Quote:
Originally Posted by biglady112
Well at one time I had a garrett T4 1.01 and 1.44 and a Borg Warner 1.25 housing all at the same time. The 1.44 was not really any bigger than the 1.25, but they were both a fair amount bigger than the 1.01.
The HX52 again is NOT a T4. And the 16cm next to the 1.25 was a noticeable difference. Not huge by any means, but appeared to be similar if not bigger than the 1.44 from memory.
I can't tell from those pictures, but at least the outside looks a fair bit larger than the T3 16cm housing. The inside is hard to see.
And the part about the revhard being unequal. So what. I did not buy it for that. I got it for less than $100 brand new. The car in this thread and another local made serious power with this thing. The other local is over 800whp. And yes, the two outer banks will be paired together.
But, when one and four fire, both inlets of the turbo will be seeing exhuast pulses at the same time. As well as when two and three fire. The same amount of energy should be hitting the wheel as if the two opposing pairs were fired together.
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Only if the lengths plus bends between the two are tuned to each other for a certain rpm (a VERY narrow interval where that would occur will result, too). IOW, no
. The 1 and 4 cylinders don't ignite at the same time, so neither does the exhaust valves open at the same time. When the number 1 exhaust valves open, one pulse will leave. If the rpm are high enough, then the number 4 will open the exhaust valves and two pulses will be traveling down the tube. Only if you have one tube EXTREMELY long and the other EXTREMELY short will the pulses meet at the collector. Where there is not so drastic a difference in the length, then the pulses of each cylinder are still striking the turbine at separate times, just like with an open header design. It is a common mistconception that a TS setup makes a turbo spool faster because of causing the pulses to "fire evenly" across the turbine wheel or because of "pulse spacing", or because of "pulse pairing".
Twinscroll is about pairing the
cylinders, not the pulses. Where 1 and 4 are paired, they will never see exhaust pressure from each other at the valves. This is the advantage of twinscroll. Many EvoM forum goofs don't understand this simple concept. There are pages of arguements and "proof" that it doesn't work with turbos gt35r and smaller. Their proof is a comparison between an open housing .63 a/r turbine and the same total a/r twinscroll housing.
The reason why you should pair 1 with 4 and 2 with 3 is not about spool speed. It is about 1) better VE for the same size individual scroll and 2) allowing your cam
retiming to increase topend with no loss in the bottem end.
Better VE. . . There is no back pressure seen by an exhaust valve when 1 and 4 are kept separate from 2 and 3. On the exhaust when number 1 opens, number 2 is closing. If there's overlap, and there always is especially for a performance based setup, then the exhaust gases that are being pushed out of number 1 will want to rush to number 2 at a point in the rpm range where the turbine is seeing more pressure than the compressor. Higher turbine pressure than compressor pressure occurs when you're pushing your turbo, when you have a smaller turbine housing for faster spool, when you have a hybrid with a t3 turbine with a t4 compressor. It commonly happens with performance build where you're extracting the most from your turbocharger. When the pulse from number one cannot see number 2, then it cannot push into the number 2 cylinder. Overall VE goes up because usable air/fuel is not being pushed out of number 2 when the intake valve for number 2 is being opened. The same when number 3 exhaust opens; since it is paired to number 2, it doesn't push into number 1 when it is closing during valve overlap. The same when number 4 exhaust opens; since it is paired to number 1, it doesn't push into number 2. The same with number 2; since paired with number 3 it doesn't push into number 4. And the firing order starts over with the same results. Better VE increases spool speed. Better VE is achieved through out the rpm range. Better VE for the same size individual scrolls means that you can now use smaller scrolls to increase spool speed and have the same overall flow as if you were running a laggier volute area with a non-twinscroll setup.
If you want to guarantee a twin scroll setup to out flow a single scroll setup but still have the same spool speed, use a twin scroll housing where each volute area is the same as open volute setup. Since exhaust gases are pulsed, each pulse sees the volute and the a/r tweeks flow and spool speed based on each pulse. For the pulses in a twin scroll turbine housing and divided runner manifold (1-4, 2-3) to see the same volute area as an open scroll setup, the individual volutes of the ts housing need to each be the same size as the one volute of the open scroll setup.
If you want faster spool speed and the same topend, you'll have to know your scroll. Since the overall VE goes up with a TS system for a given individual volute area, you can get the same flow out of the twin scroll setup though you are using smaller volutes. The higher VE makes up for the smaller scroll the individual exhaust pulses see. The pulses still see a smaller volute and spool the turbine faster. The higher VE also causes the turbine to spool faster. Therefore, a 10cm^2 (total area) twinscroll evo8 16g can flow the same or more on the hotside than an 7cm^2 single scroll evo3 16g, but spools quite a bit faster. Evo guys are geting better 20g numbers with the same evo8 hotside versus dsm guys with a 20g and the same evo3 hotside. Mitsubishi happens to know that the VE increase from isolating the cylinders allows a 5cm^2 volute area to flow as well as a 7cm^2 volute area in a non-isolated cylinder system. They like isolating cylinders: even the 1990 mitsubishi eclipse featured the divided manifold stock, to help with preventing exhaust backflow and which many port and cut out of their stock 1g/2g/evo3 manifold. It just doesn't work like a true twin scroll system. Hense, the evo 4-9.
Cam re-timing. . . Twin scroll allows one to use overlap to increase the topend (because of preventing exhaust backflow into the intake mentioned above). Overlap increases spool speed for a turbo car. But with an open scroll system the overlap allows backflow at rpms where you're psuhing the turbo, usually the topend. This KILLS topend VE and topend torque; topend power. So it is possible to retard your exhaust cam and spool even faster, while increasing your topend! So if you run a twinscroll setup with each scroll a/r equalling the individual scroll of a .63 a/r housing, you will spool as fast as the .63 a/r open housing and you will have more flow due to better VE when you push the turbo. You can then retard your exhaust cam timing, spool faster than with the open housing, and increase your topend VE even more at the same time. The faster spool speed will make up for the loss in low end VE due to increasing overlap. So more topend with no loss and, actually, maybe some increase in low end from cam tweeking.
My 19cm^2 wh1e/hx40 turbine housing has about the same area along the indvidual volutes as my open scroll .63 a/r garrett housing, from my obsevation. With a divided runner manifold, the big 19cm^2 holset housing should spool as fast as a .63 a/r garrett housing with a comparable turbine wheel to the wh1e/hx40 and flow a little more because of the better overall VE. . . I'll be finding out this upcoming summer. After i'm done with my big h1c
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Biglady, that turbo would spool 1000rpms faster with a 1-4 & 2-3 manifold, if he's not using one. The 16cm^2 holset turbine housing looks to be about the same size as the .84 a/r twinscroll garrett turbine housing. See
Holset vs. garrett divided turbine housing pics. Now the hx52 turbine wheel uses different aerodynamics than garrett gt turbos. The hx52 compressor flow is in the gt4202r range. But just like the hx40 turbine wheel in the bep .55 a/r housing flows enough to max out the super40 compressor, the hx52 turbine wheel in a twin scroll .84 a/r size (in garrett terms) turbine housing can flow alot more than a gt42 turbine wheel in a twinscroll .84 garrett turbine housing.
A side: ALL of the automotive manufacturers of whom have a turbocharged platform in this century use a twin scroll turbine housing. Except for the VTG turbos. Twinscroll VTG would be exceedingly complicated. 90% of the tubochargers used are SMALLER than the gt35r. Anyone who argues that TS is BS for smaller turbos and argues that TS is market hype are much brighter* than automotive manufacturers who wasted their money with a more complicated twinscroll system. They have cams with zero overlap* and still manage to spool their gt30r to full boost by a low* 4200rpms.
* Playful sarcasm not directed to biglady, but to those clinging to the last century
