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post #1 of 14 (permalink) Old 08-28-2018, 02:19 PM Thread Starter
 
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Question about#13 heads

Hello all. I just picked up a XH 400 from a 70 grand prix. It has #13 heads.

So here's my question. Some sites call them ram air lll and some don't. Is there different#13 heads? I understand that the#12s were manual transmission and 13s were automatic transmission.

I doubt that the 70 grand prix was a ram air, probably wasn't even a option.

So was there no automatic ram air cars????
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post #2 of 14 (permalink) Old 08-28-2018, 02:54 PM Thread Starter
 
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Here's a screen shot of a page. It shows 12 and 13s as ram air lll but not on a XH block. So why would #13 heads off a XH not be ram air lll?
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Last edited by My65goat; 08-28-2018 at 03:19 PM.
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post #3 of 14 (permalink) Old 08-28-2018, 03:22 PM Thread Starter
 
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And another one from a different site. Pontiac power.

But yet Wallace doesn't list Em as ram air lll.

So I'm a little confused. Thanks in advance.
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post #4 of 14 (permalink) Old 08-28-2018, 07:30 PM
 
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#13 heads are not RA III, shows as 350HP 400CI. #12 heads are shown as RA III. I also see another #12 head on the B-body cars and it is likely a small valve head.

Does you heads have screw-in rocker arm studs and the larger valves? Then you have the better heads.

Read this: https://www.gtoforum.com/f12/number-13-heads-128169/
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post #5 of 14 (permalink) Old 08-28-2018, 07:39 PM Thread Starter
 
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Yes they have the screw in studs and 2.11/1.77 valves.

So again why do the two sites that I took screen shots of show as auto trans ram air3 ?

The #12 and #13s show show same specs.

Did they make a automatic transmission ram air 3 car, Gto, firebird....they can't all have been manual transmission can they?
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post #6 of 14 (permalink) Old 08-28-2018, 07:49 PM Thread Starter
 
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I did read this thread, but apparently the original author was mistaken for thinking all ram air heads were round port. The early ram air heads were D port. The #12s Are D port.

Now what pinion head wrote....well that makes sense, except. ..they did not use #12s on automatic transmission cars......That's where they used the #13s .

So, can anyone confirm or deny, did they make any ram air lll car that had a automatic transmission ???? ( firebird or GTO).

I'm having a hard time believing they where all 4 speeds...
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post #7 of 14 (permalink) Old 08-28-2018, 08:04 PM
 
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Originally Posted by My65goat View Post
I did read this thread, but apparently the original author was mistaken for thinking all ram air heads were round port. The early ram air heads were D port. The #12 s Are D port.

Now what pinion head wrote....well that makes sense, except. ..they did not use #12 s on automatic transmission cars......That's where they used the #13 s .

So, can anyone confirm or deny, did they make any ram air lll car that had a automatic transmission ???? ( firebird or GTO).

I'm having a hard time believing they where all 4 speeds...
OK, #12 heads were used as RA III heads on both the manual (3-speed & 4-speed cars) with block code WS and the automatic cars with block code YZ - for the GTO

The early 1968 RA I heads #31 were D-port. The 1968 1/2 RA II #96 were round port. RA III heads for 1969-70 were D-ports and RA IV were round ports.

Looking at the Firebird engines, for 1970, I see heads 12/13 listed as RA III on the 400CI automatic car & #12 for the manual.

The difference between #12 & #13 with regards to the Firebird are unknown to me. It may be that they were used after a specific date post #12 heads. But regards to the GTO, #12 is the correct RA III head.

Just found this from another website: "70-RAIII(d-port) m/t FB's and GTO's used #12's. With a/c #13's. Some auto's w/o a/c got 13's too."

From another Trans-Am site, the #13's were typically for automatic cars, but 12/13 seem to be interchangeable for the F-Body cars only as RA III heads.

Last edited by PontiacJim; 08-28-2018 at 08:35 PM.
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post #8 of 14 (permalink) Old 08-28-2018, 08:35 PM Thread Starter
 
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OK Jim I respect your knowledge. I just find lots of conflicting info out there. For example this firebird engine was rated at 345hp but it was the same engine they put in the Gto (YZ with #13 heads auto tranny).....they underrated it at 345hp to meet GMs specs for power to weight ratio.

So I guess my initial question about 2 different #13 heads can be explained.

Maybe GM took the time to hand cc each head and take the ones with a slightly larger combustion chamber to use on the XH engine (350hp auto trans grand prix)......and then they took the tighter combustion cc heads for the good cars like Gto and firebird.....and then they could lie about the hp so it meets the Gm power to weight ratio. ( chart in second picture for 345hp YZ engine auto tranny 13 head specifically listed as ram air lll).

I see lots of conflicting info....The screen shots I provide show #13 used on YZ and XH auto engines.

Thanks for sharing your knowledge Jim, sincerely Matt
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post #9 of 14 (permalink) Old 08-28-2018, 09:00 PM
 
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Originally Posted by My65goat View Post
OK Jim I respect your knowledge. I just find lots of conflicting info out there. For example this firebird engine was rated at 345hp but it was the same engine they put in the Gto (YZ with #13 heads auto tranny).....they underrated it at 345hp to meet GMs specs for power to weight ratio.

So I guess my initial question about 2 different #13 heads can be explained.

Maybe GM took the time to hand cc each head and take the ones with a slightly larger combustion chamber to use on the XH engine (350hp auto trans grand prix)......and then they took the tighter combustion cc heads for the good cars like Gto and firebird.....and then they could lie about the hp so it meets the Gm power to weight ratio.

I see lots of conflicting info....The screen shots I provide show #13 used on YZ and XH auto engines.

Thanks for sharing your knowledge Jim, sincerely Matt
Yep, Pontiac played with HP numbers. The GTO & Firebird 400 engines were the same. The difference in keeping the weight to HP within GM guidelines was to limit the amount the secondaries on the carb opened up. This was easy enough to get around and many made the adjustment to get the full 360 HP.

I don't think Pontiac would have measured CC's of the chamber and set them aside and use them on one engine line versus another engine line as they were all machined. Typically, the cc's are more than advertised, so 72 cc's were more likely 75 cc's. The advertised cc's were used for those who would run their cars at the drags under specific divisions and then NHRA or IHRA had their minimum numbers a head chamber size could be.

In general, most big valve D-port heads flow close to the same. The casting numbers are more important to those wanting number matching or replacement numbers matching when the engine/heads are MIA. The head chamber cc's, big valves, & screw-in studs are what most look at when selecting a performance head for their engine project, and often to get a compression ratio that can use pump gas if high octane or gas additives are not wanted.
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post #10 of 14 (permalink) Old 08-28-2018, 09:07 PM
 
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Factory published literature.

YS and WS engines received the same cylinder heads. If the MPC can be trusted, then all RA III had the same heads irregardless of transmission or body style (Firebird/GTO).

Also, same part number is shown for all manual transmission 400 cubic inch manual trans 4 bbl Firebird or Tempest.

This means #12 heads would be for all RA III applications and for any Firebird or Tempest with the 400 cubic inch V8, manual trans and 4 barrel carb.

The #13 head is for 400 cubic inch V8, M40 auto trans with 4 barrel carb used in Firebird, Tempest and Grand Prix. None of the factory literature that I have shows the #13 head for any other application other then the base 400 auto 4bbl engines.

Summary:
#13 heads are NOT RA III
#12 heads could be RA III

Information found on the internet should be used for reference and not actual gospel without cross referencing with other verifiable sources such as factory published data. Does go both ways though....there are irregularities in factory literature but it's not rampant.



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