[DeTomaso] NPC: DOHC or Pushrod holy war.....Was: New CorvetteEngine

[JDeRyke at aol.com]

In a message dated 6/4/11 7:35:16 AM, wkooiman at earthlink.net writes:

> DOHC has many advantages - rev higher, more hp per cubic inch, etc. - but 
> it comes at the cost of more complexity......
> The other problem is the complexity doesn't seem to be worth it.
> 
Agreed. A DOHC's advantage is smaller mass valves for good breathing, which 
translates to higher possible rpms for a given displacement and better high 
rpm power. The problem in most DOHC motors is, manufacturers spend all 
their development money on the heads and cut corners on the bottom end.... where 
high rpms need better design and materials. So you get an artificially low 
redline.
This results in stock Ford or Maserati DOHC engines that redline at 6500- 
about the same as an equivalent 2-valve pushrod motor. Sure- DOHCs can be 
modified to much higher potential rpms, but so can the pushrod engine- and the 
mods are cheaper. The second problem is weight and mass: an all-aluminum 
DOHC V-8 will ALWAYS weigh more- sometimes much more and be far more bulky than 

non-hemi-design pushrod engines of the same displacement. The biggest Ford 
DOHC -the all aluminum 5.4 (331 cubic inch) weighs 650 lbs while the 
all-iron Ford pushrod 5.7 (351 cubic inch) weighs 550 (weights from Fords website). 
In a Pantera engine bay, the bulky DOHC looks like a Chrysler Hemi. 
Power outputs are equivalent as would be mileage if the pushrod engine were 
computer controlled to the same extent- not strictly part of the engine 
design. The final DOHC problem- for fixed-income-guys- is the 3X cost in 
modifying the things. A cam change is around $700 in a DOHC while in the Cleveland 
it's maybe $250.
It'll be a while before I get into DOHC engines, I'm afraid. Winning the 
lottery seems vital.... My 2¢- J DeRyke