Estimated HP gains - bolt on mods and reflash?

[serialk11r]

Originally Posted by Homemade WRX

you do know that the K20 is an 86mm stroke and 86mm bore as well, right?

I have a few things up my sleeve for the FA engine based off of what I already know for the FB25 and handed down from extensive EJ building and K-series work.


put simply, I'm not scared

Yeah, but it has 139mm connecting rods (from google) rather than 133 (what I calculated for the FA20, using the "same dimensions as FB20" + increased compression ratio), giving a rod:stroke ratio of 1.616 instead of 1.547. The redline is approprately, a bit higher. I just don't see how 9000rpm could work safely on a comparatively long stroke and short rod when everything else that runs >8000rpm has much longer rods and mostly shorter strokes. Even if some quick calculations give that the overall bearing load is only 0.5% less and sideloading is only 5% less, I can't help but think there's a good reason high rpm engines go for >1.6 ratio.

But I'm curious to hear what you have in mind.

[old greg]

Originally Posted by serialk11r

Yeah, but it has 139mm connecting rods (from google) rather than 133 (what I calculated...)

Uh, so what? Even with a lower rod/stroke ratio the 133mm rod FA20 has ~4% lower peak piston acceleration than the FA22C which revs to 8200rpm just fine.

[serialk11r]

Sorry if rod/stroke isn't as important as I suspect it is, but the F22C has quite a bit longer rods than the FA20. I'm just noticing that every high revving engine has better rod/stroke ratio than this, and they typically have shorter strokes. When I hear that people want to push this sort of configuration to 9000rpm it sounds a bit scary. It just seems to me like rod/stroke is a very important thing to OEMs given how the ratio is basically always higher the higher the redline. The correlation is very strong.

[Levi]

@Homemade WRX, I'd like to know what you are thinking about.


I don't think the stroke-ratio is any problem. These are the specs of the long stroke BMW S54B32T0 with ITB however:

3246 ccm
360 PS @ 7.900 RPM
370 Nm @ 4.900 RPM
87 mm (bore)
91 mm (stroke)
11.5 : 1 compresion ratio


I saw on Cosworth website they have performance and also race valve springs for the EJ. It can't be they won't do anything for the FA20.

[Dimman]

It's not simply the rpm vs stroke and rod:stroke. These affect the force on the rods, pins and bolts. It's also the materials and manufacturing of these that are resisting the forces.

[Homemade WRX]

Originally Posted by serialk11r

Yeah, but it has 139mm connecting rods (from google) rather than 133 (what I calculated for the FA20, using the "same dimensions as FB20" + increased compression ratio), giving a rod:stroke ratio of 1.616 instead of 1.547.

That 0.069 rod ratio change isn't that great of an effect on the peak piston accelerations nor the instantaneous peak piston speeds. Side loading changes aren't that great either. I will however say it isn't to be ignored. A quick crank-slider model will show you that.

Originally Posted by old greg

Uh, so what? Even with a lower rod/stroke ratio the 133mm rod FA20 has ~4% lower peak piston acceleration than the FA22C which revs to 8200rpm just fine.

Exactly. I don't think the FA20 is going to be a 9k+ screamer engine but I'll be trying to prove myself wrong. However if I find the engine hitting a brick wall, I'll go down the other shortblock avenues that I've been looking into. I'll be chasing area under the curve, not a high redline.

Originally Posted by Dimman

It's not simply the rpm vs stroke and rod:stroke. These affect the force on the rods, pins and bolts. It's also the materials and manufacturing of these that are resisting the forces.

Exactly and there is always lots to change
I keep my 9.5:1, 4" pistons to 405-410 grams (fluctuates with batches) in 2618. Newer things in the works, which I'll be starting with on the FA20 engine.


Basically, for now I'm working on everything in the shortblock, as it's the only part that I have absolutes on. I'm going to see what the shortblock and manifolds can bring to the table and by that time, their should be some aftermarket camshaft support
I start with shortblock geometry (confinements and limitations), from there I have calculated loads and start with modeling/FEA work. Then it's off to prototype testing...same as always.
Cylinder heads, I have a few potential points of interest and I really hope that the TGV and plates that extend into the heads don't carry over from the FB!!

-Micah

[Dimman]

Originally Posted by Homemade WRX

That 0.069 rod ratio change isn't that great of an effect on the peak piston accelerations nor the instantaneous peak piston speeds. Side loading changes aren't that great either. I will however say it isn't to be ignored. A quick crank-slider model will show you that.


Exactly. I don't think the FA20 is going to be a 9k+ screamer engine but I'll be trying to prove myself wrong. However if I find the engine hitting a brick wall, I'll go down the other shortblock avenues that I've been looking into. I'll be chasing area under the curve, not a high redline.



Exactly and there is always lots to change
I keep my 9.5:1, 4" pistons to 405-410 grams (fluctuates with batches) in 2618. Newer things in the works, which I'll be starting with on the FA20 engine.


Basically, for now I'm working on everything in the shortblock, as it's the only part that I have absolutes on. I'm going to see what the shortblock and manifolds can bring to the table and by that time, their should be some aftermarket camshaft support
I start with shortblock geometry (confinements and limitations), from there I have calculated loads and start with modeling/FEA work. Then it's off to prototype testing...same as always.
Cylinder heads, I have a few potential points of interest and I really hope that the TGV and plates that extend into the heads don't carry over from the FB!!



-Micah

For what it's worth, the 2GRFSE with D4-S didn't use TGVs, while the standard D4 3/4GRFSE did. So you could be in luck.

[Homemade WRX]

^^^that's what I'm hoping as TGV's are primarily used as a means of keeping port velocity up to keep HC down (caused by separation) during cold start, low mass flow conditions...for emissions, ugg
The direct injection, despite it's higher HC during cold start (compared to proper PFI), could eliminate this as it doesn't have to worry about low port velocities. Then IAC and AVCS can be used to help keep NOx down and fingers are crossed the TGV's stay out of the FA platforms.

[Dimman]

I wouldn't mind a 5-8k powerband in a done-up NA.

[serialk11r]

Hmmm well okay, speaking of internals I have a quick question:
People seem to say that aluminum connecting rods are not good because aluminum has bad fatigue resistance, but virtually all pistons are aluminum, and people don't seem concerned about replacing those? Aluminum conrods would save a lot of weight over steel ones if done right...and allow for higher revs

And yea 2GR-FSE has no TGVs, they were able to induce tumble with the injector or something.

By geometry, what do you mean exactly? (sorry if this is a retarded question)

[WingsofWar]

Originally Posted by serialk11r

Hmmm well okay, speaking of internals I have a quick question:
People seem to say that aluminum connecting rods are not good because aluminum has bad fatigue resistance, but virtually all pistons are aluminum, and people don't seem concerned about replacing those? Aluminum conrods would save a lot of weight over steel ones if done right...and allow for higher revs

And yea 2GR-FSE has no TGVs, they were able to induce tumble with the injector or something.

By geometry, what do you mean exactly? (sorry if this is a retarded question)

the problem with aluminum conrods is the tensil strength...they can get as good compression load as 300m forged rods. But the big difference is the changes in load at high RPMS. AKA rods also get pulled apart by force are multiplied at the upper registries, unlike pistons. Which result in failure. All topfuel dragsters use Aluminum rods. But they usually replace them after every race.

Short story..aluminum doesn't have the long term durability as forged steel. But forged aluminum rods in a small output engine with high revs in street application could see 100k-150k miles without problems.

[Homemade WRX]

Originally Posted by serialk11r

People seem to say that aluminum connecting rods are not good because aluminum has bad fatigue resistance, but virtually all pistons are aluminum, and people don't seem concerned about replacing those? Aluminum conrods would save a lot of weight over steel ones if done right...and allow for higher revs

By geometry, what do you mean exactly? (sorry if this is a retarded question)

Geometry: see slider crank model and that'll start to give you some perspective.


Aluminum does have it's place in the engine world and as a connecting rod, it's a short term use. The comparison to a piston, think of the loading area of a piston (both sides of the wrist pin) where the rod only has it's cross sectional area. Now the piston's forces is only part of what the rod sees.

Originally Posted by WingsofWar

the problem with aluminum conrods is the tensil strength...they can get as good compression load as 300m forged rods.

That's a very important to keep in mind. All rods will act like a spring (to an extent) however the stiffer material will absorb less of your combustion force = more force on the crankshaft.

I like my 300M rods

[serialk11r]

I'd think that the important criteria would be yield strength no? Work hardening would be bad. 7075-T6 has yield strength of ~500MPa which is decent. 4340 steel is more like 850, but if you just make the aluminum rod a bit thicker you can match the yield strength, while keeping weight down (which reduces the strength requirement too!).

All I can find is that aluminum does not have a fatigue limit, it will eventually fail from fatigue even at the lowest forces. At 10^8 cycles it appears to be around only 150MPa for 7075-T6, which I suppose is really low. IIRC the number of revs that a gas engine goes through is around that order of magnitude over its lifetime, so for the "same" durability as steel you would lose any benefit as the cross section would need to have 3 times the area (4340 has around 75000psi fatigue limit).

But the original question remains, why do aluminum pistons, which undergo the same forces at even higher temperatures, not fail? The higher temperature alloys in pistons are not as strong as the lower temperature alloys found elsewhere either.

EDIT: HomemadeWRX yes that is the geometry, and to be able to calculate the rod length of the FA20 I would've known how it works My question is, what are you trying to change?

And regards to your piston explanation, the bearing on the piston sees an equal force as what the rod exerts on it. The piston experiences equal force in the direction of its motion, and the skirts add on top of that. I don't see how a piston undergoes significantly lower stress.

EDIT2: Okay I see what you mean by both sides of the wrist pin. Hmmm...

[serialk11r]

Too many edits. Okay so the area that the wrist pin spreads the forces is much greater, that makes sense. Thanks. I see why it makes sense to use it in frequently rebuilt engines, you can cut down the mass significantly, and the aluminum rod will still survive a respectable amount of time, but if you want to increase the service life the aluminum rod needs significant strengthening which would not be worthwhile.