ALL things related to the Ford 351C
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PostPosted: Thu Apr 09, 2015 10:30 am 

Joined: Tue Oct 30, 2012 8:27 am
Posts: 64
Location: St. Louis, Missouri USA
In Hugh's build thread I referenced Mark Skwarek's 384C but I don't think I posted the build and results to the forum so here it is. Mark's previous engine was supposed to be a stroker but, when torn down, turned out to be a 0.030" over 351C with flat top pistons, Eagle rods and a stock 3.5" nodular iron crankshaft. Camshaft was a Competition Cams 308 Magnum roller which was being run with 1.6:1 ratio rockers and 0.020" intake and exhaust lash. Heads were closed chamber 4V that were filled on the intake side, along with port plates on the exhaust side. The intake was a Holley Strip Dominator with the floors raised to match the stuffed heads. Inspection revealed both heads were cracked and Mark needed headers so we had some we had some flexibility when it came to replacement cylinder heads. We ended up going with a set of Ford Motorsport A3 heads and a matching A331 intake that I had on hand. Plans were to test the raised floor Strip Dominator on the A3 heads but that didn't work out so Dave decided to do some work on the A331. Externally, the Edelbrock A331 looks like a Torker:


but has smaller A3 ports and no cross-over:


You can see how much smaller the A3 port is here:


That's a 4V gasket on top of an A3 port. What's not obvious is the A3 roof is higher (obscured behind the gasket). You can clearly see the evolution of the high port heads here:


On the left is an iron 4V modified with an aluminum high port exhaust port plate like they ran in Pro Stock. You can see the lower edge of the original exhaust port (painted blue). In the middle is an A3 port which is slightly higher with a more uniform round shape, instead of the weird area changes of the iron 4V port. At the right is a ported C302B. Note the C302B ports start out much smaller:


Based upon the iron Pro Stock 351C heads, the A3 ports were designed by Jack Roush, Bud Moore and Leonard Wood. As cast, they have the largest intake port volume (241 cc's) and exhaust port volume (134 cc's) of the high port family of Ford Motorsport heads:


There's a slight bend on intake port walls to accommodate the pushrods and the raised floor increases port radius, straightening the turn for incoming mixture and minimizing fuel separation. A3s can have a couple of different exhaust bolt patterns. Mark's heads have the later exhaust port bolt pattern and had some previous port work done. Before rebuilding them with new valves, Dave dropped in a pair of valves from Mark's old heads and put the A3s on the flow bench. He also flowed the 4V heads I could run the original engine through Dynomation for comparison purposes. Results were:

    .......A3.....A3.....Stuffed 4V

Ford Motorsport A3 High Port aluminum heads and port floor filled iron 4V heads tested on Dave McLain's SuperFlow flow bench at 10" and converted to 28". Clayed intake radius but no exhaust pipe. Tested on 4.030" diameter bore tube with a valve chamfer like a stock block. Valves used for testing were from one of Mark's old heads. As with most of the Cleveland heads we've tested, they generate little to no swirl motion. I didn't measure the port area on these A3 heads but they should be very close to the set I previously measured:

2.74 square inches minimum intake port area
1.88 square inches minimum exhaust port area
intake port 2.125" high by 1.725" wide (3.665 square inches)
exhaust port 1.65" high by 1.725"? wide (2.27 square inches)

In previous dyno testing, the Edelbrock Scorpion performed quite a bit better than the Torker. The Scorpion looks much like the Torker but is a couple of inches taller with a level carb pad. Since the Pantera mounts the engine level, Dave milled a 1" tall open spacer to level out the carb pad and welded it to the A331. The spacer also permits the porting to be extended higher up the plenum which allows larger, more gradual, radii into the tops of the runners. Dave had previously welded extensions onto the runner entries when we tested the A331 intake on my 403C. Based upon that testing, Dave decided to shorten the extensions. Several spacers were tested on dyno with the HVH 1" merge spacer being best. A simple 4 hole 1" spacer was also pretty good.

Mark races his Pantera in open road races like Silver State and the Pony Express but rarely runs it on the street. With his stock ZF gearing and tire diameter, he's RPM limited. A 3.75" stroke was chosen as it would have acceptable piston speed at maximum RPM while supporting his 550+ HP goal. Also, Mark wants to run on 92-93 octane pump gas and with the 3.75" stroke, flat top pistons and the A3 combustion chamber volume, the compression ratio worked out to be 11:1 which should work with pump gas, given the cam overlap. Previously, I wrote a program to calculate the speed in gear at a given shift point RPM, along with the RPM drop going into the next gear. Mark's Pantera has the Dash 2 ZF gearing:

1st gear = 2.23
2nd gear = 1.47
3rd gear = 1.04
4th gear = 0.846
5th gear = 0.705
final drive ratio = 4.22:1

He's running 315/35/17 tires with a calculated diameter of 25.68". Assuming a 7000 RPM shift point:

Shifting from 1st to 2nd, Fall Back Engine RPM = 4614 at 57 MPH
Shifting from 2nd to 3rd, Fall Back Engine RPM = 4952 at 86 MPH
Shifting from 3rd to 4th, Fall Back Engine RPM = 5964 at 122 MPH
Shifting from 4th to 5th, Fall Back Engine RPM = 5833 at 150.0 MPH

In 5th gear, 7000 RPM equates to 180 MPH. With the rev limiter set at 7200 RPM, that works out to 185 MPH. I also have some wind tunnel data on the Pantera (Ford tested a Pantera in a wind tunnel and the results were published in Issue 29 of the Italian design magazine "Style Auto"), along with a couple of other sources for a Pantera's frontal area and drag coefficient. I ran the numbers through a program I wrote to calculate power required to overcome aerodynamic drag and it was apparent that Mark's new engine would provide a bunch more power than required to peg the rev limiter in 5th gear. I also ran some brake specific fuel consumption figures and it looks like he could run out of fuel at the longer (90+ miles) open road races, if he was WOT the entire way, but I figure he can coast a long way from 185 MPH :-)

For this sort of application, Dave likes the Reed ULX line of solid roller lobes. The Reed ULX lobes are older designs that are relatively easy on the valve train, so work well in endurance racing and marine applications. Reed is no longer in business but Steve Demos has the lobes. I ran a cam optimization to optimize the average power between 4000 to 7000 RPM and crossed the result against the ULX lobe catalog, then ran several combinations of intake and exhaust lobes and lobe separation angles and sent the results to Dave. The cam picked was the smallest one which Dynomation predicted would be the best below 6000 RPM and close to the others on peak power. The simulation prediction was for just under 600 HP. Competition Cams solid roller lifters were chosen and, for Mark's usage, Dave recommends just changing them out every couple of years. Dave soaks the lifters in mineral spirits and blows them out 3 or 4 times to get all the assembly grease out, then soaks them in 10W-30 motor oil before installing them in the engine.

Given the sustained high RPM intended usage, several oiling system modifications were made. The right side only lifter bores were bushed and an 0.040" restrictor was placed in the back of the left side galley. The previous builder had fitted a plug under the front main bearing. Dave doesn't think that helps anything but it doesn't hurt either so he left it alone. Oil pump is a stock volume and pressure Melling M84A with a Melling oil pump drive shaft and a "10 quart" Aviad gated and baffles Pantera road race oil pan. Clearances were set at 0.0025" for the mains and 0.0022" for the rods using Federal Mogul main bearings and Clevite rod bearings.

For the cooling system, Dave made a plug with a 0.100" hole for the bypass passage in the block. A -4 AN line was run from the back of each head. They tee together and run to the suction side of the water pump where Dave put a 0.060" restrictor so that the engine always pulls coolant and any bubbles out of the back of the heads. Dave thinks that can be important in the Pantera because the engine sits level.

The MSD Pro Billet distributor from the original engine was re-used. It had the two light springs and the plain colored advance limiter bushing but wasn't very consistent so Dave locked out the timing which made the idle a lot better. On the dyno, without any flywheel mass, idle was 1200 RPM. Once it's in the car with a flywheel attached, idle can be set a bit lower. Timing was best at 30 degrees. With this much cam and only 11:1 static compression, it shouldn't be too hard to start. If Mark decided to put a curve back in the distributor, it needs to be really short. An aluminum-bronze gear was installed on the distributor and the gear on the cam de-burred to try to help make the gear last longer. Moderate heat range "Street" Autolite 3923's spark plugs were used on the dyno. In an aluminum headed application, they are hot enough to stay clean with normal driving and cold start/short trip use. For race use, Dave provided a set of AR 3910's which are about 2 heat ranges colder than the 3923's. Dave noted that engines can be quite sensitive to heat range. Several years ago he had a problem with this in a circle track engine. The customer had run the same plugs in the engine for over a season with no fouling or trouble of any kind. In the off season he changed to another car with a better chassis and Dave worked on the engine package to find some more power. He could run about four laps and burn up the plugs if the track was pretty heavy (dirt track). However, if the track was slightly slicker and had less grip the plugs would look perfect and never cause a problem. A data logger was installed on the car and the difference between the heavy and normal track as far as the engine went was almost non existent. The time the driver was off the throttle was only about 1/10 of a second less on the heavy track but it was enough to cause a problem where the plug would go from looking fine to absolutely burned up! Switching to something colder cured the problem and they still stay clean enough that he can run a set of plugs for most of a season.

The Ford Motorsport M-9439-A341 intake manifold gaskets for the A3 heads are no longer available. Fel Pro makes two intake gasket sets for the Motorsport high port heads. Though 1229 is listed for A3 heads, the port opening measures the close to C302B heads (1.35" x 2.20"). 1265 is listed for B351 and C302B heads but the port size is listed as 1.35" x 2.22". Both are "trim to fit" for the A3 heads. P/N 1229 has round holes on both ends in case coolant is run through the intake (Windsor block application). Both 1229 and 1265 of those are 0.060" thick. Fel Pro makes similar intake gaskets in thinner (p/n 12531 is 0.030", 12532 and 1253S2 are 0.045") and thicker (12535 is 0.120") sizes for Yates heads that could probably be adapted if you need to compensate for head or intake milling. On the exhaust side, Fel Pro makes two different header gaskets for high port heads. P/N 1417 is for the early exhaust bolt pattern and has a 1.94" diameter round port size. P/N 1431 is for the later pattern and has a 1.81" diameter round port size.

Dave initially ran the engine on his dyno carb, a Bobby Oliver built Holley 950 HP, to baseline against the annular booster Holley 830 from Mark's original engine. The Holley 830 is far from Dave's favorite carb. As supplied, it had 82 jets and no power valves. After considerable dyno tuning, it ended up with 92 and 96 jets with power valves front and rear. Generally speaking, taking the power valve out of the circuit makes you need to add about 10 or 12 jet sizes to make up the difference. Having to go so far on jetting usually indicates the carb (size/boosters) selected is wrong for the application. Given a choice, Dave would have opted for a Holley 4779 prepared by Competition Carburetion (Bobby Oliver) with a circle track/road racing package. This is about the same as their normal 4779 except for the float configuration and for adding a rear power valve. This reduces the jetting requirement in the rear which can help prevent loading up during a hard deceleration into a corner.

The overall parts list ended up looking like:

4.04" bore Probe forged flat top pistons (1/16", 1/16" with 3mm oil rings)
SCAT 4340 forged steel rods (6.125" long with 7/16" ARP bolts)
3.75" stroke Scat 4340 forged crankshaft, SVO (Windsor snout design with Cleveland main diameter) crankshaft, internally balanced (p/n: 4-351C-3750-6125)
4.04" bore x 3.75" stroke = 384.6 cubic inches
11:1 compression
Ford Motorsport A331 (modified by Dave McLain)
Ford Motorsport A3 high port aluminum Cleveland heads
SI stainless valves (2.19" intake, 1.71" exhaust)
Manley guide plates
1.73:1 ratio Competition Cams "gold" aluminum roller rockers
Jomar stud girdle
Solid roller cam using Reed ULX lobes:
254/258 @ 0.050" (R290ULX/R292ULX), 0.692"/0.701 less lash (0.024" and 0.026"), 110 LSA, 109 ICL
Competition Cams solid roller lifters
PBM/Erson 3850 chrome silicon double valve springs with dampers
Installed at 1.950", 223 lbs seat and 582 lbs open for the intake, 601 lbs for the exhaust
Comp Cams titanium retainers
Rollmaster timing set that's made for the Cleveland block/SVO style crank combination
Oiling mods are bushed lifter bores on the right side only with an 0.040" restrictor in the back of the left side galley
Stock volume and pressure Melling M84A oil pump, Melling oil pump drive shaft
Aviad Pantera gated and baffled road race oil pan
Clearances are 0.0025" mains 0.0022" rods using Federal Mogul mains and Clevite rod bearings
Main bearing size is 1/2 under and rods are -1 to get these clearances with the Scat forged steel crank
Romac 351C SFI spec harmonic damper, zero balance
Flow Kooler water pump
Cooling system modifications
0.100" diameter block bypass passage plug, petcocks in the back of the heads to let air out of the rear of the engine with a -4 AN line from each head that tees together and runs to the suction side of the water pump with a 0.060" restrictor so that the engine always pulls coolant and any bubbles out of the back of the heads
Cometic MLS head gaskets and Fel-Pro gaskets elsewhere
MSD Pro Billet mechanical advance distributor (small cap for Pantera firewall and rear window clearance) with aluminum-bronze distributor gear
Autolite 3923 spark plugs for street (moderate heat range), AR 3910 for race (about 2 heat ranges colder than the 3923s)
Precision Proformance high port 4-into-1 Pantera shorty headers
830 annular discharge Holley (from Mark's previous engine)
Ford Racing polished cast aluminum valve covers
double roller timing chain
neutral balance aluminum flywheel
custom length 0.080" wall push rods
Fuel pump block off plate (dyno providing the fuel flow)
Head bolts from Mark's original engine plus Grade 8's (and hardened washers) for the 4 extra long ones on the exhaust side

With Mark's carb, the best pull was 623 HP at 6800 to 6900 RPM and 521 ft-lbs at 5100 RPM through my Pantera 4-into-1 shorty high port headers and 2 1/2" diameter glass pack mufflers. The primaries on these range from 16 to 20 inches or so. Previous testing suggests the engine would make better power with 3" inlet/outlet Magnaflow mufflers and a cross-over (Hugh's 408C with A3 heads picked up a little over 20 horsepower and 10 lbs-ft of torque when the 2 1/2" glass packs were removed). Mark's original plan was to cut off the 2 1/2" collectors from the Pantera headers and weld on 3" diameter collectors but the dyno results with smaller collectors was good enough for Mark. He'll keep the stock collectors and run 3" inlet/outlet mufflers but may add a cross-over at a later date.

Dan Jones

Dan Jones
St. Louis, Missouri USA

Last edited by Daniel Jones on Tue Feb 22, 2022 12:01 pm, edited 1 time in total.

PostPosted: Tue Feb 22, 2022 6:10 am 

Joined: Tue Feb 22, 2022 6:01 am
Posts: 1
I think you mean Mark Skwarek.

Please correct and then delete this reply.

PostPosted: Tue Feb 22, 2022 12:03 pm 

Joined: Tue Oct 30, 2012 8:27 am
Posts: 64
Location: St. Louis, Missouri USA
Mea culpa. I've corrected the misspelling. Thanks, Dan

Dan Jones
St. Louis, Missouri USA

PostPosted: Fri Feb 25, 2022 8:36 am 

Joined: Mon Nov 05, 2012 3:54 pm
Posts: 132
Great info and post Dan!

Hey, where have you been? Good to see you back again.

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