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#1
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I'll try this again, LIGHTENING THE ROTATING ASSEMBLY
I started a thread on power gains from lightening pistons and rods. What I was trying to figure out was, if its worth it or not, to do other things like piston milling, crank,damper ect. I'm was looking to see how much"bang for the buck" you get by lightening it, kinda like a price per horsepower in grams. I know its impossible to say exactly, X grams = 1 hp I'm trying to justify to myself spending the extra money. ie: $150 extra for the light weight damper, if it gives me 5hp more I'd pass on it, 25 in a heartbeat.
Does the Desk Dyno factor in assembly weight? I haven't seen Roger on for a while, being an enginer I bet he could figure it out, on paper at least. As some one pointed out it is simple physics. I also thought it might be a interesting thread.......for me at least |
#2
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I read somewhere this advice: build the biggest shortblock you can afford.
I was think "best" might be a better way to think of it. Better revs, better throttle response, less rod stretch, blah blah blah. I say do it, from that point of view, even if the power isn't that big of a difference. As for the power difference? perhaps roger h is the guy to mail. I say a post of his here in the last few days (I think) try sending him a PM. What displacement of motor is this? |
#3
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Power increase?
From what I understand the power increase is very small. If parts are not lightened to the point of structural weakening, the big pay off is in longer life of the engine due to less internal stress on critical parts. Less wear means longer life. Also the engine will rev up quicker due to less drag, so you get better responce.
This comes under the heading of un-sprung weight. 1 lb of un-sprung weight removed (driveline) is worth 10 lbs of sprung weight. (fenders, bumpers, etc.) |
#4
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Quote:
I'm ordering the pistons in a couple of weeks, I think I'll get some milling done on them. $150 option on Ross piston from 440source. Any thoughts on piston pins? The pin end of the ally rods is 1.343 wide. They call for 0.0007 side clearance! 1.094 pins, I'm thinking I can safely save some weight on pins. Tapered pins should be plenty strong,eh? |
#5
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Lighter mass also accelerates quicker and really changes the feel of the engine. With a light reciprocating Assy, it's motorcycle like, quick rewing and quickly back to idle. But the major plus is less forces applied to rods etc. I have used tool steel tapered pins for several years with steel rods and 650 gram pistons. They were 130 grams each.
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#6
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Quote:
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#7
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I seem to remember Dart using either Ross or Wiseco pistons, I've used Ross pins on a couple of different combo's 1.09 tool steel, mine weighed right at 133 grams on my cheap-a$$ scale, never had any problem with either setup, well, at least no pin problems........
BTW, a couple of old drag-boat buddies have used the R&R rods with pretty good results, sound like you got a good deal on them. Also just want to say, anyone that tells you that you won't benefit from a lighter assembly has probably never had a lighter assembly. |
#8
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I agree with these replys; make everything as light as possible without sacrificing strength. The advantages are an engine that is easier on itself so it lasts longer, and uses less of the power it makes to turn itself, which is where the extra power comes from. Also, the lighter the engine, the lighter the whole car will be!...........djs
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#9
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The exception can be a low cubic inch, low torque engine that has problems with launch. In this case, you want all the same light reciprocating parts to minimize stress and wear, but you still need to have some spinning weight for inertia to help with the launch. In this case, the preffered way to accomplish the inertia requirements is to have the crank, rods, pistons, etc. as light as possible, and make up the weight at the flywheel.
torch |
#10
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What block are you using?
When I built my last 451 the rotating mass was way down, had to cut 3/4 inch off counter wieghts, it spun up like small block ( as the rotating mass was simlar ) but it had a lot of piston knock ( I used ARIAS pistons ) and when cold the slap was like diesel. I have used ARIAS pistons b4 no problems.
So with that said switching to a 400 block will really lighten things up. But do not plan to run more than 4.15 stroke in a 400 block This build up I am using a 440 block, 2 reasons 1 it is going into a power wagon and it was a org 440 truck. I am still sorting out rest of build up. |
#11
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Wild1, did you determine the cause of the piston slap? It sounds like the bores were to big. Maybe something else?..............djs
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#12
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Lightwieght internals
I agree. Lots of good advice. One other thing, lightwieght engine internals don't show a HP increase on an ENGINE dyno, because of the way the load is applied. Chassis dyno's & drag ET's do. I've read and been told this several times. Makes sense to me I guess! Whaddya think?
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#13
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Did not find slap
When it warmed up slap sound went away I guess the combo of short piston and low Si forging ( ie I had to leave it loose ). I sold it to someone else on here, I do not know if they have torn it down yet.
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