Digsy

Agreed. TBH I missed how that fitted into the system schematic

I guess the issue is that you would be running a load of airflow with little or no pressure differential across the compressor, which would run you straight into the choke line on the compressor map. IIRC compressor bypasses are usually used when you are not generating boost, so maybe dumping it oiverboard would be the better option. Might be noisy though :-)

Many modern turbos have an integrated compressor bypass that recirculates back to the intake. They work fine. It's not a perpetual motion machine :-)

How about adding compressor bypass to turbo #2? That way you could spin it up propery without building boost and without deadheading it against the flow control valve. Here's how I see it working: Off boost WG1 open WG2 open Control valve closed Comp2 bypass open Turbo 1 boosting WG1 controlled WG2 open Control valve closed Comp2 bypass open Turbo 2 pre-spool WG1 controlled (ramping from closed to 50% open) WG2 controlled (ramping from open to closed) Control valve closed Comp2 bypass open Parallel twin WG1 50% open WG2 closed Control valve open Comp2 bypass closed

The genuine replacement aerials aren't that dear from Toyota. When you extract your old areial you will probably find there is a small length of the plastic left inside the spool which you will have to remove before fitting the new part.

The throttle on my NA started to stick after it had bene stood up, but it would stick shut. A good clean out with some meths on a rag removed all the breather deposits and cured it. The closing spring should be pretty stiff, though. I'm surprised it is sticking open.

I believe that US spec Supras run a MAF sensor and J-spec ones don't?

I'd facepalm but I can't do it justice as I only have two hands and one face.

Another thing is that the 2JZ comes from an era when computer analysis techniques were in their infancy compared to what we have now, so factors of safety tended to be higher which also elped to result in an over engineered engine. Nowadays we have the ability to shave the last few fractions of a mm off everthing in the name of weight and cost - and we do. Hence no more 100% plus power hikes on modern engines unless, someone originally intended the design to do that at some point in the future.

Here's a couple of extracts from BMW's own techincal papers on their recent twin and tri-turbo diesel engines showing the operating modes of the charging system. Note that the tri-turbo has two intercoolers. The industry acronym for this kind of setup is "R2S" *Regulated Two Stage" and there is some good info on the web about it, especially on the Borg Warner site. The setup in the pictures a few posts back looks a little bit different. Is this for the gasoline engine? If so I'd like to see a proper schematic for it if anyone has one. The diesel ones get a bit confusing because of the VGT actuators. BMW 6-Cylinder Tri-Turbo Diesel.pdf The New BMW 4-6-Cylinder Diesel Engine with 2-Stage Turbocharging.pdf

Yes, the BMW turbos aren't sequential in the 2JZ sense. They are compound. The small one spins up first, then both in series, then the small one is bypassed altogether. BMW also do a tri-turbo setup where the smaller turbo(s) don't have to be bypassed at high RPM.

They really did that???

Ah. Does the new 135i I6 use a different setup, then?

That can't possibly be true. If torque remained constant then acceleration would at best remain constant IF you were driving the car on a perfectly smooth road with frictionless wheel bearings and tyres, in a vacuum. What actually happens is that frictional and aerodynamic resistance increase with speed, so the acceleration drops off. What is usually called the "power band" is actually the peak in the torque curve, but modern torque curves are nearly flat anyway so there isn't really a "band" on production cars anymore. What might be muddying the waters is people with big single turbos where their torque curves look like power curves, and you get a much more gradual rise in torque than you would on a production car.

There’s nothing trick about that though, it’s just a boggo parallel twin setup (unless there’s a proper sequential version around). The bulk of the low down torque will be down to the twin variable cam timing and direct injection. The BMW “Twin power” engines all use some form of pulse division in the exhaust manifolds. The I4s use twin scroll turbos, the V8 pictured earlier in the thread used two twin scroll turbos with crossover manifolds but the I6 can get away with two single scroll turbos because of the natural pulse division you get by dividing an I6 into two I3s. If you want to see proper advances in turbocharging, BMW’s diesels are where you need to look. Twin charging using either a low pressure and high pressure turbo or a clutched supercharger and a turbocharger will probably be the next big thing in gasoline engines. Its already happening on diesels.

High EGTs is why variable geometry turbos haven’t caught on in a big way yet in gasoline engined cars. Of course it all depends on how durable you want it to be. I believe that Porsche and Maserati are the only OEMs using VGTs on gasoline production engines, compared to turbo diesels where they are virtually standard fitment.

I had a 1994 normally aspirated Supra and it didn't have a MAF meter. I may be wrong but I think the engines with MAF were UK and Federal spec. Imports are speed/density (MAP and MAT).

I'd broadly agree with that but replace "high performance" with "almost any". But its horses for courses. If you decide early on that you are going to go absolutely all-out for a low centre of gravity and stuff everything else, then a flat engine is the obvious choice. However I rather suspect that what happened with the GT86 is that Subaru said the engine had to be a boxer because Subaru's have boxer engines, end of. I can't think of a really good reason why Toyota would have suddenly decided to design one when they have a perfectly good range of modern I4s already. I guess it will be telling if they use it in their "own" vehicles going forward. Many years ago I did some work on a job once where a company wanted to use the old Subaru SVX engine in a high tech MPV purely for the reason that they percieved that boxer 6 engines were sexy (through their association with Porsche).

I think the key there is "so many advatnages". Boxer engines have some advantages, but I don't think they have enough advantages. The vibrations of a large displacement inline 4 are only slightly worse and (and usually are) addressed through the addition of balance shafts, and how many everyday drivers are so close to the edge that they would notice the centre of gravity changing by a few cm vertically? I think justifying a flat engine in intangible terms like handling versus something as tangible as cost might be very hard. Its a nice way to get a low bonnet line in a small car while keeping to the predestrian impact regulations, though. Also, if you want to turbocharge one and get a good spool up because of the firing order you would need a manifold with crossover pipes to keep the pulses from adajacent cylinders 180 crank degrees apart (clicky). Realtively easy to do with an inline 4, but a bit harder on a flat engine.

I need to make a correction to what I wrote above. Lower frequency vibrations are EASIER to deal with than higher ones. The reason that the second order vibrations in the boxer engine are better than the first order in the flat is because the magnitude is smaller.

I really don't underdtand why you want to stay with 225's. Is it a cost thing, or (shudder) do you want to be able to break traction? If its cost then stick with 17's. They are much cheaper than 18's when it comes to tyres.

In the flat engine you have two piston and rod masses moving from left to right at one end of the engine and two more masses moving from right to left at the other end. These two opposite motions create a couple which tries to rotate the whole engine around its centre of mass. The bigger the piston / rod mass and the more seperation between the cylinders the bigger the couple. In a boxer engine there are two smaller couples which almost cancel each other out. The thing about these couples are they occur at engine speed - what we call first order. First order vibrations are bad because they are relatively low frequency and can induce resonances in other engine parts like brakets, heatshields and even heavier items like alternators and AC compressors, causing them to fail. They can also be felt or heard by the driver. I said above that in a boxer engine the first order couples almost cancel each other out. In practise they don't because the motion of the piston that is coming up the bore is slightly different to that of the piston going down the other bore. Therefore instead of cancelling out toally you still get a residual couple. The good thing about this couple is that it is small, and also it occurs two times per crank revolution. Thus it occurs at double the frequency of the larger couple present in the flat engine. It is therefore much easier to design around.

All boxer engines are flat, but not all flat engines are boxers. A flat engine has both banks opposite each other (a "180 degree V" if you like). In a flat engine you have two con rods on one crank throw, so when one piston is at TDC the other piston is at BDC. On a boxer engine each rod has its own crank throw, so that pairs of pistons are at TDC and BDC together. The piston motion is supposed to be analagous to a boxer's fists, but I've yet to see a boxer throw a punch with his left and right simultaneously

As well as the packaging and low center of gravity advantages, Boxer 4 engines have slightly better vibration characteristics than inline 4's. That is vibration as in what is felt externally rather than internal balance to make it "revvy". I.e. they are in theory slightly more refined. This is not true of flat 4 engines, which are worse for vibration than inline 4's. Their big downside is cost. They have the component count of a V configuration but they don't add enough "bang per buck" to justify it compared to a more conventional inline 4 layout, and I'll take a guess that this is a big factor in why they don't appear in more cars.

I thought the GT86 engine already had Toyota's latest DI system on it, or have they got a newer one coming out?