[bullit34]

how or what can i do to get about 400 hp out or a 455?

[bullit34]

the number on my heads is 6h, i dont know cam dementions but it is pretty thumpy.does anyone know what cc these heads are? and can they be made bigger for more power or does it even work that way? i dont know very much about heads. thanks!

[bullit34]

how or what can i do to get about 400 hp out or a 455?

[Darrell]

you wont need much. A good set of 4x or 6x heads in the 96cc area and a ram air III or ram air IV type grind in a cam. I have a similar set up and I am in the 425 to 450hp range. I have a stock intake and a qjet. I have a cheap set of $80 headers from summit. You wont have to spend alot to get 400 HP!!!!!!

[Will]

Bullit34, to ID your heads, note the locations of the relevant numbers in this picture then go look at your heads:



If your heads are original '74 455 heads (not sure what casting number that would be), then your compression is a dismally low 7.8:1 or thereabouts. Time for a head swap. The 6X castings in the above picture would be a good choice, as would several other castings from mid '70s 350 and 400 engines, such as 4X and 5C. '71 #96 would also be good, as would '72 #7K3, but those don't have the end bolt holes for the headers.

That tiny carb is hurting you. A 455 is a big engine, it needs a big carb. Think 750 cfm or bigger.

You mention a "mild" cam. How mild? Anything less than 220 @ .050" duration is throwing away most of your engine's potential.

Good luck!

[Hattmann68]

The 6h Heads are 124cc. About 7.4-7.6 comp. ratio on a 455. Valve length are 4.80,2.11 intake and 1.66 exhaust valves. Good for a blower motor.

[Steve C.]

This suggestion is similar to a example of a 455 that made 410 hp @ 5500 rpm and 512 ft.lbs. Tq @ 3600 rpm:
Bore it .030-over, use a Performer intake and a 750cfm carb of your choice with a good quality set of 1-3/4" 4-tube headers.
You didn't mention your heads.
one example, 6X reworked to to 200-210 cfm (28") at .450 lift. Then establish exhaust flow of 70-74 percent of intake.
This will pair very nicely to a Comp Magnum 280H hydrulic cam.
And I would also suggest aftermarket steel rods and good quality set forged pistons.

[PONTIAC DUDE]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Steve Coombes:
This suggestion is similar to a example of a 455 that made 410 hp @ 5500 rpm and 512 ft.lbs. Tq @ 3600 rpm:
Bore it .030-over, use a Performer intake and a 750cfm carb of your choice with a good quality set of 1-3/4" 4-tube headers.
You didn't mention your heads.
one example, 6X reworked to to 200-210 cfm (28") at .450 lift. Then establish exhaust flow of 70-74 percent of intake.
This will pair very nicely to a Comp Magnum 280H hydrulic cam.
And I would also suggest aftermarket steel rods and good quality set forged pistons. <HR></BLOCKQUOTE>

Ditto. basically a simple deal, now-a-days.

[Darrell]

Same deal with the 400 but you need better flowing heads. Those little 650 carbs are not going to cut it you need 800 to 850. I run out with my 850 at the end of the track but that is probably more fuel line related than the carb.

[prostreetpower]

great info!

Now any 1 have any combo suggestions to make 400-500 hp on a pontiac 400 from a 77 trans am with a four speed?

Thanks for any info

[bullit34]

i already have a edelbrock 650 on a performer rmp intake headers and mild cam but i'm only running a 15.3 in the quarter mile,which ads up to about 250 hp. how do i find out what heads are on it? it was manufactured in 1974.