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Stroking the 225?
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Author:  polkat [ Thu Feb 17, 2011 12:39 am ]
Post subject:  Stroking the 225?
In the articles section there's a write up by Doug Dutra that suggests one way to stroke a 225 is to offset grind the journals by .025" and then use .030" undersize bearings. He says that this alone will create a 240 engine with 9.5:1 compression. Unless my math is off (quite possible) that will only add about .0125" of stroke. Will that really raise cubic inches by 15?

Sounds pretty easy, but looking around the sites, I can't find any .030" undersize bearings (which is admittedly a pretty big undersize). And what exactly is the .005" 'journal cleanup' about (does that mean the journal is actually cut .030")? Has Doug built this, or anyone here done this. What problems besides finding the bearings are there?

Also, what engine size and compression with this mod, and say a .030" overbore result in?
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Author:  66aCUDA [ Thu Feb 17, 2011 9:15 am ]
Post subject: 
Doug is on the site here as DOC or Doctor Dodge. I would PM him and ask for his phone number. He lives just south of you.
Frank
Author:  ceej [ Thu Feb 17, 2011 9:18 am ]
Post subject: 
If you re-read that article, he was basing the displacement on a 0.100" Overbore.

Offset grinding .025 will increase the stroke .05" total. The piston will travel further down the bore as well as further up.

CJ
Author:  Shaker223 [ Thu Feb 17, 2011 9:43 am ]
Post subject: 
On a std bore engine, the offset grind of .025" is worth about 2.5 cubic inches.
Author:  Doc [ Thu Feb 17, 2011 9:57 am ]
Post subject: 
Crank grinders will need at least .005 to clean-up any "back-side" journal wear or mis-indexing issues.

The numbers I get for a 3.430 bore with a 4.175 stroke are 231 cubes with 8.9 compression. (56cc head & -.115 deck height)

For me, off-set crank grinding helps by giving you more compression, without a lot of block or head milling, more then it is about getting increased displacement.
DD
Author:  polkat [ Thu Feb 17, 2011 12:20 pm ]
Post subject: 
Thanks for clearing that up. My actual interest is in building a slant for quench (say around a .045" clearance). Maybe using 198 rods? I realize that compression would be high, but one of the benefits of quench is that it fights detonation. Would there be a better approach to doing this besides offset grinding?

Bare with me. I have lots of big block knowledge, but am fairly new to the slant. Thanks!
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Author:  Doc [ Thu Feb 17, 2011 1:21 pm ]
Post subject: 
You really need a closed chamber head to do quench in a SL6.
(and the 198 connecting rod / short piston set-up)
DD
Author:  polkat [ Fri Feb 18, 2011 8:51 pm ]
Post subject:  Question for Doc
Doc, in your articles section here you wrote about the differences with the newer head configuration; at the very bottom of the page is a picture showing what are obviously positive decked pistons. Was that acheived with a certain piston, or by milling the deck, or both?
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Author:  Doctor Dodge [ Sat Feb 19, 2011 9:54 am ]
Post subject: 
The pistons were milled first, the engine "mocked-up" and then the block deck machined to set the quench distance.

That engine did not last long for me... the edges of the high quench "dome" area on the piston super-heat, melt and clog-up the top piston rings.

Running a richer mixture may help but my general thinking is that it is hard to stick that small mass of aluminum into the "blow-torch" environment of that quench area and not get some melting. A thermal barrier coating may also solve this issue but I went back to doing "flush deck" quench set-ups, which are much easier to set the quench distance (head gasket thickness adjustments) and allow for cooler piston operation.
DD

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