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#106
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Re: TURBOs!?
:-)
First I will come up with a setup to measure both inlet and exhaust pressure and temperature and map these against air mass flow. Then try to define the design envelope for the most efficient ball bearing twinscroll candidates. Do not wait for results very soon, though Kind regards, Tapani |
#107
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Re: TURBOs!?
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All EJ2X turbos have always been greater than 1.5:1 exhaust to inlet pressure ratio. VF34P20, one of the best turbos available for the EJ207 is around 2:1 at 20psi when you push the boost up to 18-20 psi like what pretty much every second WRX owner does. It's only when you stick a big turbo say GT35R on the 2.5L engine when you see 1:1 pressure ratios. |
#108
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Re: TURBOs!?
Yeah,
The two issues must be dealt separately (to begin with). The first concern in my car is the overall restriction the small turbine introduces and potentially the exhaust pressure goes thru the roof and strangles the breathing above 5500 rpm. The stock shiftpoints are around 6300 rpm and the engine does feel struggling...., but lands exactly at the sweet spot after an upshift and pulls strong (for 5 PSI ). This I will try to measure and map across the rev range. Let's see what I can come up with. The other issue is the basic exhaust arrangement and whether the pressure pulses work against or for us - and how this affects the basics of the cam designs. I do not have a strong opinion for now, but the twin scroll might not be a bad idea to entertain with stock cams and the IRIS system working. http://www.autozine.org/technical_sc...duction_4.html http://www.modified.com/tech/modp-09...n/viewall.html Also: To summarize, pulse turbocharging is combined with constant pressure turbocharging using a conventional turborcharger in applications that are configured appropriately. The exhaust pulses need to be adequately spaced apart, or else they interfere with each other, diminishing or negating the benefit, the theory being that it is advantageous to recover the high velocity energy available from each individual cylinder's exhaust blowdown event by maintaining the velocity and directing it to the turbine inlet. When these events are spaced too close together within the exhaust manifold, they cancel each other out to the extent that they overlap (one cylinder is in effect exerting backpressure on the other). In practice, a separation of 240 crank degrees is consider optimimum, with 180° being too narrow (having interference between adjacent cylinders in the firing order), and 360° being so wide that the low velocity phase of the impulse allows the turbine to lose momentum between impulses. Applications that utilize pulse turbocharging will have exhaust manifolds that are notably smaller in cross section than those that are designed as purely constant pressure systems. The small cross section maintains the desired high gas velocity and concomitant kinetic energy to the turbine inlet. The ideal engine configuration for pulse turbocharging is the in-line six, with the exhaust manifold split between the front and rear groups of three cylinders each. The turbocharger has a divided turbine inlet with the division maintained throughout the turbine housing all the way to the end of the nozzle section. This keeps the cylinder exhaust events within each half of the divided housing spaced apart 240° (the firing order being either 1,5,3,6,2,4 or its reverse, 1,4,2,6,3,5). This configuration represents practically 100% of today's commercial vehicle diesel engine market. The net benefit of pulse turbocharging is faster spool up and a steeper boost curve. Once the boost is being controlled by the wastegate (e.g.), the benefit is unrealized. Coming back to Bill's question, individual header tubes to the turbine inlet, conforming to the principles of pulse turbocharging described above, is a working concept. Current internet-wisdom suggests that the evolution of modern turbos may have introduced potential to solve the two issues combined while keeping the low boost levels and the thermal strain on the engine in check. Kind of a "less is more" way of thinking. The attached clips greatly illustrate the basics of the related time factors which are very important in a road car - also in a race car, I would think. Kind regards, Tapani Last edited by Tapani; 10-14-2012 at 06:27 AM. |
#109
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Re: TURBOs!?
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As I said, stick a GT35R on the engine and the pressure is more 1:1 because the turbo is nice and big for the 2.5L - the GT35R has been around for 10 years and the only update by Garret is a new billet compressor wheel which increases compressor efficiency and spool. |
#110
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Re: TURBOs!?
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Dunno if you saw this, 10 psi pulls nicely. Ignore the jagged boost and power lines - car was wheel spinning on the dyno. If you put that turbo in a daily driven 3.3L it would be the most driveable car about. If you're falling over at 3-5 psi with a smaller turbo then certainly upgrade. Twin scroll is nice but a more expensive solution and usually for people with an EJ2X 2.5L / GT42R type setup who want increased spool. Last edited by bazza; 10-14-2012 at 06:06 AM. |
#111
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Re: TURBOs!?
bazza what are your thoughts on a GT3576 a/r .65 on the compressor and a/r 1.17 twin scroll turbine? its one of the options im playing with
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92 pearl SVX about to revive 92 Black 4ws (Jap spec) SVX 93 black SVX 93 Liquid Silver SVX - sti 6 speed with R180 diff, my05 sti steering wheel, sti alloy lateral links, 19x8.5 275/30 42mm offset front and 19x8.5 275/30 22mm offset on the rear, 6 pot brembo caliper with 355 rotors front, 2 pot brembos rear 95 bright red SVX 96 emerald pearl SVX about to revive |
#112
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Re: TURBOs!?
the other option im playing with is twin GT2560r with a/r .60 compressor and a/r .64 turbine, i have both options already but your thoughts would be appreciated
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92 pearl SVX about to revive 92 Black 4ws (Jap spec) SVX 93 black SVX 93 Liquid Silver SVX - sti 6 speed with R180 diff, my05 sti steering wheel, sti alloy lateral links, 19x8.5 275/30 42mm offset front and 19x8.5 275/30 22mm offset on the rear, 6 pot brembo caliper with 355 rotors front, 2 pot brembos rear 95 bright red SVX 96 emerald pearl SVX about to revive |
#113
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Re: TURBOs!?
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So, you may say that the end result should be like a 21st century OEM set up . Boring, no kick in the pants . Tapani |
#114
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Re: TURBOs!?
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#115
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Re: TURBOs!?
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92 pearl SVX about to revive 92 Black 4ws (Jap spec) SVX 93 black SVX 93 Liquid Silver SVX - sti 6 speed with R180 diff, my05 sti steering wheel, sti alloy lateral links, 19x8.5 275/30 42mm offset front and 19x8.5 275/30 22mm offset on the rear, 6 pot brembo caliper with 355 rotors front, 2 pot brembos rear 95 bright red SVX 96 emerald pearl SVX about to revive |
#116
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Re: TURBOs!?
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This is one of the things that you can't relate back to the 4 cylinder engines, when looking at the 6 cylinder. The 4 fires each cylinder 180* apart, so that when No.1 has opened its exhaust valve to evacuate the cylinder at about 60* BBDC, its piston continues to the bottom, and is on the way up the bore, 60*from the top, when, 180* later, No.2 opens its exhaust valve to pressurise the system, pushing gas into the No.1 cylinder. So the piston has 60* to push the gas back out. The 6 cylinder fires each cylinder 120* apart. So when it opens No.1 exhaust at 60* BBDC. its piston is only at 60* ABDC when the No.2 opens to pump up the pressure in No 1. that now has 120* to push the gas back out. So the interference pressure hits the 6 cyl 60* earlier, to foul the charge. That’s why the pipe connecting the two sides has to be long enough to delay the gas pressure from getting to the other side, till its piston is closer to the top of the bore. The EZ30R that Perrin used is in another situation as it has variable inlet valve timing, and lift. Low speed inlet timing. High speed inlet timing. When it is at the low speed, fully advanced timing, the inlet valve is open for the 47* that the piston is pushing the gas back, not only into the exhaust, but into the inlet system for that 47* to foul the inlet charge. When the engine gets to 4500??? (don’t know what rpms it switches), the inlet timing goes to full retard and the inlet valve is closed, so that the gas is pushed back down the exhaust only, to let the engine breath clean charge. So it is no wonder why that engine came to life when the timing changed. When it is on advanced timing all the boost, just blows down the exhaust pipe, till the exhaust closes. This timing is no good for blowing, and will suffer from the short connecting pipe interferance, more that the EG33 or EZ30. Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#117
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Re: TURBOs!?
Yeah they work really nicely. Although wastegate is usually about 7 psi which with 2 x VF34's is a fair bit of power. Also later you could get the P20 rear housing for a bit more power.
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#118
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Re: TURBOs!?
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This means 1 and 3 on the EJ fire 180' apart and 1 and 2 are obviously 360' apart. On the EG33 1 and 3 fire 240' apart which means the EG33 cast iron header is actually better off than the EJ2X cast header as it gets a touch more time between firing to clear. Also the merge is a long way from the exhaust valves and tends not to be a problem as shown with GT Spec headers on the EJ's. The merge is more about ensuring the pipe design is big enough to ensure good flow and no restriction - for example my first header design used a 3" merge into the up-pipe and was crazy responsive. Quote:
So my advice to readers is start with a proven design and then innovate from there. Going on theory without proven results is a very risky business especially when it's your coin being spent at the end of the day. Last edited by bazza; 10-16-2012 at 06:34 AM. |
#119
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Re: TURBOs!?
Further:
An old set of WRX headers (EJ2X): Here you can see the merge - the diameter is nasty yet this setup supports 100 bhp with the 1-3-2-4 firing order and high rpm. You can see how close the runners merge and they fire 180' apart. The "GT Spec" header - long runners. An upgrade for EJ's above 100 bhp (per cylinder) due to the very small diameter in the headers and nasty merge above. Note the merge location doesn't change, it's about the same length from the exhaust valves. Last edited by bazza; 10-16-2012 at 07:33 AM. |
#120
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Re: TURBOs!?
My header version 1.0. 3" up-pipe ensure massive flow at the merge. Nice fat GT35R turbine and EWG ensure low header pressure.
My header version 3.0. Planning to run > 600 bhp eventually so will need to seperate the pipes at the port level: Cast iron stock header: What not being conveyed and my point is that for low boost and low power applications such as Tapani and Bobswood, the stock header is absolutely fine. If you've got the coin to go nuts - but don't think you HAVE to build a fancy header system from the get go - that's coin you can spend wisely elsewhere - like a fully tunable ecu etc. Last edited by bazza; 10-16-2012 at 07:20 AM. |
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