Fantastic Read.... Grab A Beer

[Turbo6man]

The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

I'm still a little confused .... the XR6T makes max torque of 450nm from a low 2000rpm to 4250rpm. Ford make a big fuss that the T makes so much torque from down low, but wouldn't the T be better if max torque was produced at a higher rpm ???? Why is it such a good thing that the T makes the torque down low ???

<{POST_SNAPBACK}>

But it also says, or at least strongly infers, that a flat long lasting torque curve is even more desireable. And this is exactly what you get with a big turbo engine.

The quote "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." should be read as pertaining to naturally aspirated engines where the design may be altered to achieve either one characteristic or the other but not both. That is to say, atorquey low revving engine will feel quicker off the line and during rolling accelleration as in everyday driving BUT a somewhat less torquey but higher revving and better breathing engine will perform better at constant full throttle driving as in competition use.

A forced induction engine gives you the best of both worlds ...

[straughsberry]

Yeah nice read fwiw. Thanks.

[jsmith]

bored huh???

[straughsberry]

Mmmmmmmmmaybe a tad.

Research can suck at times and I've been doing quite a bit lately.

[Benji_vs]

Brilliant write up!!! ive been doing a little study on this myself, when you say its best to make torque higher in the rev range rather lower to make use of gearing I believe that to be true for sport applications but for everyday driving I would seem it would be better to make peak torque lower in the rev range so that the engine doesn't need to work as hard for everyday stop start traffic acceleration.

Just to extend from your previous post

Take for example a humble v6 commodore (I know but I was a big Expensive Daewoo man) Peak torque occurs at 3600 rpm and develops a respectable 304 nm. This engine can easily pull away in traffic to overtake without needing to drop back 2 or 3 gears to meet its peak torque requirement. Its final drive is also at 3.08:1. Yet saying that the car isnt terribly fast by any means due to its rather low peak power of 147kw @ 5200.

Say if you wanted to increase performance of this car? you really have two options (as with any car) you can keep peak torque the same at 3600 and increase engine speed or increase peak torque at 3600 rpm or ideally at a higher rpm as F6 Ute stated.

Mods like your extractors will increase efficiency of the engine and will indecently raise your peak torque at a higher RPM (if that is your extractor design) thus making your mid range acceleration feel faster as the engine can breath better at the higher RPM thus more torque so maybe instead of the original 304nm @ 3600 it maybe be 304nm @ 3700rpm or 3800rpm.

For our turbo cars the beaut thing about turbos is that they by definition increase efficiency compared to a n/a car due to the engine inhaling a greater volume of air at lower rpm compared to the n/a car.

Example an engine of 4 liters will suck in "roughly" 4 liters of air every crankshaft revolution and that amount is fixed the trick is to increase how efficiently the engine does it at any given RPM (usually the cam profile (lift,duration & overlap) will determine this). Turbocharges and supercharges as you all should know work by forcing air into the engine and increasing the volume inside the cylinders and like you all know more air means more fuel and the result of that is more "torque" at any given rpm.

Now when it comes to the xr6 turbo motors quoting a peak torque figure of 480nm at 2000rpm onwards to around 4500rpm I believe that that means that the turbo can feed the engine significant amount of air (therefore fuel) to create 480nm from as low as 200rpm to 4500rpm and hence the very large power output of 245kw at at low 5250 rpm.

Now imagine the likes of a n/a car like my 3.8l Late model camira earlier how fast would the motor have to spin to create that power output or how aggressive would the cam specs have to be to get that power? The cam would have to be designed to be most efficient at a very high rev range making for a fairly unpleasant daily driver as the engine would be choking at low rpm.

I think at the end of the day car manufacturers endeavor to build engines which deliver a broad torque curve across the rev range which allows low speed acceleration with high speed power.

Hope that maybe shed some more light on the topic and hopefully reinforces what F6 Ute was saying earlier.

Edited 03/05/09 05:02 AM by Benji_vs

[alexlees]

Awhile back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

its an interesting fact that James Watt actually undercut the power of a horse to help him sell steam engines. when he presented potential customers (like large mines, etc) the figures showed the engine to be more appealing than the teams of horses it would replace

[Brandonn]

man im bored as n tried reading that, failed miserbably

[mattyb]

Great read... my wife asked me to explain the difference between torque and kw as I finished reading this... I laughed at her and made her read it. She took it all in, better than me I think.

[SPIKO]

The Only Thing You Really Need to Know

Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)

That is an extremely comprehensive right up F6, I admire what you are trying to do do for everyone..

However I believe I can add something to your motto that may make it a little more understanding; here I go short version lol;

Ok lets elaborate on taking advantage of gearing & torque at higher rpm (Drag Related) if your engine spins to 6500rpm and your tune and timing is designed to give you peak torque lets say 800nm at 2200rpm and let us also assume that your tune at 4500rpm makes 650nm and at 5500rpm makes 550nm finally getting to 6500rpm and making 450nm.

When your peak is at 2200rpm and lets say you launch your car with an auto and stall @ 2800rpm this may end up being a good thing and with the right tires launching off-peak may give you a better 60ft right? after first gear has come and gone and you shift to second @ what rpm will you engage second gear? Lets say 4000 to 4750rpm right? So what you are doing is running the rest of the race with between 650nm and 450nm of power (totally OFF-peak)!!!!! Remember when you are racing most of the gears are only using between 3500rpm and 2500rpm depending on your transmission and engines rev-range... So how good is a tune that makes all the torque very early for the drag strip people??????

The key/target for a drag tune is to match your maximum torque with your usable rpm range between shifts depending on transmission/gearing!! Remember this! it all you need to know in this department (Drag Racing)

Hope this helps!!

[discostig]

Makes sense, after the first gear is gone you certainly aren't back in 2000RPM range until the race is over.

Just strip the car out to get moving quicker in 1st hahaha