In need of 283 .030 pistons

[Bobillot]

Hello Im in need of some 30 over pistons for my 283 truck engine I have some but they are 0.057 at tdc below the deck. I just had the 283 bored and honed to 3.905 and have a new everything for it. But I noticed the deck seemed high and I checked out the new and the old STD pistons.

The new to this engine 30 over pistons have a compression height of 1.78 and the originals have a height of 1.83. So with these pistons its a substantial hit to comp ratio and the engine is going back into my 1975 C30 hay hauling flat bed dump truck so it needs all the power it can get.

It would get us back hauling hay more efficiently. Thank You for any help!

[truckdude239]

i can find 1.80 compression height, but i see nothing at 1.83 https://cnc-motorsports.com/keith-bl...ore-3-905.html

[scottofksu]

It might be cheaper to have the block decked... Dial in your compression ratio by decking to the preferred compression ratio relative to your piston volumes and head gasket selection. What heads are you running and do they have good squench potential given your piston surface characteristics? Good luck, brother! I hope your hay hauler gets back up and running stronger than ever before sloppy weather hits!

[Accelo]

Your pins and rings have been installed and the block bored to the pistons. So no returns. I assume you are attempting to salvage all the work you have completed.
Other pistons may not fit the block. Forged or cast pistons take wildly different piston-to-wall clearances.
I did the same thing years ago. When I read the "* fine print" It mentioned the lower compression height. In my case, it was .020 lower.
This is done so the people who deck the block are not running into piston clearance issues.

I agree "It might be cheaper to have the block decked". That typically includes the intake manifold machining but not always. Decking the block requires disassembly.

Possibly you can find heads with smaller combustion chambers. That leaves the quench quite large and not conducive to power production.
As an interesting comparison, LS motors have the piston sticking out of the bore at a nominal .005 to maximize the quench.

[mattfranklin]

In rough back-of-the-envelope calculations...
Dang, that's 6cc! About 10% of a 64cc chamber.
and maybe worth a point of compression ratio?
Rough rule of thumb the Car Craft and Hot Rod magazine guys used to repeat was that each point of compression ratio was worth about 4% of free horsepower. (For more detail search out the classic SAE paper on that topic by Caris and Nelson at GM in the late 1950s).
Could any of us notice a 4% difference? I know it's not perfect and would probably bother me. But what's the cost of getting it right? Just putting it out there. It would bother me enough to fix it, but sometimes I make decisions out of passion for the hobby, rather than on engineering economics. :-)
EDIT: Here's a link, but they make you pay -- https://www.sae.org/publications/tec...ontent/590015/

[THI]

Silv-O-Lite cast have a compression height of 1.779 and Keith Black hypereutectic have a compression height of 1.805

[Willshook]

really don't wanna run with that kind of quench, which is even worse when you add in even a thin head gasket. So it's not just about the pistons compression height.

Take it apart and get it zero decked. run an~.040+ gasket.

[GSP7]

Originally Posted by scottofksu

It might be cheaper to have the block decked... '..................!

..

No! do not do that

Just go buy the correct pistons

.

[66 C10 383]

I have the same dilemma with a 383 I had a guy machine & assemble for me. The pistons were chosen with the head gaskets for. 045" quench. Long story short, he didn't zero deck the block like I asked him to. Found out later my pistons are
017" down from TDC.

I hadn't installed the engine or even fired it up but he's out of business now.

Since it's a 2pc rms block & I'm running hydraulic roller cam I thought about just putting everything along with a different 3.75 crank into a 1pc rms roller block.