1970 360 vs. 1978 360

[bigblack'74]

In 1970 the amc 360 had 9to1 compression. and in 1978 it was 8.25to1. is it the heads or the pistons??. this 1970 4bbl version is much higher horse power rating than the '78. i am replicating the 1970 version with heavily plained '78 heads to achieve higher compression ratio. but i wonder if it is pistons also??. i have got a 1970 intake and carb setup going and points ignition, but no dogleg heads yet. that is why i milled the '78's so far out. the bore and stroke were allso the same in 70 and 78..thanks

[bvibert]

I think the heads probably had a smaller combustion chamber to make the higher compression ratio. The big horse power differences probably has to do with the way they calculated/listed HP numbers in 70 versus 78. I know there is a difference, but I don't know the details.

[mdill]

Don't know on pistons, but the few differances I know about are
70 HP rated as gross (ie net + pumping losses)
78 HP rated as net
So even if they made the same HP in both years, the 70 would have been
rated higher.

The heads on the 70 had adjustable rockers and no dog legs,
the crank flange on the rear (flexplate end) is different between
th 70 and 78, I know there have been spacer converters to make
the 70 look like the 78, but don't beleive you can make a 78 look
like a 70, it maybe as easy as using the 78 flex plate but don't
know for sure if that is all that is needed.

Mike D.

[Rogue]

70 will be a low deck block and you have 78 heads that arent' dogleg??? hmmm....AFAIK they quit making sqaureport heads in 71...

[illegalFSJ]

You sure the intake manifold is gonna fit OK with the heads milled down so far? 'Cuz the heads are gonna sit a hair lower, making the space between the intake ports just a little bit further apart.

[Rande]

RogueStar, as I read it, He has used the dogleg 78 heads with a lot of shaving because he hasn't yet found a set of the snall chamber dogleg heads. In 70, the heads had a small combuston chamber which gives a higher compression but the had the poorer flowing exhaust port. In 71 they still had the small combustion chamber but got the new dogleg exhaust port. Then in 72, they got the larger combustion chamber for lower compression.

So, the heads to get are the 71's.......I think......

[bigblack'74]

Well i do have dogleg ported heads i mistakenly said that..ilegal- that is one thing i really hope will work..the thing about it is you are milling off thousands of an inch and you really cant go extremely far because of piston to valve clearnce. just far enough to bump compression... rogue star-what to mean by low deck..a lower deck height compaer to '78? how does this work..then you would efectively have to have shorter stroke? or shorter skirts or something. The next question can the '78 motor be built effectively into a similair machine as the '70, ie: milled heads, all pre emission eqpt. this is what i have done and i just want to get feel for what the motor will be doing..we have no close dyno or drag strip that i know of..thanks

[Rogue]

Rande is 100% right - CLICK HERE - this article should have all your answers - it is what i was trying to refer from but posting the link is easier

[youwantedbig]

When I redid my 79 360, I decked the block .020 and the heads .020, when I went to install an edelbrock manifold only the gaskets to the heads would fit so I used silicone instead for the front and back, another thing that resulted was I had to have custom pushrods made that were shorter around 90$, and the guy that did the heads installed 454 springs on the heads to hold for the compression since I put in 10:1 compression pistons.
That is all I had to do when i did mine.

[bigblack'74]

well i essmbled the intake today it didnt really line up very well at all but i got it as good i as could and **** near almost stripped every one..lucky i dont i think any stripped..also the front and rear gaskets were bulging badly!