Tech / Tech Articles

Cleveland Show: Adding Nearly 100 HP to a Free-Breathing Ford 351C

Try this experiment: Mention four-valve (4V) Ford to a few fellow enthusiasts and see what discussion pops up.

Oh, how quickly people forget! Time was when you mentioned 4V, people immediately thought of the 351 Cleveland, and the massive port openings offered by those amazing cylinder heads.

Compared to the pedestrian 2V versions, the mighty 4V heads (and intakes) reigned supreme, a fact illustrated by usage on all the top factory performance Cleveland motors. While Ford abandoned the Cleveland early on in the US, it continued to power hot motors down under in Australia for many years!

Today, the 4V designation best differentiates the 4.6L Modular Ford family from the lesser 2V combos, or conjures up a conversation on 5.0L Coyotes. Sure, time and technology have certainly marched on, and the modern 4V Coyote is head and shoulders more powerful than any factory Cleveland, but ask yourself (and your friends) this: How many NASCAR races have a Coyote ever won? For many, particularly the boys down under, 4V means ONE thing, Cleveland performance.     

For those unfamiliar with the fabulous Ford 4V, the question has to be, what exactly made the Cleveland so special? In short, what did the 351 Cleveland motor have that the other Fords (like the Windsor), or even the competition over at Chevy and Dodge, didn’t?

The answer was simple, the Cleveland family–and the 4V version more specifically–offered massive head flow.

The 351C 4V motors, and even the smaller 1969 & 1970 Boss 302, offered head flow unmatched by any (regular) production small block Ford, Chevy, or Dodge heads of the period. To put this flow into perspective, a 1987-95 5.0L Ford (E7TE) head flowed 155-160 cfm, and a Chevy Fuelie head might flow 210 cfm.

The as-cast, production Boss/351C 4V heads flowed a whopping 275 cfm!

Combine cylinder head flow with proper cam timing and a decent inductions system, and you have the makings of a serious performer. One need only look at the current crop of modern Coyote, LS/LT and Hemi motors to understand the importance placed on head flow by the manufacturers.

For this test, we wanted to illustrate just how much power was lurking in the massive 4V Cleveland heads, so we put together a near-stock displacement test motor. The original 4V, 2-bolt, 351C was disassembled and treated to some first-class machine work by L&R Automotive. The machine work included boring and honing the block to accept a fresh set of .030-over, forged slugs.

Probe Racing supplied the small-dome, forged pistons, which also featured the necessary valve reliefs for more aggressive cam profiles. The 11.0:1 Probe pistons were designed for use with the stock connecting rods. Before assembly, the stock rods were treated to polishing, shot-peening and a set of ARP rod bolts. The forged pistons and reconditioned rods were teamed with a factory cast (polished and balanced) crank. We finished up the short block with a reproduction (hydraulic flat-tappet) 351 Cobra Jet cam from Elgin.

Topping our .030-over, 351C short block was the real success of the Cleveland engine family: the 1971 4V heads. These 1971 heads got us half way to our performance goal, by featuring the desirable (smaller) quench chambers. They did, however, lack the adjustable valve train offered on the performance-oriented, solid-cammed (hard to find) Boss 351 heads. Lucky for us, this was easily cured, as L&R simply machined the non-adjustable pedestals to accept rocker studs and guideplates.

True Cleveland enthusiasts might recognize the fact that we could well have run both the hydraulic flat-tappet, 351 CJ and upgraded Comp cams with the non-adjustable valve train. But we liked the idea of having an adjustable valve train and planned to run roller rockers on this Cleveland later on. The 351C 4V heads were also treated to a new set of stainless steel (intake and exhaust) SI valves, with the more-common single grove keeper to replace the factory multi-groove versions. The heads were also treated to a multi-angle valve job and surfacing (63-cc chambers) prior to installation 

To show the stock 4V heads had plenty of offer, we first ran the Cleveland with the factory, iron 4V intake manifold and 750 Holley carburetor. The original manifold was designed to accept an Autolite carb, but the Holley carb upgrade required only the installation of a gasket and spacer. Also present during testing on the Cleveland was a Meziere electric water pump, MSD distributor and amplifier and a set of 1 7/8-inch Hooker Super Comp headers.

Run first with the stock 4V intake and mild CJ cam, the Cleveland produced 359 horsepower at 5,700 rpm and 372 ft.-lbs. of torque at 3,800 rpm. After our baseline, we replaced the Elgin CJ cam and 4V intake with a Comp XE284H cam and Edelbrock Performer RPM Air Gap intake. The Comp Cam offered a .584/.588 lift split, a 240/246-degree duration split and 110-degree LSA. The Edelbrock intake was actually designed for the smaller-port, aluminum Edelbrock heads, but worked well on the larger 4V heads.

Demonstrating that the stock 4V heads had much more power to offer, the cam and intake upgrade increased the power output by nearly 100 horsepower, pushing the peaks to 452 horsepower and 412 ft.-lbs. of torque. Given the flow rates, even this modified 351C was just scratching the surface of what OG 4V heads will support!            

How is it you can easily add nearly 100 hp to your 351 Cleveland?

The answer lies in the massive head flow offered by the 4V heads. With 275 cfm at your disposal, the 351C offered the most cylinder head flow of any production small block. What this means is that they respond very well to other performance mods, like a healthy cam and improved induction system. After replacing the stock, iron intake manifold and repro-CJ cam in our .030-over 351C, we were rewarded with a jump in power from 359 horsepower and 372 ft.-lbs. to 452 horsepower and 412 ft.-lbs. of torque. As expected of a healthy cam upgrade, both peak hp and torque occurred higher in the rev range, but the new combo only experienced losses below 3,300 rpm.

Follow along with the entire process here:

Nothing looks or sounds like the 4V Cleveland, and the only thing better than a stock one is a modified one!
The 2-bolt, 351C block was first cleaned then treated to some much-needed machine work. We combined .030 over, Probe (forged) pistons with the stock (polished) cast crank and reconditioned, stock rods. The small dome on the forged pistons produced a healthy static compression ratio of 11.0:1.
For our baseline, we installed a reproduction 351CJ cam from the boys at Elgin. Understandably mild, the hydraulic flat-tappet cam offered a .481/.490 lift split and (roughly) 206/221-degree duration split @ .050.
Though our core motor was originally equipped with non-adjustable (hyd cam) 4V heads, we upgraded them with screw-in studs and guide plates.
To get things started, we equipped the 351CJ motor with a factory, cast-iron 4V intake.
Since we lacked a factory Autolite carb, we installed a Holley 750 in its place.
After a break-in, we ran the motor with the factory Cobra Jet cam, 4V intake and 1 7/8-inch Hooker Super Comp headers. After dialing in the timing and jetting, we were rewarded with peak numbers of 359 hp and 372 lb-ft of torque. The question now, how much more power was hiding in this combo?
To prep for the intake and cam upgrade, we removed the (heavy) cast-iron intake and valve covers.
We then loosened the oil pan bolts, removed the damper, water pump and timing cover.
We replaced the factory 351CJ cam with a much stouter grind from Comp Cams. The XE284H offered a much more aggressive .584/.588 lift split, a 240/246 duration split at .050 and 110-degree lsa.
The aluminum Edelbrock Performer RPM Air Gap intake was a welcome upgrade to the hefty, cast-iron factory intake. The dual-plane design offered a broad torque curve with plenty of peak power.
This shot shows the difference in port size between the 4V gaskets and the smaller port opening on the Edelbrock intake. They originally designed their RPM Air Gap intake for use on their own Cleveland heads.
Adding the Comp XE284 cam and Edelbrock RPM intake improved the power output substantially. The peak power output of the 4V Cleveland jumped from 359 hp and 372 lb-ft of torque to 452 hp and 412 lb-ft of torque. Who doesn’t want an extra 100 hp, especially when it comes with an extra helping of torque.

   

7 Comments

  1. Pingback: Cleveland Show: Adding Nearly 100 HP to a Free-Breathing Ford 351C

  2. I’ve only had the opportunity to build one Cleveland. Was a 71 cj. Done the same as article with the exception of slightly larger crane solid lifter cam & an old school torquer intake & H/S rockers . Wow no dyno but that thing pulled like a Bear 3500/ 7500ish! Very impressed. Gonna build another a little more aggressive for a road race tribute 68 mustang. Can’t wait.

  3. Mike+Brown says:

    The very first sentence of this article is WRONG! 4V Ford Cleveland heads NEVER had 4 valves. We all know that 4V stands for 4 venturi, a.k.a. 4 barrel carburetor. I’m not doubting that this build produced a very strong engine but, c’mon Summit…do some proof reading before posting something like this!

  4. The offenhauser power port short runner tunnel ram with twin 600 Holley vac sec carbs, 12.4 trw pistons, and 108 lobe center sig Erson hi flow I M cam running AV gas was absolutely a rocket ship on the street. Could be duplicated better with new technology. Try it you’ll like it!

  5. What kind of fuel are you running to make this much horses

  6. Charles Grimes says:

    How do i get more hp with 351w

Leave a Reply

Your email address will not be published. Required fields are marked *

*

This site uses Akismet to reduce spam. Learn how your comment data is processed.