Air Cooled Hot Rod: 3 Valve Head Actually Better Than 2 or 4?

[nicholastanguma]

For more than 30 years now many Japanese air cooled engines, from little singles to big singles to huge inline 4s, have successfully been using 4 valve heads, and most of these engines are known for the typical Japanese level of bombproof reliability. Honda XR650L, Suzuki DR650, Yamaha XT600, Suzuki LS650, these are just a few of the decades old examples of four valve big singles, for instance. Look at the old air cooled Zook GSXRs and Bandits for examples of the big inline variety.

The new Harley-Davidson Milwaukee Eight pushrod V-twin is now using four valves per cylinder, too.

But sometimes in air cooled applications multivalve heads are known for overheating, especially at the exhaust ports; from what I understand, Porsche battled this issue for years. The Japanese clearly have some things figured out, however, so I can't definitively say 4 valve heads in air cooled engines will always be prone to overheating.

However, I've heard rumor that the new Milwaukee Eight four valve heads do indeed tend to overheat once hot rod fun like big bores, high compression pistons, and stroker cranks are introduced to the equation.

Fueling, the company that was making 4 valve heads for H-D Evo V-twins in the 80s and 90s, is also the company that licenses 3 valve head technology to Ford, so clearly they must know at least a little something about multivalve heads. According to this video the Milwaukee Eight heads have so much tendency to overheat when their engines are hot rodded that Fueling has been testing bolt-on 3 valve replacement heads.

With a three valve head that one big exhaust valve or that one big intake valve will, as far as I can tell, pretty much keep rpms limited to what a 2 valve head could manage. Nonetheless, engines are just complex air pumps, so cramming in as much air intake or exhaust outflow is theoretically always better than less. And correct me if I'm wrong, but it's more important to get IN as much intake air than get out exhaust gas, so I'm assuming 2 intake valves and one exhaust valve is probably the way to go.

For an air cooled hot rod, then, is a 3 valve head actually a better proposition than either a 4 valve or a 2 valve head?



Link

[Bad bug]

There is a setup for the type4 engine to run 12 valve heads the name is apfelbeck. Wally on germanlook.net was in development with friends for years with these heads but i haven't heard much about it.

It would be nice to see this project completed and working. The horsepower figures they crunched from the sim modules were amazing.

[Wreck]

https://www.thesamba.com/vw/forum/viewtopic.php?t=732502&highlight=beetspeed

[Bad bug]

Thanks for posting this wreck as i can see i was active in this thread

[Chickensoup]

is that head 3d printed! im guessing its only being used for bench flow tests?
_________________
-'85 c10 5.3 LS, 222 cam, long tubes, x pipe, 3 inch spin tech's
-'05 B5.5 TDI Wagon 17in sport rims ;EGR + BSM + ASV Delete, Stage-2 Tune, straight pipe
'65 Tourist Delivery Build
'66 RIP
'69 RIP
Hosea 4:6 "My people are destroyed for lack of knowledge"

[FreeBug]

The heating problem still persists with a car application, I think: those motorcycles have a very different power-to weight ratios, the engine spends little time being fully loaded. Pushing a car is different.

The complication isn't worth it on our engines: there's cheaper ways of adding more power, by the time your 2-valve heads become the obstacle, you're on another planet, not VW hobbying...

We could get better bottom end for equivalent top end, and the chamber has less hot points, so we could add more compression and/or more boost. AND we could put 16V emblems on the back!

I like describing my engine as a DOHV, as in Dual Over-Head Valve. Sounds very cool.

[FreeBug]

And as for 3-valve engines, I don't think any car manufacturer has kept that configuration, probably the same problem: the results are not worth the complication.

Funny fact: Almost all examples were with two intakes and one exhaust, but Bugatti did it the other way around. Did he know something we don't? Nope, he was just goofing around.

Also, some of those motorcycle engines will put out hp/barrel that a 4-valve car head can't, as the bikes can have radial valves. I don't know of a single car manufacturer who managed pulling that off.

[nicholastanguma]

[nicholastanguma]

[nicholastanguma]

[oprn]

Just turn up the boost to 10 - 12 psi and you are already way past the HP figures any NA engine can make regardless of the number of valves. The bonus is that it all happens at rpms well below what you would need to run NA and there is no loss of low end torque or drivability.
_________________
We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)