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Old 02-14-2010, 06:14 PM   #16
der affe
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Originally Posted by M3 euro ltw View Post
Technically, you should have exact same peak hp as without the lightening, but you'll have less drag on the motor, hence more area under the curve... right? Like a flywheel. Mebbe not.

Beautiful work btw...very, very thought provoking.
sort of, it will take less HP to move the lighter mass, but it more importantly will make it rev faster to make the hp faster and be able to put you into the rpm range you want (powerband) quicker.

not talking huge hp#'s. mostly it makes the engine more enjoyable to drive and twist up.

so yes it is like a lightened flywheel in a way, but a lightened everything.
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Old 02-15-2010, 09:42 AM   #17
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i really thought about it. but i coud not get a straight answer from anyone as to how important the blocks were or what their exact purpose was.
absorbing harmonics to a point is what i was thinking.
i would welcome any actual answers as to the purpose of the giant freekin block at the base of the rod caps.

i might see if i can mill .100 or so off and see what happens.
Aside from using the mass to dampen or absorb harmonic vibrations in the cap, I would think that the thicker portion of the cap resists deflections when the engine is at tdc. The inertial forces of the piston flying upwards will be resisted almost entirely by the rod cap. By reducing the depth of that metal mass on the cap, you are also reducing its moment of inertia about its major axis of bending. Because the maximum bending moment is at the center (mid-span) of the cap, I would not remove mass from that area. Instead, remove from each side (right next to where the cap becomes very thin). You would effectively be making a beam of varying moment of inertia (Ix) having the greatest Ix at the point of greatest load (mid-span) and the smallest Ix at the point of smallest load (supports).
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Old 02-15-2010, 09:58 AM   #18
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Like this:

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Old 02-23-2010, 09:51 PM   #19
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Aside from using the mass to dampen or absorb harmonic vibrations in the cap, I would think that the thicker portion of the cap resists deflections when the engine is at tdc. The inertial forces of the piston flying upwards will be resisted almost entirely by the rod cap. By reducing the depth of that metal mass on the cap, you are also reducing its moment of inertia about its major axis of bending. Because the maximum bending moment is at the center (mid-span) of the cap, I would not remove mass from that area. Instead, remove from each side (right next to where the cap becomes very thin). You would effectively be making a beam of varying moment of inertia (Ix) having the greatest Ix at the point of greatest load (mid-span) and the smallest Ix at the point of smallest load (supports).
So round off the cap as opposed to just milling the end. Right? Sounds good.
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Old 02-24-2010, 12:55 AM   #20
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Originally Posted by M3 euro ltw View Post
Technically, you should have exact same peak hp as without the lightening, but you'll have less drag on the motor, hence more area under the curve... right?
That is not really how it works. Lightening rotational mass/flywheels will get rid of a fixed amount of load. Basically, the faster your car is revving up, the more effect lightening rotational mass will have. So, if you're in 5th gear at WOT at top speed and you're not gathering revs, no difference will be noticed. But, if you're in first gear and gathering revs quickly, you'll notice a difference since the rotational mass/flywheel inertia is a significant amount of the load, and you reduced the mass and therefore inertia of said rotating assembly. If you're in neutral, the only load on the engine will be from rotational mass/flywheel inertia, and you'll notice a big difference.

Quote:
Like a flywheel. Mebbe not.
Exactly like a flywheel.
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Old 08-05-2010, 08:57 AM   #21
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i would welcome any actual answers as to the purpose of the giant freekin block at the base of the rod caps.
I always were told those were for balancing from the factory.
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Old 01-15-2018, 04:41 AM   #22
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Glad I found this thread as I'm undertaking a similar build. Any info on how the final build ran?

Profiling the CR (I-beam and piston end) has netted 20 grams. Planning on taking more weight off the crank end (haven't decided where or how much) and will taper piston end so the wrist pin hole is thinner on the top same thickness on the bottom.

Tapering wrist pin holes in piston area on both ends.

Thinking of windowing pistons to improve oiling and decrease weight.

Will be knifing crank leading edge and want to lighten counterweights but unsure if lightening will make crank unable to be balanced?
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Old 01-17-2018, 12:25 PM   #23
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What are you trying to achieve by lightening parts ? I would focus on the low hanging fruit e.g lightweight flywheel if you want it to rev quicker
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Old 01-19-2018, 04:10 AM   #24
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What are you trying to achieve by lightening parts ? I would focus on the low hanging fruit e.g lightweight flywheel if you want it to rev quicker
I've already lightened the flywheel, swapped to a motorcycle altenator, reduced water pump rpm, and removed weight from fixed portion of harmonic dampener.


This car is a track car (24 Hours of Lemons) and I'm looking to improve throttle response.


I'm replacing the valve guides with longer guides. The intake and exhaust ports will be machined to remove the "bump" by the guides, and the longer guides will also be machined flush to improve flow. Intake manifold will be pinned and matched to the head and o-ringed instead of gasket. etc etc etc
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Old 01-19-2018, 09:17 AM   #25
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swapped to a motorcycle altenator, reduced water pump rpm
Interested in the particulars on these.
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Old 01-19-2018, 10:12 AM   #26
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Interested in the particulars on these.

BMW motorcycle alt. (constructing the mounting bracket was a huge PITA).
Machined off harmonic pulley and built smaller diameter "pulley" that I then attached to the harmonic dampener.


I'll put some pics up on our facebook page "Squidrope Racing"

Pics are up minus the altenator stuff, that stuff's hiding in a box somewhere...

There are pics of the beginning of the rod lightening and pics of the lightened flywheel as well.

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Old 01-23-2018, 01:40 PM   #27
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I've put a full radius along the edges that run parallel to the rod bolts and the rods lost an additional 20 grams. That's 40 grams so far and I haven't touched the large block on the cap end, or tapered the wrist pin end.
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Old 01-24-2018, 02:19 PM   #28
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7 more grams from the wrist pin area. Rethought original narrowing of the wrist pin area. Tapered O.D. for upper 180 degrees.
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Old 01-25-2018, 05:56 PM   #29
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Best focus on rotating part of rods the reciprocating mass has little effect on how fast the engine revs up or responds.
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Old 01-25-2018, 06:32 PM   #30
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Best focus on rotating part of rods the reciprocating mass has little effect on how fast the engine revs up or responds.
Didn't know that. Thanks. The big block on the cap is going on it's diet tomorrow.
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