[rustycarr]

ive got a 1971 455 yc engine im about to pull the heads off of. They are coded 66.
valves are=2.11/1.77 114cc. Will these work with todays fuel and or will the compression be to low? should i keep them and have them gone thru or look for some other heads to up my compression? car will be a weekend driver, stock, manual tranny,hei, nothing special,just reliable and work good with todays standards, thanks

[Will]

The compression ratio with those heads is right around 8 - 8.2:1. That's a bit on the low side for optimum power production but you certainly wouldn't have any problems running 87 octane gas in that engine.

Whether you should change to different heads really depends on your overall performance goals for this engine. You can certainly make a very strong street engine out of a low compression 455, you just have to choose the cam right and make sure all the elements of the combo complement each other.

It sounds like you want a basically stock type setup with maybe a little power over stock. If it was my car and that's what I was after, I think I'd use those heads and put something like a Crower 60916 cam or Summit 2801 depending on rear gear ratio, exhaust system, and where you want your power curve.

[rustycarr]

i wasnt really planning on changing the cam, i was just going to pull the heads and have them gone thru, How much power could i gain from just adding some 6x heads?or is it not worth it for my application? it will be a 4bbl,exhaust manifolds with dual exhaust in a 64 gto with a 3.25 or 3.50 posi rear, not sure of rear ratio. (now you got me thinking about changin cam)

[Will]

If the engine is stock then you aren't going to gain any real power just changing the heads and bumping the CR up one point. You'd get a better power gain by keeping your current heads and putting more cam in.

The 455s were horribly under-cammed from the factory.

[rustycarr]

Originally Posted by Will

If the engine is stock then you aren't going to gain any real power just changing the heads and bumping the CR up one point. You'd get a better power gain by keeping your current heads and putting more cam in.

The 455s were horribly under-cammed from the factory.

even the 71 yc motor? its estimated at 325. maybe i will change it out while im there,not sure yet, trying to finish my shop first..

[b-man]

....., just click on the link below to read about it:

http://forums.maxperformanceinc.com/...22&postcount=4

If I were to do it over again I'd put the Crower 60916 cam in it. I'd also mill the heads a little to bring it up to around 8.5:1 to 8.7:1 compression so I could run premium fuel and take advantage of the added power and combustion efficiency the higher compression ratio would give.

At the very least put the factory 068 cam in yours to replace the original 067 that's likely close to being worn-out anyway.

[rustycarr]

thats a good read, any reason why you would go with the crower ?

[b-man]

Originally Posted by rustycarr

thats a good read, any reason why you would go with the crower ?

Because like Will said, the 455s are really under-cammed to begin with and even the 068 cam is super-mild in a 455. The Crower 60916 (221/229) would be superb in a low-compression 8.2:1 455. With the heads milled a tad the Crower 60243 (228/235) would be dynamite, especially with 3.25 or 3.50 gears.

I liked the 068 (212/225) in mine, but the whole reason I built my 455 that way was to see what it would do using a mix of all stock Pontiac parts running on 87 octane.

After driving it for a while I knew it could easily use more cam, even with only 8.2:1 compression and 2.56 gears.

But it was a low-buck perfectly reliable engine. I ran it for 30K miles without so much as even removing a spark plug, just oil changes every 3 to 4K miles.

[Will]

Originally Posted by rustycarr

even the 71 yc motor? its estimated at 325. maybe i will change it out while im there,not sure yet, trying to finish my shop first..

Yes. Really, when you think about it, 325 horses (gross rating) from 455 cubic inches is pretty weak.

As B-man says, even the factory 068 is a very mild cam in a 455. Get that duration up into the low 220 @ .050" range, the big engine will appreciate it.

[steve25]

I would rebuild the original heads with new valves,springs, guides and good seals, and have a 30 degree back cut added to the new exh valves and some short turn radius work in the exh port would work out nice if you have the funds.
I would only mill the heads if they had to be, not for the sake of a compression increase,as its far better fo a heavy street car to be able to run a good advance curve in the distributor for throttle responce than the 3 to 4 extra HP the motor will make above 4000 rpm. 455s love a better exh manifold above 3500 rpm so I would concider , now or at some point adding a set of RA D-port exh manifolds.
Also a modern cam will give you some extra power with just about the same Idle and low end torque.
If you will be reusing the stock rockers, check the ball seat for a ware lip. and check the flat of the rocker ball for radial factrues!

[rustycarr]

all good advice , what is the advantage of a 30 degree back cut, thanks guys

[steve25]

The back cut will increase the low lift flow during the blow down cycle so the piston does not have to work on pumping it out.