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03-28-2011, 12:34 AM | #851 |
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thats awsome, so faster spool, that would be nice, kinda thought it would make more power because of the less restrictive turbine but i guess not, either way if in reality it was only 7% and only gaines 150rpms spool i think it would be great, but with all this, really makes it look like even with the larger exhaust wheel the 8374 would be a much better fit on these 2.5 since you just run so far off the chart, or maybe if someone comes out with a few mm bigger compressor wheel to keep the efficiency up more in the higher rpms, this turbo would really not do good if you were taking it to 8000-8500
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03-28-2011, 01:32 PM | #852 | |
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03-28-2011, 01:50 PM | #853 |
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We will see how a twinscroll 1.06 7570 journal bearing Borg does in the next month or so. It may not be an efr, but it will be curious to see how it does against its single scroll successor.
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03-28-2011, 02:17 PM | #854 |
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03-28-2011, 02:21 PM | #855 | |
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I don't work for a turbo company but I've been studying every research and scientific paper I can find about twinscroll since I heard about these turbos in Fall '10. Based on everything I've read, I believe that the "spool-up area" affected by TS (and not open turbine housings) is primarily at pressure ratios less than 1.8 and shaft speeds less than 100,000 rpm. Basically the 10-15% gains are in the 5-10psi spool-up range and not at 15psi, 25psi, or 35psi. Otherwise, as you've correctly noted with your graph, people would have very large EFR turbos spooling off idle. To sit back and take a reality check, if we think about my idea that the primary gain of TS is sub-1.8PR and sub-100K shaft speed - doesn't that agree with the feeling of livelier street boost and smoother more linear boost ramp as compared to same sized open T3? Matt |
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03-28-2011, 02:49 PM | #856 | |
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03-28-2011, 04:15 PM | #857 | |
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What you say sounds realistic, and if that is the case, I would guess we could see something like this: Which would still be pretty good IMO, as this is a bigger a/r housing, so should allow for more top-end. If there was an .83 TS housing the boost threshold gains would be even more. |
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03-28-2011, 10:11 PM | #858 |
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^^^ It all depends how the A/R is measured. You said the 0.92 A/R Twinscroll housing is larger and should be less restrictive. I have my doubts on that unless the A/R is measured properly taking into account the divider wall inside the turbine housing. I think the 1.05 A/R Twinscroll housing would probably allow for the same topend flow as the 0.83 A/R Singlescroll but testing will confirm it
Anyways thumbs up for your efforts to get a more realistic image of possible spool of the TS turbos on the Subaru. I definitely hope it works out as well as it shows on the graphs! Cheers, Jasper Kopinga CS Racing Taiwan. |
03-28-2011, 10:25 PM | #859 |
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BTW. Regarding the comment about efficiency. This may be a bit controversial but has anybody ever thought of putting a restrictor on the intake of the compressor housing to boost the P/R of the turbo at THE SAME manifold pressure to get into a higher efficiency island as well as even more flow capability in some cases??
To me it seems the EFRs are kick arse at high P/R which is normally not possible but when making a restrictor you can boost P/R for a given manifold pressure. Ofcourse you do not want it to become too restrictive to limit horsepower and to be honest the best way would be to have ANOTHER fully mappable DBW throttle body on the compressor housing intake Eh, hang on...... Turbo F1 cars had that....and for a reason You can keep the turbo in it's sweet spot. Cheers, Jasper. |
03-28-2011, 11:08 PM | #860 |
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Keep in mind that output heat is a function of PR * efficiency. So if PR goes up, efficiency would have to increase by at least as much as the PR increase, just to keep output temperatures constant. If the PR increases more than the efficiency does, output temperature will increase.
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03-29-2011, 06:55 AM | #861 | |
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03-29-2011, 08:01 AM | #862 | |
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From my memory, F1 cars did have the throttle before the turbo, but it was the main throttle. I'm sure there were VE gains from having the throttle pre turbo vs post turbo. It wasn't like there was another throttle on the intake manifold. |
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03-29-2011, 08:15 AM | #863 | |
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03-29-2011, 08:56 AM | #864 |
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didn't they also run a higher boost from the turbo than they fed the engine? IE example boost to 100 psi, go through relatively small intercooler to drop temps, then expand to say 80 psi and have end result of much cooler than ambient air going into engine.
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03-29-2011, 09:11 AM | #865 | |
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However, because of the less restrictive turbine, it does give more power at the same boost level and can keep high boost all the way to redline, whereas the small turbine'd 30R could not even hold 24 psi to redline. Personally I am still amazed that such a large turbo (the 84mm wheel is ~ 72 lbs) gives such great drivebility. I hold TS largely responsible for that |
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03-29-2011, 09:14 AM | #866 | |
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03-29-2011, 10:20 AM | #867 |
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Those F1 engines did run extremely high PR's. I don't remember any published figures, but increasing PR ultimately is the only way to increase power, assuming all the other VE/rpm tricks have been exhausted. It was on the order of 80-100 psi. Thats the only way to get 1000hp/liter that I know of
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03-29-2011, 11:07 AM | #868 |
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Old F1 cars ran dual TB's as a way to regulate turbo response and in the roll of a semi-bov. The vacuum formed across the compressor allowed for higher wheelspeed (vacuum equals no molecules to force into and out of the compressor)...however having dealt with this in FSAE, I wonder how their compressor oil seals liked it. We had oil sucking issues with TB -> restrictor -> compressor.
the primary TB's kept throttle response up and the secondary/turbo TB was more of a boost response tool. |
03-29-2011, 11:07 AM | #869 |
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Old F1 cars ran dual TB's as a way to regulate turbo response and in the roll of a semi-bov. The vacuum formed across the compressor allowed for higher wheelspeed (vacuum equals no molecules to force into and out of the compressor)...however having dealt with this in FSAE, I wonder how their compressor oil seals liked it. We had oil sucking issues with TB -> restrictor -> compressor.
the primary TB's kept throttle response up and the secondary/turbo TB was more of a boost response tool. |
03-29-2011, 04:55 PM | #870 |
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carbon seals - used when a TB or a carb is in front of the turbo.
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03-29-2011, 07:11 PM | #871 | |
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03-29-2011, 08:45 PM | #872 |
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Lazy!
Just kidding, I really appreciate all the work you've done so far! I think you're onto something with the temps being higher on the road than when doing a dyno run; If true, it would really help explain the difference in feel between the 7670 and the GTX3076R on the street, when the former is "slower" on the dyno. |
03-29-2011, 09:37 PM | #873 |
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^ yeah i just dont see that.....300 rpm slower on the dyno...yet faster on the street.
if thats true....then my road tunes should take off as people should swear off dynos since there would be no point if dyno pulls dont represent the street in any way. |
03-30-2011, 02:00 AM | #874 |
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It depends on whether the car is loaded before the dyno run and/or road tune run. Steady state driving will keep the EGTs up, while a dyno run without some time to build EGTs will not build EGTs to the same temp. But 300 RPMS is a stretch
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03-31-2011, 01:47 PM | #875 |
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it stopped raining there yet? i need some logs!
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