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Old 10-14-2011, 07:44 PM
Money-pit Money-pit is offline
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Default 351C valve size ?

I'm going to build a 351C for a 71 mustang. I have a set of the later open chamber 4v heads with the 2v sized valves. I'm going to put the 4v exhaust valves in the heads but I'm wondering if I should leave the 2v sized intake valves in it. Would that help keep port velocity up at lower rpms or would it hurt the flow ? It's just going to be a street motor, around 9:1, hydro cam, 389 gears.
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Old 10-14-2011, 08:12 PM
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Quote:
Originally Posted by Money-pit View Post
I'm going to build a 351C for a 71 mustang. I have a set of the later open chamber 4v heads with the 2v sized valves. I'm going to put the 4v exhaust valves in the heads but I'm wondering if I should leave the 2v sized intake valves in it. Would that help keep port velocity up at lower rpms or would it hurt the flow ? It's just going to be a street motor, around 9:1, hydro cam, 389 gears.
The size of the intake valve in the 4v head has little to do with port velocity. The gargantuan port cross section however has everything to do with it.
Based on the little you are telling us it sounds like a pair of aussie 2v heads would suit your built better.

Open chamber 4v heads are in my opinion useless. Its not bad enough that the ports are monsterous on a 351 but to add insult to it the open chambers kill low speed torque and offer no quench, and require a bunch more total timing than the 30 degrees total the closed chamber heads require.
With high compression, a carefully tuned exhaust system, careful cam selection the 4v closed chamber heads can rock even on a 351 but the open chamber heads.... Yuck


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Old 10-14-2011, 08:36 PM
429TORQ 429TORQ is offline
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x2, smaller intake ports and valves. I built a 351c for Greg, my driver, and the car went the fastest with aluminum heads 2.08 1.65 valves and 185cc intake ports. Our backup engine had "Aussie" heads on it and it was potent also. Our 4v close chamber iron heads fell in between the other two. The 185cc closed chamber engine turned the best et's with the timing at 26 degrees total. For a street engine, I highly recommend CHI em185 3v cylinder heads(the ones our car went fastest with).
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Old 10-14-2011, 08:48 PM
torinojoe1971 torinojoe1971 is offline
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Default 351c

Go on the clevland board. I did some cking on there and in my opion for a nice street motor the open chamber heads will work fine. With the right cam intake a little port work you should be around 350 to 400hp. I'm doing a simular build and I'm using the open chamber heads. The one thing that helps on the clevland is a good torq converter, for your set up you should run around a 2500 converter makes a big diffrence. Joe
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Old 10-14-2011, 08:52 PM
turbo2256b turbo2256b is offline
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Quote:
Originally Posted by Money-pit View Post
I'm going to build a 351C for a 71 mustang. I have a set of the later open chamber 4v heads with the 2v sized valves. I'm going to put the 4v exhaust valves in the heads but I'm wondering if I should leave the 2v sized intake valves in it. Would that help keep port velocity up at lower rpms or would it hurt the flow ? It's just going to be a street motor, around 9:1, hydro cam, 389 gears.

The only factory heads I know of are 4V big valve and 2V small valve heads.
2V had open chamber only. 4V had closed chamber except the last 3 years.

What are you trying to accomplish? Dosent sound like your trying to get to wild.
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Old 10-14-2011, 09:20 PM
429TORQ 429TORQ is offline
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Quote:
Originally Posted by turbo2256b View Post
The only factory heads I know of are 4V big valve and 2V small valve heads.
2V had open chamber only. 4V had closed chamber except the last 3 years.

What are you trying to accomplish? Dosent sound like your trying to get to wild.
Although I no longer remember exact details, "Aussie" heads use the smaller valve set and 2v port cross sections. But they sport a 58cc(I believe) closed chamber.
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Old 10-14-2011, 09:32 PM
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The aussie 2v cleveland heads came on the australian 302 engine. They have a tight >60 cc chamber and 2v sized valves. They are night and day better than the open chamber 2v heads that came on both the aussie 351c's and the USA 351 c, m and 400's. Note there are slight differences between the 351 c 2v heads and the 351 m 400 heads mainly in the exhaust port.

I had a pallet of them shipped over years ago and I think I have one pair left. Used one set on a boss 302 trans am racer that made well over 460 HP at 7200 rpm with a solid flat tappet cam.


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Last edited by The Mad Porter; 10-14-2011 at 09:35 PM.
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Old 10-14-2011, 09:37 PM
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Excellent, thanx for the clarification!
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Old 10-14-2011, 09:48 PM
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I had a 351c with the closed chamber 2vs, with 10.1 comp, solid cam 246, 256 dur with 570, 590 lift ended up running 11.9 at 112mph on pump fuel. Had the engine for 8 years and no problems just a basic combo which ran well on the street aswell, ended up selling that engine to build a 545 p51 wow what a difference!!.....lol

4v are not for street use IMO, but love the high rpm, the 2vs are better for low down power were you want it for street.
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Old 10-14-2011, 09:55 PM
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Go with 4V sized valves in the "Aussie" 2V heads.
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Old 10-14-2011, 10:09 PM
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Quote:
Originally Posted by Beast View Post
Go with 4V sized valves in the "Aussie" 2V heads.
Utilising the larger 4v intake valve in the 2V castings presents a problem because you can not lay the short turn back far enough to accomodate the larger valve and have it work effectively with out hitting water nor can you properly shape the bowl to accomodate the larger valve. Long story short you can not get correct bowl geometry with the large valve. Its tough enough with the std valve. The low short turn height means the port goes turbulent at just under .600" lift.

Correctly ported 2V heads will support 500 HP with the 2.04" intake valve and maybe in a pinch one could use the 2.08" bbf intake valve but do not use a 2.19" intake valve in a 2V head.


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Old 10-14-2011, 10:10 PM
Money-pit Money-pit is offline
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Quote:
Originally Posted by turbo2256b View Post
The only factory heads I know of are 4V big valve and 2V small valve heads.
2V had open chamber only. 4V had closed chamber except the last 3 years.

What are you trying to accomplish? Dosent sound like your trying to get to wild.
These heads are the last of the 4v heads, '73 or '74 ? I don't know why Ford did that ( put 2v size valves in a open chamber big port 4v head ) but I was thinking it might have something to do with getting some port velocity or maybe even emissions. I do have a set of closed chamber 4v heads I can sell to him. It's sounding like the way I should go but he wants to run it on 89 oct.
This is just going to be a street motor for a '71 Mach 1 with a 4 speed. Probably will never do anything more than a burnout once in a while.
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Old 10-14-2011, 10:31 PM
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Quote:
Originally Posted by The Mad Porter View Post
Utilising the larger 4v intake valve in the 2V castings presents a problem because you can not lay the short turn back far enough to accomodate the larger valve and have it work effectively with out hitting water nor can you properly shape the bowl to accomodate the larger valve. Long story short you can not get correct bowl geometry with the large valve. Its tough enough with the std valve. The low short turn height means the port goes turbulent at just under .600" lift.

Correctly ported 2V heads will support 500 HP with the 2.04" intake valve and maybe in a pinch one could use the 2.08" bbf intake valve but do not use a 2.19" intake valve in a 2V head.



Guys have been doing it over here for years, I've had a set done myself. It was advised to me when doing my 351C LPG build. Worked fine. What you say makes sense though.
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Old 10-14-2011, 10:45 PM
turbo2256b turbo2256b is offline
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I have some 73 heads there big valves. Dont know of any 4V s after that.

The 4V exhaust valve in the 2V head is a good move. The bigger intake though requires a good pocket port.
C motors are my favorite.



Years ago 71 I believe ordered unknowingly an Aussy NASCAR short block and some bare heads through Holman and Moody. Strange about the heads they had 2.25 intakes and smaller than the standard closed chamber. I had already purchased titainum 2.19 valves. Lucky as a local guy wanter the valves for his Boss 302. Saved my butt.
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Old 10-15-2011, 12:04 AM
Money-pit Money-pit is offline
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Quote:
Originally Posted by The Mad Porter View Post
Utilising the larger 4v intake valve in the 2V castings presents a problem because you can not lay the short turn back far enough to accomodate the larger valve and have it work effectively with out hitting water nor can you properly shape the bowl to accomodate the larger valve. Long story short you can not get correct bowl geometry with the large valve. Its tough enough with the std valve. The low short turn height means the port goes turbulent at just under .600" lift.

Correctly ported 2V heads will support 500 HP with the 2.04" intake valve and maybe in a pinch one could use the 2.08" bbf intake valve but do not use a 2.19" intake valve in a 2V head.


So, I might not have been able to put the 2.19's in these late 4v heads in the first place ? I was thinking Ford just added material to make the bowl smaller but they may very well have redesigned the water in the late 4v heads just for the small valves. I should just try to grind one out to see if I fall through, otherwise I can't think of any use for these heads without the 4v valves.
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