Pm'd you Steve...

 

bobweight is 1750. now since i dont know if thats good or not tell me what that means.

 

The stock LT1 bobweight is about 1950. The LT4 bobweight is a bit less than that.

Most forged 383's will go with about a 1700 to 1800 bob weight depending on the cash they spend. Lighter parts can get you into 1600 range without breaking the bank.

Full-effort 383/396 assemblies are pretty guarded in what they use for a bobweight but I wouldn't be suprised to hear of 1500 or less at that range. The bobweight is also sujective to the engine's expected rpm range (I belive higher rpms require less bob weight in a effort to reduce inertial moment?)

There's also a science of "under-balanced" cranks that are intentially under balanced to reduce mass but sacrifice smooth running / bearing life to do so... I'm under the impression that an intentionally underbalanced crank is race-only, but maybe it's more common than I've heard (anyone else know?)

6" rods tend to lessen bobweight as the rod gets a bit longer/heavier, but the piston's shorter compression height makes for a lighter slug to offset the difference. Likewise I believe floating wristpins also reduce the weight a bit as press-fit pins are typically longer and a tad thicker (although there's obviously ways to reduce wristpin weights beyond this alone).

1750 sounds good. Won't have to take out much if you go the light route, and if you go with a heavy assembly (for nitrous use say) the Mallory won't get insane (that stuff's pricey).

I'm trying to pick a nice set of 6" rods to match this crank... but I need to weigh out my pistons/wirstpins and see where I am.

 

if i was to get one of these cranks,.. a set of 030 x1.420 pistons, what sort of comp ratio would it get me with a set of stock iron heads??
thanks
nick

 

Depends on the piston Shamu...... Dome/reverse dome/flat top???

 

Not to mention deck height, head gasket thickness and head gasket diameter.

 

i can only guess at these questions,.. flat top piston? with some valve reliefs=-5cc?,... stock deck height,.as for head gasket diameter,.. um?? 4.030=? gasket thickness? um?......regular lt1 iron gaskets?
i'm want the motor to be less than 11.1cr preferably 10.8,

 

Probably time for you to do a little research. Stock block height is 9.025, so with the piston your talking about I'm assuming your talking about a 5.7" rod which gives you a deck of .005, iow, your piston would be 5 thousandths "in the hole" at TDC. I don't have any head gasket specs in my head except for the Felpro 1074 which has a compressed thickness of .039 and a bore diameter of 4.130, (you probably won't find a head gasket with a 4.030 bore BTW). So using these numbers and a 54cc head with a 5cc flat top piston you come up with approx 12.6:1 cr. So you either need more dish in the piston or a larger combustion chamber volume using these numbers. This doesn't even take into account your Dynamic Compression which in many ways is more important because that's the primary consideration which will help determine if your engine will run well on pump gas. Below is a link to a DCR and SCR calculator that might help. It's decent but there are other calculators around that take even more factors into consideration, one of them being the depth of the first ring land which also affects combustion chamber volume. Good luck.

http://webpages.charter.net/darrell1/dynamiccr.htm

 

thanks for the reply,.. i obviously do not know enough,.. so yes i will have to read,..
as i stated just 10.8 cr is what i am aiming for.

 

Gotta bring this thread back up to the surface.

The crank I purchased from BigCowlImp (the Cola 3.800") is at the balance shop right now. They say it is way too light at the front of the crank. It needs 300+ something grams of Mallory or it needs a 400 Damper that you can bolt weight to. It will cost $700+ bucks to balance this thing with a neutral LT1/LT4 damper.

Has anyone here with this crank run into this problem and if so how did you solve it? A simple solution of buying a 400 damper is not so simple due to the optispark being in the way. (this is going on an LT1)

Thanks you for the quick reply. I need to find a solution or get a different crank and set this one on the shelf and lable it USELESS.

Karl Ellwein

 

I don't have the answer either, but I have the same crank and I'm about to get it balanced. If it's 700.00 I'll go get another crank and put this one up for sale. I'm sure that ton's of people will want one after looking at this thread. What about balancing it using a neutral flywheel, will this make it worse?

 

I just had mine balanced fine...swapped to 4340 rods and everything. It took 3 slugs of mallory but it balanced fine and with cleaning the block, honing and inspection, fitting the new rods and pistons, clearancing the rods and everything, it only cost $450.

I think the hardest thing is finding a machine shop that would rather earn a customer and do a good job than make a few extra dollars.

 

Ok. So yours needed 3 slugs of mallory. the balance shop told me 3 slugs too. or maybe 4? But that is a TON of mallory.
You found a great shop to do all that for $450.
Wish I could find a shop like that.

It is still too much mallory for my taste and I was thinking NO mallory.
or maybe "some" mallory.
Neutral flexplate won't help apparently.

Where is your shop located? Anywhere near Maryland.

I asked them about different rods and they said a 5.7" rod would help a tad bit but it would still need gobs of mallory.

For those about to balance, keep me posted. For those that did balance let me know the details. Thanks.

Karl

 

Karl,

What rods are you using and what length? Same question to you Dhiroc, if you guys don't mind.

Thanks.

 

Eagle H-beam 6.0" (Mahle flat top pistons and rings).


Also, I'm suprised this thread is still in "Advanced tech" wonder if it should be moved maybe to LT1 Tech. I'm just glad for the thread to see what others have done to solve the problem.


dhirocZ I am very jealous of you for having a shop that will do all of that work for so cheap. I thought you mentioned you got the mallory and balance for just $450 but I re-read and you got block work and rod-piston work and the balance with mallory for $450! That is not possible for just an average joe-blow customer like me. I don't think I'll find a shop anywhere that would do that but yea, you never know unless you look.

Karl
PS: edit: I'm really hoping someone can offer a 400 style damper and pulley solution that I can hobble together for my LT1 accessories. That would be the cheapest fix that I can see. I have no idea but am quite sure a simple 400 damper will bump the opti-spark. and you cannot just bolt on a 400 damper onto the stock hub or an ATI hub. Has anyone added weight to a stock LT4 damper? ? ? ? Maybe I can do that? ? ?