Ordering pistons

[BGNeXtreem]

How do I come up with the compression distance, dome/dish vol to get the. Correct piston ordered ? Very important to get this right as it would be a 800 dollar mistake if I get it wrong ! A little info on this Frankenstein motor its 3.860 will run a 3.550 stroke crank on a Chevy H beam 6' inch rod with a 2.100 bushed end any help much appreciated

 

[bison]

You need the deck height info and where in the hole you want the piston before you can determine compression height.

 

[BGNeXtreem]

Ok educate me on how to get these figures Bison

 

[BGNeXtreem]

Looking to get 9.5:1 compression or 9:1

 

[bison]

Ok educate me on how to get these figures Bison

To get an exact number on the deck height you will need a machine shop to measure. You need the centerline of the crank to the top of the deck. You could take half the main bearing bore diameter and use a large caliper to measure the bore to deck dimension then add half the bearing bore dimension to get a number within a couple thousandths. A machine shop will get this number within .0005 with their equipment if you want it that accurate, this doesn't consider if you cut any material off the deck after you measure either. I shoot for .010 in the hole. Which means the top of the piston us .010" below the deck surface at tdc so that in the future i can cut tge deck a few tines and still have room to avoid piston to hrsd clearance issues. .030 is as close as you should piston to head. Once you determine how far in the hole you want to be you can determine the compression height and then you can start looking at your clearance volume. You also need to know which gasket you are using and the cylinder head combustion chamber volume. Once you provide that info i can quickly tell you what cc dish you will need to get you desired CR. The deck height is required though. You can't assume it's exactly as published in the blueprint even if you are very certain the block has never been decked or line bored, Then again you could be off a couple thousandth and it won't kill you since you probably aren't blueprinting everything to the .0001 anyway. Some expensive race engines are within .0001 on everything. Every journal is ground for stroke and everything is blue printed. Everything is controlled and recorded including atmospheric conditions. An example of an engine like that would be a NASCAR engine. They run 7000rpm all day and make about 800hp.

 

[BGNeXtreem]

Thank your for laying it all out on the table im sure I'm not the only one needing to see this again thanks

 

[we4Mateo]

Thank your for laying it all out on the table im sure I'm not the only one needing to see this again thanks

You are not...

 

[dr_frankenstein]

arent you worried about turning down the rod journals to use chevy stuff?

it removes an awful lot of meat in that area

 

[Nick Micale]

arent you worried about turning down the rod journals to use chevy stuff?

it removes an awful lot of meat in that area

He should worry, here is the result of a BMS crank using a 2.100" Chevy rod.

I would NEVER do a crank like this again in a performance build.

Ordering custom pistons is a crap shoot, especially for the novice as other things must also be considered like getting the right ring package. My feeling is the machinist should be responsible for ordering and fitting the pistons to my requirements.

If the pistons are not right, guess who pays, not me!

 

[BGNeXtreem]

Awe man Nick thanks I def respect your wisdom I guess this crank is a boat anchor? :-(

 

[charlief1]

Nice door stop Nick. With the cost of H or I beam rods now I wouldn't even consider using a chevy rod unless it was an oddfire crank. It just removes way to much meat off the crank. If I'd had the $ you wouldn't have that crank and I'd hate to see it get screwed up.

 

[BGNeXtreem]

I have several options a few different blocks no big deal and if you wanted it you could have bought it still could if you wanted it Charlie F1 the guy is minutes down the road so I bought it

 

[BGNeXtreem]

I still want to go stroker Nick so penny for your thoughts

 

[charlief1]

I have several options a few different blocks no big deal and if you wanted it you could have bought it still could if you wanted it Charlie F1 the guy is minutes down the road so I bought it

If you decide not to use it I'll see about getting the $ together and get it from you. Right now the money's tight and I've got a few deadbeat customers that just don't want to pay up.

 

[BGNeXtreem]

If Nick says don't use it as he just said I'm not using it so u can pm me when your ready for it

 

[dr_frankenstein]