Pros and cons?

Uuuuhhh, I would say that most racers use non-lock up converters.

Aren't the majority lock up converters?
I thought 1/8th mile fast guys are using non lock up?

A “proper” lock up converter has a clutch in it that’s activated by the transmission.

You need both a lock up converter, and the trans to go with it.

So...... no one running a regular 727 or 904 is using a lock up converter.

Unless there’s some current technology for those transmissions I’m not familiar with.

No, like Dwayne said most everyone uses a non-lockup. But, the really fast turbo/Nitrous/outlaw types have recently started using them.

Neal Chance

Billet Lockup Racing Converters

Starting at -$7,300.00

The latest innovation from Neal Chance Racing Converters is the Full Billet Internal Lock Up Racing Converter. This unique new converter was a top secret joint project between NCRC and Rossler Racing Transmissions, but the cat is out of the bag now! This converter has captured and HELD ALL the Turbo World Records and ALL the Pro Nitrous Records in PDRA!!!

It works either with a TH400 Based Transmission such as the 3 speed, 2 speed TurboGlide, Ty-Drive or Bruno Drive. The Lockup Converter offers far more durability than a “Dry” clutch, with the ability to last an entire season in a 3.70 Nitrous car with no wear!

Perhaps the OP is confusing “non-lock up” with “spragless”??

The last few episodes of No Prep Kings have been mentioning them...

You need a power adder in order to gain any ET benefits my little 499 wouldn't recover from a 700 rpm drop from the highest load going down the track from increased wind friction for example I shifit into lockup at 7250 rpm drops to 6550 that puts me at 7.28 seconds into a 8.87 run now the motor only has 1.59 seconds to recover some and increase mph my thought it would just stall there and maybe get up to 6600-6650 mph would be down from a non lockup run.

ugh???

Both transmissions got the factory lock-up functionality around '78 I think (give or take a year?).

As applicable to drag racing I would agree that most probably run non lock-up setups. However, I for one have a lock-up 518 here and would consider running a high-stall lock-up converter in it. I haven't gotten anywhere near actually being able to prep the transmission and make the appropriate changes to use that setup in my coupe, but one of these days I would consider doing so.

I thought the transmissions got a different number designation when they went to the lock-up.
Like a 904 was a 999, or something like that.

In any case, you need a transmission that has the capability to operate the lock up clutch for it to work.

Edit: I see there are in fact lock up 727’s and 904’s....... which would be used with specific clutch equipped converters for that feature to be operational.

Your typical TA 10”, Dynamic 9.5”, 8” ATI Treemaster, etc....... are non-lock up.

I have a lock-up converter in my A340E OD transmission.
The box will take 800 hp, the converter clutch will take 350.

All the torque multiplication goes away once you lock up the converter so when used in a race application you better be bringing plenty of torque with you...as stated earlier a "Power" adder motor. Not too many (if any) Naturally aspirated motors will pick up with one.
2spd w/lockup converter

Somewhere in the back of the shed I have a big-block 727 lockup trans and converter I decided to squirrel away at one time. I believe it's a '78. 727s and 518s could be had either way but 904 variants were all lockup from some point on.

All the torque multiplication goes away once you lock up the converter

It's already gone when the car rolls out.

My new Chance 8 inch NSX all aluminum converter is non lock up.
I was worried that it wouldn't be good for 1/4 mile racing.

It doesn’t immediately “disappear” after you leave the starting line.