Need Correct Turbo Crank Forging Number


New Member
Need info on the correct forging number for a '78 Turbo 3.8 rolled fillet crank- is 1257125 a valid number for the turbo crank?

The NA crank and the turbo crank share the same stamped numbers. Look for the rolled fillets on the ROD journals for the turbo crank (all will have rolled fillets on the main journals). And make it comes from a RWD motor.
OK, here's what I did. Even though I was able to determine the crank was NOT a turbo crank, I bought this engine off eBay for $150.00. I figure I would have spent more than that on dished pistons and oil pump mods.

I also have another '79-'80 NA donor engine. I found a guy willing to sell me a true rolled fillet 3.8 Turbo/4.1 crank ground .010 under for $200.00 (He has two of them if someone else is interested) So for $350.00 plus some block honing, new bearings, and ARP bolts and studs, I should have a fairly close facsimile to a '79-'80 3.8 Turbo engine. Since I'm not planning on racing or running over 10 lbs. of boost, I think this will hold up OK even though the block isn't a listed as a turbo casting.

OK, you can start piling on now!

Thanks for all the help, everyone! Good info so far; love the Before Black site!

If you are SURE you'll never run more than 10 psi of boost, a NA crank will more than be enough. Many SFI/IC cars have run pretty fast on NA cranks. They can take a lot of abuse. Search for stories in the general tech forum.

The ebay motor looks to be a 78 or 79. It probably doesn't have a hole drilled and tapped for the knock sensor on the block. (I'm assuming your using a 1980 aluminum intake. the 78/79 had the KS on the cast iron intake manifold). No biggie, but something to that care before installation. Also, if it's a 78 motor, the heads will be low port versions (not good).

Am I right that you're are using a 1980 aluminum intake? What are using for the heads, and exhaust manifolds?
Since I was able to get the .010 ground Turbo crank, I will definitely be using it instead of the NA one. I pick up the eBay engine tomorrow, and my buddy in Midland is giving me another NA '79-'80 3.8 he has, complete block to heads

No way I will use '78 heads. Tall-port '79-'80 heads from a NA motor.

Correct on the KS hole on the back of the block. I will either have it machined into the block in the picture, or use the block from the other engine.

I believe the manifolds are from an '80 engine. Casting numbers are L: 25507801 and R: 25507802

Basically, I got a rebuilt turbo, manifold, plenum, exhaust manifolds, up-pipe, down-pipe, crossover pipe, exhaust- to-cat bent for a Vega, an MSD-6 BTM, and various pieces in a generous swap from a friend. Found an NOS '80 ESC box on eBay; need a KS and wiring. The guy who won teh Turbo Riviera carb #17080242 I was bidding on can't use it and now wants to sell it to me for his cost.

Still have questions on how some of the little stuff will fit together, but I'm trying to nail down the big stuff now.

Thanks again,
Originally posted by V6VegaTex
I believe the manifolds are from an '80 engine. Casting numbers are L: 25507801 and R: 25507802
I think those are 81/82 Manifolds. They are smaller internally, but that may or may not be bad. Some will say they are restrictive, others say this helps keep exhaust velocity up. Take a look here:

The KS is available at parts stores and possibly still from GM (I bought one two years ago). It's about $60-75. :eek:

Good find on the NOS ESC. :)
Thanks again. This thing is like a kid's scavenger hunt. Just when you think you found all the pieces to win the game, all you do is discover another clue to a missing piece. This time it's PEVR! Fortunately, I'm in no hurry to build the engine and can take my time. The car has a nice NA 3.8 with a 4.1 manifold and correct Q-jet. When it's ready, I will swap the entire Turbo engine.