In The Best Performance Determinant, you've
nicely worked out the measurements that correlate best with power/weight, and
shown that this correlates nicely with a couple of other common
What you haven't done, is show that this is the BEST
Performance Determinant, rather than just the easiest to do calculations
This is more of a philosophical question, but it is really quite
interesting. What is the measure that correlates best with how quick a car is,
or alternatively feels, on the road? My own experience is that my Nissan 300zx
running 18 psi of boost and giving about 520 Nm of torque at 3500 rpm and a peak
power of 200 kW felt like a much faster car than a similar twin cam car with
slightly more peak power but heaps less torque. This is not a result that
shows up in any of the basic performance measures.
New Car Tests
Hi, really enjoy your stuff. Don't read
all of it, but you guys provide a unique offering that I really like. Any
chance of getting back into new car reviews. I know you've got issues with
some of the manufacturers, but can't you rent something for a day once every
month or 2, borrow friends cars etc? Cheers.
John PalmerNew car
tests are normally carried out over a week, so short-term borrowings aren’t as
effective. We have some new car tests coming.
Thanks for some great
articles. I have a question that really goes back to the articles you did
on the Audi Boost controller, Brilliant Boost, etc.
Referring specifically to the Audi Boost
controller, I do not understand how part of the pressure control works, as I
will now explain: To make the question easier to explain, let’s leave the relief
valve out and deal just with the pressure regulator. We have the compressor
on one end, then the regulator, leading to the actuator of the wastegate. Now
when the wastegate actuator gets around 7psi or so of pressure the wastegate
will (start to) open because of the factory spring setting. But if the regulator
has been set to say 11psi, wanting to control boost at that level, how will the
boost pressure in the line ever get up that high, because the wastegate will
always open as soon as 7 psi is reached in the system, and never get to the
11 psi before it opens. So the way I see it, the regulator is always
fighting the 7psi setting of the actuator and the pressure will always be bled
off before the higher pressure is reached. I'm clearly missing something in the
mechanics of this. I'm sure the answer is fairly simple. Please could you
explain, as its driving me mad trying to conceptualise how it works.
You are assuming that when the pressure
regulator is set for 11 psi boost, its outlet pressure is 11 psi. It isn’t. The
pressure regulator’s outlet pressure might only be 2 psi but we say “11 psi”
(referring to manifold boost pressure) because it’s the turbo boost pressure
level that concerns us, not the pressure regulator outlet pressure.
I'd like to start with the usual "I'm a big fan of
this site" stuff as really it is the most interesting tuning website around.
I'd like to request an article on the subject of
compression ratios. My track car uses a ford cologne v6 engine which I have
added a pair of turbochargers to. I've just recently put a big hole in the
pistons 5 and 6 due to them being crappy cast items with poor support on
the ring lands which leaves me with an interesting problem.
been speaking with a company in the states called JE pistons, they custom make
pistons and will make me some to any compression ratio I desire, the only
trouble is I really don't know what I want! I'd like advise on how low to
take the compression ratio (I'm of the understanding that lower is better
for full-throttle use) and how to go about taking measurements that will allow
me to spec the size of the bowl to put into their crowns.
We could do an article on compression ratios
but it would be so lacking in any specific recommendations, it wouldn’t be very
helpful. The required compression ratio in a naturally aspirated engine depends
on the combustion chamber design, head design, cam design, fuel octane, engine
management and the climate the car will operate in. In a turbo car you can add
to that the shape and magnitude of the boost curve. There are simply so many
variables that anyone who just looks at the engine on paper and suggests a best
CR is fooling themselves. Look at what others have successfully done with the
engine you are modifying...
Re New Tech Turbocharging. I remember reading an
older book that looked at the last of the piston engines being developed for
airliners just before jets made the development obsolete. They had gone to
diesel and ran massive boost pressure, I recall reading up to 90psi. Even the
Super Connie had the turbo shaft linked to the crankshaft output.
book concluded that the piston engine simply became a clumsy way of producing
hot gas for the turbo. I wonder if the motor vehicle industry will go the same
way? Maybe in ten years time we'll be driving gas turbines that charge a
capacitor operating an electric engine that turns the wheels?
Turbo’d for Torque
I've read your 'Turbo'd for Torque' article
(great!) and I think it’s the answer I've been looking for. I have a 2003
BA XR6 sedan with 4spd tiptronic which I was hoping to turbocharge, there
in lies the dilemma... The auto is said to handle a max. of 350fwkw (though I’ve
heard of it breaking at the standard 240fwkw mark). So modifications
and turbocharging to approx. 350 – 400fwkw like I was planning is no
longer an option. Then I read your article. What if I select a turbo to supply a
max. 270fwkw (still better than a XR6T) and have heaps of low-mid
rev torque (as it’s a daily driver)? Beautiful! But... Is it the onslaught
of torque or the +350fwkw that’s going to kill my
Unfortunately transmissions are almost never
power limited – they’re torque limited. People erroneously talk about the power
rating of a transmission because the numbers make more sense to more people. So
if it the gearboxes break with standard torque, you won’t be able to safely
increase it a great deal.