Will a cast crank survive in a 400 hp 6500 rpm Common Block engine?

[kberguy]

I bought an engine that should have had the forged crank (Turbo IV out of a 1990 Shadow VNT car) but doesn't. I have been trying to find a new/remanufactured/used forged crankshaft, but so far have had no luck.

Will a properly prepared cast crank in a 1990 CB engine block be stable enough/strong enough to withstand 6500 rpm 400-425 hp? I plan on using ARP Main Studs for added strength.

My engine builder says get the forged crank, while Chris at Turbos Unleashed says the cast crank will be fine in my application. He says the common block engine block added enough stability that after testing, Chrysler decided the forged cranks were no longer required. I am sure this is true to a point, but I don't know where that point is...

Another question is will an earlier forged crankshaft fit into a late model common block? Do I need to restrict my search to just a 1989 Turbo II forged crankshaft?

[thinkofhairy]

Cast will be fine.

[4Daytonas]

Quote:

Originally Posted by kberguy I bought an engine that should have had the forged crank (Turbo IV out of a 1990 Shadow VNT car) but doesn't. I have been trying to find a new/remanufactured/used forged crankshaft, but so far have had no luck. Will a properly prepared cast crank in a 1990 CB engine block be stable enough/strong enough to withstand 6500 rpm 400-425 hp? I plan on using ARP Main Studs for added strength. My engine builder says get the forged crank, while Chris at Turbos Unleashed says the cast crank will be fine in my application. He says the common block engine block added enough stability that after testing, Chrysler decided the forged cranks were no longer required. I am sure this is true to a point, but I don't know where that point is... Another question is will an earlier forged crankshaft fit into a late model common block? Do I need to restrict my search to just a 1989 Turbo II forged crankshaft?

Early forged Crank can be used in CB.Redrill front of block for early front seal retainer and use all early stuff, Belts,crank&Cam gear, oil pan etc.

[puppet]

There is a groove cast into the CB at the front seal retainer. That groove would have to be addressed.

[4Daytonas]

Yeah some do--some don't.We used a 92 CB and it was flat.I saw another guy with a grooved block.If I had one I'd just fill with J-B weld and file flat and then redrill the ft seal holes.

[turbokid]

Larry Bufford has over 500 hp stuffed in his 2.5 cb with a cast crank and hasnt broken a crank yet.
He broke the BLOCK of a 2.5 cb and still reused the crank.
They will hold what ever you can throw at them most likely

[1983Rampage]

530+ after last weekend. He put a new exhaust manifold on and it helped him get 20 more HP. So we will see how much the thing can handle before it cracks the crank.

[xdig]

Quote:

Originally Posted by kberguy My engine builder says get the forged crank, while Chris at Turbos Unleashed says the cast crank will be fine in my application. He says the common block engine block added enough stability that after testing, Chrysler decided the forged cranks were no longer required. I am sure this is true to a point, but I don't know where that point is...

Get a new engine builder. How exactly are you planning on getting 400-425 hp out of an 8-valve motor?

[zippitta]

Quote:

Originally Posted by xdig Get a new engine builder. How exactly are you planning on getting 400-425 hp out of an 8-valve motor?

Blood, Sweat, and Tears...lol

[speedy5131981]

i broke a cast crank in a 91 shadow n/a 2.2 , but i brutly beat that car... lol.. had a kevlar clutch lightning release the clutch and stompd it down. it held up for bout a year when buddy was usin it as a tow truck. jerk strap pullin cars, and me for bout 9 mo...drivin it like above just have it mag'd for cracks... ive broken a lot of rods in n/a motors.

[Austrian Dodge]

I just bought and watched the Phoenix Convention '97 video with Ed Peters (Ex-Chrysler Engineer) the other night. In the 4 hour tech session he talked about how the early Non CB engines were experiencing crank flex due to engine acceleration and deceleration in road racing applications (heavier Daytonas). Chrysler had to go to the forged crank to reduce those failures. The newly designed common block engines incorporated 8 lb of additional structural rigidity around the mains to eliminate crank flex. This allowed Chrysler to return to the lighter crankshaft unleashing a few extra ponies. Todd Nelson even posted pictures of the common block and non common block engines on the "other" site. You can actually see the extra webbing. It just makes sense that if you are going to add extra weight to improve the integrity of an engine it's always better to add it to something stationary rather then something rotating.

Andy

[kberguy]

I have decided to stick with the cast crankshaft, but will also add four bolt main caps to the block. As this is a 5 speed car, I want to ensure the crankshaft can't move around. Although expensive, I believe this will provide the best possible foundation so I can create the power numbers 1 want.

[SpiritedShelbys]

was the crank turned at all or stock journal sizes? I'm just curious..

[speedy5131981]

check out this site www.crank-scrapers.com/chrysler.html and look at the pictures very carefully !! :)
if your good, you really dont need 4 bolts :) fab something using head studs with metric thread, and a cradle that slips on tightly and bolt it down

[speedy5131981]

you will have to have a little stand off from the cap bolt for clearance for the rod and crank throws. prob best if its constructed from 1/4 plate or similar, perferate for oil drainage and such. or better yet find sometin at a bone yard with a slight bow to it and make it into ur own windage tray