Author Topic: #48 heads worth the xtra time and money?  (Read 704 times)

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Offline 1976bober

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#48 heads worth the xtra time and money?
« on: May 19, 2013, 10:33:36 PM »
In the process of a 2brl swap to a 4 q/jet and e/b perf. intake and a 2157 e/b cam kit ,and new timing set. I have a 76 pont. F/bird w/350 and dual ex. with a/t and 308 pos.  Just wondered if anyone would have any idea if a set of 48 heads would be worth all the $'s it would take (around 600.00) to swap out for the 6x4 heads I have now ? If it would'nt add a good amount of hp. I'll surely keep the 6x's ? ? I can put the xtra towards a 400 later ! I'm not going to the track with it but I'd like to have enough get up and go to at least break the tires loose !! LOL

Offline 1976bober

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Re: #48 heads worth the xtra time and money?
« Reply #1 on: May 20, 2013, 08:52:10 PM »
I guess this was a tough question !!!! That's good ,the heads will be gone by the time I decide anyway so I'll save some $'s . Everyone must be at the lake !!

Offline Exiled

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Re: #48 heads worth the xtra time and money?
« Reply #2 on: May 22, 2013, 01:35:31 AM »
You have a whopping 7.6-1 comp with the 6x-4's. The #48 will bump your comp up to about 9.6 on a std bore 350 & 9.76 on a 30 over 350.
I know the 75-up 400 pistons have an angled top edge all the way around instead of a 90* edge.
Does the 76' 350 have that too? I know that angled edge gives a slightly lower compression than a earlier motors with a top edge that's was 90*.
I'm not familiar with the cam you have & if it matched to the 7,6 comp yo have with the 6x-4 & you decide to go with the #48 heads then you should get a different cam that will work with the 2 points higher comp you will have.

I used the Wallace Racing online calculator & that comp was figured with the usual stock piston being about .020 below deck at TDC
So yes the head swap would give you some more power if the cam is for that comp the 48's give you.

The stock 69' 350 with the #48 heads shows 325hp. I dont know what cam that came with

Offline 72blackbird

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Re: #48 heads worth the xtra time and money?
« Reply #3 on: May 26, 2013, 01:24:22 AM »
I currently have a 406 (400 .030 over) with ported no.48's in my 72 Firebird- I built this engine over 16 years ago and it makes enough power to put my Bird in the 13.0x's in the quarter with a TH-350, 2500 stall, and a 3.08 posi. The engine has 1.52 roller tip rockers, TRWs, a Crane 284H cam, a Holley 750 vac.sec. on a port-matched Performer intake. I did open up the chambers to 82cc to make the heads work with pump gas, and it does run on 91 octane.

No. 48's did come on 68-69 350 HO's- provided your existing 350P is still making good compression and your leakdown rates are decent, a pair of reworked no.48's will give you a very noticeable bump in performance over those 6x-4's, even if your 350P has chamfered pistons.