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Old 03-09-2008, 06:39 PM   #1
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351C 2v heads - Are they detonation prone?

Read a really good article on detonation and pre-ignition
http://www.streetrodstuff.com/Articl...ion/Page_5.php

One thing I picked up on that page was that the Hemi style cylinder heads are lousy for detonation control since the combustion chamber requires a pop-up piston to make decent compression. With a pop-up piston fitting into the combustion chamber, you have a LOT of surface area for the flame front to travel, which increases your burn time, which is an enabler for detonation. I might be paraphrasing wrong, but that page in the article phrases it very effectively.

Do the 2v 351C heads suffer the same problem? The combustion chamber are a similar setup, with baseball sized domes.

Does this mean a 4v combustion chamber with 2v intake/exhaust runners is a better street head? (I guess that's the Aussie head)
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Old 03-10-2008, 12:38 AM   #2
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Yes they are detonation prone and yes the aussie heads make great street heads.
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Old 03-10-2008, 01:51 AM   #3
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yeah they are detonation prone, but you can pickup some aussie head here www.ausfordparts.com they also have nice alum cleve heads and parker funnel web intakes ftw
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Old 03-10-2008, 06:21 PM   #4
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considerations are due to the quality level of the gasoline fuel that you are burning....

this is NOT just an "octane number" related thing.
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Old 03-10-2008, 09:30 PM   #5
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Are they any worse or better than 69cc D9AE heads from a 351W?

The combustion chambers look similar to me, and they both have massive cc volumes.
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Old 03-11-2008, 12:45 AM   #6
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Quote:
Originally Posted by dan50 View Post
Are they any worse or better than 69cc D9AE heads from a 351W?
They are worse than any W head.

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The combustion chambers look similar to me, and they both have massive cc volumes.
No C head chamber looks like any W head chamber. All Ws have wedge chambers (thin on one side and deep on the other). No C chamber looks like this. They are all canted valve heads that do not have wedge shaped chambers. 2V C heads have a round chamber. Remember, it's not the size of the chamber that makes a head detontation prone. It's the shape of the chamber that causes this.
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nonstroked, stock iron heads and NO NITROUS!!!!!!!!
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Old 03-11-2008, 12:50 AM   #7
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2V heads have superior valve geometry and size....and that's about it. Their ####ty chambers relegate them to the junk pile or concours restoration stuff/stock rebuilds.
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Old 03-11-2008, 03:03 PM   #8
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iI would guess that if you are lazy as murphy has stated,
then many would put them in the junk pile... but if superior airflow and you are not lazy and want to do a little work to build it right...and not follow someones LAZY additude at putting together a straight valve engine ( a winsor) out of whatever is the cheapest part from some mail order house that is going broke and closing out everything,....then the cleveland head will give you more power...

I know of quite a few 2bbl cleveland headded engines ( even if on a W block) that still run circles around a TW or E-bock head/ AFR setup....

most all of anything else still dont wanna come out and play with a 4 bbl cleveland...they are "sceeered"..... to get embarrasseddddd...!!!!!
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tires are the great equalizer
a degree wheel, EIGHT INCH dial caliper & adjustable pushrods should be just as normal as a 1/2" wrench in your toolbox
there aint no shortcuts to doing it RIGHT....
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Old 03-11-2008, 03:30 PM   #9
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Well one of the things that turns me on to the 351C 2v heads is that they flow so much better than the D9AE 351W heads, so they'd make more torque. I know the stock D9AE will make 300+ ft-lbs between idle and 3000 RPM with the stock cam.

But I remember like ten years ago right after I picked up a few 2v engines I heard that the heads were detonation prone, and that article spells out why, so this has made me really hesitant to invest $1000 into a set of 2v heads and intake manifold plates for a 351W truck build. My first Bronco detonated like a bugger and I could never get it sorted out. Previous owner had rebuilt the engine HIS way, which was the crap way apparently. I don't want to duplicate that.

So how does one make a 351C 2v head work well without detonation in a 5000 lb truck?
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Old 03-11-2008, 03:47 PM   #10
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flat quench area....
cam makes a difference
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a degree wheel, EIGHT INCH dial caliper & adjustable pushrods should be just as normal as a 1/2" wrench in your toolbox
there aint no shortcuts to doing it RIGHT....
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Old 03-27-2008, 11:11 PM   #11
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kinda off topic.
but I have a simple question about the Aussie heads IF you have the flat top pistons (like his bronco would) are you able to just bolt them on to that block? (with the normal modifications to the water ports)
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Old 03-28-2008, 05:11 AM   #12
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aussie 2 V HEADS are still a canted valve head but have smaller ports similar to a "regular us cast available head " and chambers are as like a closed chambered 4 V head....but actually the valve sits a little deeper as measued from head gasket surface.
because of the "canted valve" angle, the outer edge of both valves will get close to the ring land when the pocket is cut for clearance.

there is another post that speaks of this situation...



If you wanna check it yourself, you can fit up the rod/crank/straight valve piston, and put the pocket cut as needed depending on rocker / pushrod / cam setup and see what you get.
if the cam / rocker setup does not have much overlap / duration then the pocket only needs to be cut for one of the valves....
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I have gone down the road that you are only now about to travel.
tires are the great equalizer
a degree wheel, EIGHT INCH dial caliper & adjustable pushrods should be just as normal as a 1/2" wrench in your toolbox
there aint no shortcuts to doing it RIGHT....
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Old 03-31-2008, 12:50 PM   #13
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Yes, the 2v are prone to detonation, but don't confuse that with them not being able to work. A lot of people disregard them, and i can't say it's totally without reason, but I can assure you the heads are more capable than some people think. We run a dirt track car with a 351c, where they outlawed the aussie heads about 4 years ago, that left us with plain old 2v heads... The last one we had on the dyno made 418hp, 424tq, through a stock 2v intake, stock 2v heads, 500 cfm 2bbl, all unported. We're now around 13.5:1 compression (using flat tops btw), and have not had any failures in about 2 years now. These things require VERY little timing, and with the appropriate fuel and cam, can be made to run well.
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