F1technical.net

So from what I know, F1 N.A. engines have for a long time been engines with short strokes, big bores, relatively low torque and RPM as high as possible.

So I know that for the same amount of torque, higher RPM equals higher power, and I guess shorter strokes work better at higher RPM, but apart from that I'd like to know why they did things like they did:
Pretty much no other racing series that I know of have engines like that, so why did they do things like that in F1?

What would be the downsides of an engine with longer strokes and narrower bores? Couldn't they achieve the same power with more torque and lower revs? (All of that with N.A. engines).

Limitation of capacity.

As they were restricted to 3.5l (1989 - 1994), 3l (1995-2005) and 2.4l (2006-2013) and weren't allowed supercharging, rpm was they way to get more air through the engine, thus enabling more fuel to be burned and more power to be produced. Also, were restricted to a maximum of 12 cylinders to 2000, then 10 was mandated from 2001-2005 and 8 from 2006 to 2013.

Short strokes reduced the piston speeds and accelerations, at the cost of a heavier piston. It also allowed larger valve area to be used, which allows more air through the engine as well.

When the V8s were introduced the bore size was mandated at 98mm, which gave a stroke around 40mm.

Couldn't have explained it any better. Thank you!

Here's a good read that compares F1 to NASCAR engines:

http://www.epi-eng.com/piston_engine_te ... _to_f1.htm

wuzak wrote: ↑

28 Feb 2018, 05:21

Limitation of capacity...

Or, limitation to 4-strokes, which must run super-high ( & super-expensive) rpm,
- to get any useful work done on 'pump gas'..

(G.P. motorcycle engines were 2T, & making ~440hp/Ltr @ 13,500rpm N/A in this same period).

Another partial reason for the short stoke is to reduce the GC height of the engine. The shorter the stroke the shorter your crank throws need to be and this effectively sets your crank height in the car.

the OP has suggested short stroke high rpm NA engines had relatively low torque and this would be better with longer stroke
they didn't and it wouldn't
when the engine didn't/doesn't have to do the gearboxes job

pneumatic valve springs are rightly seen as an enabler of extremely high bore:stroke ratios
but eg 7 speed instant shift gearboxes and 'drive by wire' digital management of throttles are also vital

higher B:S ratios not only help mechanically to allow higher rpm but also allow a bigger valve area relative to any rpm


'our' F1 really began 50 years ago with the Cosworth DFV becoming widely available
it's B:S ratio was quite low as the bore centres were taken from the UK Ford 1 litre 1958 road car
I wonder what Mr Duckworth would have used if there had been a free choice ?

the BRM and Weslake V12s had even lower B:S ratios (being derived from stroking the BRM 1.5 litre V8)
Beltoise's wet 1973 ? Monaco GP win implied this gave a very driveable powerband

DiogoBrand wrote: ↑

28 Feb 2018, 04:55

So from what I know, F1 N.A. engines have for a long time been engines with short strokes, big bores, relatively low torque and RPM as high as possible.

So I know that for the same amount of torque, higher RPM equals higher power, and I guess shorter strokes work better at higher RPM, but apart from that I'd like to know why they did things like they did:
Pretty much no other racing series that I know of have engines like that, so why did they do things like that in F1?

What would be the downsides of an engine with longer strokes and narrower bores? Couldn't they achieve the same power with more torque and lower revs? (All of that with N.A. engines).

Torque and power are connected. Basically, power is torque x revolutions/time. So if you want to have more power, you need more torque or more rpm. In NA engines, this is done with more rpm (if the capacity is restricted) or with a greater capacity (the cheap options). That high revving engines have a big bore and a very short stroke has to do with the piston speed. The max piston speed (at the moment) is around 10.000 ft/s. So, if you want more revs you need to make travel of the piston as small as possible.
As time and engineering possibilities develop, F1 was going into extremes (as always) and they mandated a minimal bore to keep the stroke a bit normal (and affordable). A while back I saw some KTM pistons that looks more like plates then pistons... really amazing what they can do these days. As a final restriction they limited the amount of revs, basically levelling all engines to the same power.

With turbocharged engines this all is very different. Revs are not important because they are not the source of the amount of air going trough the engine. More air is more power because you can put in more fuel. It's all about boost pressure. Of course, in the case of efficiency there are sweet spots with capacity and revs, but in theory they don't matter. Its about how much fuel (energy) you can burn.

piston speed is never the issue - it's not a hard limit to rpm
piston etc acceleration is a hard limit to rpm as the strength requirement increases with the square of rpm
fundamentally rpm is proportional to the square root of the B:S ratio

the boosted SI engine has in principle a choice of low boost/high rpm/high CR or high boost/lower rpm/lower CR
the turbocharged engine still throws away power
compounding is a seperate factor - and of course NA compounding is possible

can do some fun things with N/A like manipulating the scavenging effect with cam specs to produce a positive pressure in the intake. ProStock engines have seen upwards of 3 psi.

well yes
but this can be done with boosted engines to get 'free supercharging' of the same % benefit as NA's
eg F1 has 6 tuned length tracts working from a plenum of pressure-boosted air
and the ram effect from the vehicle speed applies equally to both engine types

true the boosted engine tuned-length exhausting to atmosphere won't get near the % exhaust benefit that NA can
but it may be close if it gets tuned-length exhaust action where joining the boost-pressure exhaust upstream of the turbine

Tim.Wright wrote: ↑

28 Feb 2018, 08:19

Another partial reason for the short stoke is to reduce the GC height of the engine. The shorter the stroke the shorter your crank throws need to be and this effectively sets your crank height in the car.

Taking it even further ultra short crank throws and long rods(within reason) at say, 2.4:1 ratio, gives you long dwell times and higher engine speeds.

ok but ....
a 'long rod' (high rod ratio) gives more 'dwell' close to TDC but of course less 'dwell' close to midstroke

high rpm engines tend to have a problem with combustion speed not keeping ahead of piston motion
so a 'short rod' (low rod ratio) can give more power and design has been correspondingly influenced

ok the very large NA bore:stroke maybe meant the mechanical disadvantages of rod angularity were excessive with 'short rods'
and tests showed rich mixtures helping combustion 'speed' (consistency really) at very high rpm

I think that the difficulty of preventing high-rpm rotations of engines is the combustion efficiency. not piston and rod's mechanical strength

Small cylinders also get the burn done in a shorter time.