Can the stock 5 speed handle a crate 383/350 HP?

Depends.

You can tear up a T-5 with a 6-cylinder, or you can keep one alive behind a 400. It's all a matter of how you drive it.

If you avoid big smoky clutch dumps and power-shifting, especially if the car has traction, it can potentially live a pretty good while. You have to treat it like you think there's an egg in the middle of your drive train that you want to avoid cracking. But its death is inevitable. If you put one in a situation like that, start saving up your pennies for a T-56 swap. Sooner or later it will die.

Yours is 1st design, and as such, will fail by way of the hole in the front of the case for the countergear bearing, stretching out. When that happens, it leaks out all the fluid, and runs dry. Obviously that's immediately fatal. But the hole getting ovaled out also allows the gears to misalign, which tears them up even faster. Those 2 factors are how it will die. Of course you might strip the teeth off of some one of the gears, that can happen at any time when abused, but even without serious abuse, the weak case will eventually give out and kill it in one or both of those 2 ways.

Thanks for the response. Can I beef things up by installing a better clutch? Or at least protect the transmission better?

Quantify "better".......

Usually that means better power holding capacity. Which will only serve to kill the transmission faster. The more immediate and without (sprung vs. solid disc, etc) cushion the power is delivered to the input shaft of the trans, the more load you place on everything inside the trans. More load translates to a shorter life.

"Better" for the T5 would be a softer clutch. One the slips more easily and refuses to lock up hard. Then it would act like a fuse of sorts. Though this would not be much fun.

GD

GM wouldn't even put that trans behind a TPI 350, rated at 225 hp (IIRC) that year. The chances of it surviving behind a 383 would be slim to none.

Just upgrade the gearbox along with your engine swap and be done with it.

I ran my later design (world class) T5 behind my beefed up bolt on, cammed L98. It did fine, but I drive like a grandpa a lot of the time. No drag races, no slicks, minimal burnouts. Your's might survive, but the official answer would have to be no, it will NOT last.

Chevy guys tend to get in trouble with a T5 when they "upgrade" the clutch. The stock clutch probably had around 1900lbs of clamp on an organic disc, which has the capability of passing along about 342ftlbs to the input shaft. The stock T5 2.95 gearset and case can handle around 425ftlbs before you start getting into trouble, so everything was good with a 305 and a stock clutch.

Upgrade the engine to a warmed over 350 or a 383, now that 342ftlb stock clutch isn't good enough so an upgrade is needed. But you have to be careful that the capacity of the upgraded clutch you choose doesn't exceed around 425ftlbs or you will be able to damage the transmission with a simple clutch dump. Problem is even if you simply installed a dual friction disc with a stock 1900lb pressure plate, the resulting capacity of around 525ftlbs would put you about 100ftlbs over the T5's capability. You would have to drop down to about 1550lbs of pressure plate clamp to keep a dual friction disc under the T5's 425ftlb limit. You won't find many aftermarket pressure plates for an sbc that are rated that low.

A more practical solution to approaching the 425ftlb limit of the T5, without exceeding it, would be to keep the organic disc and look for a pressure plate with around 2350lbs of clamp. There are 2300lb aftermarket pressure plates out there, so 2300lb PP + 10.4" organic disc gives you an off the shelf solution with around 415ftlbs of capacity.

Keep in mind that it doesn't matter if the engine's output is lower than the T5's 425ftlb limit. Even if a given engine only made 350ftlbs, that 525ftlb capable combination of a stock pressure plate on a dual friction disc would still be able to draw an additional 175ftlbs of inertia out of the rotating assy if you dumped the clutch.

Grant

I agree with Granny's math, but the solution is to get the right transmission, not build your car around the existing one.