Here's a follow-up to the 408C that Dave Mclain built and dyno tested
for local Pantera owner Glen Hartog (original post is at the bottom).
We got a chance to finish the dyno testing this past weekend 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
**********************************************************************
Original post:
I recently spent some time on the dyno at Dave McClain's shop in Cuba,
Missouri with a friend's 408 cube Cleveland stroker. Spec's on the
engine are:
4.030" bore
SCAT 4" cast crank
6" SCAT rods with SBC pin dimensions
dished forged pistons
approximately 10:1 compression
4V closed chamber heads milled/drilled for screw in studs and guideplates
Mid-Lift 1.73:1 roller rockers
springs with 140 lbs seat pressure 320 open (approx)
Ford over-the-counter aluminum dual plane (Boss 351C with Holley carb
pattern)
Boss 351 cast aluminum valve covers with screw-in Ford rubber grommets
and push-in K&N breather
Hooker Competition headers, 1 3/4" diameter by 27" long primaries,
3" diameter by 8" long collector (probably part number HOK-6920HKR)
12 inch long collector extensions and 3" inlet/outler Magnaflow mufflers
Mallory Unilite distributor with mechanical advance only
Boss 351C valve covers
Dave's dyno carb (Competition Carburetion 950HP carburetor, 4 corner
idle, no PCV port, did not use the dyno bellmouth)
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)
Crane steel distributor gear (0.531 inch ID to match Mallory distributor)
OEM Ford 5.0L hydraulic roller lifters and spider arrangement
The engine is destined for Glen's Pantera and he wanted to stick with
the Ford dual plane intake so he could retain the stock engine screen.
Knowing the Ford intake would be a limiting factor, Dave worked on the
poorer flowing runners to bring them closer to the better ones.
Surprisingly, the worst runners were not the lower plane runners but
the upper runners which "look" better. The divider was cut down and
the plenum entry blended back to help the worst runners. Two 4 hole
spacers and one open spacer was tried. Spacer height was limited to
1" since that's all that will fit under the stock Pantera engine
screen with Ford intake. The open spacer worked best but all peaked
right around 5500 RPM.
The heads are closed chamber 4V heads with some short side radius work,
a good valve job and stainless valves with 30 degree back cuts on intake
side only. Here's what they pulled on the flow bench:
351C-4V
lift int exh int int
#1 #1 #2 #3
.050 33.6 27.1 32.7 31.1
.100 64.7 55.9 64.6 64.1
.200 123.0 100.1 129.8 134.5
.300 188.5 138.9 195.1 200.2
.400 246.4 166.4 251.7 253.3
.500 294.5 182.7 296.5 294.6
.600 322.1 186.5 322.5 322.0
.700 333.3 185.2 338.9 330.2
Flowed at 10" and converted to 28", some porting (shortside radius work),
2.19"/1.71" diameter valves, no intake manifold or exhaust pipe. Intake
port area is 3.25 sq. in. Exhaust is 3.14 sq. in. Dave's got the data
for the rest of the ports but this all I could pull off the screen dumps.
Dave said the shortside radius was everything on the 4V heads. He also
opined the 2V short side was worse and would likely respond to similar
modifications.
Flow data for head with dual plane Ford intake and 780 Holley carb body:
351C-4V
lift int int int int int
port port port port port
#1 #2 #3 #4 #5
.200 124.0 127.4 133.0 128.9 126.4
.400 217.9 228.8 228.6 231.7 228.2
.600 258.9 270.5 271.7 282.4 271.9
.800 274.4 ----- 285.3 279.7 271.8
Running through the mufflers, on Mobil 93 octane premium, the best pulls
came with 28 degrees timing, the reworked Ford aluminum intake with a 1
inch open spacer. Corrected numbers are 468 horsepower at 5500rpm and
486lbs/ft at 4500. It was a cool day and the air density ratio was very
good, 98.17% for a 1.0238 correction factor. Air temp was 56 Degrees F,
humidity 36% and abs baro 29.26 in Hg. Very good conditions for the
1100ft altitude. Dave was an EMC contestant and said his dyno is known
to be about 4% conservative when compared to other setups. Our dyno pulls
were from 3000 to 6000 RPM and the engine makes 440 or more lbs/ft from
3100 to about 5600rpm. After that, the engine drops off. The intake
and the OEM Ford hydraulic roller lifters are the possible limiting factors
in this build so we plan to try the FRPP/Crane link bar lifters and a Holley
Strip Dominator intake manifold to see if wee can pull another 500 RPM or
so. Hoping to make 500 HP through the mufflers. Once we've satisfied our
curiosity, we'll try a 750DP and GTS Pantera headers and mufflers. Kirk
Evans did some header testing a while back and found the GTS headers were
pretty decent (compared to the other Pantera headers tested) but the
mufflers were pretty bad. We'll run the tests with and without mufflers.
Also, Dave thinks we'll only lose about 10 HP with the 750DP versus the
dyno carb. Interestingly, he didn't bother to jet the dyno carb on the
dyno, claiming his previous experience with that carb was that jetting only
made a slight difference in power.
We also tested a Blue Thunder high rise intake but it actually made less
power than the modified Ford intake. The Blue Thunder made 437 horsepower
and 463 ft-lbs torque, at 5500 and 3900rpm respectively. Adding a 1" open
spacer to the Blue Thunder helped the torque about 6 HP but horsepower
stayed the same. It would be interesting to see what Dave could do with
the Blue Thunder but we're going to try a Holley Strip Dominator single
plane, instead. The heads alone flow 322 CFM at 0.600" lift but when you
add the ported dual plane intake, spacer, and carb body the flow drops
into 270 to 280 CFM range. Dave used a neat trick for the manifold testing.
He used hardware store weather stripping instead of RTV or cork gaskets.
Cheap, easy and lasts long enough for the dyno pulls.
Earlier I had taken some A/B measurements on several intakes:
A B
Holley Strip Dominator 4 5/16 5 3/8
Blue Thunder 4 7/16 5 3/8
Ford aluminum dual plane 3 1/4 4 3/8
Weiand Xcelerator 2V 4 3/16 5 1/8
I know for a fact the Weiand Xcelerator 2V will clear the stock Pantera
screen with a 2 1/4" tall 14" diameter K&N element but there isn't a lot
of room beyond that. A slightly smaller diameter air cleaner (13") should
clear the decklid and allow a bit more space. At worst, Glen will have to
either mill the spacer or the intake 1/4" or try a different style air
cleaner. If he's so inclined, a taller engine screen (or spacers under
the stock screen) can be installed.
Dave mentioned the SCAT cast crank had a Cleveland snout and did not
require the Ford Motorsport snout spacer. If you call SCAT and ask,
they'll tell you the snout spacer is needed. Note that the SCAT forged
cranks may still need the snout spacer. My 4340 forged steel SCAT crank
did need it but that crank was made a year or so ago. I don't know if
they have separate FMS and Cleveland crank part numbers now or not for
the forged cranks. 6" Scat I beam rod with SBC pin dimensions were used
and the rods and pistons were light enough quite a bit of material had
to be removed from the counterweights on the SCAT 4 inch stroke cranks
to use the 28.2oz balance factor. It would take some heavy metal to
make it internally balanced. Everything ends up pretty light:
Piston 390 grams(with ring support)
Locks 4 grams
Rings 41 grams
Pin 117 grams
Rod Big End 437
Rod Small End 173
Bearing 37
Oil 3
Total: 1676 gram bob weight for a 50% balance factor.
On the initial fire up, we heard some noise. I suspected a roller
rocker was hitting the Boss valve cover baffle since I've had that
happen before. However, Dave said he had checked that and the baffle
had been clearanced. When we removed the valve cover, there were no
marks on the rockers so that wasn't the source. Also, the sound appeared
to be coming from multiple locations. After wondering if it was just
start up slap from the cold forged pistons, Dave bumped the engine over
with the starter while I watched for valve train interference and
noticed that some of pushrods were just brushing the guide plates.
Dave made the guide plate slots deeper and that took care of the
noise. Glen thought catching was worth the dyno cost. It's one of
those things easy to catch on the dyno (and hard to verify during mock
since the lifters aren't pumped up) but would be a pain to catch and
fix in the car. Required intake and exhaust pushrods are different
lengths, BTW. That's likely due to the different intake and exhaust
lobes.
I was surprised the Hooker Competition headers were only 1 3/4" primaries.
4V headers tend to be 1 7/8" since that covers the exhaust port better.
The Hooker Super Comps are 2" but that's too large for this engine.
Some 351C headers make a sharp down turn right at the flange to clear
the narrow Mustang shock towers but the Hookers came out a few inches
before turning down. Pantera headers come straight out but the primaries
are very short and the collectors very short and small in diameter (2 1/4"
outlet). Glen is buying a set of GTS Pantera headers which have 2"
primaries feeding into a tri-y type collector of 2 1/4" diamter outlet.
It will be interesting to see how big a hit we take on those relative to
the Hooker headers.
A friend has run both the OEM Ford lifters and the Ford Motorsport
M-6500-S58 retro-fit hydraulic roller lifters (made by Crane and
sold by them under part number 36532-16 but the FMS part number is
$30 cheaper through Summit Racing) and verified the lifters are
dimensionally identical. The pushrod cup is in the same location and
the plunger travel is the same so we can use the same pushrods. Marc
mentioned they set the pre-load a full turn, rather than the 1/2 turn
we were using. The full turn includes the setting of the locks (from
zero lash to locked in place). Marc also mentioned that is what Crane
recommends.
Since Glen is going to use the left-over stock parts to build a back-up
engine, he's going to buy a set of the Ford/Crane link bar lifters and
we can swap the OEM lifters to the back-up engine. With the Strip
Dominator and the Crane lifters, we should see if the stock lifters
are a limiting factor.
I've got all the flow data for the heads and intake so I'll run this
through Dynomation when I can spare the time and see how well it predicts
the trends.
Dan Jones
Original Post
