'72 351c 2v Upgrade Help

assuming that you are wanting more performance for the street, stick with the 2V heads and the aftermarket intake. the 2V heads are much better for the street than the 4V heads are.

Edelbrock air gap is a good choice for an intake. It's taller than the stock intake but I think it will fit under your hood. You might consider headers too. Upgrading the exhaust will also improve performance. If it were mine I'd go 4V though. For a mild 351C Holley will recommend about 600 cfm with vacuum secondaries. Many people online will tell you that is small. I like Holley and I would say you could go to their website and use the online product selector. It's really good. If this is the first of many upgrades you might consider inputting your eventual goals rather than buying several different carbs as you progress. With a vacuum secondary carb the secondaries will open only as much as your engine needs, so you can over-carb it somewhat without having fuel economy and driveability problems.

if you are just doing a mild bolt on upgrade, i suggest using the edelbrock performer intake with a 600cfm edelbrock carb. if on the other hand you are going to upgrade the cam in the future, then an edelbrock performer rpm, rpm air gap, or weiand stealth intake with a 750cfm edebrock carb is the way to go, again assuming a mild build.

pushrod power said:

That is nothing but disinformation.​

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actually even ford says the 2v heads are better for the street. in fact a number of places sell plates that install between the intake an the head on a 4v motor that reduce the size of the intake ports for better street manners.

rbohm said:

actually even ford says the 2v heads are better for the street. in fact a number of places sell plates that install between the intake an the head on a 4v motor that reduce the size of the intake ports for better street manners.

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They also sell a thing called a "TORNADO" which is supposed to spin the intake air and improve performance. I won't try to stop you from buying one but I also will not recommend it.

I think some of this is an opinion thing, but 4V heads are in no way too big for the street. If the engine is built right it will work great on the street with 4V heads. The 4V heads are the biggest advantage a Cleveland has over the other non-performance engines built by Ford (351W comes to mind, along with most 302s). The Boss 351 71 Mustang was a big car, but it was the fastest stock Mustang through the quarter until recently. It also has good manners on the street.

I would only use US 2V heads if they were already on the engine and I didn't want to spend the money to open up the engine for any internal work. I would use Aussie 2V heads in a new build if they didn't need any work or my total investment was under $300 and I had a really small budget. If the heads required any more work than that I would go to 4V. IMO 2V are better for fuel economy, but nothing else. Don't invest in a valve job, porting, etc. for 2V heads. If any work needs to be done, either go to 4V or aluminum heads. Otherwise you are wasting money.

Regardless of whether you go 2V or 4V, if you are using heads with the OE Ford 2-piece valves then do yourself a BIG favor and replace with one-piece units. Also, you can upgrade the rocker arm fulcrums on the 2V heads to the ones used on the 400M.

bartl said:

Regardless of whether you go 2V or 4V, if you are using heads with the OE Ford 2-piece valves then do yourself a BIG favor and replace with one-piece units. Also, you can upgrade the rocker arm fulcrums on the 2V heads to the ones used on the 400M.

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Good advice! Although I probably wouldn't spend the money for new 2V valves. If you really want 2V the valves are a good idea to keep from destroying other parts.

all good points hack. the 4v heads though were designed to allow for larger small blocks that would have been in the offing except for the emissions laws and insurance regulations being put on the books at that time.

rbohm said:

all good points hack. the 4v heads though were designed to allow for larger small blocks that would have been in the offing except for the emissions laws and insurance regulations being put on the books at that time.

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The basic design of the 4V was first used in the Boss 302, so Ford seemed to think that the 4V head was a good performance head, even for smaller than 351 cubes. I think that Ford winning the Trans Am racing series with the Boss 302 shows that the heads were great for racing with 302 cubes. 4V Cleveland heads are slightly different, but very, very similar to Boss 302 heads. I agree with you that 4V heads can be used with more than 351 cubes. I'd say they were a little oversized for a 302 for what most people would prefer on the street, but on the 351 they are a good size for street performance.

If you want an engine that has great torque at 1,500 RPM and is all done at 5,000 RPM, 4V 351 Cleveland heads might not be for you, although you can select a combination of parts to do that if you want - it's not where the heads excel the most. The 4V 351 Cleveland was not designed for trucks and station wagons like the 302 and 351W engines. It's more of a performance offering. Of course if you want more stump pulling torque you could always stroke the engine and still use the 4V heads.

Edit: One other thing I'd like to say is that I generally disagree with car manufacturers on what is enough performance for the street.

yes ford did use the 4v heads on the boss 302s, but note that they made power way up in the rpm band, above even the 302 chevy engines they were competing against, but lower than the tunnel port heads they replaced. same with the 351c, the 4v heads make great power up to 9000 rpms, but tend to be a bit soggy on the bottom end. in the end its all good and it depends on what you are building the engine to do. for me i would use the edelbrock 3v heads or the australian 302c heads on a street engine, and a good set of closed chamber 4v heads on a race motor.

I went through this decision and back and forth between using 2v and 4v heads over the past 20+ years of running Clevelands. I have run both, and now run a set of the Aussie heads. The 4V heads can be run on the street and not be too much a headache if the engine is built right, they have better compression and allow more performance options, especially when taking more advantage of the mid to upper RPM range. If you are running stock gears I am afraid the 4V heads may be a disappointment since getting the revs up faster will be where these heads shine the best.
The 2v heads are no slouch and will give good torque from idle and through mid range and will work better with stock gearing. The are lower compression but can have detonation issues due to the open chamber design, especially with the wrong cam setup.
The Aussie heads are a mix of the two and some believe the best of both worlds, especially if you work the heads a little. I think they are a great cast iron head for hot street performance, they are absolutely wonderful with my current setup. They have also been fitted with the larger 4V valves (2.19") but be VERY careful if doing this, if not done right you can hurt port flow if the ports are not blended properly into the valve area. I spent many hours working on this and CCing the heads.
The 2v heads have good ports for the street if you want low-end torque performance, but I just don't like the large open chambers as they don't promote efficient ignition in the combustion chamber.
But like said above, run what you have, putting a 4bl carb and maybe some headers will do alot for the 2v cleveland.

Also, I would recommend the Edlebrock Performer RPM Air-gap intake as mentioned above. It does sit a good bit higher and may cause clearance issues with your hood, so be sure to check that out first if you go that route.