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Forum goer's.

My dilemma is this, my 67 has a 455 in her needing some attention. In a few weeks or so I am going to be pulling the motor, I have already acquired 6x-4 heads and they are at the machine shop. My plan was to stroke it to 461. I am using a father and son machine shop who have experience in this motor and said they could keep it around $3500 for the rebuild. I have just come across a pretty stout 500 hp 383 stroker, from carb to oil pan. The guy wants $5000 for it, aluminum heads, motor brand new. I really love the 455 and am leaning that direction, Just want some opinions on everyone's experience with what they have.

Thanks,
 

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']['exXxas']['itan
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455. No substitute for CID...

The 383 will make great midrange/upper end HP and moderate torque, but the 455 will be a monster out of the hole.

Also Don can chime in, but I'm betting those 6x heads on a 455 are going to send your compression ratio through the roof and it will no longer run on pump gas unless you run a dished piston. Not sure about the -4 part on the head number.

Not to mention, the chevy motor WILL NOT bolt the pontiac bell housing.
 

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Yeah, it won't surprise anybody when I say that I would not put any Chevy engine into a 1st gen Bird. To me it's just WRONG !

And, I can't see a 500hp 383 being very streetable. But, a good 455 will make in the neighborhood of 500ft lbs of torque and still be very streetable.

As for the 6x-4 heads: some 6x-8 heads might be better, with flat top pistons. But, if the 6x-4 heads measure 94cc, then a .030 over 455, with Speed-Pro flat tops will be aprox 9.5:1 CR.

http://www.summitracing.com/parts/slp-l2359nf30

http://www.wallaceracing.com/cr_test2.php

So, if you run a cam with a lot of seat timing, like a RA4 grind, it will bleed off some of the cylinder pressure, and reduce the dynamic compression, so that you can get by on 93 octane pump gas.

http://www.ebay.com/itm/Engine-Camshaft-Stock-MELLING-SPC-8-fits-68-70-Pontiac-Firebird-6-6L-V8-/131527250214?hash=item1e9fa29126:g:~WEAAOSw-vlVjneN&vxp=mtr

Or, as mentioned, you can go with dish pistons.

http://www.cnc-motorsports.com/icon-ic889-030-forged-dish-pistons-4-180-bore.html

Another option is to sell the 6x-4 heads, and buy some 6x-8's. There is always somebody looking for the 6x-4's. Therefore they will bring a little higher price. But, which ever heads you use, be sure to use one piece stainless valves. The old stock valves can come apart and wipe out an engine. :(

Butler sells the Ferrea 5000 series stainless valves.

http://www.jbp-pontiac.com/products/valveTrain/Ferra.html

SI also sells good stainless valves in the correct length, which is just under 5". #6001SG & #6006SG

http://www.sivalves.com/ocdomestic_valvescs_pont.html

It is always a good idea to actually measure the head chambers. Sometimes they have already been shaved some, which will increase comp. And, sometimes the chambers are slightly larger than advertised. The only way to know for sure is to measure. If they are less than 93cc, they could be very borderline for pump gas use on a .030 over 455, with flat tops.

One way to reduce comp is to enlarge the chambers slightly. But, those who know how to do it correctly usually charge quite a bit for any type of porting work. It also helps to remove the sharp edges of the piston valve reliefs.

It's also a good idea to set the deck height at somewhere between zero and .010. That will keep the quench distance between .040 and .050. This is supposed to help prevent detonation.

Anyhow, a 455 with forged rods, pistons, and 6x heads, can make a very good and strong street engine. :smile22:

http://lenwilliamsautomachine.com/455_Long_Block.html
 

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I ran 6x-4 in my .03 over 455. With the ra4 cam. it would run on 91 with 34 deg total timing, but the block was zero decked to get optimal quench. If your not going to have the block decked and squared then go with the 6x-8. I would spend the $150 to zero deck it run the ra 4 cam, roads lifters, port match the heads and intake and you should have around 450 h.p. That idles well and has 15 in of vacuum for power brakes. Jmho David
 
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