Why are cross-flows so rare?

[Caen Fred]

We will have to wait for Alan return from the rising sun country !

But here's what I think, it may come from the orginal "Prince" (read Mercedes) design of the engine, it was a licenced 6 in line Merc design minus 2 cylinders at first, then they added the 2 missing cylinders for the L6!

So I guess it was tooling cost at first that created this odity. In the other hand, we have proved to the world that the design, maybe far from perfect, could kick the strongest arse around :love: :love:

[nixcars]

Guys,

the twin cam x-flow head from the 432 model will not bolt onto a L series, only a S motor, hence S20.

There was a x-flow head made for the nissan works cars that went onto a L motor from memory, but were not twin cam & the spark plug wasn't on top like the hemi, it was on the exhaust side.

These are also quite rare & expensive.

I haven't seen a pic of one on this site, I'll see if I can find one & post it.

If any one thinks I may be wrong at all, please correct me as I'm only going by memory.

Nick.

[Brett240]

you just sparked my memory, thats spot on.

[Zedrally]

Won't try to correct you as I was going from memory as well.

The photo was in How to Hot Rod & Race your Datsun or the other How to book.

I think the USD20K + price killed any ideas of mass production!

If I remember correctly it did little by itself to lift performance anyhow!

[Gav240z]

I agree with Mike on this one. I can understand why the early Z's did not have crossflow heads. If it's true that the engine design came from Prince motorcompany who initially got there's from Mercedes then it would make sense. The 510's and other 4 cylinder Datsun's had the L engine design and the Z was just two more cylinders with the longer crank.

Where it doesn't make sense to me is when it comes to the Turbo 280zx's??? Nissan apparently did there homework on the head design and that to me is strange. If Nissan were gonna do so much engine head research why not just make it crossflow???

I guess they got the idea as they did build an RB30 but it's just not part of the L family anymore.

The S20 engine came in the KPGC10 correct my chassis prefix if I'm wrong. The Older GTR(can't remember if they were the first Skyline to wear the GTR badge I think so..).

It was also found in the 432 and 432R for those unfamiliar 4 Valves per cylinder, 3 Carbs (Think tripple Mikuni's) and 2 Cam Shafts.(Twin Cam).

These were the top of the range cars and to me that might provide some explanation.

The other engine head that was crossflow was the O.S Giken head from what Alan has told me. These were expensive to make and most were destroyed in the 80's I think by all the street racers.

I think there's one other head and don't hesitate to correct me where I'm wrong here. It was the LY28 and the engine head was used on the Works rally cars as far as I know.

In these engines though I don't think the spark plug was at the top rather on the exhaust side(LY28).

I also heard that crossflow was better because air entering the chamber doesn't have to make a 180 degree turn to leave the engine again. With all the emphasis put on emission controls car companies these days look for the cheapest most efficient ways to get power out of engines.

I suppose that's why our old cars benefit so much from new extractors and air filters etc... Whereas new cars don't get the same benefit.

I'll scout around for a nice heat shield to stop heat sink for the carbies. Also you can get header wrap that will stop a large amount of this however it has been known to shorten the life of the headers. Another solution would be to get HPC coatings done it's the stuff they used to use on Jet Engines. It keeps the tempreture down and looks very shiny :classic: .

[Z Kid]

In the absence of ALan, I will use one of the pictures he posted somewhere to answer a few questions.

The head was made by OS Giken.

[John Coffey]

> If Nissan were gonna do so much engine head research

> why not just make it crossflow???

My guess is that they easily hit the power numbers they wanted with the existing head design and decided to spend the R&D money somewhere else.

> I also heard that crossflow was better because air

> entering the chamber doesn't have to make a 180

> degree turn to leave the engine again.

Lots of folks think that, but its obviously not true. Remember, there's a compression stroke and a power stroke in between intake and exhaust openings so the mixture spends a lot of time hangning around in the combustion chamber. We're not talking about a fluid flowing though a pipe.

Crossflow heads are generally better then same side heads because port shape and length can be optimized.

[MikeW]

Originally posted by Gav240z

I also heard that crossflow was better because air entering the chamber doesn't have to make a 180 degree turn to leave the engine again.

Once the valves are closed, the fuel-air mixture is compressed, the spark fires, all hell breaks loose, and the piston is pushed back down do you think the air actually remembers which direction it came from? It's probably so confused it doesn't know which way is up ...

On a more serious note, I suspect modern engines are cross flow because many have 4 valves per cylinder. It would be kind of hard to have all 4 on the same side of the combustion chamber. At the time Nissan (or Prince) got the original design from Mercedes (as a 4 cylinder) they probably didn't have the ability or desire to make major changes and later on probably decided if it ain't broke don't fix it ...

[HS30-H]

We should not forget that the non-crossflow layout is not just a Nissan thing. The inlet-over-exhaust and non-crossflow layouts ( inc. flatheads ) have been used with good effect since the birth of the Internal Combustion Engine.

Brett hit the nail on the head; its all related to cost. When it comes down to it, a well-designed non-crossflow layout can work very well compared to a crossflow design - but the crossflow layout is theoretically superior if its potential is realised.

The design of the L-series Nissan engine predates the S30-series Z by some years. Its ancestry is somewhat contentious, as there is always talk of its being derived from one of the Mercedes patents that was licensed by the Prince Motor Co. - but Nissan enthusiasts in Japan point out that the L-series 4 and 6 cylinder engines were already at the planning stage before Nissan absorbed Prince..................

The Nissan L-series 4 & 6 make very good use of their theoretically inferior layouts, and very high efficiency can be obtained from the heads with a little extra work. In stock form, the non-crossflow layout has its advantages; one of which is fast warm-up ( always good for the longevity of an engine ). Production costs are also lower than a crossflow design, especially at the casting stage.

Nissan developed a crossflow head for the L-series engine primarily to use it in racing and rallying. This was the "LY" head, which was a two-valve, single overhead cam two-valve design with a hemispherical combustion chamber. The spark plugs were located on the exhaust side of the head. A specially-plumbed inlet manifold design was used to aid fast warm-up and efficient cooling.

There was an aftermarket crossflow head design for both the L-series 4 and 6 cylinder engines, which was made by a company called "O.S.Giken". Their TC24-B1 design for the L-series 6 was a 24-valve, twin cam hemi design with the spark plugs located centrally in the top of the engine. This was a very complicated affair and was rather expensive, as has been noted! A special front timing case casting was necessary, as were special pistons and other ancillaries. Price was very expensive!

The S20 twin cam ( derived from the Prince GR8 race engine ) was first used in the PGC10 Skyline GT-R, from late 1968. When this engine was offered in the PS30 and PS30-SB ( Fairlady Z432 and Z432-R ) in 1969, the car was described by Nissan in its sales PR as a "Fairlady Z with a Skyline GT-R engine". This design was also a 24-valve twin cam hemi, with spark plugs at the top of the hemispherical combustion chambers. No parts from the S20 engine are interchangeable with the L-series 4 or 6.

Really its all just down to costs and ease of production / use. "Our" L-6 engines are actually pretty darned good at almost everything they need to do, and that's one of the main reasons why a crossflow design was not offered in the mass-market by Nissan until much later.

Personally, I love the Nissan L-series engines. However, a nice LY28 or TC24-B1 would do very nicely too thank you:classic:

Alan T.

[Gav240z]

Well i asked to be corrected wherever I was wrong and I guess you did just that. Thank you for pointing out that a crossflow head doesn't mean the air can flow straight out the other side. The explanation's given make more sense to me now.

This also explains why an L28 could reach the 600HP mark. I always thought flow would limit it.

I have alot more faith in the ability of my L engine now and I've seen a friends turbo Z in action so I shouldn't have had any doubts.

Alan I'm with you I luv my L6 :classic: . Never been a fan of a engine swap although I do admit a bent 8 or Rb26 would be a ball of fun.

Maybe one day .

Alan was I correct about the PGC10 being the first of the Skyline series to wear the GTR badge?

Interesting conversation and it's made me wanna drive an L series with the different heads just to see how they are.

The S20 I think will always boggle me I keep thinking of the fun I had in my twin cam corolla but it would have that torquey feel to it.

Who knows if this Z obsession continues throughout my life maybe I'll build a replica 432R just like Alan :classic: .

Oh and thanks for not making too much fun of me for my crossflow head theorem.

[Mike]

Originally posted by Gav240z

Oh and thanks for not making too much fun of me for my crossflow head theorem.

No worries... we've all had our little fumbles with terminology. We'll just make fun of you because you're an Aussie instead.