A bit more rod (diurnal crowd bump)

Kinja'd!!! "gettingoldercarguy" (gettingoldercarguy)
06/12/2020 at 11:23 • Filed to: None

Kinja'd!!!6 Kinja'd!!! 16
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So, the FA24F (Ascent) rods drop right in for the FA20F (WRX) rods. The FA20E (Forester XT) rods are unverified. I’ve been limited to roughly 350 wtq anecdotally, maybe anecdotally plus. Can it be pushed? Sure, but I better have a backup car or engine block to hot swap in. Playing it on the safe side of things is something learned after one survives many close calls in life.

The rods out of the Ascent in the FA24F have performed successfully under a much higher torque output  in dyno sessions and most importantly, in real world testing. The few people who have tested this platform didn’t measure the actual dimensions of the rod. So, I ordered one. Confirming measurements, it is a drop in for the WRX.

Most aftermarket rods are 600+ USD for the WRX. They may handle massive stresses that require a further reinforced engine, but for near stock builds (<450whp) they’re overkill. A beefier factory rod will do just fine.

Whilst the factory rods are 492 grams, the ascent rods are roughly 550 grams. Clearly more beef. And at $300 a set, reasonable.

Kinja'd!!!

This is a dyno from Prime Motoring with a surprisingly stock FA24F (emphasis on the rods for this discourse)

The engine above has been through several runs, isn’t a dyno queen for those who know what that means. I’d like to say one can find a WRX that makes close to those torque numbers and still drives. However, all too frequently those owners go silent shortly after that tune only to reemerge with a newer, better, stronger engine. Hrmmm???

I thought about getting arp rod bolts, wpc treating the rods and a few other tricks that one does to extend the performance of the component. However, I’ve decided to leave them stock, perfectly stock and see what they’ll take. I’m using oem Subaru bearings, non coated, etc.

Anyways, I’m drifting off to sleep as I write this. Talk to you later Oppo.


DISCUSSION (16)


Kinja'd!!! Michael > gettingoldercarguy
06/12/2020 at 08:45

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I want you to know that the angled “heavy end” broke my brain


Kinja'd!!! Boxer_4 > gettingoldercarguy
06/12/2020 at 08:55

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Very interesting!  I haven’t looked much at the FA24 up to this point, so I didn’t realize they kept the same stroke from the FA20. 


Kinja'd!!! Boxer_4 > Michael
06/12/2020 at 08:57

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Subaru has been doing that for a while now (FA/FB engines, EZ36D, and even the EE20Z diesel).  It’s an easy way to get more stroke in the same case size. 


Kinja'd!!! 66P1800inpieces > gettingoldercarguy
06/12/2020 at 09:08

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Do you need to swap over the crank so the counterweights match the rod weight?


Kinja'd!!! Highlander-Datsuns are Forever > gettingoldercarguy
06/12/2020 at 09:26

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Gosh I’d love an fa24 dripped into my 2013 manual outback. That would give the car proper power.


Kinja'd!!! Sillysaxon > 66P1800inpieces
06/12/2020 at 10:10

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I don’t think that’s needed with just the rods as they shouldn’t be adding weight to the rotating mass in the crankcase.

Also they changed the way the FA motors are  damped 


Kinja'd!!! gettingoldercarguy > 66P1800inpieces
06/12/2020 at 11:19

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I don’t believe I should have to. From engine builder magazine:

“With a horizontally opposed four-cylinder engine, two pistons are always moving in when two pistons are moving out.

Consequently, the forces, equal and opposite, are essentially balanced provided the weights of each piston and rod assembly is equal. Balancing these types of engines is fairly simple because all you have to do is equalize the weights of the piston and rod assemblies."


Kinja'd!!! If only EssExTee could be so grossly incandescent > gettingoldercarguy
06/12/2020 at 11:34

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Classic Subaru- "I want to modify it so I better get a spare engine"


Kinja'd!!! I like cars: Jim Spanfeller is one ugly motherfucker > Michael
06/12/2020 at 11:39

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I thought it was just bent to hell. So weird. 


Kinja'd!!! gettingoldercarguy > If only EssExTee could be so grossly incandescent
06/12/2020 at 11:41

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Modifying isn’t for everybody


Kinja'd!!! Turbineguy: Nom de Zoom > gettingoldercarguy
06/12/2020 at 12:10

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What’s the reason for the rod offset? 


Kinja'd!!! gettingoldercarguy > Turbineguy: Nom de Zoom
06/12/2020 at 12:15

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Ease of servicing without splitting the case.


Kinja'd!!! Turbineguy: Nom de Zoom > gettingoldercarguy
06/12/2020 at 12:29

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I’m sorry, I seem to be having a case of the stupid today.. How does that avoid splitting open the case? 


Kinja'd!!! gettingoldercarguy > Turbineguy: Nom de Zoom
06/12/2020 at 13:04

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You can get your torque wrench to the upper and lower bolt more easily.  Limited space with everything attached.


Kinja'd!!! BoxerFanatic, troublesome iconoclast. > Turbineguy: Nom de Zoom
06/12/2020 at 22:24

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It started on the EZ36D.

It allowed the stroke to be lengthened without the rod journal bolt hitting the engine case in a crucial point near bottom-dead-center.

I think it is on the top side of the crank, just inside the crankcase near where the casing is joined. The clearance on the bottom side with the oil pan is not as tight.

It basically allows for maximizing the stroke compared to the engine’s deck height, which is the distance between t he crankshaft center and the surface of the engine block where the head gasket and cylinder head attach.

That deck height plus the cylinder head ‘height’ including the valve covers, coils, and such, multiplied by 2 is the overall engine width between the chassis rails, which is wider than most, and constrained by the steering geometry and the overall vehicle width.

Getting the most stroke length (related to the geometry of the crankshaft journal diameter and offset from the crankshaft centerline, and it’s clearance inside the crankcase is a crucial measurement, and rotation or “clocking” of those rod caps and bolts allows for that little bit more clearance.


Kinja'd!!! BoxerFanatic, troublesome iconoclast. > gettingoldercarguy
06/12/2020 at 22:39

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First and second order vibration cancellation is the hallmark of a horizontally opposed, and separate-journal boxer engine.

A 180-degree Vee engine can have overall interial cancellation, but the opposing pairs of pistons move side to side in the engine together, one rises toward the cylinder head, while the other falls to bottom dead center, and then the pair reverses direction, as they move on a common crankshaft journal that is revolving.

The Ferrari flat-12 in Berlinetta Not-a-Boxer, Testarossa, and 512TR works that way... but 6 pairs of pistons has three groups, with each pair having another pair that is 180-degrees out of phase.

A true boxer has each pair of pistons (in a boxer twin, the ONLY pair of pistons) rise away from each other and fall toward each other, 180-degrees out of phase with each other on individual crankshaft journals, and does not rely on another pair of pistons further down the crankshaft for that cancellation of inertia.

An inline 6 also has vibration cancellation, but not quite to the degree that a horizontally opposed flat 6 does, because each piston’s motion is cancelled out by a piston elsewhere in the engine, not as closely coupled, and usually firing order makes the opposite-moving piston further away, like cylinder one’s opposite being at least cylinder 3, 4, or 6, not usually cylinder 2.

plus the inline 6 is almost twice as long, and if standing near vertical, has a much higher center of gravity, but then not anywhere nearly as wide as a flat horizontally-opposed engine.