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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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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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.
[image][/image]
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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: 19,357 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
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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: 396 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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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
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gregsdart
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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
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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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polyspheric
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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.
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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
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pittsburghracer
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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
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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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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2428313
01/03/18 03:04 PM
01/03/18 03:04 PM
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Joined: Jan 2003
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fast68plymouth
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I've thrown away enough cracked stock BB Mopar cranks that came out of bracket cars to have reached the point where I now only use them in pretty basic street or street/strip stuff.
No way would I bother having one offset ground for more stroke when I can get a 4340 piece for under $800.
But that's just me.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2428355
01/03/18 04:07 PM
01/03/18 04:07 PM
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Joined: Mar 2011
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A727Tflite
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Interesting - you mention big block cranks cracking - how do the Chevy cranks do, do they crack too or not? Ford?
Just you're observation please.
Last edited by Transman; 01/03/18 06:04 PM.
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2428531
01/03/18 10:18 PM
01/03/18 10:18 PM
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Porter67
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2428836
01/04/18 01:00 PM
01/04/18 01:00 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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Can't follow the text, they refer to "adding 1/2" to the stroke", using the stock rods (no offset), and 505" with 4.00" is just under 4.500" bore - not something you would do.
Boffin Emeritus
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Re: Offset grind 3.75 crank limit
[Re: polyspheric]
#2428854
01/04/18 01:20 PM
01/04/18 01:20 PM
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Joined: Dec 2013
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Can't follow the text, they refer to "adding 1/2" to the stroke", using the stock rods (no offset), and 505" with 4.00" is just under 4.500" bore - not something you would do. They welded the journals to get to 4.250 stroke with the stock rods
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2430364
01/07/18 03:48 AM
01/07/18 03:48 AM
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Joined: Aug 2003
Posts: 43,115 Bend,OR USA
Cab_Burge
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I Win
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If your motor makes 1.2 HP per C.I. how much HP does it gain 451x1.2=541.2 HP compared to 1.2x470=564HP. Of course if it makes more or less HP per C.I. the results will vary accordingly I'm not sure about how much the torque gain and PEAK RPM for both torque and RPM are affected by stroke changes I do know that on my last pump gas street and strip car increasing the stroke .050 (went from 4.25 to 4.300)helped it by .2 ET and 2.5 MPH
Last edited by Cab_Burge; 01/07/18 04:10 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Offset grind 3.75 crank limit
[Re: PorkyPig]
#2430377
01/07/18 04:25 AM
01/07/18 04:25 AM
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How much difference would 19 cubic inches really make going from 451 to 470? My 3.75 crank is a new offshore 4340 that measures OK. But if I only go to 3.91 I don't know that it would be worth the money for new rods and pistons with only that much offset grind. If you have all the parts for the 451, rods pistons, etc stay with that. The 451 is a great motor combo.
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