ok stroker guru's, gig this one

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look guys....stroke does not really effect dwell time at tdc........rod ratio does, longer the rod..longer the dwell atdc which aids in cylinder filling and evacuation of exhaust gases.

chevy dorks say the shorter the rod, the faster it moves away from tdc and outruns detonation.lol

some chevros say the shorter rods that create the angularity at 90* crank also aid in torque from this same angularity/kicking the crank over harder, what road racer chevy dorks argue all the time.

even a certain mopar book go's on about this.


side point...when chevrosexuals pick on mopars tall deck heights that lead to heavier rotating mass, they forget that the mopar when built & stroked makes the perfect starting point as where a chevy becomes an 8 hole flower pot. sbc can't facilitate ,without going really custom [modified ford 302 pistons and custom length rods], a 4'' stroke and still use stock chevy parts/dimensions. The blocks are too short, the cam journals are in the way and require a custom cut down weight crank, a close to stock 4'' stroked sbc cost engine masters $6500 to build and all it had was a bigger cam, headers,carb...all else was stock iron intake, stock heads, it barely made 400 hp for $6500$.


now again, pertaining to this op question...rpms/poor rod ratios=side loading are what will wear out the cylinder walls faster [with all else aside] 'chevys wear out the bores bad from this.

Anyways thats why life expectancy go's down when performance/higher than stock rpms are in mind.
seriously though when the stock mopar pin is that far below the ring package...those rings/pistons are gonna be plenty square and stable.

btw I type on the fly thats why I sometimes miss letters and scatter my points, bare with me.
 
fishy68 said:
A 4" stroker has less dwell time due to higher piston speed.

MT here's something to ponder.

The SB Mopar stroker that uses a 4" stroke and 6.123" rods has a rod ratio of 1.53"

The 454 Chevy uses a 4" stroke and a 6.135" rod for a rod ratio of 1.53"

So it seems the stroked Mopar is in the same range of a stock 454 Chevy and the 454 lasted good.
Click to expand...

454's are rod cacking p's of sht

I've seem more 454's with spun rod bearings than I've seen good running one's.

early 273/318 floater rods are stronger than 454 rods, no joke, 454 rods are thin lil popsicle sticks that taper to a tooth pick at the small end.
 
Revhendo said:
Do the longer strokes have a longer dwell angle that affects how the piston loads the cylinder wall?
Click to expand...


Dwell angle is the amount of time the piston stays at TDC while the rod and crank journal traverse the arc of the circle the journal follows. Think of a dime and a quarter. Each degree of a dime's circumference is so many hundreths of an inch wide like a pie shapes slice or one degree). On the quarter, you still have the same 360°, but each degree is slightly longer in width. Meaning the pie slice has a longer "crust side". It takes the crank and rod so much time (in crank degrees) to traverse the longer peice of pie. That number of degrees is the dwell angle at TDC. This is important in terms of cylinder pressure development after the mixture is lit and desiging a stroker's timing curve. It's also why having the right timing curve while running a fast burning pump fuel is important with these engines.

However, this has nothing to do with block stress. The rod and piston, and the crank at all perfectly straight up and down at that time. Plus, the piston and rings are in the strongest part of the bore. The stress we're talking about is when the piston, rod, and crank are not aligned. That's just before the piston is at 2" up in it's travel from Botom Dead Center. The cranks basically driving the piston into the side of the wall at that point, and thats what makes what's called the "major thrust" side soooo critical in terms of sonic testing. You can have a spot in the bore as thin as .080 without a big issue unless it on the major or minor thrust sides. The major thrust needs to be at least twice that to avoid the worst case wall splitting, or power robbing wall flexing that will eventually lead to cracks.
 
Wow, this has turned out to be a good info thread! Thanks guys. Moper i understand now that I look at it with your Quarter VS. Dime analogy.
It's also why having the right timing curve while running a fast burning pump fuel is important with these engines. Am I on the correct track of thinking that the "Quarter" is going to need the timing retarded slightly more than the "Dime" will plus need a slower burning fuel (higher octane, octane slows the fuels burn rate) because normally high cylinder pressure and fast burn fuel is a recipe for disaster. I'm going to eventually build one or the other that will be built more towards torque production over h.p. (short cam, dual plane, small(ish) carb) for daily street duties.
 
moper said:
Dwell angle is the amount of time the piston stays at TDC while the rod and crank journal traverse the arc of the circle the journal follows. Think of a dime and a quarter. Each degree of a dime's circumference is so many hundreths of an inch wide like a pie shapes slice or one degree). On the quarter, you still have the same 360°, but each degree is slightly longer in width. Meaning the pie slice has a longer "crust side". It takes the crank and rod so much time (in crank degrees) to traverse the longer peice of pie. That number of degrees is the dwell angle at TDC. This is important in terms of cylinder pressure development after the mixture is lit and desiging a stroker's timing curve. It's also why having the right timing curve while running a fast burning pump fuel is important with these engines.

However, this has nothing to do with block stress. The rod and piston, and the crank at all perfectly straight up and down at that time. Plus, the piston and rings are in the strongest part of the bore. The stress we're talking about is when the piston, rod, and crank are not aligned. That's just before the piston is at 2" up in it's travel from Botom Dead Center. The cranks basically driving the piston into the side of the wall at that point, and thats what makes what's called the "major thrust" side soooo critical in terms of sonic testing. You can have a spot in the bore as thin as .080 without a big issue unless it on the major or minor thrust sides. The major thrust needs to be at least twice that to avoid the worst case wall splitting, or power robbing wall flexing that will eventually lead to cracks.
Click to expand...

Thank you and I really do mean that sincerely. I've asked that question a few times and all I've heard was piston speed. You explained it perfectly for me. (Coulda been the pizza reference).
So, just to make sure I have this nailed. Dwell angle remains the same, but the amount of time the piston spends at TDC or BDC increases? Hence the piston speed comments? Also the affect on cylinder pressure and timing curves? (Forgive me, I work with a lot of Chevy guys).
 
yes dwell time is the amount of time spent at tdc and bdc,

...longer rods have more dwell at TDC which allows long rod motors to build more combustion pressure at 'high RPM', and then less wear on cylinders/skirts.

short rod let the piston move down quicker, and supposidly produce better torque at lower RPM and typically like more timing advance, hence the road race chevro crowd.

btw the 2 are different......


tdc dwell time is not the same as bdc dwell time.
 
1wild&crazyguy said:
yes dwell time is the amount of time spent at tdc and bdc,

btw the 2 are different......


tdc dwell time is not the same as bdc dwell time.
Click to expand...

Understood, because the effective radius changes from inside the rod journal to the outside of the rod journal at the 90 and 180 points in the crank rotation.
 
yeah, in a sense the rod has to stand up straight again and that hurts piston speed/velocity

exactly where in that 90*atdc that max velocity is depends on rod/stroke
and thats where you dial in the right cam and so forth.
 
Everyone get pizza and cash references...lol
It's not so much that the timing is retarded. It just means the total timing yields better results when it's not advanced as much. Timing's still an individualistic thing, but most like a total timing of less than 34° and in some cases less than 30.
 
I LOVE FABO !!
My brain hurts after reading all that (a 3rd time) to get it all into my noodle... but now that it's in there, and I understand it.. oh the bliss is wonderful.

I have a new 408 Stroker with a six-pack, Eddy heads, solid cam..etc. See my story somewhere in here about my new AAR hood. Thanks so much (everyone) for sharing your hard-earned expertice. I learned some things here, and I know engines too! My 408 engine will be fired up within the next few weeks (cam break-in & dyno tune). I'm opting for the expense of the dyno due to the six-pack (they're the non-vacuum ford style) and ...well... anyway...

Thanks again for this very informative string.. or thread... whatever it's called. :cheers:
 

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