Offset grind 3.75 crank limit
#2427127
01/01/18 03:14 PM
01/01/18 03:14 PM
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Joined: Aug 2006
Posts: 610 long time lurker, short time p...
PorkyPig
OP
mopar
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OP
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Joined: Aug 2006
Posts: 610
long time lurker, short time p...
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I have a new 440 3.75 crank that checked out good on journal size and taper. If I have it offset ground to use a 2.20 rod, what is the most stroke I should expect? Is there any option for an even smaller rod journal size that is still strong enough for a stroked 440?
Last edited by PorkyPig; 01/01/18 03:20 PM.
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2427131
01/01/18 03:18 PM
01/01/18 03:18 PM
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Joined: Jan 2005
Posts: 4,243 Charlotte, North Carolina
sgcuda
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master
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Charlotte, North Carolina
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You can offset grind to a 3.90 stroke and use your favorite BBC rod. You could go a little more if you went with a sbc journal 2.100". I just sold a set of Manley aluminum rods exactly for that purpose.
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2427134
01/01/18 03:23 PM
01/01/18 03:23 PM
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Joined: Jan 2003
Posts: 19,367 Las Vegas
Al_Alguire
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I Live Here
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3.90 is the most common way as stated. IMO makes a very good engine package for sure. I did have one done to a 4" stroke as well. Worked fine and that crank is still alive and working as far as I know in the old Duster.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2427245
01/01/18 05:19 PM
01/01/18 05:19 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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The math: maximum offset = old journal - new journal. Stroke change: offset (- .005" or so for the grinder to spark out unless the crank is new) 2.375" (B/RB) - 2.20" (BBC) = .175" max 3.75 + .170" = 3.92" max You can have any stroke change between - the offset to + the offset.
[Please note: it's not the offset X 2]
Boffin Emeritus
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Re: Offset grind 3.75 crank limit
[Re: polyspheric]
#2427253
01/01/18 05:29 PM
01/01/18 05:29 PM
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Joined: Jan 2003
Posts: 15,439 Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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The math: maximum offset = old journal - new journal. Stroke change: offset (- .005" or so for the grinder to spark out unless the crank is new) 2.375" (B/RB) - 2.20" (BBC) = .175" max 3.75 + .170" = 3.92" max You can have any stroke change between - the offset to + the offset.
[Please note: it's not the offset X 2] That's a nice explanation. At one point I made a simple Excel spreadsheet that allowed entering stroke, rode length & deck height to calc the piston compression height. It made it easier to figure out if there was any combination of stroke/rod/CH for an already-machined block that could be used with off-the-shelf parts, rather than having to get more expensive custom pistons made. Don't have it any more, but something like it helps figure out "real world" combinations quickly.
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2427708
01/02/18 01:45 PM
01/02/18 01:45 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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Aluminum can last a long time, if you warm it up first and keep the RPM down. Triumph 3 cylinder bikes: 70,000 miles.
Boffin Emeritus
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Re: Offset grind 3.75 crank limit
[Re: BradH]
#2427779
01/02/18 03:45 PM
01/02/18 03:45 PM
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Joined: Apr 2016
Posts: 407 NH, USA
toddinNH
Egghead
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Egghead
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NH, USA
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At one point I made a simple Excel spreadsheet that allowed entering stroke, rode length & deck height to calc the piston compression height. It made it easier to figure out if there was any combination of stroke/rod/CH for an already-machined block that could be used with off-the-shelf parts, rather than having to get more expensive custom pistons made. Don't have it any more, but something like it helps figure out "real world" combinations quickly.
I only work on really odd stuff so everything is custom. Expensive yes, but I only do client's builds. Inline 4 valve stuff is a small market. At any rate, here is a decent CH calculator: Compression height calculator 1
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2427875
01/02/18 06:22 PM
01/02/18 06:22 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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New York
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A calculator? A spreadsheet? How about a hand-crank adding machine circa 1880? This is far, far simpler than calculating chamber volume.
If you're still not sure: deck height - rod length - stroke length ÷ 2 = piston CD
Boffin Emeritus
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2427910
01/02/18 07:04 PM
01/02/18 07:04 PM
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Joined: Jan 2003
Posts: 10,006 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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I Live Here
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I built a 4 inch x 4.350 440 (475cubes) offset grinding a stock crank to 2.100 using custom 7.10 rods several years ago. The rods were on 396 BME cores. For a street strip application with small port heads the stress on those rods would be very low. I talked to the guy i sold that shortblock to about fifteen years after the sale. He had been racing it , street driving it a lot, nitrous used. It was still running fine.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Offset grind 3.75 crank limit
[Re: polyspheric]
#2427938
01/02/18 08:08 PM
01/02/18 08:08 PM
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Joined: Jan 2003
Posts: 15,439 Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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A calculator? A spreadsheet? How about a hand-crank adding machine circa 1880? This is far, far simpler than calculating chamber volume.
If you're still not sure: deck height - rod length - stroke length ÷ 2 = piston CD Get over yourself. I threw the spreadsheet together for fun so that I could plug in the #s more quickly than repeating the same calculation with only one variable changing.
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2428116
01/03/18 02:04 AM
01/03/18 02:04 AM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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In the event that this has escaped your notice: My remark was about the previous posts. His remark was about me.
Boffin Emeritus
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Re: Offset grind 3.75 crank limit
[Re: polyspheric]
#2428295
01/03/18 02:34 PM
01/03/18 02:34 PM
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Joined: Feb 2005
Posts: 20,174 PA.
pittsburghracer
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"Little"John
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That’s why I stay out of these posts. I’m just a too-pid Millwright that likes to keep things simple. Lol.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: Offset grind 3.75 crank limit
[Re: polyspheric]
#2428306
01/03/18 02:49 PM
01/03/18 02:49 PM
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Joined: Oct 2011
Posts: 3,036 bean town ....Ca
WHITEDART
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Aluminum can last a long time, if you warm it up first and keep the RPM down. Triumph 3 cylinder bikes: 70,000 miles. the two things most Racers don't want to do
In the 8s N/A.with Brett miller W8's 5.07 at 133 at 2700lb
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