Hi,
I am thinking of going to a 383 and I have a question about the pistons and compression.
Note I am looking for low compression becasue of my aplication.

First of with a 383 crank, I am using 5.56 inch rods. This allows me to use standard 350 sized pistons.
now here is the question if the "Stand piston" 350 size that I have in a 350 is rated at 8.81 to 1 compression. If I use it with my 383 will it still have the 8.81 to 1 compression.?
Or would the compression increase due to been stocker?

Thank you,

 

do a search for rb83l69 he's posted the math for you to plug your numbers into

 

Just say yes or no that it will effect compression with the differnet crank?
I want low compression! Thats why I am going to use those pistons.
Could you give me a clue?

 

Think about it: The piston is going to end up in the same place at the top of the stroke, so the "small" volume number (volume at TDC) is going to stay the same. The stroke increase will increase the large volume number (volume at BDC). Since CR is large volume divided by small volume, increasing the numerator will increase the CR.

"Give a man a fish, he'll eat for a day. Teach a man to fish, and he'll eat for a lifetime."

 

Just an opinion: You'd be much better off using longer rods and buying pistons that meet the rod length and desired compression ratio requirements.

 

Thank you,

If this is the cast I am going to go to a 350,

There is NO pistons that I could use with a 383 strocker that would give me my desired cr ratio.

In that case does anyone want to trade there forged 350 crank for my scatt forged racing 383 crank. It interall balanced with about 300 dollars of Heavy Metal in it ?
Mines never used?


Shane

 

Yes it will affect it. It will go up considerably, at least half a point.

Like ede said, I've posted the calculation method; so has Vader, and seems like a couple of other people. There's compression calculators all over the Internet also, that will give you a clue if you know the specs of the parts you're using.

 

What sized combustion chambers are you using? I'll find you a piston set that will work. There's a bezillion 350 pistons available. There's almost no combo that can't be built if you look around.

Given the low compression you're shooting for can I assume this is a nitrous or blower motor?

 

How did 8.81:1 CR get cast into stone?

There are a number of ways to get to a final CR. Most published CR numbers make so many assumptions that you can't take them to the bank, anyway. You have to do everything the way they did to come up with that number, and when you get right down to it, static CR is only one factor in an engine build, anyway.

Too much compression with a given piston? Use a thicker head gasket or unshroud the chambers a little - machine the piston crowns, even.

Too little compression with a given piston? Shave the block deck and/or heads, use thinner head gaskets to reduce the TDC volume.

 

Why go to a 383, you have an "11 second 305"...
https://www.thirdgen.org/techbb2/sho...hreadid=209035

no wait it's TPI...
https://www.thirdgen.org/techbb2/sho...hreadid=209036

no wait it's got a quadrajet...
https://www.thirdgen.org/techbb2/sho...hreadid=208054

no wait it's already got a 383:
https://www.thirdgen.org/techbb2/sho...threadid=29649

no wait it's got "vortex heads and a truck intake"...
https://www.thirdgen.org/techbb2/sho...hreadid=204591

no wait it's got one turbo and you're going to bolt on another one...
https://www.thirdgen.org/techbb2/sho...hreadid=209030

I vote it's ban time.

 

"Give a kid a pill, he might be less of an idiot for a day. Give a kid a lobotomy..."


(Dang, sucked in again. Need to look closer at those usernames...)