I see that I have a choice between a 6.800 or 7.100 rod for my stroker build this winter. What is your choice and why?

440 block
4.250 crank
10:7 CR
E heads
727
3:23 gear
e body
Street 90% Strip 10%

Longer rod equals shorter lighter piston. Either will be decent rod angle. Honestly though, I doubt you or the engine are going to know the difference.

The 7.10 rod will make the lightest rotating assembly, so I would go that way. Some will say the shorter rod will make more torque, but I have read differently, from some very knowledgeable people. Besides taking stress off the main caps, the lighter 7.10 deal will have a little less side thrust on the cylinder walls, and it makes sense to me to build a stock block motor for the least stress possible. I split a cylinder in a 400 block years ago that checked OK before machining, so I like to err on the safe side.

I tend to agree with the longer rod and the lighter
piston BUT on the street which this is I like the longer
piston for better stability... yes you can do it with
either rod but everyone so far has stated LIGHT pistons
which in MOST cases is shorter.. on the street and longevity
I prefer the longer piston IF its still in the bore..
with the shorter rod you move the pin height down
(pushing the piston up for more piston in the bore)..
JMO... I'm no pro engine builder

Jim.. I was looking at your aviatar pic... is that
a back fire out the scoop or just the lighting

I agree with you guys about the taller piston, but even with a 7.1 rod, the piston in this case will still have plenty of skirt. Around 1.5 inches.
I would look at the piston heights in both kits too though, and figure out which one will be closer to zero deck. Sometimes, these kits come with a piston that's not optimum just because it makes it easy to put the kit together.

I like and use the longest rod I can get on my street and strip and all out drag race motors My 518 C.I. 400 block low deck stroker had a 6.800 long rods with the 4.300 stroke, that = a 1.58 rod length to stroke ratio, the piston was very light, 456 grams without the rings or wrist pins That long of a stroke in a low deck ends up making the pistons skirts come out of the bottom of the bores, even with a very short piston skirt I ran the motor on the street some and race it more than I did drive it on the street I shifted it at or above 7000 RPM on every pass, the piston skirts had witness marks on the skirts but had no measurable wear on them and it didn't use oil I do have several street and strip pump gas 440 blocks running on pump gas with 4.25 strokes and 7.1 long rods, that = a 1.67 rod to stroke ratio, They seem to work great also I have one bracket race (only) motor that has 7.1 long rods with a 3.91 stroke crank with a set of B1-BS heads ported to M.W. size by MCH, that motor was still gaining power at 7000 RPM on the dyno when the customer said to stop revving it at 7000 rpm Go long

This is MY opinion... but you people make way to much
out of the rod ratio... some of the quickest stock
style engines have a so called bad rod ratio... I've
learned the rod is the filler that goes between the
crank and the piston... it is what it is.. the side
load is almost non measurable for the 2 we are talking
so throw that out the window... I use to say, dwell
at the top... minasqueal.. on a STREET engine keep
the piston IN the bore... AGAIN JUST MY OPINION..
my race engine that turns HIGH RPM the pistons look
like hockey pucks and thats with the crank weights
turned down to clear.. they are super light but
ITS A RACE ENGINE not a street engine

After seeing cap walk on my flat tappet, 906 head motor with ly rods and light Venolia pistons (4.5 stroke) at only 5700 rpm max, I will go as light as possible on a deal like this. I am betting that the performance difference would be very marginal between the two, but stress on the stock block is what I would worry about first. If it is going to be a very low rpm deal, say 5200 or less, then I wouldn't worry much. But if you are looking to push 600 hp, then I would.

When I did my 508 RB I went with the Manley 6.76" rods mainly because the only 7.100 rods out there were the Eagles and the big ends of those rods were Narrow (around 1.007" vs 1.012") When you offset grind a crank the rod journal winds up being slightly wider by the time you finish machine it so with a wider journal and narrower rods the 'tolerence stack' was going the wrong way.

I think there's more 7.100 rod 2.200 journal rod options out there than there was almost 10 yrs ago so I would probably/maybe opt to go 7.100 for an RB. But that 508 with Ported Stage V's is a BEAST and it's still running strong in Paul's (PHJ426) 72 Road Runner.

The 4.25" in a low deck works amazingly with "only" a 6.535" rod, so I wouldn't stress too much about rod length either way.

Cap walk is of course amplified by detonation and it has been proven that a shorter rod is generally less prone to detonation, get the combination right and tune tune tune to optimize longevity.

I thought longer rods were less prone to detonate.

Generally for a given stroke length the shorter rod will have less 'dwell' time at TDC so it's that much less likely to 'death rattle'

Either one will work fine for you. 6.800 rods might be cheaper since that is a stocking piston. But moving the pin usually only costs a few bucks.

I switched from 6.80 to 7.10 rods in my 514 and picked up some power but that was probably due to a number of items which wouldn't necessarily apply in your case.

From what I have heard and I was going to try it on the next go round is that a 6.86 rod is faster than a 7.100 rod. Meaning it will make more power.

Even with the 7.100 rod you'll still have a mile of compression height for a good piston/ring combination. I always like a lighter piston as long as it's bore stable and not fragile in design in a street engine that requires longevity and in the case of the longer rod, neither is an issue in this application. Plus, you'll see slight advantage in loading due to improved ratio.

The power production is adjusted with valve timing for different rod lengths, so that isn't an issue here either as long as your cam guy is legit.

3.23 gear heavy car with an Auto I would just as soon build with the 6.76-6.800 mainly just because my old 508 was such a HOSS and it had 6.76".

Send a PM to Paul PHJ426, I think he's running 2.94 gears and 28" tires in a 72 b body with that old 508 and he's more than keeping up with new ZL1 Camaros....with a hydraulic Flat tappet cam and ported Iron heads....just sayin.

Built a few.....not as many as some....but a lot more than most

There's a lot more critical choices to make than Rod Length if you want a combo you're going to be really happy with.

I want to build one of these 4.25 stroke B motors for the street but have been worried about wear. When you say they work really well do you mean run well, wear well, or both? I've been wondering if I need to keep it at a 4.15 stroke for the slightly longer piston and rod ratio. This will be the only time I will be able to build an engine.

The 4.25 has a 2.200" rod journal and is actually an easier build, the smaller journal will have a big positive effect on the bobweight. You're taking the equivalent of a .068" wall thickness, 2.375" OD x 8.2-ish " long (sum of the 4 rod journals) 4340 steel pipe worth of weight off the crank compared to a 2.375" journal. Then additionally theirs less weight from smaller bearings and reduced friction losses to that mix.

1 cube is worth about 1.3-1.4 lb/ft of torque on a good street stroker, so 15 cubes is 20 lb/ft across a pretty wide powerband.

Worry more about good heads, induction and cam, a properly machined stroker is going to make so much torque you're not going to needto wind it up very often, it's like a 44 magnum, it feels good having it when you occasionally need it.

The thing I worry most about with one of my bullets is.....Tire wear