Rear Turbo Updates
08-19-2005, 01:24 AM
#61
"3.5 psi adding ~130-140rwhp is highly unlikely. "
It depends on the flow capacity of the turbo. Really big turbos deliver truly massive amounts of flow at even relatively low pressure levels. Remember that pressure is a restriction in flow. In a tremendously free breathing application with a huge turbo(say like a -90 trim compressor) and really efficient intercooler that sort of power is possible.
Lag would be highly pronounced though.
It depends on the flow capacity of the turbo. Really big turbos deliver truly massive amounts of flow at even relatively low pressure levels. Remember that pressure is a restriction in flow. In a tremendously free breathing application with a huge turbo(say like a -90 trim compressor) and really efficient intercooler that sort of power is possible.
Lag would be highly pronounced though.
08-19-2005, 01:26 AM
#62
"Usually SC installations are less problematic than turbo chargers as they are more able to be fed lubricant in the ideal operating temperature range and without the tendency for coking as in some TC installations. TC's due to their heat and operational factors, bearing type(s) and location can lead to rapid oil degradation and severe combustion system/piston/ring deposits"
That can be prevented with simple precuations, like keeping good fresh oil in the motor, letting it idle for a few secs before shutdown, running only good quality fuel, keeping the fuel filter clean, and running cooler plugs.
Think about just how many factory turbo systems are around. They're not any more dangerous than S/Cs, just a bit more complex.
Porsche has always gone with turbos. Anyone ever seen a factory Porsche SC car?
Turbos are illegal in top fuel classes. Someone ran one for a season or two back in the 80s, utterly dominated, and they were banned. It's in the Corky Bell book, im sure Google has more. They were banned from Formula 1 because they were making 800hp out of 90cid engines, and the speeds were 'unsafe'.
That can be prevented with simple precuations, like keeping good fresh oil in the motor, letting it idle for a few secs before shutdown, running only good quality fuel, keeping the fuel filter clean, and running cooler plugs.
Think about just how many factory turbo systems are around. They're not any more dangerous than S/Cs, just a bit more complex.
Porsche has always gone with turbos. Anyone ever seen a factory Porsche SC car?
Turbos are illegal in top fuel classes. Someone ran one for a season or two back in the 80s, utterly dominated, and they were banned. It's in the Corky Bell book, im sure Google has more. They were banned from Formula 1 because they were making 800hp out of 90cid engines, and the speeds were 'unsafe'.
08-19-2005, 07:44 AM
#63
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Both systems have advantages and disadvantages. Turbo is the clear winner in my mind, second is the twin screw and certainly last by a long shot is the CS.
The turbo delivers the boost right where you need it...up the middle and on the top end. CS only matches the turbo's ability at the high end where you never drive anyway. The twin screw gives you hard low and mid range but you do have to pay to drive it up top.
I can't see how if properly applied a supercharger is easier on the engine as compared to the turbo. That is a very general statement that needs some clarification. Maybe you should say "since a centrifugal supercharger doesn't make any appriciable boost mid range it is easier on the engine there" That would be a true statement, but it's also way down on mid range torque and HP there as well.
I would also be shocked if this rear mount system could deliver that much from such small manifold pressure numbers. Remember, there are always dyno correction numbers to consider as well.
The turbo delivers the boost right where you need it...up the middle and on the top end. CS only matches the turbo's ability at the high end where you never drive anyway. The twin screw gives you hard low and mid range but you do have to pay to drive it up top.
I can't see how if properly applied a supercharger is easier on the engine as compared to the turbo. That is a very general statement that needs some clarification. Maybe you should say "since a centrifugal supercharger doesn't make any appriciable boost mid range it is easier on the engine there" That would be a true statement, but it's also way down on mid range torque and HP there as well.
I would also be shocked if this rear mount system could deliver that much from such small manifold pressure numbers. Remember, there are always dyno correction numbers to consider as well.
08-19-2005, 02:14 PM
#64
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Originally Posted by m21sniper
"3.5 psi adding ~130-140rwhp is highly unlikely. "
It depends on the flow capacity of the turbo. Really big turbos deliver truly massive amounts of flow at even relatively low pressure levels. Remember that pressure is a restriction in flow. In a tremendously free breathing application with a huge turbo(say like a -90 trim compressor) and really efficient intercooler that sort of power is possible.
Lag would be highly pronounced though.
It depends on the flow capacity of the turbo. Really big turbos deliver truly massive amounts of flow at even relatively low pressure levels. Remember that pressure is a restriction in flow. In a tremendously free breathing application with a huge turbo(say like a -90 trim compressor) and really efficient intercooler that sort of power is possible.
Lag would be highly pronounced though.
Snipe, you are on top of this very well...
Louis Ott has been following this thread and says (abridged content)...
Let's see now. It takes 1 atmoshere of pressure, 14.7 lbs, 29.92 " hg, or 1 bar, however you want to measure it to make about 265 rwhp in a normal stock S4 auto. John's made about 240 rwhp. Maybe they got that figured out and didn't tell about it. Say it does make 265 rwhp. So 14.7 lbs makes 265 rwhp. That's 18 hp per lb. of pressure. With no loss, and even with the same inlet air temp, 3.5 lbs boost should give about 3.5 x 18 for 63 hp gain. 265 + 63 = 328 rwhp. When you factor in some pumping loss for the turbo, heat rise for the compression of the inlet charge (you lose 1% for each 10 deg F heat rise) you might see a bit over 300, maybe 315 at the most. Why only 3.5 lb s boost? Now if it was 6.5 lbs boost that would be 6.5 x 18 or 117 hp gain for a total of 265 + 117 = 382. Lots closer to 400.
08-19-2005, 02:45 PM
#65
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Herr,
The dyno runs at the PNW Dyno Day were corrected #'s.
What about yours? Oops, nevermind.
I would also be shocked if this rear mount system could deliver that much from such small manifold pressure numbers. Remember, there are always dyno correction numbers to consider as well.
The dyno runs at the PNW Dyno Day were corrected #'s.
What about yours? Oops, nevermind.
Originally Posted by Herr-Kuhn
I would also be shocked if this rear mount system could deliver that much from such small manifold pressure numbers. Remember, there are always dyno correction numbers to consider as well.
08-19-2005, 05:29 PM
#68
Originally Posted by Herr-Kuhn
The turbo delivers the boost right where you need it...up the middle and on the top end. CS only matches the turbo's ability at the high end where you never drive anyway.
Looks like the CS would be fine in those ranges.
08-19-2005, 07:58 PM
#70
Quote:
Lag would be highly pronounced though.
Tony Said:
and quite vocal..
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Lag would be highly pronounced though.
Tony Said:
and quite vocal..
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Yes, and he is currently missed.
08-19-2005, 08:54 PM
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I am getting really eager to see a dyno chart for the rear turbo car.
If we take a look at what Porsche has done with turboing the 928 engine, (or half of it that is
) we can get an idea of what we could expect in terms of percentage HP per psi boost.
1986 944 2.5L N/A 150chp.
1986 951 2.5L 11psi turbo intercooled 217CHP.
Since the turbo motor had lowered compression 8.0 v/s 9.5 then we have to take that into account. So we'll be generous and say that an N/A motor with 8.0 compression would loose 3% (the most I have heard) of HP per compression point. So .03x150=4.5HP. So we assume in the NA state the turbo motor would make 145.5 HP
With 11 psi and an intercooler Porsche got 71 additional CHP.
That means 6.45chp per psi boost or about 4.4% of original HP per psi boost.
So now I am thinking it is completely impossible for a rear turboed, SCed car, or regular turboed car to make 3.4 times as much HP per psi boost as the Porsche engineers were able to get.
If there is a 928 that went from around 260rwhp to 400rwhp on anything under 7 psi I'll be very very impressed.
Andy K
If we take a look at what Porsche has done with turboing the 928 engine, (or half of it that is
) we can get an idea of what we could expect in terms of percentage HP per psi boost. 1986 944 2.5L N/A 150chp.
1986 951 2.5L 11psi turbo intercooled 217CHP.
Since the turbo motor had lowered compression 8.0 v/s 9.5 then we have to take that into account. So we'll be generous and say that an N/A motor with 8.0 compression would loose 3% (the most I have heard) of HP per compression point. So .03x150=4.5HP. So we assume in the NA state the turbo motor would make 145.5 HP
With 11 psi and an intercooler Porsche got 71 additional CHP.
That means 6.45chp per psi boost or about 4.4% of original HP per psi boost.
So now I am thinking it is completely impossible for a rear turboed, SCed car, or regular turboed car to make 3.4 times as much HP per psi boost as the Porsche engineers were able to get.
If there is a 928 that went from around 260rwhp to 400rwhp on anything under 7 psi I'll be very very impressed.
Andy K
Last edited by GoRideSno; 08-19-2005 at 09:55 PM.
08-19-2005, 08:58 PM
#72
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Originally Posted by GoRideSno
I am getting really eager to see a dyno chart for the rear turbo car.
Andy K
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08-20-2005, 01:38 AM
#74
GoRideSno- Boost figures for turbos can be extremely misleading.
It really has a LOT to do with the compressor trim size you're using.
For instance a -60 trim turbo(like a garret T04E for instance) at 6psi moves a lot more air than a Garret T03 does, and with FAR less charge heating for comparable boost levels. When you get into 'stupid big' -90 sizes truly massive amounts of airflow can be achieved at very small boost levels(provided the rest of the system is as free flowing as a -90 trim compressor dictates it be).
It really has a LOT to do with the compressor trim size you're using.
For instance a -60 trim turbo(like a garret T04E for instance) at 6psi moves a lot more air than a Garret T03 does, and with FAR less charge heating for comparable boost levels. When you get into 'stupid big' -90 sizes truly massive amounts of airflow can be achieved at very small boost levels(provided the rest of the system is as free flowing as a -90 trim compressor dictates it be).
08-20-2005, 01:43 AM
#75
But isn't that also something that can cause lag? Say 5.0L using a 70 or a 90? Or even more extreme - a To4B to a 90? The smaller turbo will create lower rev power (not actually usefull when full bore accelleration above 4k is needed) where the 90 may not move very much until 4k?
Do you know what sizes Lingefelter uses for his Twin Turbo vettes? I'd like to find that out.
Do you know what sizes Lingefelter uses for his Twin Turbo vettes? I'd like to find that out.