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  #1  
Old 08-03-2017, 09:09 PM
Sam Parkinson Sam Parkinson is offline
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Default RUFFLING the feathers of motorsports tradition

Going to start this off setting up a scenario which will govern the argument I want to make here.

So you have your Dodge Ram 4x4 mudder truck with a 360V-8 that your currently testing on a chassis dynamometer under controlled conditions . It's a pre-magnum engine and has a carburetor. Lets say it has 195 Maximum horsepower at 4600 rpm and the engine is in overall real good shape running on 93 octane. There is no detonation at any rpm over the powerband. Your testing the truck with it in 2 wheel drive through the transfer case to the dyno rollers at the rear wheels. For the purposes of this scenario the weather conditions and barometric pressure are irrelevant as I'm specifying that they are the same in both scenarios.

You receive a big displacement kit for the motor for Christmas because you've been a good boy or girl. Lets say for the sake of argument that instead of a 360 it's now a 408 cubic inch motor and has both a bigger bore and longer stroke. Since you didn't want to run expensive gasoline at your mudding and pulling events you modified the tops of the pistons shorter but the same exact shape as the stock pistons . You made them short enough that when you go through the static-compression-ratio calculations the new stroker motor has the EXACT static ratio as the before 360 cubic engine had. The balance of the new rotating assembly is comparable to the littler engines balance. The stroker motor has no more windage loss in the crankcase than the smaller motor. Everything in the induction system from the carburetor down to where the heads bolt on top of the block is IDENTICAL to the smaller motor. same valves and camshaft. For sake of this discussion lets say that the stroker motor DOESN'T receive any benefit of better air flow into the cylinder because the bore is a trifle bigger than the littler engine which might cause less shrouding of the intake valves.

Here's my question: You start dynoing this bigger motor running it from high to low rpm looking for how much, and at what rpm the new horsepower reading is. Even though it may be at a different rpm than the 4600 rpm the littler motor made its max. horsepower at; WHAT MAXIMUM HORSPOWER WILL THE STROKER ENGINE MAKE AS COMPARED WITH THE LITTLER ENGINE????. Worry about max torque later.....someone first tell me how much more horsepower we will have ???
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  #2  
Old 08-03-2017, 11:48 PM
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JVMopar JVMopar is offline
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Horsepower is all about getting the most air/fuel into the cylinder as possible. I think that if you are only changing the displacement and nothing else. The cylinder heads will be the limiting factor. It may make more power down low, but I think that it will roll over at a lower rpm because the heads will be maxed out.

I think if you were looking for bang for the buck I would say a good set of heads would be more beneficial than increasing displacement.

I say get some better heads first.

So if you watch this video I think it will answer your question. Stroker will make more power, but without upgrading the heads your not taking full advantage of the displacement.
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Last edited by JVMopar; 08-04-2017 at 12:09 AM..
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Old 08-04-2017, 12:08 AM
Sam Parkinson Sam Parkinson is offline
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Bingo JV:

you nailed the whole point right away.....you'll actually end up with slightly LESS max. horsepower than the smaller engine but a stronger torque force when the bigger engine is killed down to a slow enough RPM where the NON-IMPROVED induction system can get those bigger displacement cylinders completely full of air/fuel charge

In addition, at the "rollover" point as you mentioned you now have the bigger displacement cylinders trying harder to draw air against the same sized air holes which leaves vacuum in the cylinders all the way down the intake stroke More than the littler engine which requires a bigger draw of energy OUT of your crankshaft pulling all eight cylinders against a non-satisfied vacuum above them, thus making useable energy less available at the flywheel.

If you had both engines on a dyno starting at say 800 rpm and working your way up the powerband to the point where the bigger engine starting starving from the same sized induction system you should see that the bigger engine would produce both higher torque and horsepower readings...but the bigger engine runs the same sized induction system out of air at a slower RPM than the smaller engine.

So your pulling truck actually moves down the track at a slightly SLOWER max. speed(everything else the same) than before you put the big displacement kit in.
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Old 08-04-2017, 12:26 AM
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JVMopar JVMopar is offline
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Sorry forgot the link to the video. https://www.youtube.com/watch?v=vPBs_QB6ubI

If both engines had stock heads, I think you would see the 360 perform better.
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'86 W350 360/727 '90 W150 318/NP435
'92 Lebaron 2.2L Turbo/ 5spd '92 Dakota 5.9L/A-500
'94 Voyager 2.5L/5spd '94 Sundance 2.2L/5spd Red

Last edited by JVMopar; 08-04-2017 at 12:27 AM..
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