I’d agree that the deleted thread was primarily a Simon Erland bashing thread and I for one tried to avoid that.

But in the subtext was the start of an interesting discussion re the RPM and torque needed to produce a given power output, I have a spreadsheet I produced a few years ago primarily as a bllsht buster that can predict the RPM required to produce a particular power output fairly accurately and the torque output both peak and at peak power to produce it, it can also predict the capacity required to produce a given amount of power at a particular RPM.

It uses some parameters (user tailorable) which set the maximum torque per litre for a given engine and gives guidelines for 8 valve and 16 valve engines for both production derived engines and purpose built race engines.

It gives a good indication of when someone is being outrageous in their claims because torque is the universal leveller since torque is a reflection of BMEP/capacity.

If there is sufficient interest I can post up details or carry the discussion on, I do not intend to become embroiled in another argument or talk specific claims or specific engines nor to use any of the information for any personal agenda or ‘bashing’.

However, I do think it would be useful information for much of the readership.

Yep - I’d be interested to see what you’ve used in your spreadsheet and what it comes up with compared to some of the engines I’ve come into contact with.

And is around a page and half from the bottom of the list of files.

Have a look and a play, I’ve got a better more up to date one here, that version doesnt give 4 vale peak torque/ torque at peak power, although it is simple to derive.

Interesting spreadsheet Dave.
Could you please explain how the values in the green cells are determined?
Is there any relationship with bore/stroke ratio or other parameters?

The values are all derived from the ‘torque per litre’ figures and the ‘percentage of torque at peak power’.

It’s fairly straightforward, given the torque per litre at maximum torque and the percentage of peak torque at peak power, a figure for maximum power can be derived for any particular RPM.

Calculate the maximum torque, reduce it by the %ge at peak power and apply the formula which determines power, BHP = (torque/5252)*RPM.

The reciprocal of this simple formula is used to derive the minimum RPM required to acheive a given BHP level.

For example an exceptionally good 1800 engine might make 93lb/ft per litre, so at peak torque it might produce 167lb/ft. At peak power it will produce around 90% of this maximum, E.G. 150lb/ft, if power is peaking at say… 7800 then the peak power will be (150/5252)*7800 or 222BHP, 7800RPM is the lowest possible crank speed at which the engine could produce 222BHP.

The constants for torque per litre and percentage of torque at peak power are variable in the spreadsheet.

To find the minimum RPM at which an engine of a given size can produce a given BHP, you can reverse the formula, for example for a 2litre engine to produce 300BHP… peak torque of 93lb/ft per litre will give a maximum torque of 186lb/ft (this is close to the theoretical maximum on pump fuel from a perfect engine), at peak power the engine would produce around 90% of this value, E.G. 167lb/ft, to derive the RPM required to produce 300BHP… RPM = (BHP/torque) *5252… or 9404RPM. This does not mean tha the engine revs to 9400, it means that it peaks at 9400 which is anither matter entirely.

Bore/stroke ratio, capacity/valve area ratio are used to estimate the torque per litre and these will fall into known bands for different engine types. Experience with the K series show the even with very favourable bore/stroke and capacity/valve ratios (as in the short stroke 1800 and 1700 82mm bore engines), the maxmimum torque per litre is between 90 and 93lb/ft.

The values are all derived from the ‘torque per litre’ figures and the ‘percentage of torque at peak power’.

It’s fairly straightforward, given the torque per litre at maximum torque and the percentage of peak torque at peak power, a figure for maximum power can be derived for any particular RPM.

Calculate the maximum torque, reduce it by the %ge at peak power and apply the formula which determines power, BHP = (torque/5252)*RPM.

The reciprocal of this simple formula is used to derive the minimum RPM required to acheive a given BHP level.

For example an exceptionally good 1800 engine might make 93lb/ft per litre, so at peak torque it might produce 167lb/ft. At peak power it will produce around 90% of this maximum, E.G. 150lb/ft, if power is peaking at say… 7800 then the peak power will be (150/5252)*7800 or 222BHP, 7800RPM is the lowest possible crank speed at which the engine could produce 222BHP.

The constants for torque per litre and percentage of torque at peak power are variable in the spreadsheet.

To find the minimum RPM at which an engine of a given size can produce a given BHP, you can reverse the formula, for example for a 2litre engine to produce 300BHP… peak torque of 93lb/ft per litre will give a maximum torque of 186lb/ft (this is close to the theoretical maximum on pump fuel from a perfect engine), at peak power the engine would produce around 90% of this value, E.G. 167lb/ft, to derive the RPM required to produce 300BHP… RPM = (BHP/torque) *5252… or 9404RPM. This does not mean tha the engine revs to 9400, it means that it peaks at 9400 which is anither matter entirely.

Bore/stroke ratio, capacity/valve area ratio are used to estimate the torque per litre and these will fall into known bands for different engine types. Experience with the K series show the even with very favourable bore/stroke and capacity/valve ratios (as in the short stroke 1800 and 1700 82mm bore engines), the maxmimum torque per litre is between 90 and 93lb/ft.