Good time to ask this, are 2 and 4 BBL factory exhaust manifolds different for the 351 C ?
Yes. In 2 regards. Exhaust port size, exhaust pipe size.
All 351C 4V heads(Boss, HO, CJ, quench, open) have the following exhaust port dimensions:
Heads: 1.75W x 2.16H MEASURED/Verified/DEAD ON RIGHT
Manifold Exhaust Ports: 1.75W x 2.16H (Measured by guy I bought them from...not in my hands)
Manifold Exhaust Diameter: NON Boss 2.25, Boss 2.50(Measured by guy I bought them from...not in my hands)
351 2V heads have the following dimensions:
Heads: 1.38W x 1.84W*
Manifold Exhaust Ports: Unknown
Manifold Exhaust Diameter: Unknown
I got the 4V head information from the heads sitting on my bench. I got the 2V numbers from here:
*http://www.7173mustangs.com/archive/index.php/thread-588.html
The 4V numbers in the link above don't match what I measure(1.75 x 2.00 in the link), and I am pretty sure(but don't know) that my heads are 1971 Quench Virgins. In defense of tnfastbk's post in the above link, the numbers he posted are the ones typically posted on other web sites. But I guess, no one ever bothered to measure. Not even the "experts" writing books on the subject.
Anyone want to actually measure their heads or manifolds and see what they come up with?
Oh...you can bet you Mustang I am going to run headers. And, in all honesty, you are probably right about it not really harming the headers. But $600, I just want to be a little careful.
I often wonder about the cars coming off the line. In 1984 my wife was an engineer at the (puke puke puke) Camaro/Firebird line in Van Nuys. At the end of the line, those guys didn't brake in the cams. They fired up the engine, let it idle for 1 minute while they were checking all the accessories, then they peeled rubber out of the plant. I don't think they started the engines at the engine factory.
Guys like me that don't know the best way to seal an oil pan or the intake manifold off the top of our head(what the hell are we doing) are overly cautious in most every regard...and that is putting it mildly. I am like Doc. I don't mind doing the work at all. I like the learning and the pride of getting the work done.
But after I am done with major surgery, I don't want to have to go back in to see where I screwed up. I want to enjoy my work for YEARS AND YEARS AND YEARS. A lot of you guys can take out a motor, rebuild it, and put it back in within a weekend and feel very comfortable turning that key on the new rebuild. Me, well I fret over every inch of cork and dab of sealant. Have your read our posts on distributors??? We are insane.
In any event, I figure it won't be too much trouble to take out the existing motor and trans(anyone looking for a 302?) and replace it with the just the 351 motor for break in. Then I'll remove it and add the transmission and put it back in with the headers....ah... headers.
James -
I can appreciate one being "anal" but my limited mechanical engineering knowledge begs to ask "how much difference can that make"? I can't imagine professional builders bolting a set of 4V exhaust manifolds onto the newly rebuilt motor, delivering it to the owner and saying, "make sure you bring it back after 200 miles so we can put the headers on." :huh:
Actually, there is a "good" reason for this which I believe is explained pretty well in the attached link.
http://www.sandersonheaders.com/support/knowledgebase.php?article=1
I think it is pretty common for most professional engine builders to utilize "regular" headers (or exhaust manifolds) when breaking in "new" engines.
BT
My main reason for wanting to use exhaust manifolds for break in would be the ease in which I could put the engine into my car. If I could break it in on an engine stand, I would use whatever was readily available.
But, since it is going to be mounted in my engine bay, I think manifolds are probably the quickest way to get the motor in and out...unless someone wants to break in a pair of headers for me!!!
