Torque - Discussion, Physics, Displacement And Ideas

[paulr33]

Just an open discussion on torque and how it plays a part in the cars peformance.

I noticed after driving my friends bog stock WRX it seems to pull harder than my tuned GTST with basic mods

i thought how can this be and started to check the maths - maybe CC per cylinder plays a part?

[paulr33]

maybe its a load of crap, or maybe it has some substance behind it?

i did a comparison of some common cars we know of and plotted their volume per CC

feel free to suggest new additions, i need to know car, engine name, engine size, cylinders

[UNR33L]

W427, the gay holden thing should add some big ameican V8s from mustange and corvettes oh and the 370z etc.

[gwilkinson34]

maybe its a load of crap, or maybe it has some substance behind it?

i did a comparison of some common cars we know of and plotted their volume per CC

feel free to suggest new additions, i need to know car, engine name, engine size, cylinders

So we need a chart that has cc per cylinder vs torque to really compare...

[Gerg_R31]

i still have no idea what we are trying to discuss in this thread

[PM-R33]

i still have no idea what we are trying to discuss in this thread

Whether engine torque is related to cylinder CC.

Ie. would a 2L 4 cylinder have the same torque as a 2L 6 cylinder given that everything else remained the same.

It is a very interesting subject and something I have quite often thought about in the past.

We must think about this purely from a mechanical point of view and think about how much energy is released and transferred per cylinder, whether a fewer amount of larger volumes (2L 4 cylinder) creates more/same/less energy than a greater amount of smaller volumes (2L 6 cylinder).

I think the fewer amount of larger volumes would create more energy due to not as much being transferred/lost. The more cylinders you have, the more energy would be lost in heat, noise, friction etc. So if you had a 2L 10 cylinder there would be a lot more energy lost throughout the cylinders than a 2L 2 cylinder.

I will have a better think about this over night and see whether we can get some calculations happening with the knowledge of air density/volume, estimated energy release from petrol, compression ratio etc.

Edited July 24, 2010 by PM-R33

[Gerg_R31]

larger compacity, more to compress, more to propell after the spark, as a basic mechanical principal

blocks with a bigger bore then stroke, square bore and stroke, bigger stroke then bore, mis-matched cam profiles, match cam profiles, big lift small duration cams little lift big duration cams, cam and ignition timing, turbos v superchargers, nos av-gas pump fuels, valve to chamber angles, port angles, valve seat angles, diff ratios, gear ratios, volumetric efficancy, atmospheric pressures above or below sea level with or without boost volumes, tyre compunds and pressures, all different possible set ups to create endless different vehicle characters

so id say the swept volume of a cylinder may play a small part

[jarrod83]

I think your interpretation of torque you feel and actually torque are two different things.. my rb30det makes more torque and power than my rb25det with the same gt35r turbo.. but because my rb25det kicked in so late and hard in the rpm range it felt like it pulled way harder when it kicked in, my rb30 it just so linear like the standard turbo/rb25 combo that you never really feel that huge pull

to simplify it, you notice the change in acceleration a lot more than the maximum acceleration, the only time id say a stock wrx would pull more g's is when you dump the clutch off the line and the awd hooks up.

In terms of different engines tho i seem to notice that engines with longer strokes have more torque, engines with squarer strokes rev more to make their power, engines with more cylinders seem to make more horsepower maybe because they have more valves compared to total engine size and lastly the wrx is a boxer engine which im pretty sure flow air less efficiently than the common style of engine.

Maybe you should get some torque curves of the skylines and wrx's and compare them or just drag your friends car, at a guess id say you would most likely beat him.

Jarrod

[GTRNUR]

Was the WRX a 2.5 or 2lt block?

I think just limiting the comparison between the RB25 and the WRX would be a good idea. Then compare the full weight of one car to the other. Also take a not of at what RPM the engine achieves full boost.

Ive only driven a standard my99 wrx and from what I can remember it was making boost from very low in the rev range but fell over in top end around 6000 rpm, where as a skyline tends to keep going well up to 7000 with a standard turbo setup before you notice a drop off in torque.

In terms of what kind of engine delivers more torque its been my experience that more stroke delivers more immediate power but to be honest ive never driven an engine that has been ONLY stroked. All stroked engines ive driven have also had a massive over-bore as well. Though it is logical to say that for two engines with indentical capacity (say an RB25 and an EJ25), the engine with the larger throw on the crank will on average deliver more immediate torque as each combustion event is pushing on the rod journel further out from the center line of the crank providing more leverage.

So what I am saying is that capacity per cylinder has not as much to do with torque for any given RPM, it is more how that power generated in each cylinder is converted into a rotational force. This is where you start getting into rod ratios which has got to be one of the most hotly debated topics when someone begins to whisper RB30 vs RB26/RB28.

Choice of a rod ratio all comes down to what will actually be possible to achieve in your given engine design and how you want the engine to deliver the power it makes. There are pros and cons to low and high rod ratios. On occasion you'll see people say one rod ratio is better than another, or more "ideal". There are engines out there with rod ratios ranging from 1.4 to 2.4. How they respond and deliver torque is vastly different. The same could be said for an engine that has standard cams vs another engine with 290 degree cams with 12mm lift.

You might find these two links interesting to read. The first link is about the pros and cons of different rod ratos. The 2nd is a database of different engines and what their internal dimensions are.

http://www.hotrodders.com/forum/stroke-rod-ratio-32680.html

http://www.odengines.com/Stan%20Weiss'...tio%20Table.mht

Ford, chevy and dare I say it VW engine owners have been playing with rod ratio changes for years. Swapping to larger stroke cranks, or just running longer and shorter rods with pistons that have higher or lower compression heights. RB engine owners have not been able to experiment with this as much as the RB component options to make changes like this are limited to only an RB30 block setup, or a 77.7mm crank. It doesnt leave a lot of room for experimentation. Where the SBC and vw engines are probably the two most modified and customisable types of engines on the planet.

One thing above all though that is pretty much accepted as being true is that more displacement if you can get it, is always worth a little sacrifice in the rod ratio department. The v8 guys are right in saying there is no replacement for displacement. A turbo will never be able to deliver the low end punch that pure displacemet can.

Hope I haven't ranted on too much here. I was not trying to make any kind of point... just sharing some thoughts.

Edited July 25, 2010 by GTRNUR

[paulr33]

i checked out the wrx i drove, its a EJ25 and the turbo on it is TINY

i reckon the skyline turbocharger is bigger for sure

[DVS JEZ]

just to throw a spanner in the works, gear and diff ratios will have a big part in the seat of the pants feel of torque and accelleration..

[paulr33]

Whether engine torque is related to cylinder CC.

Ie. would a 2L 4 cylinder have the same torque as a 2L 6 cylinder given that everything else remained the same.

It is a very interesting subject and something I have quite often thought about in the past.

the simplistic comparison i can think of is the 4G63 vs RB20 (both 2 litre inlines, one is 4cyl, one is 6cyl)

i think the 4G63 is light years ahead of torque ?

forgetting AWD/RWD blah blah, just the basic engine

[paulr33]

yeah i get diff ratios, gear ratios etc all play a part as does gearbox, weight, wheel size etc

but im talking more from a basic comparison purposes, ie does bigger cylinder volume per CC typically mean more torque as a general rule

this might explain why RB30DET is so much more power because the cylinder volumer per CC increases from 416cc to 500cc

[zebra]

I agree with GTRNUR - there is way more to torque production than just cc per cylinder,

Take Fords outgoing 5.4L DOHC V8 for EG it has a 90mm bore and 105.4mm stroke, now by rights it should be a low end torque monster, but it isnt, yet the SOHC 2 valve version in the F trucks is.

As for the EJ25 v RB25 debate, the subi has the advantage of twin-scroll turbo technology and varaiable inlet and exhaust cams, plus 10 years r+d poured into it after millions of people complained about the lack of bottom end in the 1st few models and that it needs to be improved, If you can Paul take a 1st gen WRX for a drive, they are laggy as hell and feel like they wouldnt pull a sailor off your sister, yet they are still fairly quick.

I think if Nissan kept with the RB25neo past 2000 and added a twinscroll turbo, constantly variable intake and exhaust cams etc, they would be a torque monster too.

[zebra]

yeah i get diff ratios, gear ratios etc all play a part as does gearbox, weight, wheel size etc

but im talking more from a basic comparison purposes, ie does bigger cylinder volume per CC typically mean more torque as a general rule

this might explain why RB30DET is so much more power because the cylinder volumer per CC increases from 416cc to 500cc

Just thought of another thing...years ago ford devoloped a 302ci (4.9l) v8 for Nascar when the norm was 350-360ci...the 302 ford was banned because it was way faster than the engines with nearly another 1000cc capacity...even pulled off the corners harder...mainly due to the engines willingness to rev....in any gear the engine was freer, with less crank and rod weight to move around (inertia) so despite the less on paper torque in the lower part of the rev range, the fact that you could breath on the throttle and the thing would hit 10k rpm in a split second made it the quicker car.

[SideOn]

Another thing to note is head design, even the RB26 doesnt like eating boost.

Edited July 25, 2010 by SideOn

[zebra]

Dont forget, the EJ25 is running some form of an MHI turbo.... When mitsubishi makes a turbo, you know not to question it. Since the evo 4 they have been able to have them on power from nearly idle, revving to 8 and making over 200kw at all 4 wheels. That rexy turbo might look small but theres a something magic going on inside.

They are an IHI turbo on the subaru's

[paulr33]

yeah sorry didnt mean to open the great debate here, just after some info and ideas etc

i think so far we have covered a lot already which is great

but you are right in that the WRX here is probably 2004/2005 model and has lots more R&D in it vs my 1997 GTST

but it is interesting to compare 2.5L 4cyl vs 2.5L 6cyl

my skyline has tons more punch on throttle and responds instantly (aggressive tune)

the wrx is very progressive but feels to pull more as you go and from the word go

ie if i bog both cars down at 60km in 5th the wrx wins easily

[GTScotT]

Gee you went straight for gold there... a 4G63 is in a league of its own, there is no comparison between it and an RB20. I use to own one of these things, one word comes to mind, ridiculous.

IMO the main ingredient in the mix here is the bore x stroke and the turbo in question. A square engine is more than the best of both worlds, its almost the best of both worlds. Unmatched torque and an ability to rev. The SR is square: 86x86, where as the 4G has a minor offset: 87x85. That slight change put together with a really well flowing head from the factory results in a motor that wants to rev infinitely and has loads of power and torque.

Surprisingly though, the EJ25 in question is nothing great in that sense, its something like 75 x 99. BUT, dare I say the whole 'boxer' principal plays a major part.

I think the major issue here is turbos. In no shape way or form do I think the RB's true character can flow through those tiny housings they come with from the factory, and high flowing is IMO no form of a fix. Run either a GTRS or 2835 and I think you will see the motor really start to shine. I am fitting a 3037 and know for a fact it will be no chop when it comes to on road feel to a 2835.. Its like an evo with its factory turbo and cams, or an SR and a T28. While they might not make eleventy billion killawasp's they definitely drive like true animals.

Dont forget, the EJ25 is running some form of an MHI turbo.... When mitsubishi makes a turbo, you know not to question it. Since the evo 4 they have been able to have them on power from nearly idle, revving to 8 and making over 200kw at all 4 wheels. That rexy turbo might look small but theres a something magic going on inside.

(Sideon needs to learn to log out of my PC)

As for IHI turbos, just a heads up - Mitsu turbos are called MHI. They have some shared models like TD turbos etc, which is what is on alot of stock rexys. I believe the development is done by mitsu for those.

FYI your Nissan CAS has a mitsu logo on it too, as does your BOV (as do the 2 BOVs on the R35) go have a look.

[soturi]

Ive heard evo's run reallllly high psi from factory...evo X in particular..is that true?