Discussion
I've owned a 2.5 and driven a 3ltr
The most noticable difference is the lack of dump valve
noise on the 3ltr as opposed to the 2.5. Both very quick and no noticable difference in performance
in my opinion.
I liked the noise of the 2.5 turbos but then only
because the noise I could get away with because the car backed it up. Otherwise I think you may be regarded
as a boy racer. Notwithstanding the 3.0 is a more refined car to drive engine wise and does have a nice growl.
IMO not much in it. £10k extra fro the 3ltr ??
The most noticable difference is the lack of dump valve
noise on the 3ltr as opposed to the 2.5. Both very quick and no noticable difference in performance
in my opinion.
I liked the noise of the 2.5 turbos but then only
because the noise I could get away with because the car backed it up. Otherwise I think you may be regarded
as a boy racer. Notwithstanding the 3.0 is a more refined car to drive engine wise and does have a nice growl.
IMO not much in it. £10k extra fro the 3ltr ??
pwig said: I thought it had Waste gates, not dump valves?
>> Edited by pwig on Tuesday 20th May 16:55
It has both, in my limited knowledge basically a wastegate will 'open' once a certain boost psi has been reached, preventing excessive boost pressures being attained, a dump valve will release to atmosphere built up excess boost pressure when lifting off the throttle.
Now if someone who is more technical than me could explain that it might make it a bit clearer!!!
Answers all in here...
http://ubermensch.org/Cars/Technical/Turbos
Wastegates:
There is such a thing as too much boost in an engine, though. As boost pressure goes up, so do the chances of pre-detonation (pinging, knocking, whatever you tend to call it). Higher-octane fuels can be used to eliminate detonation, but anything over premium pump gas (92-93 octane in most states) can cost a fortune and is difficult to find. Not to mention, if you're pushing more air into the engine than the fuel system is capable of adding enough fuel to, it'll cause your engine to run lean. Lean mixtures can cause problems in various ways, from burned blown head gaskets to engine components.
It'd be nice if one could control the turbo a little, to ensure it never reaches too high of a boost level. This is why they use wastegates on turbocharged engines.
Think of a wastegate as large valve with an inlet and two outlets. The inlet gets connected to the engine's exhaust headers (in place of the turbo described previously), while one outlet goes to the turbo's turbine housing inlet and the other outlet to the exhaust system. The turbine's outlet still gets connected to the exhaust system as well, at some point merging with the wastegate's outlet.
Under normal operation, the wastegate is "closed," meaning all exhaust that flows through it is being routing to the turbocharger.
The wastegate has one other small inlet that gets connected to the intake manifold or some other part of the intake system that is pressurized by the turbo. This inlet goes to the actuator, which is essentially a diagram riding on a spring. When the pressure gets high enough, the spring can no longer keep the diaphragm from being pushed back, which in turn opens the other outlet. Since the turbo creates resistance on the first outlet, the exhaust will tend to flow through the less restricted outlet, bypassing the turbo. No exhaust through the turbo means no more boost.
The stiffer the spring, the more intake pressure is required to open the turbo. By choosing the right wastegate spring, you can effectively limit the amount of boost a given turbocharger will generate.
Blow-Off Valves:
So, with a good turbo, wastegate, boost controller, and intercooler, you're ensuring that when you go full throttle, you're getting lots of power relatively safely. However, what happens when you need to shift and your foot comes off the gas pedal?
The throttle in the intake is simply a little plate that normally blocks the air path, but is pulled open by pushing on the gas pedal. When you take your foot off the pedal, that plate closes again. Since you were just full throttle moments before, the turbo is still making full boost temporarily. All that air it's pushing out slams into what is now a blocked intake, creating quite a bit of resistance for the turbo wheel itself. The sudden resistance not only slows down the turbo (which means its going to need to spool back up before it can make max power again), but can cause quite a bit of fatigue on the wheels and shaft (which connects the two wheels), leading to early failures.
A blow-off valve is a vacuum-activated valve used to help this problem. Its vacuum control like is connected to someplace in the manifold AFTER the throttle plate. The other input is connected to the air path before the throttle plate (like just after the intercooler). What is done with the output is sometimes a topic of debate, but it can either just vent out to the atmosphere, or be routed back to the inlet side of the turbo's compressor.
Now when the throttle plate is closed, a vacuum is created inside the manifold (because the engine is trying to suck in air while the passage is blocked). This vacuum activates the blow-off valve, which then opens to allows air to escape through its outlet. Not only does this improve the turbo's lifespan, but the wheels are now allowed to spin freely, so that when the throttle is opened again, it'll take very little time before full boost can be made again.
J
http://ubermensch.org/Cars/Technical/Turbos
Wastegates:
There is such a thing as too much boost in an engine, though. As boost pressure goes up, so do the chances of pre-detonation (pinging, knocking, whatever you tend to call it). Higher-octane fuels can be used to eliminate detonation, but anything over premium pump gas (92-93 octane in most states) can cost a fortune and is difficult to find. Not to mention, if you're pushing more air into the engine than the fuel system is capable of adding enough fuel to, it'll cause your engine to run lean. Lean mixtures can cause problems in various ways, from burned blown head gaskets to engine components.
It'd be nice if one could control the turbo a little, to ensure it never reaches too high of a boost level. This is why they use wastegates on turbocharged engines.
Think of a wastegate as large valve with an inlet and two outlets. The inlet gets connected to the engine's exhaust headers (in place of the turbo described previously), while one outlet goes to the turbo's turbine housing inlet and the other outlet to the exhaust system. The turbine's outlet still gets connected to the exhaust system as well, at some point merging with the wastegate's outlet.
Under normal operation, the wastegate is "closed," meaning all exhaust that flows through it is being routing to the turbocharger.
The wastegate has one other small inlet that gets connected to the intake manifold or some other part of the intake system that is pressurized by the turbo. This inlet goes to the actuator, which is essentially a diagram riding on a spring. When the pressure gets high enough, the spring can no longer keep the diaphragm from being pushed back, which in turn opens the other outlet. Since the turbo creates resistance on the first outlet, the exhaust will tend to flow through the less restricted outlet, bypassing the turbo. No exhaust through the turbo means no more boost.
The stiffer the spring, the more intake pressure is required to open the turbo. By choosing the right wastegate spring, you can effectively limit the amount of boost a given turbocharger will generate.
Blow-Off Valves:
So, with a good turbo, wastegate, boost controller, and intercooler, you're ensuring that when you go full throttle, you're getting lots of power relatively safely. However, what happens when you need to shift and your foot comes off the gas pedal?
The throttle in the intake is simply a little plate that normally blocks the air path, but is pulled open by pushing on the gas pedal. When you take your foot off the pedal, that plate closes again. Since you were just full throttle moments before, the turbo is still making full boost temporarily. All that air it's pushing out slams into what is now a blocked intake, creating quite a bit of resistance for the turbo wheel itself. The sudden resistance not only slows down the turbo (which means its going to need to spool back up before it can make max power again), but can cause quite a bit of fatigue on the wheels and shaft (which connects the two wheels), leading to early failures.
A blow-off valve is a vacuum-activated valve used to help this problem. Its vacuum control like is connected to someplace in the manifold AFTER the throttle plate. The other input is connected to the air path before the throttle plate (like just after the intercooler). What is done with the output is sometimes a topic of debate, but it can either just vent out to the atmosphere, or be routed back to the inlet side of the turbo's compressor.
Now when the throttle plate is closed, a vacuum is created inside the manifold (because the engine is trying to suck in air while the passage is blocked). This vacuum activates the blow-off valve, which then opens to allows air to escape through its outlet. Not only does this improve the turbo's lifespan, but the wheels are now allowed to spin freely, so that when the throttle is opened again, it'll take very little time before full boost can be made again.
J
And thus, it is the dump valves rather than the wastegates that make the cool noise in the 2.5 litre cars.
From the insane noise when lifting off, I'm presuming that the 2.5 has full-on vent-to-atmosphere valves, similar to the alloy posey things that the turbo'd boy racer posse use.
The 3 is quieter, perhaps has recirculating dump valves?? The air intakes are relocated in the 3 litre cars as well, so there aren't air filters 30 cm behind your ears. Induction noise is thus louder in the 2.5.
Whether this is good or bad is a matter of taste. However I love the silly noises, you can make people on pavements jump out of their shoes by lifting off just as you go past them
From the insane noise when lifting off, I'm presuming that the 2.5 has full-on vent-to-atmosphere valves, similar to the alloy posey things that the turbo'd boy racer posse use.
The 3 is quieter, perhaps has recirculating dump valves?? The air intakes are relocated in the 3 litre cars as well, so there aren't air filters 30 cm behind your ears. Induction noise is thus louder in the 2.5.
Whether this is good or bad is a matter of taste. However I love the silly noises, you can make people on pavements jump out of their shoes by lifting off just as you go past them
An excellent suggestion. 
Well I wouldn't describe mine as 'pretty vocal' - more like loud'n'lairy 
I'm pretty sure the 3 has the air intakes relocated to the back of the engine bay whereas the 2.5 filters are right on your shoulder.
With the drivers window open, dump valve noise is LOUD. Full boost dumps particularly scared the shit out of my girlfriend the first time she heard it
I love it!
I'm pretty sure the 3 has the air intakes relocated to the back of the engine bay whereas the 2.5 filters are right on your shoulder.
With the drivers window open, dump valve noise is LOUD. Full boost dumps particularly scared the shit out of my girlfriend the first time she heard it
I love it!
Oh yes. 2.5's have a full 1 atmo dump valve - *serious* noise.
lx993 is dead right - a suitably lifted right foot can scare all sorts of humans and animals. Even funnyier is if you get it right you can make the thing "chatter" - confusing the hell out of everyone
Having been brought up on turbo cars, it's what "sold" the M12 to me
J
lx993 is dead right - a suitably lifted right foot can scare all sorts of humans and animals. Even funnyier is if you get it right you can make the thing "chatter" - confusing the hell out of everyone
Having been brought up on turbo cars, it's what "sold" the M12 to me
J
Noble's are cool - period - full stop (i.e. the actually go as fast(er) as they look.
lx993 said: It's good fun, but if I had made the same comment on the PH general gassing and said I had a chipped up Fiesta RS Turbo, no doubt I'd be flamegrilled immediately.
Funny that having a Noble changes all that.
But as they say, bigger boys, faster toys.
(sorry for offtopic...)
Festa RS Fart machines are not.
Simple really
J
joust said:Noble's are cool - period - full stop (i.e. the actually go as fast(er) as they look.
lx993 said: It's good fun, but if I had made the same comment on the PH general gassing and said I had a chipped up Fiesta RS Turbo, no doubt I'd be flamegrilled immediately.
Funny that having a Noble changes all that.
But as they say, bigger boys, faster toys.
(sorry for offtopic...)
Festa RS Fart machines are not.
Simple really
J
fairy nuff
it's still a cool noise, though - still makes me grin even if the issuer of the whoooshing noise is a small Ford with a backward-capped fool slouching over the steering wheel
(even better, should I put a custom ally dump valve on my Smart???
)
ek993 said: LX - is yours the 2.5 or 3ltr??
Joust - do the 3ltrs have the same dump valve as the 2.5's??
Hmmm.. too many questions on this car.... I have much to learn
Mine's a 2.5. Don't think I'd upgrade to a GTO3 now, esp. if it doesn't have the cool noises. Thinking seriously about the 6 speed box and a Joust-style boost upgrade.
Then again, 0.7 bar and I never get more than 20 mpg, even off boost. More boost and it'd be even more thirsty!! 15 mpg would be a bit much
Hmmmm... now I'm wondering if I drove the 2.5 or 3ltr at Mole Valley. There certainly was plenty of whooshing and whistling (not to mention dumping... errr...) coming from the rear of the car. If it was the 3ltr I would be more than happy with that, if not and the 3ltr is missing this soundtrack I won't be all that happy. I want my 'Max Power' sound effects. Waaaaa 
ek993 said: Hmmmm... now I'm wondering if I drove the 2.5 or 3ltr at Mole Valley. There certainly was plenty of whooshing and whistling (not to mention dumping... errr...) coming from the rear of the car. If it was the 3ltr I would be more than happy with that, if not and the 3ltr is missing this soundtrack I won't be all that happy. I want my 'Max Power' sound effects. Waaaaa
I may be wrong but I think that the Mole Valley demonstrator is the last of the 2.5L models but, because they ordered it on the change cusp ,so to speak, they got a 3L engine BUT with the dump valves benhind the drivers ears a la 2.5L- (instead of where all the 3L dump vales are now - at the rear of the engine)if you see what I mean!
Some turbo questions whilst I'm on:
1. Do you need to let the turbos cool down after a run before switching off?
2. What's the turbo-lag like on the 2.5L and the 3L?
3. Is there any special procedure to take before driving off (like an unsually long warm-up period)?
Thanks.
amg merc said:
ek993 said: Hmmmm... now I'm wondering if I drove the 2.5 or 3ltr at Mole Valley. There certainly was plenty of whooshing and whistling (not to mention dumping... errr...) coming from the rear of the car. If it was the 3ltr I would be more than happy with that, if not and the 3ltr is missing this soundtrack I won't be all that happy. I want my 'Max Power' sound effects. Waaaaa
I may be wrong but I think that the Mole Valley demonstrator is the last of the 2.5L models but, because they ordered it on the change cusp ,so to speak, they got a 3L engine BUT with the dump valves benhind the drivers ears a la 2.5L- (instead of where all the 3L dump vales are now - at the rear of the engine)if you see what I mean!
Some turbo questions whilst I'm on:
1. Do you need to let the turbos cool down after a run before switching off?
2. What's the turbo-lag like on the 2.5L and the 3L?
3. Is there any special procedure to take before driving off (like an unsually long warm-up period)?
Thanks.
The MV demo car I tried (silver/titanium?) was a GTO3, and had the twin rear exit exhausts. It was not as loud as my 2.5 though. Not sure if the more recent 3 litre cars are even quieter, though...
As to the questions:
1. Yes, like any turbo. Depends on how you've treated them before you stop, of course. If the last 5 minutes of your drive were off boost cruising or in town, no problem. But don't come straight off the track, park up and switch off
2. Not sure about the 3 but mine produces full boost from around 2500-3000 rpm upwards. There is lag below this, but we're talking relative here - it's a 980 kg car with a 2.5 litre engine, even without the turbos.
3. IMO - it's a Ford engine that's been tuned up. The cams / valvegear etc. have been designed with longevity etc. in mind. I certainly don't go over 4k revs until the water is warm but I don't do this in any car. It's not like a Speed six TVR in needing 10 minutes idling like a tractor before you can drive it, though.
Turbo cars - yes you will want to warm the car up before driving off, usually 1 min or so is fine, and you *definitely* want to let the Turbos cool for 30 sec to 1 min before switching off, depending on how 'enthusiasticaly' you have been driving before you get to your destination.
Could someone with a 3ltr car confirm how vocal the dump valves / induction roar is??
Could someone with a 3ltr car confirm how vocal the dump valves / induction roar is??
Have you read the Autocar and EVO reviews as they give subjective differences between the cars. Here's a link to actech's site which currently has the Autocar article on it. www.gto3.com/press/NobleInfo/Autocar05032003%20Page%201.jpg
In essence the engine gives a hard edged note more like a flat 6 than a V6, so engine sound is better but wastegate chatter and dump valve blowoff sound is reduced, partly because of a different position and partly because of a reworking.
Dynamically there is now a more linear and stonger response from low revs which is said to improve the in-gear acceleration times. As a result the car is even easier to handle round corners because there is no sudden stab of power which can unsettle the car. (I think joust has posted something about this before).
So the GTO3 gives an increase in necessary performance (overtaking ability) and improved driveability over the GTO.
Now all I've got to do is get my own one, either type I'm not fussy.
In essence the engine gives a hard edged note more like a flat 6 than a V6, so engine sound is better but wastegate chatter and dump valve blowoff sound is reduced, partly because of a different position and partly because of a reworking.
Dynamically there is now a more linear and stonger response from low revs which is said to improve the in-gear acceleration times. As a result the car is even easier to handle round corners because there is no sudden stab of power which can unsettle the car. (I think joust has posted something about this before).
So the GTO3 gives an increase in necessary performance (overtaking ability) and improved driveability over the GTO.
Now all I've got to do is get my own one, either type I'm not fussy.
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