Why do Turbo cars have Boost peak?
- Thread starter Virdi
- Start date
yep, I'd rather have a turbo that spools quickly than lags and produces more power at high revs.
There are designable ways to overcome lag by sticking the turbo as far up the manifold as possible so that it spools up nice and fast, but big turbos have big inertia.
There are designable ways to overcome lag by sticking the turbo as far up the manifold as possible so that it spools up nice and fast, but big turbos have big inertia.
I do not think it is entirely a mapping thing.
I might be wrong but are the internals not designed to work to a certain spec? E.g The turbine vanes are at their best efficiency at a certain RPM and beyond that the efficiency drops. The turbo is matched to the application, generally giving the most gains in the most used rev ranges and not all in the low end or all in the high end.
I might be wrong but are the internals not designed to work to a certain spec? E.g The turbine vanes are at their best efficiency at a certain RPM and beyond that the efficiency drops. The turbo is matched to the application, generally giving the most gains in the most used rev ranges and not all in the low end or all in the high end.
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Either the turbo is not capable of maintaining the boost at the peak airflow requirements of the engine (very likely with the original turbo), or boost is deliberately reduced at high RPM for safety. The thermal load on the engine at high RPM and high boost rises considerably, and there is only so much cooling you can achieve through excess fuel.
and to make punters feel that the car is "nippy". the same trick is done with certain remaps. big boost spike to make the car feel quicker and give lots of dramatic wheel spin.
Caporegime
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Apart from expense, why don't more car manufacturers have one small turbo operating until the larger turbo spins up y0? And if expense is the only reason, another small turbo would surely be a drop in the ocean compared to the cost of the average turbo charged car.
Soldato
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When my mum got the 1.4 golf tsi, 08 plate so the model before your's, the dealer said tsi stands for 'turbo supercharged injection', so really, thats like what your hinting at really? Turbo for the higher rev's and then the supercharger for the lower rev's. You can tell aswell as the boost kicks in around 2k rpm
I think more tsi engines should be on the road, cracking engines they are
Because that setup is a gigantic pain in the arse to design, incredibly complex, and when it goes wrong it's difficult to diagnose and expensive to fix.
Here's a diagram of Subaru's implementation:
http://veloce.myby.co.uk/Otherttdocs/TwinTurboSetup.bmp
http://veloce.myby.co.uk/TT PDFs/Solenoid Box[1].pdf
and here's part of the FD Mazda RX7's twin turbo implementation
http://www.rx7.org/Robinette/images/hoses.gif
I rather suspect that there's more than one thing going on here. Part of it is simply down to the fact that it takes a finite time for the wastegate to open enough to let the pressure drop off. Before my car was modded, it would hit 1.3 if you wellied it, but the maximum manufacturer's setting was 1.1 bar. It just peaked at 1.3 before the wastegate had could open.
Where cars have been remapped, it's down to pragmatism. You want the maximum boost low down to produce the acceleration, but you can't sustain it would breaking something, so you map it to reduce the pressure a little higher. So my car currently peaks at 1.75 bar at about 3500rpm, but after about 400rpm this tails off to about 1.60 bar. That headline figure has been tweaked up and own as various issues have arisen, but the 1.60 figure has stayed constant. I should also point out that on cold days if I seriously boot it then that 1.75 bar figure will be exceeded for the reason given first: 1.85 bar is the highest ever.
M
Where cars have been remapped, it's down to pragmatism. You want the maximum boost low down to produce the acceleration, but you can't sustain it would breaking something, so you map it to reduce the pressure a little higher. So my car currently peaks at 1.75 bar at about 3500rpm, but after about 400rpm this tails off to about 1.60 bar. That headline figure has been tweaked up and own as various issues have arisen, but the 1.60 figure has stayed constant. I should also point out that on cold days if I seriously boot it then that 1.75 bar figure will be exceeded for the reason given first: 1.85 bar is the highest ever.
M
Compression ratios have to be matched altered too, for instance, if you have a 2.0NA engine, you can obviously bolt a turbo on, but it won't be as efficient or as powerful as a standard 2.0 turbo produced by the same manufacturer.
MK4 Astra 2.0 for example. The compression ratio caused issues when turbo charging the NA Ecotec
MK4 Astra 2.0 for example. The compression ratio caused issues when turbo charging the NA Ecotec
Soldato
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Cannot comment on Bluefin chip for the Focus ST, but Dreamscience sits 1.1bar pretty much to the limiter from 1.8kish revs.
Standard boost comes on 2.5k and tails off at 5k max boost drops after 4.
Standard
Dreamscience
Standard boost comes on 2.5k and tails off at 5k max boost drops after 4.
Standard
Dreamscience
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I think more tsi engines should be on the road, cracking engines they are
You clearly know nothing about a good engine then, a TSI engine is a smooth as falling down the stairs.
Associate
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My boost tails off from a peak of 17psi to 15 at around 15psi its is mapped for it. The reason being is the standard injectors are at max duty cycle at this point.
Which variants do you have issues with?
The supercharged and turbocharged versions I've driven are flat and linear across the rev range. Some of the newer variants like the 120bhp in the Mk6 Golf are turbocharged only.
OT: I hate it when people describe their car as a "rex" without clarifying as that term is used for both Mazda RX-? cars and for the Impreza WRX.
The latter has never had a twin turbo setup, though some people think it does because they don't know what "twin scroll" means.
The one in the Golf GT Mk5, with the Turbo and Supercharger. It was horrific to be blunt.
K. I don't agree. It's a cracking engine. Now the 2.0 in the Mk4 "GTI" ... that's a bobbins engine.