Maximum Torque Per Litre
Discussion
People's claims for this never cease to amaze me. I was browsing the web the other day and came across this.
http://www.cortina-mk1classifieds.com/forum/archiv...
Down towards the bottom someone is claiming they've seen 153 ft lbs from a 1660cc Ford Crossflow on a supposedly accurate engine dyno for god's sake. That's 92 ft lbs per litre from a 2v engine with one of the worst combustion chamber shapes ever made. God knows who calibrated that dyno.
Anyway my own views on the subject are made abundantly clear on my website in various places but to restate them you're doing well to beat 80 ft lbs per litre from 2v engines and 90 ft lbs per litre from 4v ones with modified road engines on pump fuel that are built to actually last more than 5 minutes.
I'd say the normal maxima are low 80s for 2v engines and about 93 from 4v ones.
In terms of my own engines over the years I've rarely had the chance to put them on an engine dyno and rolling road figures need to be taken with a big pinch of salt but FWIW my best figures are as below.
Rolling road, 2v engines:
Peugeot 205 1.9 rally tune 11:1 cr - 78 ft lbs per litre
Slick 50 Golf Gti 1800cc, race tune, 12.5:1 cr - 80 ft lbs per litre
Engine dyno, 4v engine
Peugeot 1600cc TU5J4 200 plus bhp, 12.5:1 cr - 93 ft lbs per litre.
Now there's an engine builder of similar 4 pot motors on another forum whose torque claims make the rest of us look like eejits. His 2v engines supposedly produce more torque than everyone else's 4v ones and his 4v ones are up to 97 ft lbs per litre. He seems to derive most of these numbers from wheel figures from a local rolling road scaled up by algorithms of his own devising to get back to flywheel ones. I'll say no more.
So I'd be interested in two things.
1) Any accurate engine dyno figures for maximum torque per litre you've come across or for engines you've built yourself. Rolling road ones too if it's a known set of rollers.
2) Answers to the V8 conundrum which is as follows. It's common to see torque per litre figures from mundane American V8s that far exceed what we normally get from small 4 pot 2v engines over here. Mid to high 80s ft lbs per litre is quite common for engine dyno results for Chevy V8s and the like on pump gas.
I have two thoughts on the matter. Firstly that perhaps the crossplane V8 crank arrangement makes some difference to the pulse tuning compared to flat plane 4 pot cranks. Secondly that maybe it's a matter of cylinder size. Big cylinders are harder to fill and obtain high bhp per litre figures from but they have a much larger ratio of volume to surface area than small cylinders and therefore possibly better thermal efficiency. i.e. less heat is lost to the cooling system. Maybe this helps the peak torque somewhat.
I'd be interested in any theory on the subject.
http://www.cortina-mk1classifieds.com/forum/archiv...
Down towards the bottom someone is claiming they've seen 153 ft lbs from a 1660cc Ford Crossflow on a supposedly accurate engine dyno for god's sake. That's 92 ft lbs per litre from a 2v engine with one of the worst combustion chamber shapes ever made. God knows who calibrated that dyno.
Anyway my own views on the subject are made abundantly clear on my website in various places but to restate them you're doing well to beat 80 ft lbs per litre from 2v engines and 90 ft lbs per litre from 4v ones with modified road engines on pump fuel that are built to actually last more than 5 minutes.
I'd say the normal maxima are low 80s for 2v engines and about 93 from 4v ones.
In terms of my own engines over the years I've rarely had the chance to put them on an engine dyno and rolling road figures need to be taken with a big pinch of salt but FWIW my best figures are as below.
Rolling road, 2v engines:
Peugeot 205 1.9 rally tune 11:1 cr - 78 ft lbs per litre
Slick 50 Golf Gti 1800cc, race tune, 12.5:1 cr - 80 ft lbs per litre
Engine dyno, 4v engine
Peugeot 1600cc TU5J4 200 plus bhp, 12.5:1 cr - 93 ft lbs per litre.
Now there's an engine builder of similar 4 pot motors on another forum whose torque claims make the rest of us look like eejits. His 2v engines supposedly produce more torque than everyone else's 4v ones and his 4v ones are up to 97 ft lbs per litre. He seems to derive most of these numbers from wheel figures from a local rolling road scaled up by algorithms of his own devising to get back to flywheel ones. I'll say no more.
So I'd be interested in two things.
1) Any accurate engine dyno figures for maximum torque per litre you've come across or for engines you've built yourself. Rolling road ones too if it's a known set of rollers.
2) Answers to the V8 conundrum which is as follows. It's common to see torque per litre figures from mundane American V8s that far exceed what we normally get from small 4 pot 2v engines over here. Mid to high 80s ft lbs per litre is quite common for engine dyno results for Chevy V8s and the like on pump gas.
I have two thoughts on the matter. Firstly that perhaps the crossplane V8 crank arrangement makes some difference to the pulse tuning compared to flat plane 4 pot cranks. Secondly that maybe it's a matter of cylinder size. Big cylinders are harder to fill and obtain high bhp per litre figures from but they have a much larger ratio of volume to surface area than small cylinders and therefore possibly better thermal efficiency. i.e. less heat is lost to the cooling system. Maybe this helps the peak torque somewhat.
I'd be interested in any theory on the subject.
I have a bulls
t busting spreadsheet that calculates the maximum BHP for any engine given the likely torque per litre for various engine types and state of tune. The maximum torque per litre I have seen from a dyno run is 94lb/ft per litre from a very trick 4 valve head produced as a one off. Most high output 4 valves I do make between 86-91lb/ft per litre, road going engines are more like 82-85lb/ft per litre.
The params I use on the spread sheet are..
2V engines
65-70 lb/ft road going
71-75 lb/ft serious road engine
76-82 lb/ft Race engine
4v engines
70-80 lb/ft road going
80-90 lb/ft serious road engine
90-94 lb/ft race engine
If you hear of an engine making infeasibly large HP figures, do the torque calcs, if these are significantly higher than the figures above then your bullst alert should sound nice and clear.
for most engines peak power is made when torque is around 90 of maximum, although this will depend on where peak power RPM is, so it is easy to predict the RPM required for a particular output from a known sized engine.
There are a large number of dyno plots on www.dyno-plot.co.uk from various engines I have produced over the years, the torque figures there would give a good idea of average torque per litre for various states of tune.
Dave
t busting spreadsheet that calculates the maximum BHP for any engine given the likely torque per litre for various engine types and state of tune. The maximum torque per litre I have seen from a dyno run is 94lb/ft per litre from a very trick 4 valve head produced as a one off. Most high output 4 valves I do make between 86-91lb/ft per litre, road going engines are more like 82-85lb/ft per litre.The params I use on the spread sheet are..
2V engines
65-70 lb/ft road going
71-75 lb/ft serious road engine
76-82 lb/ft Race engine
4v engines
70-80 lb/ft road going
80-90 lb/ft serious road engine
90-94 lb/ft race engine
If you hear of an engine making infeasibly large HP figures, do the torque calcs, if these are significantly higher than the figures above then your bulls
t alert should sound nice and clear.for most engines peak power is made when torque is around 90 of maximum, although this will depend on where peak power RPM is, so it is easy to predict the RPM required for a particular output from a known sized engine.
There are a large number of dyno plots on www.dyno-plot.co.uk from various engines I have produced over the years, the torque figures there would give a good idea of average torque per litre for various states of tune.
Dave
MattYorke said:
Isn't stroke also a function of the torque? So longer stroke = more torque at a given rpm, all other things being equal? Force * Distance.
Yes but for the same displacement, increased stroke means decreased bore, so lower piston surface area for the BMEP to act on. The theory says that you get the same torque output for any bore to stroke ratio of the same displacement since torque = BMEP * displacement.Edited by Nick1point9 on Wednesday 1st February 19:47
DOH! Yes. 
Nick1point9 said:
Yes but for the same displacement, increased stroke means decreased bore, so lower piston surface area for the BMEP to act on. The theory says that you get the same torque output for any bore to stroke ratio of the same displacement since torque = BMEP * displacement.
Edited by Nick1point9 on Wednesday 1st February 19:47
To be honest, before you even pointed it out, I'd had realised I'd forgotten we were talking per litre and therefore double the stroke meant half the piston area, so at the same cylinder pressures the F bit is halved even if the D bit is doubled.
I did study all this once - I promise! I've just forgotten most of it.
I did study all this once - I promise! I've just forgotten most of it.
MattYorke said:
Isn't stroke also a function of the torque? So longer stroke = more torque at a given rpm, all other things being equal? Force * Distance.
i think adiabatic efficiency comes into play here,the longer the stroke the quicker the expansion of combustible gas subsides due to thermal transition into the waterjacket or cooling system.does it not work a little like a triple expansion steam engine?it's all about transfer of energy,i don't know the exact physics but it's what i have deduced from my collection of ccc and ppc articles over the years.
just out of interest regarding the cross plane crank theory,would it be correct to assume a single plane v8 of a given cc would produce the same torque of two inline four pot engines of the same capacity(taking into account parasitic losses)?is it why tvr went this route.?
Nick1point9 said:
I have however noticed a slight mistake with my maths, but you have quoted me now!
(I think) it should be torque=BMEP*displacement/2
That's correct for a 4 stroke engine. For a 2 stroke it's just BMEP*displacement. There's obviously also a constant in there depending on what units are being used.(I think) it should be torque=BMEP*displacement/2
Pumaracing said:
Stan Weiss said:
Any I the only one that likes to look at this using BMEP?
Stan
Yes. Given that BMEP is directly proportional to torque per litre it serves no different purpose but is a PITA to calulate unless you can remember the constants to use off the top of your head.Stan
Stan
Just had a dig on some torque figures for the most powerful engines I've produced, these were all out and out race engines and the culmination of a lot of development.
1600cc 229BHP 146lb/ft 91 lb/ft per litre
1700cc 236BHP 154lb/ft 90.5 lb/ft per litre
1800cc 264BHP 164lb/ft 91 lb/ft per litre
1900cc 286BHP 177lb/ft 93 lb/ft per litre
I'm not sure it would be possible to see 153b/ft from a 2 valve engine.
I do remember a claim published in a magazine from a well known tuning company that a particular 1800 engine they had breathed on was producing 180lb/ft and over 200BHP at 6300 (naturally aspirated and on a plenum). If you look at the torque it doesnt add up.
Dave
1600cc 229BHP 146lb/ft 91 lb/ft per litre
1700cc 236BHP 154lb/ft 90.5 lb/ft per litre
1800cc 264BHP 164lb/ft 91 lb/ft per litre
1900cc 286BHP 177lb/ft 93 lb/ft per litre
I'm not sure it would be possible to see 153b/ft from a 2 valve engine.
I do remember a claim published in a magazine from a well known tuning company that a particular 1800 engine they had breathed on was producing 180lb/ft and over 200BHP at 6300 (naturally aspirated and on a plenum). If you look at the torque it doesnt add up.
Dave
Stan Weiss said:
With most of the engines in the states listed in ci I have the same PITA using litre. Over here it is torque per ci.
Stan
Yeah well don't get me started on you bloody colonials and your reluctance to leave the 19th century and imperial measurements. It's high time we invaded you again, gave you a bloody good thrashing, annexed you back into the Queen's Commonwealth and dragged you kicking and screaming into the 21st century and stopped you being the only country in the world that can't cope with metric measurements.Stan
While we're at it we could ban religion over there, abolish the Republican party which is near as dammit the same thing, release Sarah Palin back into the wild and then shoot the daft b1tch from a helicopter and stick a broom handle ten inches up Newt Gingrich's arse so he knows what his first two wives felt like after he shafted them.
My 5210cc road/race RV8 made 543Nm.. it is 400ft/lbs and that is 75.77ft/lbs per litre?
Our local rallydriver OHC made 245Nm and it is 2.15 or 2.2litre engine, that is over 81ft/lbs.
All measurements are made in same dyno as mine, but estimated 5 year´s before i do mine..
Other Volvo B200? stroke 101mm and bore 97mm,approx 2984cc, 8valve custom made billet head, it made 325hp/370Nm it is approx 90ft/lbs.
Same engine with 4 valve heads, it made 332hp/397Nm with weber 55carb. Approx 97.3ft/lbs Now it has got 62mm ITB´s it will made 344hp/370Nm.. Engine is for rallycross use only. And made by Kansiset our famous head tuner..
Not sure how reliable those readings are because they are made another dyno as mine..
Our local rallydriver OHC made 245Nm and it is 2.15 or 2.2litre engine, that is over 81ft/lbs.
All measurements are made in same dyno as mine, but estimated 5 year´s before i do mine..
Other Volvo B200? stroke 101mm and bore 97mm,approx 2984cc, 8valve custom made billet head, it made 325hp/370Nm it is approx 90ft/lbs.
Same engine with 4 valve heads, it made 332hp/397Nm with weber 55carb. Approx 97.3ft/lbs Now it has got 62mm ITB´s it will made 344hp/370Nm.. Engine is for rallycross use only. And made by Kansiset our famous head tuner..
Not sure how reliable those readings are because they are made another dyno as mine..
Edited by Kokkolanpoika on Thursday 2nd February 08:29
Edited by Kokkolanpoika on Thursday 2nd February 08:30
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