millenniumtree
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| posted on 29/9/05 at 06:22 AM |
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Turbo/Non-Turbo valve?
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!?!?)
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berkut
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| posted on 29/9/05 at 08:34 AM |
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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 
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NS Dev
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| posted on 29/9/05 at 11:48 AM |
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unfortunately rather pointless!!
An engine with suitable compression ratio for turbocharging will be hopeless without the turbo.
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JoelP
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| posted on 29/9/05 at 12:21 PM |
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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! 
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MikeRJ
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| posted on 29/9/05 at 01:46 PM |
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quote:
Originally posted by NS Dev
unfortunately rather pointless!!
An engine with suitable compression ratio for turbocharging will be hopeless without the turbo.
Depends on the engine. One of the light pressure turbo engines (e.g. the 150bhp VAG 1.8T) would probably be ok off boost. Obviously engines running
8:1 and high boost will be complete slugs.
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smart51
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| posted on 29/9/05 at 06:09 PM |
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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.
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JoelP
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| posted on 29/9/05 at 06:43 PM |
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except you would still be lacking compression. Whats the comp ratio on the smart as standard?
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Dale
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| posted on 29/9/05 at 11:10 PM |
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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
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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MikeRJ
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| posted on 29/9/05 at 11:21 PM |
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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.
Our "regular" unleaded grade is 95 Octane and "super" can be anything up to 99 Octane, but I have a feeling it's
measured differently here to the US?
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millenniumtree
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| posted on 30/9/05 at 03:22 AM |
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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.
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millenniumtree
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| posted on 30/9/05 at 05:04 AM |
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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]
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NS Dev
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| posted on 30/9/05 at 09:55 AM |
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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.
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smart51
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| posted on 1/10/05 at 09:08 PM |
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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.
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MikeR
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| posted on 2/10/05 at 09:54 AM |
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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)
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JoelP
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| posted on 2/10/05 at 11:43 AM |
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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.
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smart51
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| posted on 2/10/05 at 03:00 PM |
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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.
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MikeRJ
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| posted on 2/10/05 at 10:22 PM |
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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?
Turbo-charged cars under normal cruise conditions run at around zero boost. Having a low CR is what makes turbo'd cars less economical (and
less responsive) off-boost, so there is a distinct adavtange to having a higher static CR.
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Dale
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| posted on 2/10/05 at 11:40 PM |
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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
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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NS Dev
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| posted on 3/10/05 at 12:51 PM |
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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.
what?????????????????????????????????????
off boost the dynamic compression ratio will be crap and the engine will have little power if the static compression ratio is set up to be suitable
for turbocharging (and assuming the engine isn't running super high octane fuel which would then totally negate the reasons for running with no
boost anyway!!)
Dymamic compression is just linked to static compression ratio, plus valve overlap and supercharging (either by ramming on a n/a engine or mechanical
means on forced induction)
comparing non 100% throttle openings is pointless, if that's the case, just fit a smaller bloody engine.
This whole thread really is rather pointless!
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NS Dev
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| posted on 3/10/05 at 12:56 PM |
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quote:
Originally posted by smart51
The pressure in the cylinder head at ignition is determined by the throttle position multiplied by the compression ratio.
also total bollocks........................
dynamic compression is affected dramatically by valve overlap and rpm with tuned length induction or centrifugal supercharging.
If you have the valves open the compression cannot build in the cylinder!!!! (pretty obvious really!)
N/A engines use valve overlap for inertial "supercharging", which works as port air speeds build up. On turbo engines the cams/overlaps
required are TOTALLY different, with pressure charging the overlap requirements are reduced dramatically as ramming is of a tiny magnitude compared to
the actual charge pressure.
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smart51
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| posted on 3/10/05 at 02:42 PM |
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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.
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G.Man
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| posted on 3/10/05 at 02:43 PM |
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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
Opinions are like backsides..
Everyone has one, nobody wants to hear it and only other peoples stink!
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smart51
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| posted on 3/10/05 at 02:57 PM |
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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
You're right Dale. Smart ForTwos have a 600 or 700cc engine with a turbo. Under normal driving you spend most of your time at a steady speed
or gently accelerating and decelerating. (unless you live in London when you spend most of your time stationary). Beacuse you are using a most of the
power that a normally aspirated engine of the same size would deliver you are running your engine quite efficiently. An engine is more efficient
under high load than low load. A small normally aspirated engine wouldn't give much acceleration as you are using most of it's power just
to keep rolling. With turbo boost, however, you do have acceleration power when you need it.
OK, the smart is no formula 1 car but 60MPG isn't bad. Most 1100cc 60 BHP cars in europe only deliver 45 - 50 MPG
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NS Dev
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| posted on 3/10/05 at 03:29 PM |
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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.
Not at all, ok, you go put your car on the rolling road and ask the operator to do a half throttle run for you as you want maximum half throttle
power.................................if you need power you open the throttle, if you run out of power at wide open throttle you start looking for
more....
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G.Man
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| posted on 3/10/05 at 03:36 PM |
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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...
Opinions are like backsides..
Everyone has one, nobody wants to hear it and only other peoples stink!
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