DeTomaso Mailing List: February 99, Message #147

>Maybe I misunderstood, I can admit that.  But you have to admit that
>a serious shop, experienced in building multi-cam race motors for top
>competition, could create 600 HP out of the normally aspirated motor
>in full race trim. 

For reference, you might want to read SAE paper #942474, by Dan
Yerace (Ford Motor Company) and Dennis Corn (Roush Industries).
The paper documents a maximum effort, normally aspirated, DOHC 
modular motor.  They had to spin it to 8200 rpm to get 600 HP.
It lasted for one dyno pull.

Understand that nearly every component of that engine was custom
made.  There was a redesigned FWD aluminum block, a machined main cap 
girdle (replacing the cross-bolts on the main caps), an 8-counterweight

steel billet crank, custom forged pistons, forged connecting rods,
redesigned head castings, smaller base circle cams and follower gear
(to reduce the follower roller speed), dual valve springs and Titanium
retainers, mechanical valve lash and cam chain adjusters, dry sump,
custom intake and exhaust, blah, blah, blah.

Modern production engines are designed to meet a specific target,
with the aid of computer aided design and manufacturing.  All the
components tend to be matched to the desired performance goal.
Changing just one component (like an intake or cam) in the system
may not yield the payoff it once did.  Also, they tend to not be 
overbuilt.  According to the SAE paper, the 4.6 DOHC was designed
for maximum output levels of 100 BHP/L.  Beyond that, you're facing
replacing a lot of expensive parts.  

The modular motors were not designed to be user serviceable, either.
No room to be bored.  Non-rebuildable connecting rods.  Oddball 
valve springs, press-lobe hollow core camshafts (four of them
and not one of them cheap), etc, etc.  Even if they were easy to work 
on, they've got some basic design features that make them less than 
attractive.  The small bore limits valve area and thus the maximum 
air flow.  A long stroke limits safe rpm, especially in the 5.4L 
version which gets its additional displacement all from stroke. 

According to a Ford engineer, the highest output DOHC heads ever 
massaged by Ford flow less than an unported Yates or A3 head.  
They were based on custom cores with one inch raised ports that 
were completely modified for an all out race effort (for the SCORE 
off road truck series).

Oh, but they sure are shiney.

Later,
Dan Jones