Backpressure versus Boost Pressure
17-02-2006, 02:58 PM
#1
DEYTUKURJERBS
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Backpressure versus Boost Pressure
What do you consider ok?
Ive heard various things, from the backpressure is fine up until its double the boost pressure, right down to once the backpressure is equal with boost then the exhaust housing is too small and you shouldnt push it any further.
Whats the Cossie worlds opinion?
Ive heard various things, from the backpressure is fine up until its double the boost pressure, right down to once the backpressure is equal with boost then the exhaust housing is too small and you shouldnt push it any further.
Whats the Cossie worlds opinion?
17-02-2006, 03:27 PM
#3
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you know steve , I was sitting in bed the other night and was thinking exactly the same.
I stayed upto until 3am thinking about it, I just couldn't sleep.
Please could anyone put my mind at rest.
Many Thanks
Rick
Hello bigboy
I stayed upto until 3am thinking about it, I just couldn't sleep.
Please could anyone put my mind at rest.
Many Thanks
Rick
Hello bigboy
17-02-2006, 04:01 PM
#4
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Originally Posted by RSrussell
you know Steve , I was sitting in bed the other night and was thinking exactly the same.
I stayed upto until 3am thinking about it, I just couldn't sleep.
Please could anyone put my mind at rest.
Many Thanks
Rick
Hello bigboy
I stayed upto until 3am thinking about it, I just couldn't sleep.
Please could anyone put my mind at rest.
Many Thanks
Rick
Hello bigboy
Welcome back
17-02-2006, 06:02 PM
#6
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Mike Rainbird:
Optimum surely must be zero backpressure?
I thought it was best to keep the backprs to a minimum and certainly not exceed boostpressure. But then again, I think you english guys tune your engines way different compared to us here in norway.
Optimum surely must be zero backpressure?
I thought it was best to keep the backprs to a minimum and certainly not exceed boostpressure. But then again, I think you english guys tune your engines way different compared to us here in norway.
17-02-2006, 06:04 PM
#7
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Originally Posted by YBP
Mike Rainbird:
Optimum surely must be zero backpressure?
I thought it was best to keep the backprs to a minimum and certainly not exceed boostpressure. But then again, I think you english guys tune your engines way different compared to us here in norway.
Optimum surely must be zero backpressure?
I thought it was best to keep the backprs to a minimum and certainly not exceed boostpressure. But then again, I think you english guys tune your engines way different compared to us here in norway.
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17-02-2006, 07:11 PM
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I certainly know zero backpressure is impossible, it was a joke.
But did you mean keeping it below boostpressure is impossible without an unusable big exhaust housing?
But did you mean keeping it below boostpressure is impossible without an unusable big exhaust housing?
17-02-2006, 07:34 PM
#9
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Exactly, you could of course run very little boost, but that just means you lose a lot of midrange power. Back pressure is a way to quantify the gains of going to a bigger hosuing, but we all know what the side effects of this are.
18-02-2006, 01:37 PM
#10
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i guess we are talking about TIP back pressure (turbine inlet pressure)
TIP is almost always greater than inlet manifold pressure, we should always take a ratio of the two, a ratio of 2:1 is normally ok for a street/road car,,, more than this ratio and it means the exhaust housing is too smal and should be changed
a ratio of less than 2:1 will start too more to boost threshold upwards,, but normally this is the way too go for us! the lower the better,, but not above 2:1
in the f1 turbo days, the ratio was lower than 1:1
TIP is almost always greater than inlet manifold pressure, we should always take a ratio of the two, a ratio of 2:1 is normally ok for a street/road car,,, more than this ratio and it means the exhaust housing is too smal and should be changed
a ratio of less than 2:1 will start too more to boost threshold upwards,, but normally this is the way too go for us! the lower the better,, but not above 2:1
in the f1 turbo days, the ratio was lower than 1:1
19-02-2006, 05:01 PM
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Good Topic
Regarding books/info about F1 era turbo cars there was a great book called F1 ENGINE TECHNOLOGIES I read a few years back. TBH at the time it was a bit too technical for me and I let someone borrow it and never saw it again
Worth tracking a copy down as some boffin from BMW explained all sorts of technical gubbins....apart from how to fit a flux capacitor on a DeLOREAN
Regarding books/info about F1 era turbo cars there was a great book called F1 ENGINE TECHNOLOGIES I read a few years back. TBH at the time it was a bit too technical for me and I let someone borrow it and never saw it again
Worth tracking a copy down as some boffin from BMW explained all sorts of technical gubbins....apart from how to fit a flux capacitor on a DeLOREAN
19-02-2006, 05:24 PM
#16
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Originally Posted by Itsmeagain
i dunno, just engine stuff, detailed tech specs would be nice.
anywhere on the net with all that?
anywhere on the net with all that?
cam you might like this
http://www.amazon.co.uk/exec/obidos/...=1XHSF3TLD1X4X
19-02-2006, 05:50 PM
#17
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Originally Posted by GARETH T
Originally Posted by Itsmeagain
i dunno, just engine stuff, detailed tech specs would be nice.
anywhere on the net with all that?
anywhere on the net with all that?
cam you might like this
http://www.amazon.co.uk/exec/obidos/...=1XHSF3TLD1X4X
Bugger this thread is costing me money..lol
Cam
20-02-2006, 11:52 AM
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Im a bit slow, can someone explain how or why back pressure affects an engine performance either with a turbo or not? if enigne is an air pump surely you want little resistance to create power by being able to pump more air through or does back pressure help create more torque or bhp lower down the revs?
20-02-2006, 12:26 PM
#21
Originally Posted by evergreen72
Im a bit slow, can someone explain how or why back pressure affects an engine performance either with a turbo or not? if enigne is an air pump surely you want little resistance to create power by being able to pump more air through or does back pressure help create more torque or bhp lower down the revs?
However, what is beneficial is having a turbo that can spool up quickly, and the only way to do that is to have a housing small enough to produce back pressure when on boost.
If you could have a variable size housing that as boost rose the housing got bigger and bigger to maintain a very low back pressure that would be what the engine wanted, but you cant, so you have to have a compromise.
What the optimum back pressure is depends a lot on the spec of engine and whats its used for.
For example, if i was building a drag only nitrous+turbo engine i would run very very low back pressure.
20-02-2006, 09:45 PM
#22
Originally Posted by chip-3door
Back pressure is never beneficial to any turbo car on or off boost.
However, what is beneficial is having a turbo that can spool up quickly, and the only way to do that is to have a housing small enough to produce back pressure when on boost.
If you could have a variable size housing that as boost rose the housing got bigger and bigger to maintain a very low back pressure that would be what the engine wanted, but you cant, so you have to have a compromise.
However, what is beneficial is having a turbo that can spool up quickly, and the only way to do that is to have a housing small enough to produce back pressure when on boost.
If you could have a variable size housing that as boost rose the housing got bigger and bigger to maintain a very low back pressure that would be what the engine wanted, but you cant, so you have to have a compromise.
.
20-02-2006, 09:48 PM
#24
DEYTUKURJERBS
Thread Starter
Originally Posted by Mike Rainbird
Originally Posted by chip-3door
Back pressure is never beneficial to any turbo car on or off boost.
However, what is beneficial is having a turbo that can spool up quickly, and the only way to do that is to have a housing small enough to produce back pressure when on boost.
If you could have a variable size housing that as boost rose the housing got bigger and bigger to maintain a very low back pressure that would be what the engine wanted, but you cant, so you have to have a compromise.
However, what is beneficial is having a turbo that can spool up quickly, and the only way to do that is to have a housing small enough to produce back pressure when on boost.
If you could have a variable size housing that as boost rose the housing got bigger and bigger to maintain a very low back pressure that would be what the engine wanted, but you cant, so you have to have a compromise.
.
20-02-2006, 10:04 PM
#28
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this could help me.
once the fiecos is back rollin, i'm gonna fit a outlet for measureing back pressure, 1. b4 turbo 2. on down pipe.
to see wot mines running.
once the fiecos is back rollin, i'm gonna fit a outlet for measureing back pressure, 1. b4 turbo 2. on down pipe.
to see wot mines running.
20-02-2006, 10:28 PM
#29
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Thread Starter
Originally Posted by Mike Rainbird
And no fucking shopping cars running 2 psi . Come on then, spill the beans .
. Come on then, spill the beans .And not Japanese either
20-02-2006, 10:30 PM
#30
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Was it an Audi or a VW or something along those lines? I seem to remember something along the lines of variable vane turbos on a petrol engine some time ago now but can't remember what it was.
20-02-2006, 11:14 PM
#33
DEYTUKURJERBS
Thread Starter
The 89-90 Dodge-Daytona IROC 2.2 Turbo was the first petrol engine'd VNT car i know of.
Used a VNT version of the T3.
Engine was a 224bhp Lotus modified lump.
Well actually the engine was used in a few cars at once i think...
Shelby CSX-Daytona, Baron GTC, and Shadow ES
All 89-90, think they went back to conventional turbos after that.
Dont think it was all that sucsessful mind, but still, VNT turbos as standard on production petrol cars over 16 years ago
Im clever im clever, you're not your not
Used a VNT version of the T3.
Engine was a 224bhp Lotus modified lump.
Well actually the engine was used in a few cars at once i think...
Shelby CSX-Daytona, Baron GTC, and Shadow ES
All 89-90, think they went back to conventional turbos after that.
Dont think it was all that sucsessful mind, but still, VNT turbos as standard on production petrol cars over 16 years ago
Im clever im clever, you're not your not
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