[Warning: M.net content] Turbos make more power but superchargers make more 'torque' - Page 6 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-23-2010, 11:50 PM   #101
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Lol, duct tape one of those tube thingys that you whirled in circles to make that god awful noise.
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Old 02-23-2010, 11:58 PM   #102
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Twin Rotrexed LS2 with heads/cam. On 235s. Thats a great way to kick *** and learn throttle control at the same time.
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Old 02-24-2010, 12:09 AM   #103
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Twin Rotrexed LS2 with heads/cam. On 235s. Thats a great way to kick *** and learn throttle control at the same time.
235s on 7.5s in front... 295s on 10.5's in back if I recall correctly
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Old 02-24-2010, 12:34 AM   #104
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That makes more sense. I fail reading comp. Excellent.
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Old 02-24-2010, 12:38 AM   #105
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235s on 7.5s in front... 295s on 10.5's in back if I recall correctly
this

MT ET Streets
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Old 02-24-2010, 12:40 AM   #106
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That makes more sense. I fail reading comp. Excellent.
Just look at the first pic.

But yea, they took the factory wheels and supplied them to the named company and widened them to 10.5. Sort of unusual but serving a purpose in this case. A number of companies do widen wheels in that way though.

that car does indeed look sick as all hell.

But.. its not a 1.6l with a hotside 45...
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Old 02-24-2010, 09:09 AM   #107
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So much like a wastegate, except it byasses intake air charge instead of exhaust gases. I guess there would not be a loss of efficiency since the compressor will simply spin at tht RPM it spins at as opposed to spining faster and faster. probably a lot cheaper and more reliable than a variable planetary gear set.

I wanna see full boost as early as possible and maintain it to redline. Here's the torque difference that would result on my setup:



Difference of 40tq and 5psi at 4000RPM.
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Old 02-24-2010, 10:46 AM   #108
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With the 'wastevalve' setup I wonder if its then possible to run a larger compressor (both in terms of diameter and depth) so that you get more flow at lower RPMs, and then boost is controlled up top. Combine this with a small pulley. So even at say 2500 RPM you have maybe 50K rpm on the comp wheel and its a big damn comp wheel, such that you have a pressure ratio of like 1.5 right there. Its not insta-boost but its pretty good. As it is now it seems likely that they had to go with a middle of the road size comp wheel and then fit a restrictor.

But then you probably have a severely overspun unit by 5K and boom/heat. Shoot.

Yep. I wanna know about vatiable speed planetary gear sets. The wastegate/BOV thing is cool and I think it would work a hell of a lot better than a restrictor, but its not a means of more boost early.

http://www.freshpatents.com/-dt20090...0090173318.php

Looks like someone is already working/thinking on it....
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Old 02-24-2010, 04:57 PM   #109
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With a wastevalve you will still be moving air from the high pressure outlet to a low pressure inlet. This process generates heat and saps power.
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Old 02-24-2010, 06:17 PM   #110
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^ it would with a turbo, but not a supercharger. With a turbo, the loss of pressure due t the open valve then causes the wastegate to close and the turbo then spins faster, usually moving to a less efficient area of its map as it tries to mmaintain boost. With a supercharger it is just stays dumb and happy and spins at the speed that RPM determines and it's efficiency is what is. It does not care if all the air goes through the TB or not. Having less boost pressure will if anything make it more efficient as it spins at its pre-determined speeds.

Now recircing back to the inlet would have some air getting compressed multiple times which would heat things a ton. But with a speed density, non-AFM setup there is 0 need to recirc. I would just vent it to atmo. With a duck call or the tube thingy.
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Old 02-24-2010, 06:48 PM   #111
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sparetire,

It's the laws of thermodynamics.

The wastevalve requires the air flow from the higher pressure outlet (say 10 psi boost), to the inlet (atmo). It flows through a restriction (the valve). ANY flow through a restriction entails (1) loss and (2) heat generation. The shaft will draw more power, and the air that flows through the restriction heats up.

The only way to recover the energy stored in the air by compression is to move it through a turbine on the shaft lol. Turbocompounder anyone?
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Old 02-24-2010, 06:58 PM   #112
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But the air going through the restriction can just be vented to atmo. Its temp doesnt matter. If an AFM is in the mix then it gets recirced, but not with a MS or similar. The wastevalve is mounted just like a BOV or external wastegate, such that the only airflow going through it is the airflow thats being vented. The air thats goes to the TB runs a direct path with no additional restriction.

The lower pressure (being held at 10 psi instead of reaching say 15 psi) in the inlet tubing will actually reduce the power needed to spin the compressor. It's spinning at whatever rate the rpm determines, but it has less resistance in doing so.

I really think this could work. And then a person could simply run the smallest pulley that the blower can handle safely/reliably to get the fastest boost ramp up.
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Old 02-24-2010, 07:12 PM   #113
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It takes energy to push the air through the restrictor. Where does this energy come from? The crankshaft.
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Old 02-24-2010, 07:23 PM   #114
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In this case no. There is a net lower restriction compared to a straight pipe from the SC outlet to the TB. The valve is decreasing pressure at the outlet of the SC, not increasing it.

From the SCs point of veiw, it has less pressure to work against as it spins at whatever rpm it spins at. This lower back pressure (aka boost) means that it takes less force to spin the SC at X rpm.
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Old 02-24-2010, 09:20 PM   #115
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Look at a centrifugal compressor's map (e.g. GT2560 compressor on Garret's site).
Pick a point say pressure ratio=2 (15 psi boost), flow = 25 lb/min. Look at the speed line it's on. In this case, it's 121809 RPM. The power done by the compression is proportional to:

pressure ratio * flow
2*25 = 50

Let's say you add a leak to atmo so that it is now at 1.8 pressure ratio (12 psi boost), on the same speed line. The new flow is 30 lb/min. The power is
1.8*30 = 54
That requires more shaft power.

Let's take another pair.
110344 rpm speed line.
before: 1.8 PR, 20 lb/min, power = 36
with leak: 1.75, 24 lb/min, power = 42

Your other problem is if the compressor curves have horizontal parts to the various speed lines like the GT 2560 at lower flows. It means that pressure won't change much with a leak.
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Old 02-25-2010, 01:11 AM   #116
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Crap. Well, that explains why I did not see it in practice LOL.

Variable planetary gear set FTW...someday.
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Old 02-25-2010, 01:09 PM   #117
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Quote:
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^
Now recircing back to the inlet would have some air getting compressed multiple times which would heat things a ton.
Except that the air being recirced by the wastevalve is also expanding and returning back to atmo pressure, losing the heat gained from compression, because it's recirculating back to the inlet. The heat gained from mechanical inefficiency still remains but there's no heat gained from compression to speak of. In cruise conditions the system will steady-state with the temp rise at some point - most air goes around the loop, while some goes into the throttle body and is replaced by air from the intake. At freeway speeds with my system (~3200 rpm, which is 2-3psi if I go WOT) I usually see IAT around +60 from ambient. My cold air intake is only moderately effective at this point and I'm sure it's not drawing 100% ambient temp air into the intake, so that +60 rise should not be attributed entirely to the SC. Some of it sure, but not all of it.

Energy from the crankshaft required to spin the compressor in this state isn't much. The compressor isn't building and pushing against a pressure head because of the recirc loop, so the only energy required is that to push that air around the loop, and the energy needed to overcome the mechanical drivetrain losses of the supercharger itself.
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Old 02-25-2010, 07:38 PM   #118
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Yeah, under cruise its fine, but th concern is the systems main purpose, to control boost without messing with a pulley size change. If its bleeding enough air to take 15 psi down to say 10 psi, then a big penalty is paid in terms of efficiency/parasitic drag.

I still dont fully grasp it to be honest, my thermodynamics was almost 10 years ago and I have not really rigorously used it since. But there is probably a reason you dont see this method of boost controll out there.
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