[DeTomaso] carb question

[JDeRyke at aol.com]

Demon carbs flow more mixture than the same number Holleys, because Demons 
are flow-tested 'wet' while Holleys & most others are flow-tested dry. The 
liquid entrained in Demon air streams takes up space. So a 750 Demon is 
'some' amount larger than a 750 Holley (factors vary). Second, ALL double-pumpers 
are race carbs so Holley expects you to tune them. To this end, they are 
set up rich for use at sea level. Out-of-the-box, you may only get 8-10 mpg 
but decent power. The tuning comes from getting 18+ mpg and the same or more 
power. 
Bolted-on vacuum-secondary 750 Holleys are well known to add around 30 bhp 
and drop mileage by about 4 mpg over a 600 vac-sec. Around town, a 750 feels 
lazy while a 600 feels snappy on the same engine. New autocrossers often 
start with 950s and work their way down to a 600, gaining speed with each 
change to a smaller carb. There are nationally successful competition Shelby 
Mustangs running 600 Holleys. Autocrossing simulates vigorous around-town 
driving, not WOT drag or road racing where 750s & up excel. 

After spending months trying to 'tune' a new 750 Holley on a Pantera, I 
gave up, sold the thing at a loss and bought a brand new tuner-Holley 700 
double pumper from Larry Stock's Pantera Parts. Out of the box, this carb gave 20 
mpg on a long run to Las Vegas, with enough power to break the tires loose 
in 2nd & 3rd with only a mild push on the pedal. The carb has some 30 
internal modifications to the basic assembly including a dyno check-run on a 351-C 
Pantera engine (not mine). Tuner carbs cost $700-up and IMHO are worth it, 
unless -A- you feel really lucky or -B- you intend to take up a new career 
as a carb tuner working 8 hrs a day at it. I personally have other things 
that need doing. Good luck, Boyd- J Deryke