Offset grind 3.75 crank limit

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?

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.

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.

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.

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]

2.100" SBC rod journals

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.

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.

We used a GRP aluminum rod..Makes for a world of possibilities

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...

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.

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.

Aluminum can last a long time, if you warm it up first and keep the RPM down.
Triumph 3 cylinder bikes: 70,000 miles.

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

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

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.

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.

Time for a group hug😃

In the event that this has escaped your notice:
My remark was about the previous posts.
His remark was about me.

That’s why I stay out of these posts. I’m just a too-pid Millwright that likes to keep things simple. Lol.

the two things most Racers don't want to do

Lord knows I hate rpm

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.

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.

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.

Yes - scan and post please.

If you save them you can zoom them a bit and read them.

The Rest

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.

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...

I wonder how many guys put their favorite racing jacket on when they torque their bolts ?

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

My first stroker BB used a welded crank and a Ford piston...Had to get creative in the dark ages

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.

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

If you have all the parts for the 451, rods pistons, etc stay with that.

The 451 is a great motor combo.