Engine Rebuild 1970 351C-4V Cyl. Head and Cam Questions

My 1970 Cougar with an original 351C-4V and FMX has started burning a lot of oil and a quick compression check of a couple of accessible cylinders (one at 170 and the other at 80) has started me on rebuilding the engine. I’m looking at some possible moderate changes. The car is for street and highway driving so nothing extreme or adding a lot of cost is of interest. It does have Holley Sniper EFI and MSD 6EFI variable timing ignition. I’ve found a competent engine machine shop here in Houston to rebuild the short block but need to define these two items.
Cylinder Heads – I can rebuild the original heads or try to upgrade for improved low-end torque. Unfortunately, the new heads (similar to CHI 3V style) that I’ve seen so far are port matched to 2V headers rather than 4V headers. Does anyone know of heads that will match the 4V manifolds? I’m not particularly interested in replacing intake and exhausts nor in custom grinding the ports on the new heads. The original heads are 63cc closed chamber with a factory listed 11.0:1 compression ratio. The original valves are 2.19” Intake and 1.71 exhaust.
Roller Cam – I do plan on upgrading to a roller cam and looking for recommendations on cam specs. The factory durations (at 0.004 & 0.006 tappet lift) are 266 degrees intake and 270 exhaust. I don’t yet know the current lobe separation. Again, I’m looking for a street and highway car with some better low-end performance. The car currently has the factory FMX with a 3.00 rear and runs fairly high rpms at highway speeds (~80 mph). I may take this opportunity to do an AODE and a 3.50 rear conversion and change the converter stall speed, that’s probably a somewhat different cam. Any recommendations on specs or sources?
A lot of this may be influenced by availability of these parts, at best I’m looking at a two month rebuild but part lead times could make that much longer. I understanding some of the options available will help as I’ll probably be making some compromises for the sake of time.

I coveted that setup years ago and would have gone back to stock with overbore, cleanup, and generally required fixes to bring it back as close to original as possible. The 351C 4v is iconic. Windsors are low end torque motors that the trucking world will always love, but Clevelands were that magic in a bottle-crazy wild spin monster that went nuts at high RPMS. I’ve always had torque’y Windsors, but if I were wearing your shoes, I’d consider going as close as possible to stock and not having to deal with all the balancing that comes with a bunch of mods that weren’t designed to go together. Regardless, she’s yours and I look forward to following your path to your perfect setup.

I just got my first Cleveland in a 70 convertible- I’ve only had 289 302 251 W’s before. But based on your stated goals, and not wanting to change the exhaust, I’d d stay under a half inch lift cam- Something like this, might be what you are looking for. I didn’t look up retro roller cams for a C, but if the machine shops puts the assembly together, they will know enough to verify push rod length, installed and compressed valve springs, etc…


I would stick with the stock heads and exhaust manifolds. Have the heads refurbished with new valves and stellite seats on the exhaust. Then use this cam and kit:

One reason stock 351C-4V cars have “less low RPM power” is the very conservative centrifugal advance curve in an unaltered M-Code distributor. Royce’s cam is an interesting one! I winced at the narrower LSA (110), but who the hell knows! It’s a modern hydraulic roller.

My old favorite cam is still sold, though less and less and hard to find: the Melling 24224 or Speed Pro CS173R. It is (was) a flat tappet hydraulic that was first sold through the Shelby aftermarket speed parts catalog circa 1970-71. I used one. It made power all over the tachometer, and idled like a station wagon. One reason may have been its 114 LSA, which street Clevelands seem to like.

I second Royce’s recommendation you keep the stock heads, modernize them, add a multi-angle valve job as part of it, and even keep the pedestal rockers. Ditch the 3-groove stock valves for modest aftermarket replacements. Speedmaster sells some that are very attractively priced. I had this combination 1972-80 in a stick car, and enjoyed it thoroughly over 1500-5500 RPM. It would spin without complaint to 6000+ (I did so once unintentionally on a burnout), but I, a young guy with low $$$, did not press my luck. A very smooth setup!


The 110 degree lobe separation angle will enhance the low end torque and the modest duration will too. The intent was to enhance torque - what I call “fun to drive”. It will be hard on tires. And fun with a 3.00 rear axle ratio.

Should have a decent vacuum signal so no worries about headlamps working or power brakes.

Thanks Royce and others. I’ve got a few more questions.
I called Comp Cam and they are suggesting a more aggressive cam than Royce’s Magnum 205/205. They recommended a Magnum 224/224 or 32-431-8. The rational I was given was the 11:1 compression ratio on the engine. My understanding is that the 1970 351C-4V had the highest compression ratio of the series. I may not have been clear on my desire to add low end torque (30 minutes on hold doing other stuff isn’t great for concentration). The duration is a bit longer at 284/284 vs the factory 266/270 (Royce’s 260/260). Royce’s suggestion and stuff I’ve been reading says shorter duration is better for low end torque. My reading also suggests that shorter intake duration increases cylinder pressure. It’s related to when the intake closes, the sooner it closes the sooner the piston starts the compression and the higher the pressure. The current 11:1 work with premium gas but I hesitate to get any higher (might decking the block may already boost it a little?). The factory cam is listed in the shop manual with an intake closing of 72 ABC and the recommended Comp Cam is at 68. It has a 110 LSA which should be good as Royce pointed out (I didn’t find a value for the factory cam). This one has a higher valve lift 0.566" vs the factory 0.427" (and Royce’s 0.510"). Is there likely to be a clearance issue?
Delivery is an issue, they currently don’t have any cores. Summit’s guess is an early July delivery. If I pin down the specs a bit better I’ll try some other sources. I’ve started stripping out components in preparation for pulling the engine so cam delivery is an issue for getting a running car back.

If your 351C-4V is original, It has more like 10.0:1 than the advertised. My '71 M-Code, with claimed 10.7:1 C.R., was actually 9.8:1 after I cc’d everything including deck height, volume above top ring, combustion chamber, and head gasket volume (calculated). That’s one reason you have efwer fuel octane problems than one would think.

The flat tappet cam I described worked wonderfully, and I still warn against getting nutty with cams for street Clevelands. The cam linked here made a local guy’s '70 Cyclone with aftermarket pistons and even more C.R. sound neat, but it ran slower than my stock short block Cyclone at the strip, mid-14s vs. 14 flat.


A 110 LSA will lose vacuum compared to the same cam with a wider LSA. However, you will get quite the hit somewhere in the midrange (!) whereas a 114 LSA will offer a smoother torque and HP delivery. Peak HP will be slightly higher with the 110.