NS Dev
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| posted on 3/10/05 at 04:17 PM |
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quote:
Originally posted by G.Man
Basically, an engine that runs a high pressure turbo charger is gonna run pants with no boost...
An engine that relies on a low pressure turbo will run better than the above motor with no boost, but as it runs higher compression ratios is likely
to still run like a dog on 87 octane gas...
BUT
Bear in mind, americans use a different measure for their petrol than that which we use over here, so for 87 octane I think what they really mean is
normal unleaded as opposed to super unleaded/optimax...
I would probably run my cossie on normal unleaded if it was tuned to do so, and ran a decent knock sensor and closed circuit lambda fueling... and low
levels of boost rather than the 24 odd psi that I am gonna be running...
I know what you are saying there. It would tip the balance of driveability touch in your favour..................but..............with 24 odd psi of
boost it will certainly be fun to try and hang on to!!!
My mate's cossie saloon ran around that level (27 I think last time it went on the rollers) and it was just like throwing a switch when the
turbo started to blow! It had a group A spec engine build and was wire ringed etc so pretty tough. Used to break the wheels free in gear in third in
the dry and 4th and 5th in the wet so god knows what that'll be like in the MNR!!
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MikeR
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| posted on 3/10/05 at 05:31 PM |
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to be honest, to a muppet driver like me a combination of undrivable and deadly!
mate you have my respect trying to drive that!
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Dale
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| posted on 3/10/05 at 06:15 PM |
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I dont realy intend to be putting any unleaed regular in mine- propane maybe but thats another story- As far as I understand tune it to not blow up
at hight boost and and keep the air charge temp as low as possible. At that point you can turn your boost down to a bit safer levels but still have
a little peace of mind when you want to thrash the hell out it. Point also being that unless we are going for a long drive with the wife or kid then
we are very unlikely to behaving like we give a flying @#$# about the fuel milage.
Dale
Thanks
Dale
my 14 and11 year old boys 22
and 19 now want to drive but have to be 25 before insurance will allow. Finally on the road
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britishtrident
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| posted on 3/10/05 at 06:59 PM |
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As Smart 51 pointed out one of the major points missed by the op is that a turbo is an energy recovery device, it is much more energy efficient to
have the turbo do induction and compression work rather than the pistons particularly if decent inter cooler is fitted. A car with manufacturers
standard production spec turbo engine developing X horse power will burn less fuel than a naturally aspirated engine devloping the same power.
Of course if you chase horsepower F1 turbo era style and turn the turbo charged piston engine into what too ammounts to a turboshaft engine with
piston expander in the middle fuel consumption goes through the floor.
[Edited on 3/10/05 by britishtrident]
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MikeRJ
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| posted on 3/10/05 at 07:32 PM |
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quote:
Originally posted by britishtrident
As Smart 51 pointed out one of the major points missed by the op is that a turbo is an energy recovery device, it is much more energy efficient to
have the turbo do induction and compression work rather than the pistons particularly if decent inter cooler is fitted.
But the pistons always do compression! The turbo may recover energy from the exhaust, but it doesn't use that energy in a way that improves the
efficiency of the engine (as e.g. coupling the turbine shaft to the crankshaft would)! A turbo also uses some power in the form of pumping losses.
A turbo'd petrol engine with fixed compression will always have a higher brake specific fuel consumption (especialy at part throttle) than a
normaly aspirated engine.
If and when variable compression ratio technology is rolled out, there will almost certainly be a big increase in the use of turbos on small engines.
Unfortunately it's a long time comming, and though Saab had a reasonably simple/practical design in testing, GM decided to shelve it.
Anyone interested should have a look at http://www.saabnet.com/tsn/press/000318.html
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NS Dev
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| posted on 3/10/05 at 11:11 PM |
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quote:
Originally posted by Dale
I dont realy intend to be putting any unleaed regular in mine- propane maybe but thats another story- As far as I understand tune it to not blow up
at hight boost and and keep the air charge temp as low as possible. At that point you can turn your boost down to a bit safer levels but still have
a little peace of mind when you want to thrash the hell out it. Point also being that unless we are going for a long drive with the wife or kid then
we are very unlikely to behaving like we give a flying @#$# about the fuel milage.
Dale
Exactly the real world situation perfectly summarised.
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NS Dev
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| posted on 3/10/05 at 11:22 PM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by britishtrident
As Smart 51 pointed out one of the major points missed by the op is that a turbo is an energy recovery device, it is much more energy efficient to
have the turbo do induction and compression work rather than the pistons particularly if decent inter cooler is fitted.
But the pistons always do compression! The turbo may recover energy from the exhaust, but it doesn't use that energy in a way that improves the
efficiency of the engine (as e.g. coupling the turbine shaft to the crankshaft would)! A turbo also uses some power in the form of pumping losses.
A turbo'd petrol engine with fixed compression will always have a higher brake specific fuel consumption (especialy at part throttle) than a
normaly aspirated engine.
If and when variable compression ratio technology is rolled out, there will almost certainly be a big increase in the use of turbos on small engines.
Unfortunately it's a long time comming, and though Saab had a reasonably simple/practical design in testing, GM decided to shelve it.
Anyone interested should have a look at http://www.saabnet.com/tsn/press/000318.html
That is quite interesting.
I hadn't heard about that before.
I wonder if they decided to shelve it because variable supercharging technology is progressing quite well (electronically controlled fast response
variable speed drives opena whole new world of opportunity!)
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gazza285
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| posted on 3/10/05 at 11:35 PM |
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quote:
Originally posted by britishtrident
Of course if you chase horsepower F1 turbo era style and turn the turbo charged piston engine into what too ammounts to a turboshaft engine with
piston expander in the middle
What on earth are you talking about here?
DO NOT PUT ON KNOB OR BOLLOCKS!
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millenniumtree
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| posted on 4/10/05 at 02:22 AM |
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Ok, bringing this back to the original point, having an adjustable boost blowoff so I could limit the dynamic compression to about 10:1, just so I
could run with low grade fuel sometimes, would be rather pointless.
So if I understand it correctly... The engine will dog with no or very low boost because the engine wasn't meant to run like that. It's
a turbo head, optimized for 16+ psi, the fueling is wrong, the computer probably won't even know HOW to get good mileage with low boost and
cheap gas, etc...
So I should just buy the premium gas, and be ready to smoke 'em at a moments notice instead of pausing the race to add octane booster and adjust
my boost regulator. 
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NS Dev
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| posted on 4/10/05 at 01:38 PM |
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quote:
Originally posted by millenniumtree
Ok, bringing this back to the original point, having an adjustable boost blowoff so I could limit the dynamic compression to about 10:1, just so I
could run with low grade fuel sometimes, would be rather pointless.
So if I understand it correctly... The engine will dog with no or very low boost because the engine wasn't meant to run like that. It's
a turbo head, optimized for 16+ psi, the fueling is wrong, the computer probably won't even know HOW to get good mileage with low boost and
cheap gas, etc...
So I should just buy the premium gas, and be ready to smoke 'em at a moments notice instead of pausing the race to add octane booster and adjust
my boost regulator.
Yep!
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NS Dev
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| posted on 4/10/05 at 01:44 PM |
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quote:
Originally posted by gazza285
quote:
Originally posted by britishtrident
Of course if you chase horsepower F1 turbo era style and turn the turbo charged piston engine into what too ammounts to a turboshaft engine with
piston expander in the middle
What on earth are you talking about here?
Britishtrident is talking about the fact that as boost pressures and pumping losses rise, the turbocharged internal combustion engine just becomes a
closer and closer approximation to the gas turbine. There have been many hybrid engines developed in the past which used internal combustion in
cylinders with pistons but actually derived the motive force from an exhaust gas operated turbine. Still more engines which hybridised the two ideas
to bias drive from the turbine shaft to a mechanically driven crankshaft depending on the balance of torque and speed demand.
The whole area is one that fascinates me, all the more so because I have had some (limited!) involvement with infinitely variablle mechanical drive
design, which then opens up a HUGE number of possibilities..........................................................................as a hint, take a
look at www.torotrak.com and then imagine an engine (internal combustion) driving a torotrak toroidal transmission, with a second much smaller
toroidal transmission driving a positive displacement supercharger at infinitely variable ratio in relation the the
engine..................................................the performance possibilities are endless, and this is the future as I see it!!!!
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gazza285
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| posted on 4/10/05 at 02:39 PM |
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I know that, but no F1 car has ever taken its motive power from the turbine.
DO NOT PUT ON KNOB OR BOLLOCKS!
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NS Dev
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| posted on 4/10/05 at 05:23 PM |
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no, I think he was just pointing out the extremes!
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gutball
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| posted on 4/10/05 at 10:12 PM |
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Just to throw this in the mix...
My MR2 Supercharger is quite capable of running happily with the SC completely disengaged. I fitted a switch (SC is engaged by an electromagnetic
clutch, is very Mad Max and much fun!) so that I can acheive some sensible fuel economy when needed. With the supercharger engaged and in happy mood I
average 16mpg  with it disengaged I can get nearly 40!!
Compression ratio is 8.0:1
With the SC disengaged it has ~100bhp and will do 105mph+, with the SC its ~180bhp and a little bit faster.
Got to admit that I didnt really follow a lot of above discussion, and also that turbo and super mechanisms are significantly different, however, my
point is that a low comp engine designed for forced induction should be able to run quite well enough without that forced induction.
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NS Dev
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| posted on 5/10/05 at 08:02 AM |
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I thought MR2's had a positive displacement charger?
Obviously I was wrong, anybody got a pic of an MR2 supercharger?
Certainly won't run with a positive displacement charger disengaged and no alternative intake plumbing!
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G.Man
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| posted on 5/10/05 at 09:17 AM |
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quote:
Originally posted by NS Dev
quote:
Originally posted by G.Man
Basically, an engine that runs a high pressure turbo charger is gonna run pants with no boost...
An engine that relies on a low pressure turbo will run better than the above motor with no boost, but as it runs higher compression ratios is likely
to still run like a dog on 87 octane gas...
BUT
Bear in mind, americans use a different measure for their petrol than that which we use over here, so for 87 octane I think what they really mean is
normal unleaded as opposed to super unleaded/optimax...
I would probably run my cossie on normal unleaded if it was tuned to do so, and ran a decent knock sensor and closed circuit lambda fueling... and low
levels of boost rather than the 24 odd psi that I am gonna be running...
I know what you are saying there. It would tip the balance of driveability touch in your favour..................but..............with 24 odd psi of
boost it will certainly be fun to try and hang on to!!!
My mate's cossie saloon ran around that level (27 I think last time it went on the rollers) and it was just like throwing a switch when the
turbo started to blow! It had a group A spec engine build and was wire ringed etc so pretty tough. Used to break the wheels free in gear in third in
the dry and 4th and 5th in the wet so god knows what that'll be like in the MNR!!
Will not be running full 24 psi boost all the time.,..
The engine will be maxxed out about 350 bhp (flow limits of turbo, injectors etc) that should still prove exciting, and its gonna need all the grip it
can get and a cautious driving style, as well as a Boost controller...
I have raced for 5-6 years (in the past) so it doesnt phase me really, much, no honest, oh well maybe a bit...
Opinions are like backsides..
Everyone has one, nobody wants to hear it and only other peoples stink!
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NS Dev
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| posted on 5/10/05 at 04:41 PM |
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that's about the power my mate's car was making (@ wheels) I think (though obviously in something at least twice the weight in his
case!)
I wasn't thinking it would phase you but it may well phase your passengers!
I am something of a power junkie so it sounds like just my cup of tea...................................it's been too long since going in the
640hp Ultima to Le Mans
Not done any grasstrack meetings for ages either so I haven't driven anything fast for a couple of months now!! Doh!
[Edited on 5/10/05 by NS Dev]
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