like the fact that to convert to a Modular style transmission, it is a matter of changing dowel pins, but again, we are still looking at a shorter production window, and fewer made. Yes, this is all information we have on these transmissions as well, but availability reigns supreme here.

Earlier on I mentioned the LS and LT transmissions and how they were technically the same, but somewhat different due to spacing. We understand that these transmissions are getting easier to find, as the LS engines are coming up on their 30th birthday, and we want to make sure we are accommodating these as well. We are currently working on developing a new way to allow us to use pre-existing kits, and with the addition of a single part or maybe two, make the necessary adjustments so that if your heart desires, you can finally bolt that 216 Stovebolt to one of the fancy new 10 speeds. Is this the main purpose? Probably not, but those LS style 4L60’s are everywhere, and it just opens that many more transmissions for everyone in the future.

If you have any sorts of questions about any of this, feel free to reach out to us and we are happy to discuss what you may need to get your perfect transmission swap done. We are adding new kits all the time, so if you might have an oddball engine, maybe a Buick 215, International V8, or maybe something more common like a Coyote V8, you may just see that Chevy V8 automatic kit coming out soon.