Rod length to stroke ratio of v6 turbo engines.

[PlatinumZealot]

Since there is a higher loading on the pistons than before, the V6 turbo engines must have been designed with a premium on reducing side loads on the piston and increased dwell time for combustion so can it be assumed that the rod to stroke ratio is still very high?

Since the engine stroke is more or less known does anyone know the typical rod length for the V6 turbo engines?

[Tommy Cookers]

are you saying a large rod ratio is better matched to combustion speed factors ? (than a small rod ratio)

BRM found the hard way that a small rod ratio was better
these current 12000 rpm engines presumably have plenty of combustion going on at eg 60-70 deg atdc
the small rod ratio causes the piston to develop a useful delay (relative to the large ratio one) in this region
ie the heat is released earlier (less late) in the stroke so relatively more of the heat is turned into work

on P8 of this section's list of old threads, a thread 'Crankshaft Power Strokes' has many views on rod ratio
(my computer being an old fool, I can't post a link to the thread)


yes, I would like to know the ratio(s) used
(or others of recent F1)

[tuj]

I figure bore to be 80mm, stroke therefore is around 53mm. Rod? No idea.

[Vortex37]

are you saying a large rod ratio is better matched to combustion speed factors ? (than a small rod ratio)

BRM found the hard way that a small rod ratio was better
these current 12000 rpm engines presumably have plenty of combustion going on at eg 60-70 deg atdc
the small rod ratio causes the piston to develop a useful delay (relative to the large ratio one) in this region
ie the heat is released earlier (less late) in the stroke so relatively more of the heat is turned into work

on P8 of this section's list of old threads, a thread 'Crankshaft Power Strokes' has many views on rod ratio
(my computer being an old fool, I can't post a link to the thread)


yes, I would like to know the ratio(s) used
(or others of recent F1)

Add in to the above, 'special brew' fuels with weird burn patterns, multiple fuel injection times, and multiple ignition points, and it gets rather interesting.

[tuj]

multiple ignition points? I thought multi-spark was verboten?

[Vortex37]

multiple ignition points? I thought multi-spark was verboten?

No, I don't mean multiple ignition points in the cylinder. I was referring to TCs point about the number of degrees of continuing burn atdc. Sorry not clear if that's what you thought.

Just to be clear:

5.11.1 Ignition is only permitted by means of a single ignition coil and single spark plug per cylinder. No more than five sparks per cylinder per engine cycle are permitted.

[Ciro Pabón]

In times of V8 the data I read in Race Engine Technology Magazine was that "Formula One rod is an ‘H’-beam layout in titanium, with a centerline length of 102 mm (4.016 inches), 34 mm (1.34 inches) crankpin diameter, 18 mm (0.709 inches) piston pin diameter, and a stated weight in the 285 gram vicinity".

This data is for a "2.4-liter, 90° V8 configuration with a 180° crankshaft, 106.5 mm bore spacing, 98 mm maximum bore, 58 mm minimum crankshaft height" (although the crankshaft is usually taller by much, if I'm not mistaken).

Rod length to stroke ratio was 2.56 for this kind of V8. Perhaps you might like to check, given the 98 mm bore and rod length, if the approximate cubic capacity you may estimate indicates if this data seems legit.

These days you can find at F1 Fanatic that Renault Engine has a crankshaft height of 90 mm and a stroke of 53 mm for a bore of 80mm. No data about the rod length, sorry.

Thanks for the bit of info, Vortex, I had no idea that the spark plug gave several sparks per cycle, interesting.

[Tommy Cookers]

EPI Inc have an article on the F1 2.4 litre V8 compared with a Nascar V8
the rod ratios are stated as 2.56 and 1.91 respectively
given the ultra-short stroke of the N/A F1 engines, maybe some practical factor influenced the rod ratio choice ....
like simple constructional factors (or obscure issues like pin offset ?), or engine dimension rules
at high rpm cylinder wall friction from inertia loads (ie not just combustion load)
though shorter rods are lighter, EPI suggest good reasons why saving rod weight may not be beneficial

don't current rules dictate design rather strongly via mandated 'block height' dimensions ?
(rules are written to support maybe some deliberately conservative design intent)


EPI Inc
EPI Products and Services
Technical Articles
Petrol Engine Technology
22 A Comparison of ...etc

should find it
(can't get the link to post)

[Brian Coat]

I think the EPI data is used from (the same?) RET article, the 'CA dossier' one?

Although the 20,000 rpm, circa 40mm stroke, atmo engines had l/r > 5 (l/s >2.5), I'd expect the longer stroke 12,000 rpm turbos to be nearer to 4.

[PlatinumZealot]

Those rod ratios are freakishly high when comparec to those of high perforpance road cars. Wow.

[gruntguru]

TC touched on this in an earlier post. There is a geometric lower limit on the l/r ratio. When the piston is at BDC, the rod needs to be long enough for the piston skirt to clear the balance webs of the crankshaft.

The skirt height and the pin diameter are the other factors - pushing the piston pin further up and increasing the rod length. As bore size (and B/S ratio) increases the skirt needs to be longer and the pin diameter needs to be larger, both forcing the designer to use a larger l/r as B/S is increased.

[Brian Coat]

That's right.

Not certain but I wonder if the real clearance constraint might be to the webs/structure joining the piston crown back to pin boss? ... there's effectively no piston skirt where the counterweight is?

[Vortex37]

Thanks for the bit of info, Vortex, I had no idea that the spark plug gave several sparks per cycle, interesting.

Be careful, that engine rule (5.11.1), allows multiple sparks. Whether they use that number is another matter.

[Tommy Cookers]

TC touched on this in an earlier post. There is a geometric lower limit on the l/r ratio. When the piston is at BDC, the rod needs to be long enough for the piston skirt to clear the balance webs of the crankshaft.
The skirt height and the pin diameter are the other factors - pushing the piston pin further up and increasing the rod length. As bore size (and B/S ratio) increases the skirt needs to be longer and the pin diameter needs to be larger, both forcing the designer to use a larger l/r as B/S is increased.

given we have reminded ourselves that the N/A F1 had surprisingly large (ie conservative) rod ratio
and are looking for practical design reasons to explain this .....

the gudgeon pin (wrist pin) boss is structurally integral with the crown, so giving the most direct path eg for inertia loads
this direct load path chosen to enable extreme piston acceleration and rpm
so this higher pin position demands a longer rod

but the current V6 turbo engine rules enforce a conservative bore and stroke and rpm and piston acceleration and block height
the piston design will be dominated by crown heat (part-steel pistons were mentioned in the Gilles Simon article in RCE)
so the mix of design factors contributing to rod ratio is different
they might have a similarly high rod ratio, but for different reasons

[Edis]

are you saying a large rod ratio is better matched to combustion speed factors ? (than a small rod ratio)

BRM found the hard way that a small rod ratio was better
these current 12000 rpm engines presumably have plenty of combustion going on at eg 60-70 deg atdc
the small rod ratio causes the piston to develop a useful delay (relative to the large ratio one) in this region
ie the heat is released earlier (less late) in the stroke so relatively more of the heat is turned into work

on P8 of this section's list of old threads, a thread 'Crankshaft Power Strokes' has many views on rod ratio
(my computer being an old fool, I can't post a link to the thread)


yes, I would like to know the ratio(s) used
(or others of recent F1)

The majority of the combustion must be done before 20 deg atdc, heat released at 60-70 deg atdc will provide little useful energy.