Should GM abandon DOHC for TCC?

[dwightlooi]

For almost a decade and a half, the Dual Over Head Cams (DOHC) configuration dominated engine designs from foreign and domestic manufacturers. However, the DOHC layout is not without its flaws. Let's examine its advantageous and disadvantageous.

Advantageous of DOHC

• DOHC heads allow independent Intake and Exhaust Cam Phasing
  
• DOHC heads allow centrally located spark plug
  
• DOHC heads support cross-flow, 4-valve configurations
  
• DOHC heads support minimum actuated valve train mass
  

Disadvantageous of DOHC

• DOHC heads are very wide, this produces heavy and bulky engines (especially with V6 and V8 configurations)
  
• DOHC heads have more cam sprockets, more cam bearings and more frictional drag than SOHC or IBC configurations
  

Enter the Twin Concentric Cam (TCC). This was first seen in a production vehicle on the Dodge Viper 8.4 VVT V10. http://www.mechadyne-int.com/vva-products/concentric-camshafts Basically, it is one camshaft within another. The cam sprocket drives the hollow intake cam via a cam phaser. The exhuast cam resides inside the intake cam and is driven by a second cam phaser connecting the intake to the exhaust cam. The exhaust cam lobes slip over the intake camshaft and is connected to the inner exhaust cam by steel pins going through slots in the outer cam. This design allows the Dodge to implement dual cam independent VVT on what was a traditional pushrod SIBC engine. However, the TCC layout can also be used in overhead cam engines. In this case, the engine will resemble an SOHC engine, except that the "SOHC" is actually two concentric camshafts occupying the same space as a single overhead cam would. This allows the engine to enjoy the traditional benefits of an SOHC layout such as compactness and lower frictional drag, while also enjoying the one thing SOHC designs traditionally cannot support -- Independent Dual Cam Phasing.

Advantageous of TCC

• TCC heads allow independent Intake and Exhaust Cam Phasing
  
• TCC heads allow centrally located spark plug
  
• TCC heads support cross-flow, 4-valve configurations
  
• TCC heads are as narrow as SOHC heads
  
• TCC heads have the same low friction characteristics of SOHC heads
  
• TCC can also be used in a Pushrod IBC configuration
  

Disadvantageous of TCC

• Actuated Valve Train mass is similar to SOHC designs and slightly heavier than with DOHC designs (not a problem up to 7000 rpm)
  

In short, TCC heads can be used across the board to replace DOHC heads in Inline-4s and V6es. It can also be used to replace the single in block cam in Pushrod engines. The arrangement is particularly neat in that one cam phaser can be on the front of the engine while the other is on the back of the engine. This promotes excellent packaging. In overhead cam applications, the engines enjoy lower frictional loses, better efficiency and slimmer heads compared to DOHC designs. In Pushrod applications, the engines enjoy dual independent VVT.

[dado]

Disadvantageous of DOHC[/b]

[*] DOHC heads are very wide, this produces heavy and bulky engines (especially with V6 and V8 configurations)

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I think engine such as 3.8 l v8 from MCLaren MP4 (V8 with twin turbo) isn't heavy and very wide at all. But on the other hand..price probably isn't small.

Edited August 13, 2010 by dado

[Carguy]

I had forgotten about that Viper camshaft thing being so advanced. If this could be done to the next gen small block in V6 and V8 versions. I could see a new DI and AFM OHV Cadillac engine line of slower turning,large sized for torque and efficient power. The serge of torque would be like American cars of old and unlike the Asian or European brands and uniquely American as Cadillac should be!

[dwightlooi]

I had forgotten about that Viper camshaft thing being so advanced. If this could be done to the next gen small block in V6 and V8 versions. I could see a new DI and AFM OHV Cadillac engine line of slower turning,large sized for torque and efficient power. The serge of torque would be like American cars of old and unlike the Asian or European brands and uniquely American as Cadillac should be!

Actually, I am thinking that it can be used to give the Ecotecs and HF V6es a more (fuel) efficient SOHC like head.

[Drew Dowdell]

Couldn't it also be used to give pushrod V6es a new lease on life?

[Robert Hall]

I had forgotten about that Viper camshaft thing being so advanced. If this could be done to the next gen small block in V6 and V8 versions. I could see a new DI and AFM OHV Cadillac engine line of slower turning,large sized for torque and efficient power. The serge of torque would be like American cars of old and unlike the Asian or European brands and uniquely American as Cadillac should be!

I wonder if this techology is history w/ the demise of the Viper..haven't read anything about it migrating to their Hemi V8s.

[Carguy]

I wonder if this techology is history w/ the demise of the Viper..haven't read anything about it migrating to their Hemi V8s.

I hope this tech is not lost. If Chrysler does nothing with it then GM should!

[dwightlooi]

I wonder if this techology is history w/ the demise of the Viper..haven't read anything about it migrating to their Hemi V8s.

(1) Chrysler doesn't own the patents to it. It was actually developed by an independent company.

(2) GM has stipulated that it will have DI and VVT on the Gen V small block, if that VVT is dual independent this my be what they are using anyway to achieve that.

(3) However, this can also be used to replace DOHC heads with heads with the friction and packaging advantageous of an SOHC design, without giving up 4-valve induction and dual independent VVT. In essence its the best of both worlds. Well, it probably won't support more than 7000~7500 rpm or so, but for most production 4-valve engines that is "enough" rev capability.