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> If the compression is pretty much the same between stock and Aussie heads,
> is there any real advantage to running the closed chamber heads?

With closed chamber heads, you can run that compression on a lower octane fuel.
With the open chamber heads, you may need to run 91+ octane. The open chamber
heads will require more total advance and you may need to tailor the spark
curve. Vizard's testing showed a multi-strike ignition like an MSD can help reduce
pinging with an open chamber head.

Real 351C-2V (open and closed chamber) have a better exhaust port. I've
never examined early 400 heads but later 351M/400 heads have a restrictive
port with the water jacket drooped down around the valve guide. You can't
grind it away because you'll hit water. I'd examine your heads to see if
they share the 351C-2V exhaust port.

With a little work, we got 200 CFM out of a closed chamber 2V exhaust port.
It was a 393C build with ported Aussie 2V heads and we tested a series of
intakes. Even down at 3000 RPM, the single plane intakes did better than
the dual planes, including the Edelbrock Performer Air Gap. Given the cubes
and the intake port was weak relative to the exhaust, the dual plane plenum
effect wasn't needed and just presented a flow restriction. The best low
rise intake was the Holley Street Dominator and the best high rise was the
Parker Funnelweb. Their was a 351M/400 version of the Holley Street Dominator
but it is out-of-production though you can find them used.

Dan Jones
 

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Its the same damn part minus .003 valve lift, theyre even recomended by the rocker MFG's in some cases.

Ive been running them for almost 3 years now...Unless you can PROVE to me that there is a GOOD reason that i shouldnt run them, then im not wrong...Im not even the first person to have done this...Its a rocker arm...not rocket science
try proving it yourself ,. don't be cheap .. lay out the bucks and compare .
nothing to do with 1.70 vs 1.73 ratio
yes it is the same part number for the low end users .. both BBC and the Fords

Edit ..try running the cheap BBC on 8mm/5/16 valve stems with no lash caps and turn it up to 9 1/2+ rpm
 

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Its the same damn part minus .003 valve lift, theyre even recomended by the rocker MFG's in some cases.

Ive been running them for almost 3 years now...Unless you can PROVE to me that there is a GOOD reason that i shouldnt run them, then im not wrong...Im not even the first person to have done this...Its a rocker arm...not rocket science
The problem is in the push rod cup location relative to the rocker pivot and roller tip. The BBC rockers are designed to work with the location of the BBC push rod location, the rocker stud mount location, and the angle and location of the BBC valves. These three factors are different from those of a Cleveland or BBF. Sure it will work for a while but the wear and tear on your valve train components will be more severe than if you were to use the proper components in the first place. It's all in the geometry!
 

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try proving it yourself ,. don't be cheap .. lay out the bucks and compare .
nothing to do with 1.70 vs 1.73 ratio
yes it is the same part number for the low end users .. both BBC and the Fords

Edit ..try running the cheap BBC on 8mm/5/16 valve stems with no lash caps and turn it up to 9 1/2+ rpm
In response to your edit only: Why the hell would i do that? I didnt build a 9.5k engine...It rarely see's 6k

In response to your first sentence: I did prove it to myself, I bought BBC rockers, and ran them on my ford with no adverse effects to date...all the proof I need at this juncture. I would like to see some numbers comparing pushrod cup depth, distance from the stud center to the center of the roller tip and center of the pushrod cup...comparing the 1.73 fords to the 1.7 BBC rockers
 

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The problem is in the push rod cup location relative to the rocker pivot and roller tip. The BBC rockers are designed to work with the location of the BBC push rod location, the rocker stud mount location, and the angle and location of the BBC valves. These three factors are different from those of a Cleveland or BBF. Sure it will work for a while but the wear and tear on your valve train components will be more severe than if you were to use the proper components in the first place. It's all in the geometry!
That makes sense(though no proof has been presented) for completly stock configurations but, my block is decked, my heads are aftermarket, my cam is different, my valve springs are different..all of which add up to different push rods, at which point a person checks the travel of the rocker tip across the valve tip, regardless of the rocker being run...
 

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Discussion Starter · #26 ·
> If the compression is pretty much the same between stock and Aussie heads,
> is there any real advantage to running the closed chamber heads?

With closed chamber heads, you can run that compression on a lower octane fuel.
With the open chamber heads, you may need to run 91+ octane. The open chamber
heads will require more total advance and you may need to tailor the spark
curve. Vizard's testing showed a multi-strike ignition like an MSD can help reduce
pinging with an open chamber head.

Real 351C-2V (open and closed chamber) have a better exhaust port. I've
never examined early 400 heads but later 351M/400 heads have a restrictive
port with the water jacket drooped down around the valve guide. You can't
grind it away because you'll hit water. I'd examine your heads to see if
they share the 351C-2V exhaust port.


Dan Jones
Okay, so the open chamber heads are LESS prone to detonation at the 9.5:1 compression. All else equal how does the power between the open and closed chamber compare?

As far as I have read, the early 400 heads are the same as the 351C-2v heads. The water jacket in the exhaust port didn't happen until 1975 (or so) for the 400 heads.
 

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Okay, so the open chamber heads are LESS prone to detonation at the 9.5:1 compression. All else equal how does the power between the open and closed chamber compare?

As far as I have read, the early 400 heads are the same as the 351C-2v heads. The water jacket in the exhaust port didn't happen until 1975 (or so) for the 400 heads.
How do you come up with "LESS" ?

More is still correct ... change less to more , then you'll be ok
 

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Okay, so the open chamber heads are LESS prone to detonation at the 9.5:1 compression. All else equal how does the power between the open and closed chamber compare?

As far as I have read, the early 400 heads are the same as the 351C-2v heads. The water jacket in the exhaust port didn't happen until 1975 (or so) for the 400 heads.
At 9.5 compression the Open chamber heads shouldn't be a problem for detonation . The TMyers 400 pistons are a good choice as they are the only piston that brings the top of the piston to the top of the bore. The close chamber have a faster flame travel so you can use less timing but the valves are shrouded more. If you were looking for 13-1 compression the close chambers would be the best way to go but at 9.5 both heads would make power on a equal bases .
 

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"Another area that has evolved greatly in detonation suppression is the combustion chamber design. Today's small, fast-burn high mixture motion chambers combat the likelihood of detonation "

"If replacing a cylinder head with an aftermarket one, try to employ a head that mimics today's combustion chamber technology to make abnormal combustion less of a problem."

The open chambers are larger correct? They have more area to absorb heat, they have more potential for sharp edges, they have less control over the flame front and more area for another flame front to occur(pre ignition) IMHO, Open chamber heads are more prone to detonation, but with the proper pistons, you can decrease that potential significantly.

Tmeyer has a piston that works with closed chambers and gives a ratio of 9.4:1, he just cuts a big dish out of the piston used for the open chamber heads...
 

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"Another area that has evolved greatly in detonation suppression is the combustion chamber design. Today's small, fast-burn high mixture motion chambers combat the likelihood of detonation "

"If replacing a cylinder head with an aftermarket one, try to employ a head that mimics today's combustion chamber technology to make abnormal combustion less of a problem."

The open chambers are larger correct? They have more area to absorb heat, they have more potential for sharp edges, they have less control over the flame front and more area for another flame front to occur(pre ignition) IMHO, Open chamber heads are more prone to detonation, but with the proper pistons, you can decrease that potential significantly.

Tmeyer has a piston that works with closed chambers and gives a ratio of 9.4:1, he just cuts a big dish out of the piston used for the open chamber heads...
agree with you Except the more room for sharp edges . Thats backwards. think about it , don't make me explain
 

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In response to your edit only: Why the hell would i do that? I didnt build a 9.5k engine...It rarely see's 6k

In response to your first sentence: I did prove it to myself, I bought BBC rockers, and ran them on my ford with no adverse effects to date...all the proof I need at this juncture. I would like to see some numbers comparing pushrod cup depth, distance from the stud center to the center of the roller tip and center of the pushrod cup...comparing the 1.73 fords to the 1.7 BBC rockers
"9.5k engine" exactly what is that ?
not RPM , doubt its money , if you claim that dollars post details of the cost . cheaping out on a set of rockes at that level !
 

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try proving it yourself ,. don't be cheap .. lay out the bucks and compare .
nothing to do with 1.70 vs 1.73 ratio
yes it is the same part number for the low end users .. both BBC and the Fords

Edit ..try running the cheap BBC on 8mm/5/16 valve stems with no lash caps and turn it up to 9 1/2+ rpm
9.5k=9500 RPM, the same 9 1/2 rpm YOU talked about, unless you litterally ment 9 and one half rotations per minute...

K= rough equivilent to 1000 of anything, its an abrieviation...

I said, very clearly, "I DID NOT BUILD A 9.5K ENGINE, it rarely sees 6k" I didnt clarify that i ment 9.5k RPM. If i could afford to build and engine of that caliber, or if i were trying to build and engine of that caliber, i wouldnt cut corners. The whole point was a matter of economics. If hes running a street engine, and wants adjustable roller rockers, what he saves on the cost of the rockers could potentially pay for the cost of prepping the heads to recieve studs, or pay for the studs...IDK that for a fact, but the implication was the point.
 

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Thats not fact...just bias. $199 is what I paid for the adjustable BBC roller rockers ina 1.7 ratio. Find me a NEW set of 1.73-1.8 roller rockers labled ONLY for the 351C,351M,400 ford for $199...I defy you to do so...If you do that, find me the technical data to support your bias, otherwise thats all it is blind Bias...:)
Scorpion but there about 250 for the cheep ones
 
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