Engine technology thread.

[Exage]

Originally Posted by old greg

With the same deck height as an FB20, an 80mm stroke would allow 134.3mm rods. At 8000rpm that means a mean piston speed of 4200 ft/min and peak piston acceleration of 3718 g, which ought to be fairly reliable (compare that to 4724 ft/min and 4344 g for a normal FB20).

Figure a forged bottom end (that's just how Subaru rolls), probably a semi-closed deck, with forged pistons in the STi and cast in the WRX.

I found that a 82mm stroke would leave 4mm rod growth to 133.3mm to 82mm would be 1.62 (granted I didn't calculate CR reduction so it would be slightly higher). That would equal the same as 2ZZ and K20...

Perhaps a 2.0L with a 83-85mm stroke? Depending on what breathing characteristics they want it I can see 1.55-1.62. D4-S would also result in the ability for a higher CR; it wouldn't surprise me if we saw over 11.0:1 on cheapo gas.

I agree with the semi closed and the forged pistons (do Subaru run forged rods as well in the STI?).

[Dimman]

On the 72mm hypothetical, what about doming up the piston or adjusting the head-side for more CR? Otherwise, how big of a deal is decking a new block by that amount?





On the other hand the new motors being talked about in that quote are for the STI/WRX, so the higher CR is not really necessary or even desirable.

[Exage]

Ahhhh that was for the turbocharged engines... I missed that.

(9.4cm/2)squared(X)pi(X)1.089cm= 75.57cc reduction at TDC to reach 10.5:1CR with 72mm stroke. The piston is sitting quite low after the de-stroke with the 129.3mm rod... It would require some serious altercation to the piston crown or wrist pin placement.

I think they might run into cooling and structural problems taking that much material off the top of a stock FB25 block, among other things. No good solutions I can think of.

[Dimman]

Originally Posted by Exage

Ahhhh that was for the turbocharged engines... I missed that.

(9.4cm/2)squared(X)pi(X)1.089cm= 75.57cc reduction at TDC to reach 10.5:1CR with 72mm stroke. The piston is sitting quite low after the de-stroke with the 129.3mm rod... It would require some serious altercation to the piston crown or wrist pin placement.

I think they might run into cooling and structural problems taking that much material off the top of a stock FB25 block, among other things. No good solutions I can think of.

If the block isn't as long/tall, could it be a bit stiffer? Semi-closed or closed deck could help?

As for cooling... oil squirters (and front mount oil cooler), forged pistons (more heat/detonation resistance than cooling but you get the idea) and thermal coatings. Maybe an efficient electric water pump.

[old greg]

Originally Posted by Exage

I found that a 82mm stroke would leave 4mm rod growth to 133.3mm to 82mm would be 1.62 (granted I didn't calculate CR reduction so it would be slightly higher). That would equal the same as 2ZZ and K20...

I just went with keeping the wrist pin location the same at TDC, since CR will be set by combustion chamber and piston dish volumes anyway.

Originally Posted by Exage

I agree with the semi closed and the forged pistons (do Subaru run forged rods as well in the STI?).

Yes. Unfortunately they've had cast pistons for the last ~12 years, which has led to a lot of problems for people who try to push the limits of the stock internals. I'm hoping they pony up for some stronger ones this time around, but there's no guarantee that they will.

[Exage]

Originally Posted by Dimman

If the block isn't as long/tall, could it be a bit stiffer? Semi-closed or closed deck could help?

As for cooling... oil squirters (and front mount oil cooler), forged pistons (more heat/detonation resistance than cooling but you get the idea) and thermal coatings. Maybe an efficient electric water pump.

Of course, but it would have to be cast with a different mould then the stock FB25 block.

For cooling it was more of a reference to jacket coolant capacity then the oil . I personally don't know how much jacket coolant volume taking 1cm of deck off of the FB25 or any block reduces but I imagine quite a bit. With upgraded water pumps the total system temperature will be higher when compared to a normal FB25 block but equalized, reducing thermostat temperature would not become effective either. A larger radiator may cause too much thermal shock on the block (difference between inlet and outlet coolant temperatures) depending on flow rate. Semi or closed deck may help cooling with metallic surface area.

I think it starts to cut into the safety factors designed into the engine for longevity and reliability. But that's only one mans opinion, hahaha!

[Dimman]

Since we still don't have an official engine yet, and I'm bored.

EZ30 H6 is 89.2mm bore X 80mm stroke, 10.7:1 CR, Valve Lift and Timing controls, drive by wire.

Performance thoughts? Potential if this was used with 2 cylinders chopped off and more aggressive heads?

[serialk11r]

Hey guys forgive me if this is a stupid question, but how much restriction does the air filter create? I've never examined one, but seems to me like it would cause a lot of restriction. I was thinking, wait I've never seen people try to use multiple filters or a ginormous one to reduce restriction. Engines suck quite a bit of air through those so I imagine it could be significant?

[Random_Art]

That's a tough question to answer and the best one I can give is "well, it depends" The design of everything from the airbox that houses the filter, the intake, and the filter can effect how much air is restricted. Stock air filters tend to be made of a paper material that has microscopic pores in it to allow air through while blocking contaminants like dust and mice. Performance air filters have larger pores to allow for more airflow through the filter. To change out the shape of the filter, you usually have to change out the whole intake as well (like going from the square filter in a box to a cone filter.) The air filter type can only do so much without upgrading the rest of the intake to accommodate. If the pipe into the engine is too restrictive, it doesn't matter how big the filter is or how many filters you have- the engine can only get so much air through the intake.

The power gains versus amount of intake modification you do can vary widely from vehicle to vehicle. For example: just taking the cover off the air filter box on the MazdaSpeed 3 added something like 10whp according to the now defunct Sport Compact Car Magazine. While on the other hand, changing out the whole intake on the last generation Celica GT-S with a CAI only netted 2-3hp on the top end and resulted in a lot of low end bogging down when accelerating from a dead stop.

[serialk11r]

Hmmm so you're saying the other parts of the intake system can contribute a lot of restriction as well...that's somewhat of a surprise to me, since I'd imagine sucking air through a porous filter would be much worse than say a narrow tube.

So seeing that variable valve lift technology is soon to arrive en masse, eliminating the need for the throttle body to do anything, how do you guys think this could affect intake modification?

[xantonin]

Originally Posted by serialk11r

Hmmm so you're saying the other parts of the intake system can contribute a lot of restriction as well...that's somewhat of a surprise to me, since I'd imagine sucking air through a porous filter would be much worse than say a narrow tube.

So seeing that variable valve lift technology is soon to arrive en masse, eliminating the need for the throttle body to do anything, how do you guys think this could affect intake modification?

Air intake systems are designed to allow air to flow more smoothly. If you look in the tube of a stock air system they are usually rubber, maybe bumpy on the inside. While they may both be the same diameter the velocity of the air isn't the same as it travels.

So for example a smooth polished intake system is designed to allow air to flow at the right angles giving it the most velocity as it travels, with the least resistance from the interior walls and with fewer inefficient bends in the pipe.

As for the filter, you could figure it out mathematically.

If you have 4 inches of surface area using the diameter of the stock intake pipe, and your average filter restricts 30% of air per inch, and for example if you had 1 inch of paper filter then you have 0.3 inch of air flowing space. SO, to maintain that 4 inch space you'd want a filter 3.33 times as big. So you'd need 13.33 inches of filter surface to get 4 inches of air flow. Any bigger, and you're not getting anymore air because the tubing is only 4 wide.

This should already be taken into account with a decent intake system, and hence why they have folds and are cone shaped, because it allows them to provide more filtration surface.


I made up those numbers but they should be accurate.



As for the throttle body, air flows the same way regardless of if there is a throttle so it won't be affected. Plus I thought Toyota's with D4-S still use a throttle, and BMW was the one that got rid of it?

[serialk11r]

Oh well if it's not smooth then I can see why there would be a lot of restriction.

D4-S is the fuel injection system, you mean Valvematic? I thought in press releases they said it eliminated the need for a throttle body. Variable lift+duration is a much better way of controlling air intake than a throttle. I don't see why they can't coexist, the port injector just needs to be timed properly when used in less than WOT situations where the intake isn't open as long.

I was thinking variable valve lift would affect tuning in some way...for one thing maybe the mass airflow sensor would respond differently to the "pulses" of air? Perhaps ITBs will not net much of a gain? Just wondering if anyone knows anything.

[xantonin]

Originally Posted by serialk11r

Oh well if it's not smooth then I can see why there would be a lot of restriction.

D4-S is the fuel injection system, you mean Valvematic? I thought in press releases they said it eliminated the need for a throttle body. Variable lift+duration is a much better way of controlling air intake than a throttle. I don't see why they can't coexist, the port injector just needs to be timed properly when used in less than WOT situations where the intake isn't open as long.

I was thinking variable valve lift would affect tuning in some way...for one thing maybe the mass airflow sensor would respond differently to the "pulses" of air? Perhaps ITBs will not net much of a gain? Just wondering if anyone knows anything.

Oops sorry you're right I was thinking of vavematic.

[WingsofWar]

Originally Posted by serialk11r

Hmmm so you're saying the other parts of the intake system can contribute a lot of restriction as well...that's somewhat of a surprise to me, since I'd imagine sucking air through a porous filter would be much worse than say a narrow tube.

So seeing that variable valve lift technology is soon to arrive en masse, eliminating the need for the throttle body to do anything, how do you guys think this could affect intake modification?

Some intake designs are already decently optimized. The EJ251 and EJ253 N/A Impreza and Legacy engines sees almost no performance or economical gains with a upgraded/aftermarket intake systems. Only the CAI systems provided gains because of the location of the filter.

and those are ones without subarus VVL and drivebythrottle.

If we throw in the drivebythrottle mix, it greatly effects how mods are registered.