[73 ventura]

i just picked up a 70 455 to put in a 73 ventura. engine is all stock. i have a set of 6x-8 heads from 77 T/A and thought about running those for the bigger valves. the stock engine is 10:1 , so are those 6x heads going to drop too much compression? Can i mill enough to bring it back to 9:5 to 1? i just want to build a nice dependable 400HP engine. 455 was 360 to start with so shouldn't be too hard to get solid 400

[PONTIAC LARRY]

The 1970 #15 heads will have the big 2.11 intake valves and bigger than the 6X 1.77 exhaust valves just pressed studs. Stock compression rated at 10.25:1 are only about 9.7-9.8:1 or so, you could just do some minor chamber work and check CC that's already around 87 cc stock and get them to about 89-90 to be 9.5:1 , add a modest cam like a Summit 2802 and a set of nice 4 tube headers and you will there. Reuse 70 iron 4 barrel intake. A little bowl blending and good valve job can put it over the top. I am not jumping up to as hot as often recommended bigger RAIV grind because I think you may want to keep the stock 2.73-3.08 gears the Ventura has and enjoy the simplistic beauty of easy cruising with your TH350 or TH400 and stock gears

[huddie]

I think the #15 heads for the 70 455 were 1.96/1.66 but everything else I agree.Did this in a 69 firebird years ago and it was a blast.Could up the valve size and screw studs (#64 heads) I think Jim Hand used the 64's for several years and made that wagon fly.

[74Grandville]

1970 #15's are small valve press in stud heads. Flow may be a little bit better in a stock 6X-8, but as others have stated, you'll drop some compression. I don't think there will be much to gain in the swap.

Maybe send the 6X-8 heads to get worked over, "Porting, decked, new valves" then you'll be sure to make your 400hp.

[PONTIAC LARRY]

Yeah oops on the valve size thing never owned any 70 #15 , maybe I was thinking the 71 or 72 heads .. isn't there a 2.11 valved #66 head on the pressed stud version with a two barrel 455?

Any who, either set of heads will run good but the #15 are gonna be quicker with the torque increases of higher compression over 6X-8

[54nomore]

Yes Larry,

I have a set of 1971 #66 heads. They are 2.11/1.77 with pressed in studs and all 6 bolt holes on the exhaust side.

Ron.

[Chastings]

I actually have had 2 different motors in my 70 gto. Currently running a 70 455 with #15 heads and the other engine (spun a main) is a 455 with 6x8 heads.

I honestly couldn't tell much difference between the two -- I know the 15's were stock. I've never had the 6x motor apart so I have no idea what/if anything was done to it aside from a basic rebuild.

Running the #15's my motor tends to ping when it's hot out, and today's gasoline sure doesn't help much... I'm planning on running the 6x's next time around or even shopping for something else. I've heard #96's can be made to run quite well.

[screamingchief]

Originally Posted by 73 ventura

Can i mill enough to bring it back to 9:5 to 1?

Yes,should be no problemo.

.005" mill = 1 cc on open chamber iron heads.

Typical 6X-8 will be 100-102 cc or so.

Get them down to say 96cc and you'll be right @ 9.25:1 CR on a typical 455 shortblock.

That would be like .030" mill to get 6 cc's.

May or may not affect intake manifold alignment,results vary engine to engine.

I would'nt get too worried about hitting 9.5:1 CR specifically,as anything over 9.0:1 CR should work fine for a build like this.

For a mid level CR combo like that looking to get an honest 400 hp with unported 6X-8 heads,I'd probably use the Crower #60243 hydraulic cam and #68404-16 springs and I would convert to an adjustable valvetrain as well.

Good luck with this.

Bret P.

[73 ventura]

thanks for all the feedback on the compression issue. i think i will spend some money on the 6x-8 heads( unless i can find some 6x-4) and see if they do better on pump gas. the crower 60243 cam specs look good and keep good vacuum also, modest stall converter, 4 tube 1 3/4" headers with 2 1/2" exhaust. I just want to hear a little thump and be able to "light em up" when i want to- It's an old man's toy!

great help from all