ive seen a lot of cars with higher bhp ratio to torque, but recently ive been seeing the torque figures generally above bhp. i presume the higher torque figure is better for acceleration.
so my question is, does it depend on the mods alone or can cars be mapped for higher values of either?

 

In gear acceleration is much better with the higher torque, it's the 2.5's that tend to have the higher torque than hp figures, factors can alter that though

 

BHP is ALWAYS calculated from torque.

The more revs whilst sustaining torque, the more BHP = (Torque x RPM) / 5250

Thats partly why tuned EJ25s don't fare so well in BHP as a tuned EJ20, as they don't rev quite as high.

Basically its down to the torque curve at high rpms: If the torque continues to increase above 5250rpm; BHP will be very high, but if it starts to drop off before 5250rpm, then peak BHP will be lower than peak torque.

Thats why diesels have stupid high torque but poor bhp; they don't rev high enough to take advantage of that mathematical anomaly.

 

^^ What's going on with the vtec engines then - highish hp (220 in the ITR) yet low torque (150 ish)?

TX.

 

nice n clear explaination thanks

 

Torque is also more useful in day to day driving. There are certain mods that will increase BHP and decrease torgue, for a daily driving car like mine, it's not necessary.

 

Low torque BUT multiplied by lots of rpm; just like bike engines.

The rpm is a multiplier of the torque.

So mathematically, a small torque figure if multiplied enough will result in a high BHP.

 

Not alwasys the case, you are refering to torque at LOW rpms. That is good for day to day driving.

For instance a car with a huge laggy turbo will make huge torque, but if its only achiveing it at 4000rpm onwards it will be horrible to drive in town.

 

You seem to know a lot about this Ali so I'll keep asking what's "better" (a) vtec revving to 9k with 220hp but low torque or (b) diesel engine with low hp & revs but 300 torque?

TX.

 

For me it be the torquier deisel..

 

the way i see it is if you want to tow something or carring a lot of weight torque is your answer but if its just for nippy speed then bhp is what your looking for. Think i'm right?

 

Niether, as both have narrow powerbands, or the powerband starts too high up in the rev range.

I'd personally plump for a nice large capacity petrol engine that holds torque from 1000rpm right through to 7000rpm. GM's LS9 engine gets pretty cloase to that, especially if assisted via a mild upgrade to the supercharger:

http://www.lingenfelter.com/images/2...stock_1400.jpg

That has to be good for a laugh.

 

I am running 360/400 on a 20g 2.5 with a jdm 6 speed, and around town its quick.

 

torque all the way

 

When talking about being driveable around town in this context, people are usually talking of having good torque at low revs e.g. so you can drive at 30 in 6th without the engine labouring.

Ali-B is on the money with his assertions. The important thing for acceleration is torque at the wheels rather than at the fly, hence the rpm multiplier (and gearing). I too would choose the spread of torque over the vtec or diesel (and did - a relativey modest 270 ish lbft but 80% of that is available from 1500 - 8000 rpm; shame it's a bit lardy).

Guess a nice strong ej25 that can cope with high revs would be a nice engine

 

Eh no....... 30ish in 6th gear i think not. The only thing thats Lardy is you...... Are you having a laugh..........

 

Read the post FFS, then comment

 

This is a little more complicated than it first appears and it depends on the intended use of the engine. There is some variation on peak torque but when comparing a V-tec based engine to one of another manufactures they are roughly the same when compared the another manufactures engine of the small class.
You can not compare for example a normally aspirated 2ltr engine with one of the same capacity featuring forced induction.
The V-Tec issue is similar, V-Tec cams have two completely separate profiles giving the engine effectively two personalities, one set of cam lobes is for say economy and one set is for say high power. Now under particular circumstances the second set of lobes (we'll stick with the high power reference) come into play. Now if you compared a performance based V-Tec engine say for example a 2ltr K20A/F20C with from another manufactures 2ltr twin cam performance engine even on with VVT (as Honda's V-Tec is a little different to most VVT systems) but the Honda engine ran permanently in V-tec (on the high power lobe) or V-Tec engagement was brought in at a much lower point (this can be easily achieved and doing so does not limit the Rev limit) then they would have similar torque figures/curves.
Now onto RPM, on a track it is excepted that a higher revving engine is more desirable than a lower revving one producing more torque but this is obviously not necessarily the case with a Road car. Within the upper upper echelon's of Circuit racing there is a general guide line that having an 1000 extra rpm with is like having and extra 100bhp in a 3ltr engine.
To prove how affective a lower torque but high revving engine can be, you only have to look at the Super 2000 4 class of rally cars. 2ltr engines, 8500RPM limit and all wheel drive. They are slightly lighter then current <2011 2ltr turbo 7500RPM 300BHP+ WRC car's (I'm ignoring the upcoming 1.6ltr turbo class for this) but a posting very similar times.

So to very quickly sum up as I've already said it depends on the intended use of the engine.

 

I'm assuming road cars driven on the road in reference to "better in town" comments made earlier above and a strive for perfection (high torque at ALL rpms from idle to a high rpm redline):

Here a graph demonstrating higher torque than BHP, BUT with lag. Look at this and compare it the graph in my previous post:


http://i91.photobucket.com/albums/k3...b/f4979b9e.jpg

Its peaks are 301lbft and 283bhp. Sounds OK. Yes the previous graph has high peaks, but it doesn't matter in this example as the actual peak figures are not important because we are looking at the curves not the peaks - as that is what dicates the car's driveability:

Look at what its doing at 2000rpm: its barely 100lbft@2000rpm. Yet come 3000rpm, whoosh! and we have 300lbft as the turbo has spooled. Torque from that point onwards instead of climbing, starts to drop off and has dropped by 100lbft by the time it reaches 7000rpm.

This makes the initial climb in the BHP start to level off and give a lower BHP than torque. You can see this on the BHP curve - a diagonal line upto 3000rpm, but it starts to roll-off above this, so the line is mostly concave. This is because as the revs climb, there is less and less torque to multiply by, so whilst the BHP value increases with rpm, the rate of increase is reduced.

Despite the high peak torque, in town and at low revs, this car is pants. This graph is typical of a smallish capacity+large turbo engine.

Compared to the earlier graph: http://www.lingenfelter.com/images/2...stock_1400.jpg

Where there is 490lbft from 2250rpm, and it stays there right upto 6400rpm. If you look at the BHP curve, it climbs nice and evenly giving a straight diagnonal line that only starts to level out and go concave past 5000rpm.

When reading graphs, the flatter the torque curve and the straighter the BHP curve the better. As this indicates the engine's output is more consistant over a wider rev-range.

Although to drive, it won't have the "kick" of a turbo, as the kick is controlled by a delay in spool, which results in a delay in torque delivery. Instead, here you get the "kick" the very instant you crack open full throttle - at pretty much any engine speed. What people prefer is more down to personal preference over anything.

 

FYI: I haven't and never will. Anyone can get big bhp from slapping on a turbo and cranking up the boost. Getting the same from N/A requires alot more care an attention

With regards to VTEC. As an ex NSX owner: I feel it should have been a 4.0VTEC V8, not a tarted up 3.0 Legend engine - VTEC is no substitute for cubes

 

Anybody who has driven a Honda Civic Type R will know these high rev torqueless engines are hard work. In order to pass the car in front relatively quickly, you have to drop down a couple of notches instead of having the high torque from a turbo engine do it for you without touching the gear stick.

 

I had 348bhp/377ft lbs, I then had 420bhp/349ft lbs, I now have 420/400, probably stating the obvious but having a bit of both is better at first having the higher torque was nice but the power was gone by 5,500rpm so you where changing gear a lot, with the higher bhp it screamed all the way up to 7500rpm but for simple things like overtaking it felt like I was racing because you had to rev it. Having both is much better

I think that is why the 2.1Ls are becoming very popular.