Author Topic: 1976 head cyclinder swap  (Read 469 times)

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Offline Hippie459MN

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1976 head cyclinder swap
« on: September 09, 2012, 03:32:19 PM »
I have a 1976 Trans Am with the original 455/4speed (Not the SE and no t-tops) but it has the 6H heads on it and I have some 4X heads with the 4H stamp on the exh boss and it looks like they are 98cc heads and the 6H look to be 124cc heads from what I have found. About 13-14 years ago I built it up a bit using the stock heads and raced it on and off and then had some issues here about 2 years ago and its just been sitting and this winter I am going to rebuild the motor and was wondering what kind of gain I can expect in the CR of the motor. It is already .060 over and just looking to make the most power I can without spending the money for alum heads. They are pretty much stock right now and have had all new valves and valve job and new springs and all that but I am going to have the heads worked on if it is worth it. Just wondering if it is. Has to be better then the low CR I am at now.

Just looking for any input on if this would be a good swap and if so what should I put the most attention into when getting the head work done. I plan to run some 1.65 roller rockers (Already have them) but not sure on the rest of the motor components yet. Guess I want to see what kind of numbers I get from the heads first and go from there.

Great looking site. Been browsing for some time now and just signed up recently.
-Kevin

1976 Pontiac Trans Am
469ci (Original 455ci)
Factory Borg Warner 4 speed

Offline pancho400cid

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Re: 1976 head cyclinder swap
« Reply #1 on: September 10, 2012, 01:09:16 PM »
I can't get to a lot of "hobby" sites from work due to our hyper-active firewall, so I can't check anything right now... They just want us doing work related stuf....  ::)

Wallace Racing's website has good info on casting #'s vs. valve dias and chamber volumes. 

Once you know the numbers you can put actual bore (incl the .060 over) and head gasket thickness(about .040" for off-the-shelf gaskets usually If I recall - measured some after taking them out long ago) and your engine particulars into an on-line compression ration calculator:

    www.wallaceracing.com/cr_test2.php


« Last Edit: September 10, 2012, 01:10:57 PM by pancho400cid »
1978 Trans Am - Brown - Current Project
1978 Trans Am - Silver - Future Uncertain

Offline 72blackbird

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Re: 1976 head cyclinder swap
« Reply #2 on: September 10, 2012, 07:55:51 PM »
Any 98-102cc head will wake up a sleeping 455 running 8:1 SCR. Run a TC-01 HF from Pacific Performance Racing with 9-9.2:1 SCR and you will like it- idles smooth and works with the stock converter, midrange from 60-120 mph like the Space shuttle lifting off the launch pad. Want more? Port those heads, run a 2500 stall converter and a TC-02 HF- it's good for at 520 hp and 540 lb.-ft with stock e-heads on a 455, not sure about the ported iron heads.

1.65 roller rockers are okay, but be sure to elongate the tops of the pushrod holes 1" down to avoid pushrod contact with the head.

Geno

Offline Hippie459MN

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Re: 1976 head cyclinder swap
« Reply #3 on: September 15, 2012, 09:39:49 AM »
Thanks for the info guys. I didnt realize there were any replies, for some reason it didnt notify me of any in my email.

It is a 4 speed so no worries about a stall/torque converter.

The only reason I was considering running 1.65 roller rockers is I already have a set from another pontiac motor that I was going to build but the car got sold and the new owner didnt want any of the motor parts so I have a few parts I might as well put to use if I can.

Poncho400cid, Thanks for the handy tool.
-Kevin

1976 Pontiac Trans Am
469ci (Original 455ci)
Factory Borg Warner 4 speed