Increase RPM by decreasing stroke?

[cjl]

The Porche 917 race car used a 4.5 liter flat 12.

Yes, but flatplane v8 is a whole different concept. Flat engines (such as the Porsche 917 and some Ferrari racing engines, as well as Porsche's normal engines, the original VW Beetle, and nearly every Subaru ever made) have the cylinders oriented 180 degrees apart, which is one way to achieve near perfect balance.

Flatplane V8s however are still V8s -they still typically use a 90 degree angle between the two banks of cylinders. Flatplane refers to the shape of the crankshaft - a flatplane V8 has a crankshaft that looks similar to the one in an inline 4, with the two outer crank pins 180 degrees offset from the two inner ones (which are directly adjacent to each other with no offset). The more normal design for a V8 is the crossplane design, with all 4 crank pins at different angles (the two end ones are 180 degrees offset from each other, and the two middle ones are 180 degrees offset from each other, with the middle two offset 90 degrees from the outer two). This design requires fairly large counterweights to run smoothly, but with the counterweights in place, is extremely smooth running. The flatplane is a slightly higher vibration design than the crossplane (since it basically runs like 2 connected inline 4s, side by side), but it requires far less counterweight to be in balance. This means it has a much smaller rotational inertia, so it revs much more quickly and freely than a crossplane design.

Another interesting result of this is the noise they make - crossplane and flatplane V8s have a different firing order, since the piston motions are different (obviously). Each bank of a crossplane V8 has an uneven firing interval (the power strokes in each half of the engine are not evenly spaced), which is what gives them the traditional V8 "burble". Overall, the engine fires at even intervals of 90 degrees, since the two banks' unevenness cancels out, but the noise from each side firing unevenly remains. Flatplane V8s on the other hand have each bank firing every 180 degrees, with the two banks offset from each other by 90 degrees. As a result, they sound a lot smoother than the crossplane ones at idle.

Example:
Crossplane V8: www.youtube.com/watch?v=ibtU1-Hy6VQ
Flatplane V8:

(As for the rest of your post, it sounds like we agree on pretty much everything)

 

[Damo ET]

damo have yo u ever weighed a piston/con rod when balancing them?
stock 2000 liter Ford 4 cylinder con rod weighs 595 gram, piston weighs 482
big V8 Ford 429 cid rod is 765 piston is 623..don’t have wrist pin or ring weight
2000L con/piston = 1072 g while V8 totals 1388 g or a little over 20% more. A quick scan of my old balancing tables shows this to vary form 18 to 24% depending upon the manufacturer..Chrysler being heaviest. Properly prepared race engine will reduce this amount significantly. The stock pistons have huge rings and wrist pins..bulletproof but way too heavy, the forged steel con rods are junk and should be replaced.
the point is 7000 rpm is high for any production automobile engine. I got no reason , desire or need to look at motorcycles. The statement that is is a lot easier to make a 4 cylinder rev simply due to size is a universal statement and one can not make sweeping assumption based on component size. Easier is a word with unlimited meanings in this context.
this is a forum dealing with specifics and empirical data is a must.

Sorry Ranger Mike, I know you said that you weren't going to post and this is not supposed to be a cheap shot at you holding to your word, so feel free to respond if you would like. But your above post asked me a specific question which I would like to respond to.

I have only balanced a couple sets of my own rods and slugs, and have lightened a set of rods also. These being both Nissan make, RB30E (3ltr 6cylinder) and E15ET(1.5ltr 4cylinder) balanced and RB30E lightened and balanced. I found the factory forged steel Nissan rods to be remarkably consistent across the individual sets with variance between rods less than 2.6 grams total, and less than 2.75 grams between corresponding little or big ends. (This quite surprised my local machinist who stated that the typical Holden or Ford V8 (In Australia) would usually vary upto 12 grams between little ends alone!
The first set of RB30 rods+slugs I did, had the complete rods come in at 675g with rod bolts, pistons at 392g, piston pins at 121g with circlips, and 26g for the rings. This puts an assembled rod/piston at 1214 grams. But more importantly, the reciprocating mass is around 220g for the little end, and approx 540g piston+pin+rings, which makes 760g in total. This is less than your posted weight of the V8 piston alone! If I had to pick one which was going to live at 7000rpm for a duration event, I know which one it would be.
In the car enthusiast circles in Australia, the RB30 has a cult following and turbo variants of this engine make well in excess of 1000hp. Every component of the engine has been pushed to its limits and beyond, therefore a fairly accurate 'power level' of each stock component is known. It is well known that the stock, mass produced forged steel conrods will survive 500hp and 7500rpm, which is 2.5 times the factory power level or 25% past the factory redline and 1000rpm past the rev cut from that engine in "off the showroom floor" condition.

Then there is the E15ET, complete rod weighs 373g, piston 282g, pin 91g, rings 21g. Reciprocating mass around the 515g range which would be less than 50% of the V8. Take into account the 82mm stroke and I would consider these rods bullet proof at anything below 10,000rpm in standard form. Would it be easier to build a 7,000rpm 4 banger rather than a 7ltr V8? Without a doubt.
Remember, we are not talking about motorcycle engines (that would be unfair and like comparing built crate motors to factory engines!), we are talking factory, eccono box grocery getters. The E15 have been used for circle dirt racing in "Litre cars", they swap to 14:1 motorbike pistons, run methanol and turn 10 to 11k rpm using stock (balanced) rods and crank.


Damo

 

[HowlerMonkey]

Hell...a stock L28et lower end is good for 500hp and 7000 rpms courtesy of it's forged crank and rods.

Most destroking in automobiles is done for racing in that a certain displacement limit is set depending on class rules.

Sure...Honda sold the original S2000 with a 9,000 rpm redline but they know the average buyer would do this only rarely and that many would never approach within 500 rpms of the redline.

It worked and got most of them through the warranty period with the failures being guys who drove them hard often.

The guys who experienced failures before the warranty ran out very often had modifications that negated the warranty so the warranty "figures" for engine failure in that car looked good and Honda performed "goodwill warranty" for many of those guys which do not show in the books concerning durability figures but did do a lot to squelch public outcry.

Same thing happened a few years earlier with the Toyota celica GTS with the 2zz engine in which early versions had a higher rpm limit than subsequent models.

The manufacturers got their bragging rights and then brought rpm limits down in later models for durability purposes.

As far as the RB30, getting 1000hp on the single cam head will require a boost level that starts running into diminishing returns as the intake charge will start getting heated by the restriction of the cylinder head.

 

[cjl]

From what I hear, the early s2k motors were fine even under heavy use up to redline a long as you checked the oil frequently and changed it regularly. I hear the clutch and transmission were a bigger problem under hard use than the engine ever was.

 

[Damo ET]

Hell...a stock L28et lower end is good for 500hp and 7000 rpms courtesy of it's forged crank and rods.
As far as the RB30, getting 1000hp on the single cam head will require a boost level that starts running into diminishing returns as the intake charge will start getting heated by the restriction of the cylinder head.

I didn't state that the 1000hp RB30's were using the single cam head, but either way that power level has been hit many times by either the RB30 head, or RB25/26 heads.
Also, the 2nd comment doesn't make a whole lot of sense. The boost that a turbo generates is completely dictated by the flow restriction across the head. Any increase in boost pressure is going to heat the intake charge. The efficiency of the compressor wheel will dictate the delta increase in temp for a given boost level.
I think what you meant is that the increasing restriction across the inlet valve would give a diminishing return past a given boost level. You would have to know the flow across the valve at a given pressure drop to calculate the amount of additional flow for a certain increase in boost pressure.

The point being of my post was that the factory Nissan (Datsun) gear was very stout as delivered, and the quality of the steel used for the crank and rods was very high from the 70's onward. I'm not surprised that the L28 is able to cope with that amount of power.
Up until the mid/early 90's a lot of the Japanese factory engines were well over engineered, being able to cope with nearly 250% increase in loadings without failures. But around that time, live computer modeling and stressing of components meant that the manufacturers could reduce component weight substantially but still being able to have a substantial headroom over the maximum output of a given engine. This goes part way to explaining why such renowned engines like Toyota's 1UZFE when used in modified form, the rods and cranks of choice are the earlier (stronger) factory offerings. I would expect that most of the Japanese engines in this cross over period (early to late 90's) would have the earlier engines being stronger than the younger engines of the same breed.
Out of interest, the Aussy delivered RB30's and CA's all came with crank girdles as standard also. And the even older E16's (which were a stroked version of the E15) came with a fully counterbalanced crank on an engine which produced all of 60kw.

Damo

 

[HowlerMonkey]

Since the RB30 never came with a 4 valve head, you have to make the distinction that you are referencing a 4 valve equipped RB30 when mentioning the engine.

When you say "RB30" people assume it is as delivered by the oem manufacturer.

Had you said "a rb30 with a RB26dett head makes 1000hp", things would have been a bit clearer but that opens up the fact that it is not stock.

The manifold pressure is not the same as the pressure the cylinders see if the head is the restriction.

The pressure drop between the manifold and the cylinder is dictated by the head.

The 2 valve RB30 head, like the L28 head is the restriction and that's where the diminishing returns begin with the raising of boost level.

You end up with heating of the intake charge AFTER the charge cooling when you have cylinder head restriction.

We're more in agreement than conflict as far as Nissan's bottom end strength.

 

[Damo ET]

HowlerMonkey, you are 100% correct, there were no multi valve RB30's factory delivered into Australia (even though the RB30E had valve pockets cast into the stock pistons for a twin cam head), in the statement I made that you were referring to, I was actually targeting the single cam RB30's which are able to make 1000hp+, not the modified combos of RB25/6 30's as you have rightly pointed out are not 'original equipment' and don't fit the 'stock' argument.
The problem comes when someone tries to quantify 'stock' as an argument. At what point is an engine no longer standard?
Someone could argue that when you no longer use the OEM intended fuel or boost level you are referring to a modified engine. As this thread went down the path of the ease of extracting rpm and power from standard engines, I thought using stock main engine components (bottom end) was more critical than the hardware bolted to it.

I am well aware that manifold pressure is not the same as inlet pressure in the cylinder as the inlet valve is the biggest restriction to flow. Yes, the pressure drop is dictated by the head (inlet valve/s), but the diminishing returns happen on different heads at different flow levels. I agree fully that increasing boost levels will not show a linear increase in flow rate across the valve, but you still need to know what the actual restriction is.

I have to disagree with you statement "You end up with heating of the intake charge AFTER the charge cooling when you have cylinder head restriction." as the pressure across the intercooler will be the same as the pressure at the back of the valve (negating harmonics) which means there will be no increase in pressure at the valve and no increase in temp. It would actually work inversely to this in the cylinder, as the inlet charge would drop temperature as its pressure falls when it crosses the restriction of the inlet valve.

Damo

 

[HowlerMonkey]

The heating occurs throughout the entire column of air...not just at the compressor.

If the cylinder head is overly restrictive, you get more heating of the entire column of which there could be a substantial length after the charge cooler unless you use what we use on our standing mile world record car where the last stage of charge cooling is about 8 inches from the intake valve.

 

[Damo ET]

If you were compressing a fixed container of air, there may be a temp problem with column of air after the intercooler, but the air undergoing compression after the intercooler in the scenario you mention is being consumed by the engine at a far greater rate than the system is pressurizing. There wouldn't be time enough to have any of the inlet charge after the intercooler to be at a higher temp than the charge coming through the intercooler, unless:
a, the inlet plumbing has a couple of hundred litres of piping
b, radiant heat from the engine bay is heating the post intercooler plumbing and manifold which in turn is heating the charge.

What constitutes an overly restrictive head? And why would a more restrictive head heat the charge greater than a less restrictive one?
Damo

 

[HowlerMonkey]

A restrictive head is not consuming the air far faster than the system is pressurizing.

If that were the case, there would be no pressure.

Pretty sure we have strayed off the subject which is bore/stroke discussion.