6.800 vs 7.100 rod for stroker?
#1566269
01/21/14 02:30 AM
01/21/14 02:30 AM
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Joined: Jan 2003
Posts: 1,807 Mopar Country, Mi
ccdave
OP
The Ultimate
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OP
The Ultimate
Joined: Jan 2003
Posts: 1,807
Mopar Country, Mi
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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%
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Re: 6.800 vs 7.100 rod for stroker?
[Re: ccdave]
#1566272
01/21/14 02:43 AM
01/21/14 02:43 AM
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Joined: Jan 2003
Posts: 9,996 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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master
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Frostbitefalls MN (Rocky&Bullw...
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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.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: 6.800 vs 7.100 rod for stroker?
[Re: gregsdart]
#1566273
01/21/14 03:01 AM
01/21/14 03:01 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Posts: 52,972
Romeo MI
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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
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Re: 6.800 vs 7.100 rod for stroker?
[Re: MR_P_BODY]
#1566274
01/21/14 03:20 AM
01/21/14 03:20 AM
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Joined: Apr 2004
Posts: 1,981 SE Michigan
TS3303
top fuel
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top fuel
Joined: Apr 2004
Posts: 1,981
SE Michigan
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Quote:
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
X2
90% street 10% race I'll take the shorter rod taller piston for more stability. Ring seal will last a lot longer with a stable piston. besides we're not talking about factory TRW slugs weight wise.
race motor, longest rod shortest piston. But it comes apart every winter and gets new bearings and rings.
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Re: 6.800 vs 7.100 rod for stroker?
[Re: ccdave]
#1566277
01/21/14 03:46 AM
01/21/14 03:46 AM
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Joined: Aug 2003
Posts: 43,157 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,157
Bend,OR USA
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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
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: 6.800 vs 7.100 rod for stroker?
[Re: Cab_Burge]
#1566278
01/21/14 04:02 AM
01/21/14 04:02 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Romeo MI
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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
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Re: 6.800 vs 7.100 rod for stroker?
[Re: MR_P_BODY]
#1566279
01/21/14 11:48 AM
01/21/14 11:48 AM
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Joined: Jan 2003
Posts: 9,996 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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master
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Frostbitefalls MN (Rocky&Bullw...
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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.
Last edited by gregsdart; 01/21/14 11:57 AM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: 6.800 vs 7.100 rod for stroker?
[Re: gregsdart]
#1566280
01/21/14 12:05 PM
01/21/14 12:05 PM
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Joined: Jan 2003
Posts: 9,875 Weddington, N.C.
Streetwize
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Weddington, N.C.
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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.
Last edited by Streetwize; 01/21/14 12:07 PM.
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Re: 6.800 vs 7.100 rod for stroker?
[Re: jim sciortino]
#1566286
01/21/14 07:20 PM
01/21/14 07:20 PM
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Joined: Jan 2003
Posts: 9,875 Weddington, N.C.
Streetwize
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master
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Weddington, N.C.
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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.
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Re: 6.800 vs 7.100 rod for stroker?
[Re: Moneypit6]
#1566288
01/21/14 07:33 PM
01/21/14 07:33 PM
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Joined: Jan 2003
Posts: 9,875 Weddington, N.C.
Streetwize
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master
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Weddington, N.C.
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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
Last edited by Streetwize; 01/21/14 08:02 PM.
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