# Question about#13 heads



## My65goat (Jul 26, 2017)

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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## My65goat (Jul 26, 2017)

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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## My65goat (Jul 26, 2017)

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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## PontiacJim (Dec 29, 2012)

#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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## My65goat (Jul 26, 2017)

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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## My65goat (Jul 26, 2017)

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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## PontiacJim (Dec 29, 2012)

My65goat said:


> 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 [URL=https://www.gtoforum.com/usertag.php?do=list&action=hash&hash=12]#12 s[/URL] Are D port.
> 
> Now what pinion head wrote....well that makes sense, except. ..they did not use [URL=https://www.gtoforum.com/usertag.php?do=list&action=hash&hash=12]#12 s[/URL] on automatic transmission cars......That's where they used the [URL=https://www.gtoforum.com/usertag.php?do=list&action=hash&hash=13]#13 s[/URL] .
> 
> ...


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.


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## My65goat (Jul 26, 2017)

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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## PontiacJim (Dec 29, 2012)

My65goat said:


> 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.
> 
> ...


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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## Shake-N-Bake (Jun 16, 2015)

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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## PontiacJim (Dec 29, 2012)

Shake-N-Bake said:


> 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).
> 
> ...


Your info may indeed be more accurate. I got the 12/13 RA III heads for the Firebird from the Pete McCarthy book and what was posted on the Trans-Am/Firebird forums with regards to the #13 heads. And yes, on the B-body cars too. So, one of those conflicting Pontiac things?


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## Shake-N-Bake (Jun 16, 2015)

PontiacJim said:


> Your info may indeed be more accurate. I got the 12/13 RA III heads for the Firebird from the Pete McCarthy book and what was posted on the Trans-Am/Firebird forums with regards to the [URL=https://www.gtoforum.com/usertag.php?do=list&action=hash&hash=13]#13 [/URL] heads. And yes, on the B-body cars too. So, one of those conflicting Pontiac things?


I think I remember reading some owners of RA III cars reported they came with #13 heads from the factory. I don't remember if those claims were validated though... ??

Thinking out loud...
The complete engines were assembled at the engine plant before shipping out to the various assembly plants across the country. Each 2 character engine code was a recipe for how the engine was to be built. Part of that recipe was the cylinder head....which was a sub-assembly itself.

I expect the cylinder heads were machined and fitted with valves, springs, plugs etc and then moved to a "pick area" for use with the appropriate complete engine recipe. I have always wondered what method was used to identify the cylinder head assemblies from each other. Did the cast numbers at the siamese ports serve this purpose? If so, then all RA III engines called for #12 heads and that is what they all should have received.

Step back a few years to 1967. The basic cylinder head cast number at the center exhaust ports is 670. Yet we know of at least 3 different valve/spring arrangements for various engine codes. In order to identify the different cylinder head sub-assemblies, it appears the cylinder heads received a stamp on one of the round pads cast into the center exhaust ports. I don't remember the details but I think blank might have been for 2 bbl and 4bbl auto applications, Z for 4 bbl manual and X for RA engines. I wonder if this practice was abandoned for the 1968 model year on since it could have been unreliable. 

Conventional wisdom says if the cast number is different.....the casting is different. So there has to be some physical difference between the #12 and #13 heads. No clue what that difference might be though...

On a different note....but possibly related to this topic. We all have seen the performance engine specifications document for 1970 so we know there was conflicting information in there related to the WT engines related to 2 bolt vs 4 bolt mains.

Hard to say 50 years later what may or may not have happened.  Still fun to discuss.

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## My65goat (Jul 26, 2017)

Yes exactly what I was finding, pontiac power.com shows as ra3 and classic Pontiac. Com also, but Wallace and Butler don't mention anything about ra3, so yes conflicting info and that is why I asked the question. I also just read that they used the #13 heads on air conditioned cars.


Well thank you both for the info, I have learned tons of good info here!


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## PontiacJim (Dec 29, 2012)

All good points. I think it fair to say that Pontiac used different procedures & techniques that did not always follow protocol.

I don't know what the actual differences, if any, between the #12 & #13 heads would have been. I would think that the castings were the same, but I wonder if the chambers may have been a little larger (providing let's say 10.5 versus 10.0 compression) seeing they were used on the Firebirds with automatics. Automatic cars got a slightly milder cam and the lower compression would compliment the milder cams used on the automatics. With the B-body cars, they were not really performance orientated so a slightly lowered compression to start with seems fitting and then you had a different cam installation depending on transmission type.

1970 was leading into the reduced compression ratio's and net vs gross HP of the 1971 models. So it would also be interesting to compare date codes on #12 heads used on the Firebirds versus the #13 's used on the Firebirds to see if they co-existed at the same time or if the #12 's were superseded by the #13 's at/near a specific month/day through a Bulletin announcement like the change over to screw-in rocker arm studs on the [URL=https://www.gtoforum.com/usertag.php?do=list&action=hash&hash=4]#4 X[/URL] heads which were at first press-in studs and later screw-in studs - "With the discovery of issue #4 of the 1973 Craftsman Service News set, all theories were validated with a simple, one-paragraph statement on page 54 entitled, “Threaded Rocker Arm Studs”. The paragraph clearly states that all Pontiac V-8 engines would receive threaded rocker arm studs beginning with engine #709986 which was assembled on or about May 7, 1973 and would carry throughout the remainder of 1973 engine production and on to 1974.

But, if I were a betting man, my money would be on a chamber CC difference with the #13 's be slightly larger to reduce compression on the Firebird/Trans-Ams with automatics and yet still be called the RA III heads along with all the RA III specific items that were included in that package option. :thumbsup:


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## can.am455 (Oct 4, 2021)

Hi. I was reading your thread about #13 heads and I noticed that no one was talking about using them on their Pontiac. only chatting about what the hell they are, I was told by a brother Pontiac Nut that #13 heads were identical to RA III heads and that they were used on full size cars and did not need the name. Back in the late 60's and early 1970's older Pontiac buyers looked down on Trans Am's and Ram Air Goats as kid stuff. They did not want that associated with their car. They did not want to be made fun of. This type of corporate thinking was not only at Pontiac, Buick did it as well with the Super Wildcat in 1964 and 1965. They used "GS"sparingly on full size customers. I think "GS" was used just once on the big Wildcat. The car that the engine was named after. This is crazy thinking because a full grown man was driving around in command of a car called a "Wildcat". They should have called it the "Bonazamobile". The number 13 head I have had larger valves. I had mine cut to receive RA IV valves. They have a small combustion chamber, so I had to order forged pop up pistons, for the meat, then cut my own dish into them to get into the 9.5: 1 -9.75:1 neighborhood. The engine still pinged. I then started adding one gallon of 116 octane racing fuel into a 20 gallon tank of premium gas and that did the trick. A 455 with #13 heads is a MOPAR (Mostly Old People And ********) NIGHTMARE. My 455 is mounted to a built Turbo 400 and then onto a 12 Bolt with a Moroso Brute Strength Posi with 4:10 gears. I love the Ford 9 inch, but I just could not do it. Maybe if the car was a plain Jane Lemans and not a 1977 Can Am, maybe then I could have, but not something rare. My alternate set of heads were from a 1968 Firebird 400. Those heads had combustion chambers the size of a couple of tablespoons. Those heads would really wake up a 1977 400. My car was only two and a half years old when I bought her and we are still together. There is something about a Pontiac. It gets three miles to a gallon, but it's a fun mile to travel. After the upgrades, I drove it to work for a little over a month. At the end of that month I received an $800 Chevron bill. This was in late 1989. It was time to borrow dad's 80 Camaro. I wore contacts back then that had three little weights on them to keep them in place because of a astigmatism, my point is that when I would romp down on it the sudden acceleration would spin the contact lens because of those little weights and I couldn't see a blooming thing for a couple of seconds. It felt like a couple of days because I was rapidly approaching something and I was about to make a red apes ass out of myself with my car. I say use the heads. Have fun.


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## joet2442 (Nov 3, 2021)

My65goat said:


> 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.
> 
> ...


I have 70 gp with xh 400 engine 400 auto #13 heads


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## Lok (11 mo ago)

Guys I just came across this post, my experiences with pontiac heads is that castings 12 was designated manual trans 13 automatic, but yet I found them each on both. My gto numbers matching 13 heads screw in studs , we made a poly cast of the chamber (drivers side # 5 with the stock valve in place ) and measured all runs on the intake side(wanted to make a cast but it cracked twice on removal so we moved on) this was 1998. I carried that casting with me for years to swap meets and to a few other pontiac guys garages and it fit perfectly into #12 heads everytime they were stock and screw in , they also fit into #13 heads stock and screw in , as well as #16 heads 1969 screw in and large valve. I never found #48s to try accurately. I also did half assed measurement to the intake ports and they all seemed to be the same when not messed with. One thing that messed with me was when I measured a set of 13s converted to screw in it did not fit nearly as well it seemed to have hump near the intake valve edge away from the spark plug. I lost that casting around 2008. 
So in conclusion from my experience is 12s and 13s casting is either the same or very close as is 16s I do believe valve springs and perhaps the valves could be different(ie tulipped , presser for springs ect.)
Just my personal experience dating back to 1988 and wondering why so many casting looked identical on pontiac heads. 
Lok


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## PontiacJim (Dec 29, 2012)

Lok said:


> Guys I just came across this post, my experiences with pontiac heads is that castings 12 was designated manual trans 13 automatic, but yet I found them each on both. My gto numbers matching 13 heads screw in studs , we made a poly cast of the chamber (drivers side # 5 with the stock valve in place ) and measured all runs on the intake side(wanted to make a cast but it cracked twice on removal so we moved on) this was 1998. I carried that casting with me for years to swap meets and to a few other pontiac guys garages and it fit perfectly into #12 heads everytime they were stock and screw in , they also fit into #13 heads stock and screw in , as well as #16 heads 1969 screw in and large valve. I never found #48s to try accurately. I also did half assed measurement to the intake ports and they all seemed to be the same when not messed with. One thing that messed with me was when I measured a set of 13s converted to screw in it did not fit nearly as well it seemed to have hump near the intake valve edge away from the spark plug. I lost that casting around 2008.
> So in conclusion from my experience is 12s and 13s casting is either the same or very close as is 16s I do believe valve springs and perhaps the valves could be different(ie tulipped , presser for springs ect.)
> Just my personal experience dating back to 1988 and wondering why so many casting looked identical on pontiac heads.
> Lok


They may look identical on the outside, but they can be similar or very different on the inside - intake runners, D-port exhaust vs Round port exhaust, chamber volume size & depth, valve angle 14 degrees vs 20 degrees, valve sizes, valve stem lengths, valve spring installed heights, screw-in studs or press-in studs, and even accessory bolt holes can be different.

Pontiac only used 1 block size having different bores, strokes, and main bearing sizes - no big block or small block like other brands. The block/head bolt pattern is the same from 1955-1981, so you could bolt any year head on any year engine, but it does not mean that they will work on any year engine.


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## Lok (11 mo ago)

Jim I agree 100% , one thing I should also mention was I specifically stayed with 1970 , 1969 a few 1968 heads, as that was/what I am really into . I am enjoying your cam basics , it's great read, and as I am going to hyd roller this time around to compensate for lower compression (9.25 ). Using KB +17cc pistons so I can keep my stock 13 heads (which just cc`d and stock I found them to be truly 71.25 cc using a hydrualic oil), shooting for 400+ hp with stock manifolds, carb, and 2.5 inch exhaust. 
Jim the 20 degree heads are the the 66 and earlier heads , is my memory right on this , and after that they were all 14 degree? 
Thanks for all the info


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