We have DOHC engines, why not TOHC engines?

[Linux23]

I'm curious as to why there are no Tri Over Head Camshaft engines engineered. Since DOHC engines help a motor to breath more freely, I would assume a TOHC would provide a little more breathing room than DOHC, allowing better acceleration.

I would love to own a high performance car with 6-Valves per cylinder.

 

[notfred]

How many valves can you fit in the average sized cylinder head?

 

[OS]

There's only an intake and exhaust valve action anyways. What would the third cam be doing?

 

[Linux23]

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

 

[Linux23]

Originally posted by: OS
There's only an intake and exhaust valve action anyways. What would the third cam be doing?

3 intake, 3 exhaust? not sure if that would be beneficial to overall engine performance though?


Also different Cam timing profiles for maximum torque.

 

[notfred]

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

If you make the cylinder bigger than you don't really need to make it breathe more freely to get extra power out of it, you already did it by increasing displacement

 

[Linux23]

Originally posted by: notfred

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

If you make the cylinder bigger than you don't really need to make it breathe more freely to get extra power out of it, you already did it by increasing displacement

yeah, but at higher RPM's, the valves open and close so fast, most engines have trouble breathing. DOHC helps to alleviate some of that, and that's one reason they have higher RPM's compared to their OHV counterparts. Now with TOHC, you have more valves to deliver more fuel/air, and you can also have different cam profile's for maximum torque and hp output.

 

[Kadarin]

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

I think someone (Audi?) makes an engine with a 5 valve cylinder head that's available commercially.

 

[FrustratedUser]

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

You get 6 valves with DOHC, see F1.
Audi has 5 valves using DOHC.
TOHC is just too complicated without any gains.

 

[Colt45]

why not 100OHC?

 

[FrustratedUser]

Heh, 8OHV 0wnz j00!

 

[DrumminBoy]

Originally posted by: FrustratedUser
Heh, 8OHV 0wnz j00!

lol

 

[Train]

Theres no 6 minute abs! its 7, not 6!

 

[Eli]

Originally posted by: Linux23

Originally posted by: notfred

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

If you make the cylinder bigger than you don't really need to make it breathe more freely to get extra power out of it, you already did it by increasing displacement

yeah, but at higher RPM's, the valves open and close so fast, most engines have trouble breathing. DOHC helps to alleviate some of that, and that's one reason they have higher RPM's compared to their OHV counterparts. Now with TOHC, you have more valves to deliver more fuel/air, and you can also have different cam profile's for maximum torque and hp output.

lol.. but if you increase displacement by increasing bore, you lower the maximum RPM anyway, at least with the same internals.


Why don't we have 2.0L inline two-cylinder engines with 6 valves per cylinder?

Increased combustion chamber surface area = increased heatloss

Increased heatloss = decreased thermal efficiency

Decreased thermal efficiency = less power per unit of fuel burned

Less power per unit of fuel burned = sh!tty MPG

Sh!tty MPG = unhappy people

Unhappy people = lack of revenue

Lack of revenue = bankrupt company

Bankrupt company = bad.



There's more to it than that, but.. heh. I recommend you read up on how engines work.

Next you'll be asking why we don't use 2-cycle engines. "But the power to weight ratio..."

 

[FrustratedUser]

Why don't we use 2-cycle engines. The power to weight ratio is great.

 

[zephyrprime]

I read that they're working on having electromechanical valves which would effectively be INFINITE-OHC.

 

[McCarthy]

Ha, my entire engine only has 6 valves. (I-3)

You can make an engine breathe big with just two valves. Or you can have twelve tiny valves. It's a question of gross flow and fuel pattern dispersion, the latter being why more valves tend to do better. Heck that's what the whole Hemi thing is about. How you time the action of the valves is a lot more important than how many there are though and you run into increasing production costs/reliability factors as you complicate engine design with more moving parts.

Google up variable valve timing, think you'll like it more than adding valves. Not that I mind if you have 6 per cylinder, just that it's into diminishing returns (like triple or quad blade razors vs a double or even a Bic) to keep adding valves.

 

[compuwiz1]

Kinda like why you never see V-10 engines doing any serious racing. V-8's have 4 power points on the crank and maintain better balance and power to weight ratio. A 3rd cam would be like a 3rd eye on a human, it just doesn't fit, nor make sense.

 

[LS20]

exactly what action would the 3rd cam actuate, though?

 

[5ayle]

Originally posted by: Eli

Originally posted by: Linux23

Originally posted by: notfred

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

If you make the cylinder bigger than you don't really need to make it breathe more freely to get extra power out of it, you already did it by increasing displacement

yeah, but at higher RPM's, the valves open and close so fast, most engines have trouble breathing. DOHC helps to alleviate some of that, and that's one reason they have higher RPM's compared to their OHV counterparts. Now with TOHC, you have more valves to deliver more fuel/air, and you can also have different cam profile's for maximum torque and hp output.

lol.. but if you increase displacement by increasing bore, you lower the maximum RPM anyway, at least with the same internals.


Why don't we have 2.0L inline two-cylinder engines with 6 valves per cylinder?

Increased combustion chamber surface area = increased heatloss

Increased heatloss = decreased thermal efficiency

Decreased thermal efficiency = less power per unit of fuel burned

Less power per unit of fuel burned = sh!tty MPG

Sh!tty MPG = unhappy people

Unhappy people = lack of revenue

Lack of revenue = bankrupt company

Bankrupt company = bad.



There's more to it than that, but.. heh. I recommend you read up on how engines work.

Next you'll be asking why we don't use 2-cycle engines. "But the power to weight ratio..."

right on...

*too much time on his hands*

great work

 

[GalvanizedYankee]

The only TOHC I have read about was Ducati's first 125cc race engine. Two opening cams,
one closing cam for both valves. It was desmodramic valve action, there are no valve springs.
The longest production run 5 valve head is used by Yamaha M/Cs. Lambo tried a 6 valve
set-up and there were no real gains, just bragging rights.
Aside from breathing, being able to place the spark plug in the center of the chamber is
a big plus with a 4 valve head.
At low RPM port velocity is also low in a 4 valve set-up. Honda's V-Tech is a working solution
for this short coming. Good intake velocity is in the range of 250 to 350 FPS.
F-1 works with 400+ FPS. Everything shuts down at 600 FPS because the resulting frequency
is the sound barrier...................:sun:

 

[cavemanmoron]

why not make the engine 2 stroke,so you need No valves!



like my snowmobile,it is 700 cc and makes about 115hp,maybe 118?

lots lighter than a 4 stroke.

 

[Bulk Beef]

Originally posted by: Linux23

Originally posted by: notfred

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

If you make the cylinder bigger than you don't really need to make it breathe more freely to get extra power out of it, you already did it by increasing displacement

yeah, but at higher RPM's, the valves open and close so fast, most engines have trouble breathing. DOHC helps to alleviate some of that, and that's one reason they have higher RPM's compared to their OHV counterparts. Now with TOHC, you have more valves to deliver more fuel/air, and you can also have different cam profile's for maximum torque and hp output.

No offense, but I don't think you know wtf you're talking about.

 

[Nyical]

Originally posted by: FrustratedUser

Originally posted by: Linux23

Originally posted by: notfred
How many valves can you fit in the average sized cylinder head?

i'm assuming 4, but if you make the cylinder bigger, and design the top of the head differently, you should be able to squeeze 6-valves in there.

You get 6 valves with DOHC, see F1.
Audi has 5 valves using DOHC.
TOHC is just too complicated without any gains.

Just more shiet that can go wrong and make a bigger repair bill.

 

[GalvanizedYankee]

Originally posted by: cavemanmoron
why not make the engine 2 stroke,so you need No valves!



like my snowmobile,it is 700 cc and makes about 115hp,maybe 118?

lots lighter than a 4 stroke.

Pollution! I wish it wasn't so. Strokers rock. Feeling the urge as it gets on the pipe, WOW!

Honda was working with a 2 stroke that injected its fuel through a hole in the cyl wall.
Just as the piston came up and covered the ports, fuel would squirt. It never made it out of
the lab.............

:frown: