> how would you choose to freshen up this engine in terms of intake manifold, camshaft, etc.?
You might want to take a look at a similar build we did for a Pantera:
www.the351cforum.com ? View topic - Budget 351C Rebuild for Lori Drew
Economy rebuild with mild flat tappet hydraulic cam, Edelbrock Performer dual plane intake and Pantera shorty headers. The owner is very pleased with the engine and recently posted this:
"It's normally a three-hour drive, but traffic was light and moving at a constant 90 mph (!) for more than half the 165-mile distance so it took us barely two hours--a record for sure... It absolutely ran like a top the entire weekend. I am more and more impressed with the super budget Dan Jones/Dave McClain engine with each passing day...."
> Another question I have is how good are the original Cleveland exhaust manifolds?
In my dyno testing on a 6000 RPM street hydraulic roller cam 351C with unported iron 4V heads, we lost 36 HP and 30+ ft-lbs with iron 4V cast iron manifolds compared to 1 3/4" primary diameter (3" diameter collector) Hooker Competition headers (Mustang/Cougar chassis). The worst of the mufflers lost 50 HP compared to the best (Magnaflows). The big lesson learned in that series of tests was that you can throw away most of the power gain a cam/carb/intake swap with a poor exhaust.
> would be worth the hassle and expense to switch to headers if I keep the original heads and keep the engine pretty mild.
On a mild engine, stay away from the 2" primary diameter and large collector stuff. They can kill the low end and not recover until 5500 RPM or so. For an application like yours, I'd use 1 3/4" primary headers with 3" (or even smaller) collector.
> If you were going to keep the original iron heads (I looked up the date codes, they are January 1970 castings, 4V closed chamber heads),
First replace the OEM valves. The stock valves are made from two pieces, friction welded together and use loose fitting multi-groove keepers (the keepers halves contact each other instead of being wedged against the stem by retainer). If the valves don't slip out of the keeper, they'll pop the head off the stem. Unfortunately, I learned this lesson the hard way. My very first 351C rebuild (flat top pistons, closed chamber heads, standard bore block, performance cam and springs, headers) lasted only a few hours before the head of an exhaust valve detached from the stem. It fell into the cylinder, bounced around until it shattered the cast piston and damaged the head. Coolant then filled the cylinder and the rod punched a fist size hole in the side of the engine block. Lifting the hood while the engine was running revealed the rod still going up and down in the ventilated cylinder with coolant and oil gushing out.
If you retain the stock rocker arms, make sure the sled fulcrums are steel. The 4V were generally steel but some Cleveland heads came with aluminum fulcrums which can wear and fail. Also, there are two types of stock rocker arms. The ones that are smooth on top are okay but the ones that have lugs on them have a pushrod-to-rocker arm clearance problem with high lift cams (0.550" lift or so). See the linked write up for pictures of each style.
Umbrella valve seals will get brittle over time. They can crack into pieces, fall into the oil pan then gut sucked through the bypass hole in the pickup. This can momentarily jam the oil pump and bend or shear the pin in distributor gear (or even twist the oil pump driveshaft). Later 351M/400 oil pump pickups use a mesh screen without a bypass hole. These can be substituted in place of the 351C pickup. For a little extra insurance, you can drive a second shear pin in the distributor gear or replace with a hardened pin. For your purposes, a stock displacement oil pump will be fine. High volume pumps can pump too much oil to the top of the engine, especially with a stock capacity oil pan, starving the bearings. A heavy duty oil pump driveshaft is worthwhile. The Boss/HO/CJ oil pans came with an integral scraper.
Check your distributor gear closely for wear. If you have to replace it, be aware the parts store cast iron gears are junk. A friend Rockwell (B scale) tested several distributor gears. A generic auto parts cast iron gear tested at 70, an aluimnum-bronze gear at 90, and the stock Ford gear was 102. Note that the soft sacrificial aluminum bronze gear was harder than the generic auto parts cast iron gear. Check the cam and distributor gears for proper contact pattern. You may have to adjust the position of the gear on the distributor so that it has the proper end play (make sure it doesn't rub hard on the block). Also, it's worthwhile to pull the distributor after a few hundred miles to check the wear pattern. Make sure you use the proper distributor gear material for the cam core. Cast iron cores require cast iron gears, steel cores require steel or bronze gears. Make sure the oil feed hole from front main bearing is open (improperly installed cam bearings can block the oil feed passage to the gear mesh). You can drill an 0.030" hole in the main oil gallery plug just behind the gear mesh to pressure-oil the cam/distributor mesh.
The usual Ford oil filter has a bypass valve built into the filter which can allow unfiltered oil to bypass the filter. The bypass can also fail, causing a loss of oil pressure. Consider using Purolator oil filter number L30119. It's a full size replacement for the FL-1A Ford/PH8A Fram filter. It has no bypass spring in the middle but it does have the rubber flapper for anti-drainback. The original application is for a 1978 Nissan 510, 2.0L 4 cyl engine (L20B) which had the bypass valve in the engine block. This filter cross-references to a Fram PH2850, a Motorcraft FL-181, and a Wix 51452. However, those filters have not been verified and may still have the bypass. It appears after 1978, Nissan went to a half height filter. Purolator part number L22167 fits that application and does not have the bypass spring but does have the rubber flapper for anti-drainback.
Use a Cleveland specific thermostat. They have a shoulder which is sized to match the brass restrictor ring in the block (make sure it's there) which other thermostats do not have. Using a Windsor thermostat (which the parts counter guy will often mistakenly give you) will lead to over-heating because a potion of coolant will bypass the radiator. Don't run an excessively cool thermostat. It won't make a difference in steady state temperature but will slow warm-up time and increase cylinder wall wear.
After 48 years, the rubber in the original balancer can be dry-rotted. The balancer is made of an inner hub and an outer ring. In between is a rubber bond (elastomer). Over the years, the rubber can dry out and crack. Eventually, the rubber bond will fail and the ring can slip relative to the hub. This will un-balance the engine. Worse, the ring can completely separate and spin off the hub at high speed. You can do a visual inspection for cracks in the rubber bond and trim the rubber back with a knife to see how far the cracks travel. I do recommend replacing it but, at a minimum, you can paint a stripe on the balancer and keep an eye on it to see if the ring slips relative to the balancer. Cleveland balance factor is 28.2 oz-in. Stay away from gimmick dampers (TCI Rattler, Fluidamper, etc.). Stick with good quality rubber elastomer type balancer (SVO/ATI, Romac, Pioneer, etc.). Also, your original balancer can be rebuilt.
The stock timing set uses nylon coated aluminum timing gears. The gears can shed teeth and the chain can slip. Install a good quality double row true roller timing chain set. Be aware that most companies that sell timing chains simply package chains and sprockets from various suppliers. A bunch of the aftermarket companies are selling sets that use poor quality chain from India (Rolon). I disassembled a 351C with approximately 8000 miles on a Rolon chain. It was worn worse than the one I pulled from my 5.0L at 163,000 miles. Look on the chain links and avoid any that say Rolon. Iwis (Germany) is among the best. Renold (France), Morse (US and Mexico) and Daido and Tsubaki (Japan) are also quite good. Cloyes (US) is decent too but they use Iwis and Renold in their high end sets. FWIW, the Ford Motorsport 351C timing sets I've purchased have used the Renold chain but that can change so you must verify.
You'll want to remove the core plugs and mount the block on an engine stand to flush the water jackets with water and compressed air. The water jackets can be full of sand and casting slag. Be careful not to nick the cam bearings (use a cam holder) removing the old cam and installing the new one. If the cam bearings pass spec, keep them. If you have to install new cam bearings, don't be surprised if they are too tight. Cleveland cam bearings were honed in the block by the factory and new ones are often too tight and require fitting. You can cut grooves on an old Cleveland cam to use as a scraper or have a machine shop hone to fit.
If you are still running points, you might want to switch to electronic ignition. A number of ways to go here. For the 351C dual point distributors vacuum advance distributors, Pertronix is the only drop in electronic ignition conversion I know of. Also, the weights in FoMoCo 351C distributors are reversible. To quicken the advance curve, flip the weights and do a spring change.
If you stick with a flat tappet cam for cost reasons, the usual flat tappet caveats apply. With flat tappet cams, you must be very careful to get the cam lobes and lifters to break in properly. Follow the cam manufacturer's break-in procedure. Use plenty of cam lube on the lifter faces and cam lobes and make sure the oil you use has plenty of the anti-scuffing additive ZDDP (preferably blended in by the manufacturer so it plays well with the total additive package, not added in). Also, set the pre-load using the SAE method, not the Ford repair manual method (only applies to low overlap cams). Remember, paranoia is the engine builder's best friend!
My preference for head gaskets are Victor Reinz (Clevite/Mahle) 3502SG which is Nitroseal material graphite on steel core. I like the Fel Pro performance gasket set for everything else.
Total up what it will cost to rebuild your iron closed chamber heads (valves, locks, keepers, valve job, guides and seats if necessary) and the $350+ you can get from selling them to figure out if it's cost effective to switch to an aftermarket cylinder head. In recent testing on a street 351C we gained around 90 HP with TFS 195cc 351C-2V heads compared to iron 4V heads.
We tested the Edelbrock Performer with several spacers on the 351C dyno mule. It really responded to the 1" HVH Super Sucker tapered 4 hole spacer and picked up 10 HP and 15 ft-lbs of torque. The engine also responded to the MPG Stinger exhaust port stuffers. Intake choice is often limited by hood clearance. Here are some A/B height measurements I've made of dual plane Cleveland intake manifolds. The measurements represent the drop from a straight edge laid across the carb pad to the closest point where the end rail bends inward (each end). Measurements are in inches:
A B
Ford aluminum 4V 3 1/4 4 3/8
Edelbrock Performer LB 3 1/2 4 3/8
Scott Cook dual plane 3 3/4 5
Edelbrock Performer RPM Air Gap 2V 4 1/2 5 5/8
Blue Thunder/Shelby/Holman Moody 4 7/16 5 3/8
We've tested these all of these intakes. The Ford aluminum dual plane (over-the-counter Holley carb version), Edelbrock Performer and Blue Thunder all suffer from having four bad runners and four good runners. All three can be improved by porting work that brings the bad runners up to match the good runners. In one of our tests, a ported Ford dual plane made 31 HP and 25 ft-lbs more than an unported Blue Thunder. In another test, a ported Blue Thunder made 45 HP more than an unported Edelbrock Performer. The Performer is usually 10 to 20 HP better (and similar torque) than the iron 4V intake across the RPM range. The Performer RPM Air Gap is a great all around intake on a combination like this (has good flow to all runners out of the box) but is relatively tall and doesn't have a heated exhaust cross-over. A good single plane like the Holley Strip Dominator will usually make more peak HP than the Edelbrock RPM Air Gap but the Air Gap can be close on peak power but make much better peak torque. In one test, the RPM Air Gap was down 5 HP at peak but made 44 ft-lbs of torque than the Strip Dominator at 4000 RPM.
Dan Jones
