Engine Help ...455 - Pontiac GTO Forum
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post #1 of 47 (permalink) Old 03-26-2013, 11:39 PM Thread Starter
 
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Engine Help ...455

I am trying to determine the compression ratio on my '69 GTO. It has a '74 trans am 455 engine. I saw 6X casted on the side of the heads.
Are 6X heads standard on the '74 455 or are they after market?
How do you measure the stroke?
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post #2 of 47 (permalink) Old 03-27-2013, 02:50 AM
 
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You need to look for a two leter code below the pass side head and let us know what it is like YC or what yours is then we will let you know what you have.

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post #3 of 47 (permalink) Old 03-27-2013, 08:13 AM
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6x heads are Pontiac and were found on 350/400 blocks. 4x heads were common on '73/'74 455's....



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post #4 of 47 (permalink) Old 03-27-2013, 08:29 AM
 
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there are several variations of the 6-x head all having slightly different CC's also.

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post #5 of 47 (permalink) Old 03-27-2013, 06:42 PM Thread Starter
 
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Ok, I looked at the head, here is what is says.....

6X......GM8......DN.........D185

does that help???
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post #6 of 47 (permalink) Old 03-27-2013, 07:09 PM Thread Starter
 
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Ok, checked again...the passenger side is 6X GM8, the drivers side head has 6X GM6 on it.
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post #7 of 47 (permalink) Old 03-27-2013, 07:41 PM
 
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I like the wallaceracing.com website, lots of good pontiac info on coding heads and engine blocks. Can give you an idea of the various chamber volumes, etc. Without knowing "exaclty" what you have for crank, pistons, and chamber volumes, you can only guess on Compression ratio, unless you used a "Whistler" test or something similar. You would likely need to find a performance shop that would have the right equipment or a Whistler. We always had one at the local circle track tech barn for checking CR.

There may be other ways to find CR that I am missing...
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post #8 of 47 (permalink) Old 03-27-2013, 09:18 PM
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You do have to have some very accurate measurements to get an accurate CR (or access to some very high dollar test equipment).

Let me ask you, why are you looking for the information --- I mean, how does that figure into your plans?

It'd be good for you to visit some of the various sites that have information on how to decode all the various markings on Pontiac engines (Google "pontiac engine codes" for starters).
I recommend you start by positively identifying exactly what you've got there, then working from that point. By that I mean making sure it's a 455, what model year it is, what haeds are on it, etc.

We can help if you get stumped but it's more fun to figure it out on your own.

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post #9 of 47 (permalink) Old 03-27-2013, 10:35 PM Thread Starter
 
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im trying to just find out some information about my car. when i bought the car 7 months ago, i found th code on the engine. it matches a 74 trans am 455. The heads dont seem to be stock to the engine based on the numbers (D185 is not off a 74). So what could have gone into this thing? with thos heads, what kind of horsepower should I be getting? better than the 250 it advertises??? I love a mean sounding muscle car and would like to put a street/strip cam in it, but i need to know the CR.
I am slowly upgrading parts on it. Getting a HEI distributor and coil next month, getting rid of the points. Adding A/C..too damn hot in south texas...need some body work for rust issues. minor cosmetics interior (mainly just dash, rear tray, and headliner.
Its a great car. I just wanna be able to answer questions from peopl and myself about what kind of power it really has.
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post #10 of 47 (permalink) Old 03-28-2013, 01:51 AM
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D185 indicates model year 1975, so you're right about that.
What's the block date code? Casting number? Block code?

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