[DeTomaso] 408C on the dyno follow-up

[Daniel C Jones]

I made it back from Israel and got a chance to finish up dyno testing
Glen Hartog's 408C at Dave Mclain's shop in Cuba, Missouri.  This is a
10:1 compression street motor that had previously made 468 HP at 5500
RPM and 486lbs/ft at 4500 through the mufflers on 93 octane premium from
the local Mobil station.  The best pulls came with only 28 degrees total
timing and a ported Ford low rise dual plane aluminum intake manifold.
The engine makes 440 or more lbs/ft from 3100 to about 5600rpm but drops
off after that.  We knew the heads outflow the intake by a wide margin
so we suspected the intake may be holding back the combo.  However, the
Blue Thunder high rise dual plane we tried was not as good as the ported
Ford intake.  Given the heavy Cleveland valves and 1.73:1 rocker ratio,
we also suspected the OEM hydraulic lifters might not be up to the task
so we returned to finish the dyno session with a set of Crane link bar
hydraulic lifters (actually the Ford Motorsport part number lifters made
by Crane) and a Holley Strip Dominator single plane intake manifold.

We first tried the Holley Strip Dominator intake.  Equipped with a
one inch spacer, it moved the HP peak up slightly and made around 15 HP
more at the top than the OEM Ford intake.  I forget what it made without
the spacer but it was between the ported Ford intake with spacer and
the Strip Dominator with spacer.  Dave's got the numbers on his PC.
Dave opined that with more RPM, the difference would likely grow and
noted the Strip Dominator would benefit from some plenum entry work.
The torque curve with the Strip Dominator was smoother, likely due to
the Boss dual plane going into and out of tune.  I also brought along
an Edelbrock Torker and an Edelbrock A331 (raised port version of the
Torker that matches A3 Ford Motorsport high port heads).  It looked
like the A331 wouldn't seal at the bottom of the port without milling
it to drop it down, so we passed on testing it.  Though it doesn't have
much of a reputation on stock displacement 351C's, the Torker did pretty
well.  I forget the exact numbers but it was within a few HP of the
Strip Dominator.  Apparently it likes the extra cubes.

In the old (October 1993) Super Ford Article "Planes of Power",
the Strip Donminator made 498 HP at 6250 RPM.  The Torker was down
18 HP at 480 HP at 6750 RPM.  That engine was a 13.7:1 compression
ratio, 377 cube offset ground 351C crank, stroker with a Madden solid
roller cam of 264/270 degrees duration @ 0.050" lift and 0.723 inch
lift.  Not sure what the lobe centers were but springs were 210 lbs
on the seat and 510 lbs open.  Given the much larger cam and higher
compression ratio, that engine should have performed much better.
Glen's 10:1 compression ratio hydraulic roller cam motor made
substantially more torque (50+ ft-lbs) and a bit less HP at a lower
RPM.  Not a bad trade off for a pump gas motor expected to live a
long trouble free life on the street.

We didn't re-baseline the engine with the dual plane at the start,
so we slapped the ported Ford intake back on.  As mentioned above,
it was down around 15 HP to the Strip Dominator but the overall
numbers were also down relative to the first day of testing, even
though we had corrected for atmospheric conditions.

We next tried the Crane lifters.  They are dimensionally identical
to the Ford lifters so can be swapped without a pushrod change.  Dave
noted the custom length intake and exhaust pushrods on this engine are
slightly different in length.  During reassembly it was noticed that some
of the intake keepers showed signs of contact at lifter collapse so the
intake rocker arms were clearanced.  Once everything was buttoned back up,
the Crane lifters were tested and showed essentially no difference.  At
this point, we suspect the cam has too little duration to make peak power
at the desired 6000 RPM, though Dave mentioned increasing the intake valve
spring pressure would be worth a (future) test.  The cam specs are:

 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)

BTW, the cam is a stock base circle core though the exhaust base circle
is a bit smaller than the intake due to the lobe profile.

Up next was a test of the Pantera headers and exhaust.  We had baselined
the engine using a borrowed set of Hooker Competition headers (probably
part number HOK-6920HKR) with 1 3/4" diameter by 27" long primaries, 3"
diameter by 8" long collector with 12 inch long collector extensions and
3" inlet/outler Magnaflow stainless steel mufflers.  Glen had a set of
Euro GTS mufflers and had purchased the matching GTS headers from the
Pantera Performance Center.  These are nicely made with a thick flange
and ceramic coating.  The GTS headers are often refered to as tri-y's
but are, in fact, 4-into-1 headers with short tri-y collectors.  Like
most under-car Pantera headers, the primaries are very short.  The
collector is also quite short and relatively small in diameter, though
the primaries are large (2" diameter) and matched the port better than
the Mustang headers.  They also don't bend down at the head port exit
like the Mustang headers.  The GTS headers did pretty well.  Compared
to the Mustang long tubes, the GTS headers with a collector extension
was a near match.  Without the extension, they gave up some torque but
were close on HP.  Unfortunatey, the GTS mufflers were terrible and lost
some 50 HP compared to the 3" inlet/outlet MagnaFlows.  Though the body
of the GTS mufflers is short the tips are very long so the overall length
was a bit more than the much less restrictive MagnaFlows.  It looks like
the MagnaFlow muffler will fit under a Pantera and they make a version
with 3" inlet and dual 2.5" outlets which would retain the quad tip
Pantera look.  Given that the diameter of GTS collector outlet (looked
like 2 1/4" or 2 1/2" ID, I forget to measure it) is much less than the
3" pipes we used, it's possible a set of 2 1/2" pipes might not lose
any power compared to the 3" pipes.  Something to test on a future dyno
session, perhaps.  Glen likes the look of the GTS mufflers and plans on
gutting them to try gain back some of the lost power.

Finally, we tested an out-of-the-box Holley 750 double pumper.  Unlike
the vacuum secondary 750, the 750 DP uses down leg boosters (the vacuum
secondary version uses straight leg boosters).  We tried jetting it both
leaner and richer but the original jetting (71 primary jets, 80 secondary
jet with power valve on primary side only.  BTW, the carb has the HP type
reinforced metering blocks) made the most power.  It was down 10 or 11 HP
at the peak compared to the 950HP dyno carb, which is acceptable.  The
carbs were tested without the aid of a bellmouth, K&N stub stack or air
cleaner.  I had brought along a freebie 850 with annular boosters that
was in unknown condition.  We tossed it on for a quick test but it really
needs a rebuild kit.

We forgot to check the Crane steel distributor gear for wear but Dave
can do that before Glen picks up the engine.

Dan Jones