Difference between 351 boss and 351c? - Vintage Mustang Forums

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post #1 of 7 (permalink) Old 05-01-2001, 06:46 PM
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I don't know much about the boss mustangs, I was just wondering what the difference in the engines are. (Saw one today looked pretty sweet.) Also what does my 351c redline at i'm guessing about 5,500, but i've never actually been sure.

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post #2 of 7 (permalink) Old 05-01-2001, 06:49 PM
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My dad's 390 doesn't redline until 6800... So I guess the 351 isn't too far behind.

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post #3 of 7 (permalink) Old 05-01-2001, 08:54 PM
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All Boss 351's were 4 bolt main blocks with cast nodular cranks that were checked for hardness, while other 351C-4V's may have had 2 or 4 bolt mains, and the cranks were not hardness checked prior to installation. The Boss engines came with forged 11.7:1 pop-up pistons (some references say 11:1 or 11.1 :1) while other 351C-4V's came with cast flat top pistons. The Boss used a solid lifter cam instead of hydraulic, so the heads were machined for adjustable rocker arms (screw-in studs and guide plates). Hardened pushrods and locating cups for the valvesprings were also used, as were single-groove valve locks vs. multi-groove on other engines. All Boss 351 heads used a small "closed" combustion chamber for increased compression, as did 1970 and some 1971 351C-4V's; 1972 351 H.O.'s (the closest thing to a Boss351 in 1972), the mid-year 71 351 CJ, and the later 351C-4V's (commonly also called CJs) all used an open chamber design that lowered compression and reduced emissions. Some late 351C-4V engines used the large port sizes common to all 4V heads but used the smaller 351C-2V valves. The Boss used an aluminum intake with an Autolite 4300D spread-bore carb, while other 351C-4V's used iron intakes with either a std. flange (1970) or spread-bore carb. The Boss used a dual point (vs. single point), dual-vacuum diaphragm distributor, along with a rev limiter set for 6,150 rpm (they'd go higher, but not under warranty!). Cast aluminum valvecovers, larger exit exhaust manifolds, a thicker harmonic balancer, baffled oil pan and I believe a recalibrated dipstick rounded out the Boss package. Some other 351C's used baffled oil pans - I'm not sure if they are identical or not. I think that's most of it for the engine (of course, all were Ram Air equipped) - the cars had a few other features that were unique as well, and I'm sure if I missed anything someone will point it out for us. You can check mine out at http://mtwcarcrazy.homestead.com/main.html
As for your redline, 5,500 is pretty good on a stock engine. It probably won't make any additional power much above that due to conservative cam timing and restrictive intake/exhaust, and there's more stress on the parts the higher you go.

post #4 of 7 (permalink) Old 05-01-2001, 09:49 PM
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Here's an interesting page about the Boss 351 heads.....they're essential to the performance potential of this engine over a stock C engine, especially a 2V engine..


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post #5 of 7 (permalink) Old 05-01-2001, 11:41 PM
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Mark351 gave you an [color:red]EXCELLENT description of the differences between the engines... I've had my 2V up to 5500, sounds like the world is coming to an end, LOL... Now, opinion mode on: if you are building a Cleveland motor, you have to be realistic with what you expect to do w/ the car, I've driven a 70 4V, and my Mach has a 70 2V; in a street race I would destroy the 4V stoplight to stoplight, but it would kick my butt in a real drag racing environment where high revving is more common. Opinion mode off [IMG]/forums/images/icons/wink.gif[/IMG].


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post #6 of 7 (permalink) Old 05-02-2001, 12:00 AM
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Thanks for the responses everyone, I had always wondered what made the boss's engine different.

post #7 of 7 (permalink) Old 05-02-2002, 04:13 AM
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The boss 351's also came with the roller rocker set up, a first for the 70's from the factory......351C's didn't come with this, they used the normal rockers.

I also believe that the intakes were different

rods were shot peened and magged be4 install as well

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