Engine technology thread.

[Dimman]

Originally Posted by serialk11r

So you guys being really bored I found myself reading about positive displacement vs. centrifugal pumps today and I realized something about turbos: at a high pressure ratio the compressor operates at high efficiency for only a short amount of time. For high boost applications (like over 14psi average), theoretically it would be better to have twin sequential turbos but with the compressors hooked up in SERIES and of course sized properly. Jet engines use this to get its compressors and turbines operating closer to their best speed.

I remember looking into this a while ago. With a compound setup you could adjust the output of the two stages to keep in the efficiency 'islands' on the compressor maps. But that would need some pretty advanced ECU/wastegate control. And the fabrication for the plumbing of compounds is pretty ridiculous, especially if you are doing inter-stage cooling which is pretty important when you are compressing the air twice.

So you would need two electronic, independent wastegate controls, a mess of piping, the two different turbos, and probably a front mount air-air intercooler and a water-air inter-stage-cooler. Plus a standalone ECU that can handle a map and outputs for the two wastegates. Plus it would need to regulate how hard the boost comes on from the compounding as it probably wouldn't build in a linear fashion.

The practical is a headache. The theoretical is massive boost, very minimal lag, and huge power.

[misformartin]

i wonder what type of internals well see on this motor?.... the last 2 scion 4 cyl motors both had forged cranks ant the new 2ar from the new scion has a sleeved block hmmm....

[serialk11r]

So today the new pics that came up seem to show a new ! engine in the glass model...
If it is the real thing, maybe we can speculate on some stuff So I said in that thread the 2 engines look like they're the exact same dimensions, so my hopes for Valvematic are dead (weep), and VVTL-i won't be there since it has that extra rocking arm thing which similarly takes up an extra inch on either side.

So this suggests this motor has Subaru i-AVLS or something of that sort, otherwise >200hp would not be so easy to do...which I am honestly surprised with since they said Toyota is reworking just about everything.

Another possibility is that the D4-S mixes air and fuel much better and allowed them to optimize the lift for high rpm operation...

[madfast]

Originally Posted by serialk11r

So today the new pics that came up seem to show a new ! engine in the glass model...
If it is the real thing, maybe we can speculate on some stuff So I said in that thread the 2 engines look like they're the exact same dimensions, so my hopes for Valvematic are dead (weep), and VVTL-i won't be there since it has that extra rocking arm thing which similarly takes up an extra inch on either side.

So this suggests this motor has Subaru i-AVLS or something of that sort, otherwise >200hp would not be so easy to do...which I am honestly surprised with since they said Toyota is reworking just about everything.

Another possibility is that the D4-S mixes air and fuel much better and allowed them to optimize the lift for high rpm operation...

2 stage variable valve lift is dead. either you have infinitely variable lift like valvetronic or valvematic, or nothing at all... as for the FT, i dont think it will have variable valve lift of any kind. how do you make 200 hp? compression. high compression allowed by the direct injection portion of D-4S.

the mention of reworked bore and stroke also sounds promising. it just may turn out to be quite rev happy

[serialk11r]

You should tell Honda that! Where is AVTEC?

Well then, without variable valve lift, I hope this lives up to its expectations...

[Allch Chcar]

Originally Posted by serialk11r

You should tell Honda that! Where is AVTEC?

Well then, without variable valve lift, I hope this lives up to its expectations...

Honda has really fallen behind on these things... While they are still advancing their engine designs(the K series, and even the Lea for example), they are really limiting the level of new technology they add; DI or Variable cam timing.

And Subaru uses AVCS. Which, I believe, advances or retards the cam timing as needed to a certain limit. I'm just going off of memory here.

The big difference is the reversed intake. The FB201 has the opposite intake direction. I know it was different from the old display, I think.

BRZ Prologue


FB201


This was discussed in the topic and from what Ichitaka was saying, makes a big difference in piping.

[CyberFormula]

what sort of difference?

I just read from the other member saying it will have less LAG.

[serialk11r]

I dunno actually AVLS looks smaller than VTEC or VVTL-i, so maybe there's a chance. But it's still a disappointment considering the better stuff out there nowadays...

And yea AVCS is your run of the mill cam phasing, but only 2 profiles...which kinda sucks. I hope they switch to continuously variable, it lets you do interesting things with the exhaust timing to limit pumping loss, if there is no intake duration changing.

@CyberFormula - I think he means that it will be easier to run piping to a front mount intercooler. Less piping between intercooler and intake, less lag, makes sense.

[suprachica79]

Originally Posted by madfast

2 stage variable valve lift is dead. either you have infinitely variable lift like valvetronic or valvematic, or nothing at all... as for the FT, i dont think it will have variable valve lift of any kind. how do you make 200 hp? compression. high compression allowed by the direct injection portion of D-4S.

the mention of reworked bore and stroke also sounds promising. it just may turn out to be quite rev happy

This is what concerns me with the idea of FI. From what I remember, the lower the compression, the better for safe(ish) forced induction.

[serialk11r]

People with FI experience, how much headroom do the manufacturers usually leave in terms of knock resistance? I'm under the impression that moderate boost setups usually don't decrease compression ratio... Is it correct that for performance cars they usually design it to run on 91? Then with 93 a little boost wouldn't be much of a problem right?

[fatoni]

Originally Posted by serialk11r

People with FI experience, how much headroom do the manufacturers usually leave in terms of knock resistance? I'm under the impression that moderate boost setups usually don't decrease compression ratio... Is it correct that for performance cars they usually design it to run on 91? Then with 93 a little boost wouldn't be much of a problem right?

somewhere between almost none (mazdaspeed protege) and tons (evo)

[WingsofWar]

Originally Posted by serialk11r

People with FI experience, how much headroom do the manufacturers usually leave in terms of knock resistance? I'm under the impression that moderate boost setups usually don't decrease compression ratio... Is it correct that for performance cars they usually design it to run on 91? Then with 93 a little boost wouldn't be much of a problem right?

i couldn't say for sure what the manufacturing standard is for knock resistance in an engine. That sounds like a engineering question for someone in the industry, which is really for only a hand full of people in the world.

From my experience, cars that have been offered from the factory with forced induction had a few points of compression removed to make the engine perform more reliable. Even if stock boost pressures are a mear 5psi on small turbos.

Today in many more modern cars, knock is controlled via ECU or a separate device that detects pinging and tells the ECU to either reduce boost pressure or pull or add timing. So we can effectively run low-octane unleaded AND high-octane unleaded in performance cars without worrying about knocking.

So i guess to answer your question, if we turn up the boost moderately we have to make all other conditions equal during the 4 stroke process, so we have to turn up the fuel, and pull timing. This makes the compression ratio virtually unchanged allowing you to run the same amount of low-octane fuels safely and effectively, and 93 octane or similar high-octane ratings wont really have a major effect on the performance if not just better peace of mind.

When we start bumping up internal pressures from factory settings is when we need to start thinking about high octane to reduce risk of knock.

So not all performance cars have really high compression ratios from the factory, including ratios added from FI. That force makers to build the engine around certain octane ratings. But some engines have been tested and seen to run more optimally on higher octane ratings due to their nature. Probably because they have pretty high factory internal pressures or aggressive factory timing maps for performance.

[serialk11r]

Well if timing has to be retarded that's not good, as it is essentially reducing compression, so I guess I was asking how much pressure you can run literally without changing anything but the amount of fuel (but not the A/F ratio either).

[Allch Chcar]

Originally Posted by serialk11r

Well if timing has to be retarded that's not good, as it is essentially reducing compression, so I guess I was asking how much pressure you can run literally without changing anything but the amount of fuel (but not the A/F ratio either).

I thought retarding the timing was a basic requirement when turboing a high compression N/A engine on pump gas ? I didn't think you could run any boost without reducing the dynamic compression unless you plan on running race gas.