Renault RS26 internals

[manchild]

[img::]http://www.strata3d.com/gallery_images/ ... _large.jpg[/img]

I can't find animated one to update my avatar

[Tom]

Very nice, remember reading something the other day about how in performance engines the bore is larger than the stroke which was particularely evident in this pic.

Does anyone have the ratio for this engine?
Can anyone tell me what? advantages are found in this method?

[Ciro Pabón]

Well, I'm not mechanical engineer, but let's see if my "barbarisms" attract somebody who knows: when you ask for contributions, nobody appears, but when you ask for contradictions, everybody is eager to post!

It seems to me that a shorter stroke (maintaining cilinder capacity) should make your life easier and the components lighter: a longer stroke engine would have pistons that move faster. I'm not sure about the influence on the speed of pistons during the "reversal" and the acceleration implied, but you can easily imagine how that influences the friction, heat and the resistance of the package under high rpms.

Another point: if I can extrapolate what I know from column design , I would say that a longer rod will weight more, because it would buckle easier. We all civil engineers know that higher ceilings mean more weight on the columns and the difference is no small potatoes, at least for buildings. The slender (ratio of width to length) the column, the more fragile.

I have noticed that most diesel engines have longer strokes than their petrol or gasoline counterparts (for a given capacity). Long stroke engines have better torque, because you can have more leverage, if I imagine correctly the behaviour of an engine. Also, I know that the older the engine, the longer the stroke (think about how much time it took to have small-block engines). I guess this is because it is easier to machine a long cilynder than a short one and the tolerances don't have to be so small. Just think how hard would be to machine a cilynder that is much more larger than a standard one. Imagine an engine with a stroke of 1 millimeter: how large would be the piston? It wouldn't be an easy thing to manufacture and you would end with a huge block.

On the other hand, I'm pretty sure that piston pressure is higher at the beginning of compression, once most of the fuel has ignited, so a shorter stroke engine would give you more force on the rod when it's near to be tangent to the crank. The shorter stroke engine should be closer to tangent faster than the longer stroke one, if you follow my drift.

Anyway, if I were building this thing (heaven forbids! ), I would start by finding the piston pressure curve and balancing that against the mechanical leverage of the rods to find the optimum point, trying the different g-forces (and the associated strength and weight of components) before deciding for a particular combination of bore and stroke.

I also "see" that the dwell time have to change with stroke length and I have no idea how would this affect the "breathing" and the valve configuration...

So, where did I make mistakes? I guess this is going to take a dozen posts to eliminate all of the errors and wild guesses I made...

[DaveKillens]

The water's warm, I think I'll jump in too.

Every time a cylinder undergoes the power cycle, power is produced. If you can do it more times each minute, you increase the overall power produced by the powerplant. Double the RPM, you basically double the power.
Two of the major masses in an engine are the pistons and connecting rods. And they go back and forth, up and down each cycle. Incredible forces and accelerations. Two ways to reduce those forces is to reduce mass, and to make the trip shorter If a piston has to travel only 3 cm versus 4 in each cycle, then it's G loads are reduced.
So the trend is to reduce mass (see how small the cylinder skirts are?) and reduce stroke to increase RPM, so you get more power.

Interesting picture Manchild, thank you. Most of that engine is predictable, but I noticed the finger followers between the cams and pneumatic valves. Probably mainly for reliability, they would substantially reduce the side loads on the pneumatic valve buckets.

[Apex]

I hate it when people state the obvious but Wow that’s a nice pic there MC

Reminds me of the days when my Autodesk Inventor trial still worked, itching to make some of renderings like only Inventor can!

[Carlos]

Generally - with a specified displacement - an oversquare engine, that is to say a larger bore to stroke ratio provides an increase in combustion chamber size which offers increased valve area, which provides improved
intake and exhaust efficency. Also a wider bore to stroke ratio lowers piston speed which yields higher RPM. In addition an oversquare ratio
decreases the angular momentum of the connecting rods which decreases
the stress on the connecting rod and results in less rod failures.

[ginsu]

see how small the cylinder skirts are?)

This dramatically reduces friction with the cylinder bore as well. I know they use some pretty high tech coatings on the piston skirts too. Lots of friction at 19k rpms.

[G-Rock]

Generally - with a specified displacement - an oversquare engine, that is to say a larger bore to stroke ratio provides an increase in combustion chamber size which offers increased valve area, which provides improved
intake and exhaust efficency. Also a wider bore to stroke ratio lowers piston speed which yields higher RPM. In addition an oversquare ratio
decreases the angular momentum of the connecting rods which decreases
the stress on the connecting rod and results in less rod failures.
_________________
F1 Enthusiast Circa 1965

Thank you Carlo. I would also like to add that larger valves only work in high rpm engines or you won't get enough turbulence and ram effect in the combustion chambers due to a fast moving air mass.
It's the whole package in a racing engine but the main disadvantage is poor low rpm torque with a short stroke.
It's interesting to note that the Honda/Acura V-Tech SIr engine has an "undersquare bore/stoke", yet still manages to rev freely to 9000rpm. Honda claims in has a piston speed similar to a modern F1 engine! It still produces very meagre torque at over 6000rpm, i believe, even with all the variable valve timing and such.

[Carlos]

Thanks G-Rock -- Your remark about the velocity of the intake tract
reminded me of something interesting that certainly
confirms your opinion is totally accurate. In the 70's Ford built a version of
the Boss302 CID V8 called the "Tunnel Port" that featured enormous intake ports. Because they were so large, the intake velocity was well below the optimal, and the engine was
an embarassement -- very poor horse power. In the 60's the deceased Gordon
Jennings modified a 450cc Honda twin - he cut away the intake and exhaust casting areas from the head and welded on some aluminum tubes of enormous diameter - if a little is good - a lot more diameter and volume, especially on the intake tract, must be better -- intake air speed was way below any posibility of improving horsepower. Your insight into this is "spot-on." Gordon Jennings was one of the best technical writers of the last 50 years. If you should ever see a copy of his " On Motorcycle Design" - a collection of columns from Cycle World magazine - the articles on 4 stroke design are the bedrock of what knowledge I have. It was a large format paperback with a Blue cover. If you should ever find it, if anyone should ever find it -- I would be so grateful for a copy or scanned CD. I am not sure if that was the exact title, the last time I read it was in about 1966. Gordon Jennings is the "Dean" of technical writers in America, he wrote for Cycle World, Cycle, Road & Track, Car and Driver and Motorcyclist magazines - I cannot recommend him too highly - a giant in American car and cycle journalism -- a master tuner and intellect. If anyone should ever competition tune a 2 stroke - go to Amazon and search him by author, there's a great book there on 2 stroke tuning - his anaylsis of porting dynamics is a revelation, surpassing the Japanese factories R&D. Its amazing what you can do with a Dremel tool and some files. Sadly, he died in 2000, after writing for almost 50 years.

[G-Rock]

I wish I had access to those books 5 years ago when I took a dremel to my cousins moped Carlos. We had about 3 spare engines (Sachs) and noticed that one had a lot more speed than the others (about 10kmphr) so we scratched our heads and then after measuring the carburator diameters, needles etc we got down into taking the cylinders off. It turns out that the fast motor had slightly different porting so I convinced my cousin that with a dremel and a ruler, that we could match or even exceed the fast motor. After an hour of grinding we put the motor back on the moped and voila, we were up to 40kmphr just like the fast motor. Then I got greedy and ground another mm or two off, increasing the intake area and timing, and totally screwing the engine up. I think i opened the port up so much that the intake timing (2stroke) was way too early and just kept stalling. It was a lot of fun though and maybe someday, I'll get some aluminum welding rods and fix that head up to original spec.
We used to race them on my farm. Two identically prepared mopeds racing around a tight twisty track on my backyard was very addictive. It was amazing though how close my friends got to breaking bones though, especially late braking on wet grass.

[Jersey Tom]

.. pneumatic valves?

[luisandregg]

Generally - with a specified displacement - an oversquare engine, that is to say a larger bore to stroke ratio provides an increase in combustion chamber size which offers increased valve area, which provides improved
intake and exhaust efficency. Also a wider bore to stroke ratio lowers piston speed which yields higher RPM. In addition an oversquare ratio
decreases the angular momentum of the connecting rods which decreases
the stress on the connecting rod and results in less rod failures.

It's important to say that, for a V8 90° flat crankshaft, the lateral forces of 2nd order created by the engine are proportional to R/L. So when you increase R (crank) and reduce L (rod length), you get more lateral vibrations (and vertical vibrations of 4th order) from the engine.

That’s why a road car should have a low R/L ratio. And maybe that’s the reason for Ferrari to try V12 engines during long time: it’s easier to find a balance for a V12 than for a V10 or V8.

[flynfrog]

I hate it when people state the obvious but Wow that’s a nice pic there MC

Reminds me of the days when my Autodesk Inventor trial still worked, itching to make some of renderings like only Inventor can!

http://students.autodesk.com

check this out


free version of inverntor

[knighty]

manchild - the R26 V8 engine picture you have features a 90 degree cross plane crank.......surely this is wrong - I would have thought it was a 180 Degree flat plane crank.......otherwise the exhaust pulses would be all wrong and they would need to run across-over exhaust system in order to get the V8 engine firing correctly........much like a GT40 exhaust........as all F1 2.4 V8 motors run 4-into-1 ex manifolds - surely this is an indicator of a 180degree flat plane crank????.....

[manchild]

I didn't make the pic I only found it on the web. It was made by same guy who makes animations for RAI... Reca knows his name, I can't remember it now.