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#2427127 - 01/01/18 12:14 PM Offset grind 3.75 crank limit
PorkyPig Offline
mopar

Registered: 08/31/06
Posts: 575
Loc: home in bed
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?


Edited by PorkyPig (01/01/18 12:20 PM)

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#2427131 - 01/01/18 12:18 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
sgcuda Offline
master

Registered: 01/28/05
Posts: 3857
Loc: Charlotte, North Carolina
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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#2427134 - 01/01/18 12:23 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Al_Alguire Offline


Registered: 01/20/03
Posts: 16743
Loc: Rockville MD & Las Vegas
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.
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#2427187 - 01/01/18 01:03 PM Re: Offset grind 3.75 crank limit [Re: Al_Alguire]
Streetwize Offline
master

Registered: 01/20/03
Posts: 9612
Loc: Weddington, N.C.
There was an Engine Masters article where Buck Hinkle took an old 361 B and put a B based 3.74 crank offset ground from a 3.375" stroke B with a long 2.00" (327) SB Chevy rod and +.060 400 SBC 4.185" piston in it, so at the extreme with an RB 3.75" crank it looks like you could go easily to 4+ inches by going less than the 2.200 BBC journal, provided you can find a long enough and wide enough rod to work and a piston/pin combination as well.

Whether it's practical do do is another matter, buck actually also took the MAINS down to 2.45" SBC size and make steel bearing cap spacers to cut down on the bearing speed.
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#2427245 - 01/01/18 02:19 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
polyspheric Offline
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Registered: 10/10/07
Posts: 2658
Loc: New York
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]
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#2427249 - 01/01/18 02:22 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Al_Alguire Offline


Registered: 01/20/03
Posts: 16743
Loc: Rockville MD & Las Vegas
2.100" SBC rod journals smile
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#2427253 - 01/01/18 02:29 PM Re: Offset grind 3.75 crank limit [Re: polyspheric]
BradH Offline
I Live Here

Registered: 01/30/03
Posts: 13762
Loc: Valhalla... eventually
Originally Posted By polyspheric
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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#2427256 - 01/01/18 02:32 PM Re: Offset grind 3.75 crank limit [Re: Al_Alguire]
BradH Offline
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Registered: 01/30/03
Posts: 13762
Loc: Valhalla... eventually
Originally Posted By Al_Alguire
2.100" SBC rod journals smile

I was wondering about that, but I don't know if they're made long enough to work with an RB block the way the OP described it. shruggy
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#2427266 - 01/01/18 02:46 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Al_Alguire Offline


Registered: 01/20/03
Posts: 16743
Loc: Rockville MD & Las Vegas
We used a GRP aluminum rod..Makes for a world of possibilities smile

Motor didn't make huge power for sure. Ran 9.60's in a 3150lb back half Duster with iron heads. Not sure if I have any pics from the engine build it was a long time ago for sure. The engine was in the car when I purchased it and was assumed it was a 3.9" stroke deal. When I tore it down after making a few passes is when we found the 4" stroke and SBC journal, had Groden rods in it then. I replaced rods and pistons as well as new cam and rebuilt it. Was in this one from way back when...





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#2427268 - 01/01/18 02:52 PM Re: Offset grind 3.75 crank limit [Re: BradH]
sgcuda Offline
master

Registered: 01/28/05
Posts: 3857
Loc: Charlotte, North Carolina
Originally Posted By BradH
Originally Posted By Al_Alguire
2.100" SBC rod journals smile

I was wondering about that, but I don't know if they're made long enough to work with an RB block the way the OP described it. shruggy


Like I said, I just sold a set of Manley aluminum rods. 2.100 big end. .990 small end. 6.72 length. They were custom cut at the time, but I'm sure I didn't have the only set.

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#2427671 - 01/02/18 09:14 AM Re: Offset grind 3.75 crank limit [Re: sgcuda]
PorkyPig Offline
mopar

Registered: 08/31/06
Posts: 575
Loc: home in bed
I don't like the idea of aluminum rods in a street strip car. Looks like 3.9 is what I should expect staying with a 2.2 steel rod.

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#2427708 - 01/02/18 10:45 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
polyspheric Offline
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Registered: 10/10/07
Posts: 2658
Loc: New York
Aluminum can last a long time, if you warm it up first and keep the RPM down.
Triumph 3 cylinder bikes: 70,000 miles.
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#2427779 - 01/02/18 12:45 PM Re: Offset grind 3.75 crank limit [Re: BradH]
toddinNH Offline
member

Registered: 04/21/16
Posts: 8
Loc: NH, USA
Originally Posted By BradH



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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#2427875 - 01/02/18 03:22 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
polyspheric Offline
master

Registered: 10/10/07
Posts: 2658
Loc: New York
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
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#2427910 - 01/02/18 04:04 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
gregsdart Offline
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Registered: 01/21/03
Posts: 8252
Loc: Frostbitefalls (Rocky&Bullwink...
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.
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#2427938 - 01/02/18 05:08 PM Re: Offset grind 3.75 crank limit [Re: polyspheric]
BradH Offline
I Live Here

Registered: 01/30/03
Posts: 13762
Loc: Valhalla... eventually
Originally Posted By polyspheric
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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#2428086 - 01/02/18 09:47 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
TRENDZ Offline
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Registered: 01/24/05
Posts: 1668
Loc: Milwaukee WI
Time for a group hug😃
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#2428116 - 01/02/18 11:04 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
polyspheric Offline
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Registered: 10/10/07
Posts: 2658
Loc: New York
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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#2428295 - 01/03/18 11:34 AM Re: Offset grind 3.75 crank limit [Re: polyspheric]
pittsburghracer Offline
Slowride

Registered: 02/02/05
Posts: 12941
Loc: PA.
That’s why I stay out of these posts. I’m just a too-pid Millwright that likes to keep things simple. Lol.
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#2428306 - 01/03/18 11:49 AM Re: Offset grind 3.75 crank limit [Re: polyspheric]
WHITEDART Online   laugh2
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Registered: 10/06/11
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Loc: bean town
Originally Posted By polyspheric
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
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#2428310 - 01/03/18 11:55 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Al_Alguire Offline


Registered: 01/20/03
Posts: 16743
Loc: Rockville MD & Las Vegas
Lord knows I hate rpm smile
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#2428313 - 01/03/18 12:04 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
fast68plymouth Offline
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Registered: 01/20/03
Posts: 10875
Loc: So. Burlington, Vt.
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.
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#2428355 - 01/03/18 01:07 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Transman Offline
super stock

Registered: 03/27/11
Posts: 744
Loc: Michigan
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.


Edited by Transman (01/03/18 03:04 PM)

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#2428384 - 01/03/18 02:36 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
EV2Bird Online   penguin-006
No more politics

Registered: 06/23/14
Posts: 3824
Loc: Kansas Roads Between 0 and 140...
May 1980 Hot Rod Mag Al K built a 9:1 505 bracket motor offset a 440 crank to 4.00, six pack rods, iron heads, 332 DC mushroom cam. Mid 10-s in a cuda. Crank work was $300 then.


I can scan it if anyone wants to read it/pics ect.

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#2428401 - 01/03/18 03:05 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Transman Offline
super stock

Registered: 03/27/11
Posts: 744
Loc: Michigan
Yes - scan and post please.

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#2428530 - 01/03/18 07:17 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
EV2Bird Online   penguin-006
No more politics

Registered: 06/23/14
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Loc: Kansas Roads Between 0 and 140...
If you save them you can zoom them a bit and read them.


Attachments
1.JPG

2.JPG

3.JPG

4.JPG



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#2428531 - 01/03/18 07:18 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
EV2Bird Online   penguin-006
No more politics

Registered: 06/23/14
Posts: 3824
Loc: Kansas Roads Between 0 and 140...
The Rest


Attachments
5.JPG

6.JPG

7.JPG

8.JPG



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#2428635 - 01/03/18 09:49 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Transman Offline
super stock

Registered: 03/27/11
Posts: 744
Loc: Michigan
Thanks- I remember the article now that I see it. Corky was one of the premier porters back in the 70's and early 80's, Elkins at Diamond was at the top of the heap.

Note the 1.81" exhaust valve, we used those back in the mid 70's - cutting the maxwedge 1.88" down. I sold of bunch of those Stage IV heads back in the day that Corky did for me. Wish I had saved a few sets.

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#2428725 - 01/04/18 01:10 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
EV2Bird Online   penguin-006
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Registered: 06/23/14
Posts: 3824
Loc: Kansas Roads Between 0 and 140...
Its probably been 15 years since I looked at that mag but even then decent mopar builds were not super common then and ive welded and cut alot of cranks over the years for myself, there ugly when balanced but so is my sister and she had two kids. So...

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#2428766 - 01/04/18 07:31 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Transman Offline
super stock

Registered: 03/27/11
Posts: 744
Loc: Michigan
I wonder how many guys put their favorite racing jacket on when they torque their bolts ?

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#2428836 - 01/04/18 10:00 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
polyspheric Offline
master

Registered: 10/10/07
Posts: 2658
Loc: New York
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.
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#2428854 - 01/04/18 10:20 AM Re: Offset grind 3.75 crank limit [Re: polyspheric]
GTS340 Offline
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Registered: 12/06/13
Posts: 320
Loc: Romulus, MI
Originally Posted By polyspheric
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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#2428975 - 01/04/18 02:10 PM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Al_Alguire Offline


Registered: 01/20/03
Posts: 16743
Loc: Rockville MD & Las Vegas
My first stroker BB used a welded crank and a Ford piston...Had to get creative in the dark ages smile
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#2430211 - 01/06/18 07:24 PM Re: Offset grind 3.75 crank limit [Re: Al_Alguire]
PorkyPig Offline
mopar

Registered: 08/31/06
Posts: 575
Loc: home in bed
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. As a 451 440 block it can run in the high 10s.

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#2430364 - 01/07/18 12:48 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Cab_Burge Offline
I Win

Registered: 08/23/03
Posts: 30928
Loc: Bend,OR USA
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 shruggy
I'm not sure about how much the torque gain and PEAK RPM for both torque and RPM are affected by stroke changes confused work
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 shruggy


Edited by Cab_Burge (01/07/18 01:10 PM)
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#2430377 - 01/07/18 01:25 AM Re: Offset grind 3.75 crank limit [Re: PorkyPig]
Sport440 Offline
master

Registered: 01/20/03
Posts: 6568
Loc: Canton, Ohio
Originally Posted By PorkyPig
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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