can,t find matching pistons

Grumpy · Oct 24, 2017

grumpy I've purchased a set of aluminum big block cylinder heads and after doing some research Ive found several places that mention the fact that the heads I purchased don,t have the spark plug located in exactly the same location.
now thats not an issue with most flat top pistons and reasonably low compression engines but I've seen several references that indicate that even moderate dome height pistons must be custom machined to clear, and I.m building an engine with a domed piston to get about 12.5:1 compression, I sure don,t want the pistons hitting the spark plugs, any suggestions?

Any decent, experienced machine shop can measure your cylinder heads combustion chamber,
and calculate the required clearances after measuring your heads combustion chamber, and then do the correct machine work on your piston domes,
machining the domes for adequate,spark plug,clearance,
this is a very common issue and easily resolved,always deal in proven facts, and it damn sure helps to have precision measuring tools.

common sbc pin height info
Specs

Comp Height 5.565" Rod - 1.561

Comp Height 5.7" Rod - 1.433

Comp Height 6.0" Rod - 1.13

Pin Diameter - 0.9272

https://www.enginelabs.com/engine-tech/engine-blueprinting-how-to-check-piston-to-valve-clearance/

and it seldom costs much to have done.
you can also order custom pistons, exactly matching your heads, very easily, just talk too the piston manufacturers about your particular combo, most will be well aware of issues dealing with clearances while using different cylinder heads and can either suggest a matching design piston or provide custom clearance work on an ordered set of pistons for usually a nominal cost.
If you want to get it exactly matched take 6-7 large well lighted, clear pictures of the cylinder heads and combustion chambers with a ruler laid on the head as a reference, then, you can level the cylinder head carefully with the combustion chamber facing up and the heads mating surface level, spray a combustion chamber with furniture wax coat it with a thin coat of saran plastic wrap and pour fiberglass resin into it, once it hardens, send that to a piston manufacturer of your choice and they can match the dome machine work precisely,
don,t forget to check the valve clearance relief notches and use some clay to verify piston to cylinder head combustion camber and valve clearances during the pre-assembly checks,
I don,t know any old school racers that don,t have a block of clay in their tool box for that reason.

https://uempistons.com/p-32-piston-compression-height-calculator.html

https://www.lunatipower.com/compression-height

http://www.wallaceracing.com/Calc-Piston-Pin-Height.php

0607em_20_z+engine_assembly+clay_method.jpg

no, if you have any engine and want too find the rure compression you need to deal in verified fact, not assume what the manufacturers suggest is always correct.
you just cc the heads, combustion chamber volume, place the piston 1" down the bore and seal the rings gap around the pistons,
above the rings with moly grease or Vaseline and measure that volume and calculate what a bore diameter cylinder 1" tall would
contain, minus the volume you,ve measured, the piston dome took up.then calculate the true compression.

read related linked info

http://garage.grumpysperformance.co...n-chamber-or-piston-dome-or-port-volume.2077/

http://garage.grumpysperformance.com/index.php?threads/ccing-my-heads.14187/#post-71989

http://garage.grumpysperformance.co...ng-combustion-chambers.2630/page-3#post-77963

can,t find matching pistons

Grumpy

The Grumpy Grease Monkey mechanical engineer.