[DeTomaso] Minimum Idle Vacuum?

[Daniel C Jones]

Art,

I'll ask Glen what his 408C makes for idle vacuum.  Since you want to
keep it under 6000 RPM, the cam that Kaase spec'd for Glen's engine
should be in the ballpark:

 Crane Cams grind number (custom):  HR-232/352-2S-8
 Intake  232 deg duration @ 0.050" tappet lift
         294 deg duration @ 0.004" tappet lift.
         0.609" lift with 1.73:1 rocker ratio
 Exhaust 236 deg duration @ 0.050" tappet lift
         298 deg duration @ 0.004" tappet lift.
         0.621" lift with 1.73:1 rocker ratio
 108 degrees lobe separation, intake centerline 103 ATDC
 degreed in at 102.25 intake centerline with new chain
 (should lose about .5 to 1 degree once timing chain loosens up)

On Glen's 408C with 4V heads and dual plane intake, it peaked in the
5500 to 5600 RPM range.  For best acceleration, you want to shift
something like 400 to 500 RPM above HP peak so that cam is in the
ballpark for your application.  I've not had a chance to drive it
yet but Glen says it doesn't lack for torque and pulls 5th gear just
fine at 1500 RPM.  IIRC, we started the dyno pulls at 3100 RPM at
which point it was making 440+ ft-lbs.  Peak was something like
486 ft-lbs.

Specifying the vacuum level will drive the lobe center angle that
Vizard's cam selection software returns.  If you didn't care about
idle vacuum, it would return something like 104 degrees LSA with a
shorter seat duration.  Setting it at Glen's level will probably
return a lobe separation similar to the one we used (108 degrees).
Vizard also suggests using a dual patter cam with the exhaust rocker
ratio about 0.1 shorter than the intake.  For the 351C, that usually
means running 1.73:1 intake and 1.65:1 exhaust, though 1.7:1 and
1.6:1 are also avialable.  Your CHI heads have smaller ports and a
better exhaust so I'd expect the difference between intake and
exhaust might be a bit less than Glen's but that might depend upon
the available lobes.

Dan Jones