Vortec350ss

iTrader: (20)

frankly its probably less efficient than both. The stock 80e converter is so huge and tight that it would be OK up top but it wouldnt perform worth a ****.

The 258mm billet unit would allow more stall speed and be more efficient by say 5k or 5500 RPM than the 278 is.

lxcoupe

iTrader: (9)

Hmmm sounds like I need to unload this 278mm that I got into the river and source me a stock converter! I was hoping not to have a super loose converter in this thing and the 258mm will be even looser than the 278, no question.

MaroonMonsterLS1

Saw your same question on LS1tech. Jakes performance has started to offer very affordable 4l80e converters.

You're going to want something more in line with a diesel converter based on how early you make torque. Low stall, large diameter...ironically what a stock converter would be.

Any of the sponsors on this site, and any major converter builder can spec you one.

Fti
Circle D
Yank
PTC
Pro Torque
Jakes Performance
etc etc etc etc etc

MikeGyver

iTrader: (5)

I have a billet diesel converter. The stall speed is great for my application, it pulls good from below 2000 rpm. It still has no problem spinning the tires, I just need to push the pedal farther. I would like to try a stock diesel converter back to back with mine, though, because it seems that the extra weight of the billet case makes the engine less snappy at any rpm. Something for people to consider.

Vortec350ss

iTrader: (20)

Not necessarily. They can build a 258 pretty damn tight. It would drive like the 278 but by 4500 or to already be a ton more efficient than the 278mm is.

lxcoupe

iTrader: (9)

Mike what is your combo?

MikeGyver

iTrader: (5)

In my signature

BigKID

iTrader: (5)

A 10.5"/265mm is going to be about the best compromise of tight street manners and top end performance with a PD supercharger in a truck. A larger converter will feel tighter for a given wot stall speed than a smaller converter but will not hit as hard when flashed or spin up as fast up top.
I have a 10.5" FTI single disk that flashes 3400 at the track and accelerates well at 2000 in part throttle on the street. However under part throttle acceleration I can feel it pull harder once it locks up. It was nearly perfect on the street when first installed when I was only running 9.5# on a mile h/c setup. Now at 15# on a more aggressive h/c setup, it is looser than I would like on the street and autox course. When ever the transmission comes out next for a refresh, the converter will go back for a restall. I'm going to shoot for a 2800 stall which should bring the part throttle acceleration speed down to around 1700.

terravast4

iTrader: (25)

im running a circle D ripple disc 265mm 1a. its super tight and stalled about 2600-2800