it once happened in my RST (the clip fell of the mounting ysstem and the actuator jumped off the wastegate), no boost + the sould of a open exaust
Would it be possible to run a turbo engine in a non-turbo mode by fitting it with a butterfly valve that bypasses the turbocharger?
Or maybe fit the 'charger with two blowoff valves (one of which is set to 0psi) and then butterfly between the two valves?
Would this be possible? I want a turbo engine, but I would like the option of running it completely without boost sometimes... (possibly be able to
use cheap gas on no-boost setting!?!?)
just open the wastegate
it once happened in my RST (the clip fell of the mounting ysstem and the actuator jumped off the wastegate), no boost + the sould of a open exaust
unfortunately rather pointless!!
An engine with suitable compression ratio for turbocharging will be hopeless without the turbo.
more suitable for your needs would be an adjustable boost valve, so you could at least reduce it as required. As nsdev says, its going to run totally
crap with no boost at all! 
quote:
Originally posted by NS Dev
unfortunately rather pointless!!
An engine with suitable compression ratio for turbocharging will be hopeless without the turbo.
I have a turboed engine. It has a 0.8 bar [peak] boost. The air pressure in the manifold at full throttle is therefore 1.8 bar. I guess that at 50%
throttle the manifold pressure is 0.9 bar. If I were to take the turbo off, at full throtte I would expect to have a manifold pressure of about 0.9
bar. The engine would run just as well on this air / fuel mixture under either scenario, except that without the turbo, the exhaust gasses would
escape more freely.
Removing the turbo would be like putting a block under the accelerator pedal to limit travel. It wouldn't run any worse.
except you would still be lacking compression. Whats the comp ratio on the smart as standard?
I think if you just want to be able to use cheaper gas set it up on your 87 octain gas and tune till just below detination. Tune it again on hi test
and make yourself of two valves with those to bleed leves to your waste gate. I intend to do just this so I dont have to fiddle with a boost valve.
Will set my self up at 10 , 18-20, 25lbs the last requiring alchol injection to keep the detination at bay. The last would be for short runs only-
maybe the 1/4 mile.
Dale
quote:
Originally posted by Dale
I think if you just want to be able to use cheaper gas set it up on your 87 octain gas and tune till just below detination.
Wow, maybe that's a bit of why your gas is so expensive (besides the massive taxes)
The three grades we get stateside are:
Regular = 87 octane
Midgrade = 89 octane
Super = 91 octane
If you want anything higher than that, you need to use a bottle of octane booster.
I'll do some research on the un-boosted compression ratio of the engine and post again.
Wheew! That took quite a while to find!
The NA engines (not the one I want) had 9.2:1 compression, and the turbo engine has 8.4:1
For 87 octane fuel, I think the maximum safe compression ratio would be around 9:1 so according to
this page, that means 1psi of boost! woo! It'd probably be easier just to blow off ALL
boost and run with 8.4:1. Or else, I could just break out the extra 20 cents a gallon and buy premium gas all the time. 
One more question, are adjustable blowoff valves easy to locate, and how do they work? do you just spin the dial from 5psi to 15, or do you have to
guess what the valve is set to at any given setting?
[Edited on 30/9/05 by millenniumtree]
just buy cheap gas and add cellulose thinners to it (if that's what you call it over the pond) (mixture of mainly toluene, with Xylene and 4%
methanol)
It's around £12.50 for 25 litres over here and boosts octane very easily and cheaply.
Low compression doesn't matter. Compression is only a mathematicaly derived number - it is the ratio of the cylinder volume with the piston all
the way out to all the way in.
The pressure in the cylinder head at ignition is determined by the throttle position multiplied by the compression ratio. An engine with a 12:1
compression ratio with an 83% open throttle will have the same pressure as a 10:1 engine with 100% throttle
So it is with a turboed engine. It may have a compression ratio of 8:1 but if the turbo is pushing air in at 1.5 times atmospheric pressure then the
cylinder head pressure is the same as the 12:1 normally aspirated engine at 100% throtte. So what does it matter if you have the turbo running with a
40% throttle or the turbo off with a 60% throttle? The same volume of air and fuel is flowing into the same cylinder of the same engine. It will
spark and run in just the same manner. Think. The cylinder doesn't know what the induction system is doing, it just compresses what ever is
sent to it.
ok, get what youre saying but aren't you going to mess up your fueling by not running the turbo ?
(suppose it depends if you add the fuel before or after the turbo, before won't be a problem)
i think its a daft idea anyway. Adjustable boost valves are common and easy to fit, why put up with a crap solution when you can pick and choose the
boost you want? And if smart is correct and it runs right, its still going to be totally lacking in power with no boost at all.
And anyway, i really would have to see it to believe it. Ive had many turbo'd cars myself (8 petrols and 4 diesels) and they were all terrible at
low revs with no boost.
Fuel injection would be after the turbo I would think. If you use a MAF sensor or a MAP sensor then the fueling wouldn't be a problem. If you
used a TPS then it would. I doubt that anyone would use a TPS because you couldn't allow for the amount of turbo boost. Think of turbo lag.
Yes, a variable boost solution would be best. Better to be able to control the boost pressure rather than merely switching it off or on. Then off /
on gives you more choice than just on. If you have a massive power engine and want to go out in potentially icy weather, switching the turbo off may
not be such a bad idea.
quote:
Originally posted by smart51
So what does it matter if you have the turbo running with a 40% throttle or the turbo off with a 60% throttle?
The exact same thing also gives them their economy advantage in total though. A smaller engine that can run economically under normal use but can have
the power for overtaking ect when under boost. It may not be as cheep to run as small motor under less load but if you have to use a bigger engine to
get the power you want for accel then your suffer the gas milage under easy use. Same as trying to get more power out of a smaller engine- whats a
small 1600 cross flow get for milage when its been tuned to get 150 hp compared to a turbocharged engine tuned to 200 hp. Both are going to have bad
milage under hard use but when your cruisijng I would think the turbo engine is going to be far cheaper to run.
Dale
quote:
Originally posted by smart51
Low compression doesn't matter. Compression is only a mathematicaly derived number - it is the ratio of the cylinder volume with the piston all the way out to all the way in.
The pressure in the cylinder head at ignition is determined by the throttle position multiplied by the compression ratio. An engine with a 12:1 compression ratio with an 83% open throttle will have the same pressure as a 10:1 engine with 100% throttle
So it is with a turboed engine. It may have a compression ratio of 8:1 but if the turbo is pushing air in at 1.5 times atmospheric pressure then the cylinder head pressure is the same as the 12:1 normally aspirated engine at 100% throtte. So what does it matter if you have the turbo running with a 40% throttle or the turbo off with a 60% throttle? The same volume of air and fuel is flowing into the same cylinder of the same engine. It will spark and run in just the same manner. Think. The cylinder doesn't know what the induction system is doing, it just compresses what ever is sent to it.
quote:
Originally posted by smart51
The pressure in the cylinder head at ignition is determined by the throttle position multiplied by the compression ratio.
quote:
Originally posted by NS Dev
comparing non 100% throttle openings is pointless, if that's the case, just fit a smaller bloody engine.
TBH I wouldnt let 87 octane gas anywhere near my performance turbo charged engine, but if you must, consider running a standalone engine management
system with switchable maps...
1 map for turbo charged and 1 map for non-turbo charged with different ignition and fuel values
Gonna double your setting up costs etc for the sake of a small gas saving...
Not worth the effort IMHO
quote:
Originally posted by Dale
The exact same thing also gives them their economy advantage in total though. A smaller engine that can run economically under normal use but can have the power for overtaking ect when under boost
quote:
Originally posted by smart51
quote:
Originally posted by NS Dev
comparing non 100% throttle openings is pointless, if that's the case, just fit a smaller bloody engine.
what proportion of the time does a typical engine spend at 100% throttle? Pointless considering anything less than 100%? What an odd point of view.
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...
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...
to be honest, to a muppet driver like me a combination of undrivable and deadly!
mate you have my respect trying to drive that!
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 @#$# about the fuel milage.
Dale
As Smart 51 pointed out one of the major points missed by the op is that a turbo is an energy recovery device, it is much more energy efficient to
have the turbo do induction and compression work rather than the pistons particularly if decent inter cooler is fitted. A car with manufacturers
standard production spec turbo engine developing X horse power will burn less fuel than a naturally aspirated engine devloping the same power.
Of course if you chase horsepower F1 turbo era style and turn the turbo charged piston engine into what too ammounts to a turboshaft engine with
piston expander in the middle fuel consumption goes through the floor.
[Edited on 3/10/05 by britishtrident]
quote:
Originally posted by britishtrident
As Smart 51 pointed out one of the major points missed by the op is that a turbo is an energy recovery device, it is much more energy efficient to have the turbo do induction and compression work rather than the pistons particularly if decent inter cooler is fitted.
quote:
Originally posted by Dale
I dont realy intend to be putting any unleaed regular in mine- propane maybe but thats another story- As far as I understand tune it to not blow up at hight boost and and keep the air charge temp as low as possible. At that point you can turn your boost down to a bit safer levels but still have a little peace of mind when you want to thrash the hell out it. Point also being that unless we are going for a long drive with the wife or kid then we are very unlikely to behaving like we give a flying @#$# about the fuel milage.
Dale
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
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
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.
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.
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?
I know that, but no F1 car has ever taken its motive power from the turbine.
no, I think he was just pointing out the extremes!
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.
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!
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!!
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]