Quote:
Originally Posted by Tapani
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.
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 |
Quote:
Bazza. EG33 have one bank firing cylinders 240' apart. The EJ2X turbo has one bank firing 180' apart (1 4 2 3) and the stock header for the EJ2X is near identical to the EG33 header and is what Perrin copied and what I also did. EJ2X header is good for 100 bhp per cylinder before the pulses create to much of a restriction. Means the EG33 is good for about 600 bhp theoretically before the stock headers become a restriction. I saw 580 odd bhp but the cams were the issue. Now cams fixed I expect it will hit 600 bhp no problems at 6500-7000 rpm.
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.
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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.