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Discussion Starter #1
What factors are most important for low RPM torque given the same cubic inches? Longer stroke, more cylinders, more compression, heavy reciprocating assembly, heavy rotating assembly, intake velocity?
 

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Intake runner length, and header primary size can play a roll in that. Camshaft is obviously number 1.
 

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Long Live The King
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Is this topic posted for General Discussion, or do you have a specific project in mind ?

Post some specifics ( intended use, engine type) and you’ll get more responses
 

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OP already stated "given the same cubic inches?

Perhaps you meant volts/amps/watts :p

["QUOTE=Mark O'Neal;71758627]Cubic inches.[/QUOTE]
 

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Intake runner size and length...

True story!! Many years ago I put a 351ci very hot street motor in a 1966 Mustang coupe I owned.. It had ported heads and a big solid lifter street cam..

I had trouble with my intake, so the initial startup was made with the stock cast iron 4 barrel intake.. With a re-jetted Autolite carburetor..

Setup like that, it was so responsive with so much lowed torque.. It felt like I had taken a thousand pounds off the car.. It was a rocket all the way to about 4000 rpm.. Where it would completely nose over..

It felt much like a friends 1986 "tuned port" Corvette.. Mega lowend torque, but no rev ability at all..
 

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As much compression you can stand with camshaft to match the compression and rpm you want to turn, head flow/runner length/header size and length/as well as everything else "sized" for the rpm you want to run. The engine will not care much what bore and stroke you have as long as the heads/intake system can flow what you need.
 

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Earlier intake valve close moves torque lower; it won’t want or tolerate much compression when you build peak torque really early.
 

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Referring to the first post, would the weight of the rotating /reciprocating assembly actually make a difference in torque production?
 

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So talking about runners both intake and heads is a long and small runner more torque producing or is a short and big runner better? Say this is for a truck with a 454 for argument sake. I'm assuming that's what the OP is asking. I'm interested as well cause soon I plan to pull the 366 out of my 1982 Chevy C60 and maybe go with a 454 for a bit more between the fenders. In that truck the rpm ceiling is maybe 4000 at very most
 

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Been there done that on a tall deck truck engine to short deck on a big truck. Lots of details are different. Everything from flywheel, crank damper, intake manifold double thermostat, backward throttle linkage, and air pump oil drain to block are just a few. Plan ahead.
 

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Referring to the first post, would the weight of the rotating /reciprocating assembly actually make a difference in torque production?
compared to the other factors involved .... not really.

you wouldn't add 25 lbs to the rotating assembly (or just the crank) with the hope of gaining trq
 

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Anyone remember the Engine Masters Magazine a few years back where this was mentioned??

A builder (Ford I believe) stated he gained torque when switching to heavier pistons.

He switched pistons for some reason and was surprised to gain torque, not what he expected
 

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Discussion Starter #18
My question was prompted from a discussion on another site. Someone there was blaming lightweight pistons for lack of low RPM torque production. By low RPM - think 1,500 to 2,000 RPM. More the RPM range where you would be using a diesel IMO.

The trouble is... most would never add reciprocating weight to gain torque because this will limit the engines ability to RPM. But what if you really never did take the engine over 3,500 RPM or so? Would you actually WANT a heavy reciprocating assembly or would you want more rotating mass?
 

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My question was prompted from a discussion on another site. Someone there was blaming lightweight pistons for lack of low RPM torque production. By low RPM - think 1,500 to 2,000 RPM. More the RPM range where you would be using a diesel IMO.

The trouble is... most would never add reciprocating weight to gain torque because this will limit the engines ability to RPM. But what if you really never did take the engine over 3,500 RPM or so? Would you actually WANT a heavy reciprocating assembly or would you want more rotating mass?
Any torque production is all about getting and trapping air fuel mixture in the cyl. at any rpm. So how can lightweight pistons have anything to do with the lack of low rpm torque?
 
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