Head clearance
Thread Starter
Racer
Joined: Apr 2006
Posts: 300
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From: Joplin Missouri
Head clearance
What is the minimum clearance between the top of the piston dome and the bottom of the valves? Im affraid that I dont have enough room. If I dont what are some of my options thicker gaskets, spacer, or shaving the dome? Thanks for all of your help. 
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Joined: Sep 2005
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From: South of giving a damn
St. Jude Donor '11, '17
Throw us a bone here. What are the piston & head specs? What is your deck height? Yes, you can go with thicker head gaskets. I believe there is some putty like compound that you can put on the pistons, assemble the engine & hand rotate the assembly, then pull the heads & measure the putty thickness. I know with flat top pistons you need .040 -.050 for proper quench.
Thread Starter
Racer
Joined: Apr 2006
Posts: 300
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From: Joplin Missouri
My heads are big block '188's with 118cc combustion chamber. The block is a standard deck, the pistons are JE open chambered with + 45cc dome. The cylnders are bored +.60 with with a 4.25 crank and +.25 rods. According to JE's website I am looking at about a 13:1 comp ratio a bit more than I wanted but hopefully enough to get me my desired 600 hp. Thanks
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
I can not see a 1/4 inch stroker crank plus 1/4 inch longer rods fitting inside a stock 454 block. It just doesn't fit.
You are not getting the right information.
If you went to a stroker crank you need matching pistons with raised wrist pins.
As for the 1/4 inch longer rods they just won't fit.
You are not getting the right information.
If you went to a stroker crank you need matching pistons with raised wrist pins.
As for the 1/4 inch longer rods they just won't fit.
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
A 1/4 inch stroker crank is actually only 1/8th inch longer stroke so it pushes a piston 1/8 inch or .125 higher up the bore. A average stock block will have about .030 deck height or the piston will be down in the hole below the head surface by .030. Ideally you want zero deck height so if you take the .125 minus the .030 you need to machine .095 off the head of each piston. This can be done but not usually with domed pistons, flat top yes.
As for the 1/4 inch rods impossible
As for the 1/4 inch rods impossible
Thread Starter
Racer
Joined: Apr 2006
Posts: 300
Likes: 0
From: Joplin Missouri
The kit I was told to buy is a 4.25 stroke and 6.385 rods. The pistons were said to be what I needed with this set up. I plan to put some clay on the piston to see where Im hitting. Am I correct in saying I need to have about a .05 clearance for proper quench?
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He's basically got the same thing you do Norval with the 540. He has a short deck block, a 4.250 crank and the 6.385 rods. It will need a piston with a 1.270-1.290 compression height. The wristpin will slightly intrude into lower ring land and need support rails for rings. He just doesn't have that nice big 4.500 bore!!
Anyway, you're building a bad boy race gas motor..so shoot for all the compression you can get. If you have steel rods you can run quench down in the .030-.035 range. My 540 is at .028!! Now my pistons are REAL close and slightly kiss heads.....but works great.
A thing you will have to consider is piston to wall clearance..if it's loose you will get more piston rock and will need more quench distance. Also be sure to really check the dome area..sometimes they will kiss chamber even though deck clears fine.
JIM
Anyway, you're building a bad boy race gas motor..so shoot for all the compression you can get. If you have steel rods you can run quench down in the .030-.035 range. My 540 is at .028!! Now my pistons are REAL close and slightly kiss heads.....but works great.
A thing you will have to consider is piston to wall clearance..if it's loose you will get more piston rock and will need more quench distance. Also be sure to really check the dome area..sometimes they will kiss chamber even though deck clears fine.
JIM