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351 4V Open port heads
#1
runninpony 
I just found and bought a 1970 351C 4V engine with a C6 trans 3000 stall converter. I didn't have a camera with me and the engine was back in a corner where I couldn't get to see the numbers or dimples on the heads. He said they’re open chamber heads and the rebuild was done stock with a 30 over bore. It has factory type exhaust manifolds and less then 20K on the rebuild.
I don't really understand how the bounce back stuff works on the 4V heads and my question is.... If these are open chamber heads, is it better to stay with factory exhaust headers or go with aftermarket headers? I had always thought aftermarket headers let the engine breath better and gained HP but after reading an article "The Amazing 351C 4V" I was left confused. Help me out hereHuh

Mike
72 Mach 1
1979 Ranchero GT
1979 Corvette (yes... the "C" word)
2003 Pro-Street American Motorcycle
Which was the mid-life crisis???? Big Grin
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#2
I have 1970 closed chamber heads on my 1973 q-code block and I have installed a pair of hooker headers. The before and after showed that it let breathe the engine much more now, even at lower rpm which is not the dominant range of our 351C's... They give you more push in the lower rpm area and in the upper range it let the engine turn much more freely.

But I also changed the smaller 2 1/4" exhaust system into 2,5" with Flowmaster mufflers.

Tim

Tim

Never drive faster than your guardian angel can fly Angel
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#3
Ignore the "bounce" factor and go with headers and a 2 1/2 exhaust. Open chamber heads are awesome and I am planning to build up a set in the future- I have some nice cores in the basement.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#4
I was under the impression that the heads for a 4V engine in 1970 were closed chambered for our 351C's? You have to keep in mind the stock 4V exhaust manifolds have huge ports so I would think headers would make less of a difference than with 2V exhaust manifolds.

Jim

M code 71 Mach 1, 351 4V Cleveland, Ram Air (not factory), C6 Trans, 3.5 rear
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#5
Jim and Jutta;172795 Wrote:I was under the impression that the heads for a 4V engine in 1970 were closed chambered for our 351C's? You have to keep in mind the stock 4V exhaust manifolds have huge ports so I would think headers would make less of a difference than with 2V exhaust manifolds.

Jim, you are right - I have CLOSED chamber ports. I confuses them often...

I felt still a difference before and after, especially in the lower rpm range because of the headers tubes are a bit narrower than the exhaust ports of the heads. And, ok, the 2,5" exhaust pipes certainly made their contribution too...

Tim

Never drive faster than your guardian angel can fly Angel
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#6
Thanks guys, I'll take a better look at it when I get the engine and trans home then I'll be able to see the stampings and will take some pics

Mike
72 Mach 1
1979 Ranchero GT
1979 Corvette (yes... the "C" word)
2003 Pro-Street American Motorcycle
Which was the mid-life crisis???? Big Grin
  Reply
#7
timachone;172797 Wrote:I felt still a difference before and after, especially in the lower rpm range because of the headers tubes are a bit narrower than the exhaust ports of the heads. And, ok, the 2,5" exhaust pipes certainly made their contribution too...

What kind of mufflers were on it before going to Flowmasters?
Miy Mach1 351-4v has stock manifolds and stock 2.25 pipes. It also had stock style (quiet) mufflers. All I did was swap in some Flowmaster 44s and it felt like it picked up 15hp, very noticable.
I have heard the stock 4v manifolds actually flow pretty good, so much so that shorty headers won't make much difference. Not sure but my guess is that the Boss 351 and 351-4v have the same exh manifolds.
Long tubes may make a HP diff, but with those I worry about other issues too: fitment, ground clearance, noise, engine bay heat in summer.

1971 Mach1
351C-4v
C6 is history-->>now TKO-500
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#8
It isn't only the size of the tubes that make headers worth while, it is the length and independence of each tube much further down and the more efficient collectors. Headers are also lighter, but with a ceramic coating do just as good a job of retaining heat.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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