# 455 360 hp



## JD 63 (Mar 21, 2019)

I have a 455 in a 1970 bonneville #15 heads and a yh block is it a drivable motor nowadays or I’m I better off using a 400 out of a early 70s
If I were to sell the 455 anything rare about being the 360 hp?
I want to put one in my 81 trans am with a 3.42 gears and a auto over drive
It has a 301 and I stuffed a 455 olds in it but have never been happy with the way it fit


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## bigD (Jul 21, 2016)

I think it's advertised at 10:1 CR. But, if it is still near factory spec, it probably has closer to 9.5 CR than 10.0. 

The heads are rated at 87cc. Many have posted that most Pontiac head chambers come in a little bigger than listed. It has also been posted that many Pontiac engines came from the factory with the pistons at least .020 down in the hole.

I plugged in a std bore 455, with 87cc heads, 6.6cc valve reliefs, .045" x 4.3" head gaskets, & .020 deck height. The CR calculator said 9.59 CR. 

Compression Ratio Calculator - Wallace Racing

Even if the actual CR is closer to 10:1, you could probably get by with it, by keeping the timing advance a little lower than normal. A cam with more advertised duration would also bleed off some of the cylinder pressure, at lower rpm. BUT, I think the #15 heads have press-in studs. So, a bigger cam, with more spring pressure could possibly pull a stud. If the heads are converted to screw-in studs, then the correct cam should make the engine streetable, with pump gas, IMO.

"...If I were to sell the 455 anything rare about being the 360 hp?..."

In some places ANY 455 is rare, nowadays. I'd say a '70 455 is a lot more rare than the later model D-port 455's.


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