[DeTomaso] 408C on the dyno follow-up

[Dave Doddek]

Dan, Two thing would be interesting next time you experiment.  One is my
modification to the GTS mufflers.  It would be intresting to see if it
improves performance and by how much if any.  The other would be to try a
Throttle body EFI system and see how it would compare in Horsepower. I have
the components that could set up such a system.

Dave "would love to have a dyno" D

At 10:16 AM 12/19/2006 -0600, you wrote:
>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
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