Bob Weight

**Old55** · 05-16-2012, 06:06 AM

I'm new to LS builds. Been through a few SBC deals but need some info on an 6.0lt LS shortblock. I'm specing some replacement forged psitons and upgraded rods for this build. Although it'll need a balance job I'd like to get close or lighter on the piston/rod assembly. What's the bob wieght on a stock LS crank?

I tried to search for a thread with this info but was not successful.

Thanks for any info you can give me.

**Old55** · 05-16-2012, 01:05 PM

No one has this info? Any reccommend where I can get it?

**jrbonds** · 05-16-2012, 01:17 PM

Firebirdjones is usually the go to authority on 6.0 builds. I know he helped me on mine. Maybe he will chime in later this evening.

**Firebirdjones** · 05-17-2012, 03:28 PM

An excellent question. You'll need a starting point for bob weight to begin balancing, as I'm sure you are aware, that's going to change since you are using aftermarket rods and pistons.

I haven't had the pleasure of working with a 6.0 crank, and I'm certain the bob weight would be different from the 5.3/5.7 cranks since the pistons in a 6.0 are larger (aka: heavier). Unfortunately I don't have access to that kind of information anymore since I've moved, but if I had to make an educated guess I'd say a bob weight of 1800 would be in the ball park, if not very close.

A good machinist would know or should have access, especially one that has done alot of LS specific stuff.

**2002ssslp** · 05-17-2012, 04:38 PM

The bob weight should be around 1815g but I would call a machine shop to check those numbers.

**Old55** · 05-18-2012, 08:00 AM

Thanks for the info guys.

I have a set of SCAT I-beams w/7/16" capscrew bolts. They're balanced and weigh in at just over 590gms. I don't rememeber the big end/sm end split.
I'm waiting on a set of SRP FT's. They're supposed to weigh in at about 523gms w/pins. Don't know for sure but I'll weigh them + rings and locks. I'm shooting for ~1800-1810gms. If the bob weight of the crank is >1800gms. This should work w/o adding any weight to the crank.

My local machine shop doesn't have a torque plate for LS stuff. Anyone know a reputable machine shop in the Southern Ok or North Tx area that can torque plate hone my block?

**Firebirdjones** · 05-18-2012, 09:37 AM

Originally Posted by Old55

Thanks for the info guys.

I have a set of SCAT I-beams w/7/16" capscrew bolts. They're balanced and weigh in at just over 590gms. I don't rememeber the big end/sm end split.
I'm waiting on a set of SRP FT's. They're supposed to weigh in at about 523gms w/pins. Don't know for sure but I'll weigh them + rings and locks. I'm shooting for ~1800-1810gms. If the bob weight of the crank is >1800gms. This should work w/o adding any weight to the crank.

My local machine shop doesn't have a torque plate for LS stuff. Anyone know a reputable machine shop in the Southern Ok or North Tx area that can torque plate hone my block?

If it all comes in as you hope, then you'll save alot of money balancing, since adding mallory gets expensive.

Not familiar with that area of the country, but I believe a little further south towards Dallas would yield something.

**Old55** · 05-18-2012, 10:26 AM

Thanks FBJones.

I just ran the numbers through my formula and the rotating assemble should be right at 1700gms. We'll drill a few holes in that stock crank. LOL

Again, I'm no LS expert(Actually now expert at all), but I hear the stock cranks are pretty tough for a cast unit. Is that the case? I'm planning a nice little street deal with a carb and a little giggle gas. Maybe 450 on nuts and 600HP on the bottle. If I had more $$$'s i go for a forged crank (with more stroke). But you know how it is. Money's tight.

**Firebirdjones** · 05-18-2012, 10:33 AM

Sounds like a cool project. Cast cranks are pretty decent pieces. If I were building on a budget I wouldn't hesitate to use it and then possibly spend that money saved somewhere else on the engine.

If you were really worried about it, (and a 150 shot isn't all that much) you could use a progessive controller so you don't hit it all at once, it's a little easier on parts that way.

**Old55** · 05-18-2012, 11:01 AM

Yeah. I'm a gas user but on on "Old" SBC's. I have a full bodied 55Post car with a little sniff on it. Weighs 3750#'s and runs 9's. I am familiar with progressive controllers.

Bought a new 5.3l truck and was very impressed with it's performance(Especially after a Blackbear tune). Decided to build a 6.0l for a hotrod. We'll see how it goes.

**Firebirdjones** · 05-18-2012, 11:22 AM

Originally Posted by Old55

Yeah. I'm a gas user but on on "Old" SBC's. I have a full bodied 55Post car with a little sniff on it. Weighs 3750#'s and runs 9's. I am familiar with progressive controllers.

Bought a new 5.3l truck and was very impressed with it's performance(Especially after a Blackbear tune). Decided to build a 6.0l for a hotrod. We'll see how it goes.

Bit with the LS bug I see? I'm the same old school fart here with classic cars (mainly 60's muscle cars but I do have a 56 nomad) and I was bitten with the LS bug when we bought our first LS powered 4th gen camaro.
I've since swapped a 6.0 in my 72 blazer daily driver (sounded like a good idea

) However I still love the "old" engines just as much.