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Old 11-18-2019, 09:43 PM   #1
Phil Gillespie
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Default 8ba Heads 7RT or EAB

Have an 8BA fitted to 38 PU. Doing a bit of work on it. Presently have inlet manifold off to check all valve clearances.
This PU runs well with approx 12500 mls on rebuilt engine. I did not do the work. Its presently fitted with 8RT heads C/R 6.8 :1 . I have a good set of EAB heads C/R 7.2 :1 I understand. Would there be any notticeable improvement with changing out these heads. Engine pretty much stock 40 over, Max 1cam and single 97 carb with a newly rebuilt Charlie NY chev distributor fitted with adjustable mech and adjustable vacuum advance. Not sure what present piston to head clearance is.
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Old 11-18-2019, 10:00 PM   #2
51504bat
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Default Re: 8ba Heads 7RT or EAB

I'm running EAB heads on the 8ba in my '39 p/u. Stock rebuild with a supposed Merc cam but that is it came with a bunch other other Merc parts I bought and the machinist said it was in better shape then the one that was in the engine at the time. Other than the cam(?) and EAB heads, a Bubba mechanical advance distributor, and a Charlie NY carb its 100% stock. It runs great. I think you'll notice an improvement with the EAB heads over the 8rt ones you're running now but that's JMO.
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Old 11-18-2019, 10:04 PM   #3
51 MERC-CT
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Default Re: 8ba Heads 7RT or EAB

IMO it won't make that much difference unless the heads are shaved/massaged to get the much touted .050" head to piston clearance.
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Old 11-19-2019, 12:41 AM   #4
Phil Gillespie
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Default Re: 8ba Heads 7RT or EAB

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Originally Posted by 51 MERC-CT View Post
IMO it won't make that much difference unless the heads are shaved/massaged to get the much touted .050" head to piston clearance.
Yes thats my thinking also. Coud remove one head and check where the 8RT head is at with piston to head clearance and go from there.
Or just complete valve clearance checking and keep on trucking.
Phil NZ
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Old 11-19-2019, 01:06 AM   #5
Tinker
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Default Re: 8ba Heads 7RT or EAB

Depends on what you want to achieve. You could clay or make tin foil balls. People can get too aggressive and over mill heads. I'm a stocker with a bit of mill and lift.


Always something that when people post, I have some old heads and bolting them on. Well, but ya sure you know what condition your condition is in?

Old iron heads are capable of 8:1.


A good question for Ol Ron and others.




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Last edited by Tinker; 11-19-2019 at 01:16 AM.
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Old 11-19-2019, 02:21 AM   #6
Lawrie
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Default Re: 8ba Heads 7RT or EAB

8rt heads are truck ones ,and have a larger chamber.
I sure noticed the difference on our 33 with using heads with the larger chamber,
Less MPG and torque.
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Old 11-19-2019, 04:35 AM   #7
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Default Re: 8ba Heads 7RT or EAB

Yes, there will be a noticeable power, efficiency, and drivability improvement if you make the proposed head swap. If you read my book you will see the actual numerical differences which I do not remember as I write this.
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Old 11-19-2019, 04:52 AM   #8
Phil Gillespie
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Default Re: 8ba Heads 7RT or EAB

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Yes, there will be a noticeable power, efficiency, and drivability improvement if you make the proposed head swap. If you read my book you will see the actual numerical differences which I do not remember as I write this.
Thanks for confirmation on this one John. I do actually have a copy of your book and will again revisit it and refresh myself.
Just to recheck with the foil balls and get that 50 thou piston to head clearance.
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