i'm only 17 and am still learning. but i resently found out i can turn my 351m into a 400. if i do this will it out proform a 351c with 4v heads? i'm not to sure wat 4v heads are, but i've read allot of posts and they say that the clevelands are power houses with 4v heads instead of 2v. and can you put 4v heads on a 400? i don't mean to sound ignorant, i'm just curious.

 

In my opinion the 400 can be built to out perfrom a 351C because a 400 is essentally just Cleveland with 49 extra cubes. If you are running a truck that won't see 7500rpms and doesnt have a big blower on it you are better off with the 2V heads. The 4V heads don't make any power down low and are only sutible for all out high rpm racing applications. You could put the 4V heads on a 400 but you need to find the intake manifold adapter made by Weiand to use a 351C 4V intake on a 400. As for what the 4V heads are that mean 4 venturi, as in carberature venturies. The 4V head cam on 351s that came factory with 4 barrel carbs, they have huge ports and valves, they actually out flow factory big block cheby heads, but all this flow comes at a price, no port velocity wich translates into no touque below 4500 rpms. Just my $.02 hope i answred some of your questions.
-johnboy

 

The 4V heads have torque and power at low RPM's they just don't have as much as the 2V heads. At high RPM's the positions are reversed and the 4V heads will outperform the 2V heads. Your choice of engine, cam, and heads etc will depend on your application. No single build is right for all applications.

 

I can't figure how a 400 can compete with the original 351C 4V 4 bolt main GT engines from the early 70's in HP and torque.

Not only did these engines power Fords, and many street race cars of the era...but was also used in Panteras. If the 400 was so good, why didn't Ford/Detomoso use it?

 

The 400 was not designed to compete with the 351C 4V. It was built to replace the aging FE engine series. The 4V C heads went away for emission reasons more than anything else. I wish I had a dollar for every time someone brought up the 4V head stereotype. How's this for a torqueless 4V engine?

383C/3514V 1-3/4" primary headers
950HP Holley, stock iron intake, ported Boss heads
Intake duration
228deg @ .050
Dyno tested:
435tq @ 3000
463tq @ 4600

I'd get into this but I fear the return of Fomocofan and another locked thread.

 

it was hard times. the Cleveland only had a 5 year lifespan, real 4V heads only 3. the 351M/400 was so extremely detuned that it fell off the radar as having any chance of being considered a performance engine. the learning curve of emissions technology is what killed them. the muscle era didn't recover if at all until the 335 series engine was long out of production. if not for the 1973 gas BS i think Offy, Holley and Edelbrock would've all had intakes for a 4V 400, and they would've been inch for inch Hemi killers like they are now. it took over 30 years to get back to where we were in 1971: hey, these 4V heads will bolt right on the 400 block! yeah but there's no intake...oh well, too bad, that engine would really rock...were they ready for 500+ HP?

the 4V clevelands of the day suffered from the cam tech of the day, and the too much cam learning curve. the fastest way to dog a 4V C is to overcam it with not enough gear and stall. instant stereotype. then consider that the 4V heads were introduced ona 302" engine where they originally picked up the "no low velocity" stereotype. add 50, 100, 135 or more inches to the equation and see what happens, those heads are gonna start to really flow, as some of us now know.

 

I know the 400 wasn't designed to compete with the 351C...if I thought that...I'd be pretty damn dumb. My post had to do with the power of a 400 over a 351C...and there's no argument there. The 400's were gutless..especially the 77 and later variaties.

 

thanks for all the replies, much appreciated.

 

of the 2 (cleve or 400) id build a 400. I have trucks, you get 48 extra cubes and a better rod ratio. The latter point is #1 when it comes to building a short block..

but to stay on topic, youre 17...if the vehicle the engine is in is ok, get the engine running nicely and all tuned up. Do some bolt ons, little things while stock piling all the crap you need to put the engine together the way you want/dream. Dont tear into it untill you have EVERYTHING you need to complete it. I dont know what your plans are, just a little piece of advice im offering. I had the engine ripped out of my stang the day after I got it, didnt have everything to complete it, and I ended up having to sell it before I could even enjoy the thing. Pisses me off to this day still. Responsible fun is #1

 

ya, well the 351m runs. but i'm gettin another truck that i wanted to put it in later on this winter. so what i'm gettin at, while i'm switching the motors out. should i make it 400, or keep it how it is? i've been reading post by other people and they all say make it a 400. i'm just trying to get people opinions without them being smart @$$e$.

 

make it a 400 sure, but budget in boring it out and getting a rebuild kit for the overbore size. That way if you pull the bottom end apart and the cylinders definately look like they need to be bored you wont have to put the engine together that way, or you wont have to have it sitting around waiting for you to get the cash to pay to get it fixed. You know what I mean? it sucks when that happens. Id rather take a 200hp running engine over a potential 400hp engine sitting in pieces because I cant afford to finish it. Not trying to discourage your power mods, just letting you in on a little way to do things that helps keep you in a happy place lol. Plus if you budget in needing to do the extra repair/replacement work on whatever you do, if it turns out you dont need to go that extra mile then you have extra cash you can spend on other parts of the truck.

 

Stock for Stock a 400 can't compete unless it is the first year when it wasn't detuned so bad and even then it didn't have the power the 351C had. As stated above you can easily build a 400 to compete with a 351C easily and rather inexpensively. check out this HotRod article from a few years back:

http://www.1ton4x4.com/400/

I would add $1K or $2K to that total since that article is 8 years old. Still for $3K-$4K those are some nice performance numbers.

 

that's a mild build that had "kalifornia emissions" in mind. no mention of zero deck, 268 cam and 2V heads. bring the pistons to the top, more carb, cam, heads and look out!