Factors affecting torque.

[fletchie55]

if or when my turbos die, I will be getting K04s and asking for max torque rather than BHP as max BHP is only achieved at the top of the rev range which I rarely use anyway. occasionally ie when doing VAGcom logs I might rev to 6k but 98% of the time Im changing gear before 5k, so a map that will give me 450BHP at 7000RPM isnt much use, id rather have a map that allows the car to pull hard from low revs until about 5.5k. As I understand it though, the re-maps can change the way the turbos come in ie smooth or all at once, but you cant make the turbos spool up any faster, so there will always be a minimum RPM at which both KO3 and KO4 turbos dont really produce anything.

one way to achieve faster spooling turbos & hence more low down torque is to get roller bearing turbos, has anyone done this?

[musty1]

one way to achieve faster spooling turbos & hence more low down torque is to get roller bearing turbos, has anyone done this?

Will be using 2 GT2871R soon let you know once done just rebuilding the engine at the moment but costs are just stacking hopefully finsed by the end of the year

[Dippy]

Fine. I'm with you with that. What I don't get is why then we are so bothered with BHP. Why have an MRC 400/500 BHP. Why not an MRC 475ft-lb.

Primarily it is because peak power is a "rough and ready" way to describe engine performance whereas peak torque is not. If you are dealing with torque then you need to describe the curve to get any sense out of it. Audi DID do this when marketing the B5 S4, as their specs stated something like 400Nm between 1800rpm and 3600rpm.

Another analogy I can give is a windmill or waterwheel. Both have massive peak torque, but a very narrow rev range. The power is relatively low. In car terms not very usable without lots of gears. However then consider an F1 engine producing around 700-800 bhp. AFAIK these engines don't actually have huge torque, I think maybe around 300Nm, but that peaks somewhere around 15,000rpm. These engines are great for the racetrack but totally useless for a road car.

So back to typical road cars, the more realistic comparison is between a decent diesel engine and a high-revving petrol one. Now whereas I quite like driving cars with lively diesel engines, I admit that whilst they are good off the line, lack of top-end power means that the fun goes away when driving fast. However for a high-revving petrol engine you know that the low-down torque may not be great, but once moving the car is much more fun to drive.

And that's why I think peak power has become so popular as a single simple measure of relative performance.

It's the differences I don't get-ok it could be down to mapping but all three cars I've mentioned are MRC tuned. Is it purely the different maps that are creating the torque figure differences, or is it parts installed that are giving a major diference. Or just that you get a 'lucky' car?

Yes there are differences in engines, however I think I can still answer your question. The core of all three engines is (I assume) the same: 2.7 litre with twin K04s. That means that for the three cars, the majority of the torque curve will be the same up to a point. That point is where the "breathing" starts to get limited, at the top of the rev range. This is where de-catting, airbox mods etc, allows a higher air flow at higher revs, and this is what is crucial for increasing peak power.

So there will be fundamental differences between Doug's car and the other two to account for the 100bhp. As you note the maps will be different, and there will be different components (fuel pump, injectors, ICs etc.) with slight variation in performance, especially in relation to the torque curve. This is what will account for the slight differences in peak torque. In basic terms think of a K03 vs a K04. The former is POTENTIALLY capable of producing a better torque curve at the low end than the latter.

Does this make sense? I don't think I'm talking BS...

[Ads4]

Does this make sense?

It does indeed, many thanks....I'm getting there!