Stock block plus 2.000 sbc rods, longset stroke?

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gregsdart

gregsdart

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Title says it, how much stroke can you stuff into a magnum 5.9 block using the small rods? Kinda curious about A BIG street motor
 
If you want zero deck for the pistons compression height (CH) : (9.585" - rod length - compression height) x 2

For a 5.700" rod and a 1.500 CH, that would be 4.77". If you used a piston with a common CH for a 360 stroker, like 1.465" then it is 4.84".

Gonna need to do some work to control the compression ratio with that big stroke. Rod to stroke ratio is getting down to 1.2 or less, which is waaaay below the normal range for a car engine. And piston speed is going to be VERY high too and will limit the RPM's to under 5-5.5k if you want to stay within 'normal' bounds.
 
BPE

he sells stroker kits and has had 4.125 and 4.25 stroke cranks available with 2.00 rods on the crank
 
I have studied this before and wonder if it might be a "fool's errand" to attempt such a thing, but can't afford to find out, lolol! To make this live you're probably looking at a billet crank ( i.e. Ohio Crankshaft) and a set of custom Oliver, Crower, or Carillo rods to make this work reliably, maybe you could even go with honda (1.88 I.R.R.C.) bearing journals for more cubes. Look at Molnar Technologies for the differences in chrysler and chevy small block rods and then look at victory library and think about the forces and stresses involved with long strokes and sharp angles. Try to target a 6.35 inch rod length to keep the rod ratio at around 1.5. Less rod ratio is viable but bear in mind the faster the piston speed at TDC and BDC, the more "MEGAFLOW" you'll need from your heads. Ever wonder why a race hemi doesn't start to really pull until it sounds like it's going to sling it's guts out? Think about the 1.83 rod ratio and the lazy piston speeds combined with the huge ports, valves, cams, etc. No wonder those things need 5.38-5.86 :1 gears to work....
 
Oh yeah, I think that Magnum 5.9 liter block is going to have a horsepower limit of around 550 horsepower before the crankcase splits parallel to the crank, and I don't know of any magnum based heads that would merit a "mega inch" build. Sure, Mopar Performance made a 440 inch small block Commando with new "Commando" heads but the stock pinch point in the port becomes a limiting factor at around 5900 if I recall the HR magazine dyno test correctly. To me, this is really territory for an R-3 (Okay, Maybe a T/A 340 race block with 4 bolt Caps) and W-5 heads at a minimum. My preference would be a Ritter aluminum block and P5 pro-stock small block hemi heads, Cubic Dollars on top of Cubic inches, lolol!
 
IMO - waste of effort. Too expensive for a stock block if you're making the power I think you could make with a serious effort.
 
Max1196 said:
Is some "custom" crank in your future?
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Just speculating. I am down with a back injury and too much time on my hands! If there is a crank core out there that could be ground on a bigger stroke for a somewhat reasonable price, it might be an interesting project. My 408 is a great motor, but even with the airgap dual plane and 235/249/107 duration cam make for the need of a looser converter than i like. The converter i have is a ten inch. A&A said it would be tight, but i would like a tighter converter yet and the only way to get that is all the cubes i can stuff in a stock block. The 408 would make a great ten second backup motor for my race car if I ever need it. Almost zero maintanace and no fire suit needed! Greg
 
moper said:
IMO - waste of effort. Too expensive for a stock block if you're making the power I think you could make with a serious effort.
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Exactly, the same reason I am planning on the 3.78 inch Molnar crank if I am fortunate enough to do something with my ‘75 360. Targeting a .040 over, 387 inch build with some “decent” cylinder heads because I do want to wind it pretty hard but I don’t want to drive over top of the crank and rods in the process.
 
moper said:
IMO - waste of effort. Too expensive for a stock block if you're making the power I think you could make with a serious effort.
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This would be a torque build. My first ever stroker was a 535 rb motor with 906 heads. It had so much torque it shredded a stock Hemi converter in three passes. I miss that. The EQ heads i have flow the same as those old 906 bb heads! So rpm would be less than about 5800 maybe, and probably 530 hp. But i should see some very serious low speed torque which is everything to me in a street car. I would run the same cam,intake,heads. Think TRACTORDART .probably look for about a 3.08 rear gear too!
 
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OK. I thought this was a track effort and I figured you'd just break it.
 
Were you planning on exceeding 4.25 stroke? At 4.25 you'll be at 434 inch (360+.030)
 
In that case, I don’t see anything wrong with your build. just be sure to use main studs. My machinist milled and 1/2 inch steel strapped a set of Milodon ductile iron caps on his 438 based on a 71 340 block. His massively ported edelbrock heads flow 330 at .700 but he under cammed, under headered, and under intake manifolded it for street usage. He doesn’t rev the living pee water out of it and it has gotten a lot of track time in the last 10 years with only the usual maintenance. Torque monsters are a lot of fun, too!
 
gregsdart said:
Just speculating. I am down with a back injury and too much time on my hands! If there is a crank core out there that could be ground on a bigger stroke for a somewhat reasonable price, it might be an interesting project. My 408 is a great motor, but even with the airgap dual plane and 235/249/107 duration cam make for the need of a looser converter than i like. The converter i have is a ten inch. A&A said it would be tight, but i would like a tighter converter yet and the only way to get that is all the cubes i can stuff in a stock block. The 408 would make a great ten second backup motor for my race car if I ever need it. Almost zero maintanace and no fire suit needed! Greg
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If I'm understanding you correctly your looking at how the converter acts totally opposite of what it is. Big cubes = big torque. Big torque = more stall speed from the same converter which makes it feel looser
 
I think you would run into serious trouble fitting a larger stroke than 4.25" into a SBM in terms of crankshaft clearancing.
No matter how small the small end of the rods is. So probably no need to go any shorter with the rod than the standard
6.123 inches, see Brian's reply. Hughes at a time was offering a 426" small block package with a 4.18 stroke in a 360 block...
 
Bouchillon Performance Engineering (BPE) offered both the 4.125 and the 4.250 crank a few years back, I don't think you'll find the 4.250 available anymore, besides I think it used the Honda con rod not the 2.000 chev size you suggested.
DJVCUDA worked on something in the 430 cid range if you search his post about 8 years ago.
 
fishy68 said:
If I'm understanding you correctly your looking at how the converter acts totally opposite of what it is. Big cubes = big torque. Big torque = more stall speed from the same converter which makes it feel looser
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I would like to tighten the converter and run a taller rear gear to drop rpm and increase the throttle response. I just don't care for a "loose" feeling setup in a street driver. As far as how much stroke i want, it would be what ever i can put together for a modest price, like under a grand for the crank. I see there are already 4.25 cranks, just curious how far this can be taken and in a price range not a lot above an off the shelf stroker kit.
 
Brian, the whole top end of EQ 2.02 heads and Comp Thumpr cam would be used. I have your cam and valvetrain combo on the 408, will use those items if i do this, including the 850 and airgap intake. The end result using the intake and cam i have may put the power peak down around 5400 if i get 440 cubes out of it? I would be fine with that.
 
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With R3, 48* block though. Cool deal but he says it's a $25K build and I'd bet even using a factory block and fully prepping it you will spend close to that these days.
 
I thought there was an article where someone put the same stroke into a factory 2 bolt block. Was in Mopar muscle or action can't remember. And I laughed cause it took very little clearancing of the block for that large crank. Tried looking in the magazine's I have thought I kept that one, but I didnt.
 
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