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#1
07-06-2012, 12:18 PM
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1970 350/255HP #11 heads combustion chamber size
Hi, all... re-emerging after a ten (!) year hiatus.
I've always wondered why Pontiac cylinder head references never provide combustion chamber volume info for the 350/255HP #11 heads. (Factory lists the compression ratio as 8.8:1 with the stock flat-top pistons.) Here's an example: http://www.wallaceracing.com/head1.htm I understand that these are "small valve" heads and probably not very useful for performance minded folks, but surely, someone must have measured the combustion chambers on these heads at some point in the past. (I note that, last time I looked, the AMA specs for the 350 do not list the CC volume either!) So, what's up with that? Anyone out there know the CC volume of the #11 1970 heads? Or is there an online reference with such information?
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Bought: 1970 Le Mans Sport Convertible (second owner,) Palladium silver, 350/2bbl (sigh) with Comp Cams 268H grind (installed by previous owner), TH350 Trans. Mods: Front suspension: Global West negative roll tubular upper arms, Del-a-lum bushings, Koni shocks, 12" disc brake conversion, 1.1" front sway bar, Rear suspension: Global West tubular control arms, springs, sway bar. Exhaust: Flowmaster 2.5" American Thunder system. Mostly complete: Firewall-forward engine compartment restoration |
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#2
07-06-2012, 01:29 PM
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Pontiac dude lists 1970 #11 heads on a 400 have 80cc chambers. This would place a 350 near 8:1 scr. The factory overstated compression on most engines from what I read and the only way you will know is to cc them yourself.
Karl 
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#3
07-09-2012, 06:34 PM
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Quote:
__________________
Bought: 1970 Le Mans Sport Convertible (second owner,) Palladium silver, 350/2bbl (sigh) with Comp Cams 268H grind (installed by previous owner), TH350 Trans. Mods: Front suspension: Global West negative roll tubular upper arms, Del-a-lum bushings, Koni shocks, 12" disc brake conversion, 1.1" front sway bar, Rear suspension: Global West tubular control arms, springs, sway bar. Exhaust: Flowmaster 2.5" American Thunder system. Mostly complete: Firewall-forward engine compartment restoration |
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#4
07-09-2012, 07:07 PM
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__________________
 ___________________________________ "Objects in mirror are closer than they appear" 
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#5
07-09-2012, 07:40 PM
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Mine were closer to 89cc.
these heads were found on 350 and low performance 400 of 1970 |
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#6
07-09-2012, 09:36 PM
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11s
Mine are also 89cc, don't think I've ever heard of anyone finding 80cc 11s...
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1974 Lemans Sportecoupe GT (daily driver) .030 over 354, #47 heads (84cc), Lunati voodoo 700 camshaft (207/213 @ .050), logs, 2.5 duals, X-pipe and Dynomax super turbo mufflers, 3.08 rear |
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#7
07-09-2012, 10:33 PM
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Quote:
Long ago when I had the motor apart, I did a quick and dirty volume measurement, and came up with a number closer to 90cc than 80cc. (But I didn't trust my measurements so... asking for other sources.) The lack of widely-published numbers seems puzzling, even if these are small-valve heads. I was always surprised to see head listings showing nothing more than the factory's published CR for the 11 heads while most every other head has a volume measurement listed.
__________________
Bought: 1970 Le Mans Sport Convertible (second owner,) Palladium silver, 350/2bbl (sigh) with Comp Cams 268H grind (installed by previous owner), TH350 Trans. Mods: Front suspension: Global West negative roll tubular upper arms, Del-a-lum bushings, Koni shocks, 12" disc brake conversion, 1.1" front sway bar, Rear suspension: Global West tubular control arms, springs, sway bar. Exhaust: Flowmaster 2.5" American Thunder system. Mostly complete: Firewall-forward engine compartment restoration |
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#8
07-09-2012, 10:33 PM
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Quote:
__________________
Bought: 1970 Le Mans Sport Convertible (second owner,) Palladium silver, 350/2bbl (sigh) with Comp Cams 268H grind (installed by previous owner), TH350 Trans. Mods: Front suspension: Global West negative roll tubular upper arms, Del-a-lum bushings, Koni shocks, 12" disc brake conversion, 1.1" front sway bar, Rear suspension: Global West tubular control arms, springs, sway bar. Exhaust: Flowmaster 2.5" American Thunder system. Mostly complete: Firewall-forward engine compartment restoration |
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#9
07-09-2012, 11:19 PM
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3 people with the same results, must not be a fluke
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#10
07-10-2012, 12:20 AM
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I have also heard that the 7H1 were a 80cc head. But when i checked mine reasonally they came out to 90cc.
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#11
07-10-2012, 06:16 AM
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I have a pair of 1971 #94 heads that are probably very similar to the 11's. They also measured at right around 90cc. I was hoping for 80cc chambers when I bought them. I had them cut .030" to get them down around 84-85cc.
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#12
07-10-2012, 07:49 AM
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my 1970 #11 headed 350, with performer, qjet and unknown cam ran great, shoulda kept it for backup...
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#13
07-10-2012, 08:14 AM
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Agreed, I had one in a 70 LeMans Sport and it would burn rubber right through first gear even though it had the OEM 2.56:1 and 2 barrel carb.
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___________________________________ "Objects in mirror are closer than they appear"
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#14
07-10-2012, 09:11 AM
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Quote:
It seems every one of them had different cc's. Most list the factory rating, which most of the times weren't accurate either. The earlier heads were listed in the Service Manual with the cc's, while the later ones weren't. So, if you want to know the cc's of a head, Measure it.  The factory usually rated the 13/12 heads as 72 cc's. But most are not, usually 74-78 cc's for 13 heads. NHRA shows them as 64 cc's.  So, I should probably just list the cc's or CR as check them yourself.
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John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
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#15
07-10-2012, 03:03 PM
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Quote:
Karl
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#16
07-10-2012, 06:53 PM
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I measured my 350 #11 untouched virgin proud valves @ 85cc`s
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If your not at the table you're on the menu A man who falls for everything stands for nothing. |
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#17
07-10-2012, 07:46 PM
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Quote:
Bore it .030 over and zero deck it you would be near 8.3:1scr Karl
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#18
07-10-2012, 08:37 PM
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They will never see a 350 again.. better options available
__________________
If your not at the table you're on the menu A man who falls for everything stands for nothing. |
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#19
07-10-2012, 10:31 PM
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Quote:
Karl
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#20
07-10-2012, 10:52 PM
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Quote:
fwiw small valve heads have same port size as big valve till you get to the seat area... Excellent candidates for big valves without worrying about sunk valve seats on big valve heads. Plus often @1/2 point less compression than same year 4 barrel heads. Most times you can get these type heads cheap...even free sometimes...dont overlook them. Last edited by BruceWilkie; 07-10-2012 at 10:58 PM. |
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